Platinum(II) and palladium(II) complexes derived from 1-ferrocenylmethyl-3,5-diphenylpyrazole. Coordination, cyclometallation or transannulation?

Abstract

The synthesis and characterization of the novel pyrazole derivative [1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)] (2) {Fc = (η⁵–C₅H₅)Fe(η⁵–C₅H₄)–} with a ferrocenylmethyl substituent on position 1 of the heterocycle is described. The study of the reactivity of 2 with cis-[MCl₂L₂] (M = Pt and L = dmso or M = Pd and L = dmso or CH₃CN), Pd(AcO)₂ or Na₂[PdCl₄] under different experimental conditions, has allowed us to isolate and characterize a wide variety of platinum(II) or palladium(II) complexes: trans-[Pt{1-(Fc–CH₂)-3,5-Ph₂-(C₃HN₂)}Cl₂(dmso)] (3), the cis- isomers of [M{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}Cl₂(dmso)] {M = Pt (4) or Pd (7)}, trans-[Pd{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}₂Cl₂] (8), the cyclometallated compounds [M{1-(Fc–CH₂)-(3–C₆H₄)-5-Ph–(C₃HN₂)}Cl(L)] {with M = Pt and L = dmso (5) or PPh₃ (6) or M = Pd and L = PPh₃ (9)} and the palladium(II) complex [Pd{1-[(η⁵–C₅H₄)Fe{(η⁵–C₅H₄)–CH₂]-3,5-Ph₂–(C₃HN₂)}Cl(PPh₃)] (10) that arises from a transannulation process. The crystal structures of the free ligand 2 and compounds 4, 7, 9 and 10 are also reported and confirm the cis- disposition of the Cl⁻ ligands in 4 and 7, the trans- arrangement of the phosphorous and the nitrogen atoms in 9 and 10, the mode of binding of the ligand in 4, 7, 9 and 10 and the nature of the metallated carbon atom {C(sp², phenyl) in 9 or the C(sp², ferrocenyl) of the C₅H₅ ring in 10}. In order to rationalize the different nature of the products isolated in the reactions of 2 with Pd(AcO)₂ or Na₂[PdCl₄] and NaAcO density functional theory (DFT) calculations of the complexes have also been carried out.

---

Introduction

Ferrocene heterocyclic systems have attracted great interest in recent years ^1–3 because of their physical and chemical properties as well as their applications in a wide variety of areas including homogeneous catalysis^1,2d,3c and biomedicine.^2e In this class of compounds, the presence of heterocycles with one or more atoms with good donor abilities is especially interesting in view of their use as ligands for transition metals to give heteropolymetallic complexes in which the existence of two or more proximal metal ions may induce a co-operative effect.^1–4

On the other hand, the investigation of palladium(II) and platinum(II) coordination complexes with pyrazoles as ligands is one of the research areas that has undergone rapid development during recent years.^5–8 Compounds of this kind exhibit greater antitumoral activity and lower toxicity than cis-[PtCl₂(NH₃)₂] or antibacterial activity have been reported.^6c Furthermore, some examples of their utility in macromolecular chemistry,^7a or in homogeneous catalysis^7b have also been published.

In addition, cyclometallated Pd(II) and Pt(II) complexes of N– donor ligands are particularly relevant due to their photophysical properties, biological activity and applications in homogeneous catalysis, or as building blocs in supra- and macromolecular chemistry.^9–15

Despite of: a) the increasing interest in new ferrocene derivatives containing pyrazole units,¹⁶ b) their use as ligands in front of transition metals,^4b,4c,7 c) the study of heterodi-, tri- or in general polymetallic complexes with ferrocenyl units,^1,3,4 or d) the relevance of palladium(II) and platinum(II) in synthesis,^9,10a,b,14 only a few palladium(II) complexes containing hybrid ferrocene-pyrazole units have been reported so far,^4b,4c and as far as we know, platinum(II) derivatives are unknown.

We have recently described the syntheses of [3,5-Ph₂-4-(Fc–CH₂)–(C₃HN₂)] (1) {Fc = (η⁵–C₅H₅)Fe(η⁵–C₅H₄)–} (Fig. 1) and a few palladium(II) and platinum(II) complexes where 1 behaves as an (N) or [C(phenyl), N(pyrazol)]⁻ ligand.^4b In view of the results obtained in these studies, and in order to elucidate whether the position of the Fc–CH₂– unit on the heterocycle could affect: a) the reactivity of this sort of compound, b) the nature of the palladium(II) and platinum(II) complexes formed or c) their properties, we decided to prepare and characterize the new ligand [1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)] (2) (Fig. 1).

Fig. 1 Chemical formulae of 1-methyl-3,5-diphenyl-4-ferrocenylene-pyrazole (1) studied before^4c and of the new ligand [1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)] (2) prepared and used in this work.

In compound 2, the presence of the Fc–CH₂– unit on position 1 of the heterocycle has an additional interest due to the existence of different types of carbon atoms [C(phenyl) and C(ferrocenyl)] susceptible to metallation. The activation of the σ[C(phenyl)–H] bond would produce five-membered metallacycles (Fig. 2, A); while the metallation of the C₅H₄ ring of the ferrocenyl unit, that induces planar chirality, would give chiral compounds (R_p or S_p isomers) containing six-membered rings (Fig. 2, B). Moreover, since a few uncommon examples of palladacycles arising from a transannulation process have been recently reported,^4a,18 the formation of palladium(II) or platinum(II) complexes arising from the activation of the σ[C(ferrocene)–H] bond of the unsubstituted C₅H₅ ring of the Fc moiety (Fig. 2, C) or complexes containing [C,N,C']²⁻ pincer ligands (Fig. 2, D and E) formed by the activation of two σ(C−H) bonds cannot be ruled out.¹⁹

Fig. 2 Schematic view of the different types of pallada- and platinacycles that could be formed through: a) activation of a σ(C_phenyl–H) bond (A) or one of the two σ[C(ferrocenyl)–H] bonds on the ortho site of the C₅H₄ ring (B) {in this case two enantiomers: (S_p) and (R_p) could be formed}, b) from a transannulation process (C) or c) from a more complex reaction involving a double cyclometallation (D) or a transannulation and a cyclometallation reaction simultaneously (E).

In this paper we present the synthesis of ligand 2 and the study of its coordination chemistry in front of palladium(II) and platinum(II) in view of the potential applications of the complexes in different fields.

Results and discussion

The ligand

The new ferrocene derivative [1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)] (2) was prepared in good yield (96%) by electrophillic coupling at the nitrogen of 3,5-diphenylpyrazole using ferrocenylmethanol in a two-phase dichloromethane : aqueous tetrafluoroboric acid (Scheme 1).^20–21

Scheme 1 i) in CH₂Cl₂, treatment with aqueous HBF₄, 1 h at room temperature.

Elemental analyses (experimental section) of 2 were consistent with the proposed formula, its mass spectra showed a peak at m/z = 419.1, that agrees with the value expected for the {[M] + H}⁺ cation and the infrared spectrum of 2 exhibited the typical bands due to monosubstituted ferrocene derivatives.²²

The X-ray crystal structure of 2 is depicted in Fig. 3. Average values of bond lengths [Fe–C_ring: 2.07(4) Å and C_ring–C_ring: 1.43(3) Å] and angles of the Fc unit fall in the range reported for most monosubstituted ferrocene derivatives.²³ The two pentagonal rings are planar, nearly parallel (tilt angle = 1.69°) and they deviate by ca. 18° from the ideal eclipsed conformation.

Fig. 3 ORTEP plot of [1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)] (2), 50% probability displacement ellipsoids are shown and hydrogen atoms have been omitted for clarity. Selected bond lengths (in Å) and angles (in deg): C(10)–C(11), 1.513(5); C(11)–N(2), 1.449(4); N(1)–C(12), 1.318(4); C(12)–C(13), 1.390(5); C(13)–C(14), 1.393(4); C(14)–N(2), 1.340(4); N(1)–N(2), 1.367(4); C(14)–C(15), 1.514(4); 1.480(4); C(14)–C(21), 1.480(4); Fe–C (average value), 2.07(4) (C–C) of Fc (average value), 1.43(3); C(6)–C(10)–C(9), 105.4(3); N(2)–C(11)–C(10), 111.2(3), C(6)–C(10)–C(11), 125.0(3); C(9)–C(10)–C(11), 129.3(3); N(1)–C(12)–C(13), 109.2(3); N(1)–C(12)–C(15), 120.8(3); N(2)–C(14)–C(13), 103.7(8); N(2)–C(14)–C(11), 123.3(3); C(12)–C(13)–C(14), 108.1(3) and C(13)–C(14)–C(21), 133.0(3).

The pyrazole ring is planar, its main plane forms an angle of 80.9° with the C₅H₄ ring of the ferrocene and the N(1)–N(2) bond is located on the same direction as the Fe(η⁵–C₅H₅) moiety. As a consequence of this arrangement of groups, the N(1) atom is quite close to one hydrogen atom of the –CH₂– {separation N(1)⋯H(11A) = 2.50 Å} and proximal to the H(1) and H(2) atoms of the (η⁵–C₅H₅) unit, {the distances N(1)⋯H(1) and N(1)⋯H(2) = 2.90 Å and 3.02 Å}. The two phenyl rings defined by the sets of atoms [C(15)–C(20)] and [C(21)–C(26)] are planar and their mean planes form angles of 2.6° and 63.6° with the pyrazole ring respectively.

In the crystal, the relative orientation of two neighbouring molecules with a head-to-tail disposition is such that the separation between N(1) atom of one unit and the H(20) atom of the other one (and vice versa) is 2.540 Å. This suggests the existence of two C–H(20)⋯N(1) intermolecular interactions that results in the formation of a dimer which is connected to proximal ones by C–H⋯π interactions,‡as shown in Fig. 4, b.

Fig. 4 a) Schematic view of the assembly of a molecule of compound 2, at (x, y, z) with a close one located at (1 − x, 1 − y, − z) through C–H⋯N interactions {atoms marked with an asterisk belong to the molecule at (1 − x, 1 − y, −z)}} and b) the connectivity of these dimeric units by different sorts of C–H⋯π intermolecular interactions.

Compound 2 was also characterized in solution by mono- [¹H and ¹³C{¹H}] and two dimensional [{¹H–¹H} NOESY and COSY and {¹H–¹³C}–HSQC and HMBC] NMR experiments. The most relevant features observed in the ¹H–NMR spectrum was the presence of a group of two singlets of relative intensities 2 : 7 in the range 4.00–4.20 ppm, the less intense one is due to the pair of protons H³ and H⁴ of the C₅H₄ ring, while the other one was assigned to the remaining protons of the Fc group. The two additional singlets at δ = 6.56 and 5.09 ppm (of relative intensities 1 : 2) were ascribed to the proton on position 4 of the pyrazolyl ring and to those of the –CH₂– unit.

Study of the reactivity of 2 in front of platinum(II)

In a first attempt to evaluate the potential coordination abilities of ligand 2 to platinum(II), its reactivity with cis-[PtCl₂(dmso)₂]²⁴ was studied under different experimental conditions (Table 1 and Scheme 2).

Scheme 2 i) cis-[PtCl₂(dmso)₂] {in a molar ratio 2:Pt(II) = 1} in refluxing methanol. ii) SiO₂ column chromatography. iii) cis-[PtCl₂(dmso)₂] and NaAcO (in a molar ratio: 2 : Pt(II)OAc⁻ = 1 : 1 : 2) in a mixture of toluene : methanol (5 : 1) under reflux. iv) Addition of PPh₃ (in a molar ratio 5 : PPh₃ = 1) in CH₂Cl₂ at 298 K for 1.5 h.

Table 1 Summary of experimental conditions [reagents, molar ratios, solvents, temperature (T), reaction time (t, in h)] used in the study of the reactivity of 2 with cis-[PtCl₂(dmso)₂] and the final products isolated

Entry	Reagents (molar ratios)	Solvent	T	t	Products (molar ratios)
a A (5 : 1) mixture. b The ^1H–NMR spectrum of the crude material revealed the presence of 3 as the minor component. c Since only small amounts of 3 (8 mg) were isolated from the SiO2 column, the molar ratio 4 : 5 is given. d Traces of 4 (≈3 mg) were also obtained during the work up of the column.
I	2 and cis-[PtCl2(dmso)2]	MeOH	reflux	1.0	3 and 4
	(1 : 1)				(1.00 : 0.11)
II	2 and cis-[PtCl2(dmso)2]	MeOH	reflux	3.5	3 and 4
	(1 : 1)				(0.21 : 1.00)
III	2, cis-[PtCl2(dmso)2] and NaAcO	Toluene/MeOH^a	reflux	3.5	3 ^b, 4 and 5
	(1 : 1 : 1)				(1.00 : 0.18)^c
IV	2, cis-[PtCl2(dmso)2] and NaAcO	Toluene/MeOH^a	reflux	3.5	4 and 5
	(1 : 1 : 2)				(0.36 : 1.00)
IV	2, cis-[PtCl2(dmso)2] and NaAcO	Toluene/MeOH^a	reflux	7.0	5 ^d
	(1 : 1 : 2)
V	5 and PPh3	CH2Cl2	298 K	1.0	6
	(1 : 1)

---

The treatment of equimolar amounts of 2 and cis-[PtCl₂(dmso)₂] in refluxing methanol for 1.0 h followed by the work up of a SiO₂ column chromatography afforded the trans- and cis- isomers of [Pt{1-(Fc–CH₂)-3,5-Ph₂–C₃HN₂}Cl₂(dmso)] (3) and (4) respectively, in a molar ratio 3 : 4 =1.00 : 0.11 (Table 1, entry I). Longer refluxing periods (t = 3.5 h, Table 1, entry II)} also produced a mixture of the two isomers but with the molar ratio 3 : 4 inverted (0.21 : 1.00). Thus indicating that longer reaction periods induced the preferential formation of the cis- isomer (4). This finding, is consistent with previous work on the reactivity of cis-[PtCl₂(dmso)₂] with related N–donor ligands^4a,4c,25 and has allowed us to optimize the synthesis of 4.

Compounds 3 and 4 were characterized by elemental analyses, mass spectrometry, IR and mono and two-dimensional NMR studies and product 4 was also characterized by X-ray diffraction (see below). Elemental analyses were consistent with the proposed formulae and the IR spectra of 3 and 4 showed the typical bands due to the coordinated dmso ligand.²⁶ The assignment of the signals observed in the ¹H NMR spectra of 3 and 4 was achieved with the aid of {¹H–¹H} NOESY and COSY experiments. ¹⁹⁵Pt{¹H} NMR spectra of 3 and 4 showed a singlet (at δ = −2998 and −2850 ppm, respectively). The variation of the chemical shift Δδ(¹⁹⁵Pt) = δ(for 4) − δ(for 3) = 148 ppm agrees with the values reported for the trans- and cis- isomers of the related [Pt(N–donor ligand)Cl₂(dmso)] complexes.^{4b,4c,25,27,28}

The crystal structure of 4 consists of discrete molecules of [Pt{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}Cl₂(dmso)] (Fig. 5) in which the platinum(II) is bound to the nitrogen N(1) of the pyrazolyl unit, the sulphur, S(1), of the dmso ligand and two chloride ligands {Cl(1) and Cl(2)} in a cis- arrangement {Cl(1)–Pt–Cl(2) bond angle = 90.61(5)°}. Bond lengths as well as bond angles around the platinum(II) are consistent with those reported for related cis-[Pt(N–donor ligand)Cl₂(dmso)] complexes.^23,25,27,29

Fig. 5 ORTEP plot of cis-[Pt{1-(Fc−CH₂)-3,5-Ph₂–(C₃HN₂)}Cl₂(dmso)] (4) showing 50% probability displacement ellipsoids. Hydrogen atoms have been omitted for clarity.

The three rings of the 3,5-Ph₂–C₃HN₂ moiety are planar and the two phenyl rings, defined by the sets of atoms [C(15)–C(20)] and [C(21)–C(26)] form angles of 47.5° and 49.6°, respectively with the main plane of the heterocycle. The N(1)–N(2) bond of the pyrazole ring is directed in the opposite direction to the Fe(η⁵–C₅H₅) unit. As expected, the bond lengths and angles of the ferrocenyl unit are consistent with those of monosubstituted ferrocene derivatives,²³ the two pentagonal rings are parallel (tilt angle = 0.41°) and their relative orientation deviates by ca. 8.8(8)° from the ideal eclipsed conformation.

Due to the increasing interest on platina- and palladacycles containing planar N–donor ligands due to their applications in different areas,^11–17 and since it is well-known that the formation of platina- (or palladacycles) with bidentate [C(phenyl), N]⁻ or [C(ferrocenyl), N]⁻ ligands commonly requires the presence of a base (i.e.NaOAc or the ligand itself),^{4b,4c,10a,10b,25b,30} we also explored the reactivity of ligand 2 toward Pt(II) in the presence of sodium acetate.

When compound 2 was treated with equimolar amounts of cis-[PtCl₂(dmso)₂]²⁴ and NaAcO in a mixture of toluene : methanol (5 : 1) under reflux for 3.5 h (Table 1, entry III) the formation of a platinum mirror on the walls of the Erlenmeyer flask was observed and a deep-brown solution was obtained. Concentration of the solution, followed by silica gel column chromatography, gave traces of 3, compound 4 and a new platinum(II) complex, 5. Characterization data of 5 (see the experimental section) were consistent with those expected for [Pt{3-(C₆H₄)-5-Ph-1-(Fc−CH₂)–(C₃HN₂)}Cl(dmso)] (5), in which ligand 2 behaves as a monoanionic bidentate [C(phenyl), N(pyrazole)]⁻ ligand (type B in Fig. 2) and the dmso is in a cis-arrangement to the metallated carbon atom in agreement with the transphobia effect.³¹

Several additional experiments were carried out in order to increase the yield of 5. Shorter refluxing periods (t) (1.0 h ≤ t < 3.5 h) produced a significant decrease of the molar ratios 5 : 4. and for longer reaction times (4 h ≤ t ≤ 24 h) the amount of metallic platinum formed increased, but the yield of 5 did not improve significantly.§ Better results were obtained when the reaction was performed using a two-fold excess of sodium acetate (molar ratio NaAcO:Pt(II) = 2, Table 1, entry IV and Scheme 2, step B) and long refluxing periods (t = 7.0 h), in this case 5 was the major product. Furthermore, it should be noted that the ¹H–NMR spectra of the crude materials isolated in any of these reactions did not provide evidence of the presence of any other type of platinacycle suggesting that under the experimental conditions used, the activation of the σ[C(phenyl)–H] bond of 2 is preferred over that of the σ[C(ferrocenyl)–H] bond.

The results presented in this section suggest that the formation of the platinacycle 5 is a multistep process that involves the replacement of one dmso ligand of the starting material by methanol to give cis-[PtCl₂(MeOH)(dmso)] which may isomerize to the trans- form. Further coordination of the N–donor ligand 2 would produce the cis- and trans- isomers of [Pt{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}Cl₂(dmso)] respectively. Finally, the activation of the σ[C(sp², phenyl)–H] bond of 3 would give the platinacycle 5. This in good agreement with the mechanism postulated for the cycloplatination of aryloximes and related N–donor ligands and the results obtained recently from a DFT based theoretical study of the cycloplatination process that points out that the trans- isomers of [Pt(L)Cl₂(dmso)] are the key intermediates of the process.^30b However, it should be noted that ligand 2 has different σ(C–H) bonds which are susceptible to metallation (Fig. 1) and although ferrocene derivatives are more prone to electrophillic attacks than their phenyl analogues,¹ the formation of 5 should be ascribed to the closer orientation between the platinum(II) bound to heterocyclic nitrogen and the σ[C(phenyl)–H] rather than the σ[C(ferrocenyl)–H] bonds.

The use of molecular models for the cis- (3) and trans- (4) isomers of [Pt{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}Cl₂(dmso)] reveals that the “PtCl₂S_dmso” moiety should be nearly orthogonal to the pyrazole ring to minimize steric hindrance between the phenyl ring and the Cl or dmso ligands. This is the typical orientation found in the crystal structures of cis- or trans-[Pt(planar N–donor ligand)Cl₂(dmso)].^23,24,25,29 The formation of the metallacycle 5 from 3 requires the release of one of the ligands in a cis- arrangement to the σ(Pt–N) bond and the rotation of the phenyl ring (on position 3 of the pyrazole ring) to achieve a proper orientation between the σ[C(phenyl)–H] bond and the platinum(II).

Further treatment of the cycloplatinated complex 5 with the equimolar amount of PPh₃ in CH₂Cl₂ produced [Pt{3-(C₆H₄)-5-Ph-1-(Fc−CH₂)–(C₃HN₂)}Cl(PPh₃)] (6) (Scheme 2, step C and Table 1, entry V) in a fairly good yield. Elemental analyses of 6 were consistent with the proposed formula. The IR spectrum suggested the binding of the PPh₃ ligand to the platinum(II) and ¹H, ³¹P{¹H} and ¹⁹⁵Pt{¹H} NMR spectra indicated the presence of a [C(phenyl), N(pyrazole)]⁻group and a PPh₃ ligand in a cis- arrangement to the metallated carbon, in agreement with the transphobia effect.³¹

Study of the reactivity of 2 in front of palladium(II)

In a first attempt to evaluate the potential coordination abilities of ligand 2 to palladium(II), its reactivity with cis-[PdCl₂(dmso)₂] was studied under different experimental conditions (Table 2 and Scheme 3).

Scheme 3 i) Equimolar amount of [PdCl₂(dmso)₂], in refluxing MeOH at 298 K for 0.5 h. ii) [PdCl₂(CH₃CN)₂] or Na₂[PdCl₄] {molar ratio 2:Pd(II) = 1 or 2 (see text)} in MeOH at 298 K, 24h. iii) Equimolar amount of Pd(OAc)₂ in toluene under reflux for 3.5 h followed by the addition of PPh₃ in CH₂Cl₂ under stirring at 298 K for 1.5 h, subsequent treatment with LiCl in acetone for 2.5 h. iv) SiO₂ column chromatography. v) Reaction with Na₂[PdCl₄] and Na(OAc)·3H₂O (in a 1 : 1 : 1 molar ratio) in MeOH at 298 K for 24 h, followed by the addition of PPh₃ in CH₂Cl₂ for 1.5 h at 298 K.

Table 2 Summary of experimental conditions [reagents, molar ratios, solvents, temperature (T), reaction time (t)] used in the study of the reactivity of 2 with palladium(II) salts or complexes and the final products isolated

Entry	Reagents (molar ratios)	Solvent	T	t	Products
a See text. b Yields of 8 were 35% or 89% for molar ratios 2 : Pd(II) = 1 and 2, respectively. c Followed by: i) treatment with the equimolar amount of PPh3 in CH2Cl2 at 298 K, ii) subsequent addition of LiCl in acetone and stirring of the mixture at 298 K for 2.5 h, and iii) SiO2 column chromatography. d Small amounts of [PdCl2(PPh3)2] were also isolated as a by-product. e Treatment with a slight excess (15%) of PPh3 in CH2Cl2 at 298 K for 1.5 h and the subsequent separation of 10 and [PdCl2(PPh3)2] by SiO2 column chromatography. f When this reaction was performed at higher temperatures, mixtures containing 9 and 10 were isolated.
I	2 and cis-[PdCl2(dmso)2]	MeOH	reflux	0.5	7
	(1 : 1)
II	2 and cis-[PdCl2(CH3CN)2]	MeOH	298 K	24.0	8
	(1 : 1) or (2 : 1)^a
III	2 and Na2[PdCl4]^b	MeOH	298 K	24.0	8
	(1 : 1) or (2 : 1)
IV	2 and Pd(AcO)2^c	Toluene	reflux	3.5	9 ^d
	(1 : 1)
V	2, Na2[PdCl4] and NaAcO·3H2O^e	MeOH	298 K^f	24.0	10 ^d
	(1 : 1 : 1)

---

The reaction between equimolar amounts of 2 and cis-[PdCl₂(dmso)₂] in refluxing methanol for 0.5 h (Scheme 3, A and Table 2, entry I) produced a yellow solid that was identified according to its elemental analyses, mass spectra and NMR studies (see experimental section) as cis-[Pd{1-(Fc-CH₂)-3,5-Ph₂–(C₃HN₂)}₂Cl₂] (7). Compound 7 is similar to complex 4, except for the nature of the metal atom {M = Pt (in 4) or Pd (in 6)} and in fact X-ray studies reveal that they are isostructural.

The crystal structure of 7 consists of discrete molecules of [Pd{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}Cl₂(dmso)] (Fig. 6). In each of these molecules the palladium(II) atom is in a slightly distorted square-planar environment and it is bound to the nitrogen N(1) of the pyrazolyl unit, two chloride ligands {Cl(1) and Cl(2)} in a cis- arrangement {Cl(1)-Pd–Cl(2) bond angle = 90.74(7)°} and the sulphur, S(1), of the dmso ligand. Bond lengths and angles around the palladium(II) (Table 3) are similar to those of related cis-[Pd(N–donor ligand)Cl₂(dmso)] complexes.^23,32 The two phenyl rings, defined by the sets of atoms [C(15)–C20)] and [C(21)–C(26)] are planar and form angles of 47.0° and 48.9°, respectively with the main plane of the heterocycle.

Fig. 6 ORTEP plot of cis-[Pd{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}Cl₂(dmso)] (7), 50% probability displacement ellipsoids are shown and hydrogen atoms have been omitted for clarity.

Table 3 Selected bond lengths (in Å) and angles (in deg.) for cis-[M{1–(Fc–CH₂)-3,5-Ph₂–C₃HN₂}Cl₂(dmso)] {with M = Pt (4) or Pd (7)}

	M = Pt (4)	M = Pd (7)
a Average values for the Fc moiety.
Bond lengths
M–N(1)	2.021(3)	2.010(5)
M–Cl(1)	2.2813(12)	2.2630(17)
M–Cl(2)	2.3166(10)	2.3151(18)
M–S(1)	2.2044(10)	2.1965(19)
N(1)–N(2)	1.362(3)	1.355(9)
N(2)–C(11)	1.450(4)	1.444(11)
N(2)–C(12)	1.363(4)	1.382(10)
C(10)–C(11)	1.515(5)	1.471(13)
C(12)–C(19)	1.367(5)	1.400(8)
Fe–C^a	2.039(7)	2.04(4)
C–C^a	1.41(1)	1.41(2)
Bond angles
Cl(1)–M–Cl(2)	90.61(5)	90.74(7)
Cl(1)–M–S(1)	89.94(5)	90.04(7)
N(1)–M–Cl(2)	88.84(8)	88.35(19)
N(1)–M–S(1)	90.68(8)	90.92(19)
M–N(1)–N(2)	123.29(19)	121.8(5)
C(10)–C(11)–N(2)	112.4(3)	115.1(7)
C(12)–N(2)–N(1)	108.9(2)	106.0(6)
C(11)–N(2)–N(1)	121.1(2)	124.8(7)
N(2)–C(12)–C(13)	122.4(3)	124.7(7)

---

As expected, the bond lengths and angles of the ferrocenyl unit are consistent with those of monosubstituted ferrocene derivatives.²³ The two pentagonal rings are parallel (tilt angle = 0.41°) and their relative orientation deviates by 8.8(8)° from the ideal eclipsed one. In this compound the orientation of the pyrazolyl ring and the Fe(η⁵–C₅H₅) unit it is similar to that of 4, suggesting that the formation of 4 or 7 requires rotation around the N–CH₂– or the Fc–CH₂– bonds to reduce steric effects.

When the reaction was carried out using equimolar amounts of ligand 2 and cis-[PdCl₂(CH₃CN)₂] in methanol for 24 h (Table 2, entry II and Scheme 3, step B), a yellow solid was obtained and its characterization data (see experimental section) was consistent with those expected for the trimetallic complex trans-[Pd{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}₂Cl₂] (8). The yield of this synthesis was low but it improved considerably when a two fold excess of 2 was used. Compound 8 was also isolated by treatment of the ligand and Na₂[PdCl₄] {in molar ratios (1 : 1) or (2 : 1)} in methanol at room temperature (Table 2, entry III).

It should be noted that no evidence of the presence of any other type of palladium(II) complex was detected by ¹H–NMR studies of the crude (as well as of the mother liquors) of any of the experiments presented in Table 2, entries I–III.

In view of these results and in a further attempt to achieve cyclopalladated complexes, we decided to use more severe experimental conditions based on the reaction of the ligand 2 and Pd(AcO)₂ (in a 1 : 1 molar ratio) in refluxing toluene for 3.5 h (Scheme 3, C), subsequent treatment of the crude with a slight excess of PPh₃ (in CH₂Cl₂) followed by LiCl (in acetone) (Scheme 3, step C). Evaporation of the solvent produced a brownish residue, which was later on purified by silica gel column chromatography. The use of CH₂Cl₂ as eluant released a band that was collected and concentrated to dryness giving a bright yellow solid 9, whose elemental analyses (see the experimental section) were consistent with those expected for a palladacycle of the type: [Pd(C,N)Cl(PPh₃)]. Mono- and two dimensional NMR spectra revealed that 9 contains: a) a five-membered palladacycle in which compound 2 acts as a [C(phenyl), N(pyrazolyl)]⁻ ligand (Fig. 2, type A), and b) the PPh₃ ligand occupies the adjacent position to the metallated carbon atom in the coordination sphere of the palladium(II). All these findings suggested that 9 was [Pd{3–(C₆H₄)–5-Ph-1-(Fc-CH₂)–(C₃HN₂)}Cl(PPh₃)] (9), which is similar to complex 6, except for the nature of the metal atom.

X-ray diffraction studies revealed that the crystals contained a 1 : 1 array of molecules of CH₂Cl₂ and [Pd{3–(C₆H₄)-5-Ph-1-(Fc–CH₂)–(C₃HN₂)}Cl(PPh₃)] (9). In each one of these heterodimetallic units (Fig. 7 and Table 4), the palladium(II) is in a slightly distorted square-planar environment, where it is bound to the heterocyclic nitrogen of the pyrazole ring and the C(26) atom, thus confirming that metallation occurred on the phenyl ring on position 3 of the heterocycle. The two remaining coordination sites are occupied by a chloride and the phosphine ligand. The value of the P–Pd–C(26) bond angle {93.18(8)°} indicates that the PPh₃ ligand is in a cis position in relation to the Pd–C bond, in agreement with the transphobia effect.³¹ Bond lengths and angles around the palladium(II) (Table 4) are similar to those reported for related palladacycles of the type [Pd{C(sp², phenyl),N}Cl(PPh₃)].²³

Fig. 7 ORTEP plot of compound [Pd{[3-(C₆H₄)–5-Ph-1-{(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂}–(C₃HN₂)]}Cl(PPh₃)] (9), 50% probability displacement ellipsoids are shown and hydrogen atoms have been omitted for clarity.

Table 4 Selected bond lengths (in Å) and angles (in deg.) for compounds 9 and 10

	9	10
a This refers to the C(26) atom of complex 9 or to the C(1) atom of 10. b Average value for the Fc unit.
Bond lengths
Pd–P	2.2492(12)	2.2314(14)
Pd–Cl	2.4007(14)	2.3907(14)
Pd–N(1)	2.122(2)	2.128(3)
Pd–C^a	2.043(3)	2.017(4)
N(1)–N(2)	1.365(2)	1.339(4)
N(2)–C(11)	1.477(3)	1.371(5)
C(11)–C(10)	1.500(4)	1.521(6)
Fe–C^b	2.037(7)	2.04(2)
C–C^b	1.41(2)	1.43(1)
Bond angles
N(1)–Pd–C^a	80.46(10)	91.53(15)
N(1)–Pd–Cl	97.13(7)	84.63(10)
P–Pd–Cl	91.05(5)	94.20(5)
P–Pd–C^a	93.18(8)	91.08(12)

---

In the crystal, two molecules of [Pd{3–(C₆H₄)–5-Ph-1-(Fc–CH₂)–(C₃HN₂)}Cl(PPh₃)] are assembled in pairs by C–H⋯π interactions involving the hydrogen atom H(29) of a molecule and the ring defined by the set of atoms [C(39)–C(44)] [the distance H(29)⋯centroid of this ring is 3.491 Å] of the other one and vice versa. In addition, in each one of these units, the separation between the Cl(1) atom and the H(45A) atom of the CH₂Cl₂ molecule (2.837 Å) suggests a weak C–H⋯Cl interaction.

For ligand 2, the activation of any of the two ortho σ[C(ferrocene)–H] bonds of the Fc unit would give the six-membered metallacycles with a σ[Pd–C(ferrocene)] bond (B-type in Fig. 1) but none of the reactions studied here allowed us to isolate this sort of product. In view of this, and since it is well-known that one of the most common methods used to obtain palladacycles with [C(ferrocene),N]⁻ ligands consists of the treatment of the ferrocenyl ligand, M₂[PdCl₄] (M = Li⁺ or Na⁺) and NaAcO·3H₂O, in methanol at room temperature,^17b,33,34 we also decided to explore whether for ligand 2 this procedure could allow us to isolate metallacycles with a σ[Pd–C(ferrocene)] bond.

Reaction of 2 with Na₂[PdCl₄] and NaAcO·3H₂O in methanol at room temperature for 24 h produced a brown solid (Scheme 3, D). Further treatment with PPh₃ in dichloromethane and the subsequent purification of the crude by column chromatography on silica gel gave an orange solid 10. Its elemental analyses were consistent with those expected for a palladacycle of the type [Pd(C,N)Cl(PPh₃)], but its ¹H and ³¹P{¹H}–NMR spectra were markedly different from those of 9. The position of the singlet detected in the ³¹P{¹H} NMR spectrum (δ = 38 ppm) was similar to those reported for related compounds with N–donor ferrocenyl ligands and a σ[Pd–C(sp²,ferrocene)] bond (35 ppm < δ < 40 ppm),³³ and was up-field shifted when compared with 9 (δ = 46 ppm). Its ¹H–NMR spectrum was more complex than expected and showed six singlets with relative intensities (1 : 1 : 2 : 1 : 1 : 1) in the range 3.0 < δ < 4.2 ppm. This pattern, which is markedly different from those of compounds 3–9 or of five-membered palladacycles formed by metallation of the (η⁵–C₅H₄) ring of the Fc group,³³ suggests the presence of a σ(Pd–C) bond generated by a transannulation process.

The X-ray crystal structure of 10 (Fig. 8) revealed that the palladium(II) was bound to the nitrogen atom N(1) and the C(1) atom of the unsubstituted (η⁵–C₅H₅) ring of 2. Two remaining coordination sites are occupied by a chloride, and the phosphorous atoms of the PPh₃ ligand, which is in the adjacent position to the Pd–C bond in agreement with the transphobia effect.³¹

Fig. 8 ORTEP plot of compound [Pd{1-[(η⁵–C₅H₄)Fe(η⁵–C₅H₄)–CH₂]-3,5-Ph₂-1-(C₃HN₂)}Cl(PPh₃)] (10, 50% probability displacement ellipsoids are shown and hydrogen atoms have been omitted for clarity.

As a consequence of the different mode of binding, the separation between the two metal centres (3.563 Å) is smaller than in 9 (5.358 Å) or in the coordination complexes 5 and 7, but it clearly exceeds the sum of the van der Waals radii of these two atoms.³⁵ This precludes the existence of any direct interaction between iron and palladium.

The average values of the Fe–C and C–C bond lengths of the Fc moiety are similar to those reported for related 1,1′ disubstituted ferrocene derivatives.²³ Moreover, the two pentagonal rings of this unit are planar, parallel (tilt angle of 1.44°) and they deviate by ca. 9° from the ideal eclipsed conformation. The pyrazole ring is planar and it is nearly orthogonal to the rings of the Fc unit (angles between their mean planes = 89.0° and 90.0°). This arrangement of substituents is very similar to that of the free ligand¶ and differs from those found in 7 and 9 in which the pyrazole and the Fe(η⁵–C₅H₅) unit are on opposite sides of the coordination plane of the metal.

According to the mechanism accepted for the cyclopalladation and cycloplatination of N– donor ligands, the reaction proceeds through coordination of the metal(II) ion to the nitrogen followed by the subsequent electrophillic attack at the carbon atom.³⁶ Once the M–N bond is formed the relative orientation between the metal centre and the σ(C–H) bonds susceptible to metallation appears to be particularly relevant in determining the regioselectivity of the process.

It should be noted that since: a) previous theoretical studies revealed that six-membered palladacycles are expected to be more stable than those containing five-membered ring³⁷ and b) compound 10 was isolated under milder experimental conditions (room temperature) than 9 (under reflux and using longer reaction periods), we tentatively propose that 10 arises from kinetic control while 9 is formed under thermodynamic control. In order to confirm this hypothesis, we decided to investigate the reaction between equimolar amounts of ligand 2, Na₂[PdCl₄] and NaAcO·3H₂O in methanol for 24 h, followed by the treatment of the raw material with PPh₃. When the reaction was carried out at room temperature the ¹H–NMR spectrum of the crude revealed the presence of 10 and 9 in a molar proportion 6.0 : 0.8 and when the reaction was performed under reflux during the same period of time the molar ratio 10:9 was 2.3 : 1.0. This suggests that the proclivity of 2 to undergo the transannulation process to give 10 decreases upon heating when compared with metallation of the phenyl ring to produce 9.

It should be noted that despite this, it is well-known that: a) ferrocene derivatives are more prone to electrophillic attacks than their benzene analogues¹ and b) pallada- and platinacycles derived from the metallation of the substituted (η⁵–C₅H₄) ring of the Fc moiety are known,^4,33,34 and in the case of ligand 2 the presence of this type of six-membered palladacycles were not detected in any of the reactions investigated.

Theoretical studies

In a first step to rationalize the results obtained in the reactions of 2 with palladium(II) salts or complexes, we decided to undertake DFT calculations³⁸ for the three different types of metallacycles, A–C, depicted in Fig. 2 that arise from the metallation of the phenyl (A), the C₅H₄ ring (B) or formed by a transannulation process (C). The models used contained a chloride and an additional neutral L ligand (in a cis- arrangement to the metallated carbon) and also two different L ligands (PH₃ and dmso) in order to find out if the nature of this group could induce significant variations in the stability of the complexes. The choice of PH₃ instead of the PPh₃ ligand present in the palladium(II) complexes 9 and 10 was done in order to simplify the calculations and to minimize computational time.

For these six model compounds, the geometries were optimized before the calculations and their total energy was determined. The results (Table 5) obtained showed that the total energy of type A molecules was smaller than those of their isomers arising from the metallation of any of the two rings of the Fc unit (types B or C). For compounds with L = PH₃ the total energy of the molecule increased according to the sequence A < C < B and an identical trend was found for their analogues with dmso. Consequently, from a theoretical point of view, the formation of A-type palladacycles with a σ[Pd–C(sp², phenyl)] bond appears to be strongly favoured in the gas phase.

Table 5 Comparison of the calculated relative energies (in Kcal mol⁻¹)^a obtained for the three types of palladacycles A–C depicted in the lower part of the table in which the neutral ligand L represents PH₃, dmso or PPh₃ in the gas phase and in toluene or methanol solutions

L	Complex Type	Relative total energies^a
a .Relative energies to their corresponding A isomer.
		Gas Phase	Toluene	MeOH
PH3	A	0.0	0.0	0.0
PH3	B	6.7	5.6	4.3
PH3	C	4.1	3.2	2.3
dmso	A	0.0	0.0	0.0
dmso	B	7.3	6.0	4.3
dmso	C	5.5	4.2	2.6
PPh3	A	0.0	0.0	0.0
PPh3	B	5.8	4.2	3.3
PPh3	C	2.6	1.5	1.3

---

Since the polarity of the solvents used was different in the preparation of 9 and 10, we carried out additional computational studies in order to elucidate whether the solvent (toluene or methanol) could affect the relative stability of the three models. As can be easily seen in Table 5, in both solvents the minimum energy was obtained for A-type palladacycles and, for an identical neutral ligand, the energy of model B was again higher than that of its C-type analogue. When toluene is replaced by methanol the relative total energy of models B and C decreased, thus indicating that the polarity of the solvent may play a key role.

In a further step and in order to modelize the isolated products, we also calculated the total energies of complexes containing PPh₃. This family of products shows the same stability trend (Table 5) as the simpler models with L = PH₃ or dmso, and again the replacement of toluene by methanol reduces the differences ΔE_r = [E_T (for B or C types) − E_T (for A-model)]. Thus, according to these computational studies the cyclometallation of the phenyl ring is strongly preferred over the transannulation process or the metallation of the (η⁵–C₅H₄) unit.

In view of this, we focused our attention in other factors that could affect these metallation processes. First, structural studies have shown that the orientation of the pyrazole ring in the free ligand 2 and in complex 10 is similar.¶ This is in agreement with the results obtained for 4-ferrocenyl-1,3-oxazolidine (11) and its palladium(II) complex formed by metallation of the (η⁵–C₅H₅) ring.^4a Second, in 9 (as well as in the coordination compounds 4 and 7, which were also isolated under refluxing conditions) the heterocycle is in the opposite direction to Fe(η⁵–C₅H₅). This requires a change of the conformation of the ligand before or after the formation of the N–metal bond (Pd or Pt). Consequently, we decided perform molecular mechanics calculations to evaluate the variation of the total energy of ligand 2 for different orientations of the (η⁵–C₅H₄) ring of the Fc moiety and the heterocycle using the MM3 method.³⁹ Such arrangements of substituents were generated by modifying the torsion angles defined by the atoms C^2Fc–C^1Fc–C–N² and C^1Fc–C–N²–N¹ {hereinafter referred to as Φ(1) and Φ(2), respectively} in the range: [−180°, +180°].

The conformational map shows that if the free ligand is to achieve the same orientation as in 9 (or products 4 or 7), prior to the binding of the metal, this requires the change of Φ(1) and Φ(2) and an energy input. This would be more likely to occur if the reactions are performed under reflux (as happens in the preparation of 4, 7 and 9).

On the other hand, 9 and 10 were isolated using different starting reagents {Na₂[PdCl₄] or Pd(AcO)₂}, and then the first step of the process consists of the coordination of the PdCl_3̄ moiety (for 10) or of Pd(AcO)_3̄ (for 9) to the nitrogen of ligand 2. In the former case, where the reaction is performed in methanol at 298 K: a) according to the calculations, the difference between the relative total energy of the A and C–types decreases and b) the change of the conformation of the ligand requires an energy input and appears to be less likely to occur; consequently, once the Pd–N bond is formed the σ(C–H) bond of the C₅H₅ ring is extremely close to the metal centre and has the proper orientation as to undergo activation, this would lead to the C–type metallacycles.

In contrast with these findings, the first step of the formation of 9 consists of the binding of the Pd(AcO)_3̄ unit, (with a greater effective bulk than the PdCl_3̄ unit) and in order to minimize steric effects, the conformation of 2 should change. This may be promoted at high temperatures (under reflux). A similar argument can be used to explain the variation observed in the arrangement of the ferrocene and pyrazole units in cis-[M[1-{(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂}-3,5-Ph₂–C₃HN₂]Cl₂(dmso)] {M = Pt (4) or Pd (7)} when compared with those of 2 or 9.

For this arrangement of groups the σ[C(phenyl)–H] bond on the ortho site is closer to the M(II) centre and has a better orientation than any of the σ[C(sp², ferrocene)–H] bonds of the (η⁵–C₅H₅). Thus the cyclometallation of the phenyl ring is strongly preferred over the transannulation process.

Conclusions

The new 3,5-diphenylpyrazole derivative [1-(Fc−CH₂)-3,5-Ph₂–(C₃HN₂)] {Fc = (η⁵–C₅H₅)Fe(η⁵–C₅H₄)−} (2) with a Fc–CH₂– unit on position 1 of the heterocycle has been prepared and characterized. The study of its reactivity in front of platinum(II) and palladium(II) salts has lead to heterodi- (3–7, 9 and 10) or heterotrimetallic complexes (8) complexes, where 2 acts as a neutral N– donor ligand (in 3, 4, 7 and 8) or as a bidentate [C(sp²,phenyl),N]⁻ (in 5 and 6 or 9) or [C(sp², ferrocene),N]⁻ in 10.

Furthermore, we have demonstrated that the proper selection of the initial Pd(II) starting material {cis-[PdCl₂L₂] (L =dmso or CH₃CN), Na₂[PdCl₄] or Pd(AcO)₂} and the experimental conditions {temperature, solvents (methanol or mixtures of toluene/methanol); the presence or absence of additional NaAcO} allows the control of: a) the type of final product {heterodi- (in 7, 9 and 10) or trimetallic (in 8)}, b) the mode of binding of the ligand {monodentate (in 7 and 8) or bidentate (C,N)⁻ (in 9 and 10)} and c) the regioselectivity of the cyclometallation process and the type of σ(Pd–C) bond formed {σ[Pd–C(sp², phenyl)] (in 9) or σ[Pd–C(sp²,ferrocene)] (in 10)}.

The formation of compound 10 bond takes place under milder experimental conditions than that of the metallacycle 9 with a five-membered ring and a σ[Pd–C(sp²,phenyl)] bond. The computational studies undertaken for the simplified models of the palladacycles (A–C) indicate that complexes formed by metallation of the phenyl ring (A-type) are more stable than type C (transannulation products) and B models (with a 1,2-disubstituted ferrocene unit) that are the less stable products.

In addition, the studies summarized here provide conclusive evidences of the crucial role of the solvent, the temperature and the steric effects induced by the palladium(II) or platinum(II) salt or complex used as starting material in determining the nature of the C–H bond to be activated. Both theoretical and experimental data suggest that: a) the formation of the metallacycles with a σ{M–C(sp², phenyl)} bond (5, 6, and 9 with A-types cores) is strongly favoured at high temperatures (refluxing toluene or methanol or mixtures of both) which may provide the energy input required to change the orientation of the ligand and when the starting reagents are bulky {[MCl₂(dmso)₂] or Pd(AcO)₂}; b) the activation of the C–H bond of the unsubstituted (η⁵–C₅H₅) ring, to form 10 (C–type) is favoured at low temperature (methanol) and c) metallacycles with a 1,2-(η⁵–C₅H₃) ring (B-type cores) are the less stable ones in both solvents and have not been obtained in any experiment.

Finally, since it is well-known that palladium(II) and platinum(II) complexes containing bidentate (C,N)⁻ ligands have a variety of applications in several fields (i.e. organometallic synthesis and homogeneous catalysis) and are attractive in view of their potential photo-optical properties or biological activities, the new products presented here appear to be excellent candidates to be studied in these fields.

Experimental

Materials and methods

FcCH₂OH and the complexes [MCl₂(dmso)₂] (M = Pd or Pt) were prepared as reported previously.^20,24,40 The remaining reagents were obtained from commercial sources and used as received. Except methanol (which was HPLC-grade), the remaining solvents were dried and distilled before use.⁴¹ Elemental analyses were carried out at the Serveis de Cientifico-Tècnics (Universitat Barcelona). Mass spectra (ESI⁺) were performed at the Servei d'Espectrometria de Masses (Universitat de Barcelona). Infrared spectra were obtained with a Nicolet 400FTIR instrument using KBr pellets. The R_f values were obtained using SiO₂ (Merck silica gel 60 F254) plates and the solvents specified in the characterization section of the corresponding product. High resolution ¹H–NMR spectra and the two-dimensional {¹H–¹H}–NOESY and COSY experiments were registered with a Varian VRX-500 or a Bruker Avance DMX-500 MHz instruments. ¹⁹⁵Pt{¹H}–NMR spectra of compounds 3–6 were obtained with a Bruker-250 MHz instrument. ³¹P{¹H}–NMR spectra of 6, 9 and 10 were recorded with a Varian-Unity-300 instrument. In all cases the solvent for the NMR experiments was CDCl₃ (99.9%) and the references were SiMe₄ [for ¹H NMR], P(OMe)₃ [δ(³¹P) = 140.17 ppm] for ³¹P–NMR and H₂[PtCl₆] [δ¹⁹⁵Pt{H₂[PtCl₆]} = 0.0 ppm] for ¹⁹⁵Pt{¹H}–NMR experiments. All these NMR studies were performed at 298 K. The chemical shifts (δ) are given in ppm and the coupling constants (J) in Hz. In the characterization section of each product, the assignment of the signals detected in the ¹H–NMR spectra refer to the labelling patterns presented in Schemes 1, 2 and 4. UV-vis. spectra of 1.0 × 10⁻⁴ M solutions of the compounds in CH₂Cl₂ were recorded with a Cary 100 scan Varian UV spectrometer at 298 K.

Preparation of the ligand.
[1-{(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂}-3,5-Ph₂–C₃HN₂] (2). 3,5-Diphenylpyrazole (0.5 g, 2.27 × 10⁻³ mol) and Fc–CH₂OH (0.49 g, 2.27 × 10⁻³ mol) were dissolved in 50 mL of CH₂Cl₂. Then a solution formed by 9 mL of HBF₄ and 6 mL of H₂O was added dropwise under stirring. The resulting mixture was magnetically stirred at 298 K for 1 h and afterwards it was treated with 100 mL of H₂O. The mixture was extracted with two 50 mL portions of CH₂Cl₂ and the organic layer was then dried over Na₂SO₄ and concentrated. Further purification by flash chromatography on silica gel using CH₂Cl₂ as eluant produced the release of an orange band that was concentrated to dryness on a rotary evaporator. The solid formed was collected and dried in vacuum for 24 h. (Yield: 0.91 g, 96%). ¹H–NMR data: δ = 4.06 (s, 2H, H^2Fc and H^5Fc), 4.12 (s, 7H, H^3Fc, H^4Fc and Cp), 5.09 (s, 2H, –CH₂–), 6.56 (s, 1H, H⁴), 7.33 (br, 2H, H^4a and H^4b), 7.40–7.70 (br.m, 6H, H^3a, H^5a, H^2b, H^3b, H^5b and H^6b) and 7.95 (dd, 2H, J = 8 and 1, H^2a and H^6a). IR (solid, cm⁻¹): 1969(w), 1774(w), 1723(w), 1637(w), 1602(m), 1547(m), 1514(s), 1484(s), 1460(s), 1368(s), 1313(s), 1236(m), 1193(m), 1103(s), 1079(s), 997(s), 957(m), 820(s), 766(s), 703(s), 565(m) and 495(s). UV-vis. data: λ in nm (ε in M⁻¹ cm²) = 244 (42250), 246 (42140), and 438 (4850). R_f (in CH₂Cl₂) = 0.88. MS (ESI⁺): m/z = 419.1 {[M] + H}⁺. Elemental analysis calc. for C₂₆H₂₂N₂Fe; C 74.65, H 5.30, N, 6.70 (6.69), found: C 74.53, H 5.27, N 6.69.

Preparation of the palladium(II) and platinum(II) complexes ||.
Trans-[Pt[1-{(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂}-3,5-Ph₂–C₃HN₂]Cl₂(dmso)] (3). Cis-[PtCl₂(dmso)₂] (249 mg, 5.90 × 10⁻⁴ mol) was suspended in 30 mL of methanol and refluxed until complete dissolution. Then the hot solution was filtered out and the filtrate was poured on a solution containing 247 mg (5.90 × 10⁻⁴ mol) of 2 and 5 mL of methanol. The resulting reaction mixture was refluxed for 1 h. After this period, the solution was filtered out, the resulting filtrate was concentrated to dryness on a rotary evaporator and the brownish residue was air dried for 24 h. After this period the solid was dissolved in the minimum amount of CH₂Cl₂ (≈15 mL) and passed through a SiO₂ column (8.5 cm × 3.0 cm). Elution with CH₂Cl₂ released two yellow bands that were collected and concentrated to dryness on a rotary evaporator. The first eluted band gave after concentration to dryness on a rotary evaporator the cis- isomer (4) (≈39 mg). Identical work up of the second eluted band, produced compound 3 (351 mg, 78%) as an orange-yellow microcrystalline material. ¹H–NMR data: δ 3.68 [s, 6H, ³J_Pt,H = 19, Me(dmso)], 4.03 (s, 2H, H^3Fc and H^4Fc), 4.14 (s, 5H, Cp), 4.30 (s, 2H, H^2Fc and H^5Fc), 5.89 (s, 2H, –CH₂–), 6.45 (s, 1H, H⁴), 7.32–7.60 (m, 8H, H^3a–H^5a and H^2b–H^6b) and 8.76 (d, 2H, J = 7.8, H^2′′ and H^6′′). ¹⁹⁵Pt{¹H}–NMR: δ −2998. IR (solid, cm⁻¹) 1638(s), 1553(w), 1481(m), 1459(m), 1383(m), 1297(w), 1149(s), 1105(m), 1022(s), 920(w), 817(w), 761(m), 697(s) and 482(s) cm⁻¹. UV-vis. data: λ in nm (ε in M⁻¹ cm²) = 242 (36870). R_f (in CH₂Cl₂) = 0.64. MS (ESI⁺): m/z = 780.1{[M] + (NH₄)}⁺. Elemental analysis calc. for C₂₈H₂₈N₂OSCl₂FePt C 44.11, H, 3.70, N, 3.67, S, 4.21, found, C 44.13, H 3.71, N 3.67 3.59, S 4.18.
Cis-[Pt[1-{(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂}-3,5-Ph₂–C₃HN₂]Cl₂(dmso)] (4). This compound was also obtained as a by-product during the preparation of 3 (see preceding section) but the method described here allows its isolation in a higher yield. The procedure is identical to that described above for the trans- isomer (3), except that the refluxing period was 3.5 h. The first eluted band produced after concentration 272 mg of compound 4 and small amounts (58 mg) of 3 were also isolated from the band collected afterwards. Crystals suitable for X-ray analyses were obtained by slow evaporation of a saturated CH₂Cl₂ solution of 4 at 270 K. ¹H–NMR data: δ 2.43 [s, 3H, ³J_Pt,H = 20, Me(dmso)], 2.79 [s, 3H, ³J_Pt,H = 20, Me(dmso)], 3.67(s, 5H, Cp), 4.06 (s, 1H, H^4Fc), 4.10 (s, 1H, H^3Fc), 4.15 (s, 1H, H^2Fc), 4.20 (s, 1H, H^5Fc), 5.51 (d, 1H, ²J = 15.0, –CH₂–), 6.06 (d, 1H, ²J = 15.0,–CH₂–), 6.49 (s, 1H, H⁴), 7.45–7.78 (br. m, 8H, H^3a–H^5a and H^2b–H^6b) and 8.21(d, 2H, ³J = 7.8, H^2a and H^6a). ¹⁹⁵Pt{¹H}–NMR data: δ = −2850. IR (solid, cm⁻¹) data: 1637(s), 1553(w), 1481(m), 1449(m), 1385(m), 1311(w), 1149(s), 1105(mn), 1075(m), 921(w), 821(w), 760(m), 699(s) and 482(s). UV-vis. data: λ in nm (ε in M⁻¹ cm²) = 237 br.(39920). R_f (in CH₂Cl₂) = 0.81. MS (ESI⁺): m/z = 780 {[M] + (NH₄)}⁺ and 726 {[M]–Cl}⁺. Elemental analysis calc. for C₂₈H₂₈N₂OSCl₂FePt: C 44.11, H 3.70, N, 3.62, S 4.21, found: C 44.03, H 3.67, N 3.57; S 4.01.
[Pt{[3–(C₆H₄)-5-Ph-1-{(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂}–C₃HN₂]Cl(dmso)] (5). Ligand 2 (247 mg, 5.90 × 10⁻⁴ mol) and cis-[PtCl₂(dmso)₂] (249 mg, 5.90 × 10⁻⁴ mol), were suspended in 25 mL of toluene. Then a solution formed by 100 mg (1.18 × 10⁻³ mol) of NaAcO and 5 mL of methanol was added and the mixture was refluxed for 3.5 h. After this period the hot solution was carefully filtered out, the filtrate was concentrated to dryness on a rotary evaporator and the residue was air-dried for 24 h. Afterwards, the raw material was dissolved in the minimum amount of CH₂Cl₂ (≈15 mL) and passed through a SiO₂ column (8.5 cm × 3.0 cm). Elution with CH₂Cl₂ released two yellow bands that were collected and concentrated to dryness on a rotary evaporator. The first eluted band gave, after concentration to dryness on a rotary evaporator, traces (≈3 mg) of the cis- isomer (4). Identical work up of the second eluted band, produced compound 5 (269 mg) as a bright yellow-microcrystalline material. ¹H–NMR data: δ = 2.79 [s, 3H, ³J_Pt,H = 20, Me(dmso)], 2.87 [s, 3H, ³J_Pt,H = 19, Me(dmso)], 3.90 (s, 5H, Cp), 4.01 (s, 1H, H^4Fc), 4.07 (s, 1H, H^3Fc), 4.19 (s, 1H, H^5Fc), 4.90 (s, 1H, H^2Fc), 5.20 (d, 1H, ²J = 15.2, –CH₂–), 5.81 (d, 1H, ²J = 15.2, –CH₂–), 6.40 (s, 1H, H⁴), 6.60 (d, 1H, J = 7.5 and ³J_Pt,H = 39.4, H^3a), 6.95 (m, 1H, H^4a), 7.45–7.78 (br. m, 6H, H^5a and H^2b–H^6b) and 8.05 (d, 2H, H^6a). ¹⁹⁵Pt{¹H}–NMR data: δ −3875. IR (solid, cm⁻¹) 1683 (m), 1532(m), 1482(m), 1449(m), 1383(m) 1291(m), 1149(s), 1104(m), 1023(s), 999(m), 822(m), 763(2), 699(m), 496 (w), 481(m) and 436(m). UV-vis. data: λ in nm (ε in M⁻¹ cm²) = 243 (49321), 272 (45920) and 355 (5931). R_f (in CH₂Cl₂) = 0.68). MS (ESI⁺): m/z = 698{[M]–Cl}⁺. Elemental analysis calc. for C₂₈H₂₇ClN₂FeOPS: C 46.32, H 3.75, N 3.86, S 4.42, found: C 46.25, H 3.8, N 3.7, S 4.35.
[Pt{[3-(C₆H₄)-5-Ph-1-{(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂}–C₃HN₂]Cl(PPh₃)] (6). Compound 5 (88 mg, 1.2 × 10⁻⁴ mol) was dissolved in 50 mL of CH₂Cl₂ and then an equimolar amount (32 mg) of PPh₃ was added. The resulting mixture was stirred at 298 K for 1 h and then the undissolved materials were removed by filtration and discarded. The filtrate was then concentrated to ca. 5 mL and passed through a short SiO₂–column (1.0 cm × 2.5 cm) to remove the free dmso. Elution with a CH₂Cl₂ : MeOH (100 : 0.1) mixture produced the release of a bright yellow band that was collected and concentrated to dryness on a rotary evaporator. The solid formed was collected, air-dried and then dried in vacuum for 2 days. (Yield: 95 mg, 87%). ¹H–NMR data: δ 3.85 (s, 2H, H^2Fc, H^5Fc) 4.00 (s, 2H, H^3Fc, H^5Fc), 4.05 (s, 5H, Cp), 6.12 (s, 2H, –CH₂–), 6.35 (td, 1H, J = 7.5 and 1.5 H^5a), 6.40 (br, 2H, H⁴ and H^3a), 6.85 (td, 1H, J = 7.5 and 1.5, H^4”), 7.32–8.15 (br m, 21H, H^6a, H^2b–H^6b and aromatic protons of the PPh₃ ligand). ³¹P{¹H}–NMR data: δ = 16.7 (d, ¹J_P,Pt = 4180). ¹⁹⁵Pt{¹H}–NMR data: δ −4226 (¹J_Pt,P = 4180). IR (solid, cm⁻¹): 1615(w), 1585(w), 1543(w), 1480(s), 1433(s), 1420(w), 1390(w), 1189(w), 1095(s), 1033(m), 810(w), 784(s), 693(s) and 520(broad) cm⁻¹. UV-vis. data: λ in nm (ε in M⁻¹ cm²) = 239 (48761), 275(sh) and 342(6538). R_f [in CH₂Cl₂: MeOH (100 : 0.2)] = 0.86. MS (ESI⁺): m/z = 873.6 {[M]–Cl}⁺. Elemental analysis calc. for C₄₄H₃₆Cl₂N₂FePPt: C 58.07, H 3.99, N, 3.08; found C 57.95, H 3.99 4.05; N, 2.95.
Cis-[Pd[1-{(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂}-3,5-Ph₂–(C₃HN₂)]Cl₂(dmso)] (7). A solution formed by cis-[PdCl₂(dmso)₂] (197 mg, 5.90 × 10⁻⁴ mol), ligand 2 (247 mg, 5.90 × 10⁻⁴ mol) and methanol (30 mL) was refluxed for 30 min. After this period, the solution was filtered out, the resulting filtrate was concentrated on a rotary evaporator to 10 mL. The solid formed was collected by filtration and air-dried for 24 h Afterwards it was dissolved in the minimum amount of CH₂Cl₂ and the resulting bright yellow solution was kept at 270 K for one day. The yellow crystals formed were collected by filtration and dried in vacuum for two days. (Yield: 321 mg, 81%). ¹H–NMR data: δ 2.25 [s, 3H, Me(dmso)], 2.78 [s, 3H, Me(dmso)], 3.82 (s, 5H, Cp), 4.08 (s, 1H, H^3Fc), 4.10 (s, 1H, H^4Fc), 4.16 (s, 2H, H^2Fc), 4.95 (s, 1H, H^5Fc), 5.48 (d, 1H, ²J = 15.0, –CH₂–), 5.92 (d, 1H, ²J = 15.0, –CH₂–), 6.10 (s, 1H, H⁴), 8.32 (d, J = 7.5, 2H, H^2a and H^6a),7.30–7.90 (8H, H^3a–H^5a and H^2b–H^5b). IR (solid, cm⁻¹) 1587(w), 1474(m), 1446(m), 1385(m), 1326(m), 1156(w), 1104(m), 1075(m), 819(w), 778 (m), 757(s), 700(s) and 484(m) cm⁻¹. UV-vis. data: λ in nm (ε in M⁻¹ cm²) = 239br. (43921). MS (ESI⁺): m/z = 636{[M]–Cl}⁺. Elemental analysis calc. for C₂₈H₂₈Cl₂N₂FeOPdS C, 49.91, H 4.19, N 4.16, S 4.76; found: C 50.0, H 4.2, N 4.05, S, 4.6).
Trans-[Pd{1-[(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂]-3,5-Ph₂–(C₃HN₂)}₂Cl₂] (8). This compound was obtained using two alternative procedures that differ in the nature of the starting palladium(II) complex used as reagent: cis-[PdCl₂(CH₃CN)₂] or Na₂[PdCl₄] {methods a) and b), respectively}.
Method a). A 300 mg amount (7.18 × 10⁻⁴ mol) of ligand 2 was dissolved in the minimum amount of MeOH. Then a solution formed by 101 mg (3.59 × 10⁻⁴ mol) of [PdCl₂(CH₃CN)₂] and 30 mL of methanol was added. The resulting mixture was stirred at 298 K for 24 h and after this period the yellow solid formed was collected by filtration, air-dried and finally dried in vacuum for one day. (Yield: 305 mg, 84%).
Method b). A solution containing Na₂[PdCl₄] (105 mg , 3.57 × 10⁻⁴ mol) and 10 mL of methanol was treated with a mixture formed by ligand 2 (300 mg, 7.18 × 10⁻⁴ mol) and 5 mL of methanol. The reaction mixture was kept under continuous stirring for 24 h and the solid formed was then collected by filtration and dried as in Method a). (Yield: 324 mg, 89%).¹H–NMR data: δ = 4.07 [br.s, 4H, 2(H^2Fc and H^5Fc)], 4.11 (s, 10H, 2 Cp), 4.22 [br.s, 4H, 2(H^3Fc and H^4Fc)], 5.92 (s, 4H, 2 –CH₂–), 6.35 (s, 2H, 2 H⁴), 7.30–7.89 [br. m, 2(H^2b–H^6b and H^3a–H^5a)] and 8.09 [br, 4H, 2(H^2a and H^6a)]. IR (solid, cm⁻¹) 1637(s), 1557(w), 1483(s), 1447(s), 1373(m), 1325(m), 1174(w), 1103(mn), 1040(m), 1028(m), 810(w), 765(s), 751(s), 700(s) 507(w) and 496(s) cm⁻¹. UV-vis. data: λ in nm (ε in M⁻¹ cm²) = 239br. (62391). MS (ESI⁺): m/z = 976{[M]–Cl}⁺ and 470.5 {[M]–2Cl}²⁺/2. Elemental analysis calc. for C₅₂H₄₄Cl₂N₄Fe₂Pd: C 61.60, H 4.37, N 5.53; found, C 61.55, H 4.30, N 5.60.
[Pd{[3-(C₆H₄)-5-Ph-1-{(η⁵–C₅H₅)Fe(η⁵–C₅H₄)–CH₂}–(C₃HN₂)]Cl(PPh₃)] (9). Pd(OAc)₂ (161 mg, 7.23 × 10⁻⁴ mol) was added to a solution containing 300 mg (7.18 × 10⁻⁴ mol) of 2 and 20 mL of toluene and the mixture was refluxed for 3.5 h. After this period the resulting hot solution was filtered through a small plug (2.0 cm × 3.5 cm) of Celite. The bright yellow solution was concentrated to dryness and kept for further use. The Celite was allowed to dry overnight and then it was washed with two (10 mL) portions of CH₂Cl₂. These washings were collected in the same flask containing the residue and finally, the solution was concentrated to ca. 10 mL a rotary evaporator. Then, PPh₃ (188 mg, 7.18 × 10⁻⁴ mol) was added and the mixture was stirred for 1.5 h at 298 K. After this period it was filtered and the filtrate was concentrated to dryness on a rotary evaporator giving a brownish residue which was then suspended in 30 mL of acetone and treated with LiCl (32 mg, 7.18 × 10⁻⁴ mol) and the resulting suspension was stirred at 298 K for 2.5 h. After removing the undissolved materials by filtration, the filtrate was concentrated to dryness on a rotary evaporator and dried in vacuum overnight. The yellowish-brown residue was dissolved in 10 mL of CH₂Cl₂ and passed through a SiO₂ column (3.0 cm × 9.0 cm) using CH₂Cl₂ as eluant. This produced the release of two yellow bands that gave after concentration to dryness [PdCl₂(PPh₃)₂] and compound 9 respectively. (Yield: 537 mg, 91%).). ¹H–NMR data: δ = 3.90 (s, 2H, H^2Fc and H^5Fc), 4.02 (s, 1H, H^3Fcand H^5Fc), 4.03 (s, 5H, Cp), 6.02 (s, 2H, –CH₂–), 6.35 (td, 1H, J = 7.5 and 1.5, H^5a), 6.43 (this resonance was partially masked by the signal due to H⁴, 1H, H^3a), 6.44 (s, 1H, H⁴), 6.85 (td, 1H, J = 7.5 and 1.5, H^4”), 7.35–8.01 (br m, 21H, H^6a, H^2b–H^6b and aromatic protons of the PPh₃ ligand). ³¹P{¹H} NMR data: δ 46.1. IR (solid, cm⁻¹) 1618(w), 1588(w), 1546(w), 1479(s), 1436(s), 1419(w), 1383(w), 1185(w), 1096(s), 1035(m), 812(w), 785(s), 696(s), 532(s) and 515(m) cm⁻¹. UV-vis. data : λ in nm (ε in M⁻¹ cm²) =244 (49550), 268 (46000), 336 (6264). R_f(CH₂Cl₂) = 0.44.MS (ESI⁺): m/z = 785.1 {[M]–Cl–(CH₂Cl₂)}⁺. Elemental analysis calc. for C₄₄H₃₆N₂PClFePd·CH₂Cl₂: C 59.63, H 4.23, N 3.09; found: C 59.5, H 4.3, N 3.0.
[Pd{1-[(η⁵–C₅H₄)Fe(η⁵–C₅H₄)–CH₂]-3,5-Ph₂-1-(C₃HN₂)}Cl(PPh₃)] (10). A mixture containing compound 2 (250 mg, 5.98 × 10⁻⁴ mol), Na₂[PdCl₄] (176 mg, 5.98 × 10⁻⁴ mol) NaOAc·3H₂O (81 mg, 5.98 × 10⁻⁴ mol) and 30 mL of methanol was stirred for 24 h at 298 K. After this period the deep-orange precipitate formed was filtered out and dried in vacuum for two days. Then it was dissolved in 20 mL of CH₂Cl₂, treated with PPh₃ (157 mg, 5.98 × 10⁻⁴ mol) and stirred for 1.5 h at 298 K. After this period, undissolved materials were removed by filtration and discarded and the filtrate was concentrated to dryness on a rotary evaporator giving a yellowish-brown residue which was then dissolved in minimum amount of CH₂Cl₂ and passed through a SiO₂ column (2.0 cm × 8.5 cm) using CH₂Cl₂ as eluant. The deep orange band was collected and concentrated to dryness on a rotary evaporator giving 10 as a deep orange microcrystalline material. This solid was collected, air-dried and then dried in vacuum for 3 days (Yield: 270 mg, 55%). ¹H–NMR data: δ 3.12 (s, 1H, H^2'Fc); 3.45 (s, 1H, H^4'Fc), 3.60 (s, 1H, H^4'Fc), 3.82 (s, 1H, H^5'Fc), 3.90, 4.05 and 4.12 (s, relative intensities 2 : 1 : 1, 4H, H^2Fc–H^5Fc), 4.50 (br. 1H, –CH₂–), 5.20 (br. 1H, –CH₂–), 6.85 (s, 1H, H⁴) and 7.40–8.30 (br.m. 25H, H^2a–H^6a, H^2b–H^6b and aromatic protons of the PPh₃ ligand). ³¹P{¹H} NMR data: δ 38.1. IR (solid, cm⁻¹) 1551(w), 1479(m), 1465 (m) 1433(s) 1377 (w) 1307(m) 1181(w), 1152(w) 1095(m), 1027(m), 866(w), 820 (m), 756(s), 692(s), 534(s),517 (m) 495(m) and 489 (m) cm⁻¹. UV-vis. data: λ in nm (ε in M⁻¹ cm²) = 243 (49450), 255 (45986), 316 (7492), 393 (3390), and 469 (1329). R_f (CH₂Cl₂) = 0.35. MS (ESI⁺): m/z = 785.1 {[M]–Cl}⁺. Elemental analysis calc. for C₄₄H₃₆N₂PClFePd:C 64.33, H, 4.39, N, 3.41 found C 64.24, H 4.61, N 3.33.

Crystallography

A prismatic crystal of compounds 2, 4, 7, 9 and 10 (sizes in Table 6), was selected and mounted on a MAR345 diffractometer with image plate detector. Unit-cell parameters were determined from 1237 (for 2), 1203 (for 4), 7287 (for 7), 217 (for 9) and 257 (for 10) reflections (in the range 3° < θ < 31°) and refined by the least-squares method. Intensities were collected with graphite monochromatized Mo-Kα radiation.

Table 6 Crystal data and details of the refinement of the crystal structures of the free ligand [1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)] (2) and cis-[M{1-(Fc−CH₂)-3,5-Ph₂–C₃HN₂}Cl₂(dmso)] {M = Pt (4) or Pd (7)} and the palladium(II) complexes 9 and 10

	2	4	7	9	10
Empirical formula	C26H22FeN2	C28H28Cl2FeN2OPtS	C28H28Cl2FeN2OPdS	C44H36ClFeN2PPt·CH2Cl2	C44H36ClFeN2PPd
Formula weight	418.31	762.42	673.74	906.34	821.42
Crystal size/mm× mm× mm	0.2 × 0.09 × 0.09	0.2 × 0.1 × 0.1	0.2 × 0.1 × 0.1	0.2 × 0.1 × 0.1	0.1 × 0.09 × 0.09
Crystal system	Triclinic	Orthorhombic	Orthorhombic	Triclinic	Triclinic
Space group	P1̄	Pbca	Pbca	P1̄	P1̄
a/Å	10.345(7)	15.865(4)	15.938(5)	9,817(6)	10.625(6)
b/Å	10.589(6)	13.213(6)	13.226(5)	11.219(5)	12.789(5)
c/Å	11.221(4)	26.348(10)	26.424(4)	19.794(9)	14.469(6)
α (°).	67.47(4)	90.0	90.0	76.47(3)	93.58(2)
β (°).	67.79(4)	90.0	90.0	82.46(3)	105.398(2)
γ (°).	82.84(5)	90.0	90.0	69.94(3)	107.09(2)
T/K	293(2)	173(2)	293(2)	293(2)	233(2)
λ/Å	0.71073	0.71073	0.71073	0.71073	0.71073
V/Å^3	1050.8(10)	5523(4)	5570(3)	1987.9(18)	1790.71(14)
Z	2	8	8	2	2
D calc./Mg × m-^3	1.322	1.834	1.607	1.514	1.523
μ/mm^−1	0.731	5.879	1.458	1.094	1.062
F(000)	436	2976	2720	920	836
Θ range for data collection/deg.	from 2.66 to 32.98	from 2.57 to 32.53	from 2.98 to 32.39	from 2.59 to 32.58	from 2.87 to 32.12
N. of collected reflections	10793	38751	40442	18781	16450
N. of unique reflections {R(int)}	5687{0.0606}	7641{0.0833}	7038{0.0542}	10074{0.0481}	8927{0.0502}
N. of parameters	263	327	326	478	452
Completeness to Θ = 25°	93.0%	96.3%	90.2%	92.5%	92.4%
Absorption correction	Empirical	Empirical	Empirical	Empirical	Empirical
Max. and min transmission	0.94 and 0.92	0.55 and 0.49	0.86 and 0.83	0.89 and 0.88	0.91 and 0.90
Goodness of fit on F^2	1.130	1.083	1.082	1.078	1.089
R indices {I > 2σ(I)}	R 1 = 0.0568,	R 1 = 0.0414,	R 1 = 0.0675,	R 1 = 0.0401	R 1 = 0.0624
	wR2 = 0.1842	wR2 = 0.1174	wR2 = 0.2041	wR2 = 0.0995	wR2 = 0.1884
R indices (all data)	R 1 = 0.0827,	R 1 = 0.0440,	R 1 = 0.0761,	R 1 = 0.0502	R 1 = 0.0763
	wR2 = 0.1949	wR2 = 0.1148	wR2 = 0.2098	wR2 = 0.1034	wR2 = 0.1198

---

Crystal structures were solved by direct methods (for 2, 7 and 9) or by Patterson synthesis (for 4 and 10), using SHELXS computer program⁴² and refined by full-matrix least-squares method with the SHELX97 computer program.⁴³ Lorentz–polarization corrections were made in all cases and absorption corrections were also carried out for 2,4 and 10.

For the five compounds, all hydrogen atoms were computed and refined using a riding model with an isotropic temperature factor equal to 1.2 times the equivalent temperature factor of the atom to which is linked. The final R(on F) and wR(on │F│²) factors were 0.057 and 0.194, respectively (for 2); 0.041 and 0.115 (for 4); 0.067 and 0.204 (for 7); 0.040 and 0.099 (for 9) and goodnesses of fit = 1.130, 1.083, 1.082, 1.078 and 1.088 (for 2, 4,7, 9 and 10, respectively) for all the observed reflections. The number of parameters and other relevant data concerning the resolution and refinement of these structures is presented in Table 6.

The crystallographic information files of the crystal structures of compounds 2, 4, 7, 9 and 10 have been deposited at the Cambridge Crystallographic Data Centre (deposition numbers: CCDC 826854–826858).

Computational details

The conformational map has been searched at the molecular mechanics level, using the augmented MM3 method³⁹ as implemented in Cache.⁴⁴ The two dihedral angles {Φ(1) and Φ(2)} have been sampled every 10 degrees, and the remaining geometric parameters have been fully optimized. DFT calculations have been performed at the B3LYP level⁴⁵ using the Gaussian 03 software.³⁸ The basis set has been chosen as follows: LANL2DZ⁴⁶ for Pd, Fe, S and Cl, including polarization functions for S and Cl,⁴⁷ 6-31G⁴⁸ for hydrogen, and 6-31G(d) including polarization functions^48,49 for the remaining atoms. Solvent effects have been calculated using the C-PCM model.⁵⁰

Acknowledgements

This work was suported by the Ministerio de Ciencia e Innovación of Spain {grant number CTQ2009-1150, (subprogram BQU)}, FEDER Funds and by the Generalitat de Catalunya (grant number 2009-SGR-1111).

References

1. (a) Ferrocenes. Homogeneous Catalysis, Organic Synthesis. Materials Science, (ed) A. Togni and T. Hayashi, VCH, Weinheim (Germany), 1995; (b) Ferrocene. Ligands, Materials and Biomolecules, (ed.) P. Stepnicka, Wiley, Weinheim (Germany), 2008.
2. (a) For recent reviews on the properties or utility of ferrocene heterocycles, see: L. V. Snegur, Y. S. Nekrasov, N. S. Sergeeva, Z. V. Zhilina, V. V. Gumenyuk, Z. A. Starikova, A. A. Simenel, N. B. Morozova, I. K. Sviridova and V. N. Babin, Appl. Organomet. Chem., 2008, 22, 139–147; (b) G. Fu, Asymm. Synth., 2007, 186–90; (c) J. Yoon, S. K. Kim, N. J. Singh and K. S. Kim, Chem. Soc. Rev., 2006, 35, 355–360; (d) R. Gómez Arrayas, J. Adrio and J. C. Carretero, Angew. Chem., Int. Ed., 2006, 45, 7674–7715; (e) D. R. van Staveren and N. Metzler-Nolte, Chem. Rev., 2004, 104, 5931–5985.
3. (a) For recent advances on this field, see: M. E. Weiss, D. F. Fischer, Z. Xin, S. Jautze, W. B. Schweizer and R. Peters, Angew. Chem., Int. Ed., 2006, 45, 5694–5698; (b) C. E. Anderson, Y. Donde, C. J. Douglas and L. E. Overman, J. Org. Chem., 2005, 70, 648–657; (c) D. Pou, A. E. Platero-Prats, S. Pérez, C. López, X. Solans, M. Font-Bardía, P. W. N. M. van Leeuwen, G. P. F. van Strijdonck and Z. Freixa, J. Organomet. Chem., 2007, 692, 5017–5025; (d) S. Pérez, C. López, A. Caubet, X. Solans, M. Font-Bardía, A. Roig and E. Molins, Organometallics, 2006, 25, 596–601; (e) S. Jautze, S. Diethelm, W. Frey and R. Peters, Organometallics, 2009, 28, 2001–2004; (f) T. Mochida, H. Shimizu, K. Ozakawa, F. Sato and D. Kuwahara, J. Organomet. Chem., 2007, 692, 1834–1844; (g) R. Peters, D. F. Fischer, S. Jautze, F. M. Koch, T. Kull, P. S. Tiseni, Z. Xin and M. Zajac, Chimia, 2008, 62, 497–505.
4. (a) A. Moyano, M. Rosol, R. M. Moreno, C. López and M. A. Maestro, Angew. Chem., Int. Ed., 2005, 44, 1865–1869; (b) A. González, C. López, X. Solans, M. Font-Bardía and E. Molins, J. Organomet. Chem., 2008, 693, 2119–2131; (c) P. K. Basu, A. González, C. López, M. Font-Bardía and T. Calvet, J. Organomet. Chem., 2009, 694, 3633–3642.
5. (a) J. J. Li and G. W. Gribble, Palladium in Heterocyclic Chemistry, Pergamon, 2000, New York (USA).
6. (a) V. Montoya, J. Pons, X. Solans, M. Font-Bardía and J. Ros, Inorg. Chim. Acta, 2005, 358, 2312–2318; (b) V. Montoya, J. Pons, X. Solans, M. Font-Bardía and J. Ros, Inorg. Chim. Acta, 2005, 358, 2763–2769; (c) J. Chakraborty, M. K. Saha and P. Benerjee, Inorg. Chem. Commun., 2007, 10, 671–676.
7. (a) K. Li, M. S. Mohlala, T. V. Segapelo, P. M. Shumbula, I. A. Guzei and J. Darkwa, Polyhedron, 2008, 27, 1017–1023; (b) R. Y. Mawo, D. M. Johnson, J. L. Wood and I. P. Smoliakova, J. Organomet. Chem., 2008, 693, 33–45; (c) I. Ara, L. R. Falvello, J. Fornies, R. Lasheras, A. Martin, O. Oliva and V. Sicilia, Inorg. Chim. Acta, 2006, 359, 4574–4584; (d) I. Ara, J. Forniés, R. Lasheras, A. Martin and V. Sicilia, Eur. J. Inorg. Chem., 2006, 948–957; (e) Y. Han, H. V. Huynh and G. K. Tan, Organometallics, 2007, 26, 6581–6585; (f) F. Churruca, R. SanMartin, I. Tellitu and E. Domínguez, Synlett., 2005, 3116–3120; (g) F. López-Linares, O. Colmenares, E. Catari and A. Karam, React. Kinet. Catal. Lett., 2005, 85, 139–144; (h) A. Satake and T. Nakata, J. Am. Chem. Soc., 1998, 120, 10391–10396; (i) E. Budzisz, U. Krajewska, M. Rozalski, A. Szulawska, M. Czyz and B. Nawrot, Eur. J. Pharmacol., 2004, 502, 59–65; (j) M. C. Torralba, M. Cano, J. A. Campo, J. V. Heras, E. Pinilla and M. R. Torres, Inorg. Chem. Commun., 2002, 5, 887–890.
8. (a) S. Y. Chang, J-L. Chen, Y. Chi, Y-M. Cheng, G-H. Lee, C-M. Jiang and P. T. Chou, Inorg. Chem., 2007, 46, 11202–11212; (b) A. Eisenwiener, M. Neuburger and T. A. Kaden, Dalton Trans., 2007, 36, 218–233; (c) A. V. Khripun, M. Haukka and V. Y. Kukushkin, Russ. Chem. Bull., 2006, 55, 247–255; (d) A. V. Khripun, S. I. Selivanov, V. Y. Kukushkin and M. Haukka, Inorg. Chim. Acta, 2006, 359, 320–6; (e) E. Ciesielska, A. Szulawska, K. Studzian, J. Ochocki, K. Malinowska, K. Kik and L. Szmigiero, J. Inorg. Biochem., 2006, 100, 1579–1585.
9. (a) For a general overview on cyclopallada- and cycloplatinated compounds their applications, see: J. Dupont and M. Pfeffer, Palladacycles. Synthesis, Characterization and Applications, Wiley-VCH, Weinheim (Germany), 2008; (b) M. Ghedini, I. Aiello, A. Crispini, A. Golemme, M. La Deda and D. Pucci, Coord. Chem. Rev., 2006, 250, 1373–1390; (c) D. A. Alonso and C. Najera, Chem. Soc. Rev., 2010, 39, 2891–2902; (d) I. Omae, J. Organomet. Chem., 2007, 692, 2608–32; (e) K. Godula and D. Sames, Science, 2006, 312, 67–72; (f) J. Dupont, C. S. Consorti and J. Spencer, Chem. Rev., 2005, 105, 2527–2571.
10. (a) For recent advances in pallada- and platinacycles, see: J. Albert, R. Bosque, M. Crespo, J. Granell, J. Rodriguez and J. Zafrilla, Organometallics, 2010, 29, 4619–4627; (b) M. Crespo, T. Calvet and M. Font-Bardia, Dalton Trans., 2010, 39, 6936–6938; (c) M-Y. Yuen, S. C. F. Kui, K-H. Low, C.-C. Kwok, S. S.-Y. Chui, C.-W. Ma, N. Zhu and C.-M. Che, Chem.–Eur. J., 2010, 16, 14131–14141; (d) C. López, S. Pérez, X. Solans, M. Font-Bardía, A. Roig, E. Molins, P. W. N. M. van Leeuwen and G. P. F. van Strijdonck, Organometallics, 2007, 26, 571–576; (e) T-K. Zhang, K. Yuan and X-L. Hou, J. Organomet. Chem., 2007, 692, 1912–19; (f) P. G. Evans, N. A. Brown, G. J. Clarkson, C. P. Newman and J. P. Rourke, J. Organomet. Chem., 2006, 691, 1251–1256.
11. (a) For applications of palladacycles in homogeneous catalysis, see: A. S. Gruber, D. Zim, G. Ebeling, A. L. Monteiro and J. Dupont, Org. Lett., 2000, 2, 1287–1290; (b) D. Zim, A. S. Gruber, G. Ebeling, J. Dupont and A. L. Monteiro, Org. Lett., 2000, 2, 2881–2884; (c) J. Dupont, M. Pfeffer and J. Spencer, Eur. J. Inorg. Chem., 2001, 1917–1927; (d) I. Moreno, R. San Martin, M. T. Herrero and E. Dominguez, Curr.Topics Catal., 2009, 8, 91–102 and references cited in these articles..
12. (a) For examples of the antitumoral activity of this sort of compounds, see: G. Xu, Z. Yan, N. Wang and Z. Liu, Eur. J. Med. Chem., 2011, 46, 356–363; (b) L. Ronconi and P. J. Sadler, Dalton Trans., 2011, 40, 262–268; (c) J. Aleman, V. del Solar, L. Cubo, A. G. Quiroga and C. Navarro-Ranninger, Dalton Trans., 2010, 39, 10601–10607; (d) R. W-Y. Sun, D. L. Ma, E. L-M. Wong and C-M. Che, Dalton Trans., 2007, 35, 4884–4892; (e) A. P. Neves, G. B. da Silva, M. D. Vargas, C. B. Pinheiro, L. C. Visentin, J. D. B. M. Filho, A. J. Araujo, L. V. Costa-Lotufo, C. Pessoa and M. O. de Moraes, Dalton Trans., 2010, 39, 10203–10216; (f) G. Wagner, A. Marchant and J. Sayer, Dalton Trans., 2010, 39, 7747–7759; (g) N. Margiotta, N. Denora, R. Ostuni, V. Laquintana, A. Anderson, S. W. Johnson, G. Trapani and G. Natile, J. Med. Chem., 2010, 53, 5144–5154; (h) J. S. Saad, M. Benedetti, G. Natile and L. G. Marzilli, Inorg. Chem., 2010, 49, 5573–5583; (i) K. L. Ciesienski, L. M. Hyman, D. T. Yang, K. L. Haas, M. G. Dickens, R. J. Holbrook and K. J. Franz, Eur. J. Inorg. Chem., 2010, 2224–2228; (j) Y. Y. Scaffidi-Domianello, K. Meelich, M. A. Jakupec, V. B. Arion, V. Y. Kukushkin, M. Galanski and B. K. Keppler, Inorg. Chem., 2010, 49, 5669–5678; (k) F. J. Ramos-Lima, V. Moneo, A. G. Quiroga, A. Carnero and C. Navarro-Ranninger, Eur. J. Med. Chem., 2010, 45, 134–141.
13. (a) For macromolecules containing cyclopalladated or cycloplatinated units: M. López-Torres, A. Fernández, J. J. Fernández, A. Suárez, S. Castro-Juiz, J. M. Vila and M. T. Pereira, Organometallics, 2001, 20, 1350–1353; (b) C. López, A. Caubet, S. Pérez, X. Solans and M. Font-Bardía, J. Organomet. Chem., 2003, 681, 82–90; (c) A. Fernández, E. Pereira, J. J. Fernández, M. López-Torres, A. Suarez, R. Mosteiro, M. T. Pereira and J. M. Vila, New J. Chem., 2002, 26, 895–901; (d) I. Aiello, U. Caruso, M. Ghedini, B. Panunzi, A. Quatela, A. Roviello and F. Sarcinelli, Polymer, 2003, 44, 7635–7643.
14. (a) For examples of their utility in organic and organometallic synthesis, see: X-F. Wu, P. Anbarasan, H. Neumann and M. Beller, Angew. Chem., Int. Ed., 2010, 49, 9047–9050; (b) A. Dumrath, X-F. Wu, H. Neumann, A. Spannenberg, R. Jackstell and M. Beller, Angew. Chem., Int. Ed., 2010, 49, 8988–8992; (c) A. Sivaramakrishna, H. S. Clayton, M. M. Mogorosi and J. R. Moss, Coord. Chem. Rev., 2010, 254, 2904–2932; (d) E. Negishi, G. Wang, H. Rao and Z. Xu, J. Org. Chem., 2010, 75, 3151–3182; (e) M-J. Jin and D-H. Lee, Angew. Chem., Int. Ed., 2010, 49, 1119–1122.
15. Y. Donde and L. E. Overman, J. Am. Chem. Soc., 1999, 121, 2933–2934.
16. (a) M. D. Joksovic, V. Markovic, Z. D. Juranic, T. Stanojkovic, L. S. Jovanovic, I. S. Damljanovic, K. M. Szecsenyi, N. Todorovic, S. Trifunovic and R. D. Vukicevic, J. Organomet. Chem., 2009, 694, 3935–3942; (b) I. Damiljanovic, M. Vukicevic, N. Radulovic, R. Palic, E. Ellmerer, Z. Ratkovic, M. D. Joksovic and R. D. Vukicevic, Bioorg. Med. Chem. Lett., 2009, 19, 1093–1096; (c) M. Zora and M. Goermen, J. Organomet. Chem., 2007, 692, 5026–5032; (d) M. Joksovic, Z. Ratkovic, M. Vukicevic and R. D. Vukicevic, SynLett., 2006, 2581–2584; (e) J. L. Delgado, M. E. El-Khouly, Y. Araki, M. J. Gomez-Escalonilla, P. De la Cruz, F. Oswald, O. Ito and F. Langa, Phys. Chem. Chem. Phys., 2006, 8, 4104–4111; (f) W-Q. Shen, Y-J. Wang, K-L. Chen, G-H. Lee and C. K. Lai, Tetrahedron, 2006, 62, 8035–8044; (g) A. H. Ilkhechi, M. Bolte, H-W. Lerner and M. Wagner, J. Organomet. Chem., 2005, 690, 1971–1977; (h) U. Burckhardt, D. Drommi and A. Togni, Inorg. Chim. Acta, 1999, 296, 183–194.
17. (a) Y-N. Liu, G. Orlowski, G. Schatte and H-B. Kraatz, Inorg. Chim. Acta, 2005, 358, 1151–61; (b) G. L. G. Effendy, M. Pellei, C. Pedinari, C. Santini, B. W. Skelton and A. H. White, Inorg. Chim. Acta, 2001, 315, 153–62.
18. (a) H. Qian, X. Cui, M. Tang, C. Liu, C. Liu and Y. Wu, New J. Chem., 2009, 33, 668–674; (b) L. L. Troitskaya, Z. A. Starikova, T. V. Desmeshchik, S. T. Ovseenko, E. V. Vorontsov and V. I. Sokolov, J. Organomet. Chem., 2005, 690, 3976–3982.
19. (a) A. Zucca, G. L. Petretto, S. Stoccoro, M. A. Cinellu, G. Minghetti, M. Manassero, C. Manassero, L. Male and A. Albinati, Organometallics, 2006, 25, 2253–2265; (b) I. Moreno, R. SanMartin, B. Ines, M. T. Herrero and E. Dominguez, Curr. Org. Chem., 2009, 13, 878–895.
20. (a) V. I. Boev, L. V. Snegur, V. N. Babin and Y. S. Nekrasov, Russ. Chem. Rev., 1997, 66, 613–636; (b) K. Pagel, A. Werner and W. Friedrichsen, J. Organomet. Chem., 1994, 481, 109–123.
21. A. González, J. Marquet and M. Moreno-Mañas, Tetrahedron, 1986, 42, 4253–4257.
22. M. Rosemblum and W. G. Howels, J. Am. Chem. Soc., 1962, 84, 1167–1172.
23. F. H. Allen, Acta Crystallogr., Sect. B: Struct. Sci., 2002, B58, 380–388.
24. J. H. Price, A. N. Williamson, R. F. Schramm and B. B. Wayland, Inorg. Chem., 1972, 11, 1280–4.
25. (a) S. Pérez, C. López, A. Caubet, X. Solans and M. Font-Bardía, Eur. J. Inorg. Chem., 2008, 1599–1612; (b) C. López, A. Caubet, S. Pérez, X. Solans and M. Font-Bardía, Chem. Commun., 2004, 540–541.
26. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed., Wiley, New York, USA, 1997.
27. (a) E. Szłyk, I. Lakomska, A. Surdykowski, T. Glowiak, L. Pazderski, J. Sitkowski and L. Kokerski, Inorg. Chim. Acta, 2002, 333, 93–99; (b) N. Nédélec and F. D. Rochon, Inorg. Chem., 2001, 40, 5236–5244; (c) N. Nédélec and F. D. Rochon, Inorg. Chim. Acta, 2001, 319, 95–98.
28. (a) B. M. Still, P. G. A. Kumar, J. R. Aldrich-Wright and W. S. Price, Chem. Soc. Rev., 2007, 36, 665–686.
29. (a) For compounds with N-donor heterocyclic ligands see for instance: A. Cornia, A. C. Fabretti, M. Bonivento and L. Cattalini, Inorg. Chim. Acta, 1997, 255, 405–409; (b) R. Melanson and F. D. Rochon, Inorg. Chem., 1978, 17, 679–681.
30. (a) X. Riera, C. López, A. Caubet, V. Moreno, X. Solans and M. Font-Bardía, Eur. J. Inorg. Chem., 2001, 2135–2141; (b) R. Martin, M. Crespo, M. Font-Bardia and T. Calvet, Organometallics, 2009, 28, 587–597; (c) J. Rodríguez, J. Zafrilla, J. Albert, M. Crespo, J. Granell, T. Calvet and M. Font-Bardia, J. Organomet. Chem., 2009, 694, 2467–2475.
31. J. Vicente, J. A. Abad, A. D. Frankland and M. C. Ramírez de Arellano, Chem.–Eur. J., 1999, 5, 3066–3075.
32. I. Lakomska, M. Barwiolek, A. Wojtczak and E. Szlyk, Polyhedron, 2007, 26, 5349–5354.
33. (a) C. López, J. Sales, X. Solans and R. Zquiak, J. Chem. Soc., Dalton Trans., 1992, 2321–2328; (b) R. Bosque, C. López, J. Sales, X. Solans and M. Font-Bardía, J. Chem. Soc., Dalton Trans., 1994, 735–745.
34. Y. Wu, S. Huo, J. Gong, X. Cui, L. Ding, K. Ding, C. Du, Y. Liu and M. Song, J. Organomet. Chem., 2001, 637-639, 27–46.
35. A. Bondi, J. Phys. Chem., 1964, 68, 441–451.
36. (a) A. D. Ryabov, S. Otto, P. V. Samuleev, V. A. Polyakov, L. Alexandrova, G. M. Kazankov, S. Shova, M. Revenko, J. Lipkowski and M. H. Johansson, Inorg. Chem., 2002, 41, 4286–4294; (b) S. Otto, A. Chanda, P. V. Samuleev and A. D. Ryabov, Eur. J. Inorg. Chem., 2006, 2561–2566.
37. R. Bosque and F. Maseras, Eur. J. Inorg. Chem., 2005, 4040–4047.
38. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R .L. Martin, D.J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03 (Revision C.02). Gaussian, Inc., Wallingford, CT, 2004.
39. N. L. Allinger, Y. H. Yuh and J. H. Lii, J. Am. Chem. Soc., 1989, 111, 8551–8566.
40. Z. Szafran, R. M. Pike and M. M. Singh, Microscale Inorganic Chemistry. A Comprehensive Laboratory ExperienceJohn Wiley & Sons, New York (USA), 1991, p. 218.
41. D. D. Perrin and W. L. F. Armarego, Purification of Laboratory Chemicals, 4th Ed. Butterworth–Heinemann, 1996, Oxford (UK).
42. G. M. Sheldrick, SHELXS A program for automatic solution of crystal structure refinement, 1997, Univ. Goettingen, (Germany).
43. G. M. Sheldrick, SHELX97A program for crystal structure refinement, 1997, Univ. Goettingen, (Germany).
44. CacheWork System Pro Version 7.5.085 UserGuide, Fujitsu, Beaverton, Oregon, USA, 2007.
45. (a) A. D.Becke, J. Chem. Phys., 1993, 98, 5648–5652; (b) C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785–789.
46. (a) W. R. Wadt and P. J. Hay, J. Chem. Phys., 1985, 82, 284–298; (b) P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299–310.
47. A. Höllwarth, M. Böhme, S. Dapprich, A. W. Ehlers, A. Gobbi, V. Jonas, K. F. Köhler, R. Stegmann, A. Veldkamp and G. Frenking, Chem. Phys. Lett., 1993, 208, 237–240.
48. W. J. Hehre, R. Ditchfield and J. A. Pople, J. Chem. Phys., 1972, 56, 2257–2261.
49. P. C. Hariharan and J. A. Pople, Theor. Chim. Acta, 1973, 28, 213–222.
50. M. Cossi, N. Rega, G. Scalmani and V. Barone, J. Comp. Chem., 2003, 24, 669–681.

---

Footnotes

† Electronic supplementary information (ESI) available: Conformational map showing the variation of the total energy of the ligand as a function of the torsion angles Φ(1) and Φ(2) (Fig. S1) and tables containing final atomic coordinates of the optimized geometries of the three types of complexes (A–C, shown in the lower part of Table S5) with L = PH₃, dmso or PPh₃ used as models in the DFT study together with their calculated total energy in vacuum, in toluene and in methanol (Tables S1-S9). CCDC reference numbers 826854–826858. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c1ra01080h

‡ The separation between the centroid of the ring defined by the set of atoms [C(6)–C(10] of a molecule at (x, y, z) and the H(18) atom of a close one located at (−x, −y, 1 − z) is 2.997 Å and the distance between the center of the ring [C(6)–C(10)] of the unit at (x, y, z) and the H(24) of another one at (2 − x, 1 − y, −z) is 3.036 Å. The separation between the H(16) atom and the phenyl ring [C(21)–C(26)] of another unit is 3.963 Å.

§ For illustrative purposes, the yields of 5 for different reaction periods (t) are given: 67.8, 69.1 and 70.2% for t = 3.5, 12 and 24 h, respectively.

¶ In 2, the main plane of the heterocycle forms angles of 80.9° and 80.3° with the two pentagonal rings of the Fc unit.

|| The success of all preparations described in this section is strongly dependent on the quality of the methanol used. The presence of small amounts of water reduces significantly the yield of the process. Thus the use of high quality (HPLC-grade) methanol is strongly recommended. In all cases the reaction flask was protected from the light with aluminium foil.

---