Transition of trigonal-bipyramidal to square-planar geometries by oxidation of a coordinated tripodal polyphosphine in Pd(II) and Pt(II) complexes

Abstract

The oxidation reactions of the unusual d⁸ trigonal-bipyramidal systems [MX(PP₃)]X (M = Pd: X = Cl(1), Br(2), I(3); M = Pt: X = Cl(4), Br(5), I(6); PP₃ = tris[2-(diphenylphosphino)ethyl]phosphine) by dissociation of the bound phosphino groups with H₂O₂ in chloroform and with DMSO-d₆ in the presence of reduced glutathione (GSH) have been explored with emphasis on the factors that influence the number of M–X and P=O functionalities of the resulting products. The oxidations with H₂O₂ required a higher concentration for Pd than Pt and occurred with formation of both ionic distorted square-planar compounds [MX(PP₂PO)]X [M = Pd: X = Cl(7); M = Pt: X = Cl(10), Br(11)], that contain one dangling P=O group, and the less common neutral species [MX₂(PP(PO)₂] [M = Pd: X = Br(8), M = Pt: X = I(12)] showing MX₂P₂ environments and two P=O arms, or with release of all bound phosphorus from 3 to give OP(PO)₃ (9). Although there was no evidence of the formation of neutral species with two Pt–Cl bonds and dissociation of one bound phosphorus by adding H₂O₂ or M′Cl (M′ = Cu, Ag) to 10, the interaction with [AuCl(tdg)] (tdg = thiodiglycol) afforded [PtAuCl₃(PP₂PO)] (10a) containing dangling P=O and PAuCl arms and one chiral central phosphorus. Thus, while the halide anions and ligands allowed both ionic (7, 10, 11) and neutral (8, 9, 10a, 12) systems, the larger anions [S(CH₃)₃(CH₂)₃(SO₃)]⁻ or GS⁻ favour only the ionic compounds, namely [PdCl(PP₂PO)][S(CH₃)₃(CH₂)₃(SO₃)] (7a), obtained in coexistence with [Pd(GS)(PP₂PO)]Cl (7a′) from the reaction of 1 + 3 eq. GSH in DMSO-d₆. The X-ray structure of 7a confirmed the distorted ClPdP₃ arrangement and the presence of a dangling P=O group predicted by LSI-MS and ³¹P{¹H}NMR data.

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Introduction

The chemical modifications of phosphines^1–6 to afford phosphine oxides^6–32 is an important aim of synthetic studies because of their various applications in catalysis and medicine, the preparation of mixed-metal assemblies or polymers, the use as extractive agents or carriers and the construction of nanoparticles, depending on the number of P=O functionalities.^8,9,24–32 In previous work, we have described the ligand exchange and selective phosphine oxidation of the distorted square-planar Pd(II)–triphos complex [PdBr(triphos)]Br (triphos = bis(2-diphenylphosphinoethyl)phenylphosphine)^14e to give the ionic system [Pd(triphos-O)₂][PdBr₄] with the square-planar cation showing a 1 : 2 Pd to ligand ratio and two dangling P=O arms. Recently, we confirmed that PP₃ produces dissociation of two bound phosphino groups of the uncommon trigonal-bipyramidal d⁸ complexes [MX(PP₃)]X (M = Pd, Pt; X = Cl, Br, I)³³ leading to [M(PP₃)₂]X₂ (X = Cl, Br) that show an MP₄ square-planar arrangement and four dangling phosphorus available for oxidation. With the aim of increasing the knowledge about oxidations of coordinated phosphines, in this paper we report studies on the stepwise selective oxidation with H₂O₂ for [MX(PP₃)]X and their halo-ligand/counter anion substitution reactions with glutathionate/S(CH₃)₃–propane sulfonato.

Results and discussion

The use of donor solvents was restricted to the reactions involving species with low solubility in the common non-coordinating solvents.

Two routes have been employed for the synthesis of Pd(II)/Pt(II) complexes of the type [MX′(PP₂PO)]X′′ : a) The reaction of the trigonal-bipyramidal d⁸ systems [MX(PP₃)]X^6a,34–36 [M = Pd: X = Cl(1), M = Pt: X = Cl, Br (4, 5)] with H₂O₂ in chloroform (X′ = X′′= X: 7, 10, 11 shown in Scheme 1) and b) The reaction of [MX(PP₃)]X [M = Pd: X = Cl, I (1, 3); M = Pt: X = Cl, I (4, 6)] in dimethylsulfoxide with aqueous GSH under acid conditions (X′ = X and M = Pd (7a, 7b); X′ = GS and M = Pd or Pt (7a′, 7b′ or 10a′, 10b′) shown in Scheme 2). The less common compounds [PdBr₂(PP(PO)₂)] (8) and [PtI₂(PP(PO)₂)] (12) were prepared by the reaction of [MX(PP₃)]X [M = Pd: X = Br(2); M = Pt: X = I (6)] with H₂O₂ in chloroform (Scheme 1).

Scheme 1 Oxidations with H₂O₂ of complexes 1–6 in CDCl₃.

Scheme 2 Reactions with GSH for halo complexes containing the tripodal ligands PP₃ and NP₃.

The preparation of mononuclear complexes [Pd(PP(PO)₂)₂]X₂ [X = Cl(13), Br (14)] exhibiting four dangling P=O groups by reaction of 1/2 with PP₃³³ and subsequent oxidation of [Pd(PP₃)₂]X₂ [X = Cl(13*)/Br(14*)] with H₂O₂ (Scheme 3, eqn (1)) supported a dissociative mechanism for explaining the formation of P=O groups rather than oxidations taking place at the coordinated P atoms.^14a,37

The entering PP₃ was able to originate the dissociation of two bound phosphino groups of 1/2 leading to square-planar cationic complexes for which the X-ray crystal structure (Fig. S1, ESI†) shows a square-planar PdP₄ arrangement, two phosphines acting as bidentate chelating ligands and four dangling arms available for oxidation. The mass spectra of 13/14 confirm the 1 : 2 stoichiometry observing peaks attributable to [Pd(PP(PO)₂)₂]X and Pd(PP(PO)₂)₂ fragments. The ³¹P{¹H}NMR data in DMSO-d₆ (Fig. 1) consist of three resonances exhibiting the expected 1(P^I) : 1(P^J) : 2 (P^K) integration ratio.

Fig. 1 ³¹P{¹H}NMR spectrum (r.t.) in DMSO-d₆ for 13·3CH₂Cl₂.

Another example of dissociation of coordinated phosphorus in Pd(II) complexes containing the linear ligand triphos, that can occur with or without addition of phosphine depending on the halogen, is shown in Scheme 3. While it was necessary to add 1 equivalent of triphos to [PdCl(triphos)]Cl prior to affording the cationic species with a 1 : 2 Pd to triphos-O ratio, [PdBr(triphos)]Br reacted with H₂O₂ in acetone–ether (2 : 1) forming an ionic compound, where the cation contains two triphos-O ligands with a square-planar P₄ donor set to Pd(II) and [PdBr₄]²⁻ is acting as counter anion (eqn S1, ESI†).

Scheme 3 Oxidations with H₂O₂ of palladium(II) complexes containing PP₃ and the linear ligand triphos.

The related square-pyramidal complex [PdBr(triphos-O)₂]Br, afforded from solutions of [PdBr(triphos)]Br in the same solvent system and characterized by X-ray diffraction,^14e would be considered as an intermediate of the reaction where the weakly coordinated axial bromo ligand left the five-coordinate structure, giving the corresponding square-planar cation and counter anion. The X-ray analysis (Fig. 2, Tables 1 and 2) for single crystals of 13·6H₂O·2CH₃OH, obtained from DMSO solutions containing the solid of the reaction in CH₃OH between 13·3CH₂Cl₂ and SnCl₂, confirmed the structure predicted in solution. Inspection of the P–O bond distances (1.485(6) Å) reveals similar values to those found for [PdBr(triphos-O)₂]Br (1.477(9)–1.457(10) Å)^14e or [Pd(dppfcO)₂]Cl₂ (dppfcO = Ph₂PC₅H₄P(O)Ph₂) (1.487(3) Å)³⁸ and lengthened distances with respect to the neutral square-planar compound [Pd(tripod–O_0.5)Cl₂] (tripod = CH₃C(CH₂PPh₂)₃; 1.39(2) Å).³⁹ On this basis, the dissociation processes of coordinated PP₃ responsible for the preparation of complexes 7–12 presumably occurred via a preassociative mechanism leading to equilibria (Scheme S1, ESI†) involving five- and four-coordinate species prior to oxidation of the resulting dangling phosphorus. The rapid exchange between chelate ring-opened and ring-closed forms seems to assure the appearance of pendant arms from both Pd(II) and Pt(II) precursors. However, the higher inertness of the dissociated species formed for M = Pt compared to Pd may explain the lower concentrations required of precursors 4–6 (ca. 3 × 10⁻³ M) compared to 1–3 (ca. 8 × 10⁻³ M). The ³¹P{¹H}NMR spectrum of 7 (Fig. S2, ESI†) along with 10 (Fig. 3) and 11 consisted of three resonances showing integration ratios 1(P^A): 2 (P^B): 1 (P^C=O) in agreement with PP₃ acting as tridentate chelating ligand and oxidation of just a terminal coordinated phosphorus of 1, 4 and 5, respectively (eqn (2)).

Fig. 2 ORTEP diagram for 13. 50% probability of thermal ellipsoid drawn and solvents removed for clarity.

Fig. 3 ³¹P{¹H}NMR spectra (r.t.) in CDCl₃ for 10·2H₂O (top) and 10a·CHCl₃ (bottom).

The coupling constants between P^A and P^C of 35(7), 39(10) and 37(11) Hz were as expected for distorted square-planar ionic complexes formed via a chelate ring-opening from the precursors.^34–36 The ¹J(³¹P^A, ¹⁹⁵Pt) and ¹J(³¹P^B, ¹⁹⁵Pt) couplings for 10–11ca. 2900 and 2500 Hz are typical of P^Atrans to X and P^Btrans to each other, respectively, and consistent with ¹⁹⁵Pt{¹H}NMR data for 10 (Fig. S3, ESI†). Considering the enhancement of the dissociative character and steric hindrance going down the halogen group, and both the reductor behaviour and π-accepting ability of halide anions and ligands following the order I⁻> Br⁻> Cl⁻, one can explain, by the steric and electronic factors, why the extent of oxidations increases from Cl⁻ or Br⁻ to I⁻. Indeed, the ³¹P{¹H}NMR spectra for 8 (Fig. S2, ESI†) and 12 (Fig. 4) exhibit three signals with an integration ratio 1(P^D) : 1(P^E) : 2(P^F=O) and couplings between P^D and P^F of 54 and 50 Hz, indicative of the formation of neutral species (eqn (3) and (4)) where the ligand is coordinated to the metal through the central and one terminal phosphorus and the two remaining dangling phosphorus are oxidized.

Fig. 4 ³¹P{¹H}NMR spectrum (r.t.) in CDCl₃ for 12·H₂O.

Concentrations of H₂O₂ greater than that used for the oxidation of 1 with 12 equivalents of H₂O₂ resulted in the appearance of three signals assigned to the ionic complex 7, as well as three resonances at δ 83.2, 65.1 and 31.2 ascribed to the neutral system [PdCl₂(PP(PO)₂)] bearing the same structure as 8 and 12. However, oxidation of complex 3, under similar conditions to 1 or 2, led to the appearance of two signals (Fig. S2, ESI†) with integration ratios 1(P^G) : 3(P^H) due to OP(PO)₃ (9) (eqn (5)).

In consequence, complexes 7, 10–11 seem to be the result of the action of H₂O₂ on the square-pyramidal intermediates I_a (having just one terminal pendant arm, Scheme S1, ESI†), while the formation of 12 from 6 required the oxidation of I_a (by using the smallest concentration of H₂O₂) and subsequent evolution to I_b. Since in absence of H₂O₂ the iodo complex 6 was stable in non deoxygenated chloroform, a mechanism whereby O₂ oxidized a terminal coordinated phosphorus of I_b was considered the most likely. The fact that the oxidation of 3 with less than 12 equivalents of H₂O₂ gave mixtures containing 3 and mono- and/or dioxidized complexes indicates rapid equilibria between dissociated and non dissociated forms that persisted by exposure to O₂ and disappeared to give 9 by increasing the amount of hydrogen peroxide.

Although greater concentrations of H₂O₂ did not produce neutral species, with the same X₂PtP₂ arrangement to 12 (X = I), starting from the chlorocomplex 10 or the related compounds [MAuCl₂(PP₃)]Cl (M = Pd, Pt),³⁴ the addition of [AuCl(tdg)] induced a chelate ring-opening affording [PtAuCl₃(PP₂PO)] (10a) with a chiral central phosphorus (Fig. 3) or [MAu₂Cl₄(PP₃)] (Scheme 4). The increase in concentration of chloride ions lead to an associative mechanism via a trigonal-bipyramidal 18-electron intermediate (I_b) proposed for reaction mechanisms of common four-coordinate square-planar Pd(II) and Pt(II) compounds.^40,41 However, the propensity of M′Cl salts (M′ = Cu, Ag) to undergo oligomerization with phosphines³⁵ can justify the absence of ring-opening reactions by adding to 10 an excess of these chlorides (Fig. S4, ESI†). None of the reactions explored between [MX(PP₃)]X in DMSO-d₆ and GSH in D₂O afforded neutral dioxidized complexes^6c or the complete oxidation of PP₃. The monoxidized systems coexisted in a mixture containing the unreacted (1) or regenerated (3, 6; vide infra) precursors and the trigonal-bipyramidal Pd(II)/Pt(II) complexes showing glutathionate (GS⁻) as a monodentate thiolato ligand (1a, 3a or 4a and 6a: Scheme 2), with the formation of 4a (M = Pt) as the predominant species needing a greater amount of GSH (Fig. S5, ESI†) than 1a (M = Pd).

Scheme 4 Reactions of chloro complexes containing dangling P=O and PAuCl groups.

The ³¹P{¹H}NMR data for 1 + 1 eq. GSH and the spectrum for 1 + 2 eq. GSH, shown in Fig. 5, confirm the coexistence of 1, 1a and the two oxidized complexes [PdCl(PP₂PO)][S(CH₃)₃(CH₂)₃(SO₃)] (7a) and [Pd(SG)(PP₂PO)]Cl (7a′). Single crystals of 7a·4H₂O studied by X-ray diffraction were obtained by the addition of water to the sample for the reaction 1 + 3 eq. GSH (Fig. S6, ESI†), where the intensity of the signals due to 7a (with low solubility in H₂O) and 1 (consumed in the formation of 7a) decreased by comparison with the spectrum for 1 + 2 eq. GSH. The solid state structure (Fig. 6 and Tables 1 and 2) is consistent with the presence of cations showing a distorted square-planar geometry with a ClP₃ arrangement to Pd(II) and one dangling P=O group. The P–O and Pd–P bond distances are in the same range and slightly shorter, respectively, than for 13. The average of 2.286(3) Å for Pd–P bond lengths agrees with the low trans influence of Cl compared to P and the two fused and non fused five-membered chelate rings imparted by 7a and 13, respectively. The S(1) and S(2) atoms of the counter anion are located below the distorted square-planar P(1)P(2)Pd(1)Cl(1)P(3) arrangement at 9.837 and 10.580 Å, respectively from Pd(1). Taking account of the relatively strong π-donating ability of thiolates to dissociate neighbouring coordinated phosphino groups, it is possible that one terminal phosphorus atom of 1a was dissociated, in part, by GS⁻ giving the square-planar thiolate with a dangling phosphorus, followed by the irreversible oxidation (7a′) in non deoxygenated DMSO-d₆ + D₂O. Dimethylsulfoxide would produce the oxidation of the dissociated phosphorus undergoing reduction to sulphide with further formation of a trimethyl sulfonium fragment. This agrees with the formation of 7a from 7a′, in a process where the excess of reduced glutathione in the solvent system used presumably favored the glutathionato ligand substitution with chloride, subsequent fragmentation and oxidation of the thiol and generation of the propane sulfonato moiety of the [S(CH₃)₃(CH₂)₃(SO₃)]⁻ counter anion, instead of acting as a bulky entering ligand able to produce the neutral dioxidized complex [Pd(GS)₂(PP(PO)₂].

Fig. 5 ³¹P{¹H}NMR spectrum (r.t.) for 1 + 2 eq. GSH in DMSO-d₆ + D₂O (pH = 4.2).

Fig. 6 ORTEP diagram for 7a. 50% probability of thermal ellipsoid drawn and solvents removed for clarity.

In the case of the reactions between 4 or 6 and GSH (followed by ³¹P (Experimental part) and ¹H (Fig. S7 NMR, ESI†), the significant affinity of Pt(II) for the thiolato S atom prevents the appearance of square-planar species other than [Pt(GS)(PP₂PO)]Cl(10a′) or [Pt(GS)(PP₂PO)]I (10b′). In fact, the titration of 10 (in DMSO-d₆) with aqueous GSH demonstrated the quantitative chloro ligand substitution reaction with glutathionato to give 10a′ from the first addition of thiol (Fig. S8, ESI†). The singlet at δ 98.5 assigned for both, 10a′ and 10b′, to the bound phosphorus P^A, supports the absence of the square-planar halo complexes.

Table 1 Summary of crystal parameters, data collection, and refinement for 7a , 13∗ and 13

Complex	7a·4H2O	13∗·4CHCl3	13·6H2O·2CH3OH
Empirical formula	C48H57ClO8P4PdS2	C88H84Cl14P8Pd	C86H90Cl2O12P8Pd
Formula weight	1091.79	1992.01	1740.64
T (K)	293(2)	293(2)	293(2)
Wavelength (Å)	0.71073	0.71073	0.71073
Crystal size (mm)	0.26 × 0.24 × 0.07	0.15 × 0.07 × 0.07	0.36 × 0.34 × 0.21
Colour/habit	Yellow/prisms	Colorless/needles	Colorless/prisms
Crystal system	Monoclinic	Monoclinic	Triclinic
Space group	C/2c	P21/c	P1̄
a (Å)	36.211(5)	14.942(2)	11.808(6)
b (Å)	14.7523(19)	18.073 (3)	13.975(7)
c (Å)	20.890(3)	17.298(3)	15.675(7)
α (°)	90	90	105.495(7)
β (°)	106.565(3)	93.440(4)	98.909(7)
γ (°)	90	90	102.948(7)
Volume (Å^3)	10696(2)	4662.8(13)	2364.9 (19)
Z	8	2	1
Calculated density (Mg m^−3)	1.356	1.419	1.222
Absorption coefficient (mm^−1)	0.642	0.780	0.441
F(000)	4512	2032	902
θ range for data collection (°)	1.17 to 24.71	1.63 to 26.41	1.38 to 26.43
Index ranges	−42 ≤ h ≤ 40	−18 ≤ h ≤ 18	−14 ≤ h ≤ 14
	0 ≤ k ≤ 17	0 ≤ k ≤ 22	−17 ≤ k ≤ 16
	0 ≤ l ≤ 24	0 ≤ l ≤ 21	0 ≤ l ≤ 19
Reflections collected	33386	28588	25012
Independent reflections	9091 [Rint = 0.0930]	9528 [Rint = 0.0848]	9623 [Rint = 0.0368]
Max. and min. transmission	0.9564 and 0.8507	0.9474 and 0.8919	0.9131 and 0.8574
Data/restraints/parameters	9091/0/572	3947/0/502	7033/0/489
Goodness of fit on F^2	0.891	0.908	1.095
Final R indices [I > 2σ(I)]	R 1 = 0.0645	R 1 = 0.0672	R 1 = 0.0685
	wR2 = 0.1523	0.1506	wR2 = 0.2029
Largest diff. peak and hole (e Å^−3)	0.596 and −0.857	1.325 and −2.433	1.686 and −1.268

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Table 2 Selected Distances (Å) and Angles (deg.) for 7a, 13∗ and 13

Complex	7a·4H2O^a	13∗·4CHCl3^a	13·6H2O· 2CH3OH^a
a Pd(1)⋯S(1) = 9.837 Å, Pd(1)⋯S(2) = 10.580 Å (7a),Pd(1)⋯Cl(1) = 12.640 Å (13∗), 15.357 Å (13).
Pd(1)–P(1)	2.217(3)	2.3366(18)	2.3406 (13)
Pd(1)–P(2)	2.323(3)	2.3231(19)	2.3386(14)
Pd(1)–P(3)	2.318(3)
Pd(1)–Cl(1)	2.358(2)
P(3)–O(1)			1.485(6)
P(4)–O(1)	1.497(7)
P(4)–O(2)			1.484(6)
S(2)–O(20)	1.359(10)
S(2)–O(21)	1.385(11)
S(2)–O(22)	1.520(15)
S(1)–C(46)	1.846(11)
S(1)–C(47)	1.898(11)
S(1)–C(48)	1.909(12)
P(1)–Pd(1)–P(2)	84.23(10)	83.62(7)	83.67(5)
P(1)–Pd(1)–P(3)	84.29(10)
P(2)–Pd(1)–P(3)	157.28(9)
P(1)–Pd(1)–P(1_2)		180.00(7)	180.00(5)
P(1).Pd(1)–P(2_2)		96.38(7)	96.33(5)
P(1)–Pd(1)–Cl(1)	174.15(9)
P(2)–Pd(1)Cl(1)	97.51(9)
P(3)–Pd(1)–Cl(1)	95 .89(9)

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The decisive role of dimethylsulfoxide in the oxidation processes leading not only to 7a, but also 7a′ and 10a′, was in accordance with the preparation of [M(SG)(PP₃)]Cl·nH₂O [n = 5 (M = Pd, 1a), 4 (M = Pt, 4a)] as solids (without signs of oxidized species in CD₃OD)⁴² by interaction between solutions of 1 or 4 in methanol and aqueous GSH. Likewise, the coexistence in DMSO-d₆ of [PdI(PP₂PO)]I (7b) with 3 is in keeping with a behaviour as the oxidant of the solvent. In the presence of GSH, complexes 7b′ and 10b′ were formed via a five-coordinate intermediate I_a (Scheme S2, ESI†) from 3a and 6a, respectively. With excess GSH, both GS⁻ and I⁻ compete for the axial coordination site with the apparent prevalence of I⁻ regenerating the cations of 3 and 6 (Fig. S9, ESI,† shows the prevalence of the resonance due to 3 as the concentrations of aqueous GSH were increased), in contrast with the behaviour observed for 1 and 4 (vide supra). However, the flexible coordination behaviour of the hemilabile ligand NP₃ (Scheme S3, ESI†),^43,44 seems to be responsible for the higher selectivity of both [PdCl(NP₃)]Cl (which disappears by titration with GSH, Figure S10, ESI†) and [PtI(NP₃)]I (Scheme 2) towards the square-planar thiolates containing one phosphine oxide group than the analogous PP₃ compounds, 1 and 6.

Conclusions

The extent of the oxidations of [MX(PP₃)]X with H₂O₂ in chloroform to afford ionic and neutral square-planar compounds increases from Cl⁻ or Br⁻ to I⁻, while in the presence of GSH and dimethylsulfoxide all oxidations conclude with the formation of ionic complexes containing just one P=O arm. For M = Pt, the reaction with GSH led to [Pt(GS) (PP₂PO)]X (X = Cl, I) and with H₂O₂ to [PtX(PP₂PO)]X (X = Cl, Br) and [PtI₂(PP(PO)₂)]. Subsequent addition of [AuCl(tdg)], when X = Cl, produces the neutral species [PtAuCl₃(PP₂PO)]. For a metal as labile as Pd(II), [PdCl(PP₃)]Cl gives a mixture of [Pd(GS)(PP₂PO)]Cl + [PdCl(PP₂PO)][S(CH₃)₃(CH₂)₃(SO₃)] under reaction with GSH and [PdX(PP₃)]X (X = Cl/Br) afford [PdCl(PP₂PO)]Cl/[PdBr₂(PP(PO)₂] with H₂O₂, while the iodide forms [Pd(GS)(PP₂PO)]I by adding GSH and OP(PO)₃ by treatment with H₂O₂.

Experimental section

General procedures and instrumentation

Palladium chloride, palladium bromide and potassium tetrachloroplatinate were purchased from Strem Chemicals, copper chloride, silver chloride, silver nitrate, tris[2-(diphenylphosphino)ethyl]phosphine, 2,2′-thiodiethanol (tdg = thiodiglycol) and reduced form of glutathione from Aldrich, sodium chloride, bromide and iodide and H₂O₂ (30% w/v) from Panreac and gold metal from S.E.M.P.S.A. Microanalyses were performed on a Fisons Instrument EA 1108 CHNS–O. Liquid Secondary-Ion (LSI MS) mass spectra were obtained in a Micromass Autospec spectrometer using nitrobenzylic alcohol as the matrix. Infrared spectra were recorded at ambient temperature as KBr pellets (4000–500 cm⁻¹) and Nujol mulls (500–100 cm⁻¹) on a Mattson Cygnus 100 spectrophotometer. The bands are reported as vs = very strong, s = strong, m = medium, w = weak, sh = shoulder, br = broad. ¹H, ³¹P{¹H} and ¹⁹⁵Pt {¹H}NMR spectra were recorded on a Brucker AMX500 spectrometer at 500.1, 202.46 and 107.52 MHz, respectively. A 2 s relaxation delay and a 30 degree pulse angle were used to favor measurable integration data. Chemical shifts (δ) are reported in ppm relative to external sodium 3-(trimethylsilyl)propionate (¹H), 85% H₃PO₄ (³¹P) and 1 M Na₂PtCl₆ (¹⁹⁵Pt) ; s = singlet, d = doublet, t = triplet, q = quartet, m= multiplet, dd = doublet of doublets, dt = doublet of triplets, br = broad signal, J = coupling constant in Hz. Conductivities were measured at 25 °C using 10⁻³ M solutions in DMF on a WTW model LF-3 instrument. The pH values of the solutions were determined using a Corning 240 pH meter. The crystallizing solvents in the solids were confirmed by infrared and X-ray diffraction.

Solutions of Au(I)

Solutions containing [AuCl(tdg)] were prepared by procedures similar to those reported.⁴⁵

Preparation of [MX(PP₃)]X (1–6)

The precursors, 1–6, were prepared following the procedures previously described.^34–36

Preparation of [MCl(PP₂PO)]Cl [M = Pd (7), Pt (10)] and [PtBr(PP₂PO)]Br (11)

Solutions containing [PdCl(PP₃)]Cl (1) (red color, 0.0913 g, 0.1077 mmol), [PtCl(PP₃)]Cl (4) (yellow color, 0.0894 g, 0.0954 mmol) and [PtBr(PP₃)]Br (5) (yellow color, 0.0737, 0.07186 mmol) in CHCl₃ [15 mL (1)/25 mL (4, 5)] were reacted with 1.2924, 0.7632 and 0.3397 mmol of H₂O₂, respectively. The mixtures of reaction were stirred at room temperature for 12, 18 and 2 h with formation of a suspension (7, 10) or a colorless solution (11). After that, Et₂O (80 mL) was added to complete or provoke the precipitation. The solids were filtered off, washed with ether and dried in vacuo. 7·CHCl₃ : Yield: 89%, white solid, mp 140–145 °C. Found: C, 52.8; H, 4.7. C₄₃H₄₃P₄PdCl₅O requires: C, 52.5; H, 4.4%. MS (LSIMS): m/z (rel. intensity) 862 (1%, M⁺), 827 (93%, M⁺ − Cl), 792 (5%, M⁺ − 2Cl), 579 (5%, M⁺ − 2Cl − (CH₂)₂PPh₂). IRν_max/cm⁻¹: (Pd–Cl) 310w, (Pd–P) 355w, 360w, (Pd=O) 1178 m. ³¹P{¹H}NMR (298 K, DMSO-d₆): δ 111.0d [1P^A], 43.4s [2P^B], 31.2d [1P^C=O]; ³J(P^A–P^C) = 35.0 Hz. Λ(DMF) = 66.3 ohm⁻¹ cm² mol⁻¹. 10·2H₂O: Yield: 88%, white solid, mp 195–205 °C. Found: C, 50.8; H, 4.8. C₄₂H₄₆P₄PtCl₂O₃ requires: C, 51.0; H, 4.7%. MS (LSIMS): m/z (rel. intensity) 916 (91%, M⁺ − Cl), 881 (2%, M⁺ − 2Cl), 668 (3%, M⁺ − 2Cl − (CH₂)₂PPh₂). IRν_max/cm⁻¹: (Pt–Cl) 315 s, (Pt–P) 356w, (P=O) 1182 m. ³¹P{¹H}NMR (298 K, DMSO-d₆): δ 84.2d [1P^A], 39.4s [2P^B], 30.8d [1P^C=O]; ³J(³¹P^A–³¹P^C) = 39 Hz; ¹J(³¹P^A–¹⁹⁵Pt) = 2902 Hz; ¹J(³¹P^B–¹⁹⁵Pt) = 2505 Hz. ¹⁹⁵Pt NMR (298 K, DMSO-d₆): δ 4829.6 dt; ¹J(³¹P^A–¹⁹⁵Pt) = 2912 Hz; ¹J(³¹P^B–¹⁹⁵Pt) = 2524 Hz. 11·2H₂O : Yield 80%, white solid, mp 190–200 °C. Found: C, 45.4; H, 4.7. C₄₂H₄₆P₄PtBr₂O₃ requires: C, 45.3; H, 4.5%. MS (LSIMS): m/z (rel. intensity) 960 (66%, M⁺ − Br), 881 (2%, M⁺ − 2Br), 668 (4% , M⁺ − 2Br − (CH₂)₂PPh₂). IRν_max/cm⁻¹:(Pt–Br) 254w, (Pt–P) 342 m, (P=O) 1183 m. ³¹P{¹H}NMR (298 K, DMSO-d₆): δ 88.0 s [1P^A], 39.9 s [2P^B], 30.6d [1P^C=O]; ³J(³¹P^A–³¹P^C) = 37 Hz; ¹J(³¹P^A–¹⁹⁵Pt) = 2900 Hz; ¹J(³¹P^B–¹⁹⁵Pt) = 2474 Hz.

Preparation of [MX₂(PP(PO)₂)] [M = Pd: X = Br(8). M = Pt: X = I(12)]

Solutions containing [PdBr(PP₃)]Br (2) (red, 0.1165 g, 0.1243 mmol) and [PtI(PP₃)]I (6) (yellow, 0.1220 g, 0.1090 mmol) in CHCl₃ [15 mL (2)/30 mL (6)] were treated with 1.4916 and 0.1090 mmol of H₂O₂, respectively. The reaction mixtures were stirred for 2 and 14 h, affording a yellow solution (8) and a suspension (12). Et₂O (70 and 120 mL) was added to provoke and complete the precipitation. The solids were filtered off, washed with ether and dried in vacuo. 8·3H₂O: Yield: 80%, yellow solid, mp 70–80 °C. Found: C, 49.0; H, 5.0. C₄₂H₄₈P₄PdBr₂O₅ requires: C, 49,3; H, 4.7%. MS (LSIMS): m/z (rel. intensity) 950 (1%, M⁺), 871 (2%, M⁺ − Br), 579 (15% M⁺ − 2Br − (CH₂)₂P(O)Ph₂). IRν_max/cm⁻¹:(Pd–Br) 255 m, 250 sh, (Pd–P) 357 s, (P=O) 1158vs. ³¹P{¹H}NMR (298 K, DMSO-d₆): δ 82.0t [1P^D], 67.0d [1P^E], 36.1d [2P^F=O]; ³J(³¹P^D, ³¹P^F) = 54 Hz. 12·H₂O: Yield: 40%, beige solid, mp 170–180 °C. Found: C, 42.8; H, 3.6. C₄₂H₄₄P₄PdI₂O₃ requires: C, 43.1; H, 3.8%. MS (LSIMS): m/z (rel. intensity) 1151 (5%, M⁺), 1024 (100%, M⁺ − I), 879 (3%, M⁺ − 2I), 668 (9%, M⁺ − 2I − (CH₂)₂P(O)Ph₂). IRν_max/cm⁻¹: (Pt–I) 155 s, 170 s, (P=O) 1182 s. ³¹P{¹H}NMR (298 K, DMSO-d₆): δ 58.9t [1P^D], 48.9s [1P^E], 30.1d [2P^F=O]; ³J(³¹P^D, ³¹P^F) = 50 Hz; ¹J(³¹P^D–¹⁹⁵Pt) = 3257 Hz; ¹J(³¹P^E–¹⁹⁵Pt) = 3406 Hz.

Preparation of OP(PO)₃ (9)

To a solution of PP₃ (0.1890 g, 0.2810 mmol) in CH₂Cl₂ (10 mL), H₂O₂ (1.9412 mmol) was added. The reaction mixture was stirred for 3 h with formation of a precipitate by addition of Et₂O (70 mL). The solid was filtered off, washed with ether and dried in vacuo. This oxide was also prepared by reaction of 3 (0.1300 mmol) in CDCl₃ (15 mL) with 1.5600 mmol of H₂O₂. 9·3H₂O: Yield: 92%, white solid, mp 190–200 °C. Found: C, 64.3; H, 6.0. C₄₂H₄₈P₄O₇ requires: C, 64.0; H, 6.1%. ³¹P{¹H}NMR (298 K, DMSO-d₆): δ 49.5q [1P^G=O], 32.0d [3 P^H=O]; ³J(³¹P^G–³¹P^H) = 48 Hz.

Titrations of 10 with CuCl, AgX (X = Cl, NO₃) and [AuCl(tdg)]

To solutions of 10·2H₂O in CDCl₃, CuCl and AgCl as solids or solutions of AgNO₃/[AuCl(tdg)] in CD₃OD/CH₃OH were added in different stoichiometric ratios. The reaction mixtures were stirred for 24 h and those involving AgX salts protected from the light. The AgCl precipitate formed (for titrations with AgNO₃) was removed by filtration. The ³¹P{¹H}NMR spectra of the solutions were recorded after each addition. ³¹P{¹H}NMR (298 K, CDCl₃ + CH₃OH) : 10 + 1 eq. [AuCl(tdg)] δ 54.8t [1P^M], 42.9 s [1P^L], 33.8d [1P^N = O], 30.0d [1P^P]; ³J(³¹P^M–³¹P^N) = 51 Hz; ³J(³¹P^M–³¹P^P) = 56 Hz; ¹J(³¹P^M–¹⁹⁵Pt) = 3522 Hz; ¹J(³¹P^L–¹⁹⁵Pt) = 3637 Hz. (298 K, CDCl₃ + CD₃OD) : 10 + 1 eq. AgNO₃δ 75.3d [1P^A], 44.7s [2P^B], 32.5d [1P^C=O]; ¹J(³¹P^A–¹⁹⁵Pt) = 3218 Hz; ¹J(³¹P^B–¹⁹⁵Pt) = 2574 Hz. 10 + 2 eq. AgNO₃δ 76.2d [1P^A], 45.0 s [2P^B], 32.7d [1P^C=O]; ¹J(³¹P^A–¹⁹⁵Pt) = 3269 Hz; ¹J(³¹P^B–¹⁹⁵Pt) = 2571 Hz. (298 K, DMSO-d₆): 10 + 1 eq. CuClδ 84.1d [1P^A], 39.3 s [2P^B], 31.1s [1P^C=O]; ¹J(³¹P^A–¹⁹⁵Pt) = 2943 Hz; ¹J(³¹P^B–¹⁹⁵Pt) = 2490 Hz. (298 K, CDCl₃): 10 + 1 eq. AgClδ 84.2d [1P^A], 39.4s [2P^B], 30.7d [1P^C=O]; ¹J(³¹P^A–¹⁹⁵Pt) = 2920 Hz; ¹J(³¹P^B–¹⁹⁵Pt) = 2500 Hz.

Preparation of [PtAuCl₃(PP₂PO)] (10a)

A solution containing [PtCl(PP₃)]Cl (4) (0.1239 g, 0.1320 mmol) in CHCl₃ (30 mL) was treated with 0.9912 mmol of H₂O₂.The reaction mixture was stirred for 6 h. After that, a solution of [AuCl(tdg)] (0.0260 g of Au, 0.1320 mmol) in CH₃OH (8 mL) was added dropwise. The resultant solution was stirred for 16 h. The solid formed, after addition of ether (80 mL), was removed by filtration and dried in vacuo. 10a·CHCl₃: Yield: 65%, white solid, mp 100–107 °C. Found: C, 39.7; H, 3.3.C₄₃H₄₃P₄PtCl₆AuO requires: C, 39.6; H, 3.3%. MS (LSIMS): m/z (rel. intensity) 1148 (1%, M⁺ − Cl), 668 (3%, M⁺ − 3Cl − Au − (CH₂)₂PPh₂). IRν_max/cm⁻¹: (Pt–Cl) 303 m, (Au–Cl) 285 m, (Pt–P) 346w, 350w, (P=O) 1169 m. ³¹P {¹H}NMR (298 K, DMSO-d₆): δ 55.0t [1P^M], 42.5s [1P^L], 33.9d [1P^N=O], 29.8d [1P^P]; ³J(³¹P^M–³¹P^N) = 52 Hz; ³J(³¹P^M–³¹P^P) = 57 Hz; ¹J(³¹P^M–¹⁹⁵Pt) = 3506 Hz; ¹J(³¹P^L–¹⁹⁵Pt) = 3639 Hz

Preparation of [Pd(PP(PO)₂)₂]X₂ [X = Cl (13), Br (14)]

To solutions of [PdCl(PP₃)]Cl (1) (0.0586 g, 0.0692 mmol) and [PdBr(PP₃)]Br (2) (0.0711 g, 0.0760 mmol) in CHCl₃ (25 mL) solutions of PP₃ [0.0464 g, 0.0692 mmol (X = Cl); 0.0509 g, 0.0760 mmol (X = Br)] in CHCl₃ (20 mL) were added. The resultant mixtures were stirred for 12 h. The solids formed were filtered off, dissolved in 25 mL of CH₂Cl₂ and treated with H₂O₂ [0.5536 mmol (X = Cl), 0.6080 mmol (X = Br)]. The resultant suspensions were stirred for 16 h (X = Cl) and 8 h (X = Br). The final solids were filtered off, washed with ether and dried in vacuo. 13·3CH₂Cl₂: Yield: 73%, white solid, mp 140–150 °C. Found: C, 56.9; H, 4.9. C₈₇H₉₀P₈PdCl₈O₄ requires: C, 56.7; H, 4.7%. MS (LSIMS): m/z (rel. intensity) 1545 (25%, M⁺ − Cl), 1510 (21%, M⁺ − 2Cl), 808 (18%, M⁺ − 2Cl − P(CH₂CH₂PPh₂)(CH₂CH₂P(O)Ph₂)₂) 579 (21%, M⁺ − 2Cl − P(CH₂CH₂PPh₂)(CH₂CH₂P(O)Ph₂)₂ − (CH₂)₂P(O)Ph₂). IRν_max/cm⁻¹: (Pd–P) 343 m, 356sh, (P=O) 1179 m. ³¹P{¹H}NMR (298 K, DMSO-d₆): δ 61.0d [2P^I], 57.6d [2P^J], 32.5dd [4P^K=O]; ³J(³¹P^I–³¹P^J) = 17 Hz; ³J(³¹P^I–³¹P^K) = 39 Hz. Λ(DMF) = 81.0 ohm⁻¹ cm² mol⁻¹. 14·2H₂O: Yield: 60%, white solid, mp 125–130 °C. Found: C, 59.0; H, 5.0. C₈₄H₈₈P₈PdBr₂O₆ requires: C, 59.1; H, 5.2%. MS (LSIMS): m/z (rel. intensity) 1589 (25%, M⁺ − Br), 1510 (6%, M⁺ − 2Br), 808 (14%, M⁺ − 2Br − P(CH₂CH₂PPh₂)(CH₂CH₂P(O)Ph₂)₂), 579 (22%, M⁺ − 2Br − P(CH₂CH₂PPh₂)(CH₂CH₂P(O)Ph₂)₂ − (CH₂)₂P(O)Ph₂). IRν_max/cm⁻¹: (Pd–P) 349 m, 359 sh, (P=O) 1184 s. ³¹P{¹H}NMR (298 K, DMSO-d₆): δ 59.2d [2 P^I], 51.3d [2P^J], 30.1dd [4P^K=O]; ³J(³¹P^I–³¹P^J) = 18 Hz; ³J(³¹P^I–³¹P^K) = 37 Hz. Λ (DMF) = 95.7 ohm⁻¹ cm² mol⁻¹.

Titrations of 1, 3, 4 and 6 with reduced glutathione (GSH)

Solutions containing [PdX(PP₃)]X [X = Cl (1), I (3)] and [PtX(PP₃)]X [X = Cl (4), I (6)] in DMSO-d₆ (0.6 mL) were treated with solutions containing one equivalent of GSH in D₂O (0.3 mL). The products of reaction were stirred for 24 h and the precipitate (X = I) was removed by filtration. The pH was measured and the ³¹P and ¹H (Figure S7, ESI†) NMR spectra were recorded. This procedure was repeated after additions of two and three molar equivalents of GSH in D₂O (0.1 mL). ³¹P{¹H}NMR (298 K, DMSO-d₆ + D₂O): (1 + 1 eq. GSH) (pH = 3.7) δ 141.6s [1P^ax, 1 and 1a], 35.2s [3P^eq ,1], 34.4s [3P^eq, 1a], 122.0s [1P^A, 7a], 50.6 s [2P^B, 7a], 38.0d [1P^C=O, 7a and 7a′], 112.9s [1P^A, 7a′], 53.4s [2P^B, 7a′]; ³J(³¹P^A–³¹P^C) = 39 Hz. (3 + 1 eq. GSH) (pH = 4.9) δ 156.0 s [1P^ax, 3 and 3a], 36.3 s [3P^eq, 3], 34.3 s [3 P^eq, 3a], 124.9 s [1P^A, 7b], 52.0 s [2P^B, 7b], 37.5 s [1 P^C=O, 7b and 7b′], 112.9 s [1 P^A, 7b′], 53.4 s [2 P^B, 7b′]. (4 + 3 eq. GSH) (pH = 4.2) δ 123.7 s [1P^ax, 4], 30.9 s [3P^eq, 4], 130.5 s [1P^ax, 4a], 24.0 s [3P^eq, 4a], 98.5d [1 P^A, 10a′], 49.5 s [2P^B, 10a′], 38.2d [1P^C=O, 10a′]; ³J(³¹P^A–³¹P^C) = 38 Hz (10a′); ¹J(³¹P^eq–¹⁹⁵Pt) = 2570 Hz (4) 2616 Hz (4a); ¹J(³¹P^ax–¹⁹⁵Pt) = 2007 Hz (4a); ¹J(³¹P^B–¹⁹⁵Pt) = 2573 Hz (10a′). 6 + 2 eq. GSH) (pH = 5.4) 136.0br [1P^ax, 6 and 6a], 23.7 s [3P^eq, 6], 18.0s [3P^eq, 6a], 98.5 s [1 P^A, 10b′], 49.0 s [2 P^B, 10b′], 38.0 s [1P^C=O, 10b′]; ¹J(³¹P^eq–¹⁹⁵Pt) = 2574 Hz (6); ¹J(³¹P^ax–¹⁹⁵Pt) = 2349 Hz (6a).

Preparation of crystals

Single crystals of 7a·4H₂O were afforded by addition of H₂O (0.3 mL) to a sample containing [PdCl(PP₃)]Cl (0.0125 mmol) + 3 eq. GSH in DMSO-d₆ + D₂O (0.6 + 0.5 mL), collected by filtration, washed with ether and dried in vacuo. Crystals of 13∗·4CHCl₃ were prepared by reaction of [PdAgCl₃(PP₃)]³⁵ (0.0195 mmol in 2 mL CDCl₃) with four equivalents of PP₃ (1 mL CDCl₃), filtered off, washed with ether and dried in vacuo. Crystals of 13·6H₂O·2CH₃OH, used for X-ray diffraction, were prepared by addition of 6 equivalents of SnCl₂ to 13·3CH₂Cl₂ (0.0150 mmol) in 2 mL of CH₃OH, removal of the white solid formed and recrystallization in DMSO (2 mL).

X-ray crystallography

Yellow and colorless prisms of 7a·4H₂O and 13·6H₂O·2CH₃OH, respectively, and colorless needles of 13∗·4CHCl₃ were mounted on glass fibers and used for data collection. Crystal data were collected at 293(2) K using a BRUKER SMART CCD 1000 diffractometer. Graphite monochromated Mo-Kα radiation was used throughout. The quality of the 7a·4H₂O crystals did not allow a larger theta-range The data were processed with SAINT⁴⁶ and empirical absorption correction was made using SADABS.⁴⁷ The structures were solved by direct methods using the SIR-92.⁴⁸ The structures were refined by full-matrix least-squares techniques against F² using SHELXL-97.⁴⁹ Positional and anisotropic displacement parameters were refined for all non-hydrogen atoms. Hydrogen atoms were placed geometrically, and positional parameters were refined using a riding model. Atomic scattering factors were obtained with the use of International Tables for X-ray Crystallography.⁵⁰ Molecular graphics were obtained from ORTEP-3 for windows.⁵¹

Acknowledgements

We thank Xunta de Galicia (Spain) for financial support.

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Footnote

† Electronic supplementary information (ESI) available: Equation S1; Schemes S1–S3 and Figures S1–S10 including NMR spectra. CCDC reference numbers 835445–835447. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c1ra00897h

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