Stabilization of η³-indenyl compounds by sterically demanding N,N-chelating ligands in the molybdenum coordination sphere

Abstract

A series of η³-indenyl molybdenum compounds [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(^N,NL)Cl] (^N,NL = bpy, phen, pyma), isostructural with well-known η³-allyl compounds, was synthesized from the recently established halide synthon [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂]. The low stability of the hexacoordinated η³-indenyl molybdenum species in solution has been overcome by a modification of the chelating ligand. Hence, the dissociation of the compounds bearing ligands with methyl groups beside nitrogen donor atoms (e.g. 6,6′-Me₂-bpy, 2,9-Me₂-phen; 2,9-Me₂-4,7-Ph₂-phen) is strongly disfavored due to the steric requirements of the substituents. The considerable discrimination of the pentacoordinated species enables the use of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)][BF₄] for the assembly of derivatives bearing other halides and pseudohalides in the coordination sphere of molybdenum. The current study further describes some other new indenyl complexes accessible from [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂]. All structural types presented in this experimental study were supported by X-ray crystallographic data.

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Introduction

Organometallic molybdenum compounds are currently under comprehensive scrutiny due to their interesting properties. Allyl compounds [(η³-C₃H₅)Mo(CO)₂(^N,NL)Cl] (^N,NL = N,N-chelating ligand) show a rich coordination chemistry and have found several applications in organic synthesis and catalysis.^1–11 Promising cytotoxic properties have been observed for cationic cyclopentadienyl and indenyl compounds [(η⁵-Cp′)Mo(CO)₂(^X,XL)][BF₄] (Cp′ = Cp = C₅H₅, Ind = C₉H₇), where ^X,XL is N,N-, P,P- or S,S-chelating ligands, and their congeners with substituted π-ligands.^12–14 Neutral cyclopentadienyl compounds [(η⁵-Cp′)Mo(CO)₃X] (Cp′ = substituted Cp, X = anionic ligand) are well-established precursors of catalysts for oxidation reactions (e.g. olefin epoxidation or sulfoxidation).^15–21 Recently, we have described a synthesis of [{(η⁵-Ind)Mo(CO)₂(μ-Cl)}₂] (1; Scheme 1) that was found to be a versatile synthon for various η³-indenyl compounds.²² Furthermore, this compound seems to be a suitable precatalyst for isomerization of α-pinene oxide to campholenic aldehyde²³ and a precursor of hydrolytically active species for promoted hydrolysis of phosphoesters.²⁴

Scheme 1 Molecular formula of 1.

Although the cyclopentadienyl and indenyl molybdenum compounds have often a similar molecular structure, a different reactivity is expected since a replacement of the cyclopentadienyl ligand with the indenyl accelerates reaction rates due to a lower energetic barrier of the haptotropic shift of the π-ligand.^25–29 The kinetic “indenyl effect” has been comprehensively scrutinized on various molybdenum compounds by Romão and Calhorda.^30–32 For instance, they have recently demonstrated that the indenyl compound [(η⁵-Ind)Mo(CO)₂(κ²-ttcn)][BF₄] (ttcn = 1,4,7-trithiacyclononane) undergoes an acid-activated C–S cleavage to give [(η⁵-Ind)Mo(CO){κ³-(SCH₂CH₂)₂S}][BF₄], while the cyclopentadienyl analogue is stable under similar conditions.³³ An activation of coordinated ligand was also observed for complexes with η⁴-bonded spiro[2.4]hepta-4,6-diene. The cyclopentadienyl compound [(η⁵-Cp){η⁴-C₅H₄(CH₂)₂}Mo(CO)₂][BF₄] is unusually stable, while the indenyl analogue undergoes a spontaneous and very fast ring-opening to [(η⁵-Ind)(η⁵-C₅H₄CH₂-η¹-CH₂)Mo(CO)][BF₄].^34,35

The aim of this study is to bring a detail description of the coordination properties of [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2) in attempt to synthesize new η³-indenyl compounds structurally related with the well-known complexes bearing η³-allyl [(η³-C₃H₅)Mo(CO)₂(^N,NL)Cl]. It will be shown that a steric congestion of the chelating ligand is critical for the stability of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(^N,NL)Cl] and could be used for the control of the indenyl ring slippage. When this work was in progress, the first notes about reactivity of the parent compound 1 with coordinating solvents have appeared in literature^23,24 but the detailed description of the coordination behavior is still missing. Our current study deals with species bearing 4,7-dimethyl indenyl ligand mainly due to higher solubility of 2 in organic solvents.²² This substitution pattern usually has only negligible effect on the reactivity due to subtle steric and electronic effects of two methyl groups in the C₆-ring.^36,37

Results and discussion

Reactions of [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2) with py, bpy, phen and pyma

Reaction of [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2) with pyridine (py) gives a monomeric compound with η⁵-bonded indenyl ligand [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(py)Cl] (3), see Scheme 2. The expected η³-indenyl species, which could appear upon coordination of further py molecule to molybdenum, was not detected even when a large excess of the reagent was used. Although the compound 3 is a structural analogue of the previously described cyclopentadienyl compound [(η⁵-Cp)Mo(CO)₂(py)Cl],³⁸ the original route is not suitable for 3 due to a low stability of the indenyl precursor [(η⁵-Ind)Mo(CO)₃Cl] at elevated temperature.³⁹

Scheme 2 Reaction of 2 with pyridine.

¹H NMR spectrum shows the signal of H² at a high field that is typical for the species with η⁵-coordinated indenyl ligand.⁴⁰ The spectrum pattern with magnetically inequivalent protons H¹ and H³ imply the C₁ point symmetry for the molecule of 3 that is fully in agreement with the solid state structure revealed by single crystal X-ray analysis (Fig. 1 and Table 1). The molecule of 3 has a square pyramidal structure with the η⁵-bonded indenyl ligand in the apical position. The basal plane is occupied with two cis-coordinated carbonyl ligands, one chloride and the nitrogen donor atom of pyridine. The η⁵-coordination mode of the indenyl ligand is confirmed by a low value of the envelope fold angle [Ω = 7.4(2)°] and also by Δ(M–C) [0.212(2) Å].

Fig. 1 ORTEP drawing of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(py)Cl] (3). The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 30% probability level.

Table 1 Geometric parameters of the neutral and cationic pentacoordinated molybdenum species^a

	3 ^e	4b-BF4	5b-9·CH2Cl2	8-BF4	10b-BF4·0.5(Me2-phen·HBF4)
a Distances are given in Å; angles and dihedral angles are given in °. b Pl^1 is defined by Mo and two nitrogen donor atoms; Pl^2 is defined by two nitrogen donor atoms and two adjacent carbon atoms of the chelate ring. c Ω is the envelope fold angle defined for the indenyl ligand as the angle between planes defined by C3, C4 and C5 and that of C1, C2, C3 and C5.^41 d Δ(M–C) represents the differences in the metal–carbon bonds. It is defined for the indenyl compounds as the difference between the averages of the metal–carbon distances M–C1 and M–C2 and those of M–C3, M–C4, and M–C5.^41 e Mo–Cl = 2.4998(6) Å; N–Mo–Cl = 82.24(4)°.
Mo–Cg(C5)	2.0236(9)	1.9979(12)	2.004(3)	1.990(2)	2.0154(18)
Mo–C(CO)	1.929(2)	1.960(3)	1.950(9)	1.968(5)	1.945(6)
	1.956(2)	1.970(3)	1.980(9)	1.969(4)	1.957(6)
Mo–N	2.280(2)	2.190(2)	2.196(5)	2.180(4)	2.244(4)
		2.191(2)	2.208(6)	2.182(4)	2.250(4)
C(CO)–Mo–C(CO)	72.71(10)	74.72(12)	74.8(4)	74.3(2)	69.5(2)
N–Mo–N	—	72.88(8)	73.3(2)	78.93(14)	74.45(13)
Pl^1–Pl^2^b	—	7.8(2)	6.8(4)	—	22.4(2)
Ω ^c	7.4(2)	5.1(3)	5.7(8)	6.7(5)	6.3(4)
Δ(M–C)^d	0.212(2)	0.149(3)	0.157(8)	0.160(5)	0.178(4)

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From a mechanistic point of view, the η⁵–η³ rearrangement of the indenyl ligand is stimulated by a coordination of two 2e donors to molybdenum that could be further enforced by a chelating effect. Nevertheless, this process is further complicated by a coordination or abstraction of chloride as will be documented on the reactions with 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) and trans-N-(2-pyridylmethylene)aniline (pyma).

Reaction of 2 with two equivalents of bpy, phen and pyma gives, after standard work up, the desired η³-indenyl compounds [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(^N,NL)Cl] (4a: ^N,NL = bpy, 5a: ^N,NL = phen, 6a: ^N,NL = pyma), see Scheme 3. Infrared spectra of the solid-state samples show two CO stretching bands at low frequencies (Table 2) indicating the proposed neutral structure. Hence, cationic complexes [(η⁵-Ind)Mo(CO)₂L₂]⁺ have much lower electron density on molybdenum atom than neutral compounds with slipped indenyl ring [(η³-Ind)Mo(CO)₂L₂Cl] as could be documented on the CO stretching band frequencies of the pairs bearing monodentate ligands (cf. data for compounds bearing DMF or MeCN in Table 2).

Scheme 3 Reaction of 2 with two equivalents of bpy, phen and pyma.

Table 2 Summary of the infrared data for the molybdenum complexes^a

	ν a(CO)	ν s(CO)	Ref.
a The stretching frequencies are given in cm^−1.
4a	1940	1862
4b-BF4	1970	1894
[(η^5-Ind)Mo(CO)2(bpy)][BF4]	1974	1878	13
5a	1919	1844
5b-BF4	1967	1880
[(η^5-Ind)Mo(CO)2(phen)][BF4]	1968	1874	13
6a	1934	1855
[(η^3-Ind)Mo(CO)2(NCMe)2Cl]	1954	1851	23
[(η^5-Ind)Mo(CO)2(NCMe)2][BF4]	1970	1880	23
[(η^3-Ind)Mo(CO)2(DMF)2Cl]	1934	1830	24
[(η^5-Ind)Mo(CO)2(DMF)2][BF4]	1962	1865	24

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The solid state structure of the compound 6a was determined by X-ray diffraction analysis, see Fig. 2. The molecule has a distorted octahedral structure. When the bond Cg(C₃)–Mo is defined as the principal axis, indenyl and chloride occupy the axial positions while the cis-coordinated carbonyl ligands and the nitrogen donor atoms of pyma are in the equatorial plane. High values of Ω [23.1(6)°] and Δ(M–C) [0.849(6) Å], observed for indenyl ligand, are in line with desired η³-coordination mode.^22,42,43 According to the initial aim, the compound 6a is isostructural with allyl complex [(η³-C₃H₅)Mo(CO)₂(pyma)Cl] (6-allyl) that was also confirmed by X-ray diffraction analysis (cf.Fig. 2 and 3). The allyl counterpart 6-allyl was prepared by a ligand exchange reaction starting from [(η³-C₃H₅)Mo(CO)₂(NCMe)₂Cl] and pyma. The geometric parameters of 6a and 6-allyl, describing the coordination sphere of molybdenum, are very similar (see Table 3). Only the distance Mo–Cg(C₃) in 6a is longer due to an electron-withdrawing character of the annulated benzene ring that weakens the donor properties of indenyl.

Fig. 2 ORTEP drawing of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(pyma)Cl] (6a). The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 30% probability level.

Fig. 3 ORTEP drawing of [(η³-C₃H₅)Mo(CO)₂(pyma)Cl] (6-allyl). The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 30% probability level.

Table 3 Geometric parameters of the neutral hexacoordinated molybdenum species^a

	6a	6-allyl	10a·CH2Cl2^b	10a·CH2Cl2^b	10a·CHCl3	10-allyl	10c
a Distances are given in Å; angles and dihedral angles are given in °. b Two crystallographically independent molecules in the unit cell. c For definition see footnote of Table 1.
Mo–Cg(C3)	2.1027(18)	2.040(2)	2.106(3)	2.109(2)	2.1202(16)	2.040(5)	2.126(3)
Mo–X	2.4736(14)	2.4957(5)	2.4649(7)	2.4761(7)	2.4690(7)	2.4858(4)	2.6189(4)
Mo–C(CO)	1.977(7)	1.957(3)	1.957(2)	1.953(2)	1.945(3)	1.9466(14)	1.958(3)
	1.964(5)	1.959(3)	1.958(2)	1.957(2)	1.966(2)	1.9498(15)	1.960(3)
Mo–N	2.231(6)	2.248(2)	2.277(2)	2.279(2)	2.280(2)	2.2984(11)	2.261(2)
	2.262(4)	2.279(2)	2.283(2)	2.281(2)	2.287(2)	2.2958(11)	2.283(2)
Cg(C3)–Mo–X	173.35(8)	175.83(9)	174.81(7)	175.27(6)	176.05(6)	177.20(6)	175.49(8)
C(CO)–Mo–C(CO)	79.1(3)	78.02(11)	76.15(10)	77.30(10)	75.27(12)	76.75(6)	75.07(12)
N–Mo–N	73.25(18)	72.39(7)	74.26(6)	73.85(7)	73.59(7)	73.06(4)	74.57(9)
Pl^1–Pl^2^c	2.0(3)	0.4(1)	10.0(2)	14.4(2)	13.2(2)	14.11(8)	9.8(2)
Ω ^c	23.1(6)	—	23.2(3)	23.4(2)	22.5(3)	—	21.3(3)
Δ(M–C)^c	0.849(6)	—	0.840(3)	0.847(3)	0.838(3)	—	0.805(3)

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Although the indenyl compounds 4a–6a are isostructural with the well-known allyl complexes [(η³-C₃H₅)Mo(CO)₂(^N,NL)Cl] their behavior in solution is very different. The allyl compounds are stable in solution of common organic solvents while a dissolution of the η³-indenyl compounds 4a–6a, even in non-coordinating solvents, leads to a chloride abstraction to give cationic pentacoordinated species [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(^N,NL)]⁺ (4b: ^N,NL = bpy, 5b: ^N,NL = phen, 6b: ^N,NL = pyma) as evidenced by the ¹H NMR spectroscopy, see Scheme 3. The complexes bearing bpy (4a) and phen (5a) undergo a complete ionization in solution while the compound 6a only a partial one as evidenced by two sets of signals. It suggests that the chloride abstraction is an equilibrium reaction that is further supported by a fact that a solvent evaporation gives back the initial hexacoordinated species 4a–6a, see Scheme 3.

The assignment of the sets of signals to the η³ -or η⁵-indenyl species is done according to chemical shift of the proton at the 2-position. Hence, low-fielded triplet of H² is diagnostic to η³-coordination mode while high-fielded one implies the η⁵-bonding of the indenyl ligand.⁴⁰ This assignment is confirmed by the use of an alternative chloride-free protocol for the cationic species 4b and 5b compensated with a weakly coordinating tetrafluoroborate, see Scheme 4.

Scheme 4 Synthesis of cationic molybdenum compounds.

Protonation of allyl compound [(η³-C₃H₅)(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂] (7) in presence of acetonitrile gives the cationic compound [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(NCMe)₂][BF₄] (8-BF₄). Following ligand exchange produces the desired chelate complexes [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(bpy)][BF₄] (4b-BF₄) and [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(phen)][BF₄] (5b-BF₄). As expected, the solution ¹H NMR spectra are identical with chloride analogues 4b-Cl and 5b-Cl. High CO stretching frequencies observed for solid samples of 4b-BF₄ and 5b-BF₄ are in line with the presence of weakly coordinating anion (cf. with 4a and 5a in Table 2) and prove retention of 4b-BF₄ and 5b-BF₄ in the solid state. The structures of 8-BF₄ and 4b-BF₄ were determined by X-ray diffraction analysis. Both cations have a square-pyramidal structure, see Fig. 4 and 5. The apical position is occupied with the η⁵-bonded indenyl ligand (for Ω and Δ(M–C) see Table 1). The cis-coordinated carbonyl ligands and two nitrogen donor atoms of remaining ligands form the basal plane. The structural parameters, describing the coordination sphere of molybdenum, are in line with data of structurally related cyclopentadienyl and indenyl compounds described previously.^{13,14,44–46}

Fig. 4 ORTEP drawing of cation [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(NCMe)₂]⁺ present in the crystal structure of 8-BF₄. The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 30% probability level.

Fig. 5 ORTEP drawing of cation [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(bpy)]⁺ present in the crystal structure of 4b-BF₄. The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 30% probability level.

The reaction of 2 with lower than stoichiometric amount of bpy or phen gives a material insoluble in common organic solvents that strongly contrasts with properties of the starting compounds as well as the products 4a and 5a. Elemental analysis of the products together with their insolubility suggests an appearance of the ionic pair consisting of a large complex cation and a large complex anion [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(^N,NL)][(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂Cl₂] (4b-9: ^N,NL = bpy, 5b-9: ^N,NL = phen), see Scheme 5. Slow diffusion of a phenanthroline solution into a solution of the starting compound (2) gives single crystals suitable for the X-ray diffraction analysis that confirmed the proposed ionic structure of 5b-9 (see Fig. 6). The cationic part is isostructural with bipyridine complex 4b-BF₄. The anionic part forms square-pyramid with two cis-coordinated carbonyl ligands and two chlorides in basal plane. The η⁵-coordinated indenyl (for Ω and Δ(M–C) see Table 4) occupies the apical position. The geometric parameters describing the coordination sphere of anionic part are very close to the data recently published for starting dimeric species [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2).²² The crystal structure of 5b-9 is stabilized by intramolecular π–π stacking involving phenanthroline ligand of 5b and indenyl ligand of 9. The distance between the centroid of central phenanthroline ring and centroid of the C₆-ring of the indenyl ligand was found to be 3.493(5) Å.

Scheme 5 Reaction of 2 with one equivalent of bpy or phen.

Fig. 6 ORTEP drawing of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(bpy)]⁺ and [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂Cl₂]⁻ present in the crystal structure of 5b-9·CH₂Cl₂. The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 20% probability level.

Table 4 Geometric parameters of the anionic molybdenum species [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂Cl₂]⁻ present in the crystal structure of 5b-9·CH₂Cl₂^a

a Distances are given in Å, angles and dihedral angles are given in °. b For definition see footnote of Table 1.
Mo–Cg(C5)	2.036(4)	C(CO)–Mo–C(CO)	74.0(4)
Mo–C(CO)	1.942(9)	Cl–Mo–Cl	81.56(8)
	1.909(9)
Mo–Cl	2.495(2)	Ω ^b	9.9(10)
	2.514(2)
		Δ(M–C)^b	0.239(10)

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Since the anionic complex (9) is unprecedented an alternative method of the synthesis was developed. It is given by the reaction of 2 with a common source of chlorides. Namely, the soluble ammonium salt, [Me₄N][(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂Cl₂] (Me₄N-9), was prepared by the reaction of 2 with [Me₄N]Cl (Scheme 6). The infrared spectra of Me₄N-9 show the CO stretching bands at low wavenumbers [ν_a(CO): 1936, 1922 cm⁻¹; ν_s(CO): 1820 cm⁻¹] that is consistent with the high electron density on molybdenum. The appearance of two bands of the ν_a(CO) is due to a vibration coupling of the carbonyl ligands in the crystal lattice. ¹H NMR spectrum of Me₄N-9 shows a typical pattern of the η⁵-indenyl ligand with a highfielded signal of H² (δ = 4.87 ppm).

Scheme 6 Synthesis of [Me₄N][(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂Cl₂] (Me₄N-9).

Reaction of 2 with sterically demanding N,N-chelating ligands

Dissociation of the complexes bearing bpy, phen and pyma led us to a more sterically demanding N,N-chelating ligand, 2,9-dimethyl-1,10-phenanthroline (2,9-Me₂-phen), in attempt to stabilize the η³-indenyl species in solution.

The product of the reaction between [η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2) and 2,9-Me₂-phen shows similar frequencies of the CO stretching bands [ν_a(CO): 1927 cm⁻¹; ν_s(CO): 1848 cm⁻¹] as observed for the hexacoordinated species 4a–6a that implies a similar molecular structure in the solid state, [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)Cl] (10a), see Scheme 7. The enhanced stability of 10a in solution was confirmed by ¹H NMR spectroscopy. Hence, the spectrum shows only one set of signals. The signal of the indenyl proton H² appears at high field (δ = 5.84 ppm) that is typical for η³-coordination mode. The observed spectrum pattern is consistent with C_s molecular symmetry that confirms a configuration with the nitrogen donor atoms of the chelating ligand in trans-positions to the cis-coordinated carbonyl ligands. The X-ray structure analyses of 10a·CH₂Cl₂ and 10a·CHCl₃ confirm appearance of this isomer in the solid state, see Fig. 7. The η³-coordination mode of the indenyl ligand is evidenced by slipping parameters Ω (∼23°) and Δ(M–C) (∼0.84 Å), see Table 3.

Scheme 7 Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)Cl] (10a).

Fig. 7 ORTEP drawing of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)Cl] present in the crystal structure of 10a·CH₂Cl₂. The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 30% probability level. Only one of two crystallographically independent molecules is shown for clarity.

Although the coordination sphere of molybdenum seems to be very similar to the pyma complex 6a (cf. bond distances and bond angles in Table 3), the methyl groups in the near neighborhood of carbonyl ligands prevent an appearance of a planar chelate cycle. Hence, the methyl groups of 2,9-Me₂-phen are forced below the equatorial plane, defined by molybdenum and carbonyl ligands, that causes an envelope folding of the chelate cycle of ∼14°. This distortion is caused by steric repulsion of the methyl groups with the carbonyl ligands as evidenced by short nonbonding distances C(CH₃)–C(CO) of 3.064(4)–3.138(4) Å those are considerably shorter than sum of van der Waals radii of two carbon atoms (3.4 Å).⁴⁷ The folding of the chelate cycle seems to be independent on nature of η³-ligands. Hence, the η³-allyl analogue 10-allyl is distorted in the same way as 10a; cf.Fig. 7 and 8 and Pl₁–Pl₂ in Table 3.

Fig. 8 ORTEP drawing of [(η³-C₃H₅)Mo(CO)₂(2,9-Me₂-phen)Cl] (10-allyl). The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 30% probability level.

The high stability of 10a toward the loss of chloride suggests that the cationic complex bearing 2,9-Me₂-phen, 10b-BF₄, should be a suitable precursor for the assembly of hexacoordinated complexes bearing various anionic 2e ligands (Scheme 8). The starting 10b-BF₄ was synthesized using the standard protocol outlined above for 4b-BF₄. The X-ray diffraction analysis of the 10b-BF₄·0.5(Me₂-phen·HBF₄) reveals the expected square-pyramidal structure (Fig. 9) with the η⁵-coordinated indenyl ligand as documented by slippage parameters [Ω = 6.3(4)°; Δ(M–C) [0.178(4) Å]. The folding of the chelate cycle [Pl₁–Pl₂ is 22.4(2)°] is, in this case, much heavier than observed for 2,2′-bipyridine analogue 4b-BF₄ [7.8(2)°] and even that in hexacoordiated species 10a [10.0(2)–14.4(2)°]. This distortion is accompanied with prolongation of the bonds Mo–N (cf.10b-BF₄·0.5(Me₂-phen·HBF₄) with 4b-BF₄ and 5b-9·CH₂Cl₂ in Table 1). These observations imply that a repulsion of the phenanthroline methyl groups from the carbonyl ligands is weaker for hexacoordinated species and seems to be a driving force for its stabilization in solution. The crystal structure of 10b-BF₄·0.5(Me₂-phen·HBF₄) reveals π–π stacking interactions involving two molecules of cationic complex 10b and a protonated ligand. The distance between centroid of the central phenanthroline rings are 3.598(3) Å.⁴⁸

Scheme 8 Optimized synthesis of η³-indenyl compounds. X = Cl, Br, I, NCO and NCS for compounds denoted a, c, d, e and f, respectively.

Fig. 9 ORTEP drawing of cation [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)]⁺ present in the crystal structure of 10b-BF₄·0.5(Me₂-phen·HBF₄). The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 20% probability level.

The instability of the pentacoordinated cationic species in presence of free monoanionic ligands was evidenced on reactions of 10b-BF₄ with a series of halides and pseudohalides. An apearance of the hexacoordinated species [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)X] (10a: X = Cl, 10c: X = Br, 10d: X = I, 10e: X = NCO, 10f: X = NCS) is documented by the infrared and NMR spectroscopy. The compounds 10c–10f are stable in solution. The ¹H NMR spectra of the isolated products confirm that the dissociation reaction is highly disfavored similarly as in case of the parent chloride complex 10a. The infrared spectra reveal that cyanate ligand in 10e and thiocyanate ligand in 10f are bonded to molybdenum via the nitrogen donor atom. It is documented by low stretching frequencies of the C=N bonds (10e: 2195 cm⁻¹, 10f: 2063 cm⁻¹). This observation is in line with literature data reported for allyl analogues [(η³-C₃H₅)Mo(CO)₂(Ph₂PCH₂CH₂PPh₂)(NCO)],⁴⁹ [(η³-C₃H₅)Mo(CO)₂(phen)(NCS)],^50,51 [(η³-C₃H₄Ph)Mo(CO)₂(phen)(NCS)],⁵² [(η³-C₃H₅)Mo(CO)₂(NCMe)₂(NCS)].⁵³ Structure of the bromide complex 10c was determined by X-ray analysis, see Fig. 10. The coordination sphere of the central metal is very similar as in case of the chloride analogue 10a. The bond distance Mo–Br was found to be shorter [2.6189(4) Å] than in case of similar allyl complexes [(η³-C₃H₅)Mo(CO)₂(^N,NL)Br)] (^N,NL = bpy: 2.650(3) Å, ^N,NL = phen: 2.645(2) Å] that is a result of different donor properties of the ligand in trans-possition to bromide.⁵⁴

Fig. 10 ORTEP drawing of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)Br] present in the crystal structure of 10c. The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 30% probability level.

A variation of the electronic properties of the bidentate ligands has only minor effect on stability of the η³-indenyl complexes as documented on experiments with series of modified N,N-chelating ligands, namely 3,4,7,8-Me₄-phen, 2,9-Me₂-4,7-Ph₂-phen, 4,4′-Me₂-bpy and 6,6′-Me₂-bpy. Although the donor ability of the 1,10-phenanthroline ligands decreases in the line 3,4,7,8-Me₄-phen > 2,9-Me₂-4,7-Ph₂-phen > 2,9-Me₂-phen > phen,^55,56 the stability of the molybdenum complexes does not follow this relation. Derivatives bearing methyl groups beside the nitrogen donor atom (i.e. 2,9-Me₂-phen and 2,9-Me₂-4,7-Ph₂-phen) form much more stable complexes (10a and 12a) than the rest of the series (i.e. phen and 3,4,7,8-Me₄-phen), see Schemes 3, 9 and 10. Hence, complexes 10a and 12a are stable in solution, while compounds 5a and 11a undergo dissociation giving cationic complexes 5b-Cl and 11b-Cl, respectively. These observations reveal that the stability of the products is mainly influenced by steric effects of the chelating ligands, overshadowing the electronic ones. Similar conclusion was achieved based on experiments with dimethyl substituted 2,2′-bipyridines. Although donor ability of 4,4′-Me₂-bpy is comparable to 6,6′-Me₂-bpy, only the later ligand gives a stable hexacoordinated species (14a) that does not undergo dissociation in solution and cloud be easily synthesized by reaction of 14b-BF₄ with common source of chlorides (e.g. [Me₄N]Cl), see Scheme 10. In contrary, 4,4′-Me₂-bpy produces complex with ionic structure (13b-Cl) both in solution and in solid state, see Scheme 9.

Scheme 9 Reaction of 2 with two equivalents of 3,4,7,8-Me₄-phen and 4,4′-Me₂-bpy.

Scheme 10 Syntheses of complexes bearing 2,9-Me₂-4,7-Ph₂-phen and 6,6′-Me₂-bpy.

Conclusions

Although sterically demanding ligands are commonly used for the stabilization of low-coordinate metal compounds^57,58 or complexes in a low oxidation state,^59,60 an application of this approach for the stabilization of low hapticity of the indenyl ligand is rather unusual.²⁵ In current study, we clearly demonstrated that modification of the steric properties of a N,N-chelating ligand is a suitable approach for the hapticity adjustment in the indenyl molybdenum compounds. Hence, powerful steric effect of methyl groups in positions beside nitrogen donor atoms activates [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂]⁺ core toward association of 2e anionic ligand (e.g. halide) that is otherwise highly disfavored. Such nucleophile-induced indenyl ring slippage enables the assembly of η³-indenyl species isostructural with highly attended allyl complexes. This observation strongly contrasts with less demanding ligands (e.g. bpy, 4,4′-Me₂-bpy, phen, 3,4,7,8-Me₄-phen) those form pentacoordinated cationic species [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(^N,NL)]⁺ in solution and desired η³-compounds were stable only in particular cases in the solid state.

Experimental section

Methods and materials

All operations were performed under nitrogen using conventional Schlenk-line techniques. The solvents were purified and dried by standard methods.⁶¹ Starting materials were available commercially or prepared according to literature procedures: [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2),²² [(η³-C₃H₅)(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂] (7),²² [(η³-C₃H₅)Mo(CO)₂(NCMe)₂Cl],⁶² The infrared spectra were recorded in the 4000−400 cm⁻¹ region (resolution 2 cm⁻¹) on a Nicolet Magna 6700 FTIR spectrometer using a Diamond Smart Orbit ATR. ¹H and ¹³C{¹H} NMR spectra were measured on a Bruker Avance 400 and a Bruker Avance 500 spectrometers at room temperature. The chemical shifts are given in ppm relative to TMS.

Synthesis of 6,6′-dimethyl-2,2′-bipyridine (6,6′-Me₂-bpy)

A solution of bpy (1.00 g, 6.4 mmol) in THF (100 mL) was cooled at −50 °C, treated with MeLi (17 mL, 1.6 mol L⁻¹, 27.2 mmol) and stirred at this temperature for 1 h. The solution was warmed to room temperature, stirred for another 1 h and then refluxed overnight. After cooling at room temperature, the reaction mixture was transferred into a mixture ice-water. The organic layer was separated and the aqueous layer was extracted three times with CH₂Cl₂. The combined organic layers were drier with MgSO₄ and filtered. The volatiles were vacuum evaporated on a rotavapor. Resulting brown oil was oxidized by a saturated solution of KMnO₄ in acetone until formation of MnO₂ ceased. The MnO₂ was removed by vacuum filtration through short pad of celite on a glass frit. Acetone was vacuum evaporated on a rotavapor and the crude product was purified by column chromatography on silica (hexane/ethyl acetate = 1 : 1). R_f(TLC) = 0.70 (hexane/ethyl acetate = 1 : 1). Yield: 0.29 g (25%, 1.57 mmol). Analytical and spectroscopic date were consistent with those reported elsewhere.⁶³

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(py)Cl] (3)

[{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 200 mg, 0.30 mmol) was dissolved in CH₂Cl₂ (50 mL) and treated with py (475 mg, 6.0 mmol). The solution was stirred at room temperature overnight. The volatiles were vacuum evaporated. The crude product was washed with ether and recrystallized from the mixture CH₂Cl₂/ether and vacuum dried. Yield: 205 mg (83%, 0.50 mmol). Red powder. Mp: 150–160 °C (dec.). Anal. calcd for C₁₈H₁₆ClMoNO₂: C, 52.77; H, 3.94; N, 3.42. Found: C, 52.98; H, 3.87; N, 3.60. ¹H NMR (CDCl₃; 400 MHz; δ (ppm)): 8.70 (s-br, 1H, py), 8.13 (dd, ³J(¹H,¹H) = 6.4 Hz, ⁴J(¹H,¹H) = 1.4 Hz, 2H, py), 7.68 (tt, ³J(¹H,¹H) = 7.6 Hz, ⁴J(¹H,¹H) = 1.4 Hz, 1H, py), 7.11 (m, 1H, py), 7.03 (d, ³J(¹H,¹H) = 7.2 Hz, 1H, C₉H₅, H^5,6), 6.91 (d, ³J(¹H,¹H) = 7.2 Hz, 1H, C₉H₅, H^5,6), 5.87 (d, ³J(¹H,¹H) = 2.8 Hz, ⁴J(¹H,¹H) = 1.5 Hz, 1H, C₉H₅, H^1,3), 5.69 (d, ³J(¹H,¹H) = 2.8 Hz, ⁴J(¹H,¹H) = 1.5 Hz, 1H, C₉H₅, H^1,3), 5.31 (t, ³J(¹H,¹H) = 2.8 Hz, 1H, C₉H₅, H²), 2.37 (s, 3H, CH₃), 1.47 (s, 3H, CH₃). FTIR (ATR, cm⁻¹): 1940 vs [ν_sa(CO)], 1848 vs [ν_s(CO)], 1819 vs [ν_s(CO)]. Single crystals of 3 suitable for X-ray diffraction analysis were prepared by overlayering of the CH₂Cl₂ solution with hexane.

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(bpy)Cl] (4a)

[{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 200 mg, 0.30 mmol) was dissolved in CH₂Cl₂ (50 mL) and treated with bpy (94 mg, 0.60 mmol). The solution was stirred at room temperature overnight. The volatiles were vacuum evaporated. The crude product was washed with ether and recrystallized from the mixture CH₂Cl₂/ether and vacuum dried. Yield: 285 mg (98%, 0.59 mmol). Dark red powder. Mp: 150–160 °C (dec.). Anal. calcd for C₂₃H₁₉ClMoN₂O₂: C, 56.75; H, 3.93; N, 5.75. Found: C, 56.92; H, 4.12; N, 5.57. ¹H NMR (CDCl₃; 400 MHz; δ (ppm); 4b-Cl): 9.54 (s-br, 2H, bpy), 8.91 (d, ³J(¹H,¹H) = 5.5 Hz, 2H, bpy), 8.22 (s-br, 2H, bpy), 7.47 (t, ³J(¹H,¹H) = 6.1 Hz, 2H, bpy), 6.57 (s, 2H, C₉H₅, H^5,6), 6.09 (d, ³J(¹H,¹H) = 2.6 Hz, 2H, C₉H₅, H^1,3), 5.53 (t, ³J(¹H,¹H) = 2.6 Hz, 1H, C₉H₅, H²), 1.91 (s, 6H, CH₃). FTIR (ATR, cm⁻¹): 1940 vs [ν_a(CO)], 1862 vs [ν_s(CO)].

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(bpy)][BF₄] (4b-BF₄)

[(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(NCMe)₂][BF₄] (8-BF₄; 100 mg, 0.22 mmol) was dissolved in CH₂Cl₂ (50 mL) and treated with bpy (34 mg, 0.22 mmol). The solution was stirred at room temperature overnight. The volatiles were vacuum evaporated. The crude product was washed with ether and recrystallized from the mixture CH₂Cl₂/ether and vacuum dried. Yield: 115 mg (99%, 0.21 mmol). Red powder. Mp: 180–190 °C (dec.). Anal. calcd for C₂₃H₁₉BF₄MoN₂O₂: C, 51.33; H, 3.56; N, 5.21. Found: C, 51.06; H, 3.71; N, 5.18. ¹H NMR (CDCl₃; 400 MHz; δ (ppm)): 8.89 (d, ³J(¹H,¹H) = 5.7 Hz, 2H, bpy), 8.64 (d, ³J(¹H,¹H) = 8.6 Hz, 2H, bpy), 8.14 (t, ³J(¹H,¹H) = 7.8 Hz, 2H, bpy), 7.50 (t, ³J(¹H,¹H) = 6.5 Hz, 2H, bpy), 6.62 (s, 2H, C₉H₅, H^5,6), 6.09 (d, ³J(¹H,¹H) = 2.9 Hz, 2H, C₉H₅, H^1,3), 5.56 (t, ³J(¹H,¹H) = 2.9 Hz, 1H, C₉H₅, H²), 1.91 (s, 6H, CH₃). FTIR (ATR, cm⁻¹): 1970 vs [ν_a(CO)], 1894 vs [ν_s(CO)], 1040 vs [ν(BF)]. Single crystals of 4b-BF₄ suitable for X-ray diffraction analysis were prepared by overlayering of the CH₂Cl₂ solution with ether.

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(phen)Cl] (5a)

Steps of the synthesis followed the procedure for the compounds 4a. Reagents: [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 200 mg, 0.30 mmol) and phen (108 mg, 0.60 mmol). Yield: 265 mg (86%, 0.52 mmol). Dark red powder. Mp: 150–160 °C (dec.). Anal. calcd for C₂₅H₁₉ClMoN₂O₂: C, 58.78; H, 3.75; N, 5.48. Found: C, 58.83; H, 3.96; N, 5.44. ¹H NMR (CD₃CN; 400 MHz; δ (ppm); 5b-Cl): 9.57 (dd, ³J(¹H,¹H) = 5.4 Hz, ⁴J(¹H,¹H) = 1.3 Hz, 2H, phen), 8.67 (dd, ³J(¹H,¹H) = 8.3 Hz, ⁴J(¹H,¹H) = 1.2 Hz, 2H, phen), 8.08 (s, 2H, phen), 7.94 (dd, ³J(¹H,¹H) = 8.2 Hz, ⁴J(¹H,¹H) = 5.2 Hz, 2H, phen), 6.45 (d, ³J(¹H,¹H) = 2.8 Hz, 2H, C₉H₅, H^1,3), 6.16 (s, 2H, C₉H₅, H^5,6), 5.69 (t, ³J(¹H,¹H) = 2.8 Hz, 1H, C₉H₅, H²), 1.84 (s, 6H, CH₃). FTIR (ATR, cm⁻¹): 1919 vs [ν_a(CO)], 1844 vs [ν_s(CO)].

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(phen)][BF₄] (5b-BF₄)

Steps of the synthesis followed the procedure for the compounds 4b-BF₄. Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(NCMe)₂][BF₄] (8-BF₄; 50 mg, 0.11 mmol) and phen (20 mg, 0.11 mmol). Yield: 65 mg (99%, 0.11 mmol). Red powder. Mp: 160–170 °C (dec.). Anal. calcd for C₂₅H₁₉BF₄MoN₂O₂: C, 57.08; H, 3.14; N, 4.59. Found: C, 57.17; H, 3.19; N, 4.42. ¹H NMR (CD₂Cl₂; 400 MHz; δ (ppm)): 9.41 (dd, ³J(¹H,¹H) = 5.4 Hz, ⁴J(¹H,¹H) = 1.2 Hz, 2H, phen), 8.62 (dd, ³J(¹H,¹H) = 8.1 Hz, ⁴J(¹H,¹H) = 1.2 Hz, 2H, phen), 8.07 (s, 2H, phen), 7.96 (dd, ³J(¹H,¹H) = 8.1 Hz, ³J(¹H,¹H) = 5.4 Hz, 2H, phen), 6.27 (s, 2H, C₉H₅, H^5,6), 6.27 (d, ³J(¹H,¹H) = 2.8 Hz, 2H, C₉H₅, H^1,3), 5.67 (t, ³J(¹H,¹H) = 2.8 Hz, 1H, C₉H₅, H²), 1.86 (s, 6H, CH₃). ¹³C NMR (CD₂Cl₂; 101 MHz; δ (ppm)): 252.3 (2C, CO), 133.1, 132.3 (2 × 1C_q), 156.6, 139.0, 129.0, 128.1, 125.1 (5 × 2C, phen and C₉H₅), 91.3 (1C, C² of C₉H₅), 79.5 (2C, C^1,3 of C₉H₅), 19.0 (2C, CH₃). FTIR (ATR, cm⁻¹): 1967 vs [ν_a(CO)], 1880 vs [ν_s(CO)].

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(pyma)Cl] (6a)

Steps of the synthesis followed the procedure for the compounds 4a. Reagents: [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 200 mg, 0.30 mmol) and pyma (109 mg, 0.60 mmol). Yield: 285 mg (93%, 0.56 mmol). Purple powder. Mp: 150–160 °C (dec.). Anal. calcd for C₂₅H₂₁ClMoN₂O₂: C, 58.55; H, 4.13; N, 5.46. Found: C, 58.44; H, 4.25; N, 5.59. ¹H NMR (CD₃CN; 400 MHz; δ (ppm); 6a and 6b-Cl in the ratio 1 : 3): 8.61 (d, ³J(¹H,¹H) = 5.4 Hz, 1H of a, pyma), 8.60 (s, 1H of a, pyma), 8.41 (s, 1H of b, pyma), 8.25 (d, ³J(¹H,¹H) = 7.8 Hz, 1H of b, pyma), 8.10 (m, 1H of a and 1H of b, pyma), 7.60–7.25 (m, 7H of a and 7H of b, pyma), 7.20 (d, ³J(¹H,¹H) = 7.2 Hz, 1H of b, C₉H₅, H^5,6), 7.07 (d, ³J(¹H,¹H) = 7.0 Hz, 1H of a, C₉H₅, H^5,6), 6.93 (d, ³J(¹H,¹H) = 7.2 Hz, 1H of b, C₉H₅, H^5,6), 6.64 (d, ³J(¹H,¹H) = 7.0 Hz, 1H of a, C₉H₅, H^5,6), 6.61 (t, ³J(¹H,¹H) = 3.6 Hz, 1H of a, C₉H₅, H²), 6.16 (dd, ³J(¹H,¹H) = 2.8 Hz, ⁴J(¹H,¹H) = 1.5 Hz, 1H b, C₉H₅, H^1,3), 6.10 (dd, ³J(¹H,¹H) = 2.8 Hz, ⁴J(¹H,¹H) = 1.5 Hz, 1H of b, C₉H₅, H^1,3), 5.72 (t, ³J(¹H,¹H) = 2.8 Hz, 1H of b, C₉H₅, H²), 5.09 (dd, ³J(¹H,¹H) = 3.6 Hz, ⁴J(¹H,¹H) = 2.5 Hz, 1H of a, C₉H₅, H^1,3), 4.25 (dd, ³J(¹H,¹H) = 3.6 Hz, ⁴J(¹H,¹H) = 2.5 Hz, 1H of a, C₉H₅, H^1,3), 2.07 (s, 3H of a, CH₃), 2.06 (s, 3H of b, CH₃), 1.73 (s, 3H of a, CH₃), 1.57 (s, 3H of b, CH₃). FTIR (ATR, cm⁻¹): 1934 vs [ν_a(CO)], 1855 vs [ν_s(CO)]. Single crystals of 6a suitable for X-ray diffraction analysis were prepared by overlayering of the CHCl₃ solution with hexane.

Synthesis of [(η³-C₃H₅)Mo(CO)₂(pyma)Cl] (6-allyl)

[(η³-C₃H₅)Mo(CO)₂(NCMe)₂Cl] (200 mg, 0.64 mmol) was dissolved in CH₂Cl₂ (50 mL) and treated with pyma (117 mg, 0.64 mmol). The solution was stirred at room temperature overnight. The volatiles were vacuum evaporated. The crude product was washed with ether and recrystallized from the mixture CH₂Cl₂/ether and vacuum dried. Yield: 250 mg (95%, 0.61 mmol). Dark puple powder. Mp: 160–170 °C (dec.). Anal. calcd for C₁₇H₁₅ClMoN₂O₂: C, 49.72; H, 3.68; N, 6.82. Found: C, 49.61; H, 3.70; N, 6.94. ¹H NMR (CD₃CN; 400 MHz; δ (ppm): 8.84 (d, ³J(¹H,¹H) = 5.1 Hz, 1H, pyma), 8.53 (s, 1H, pyma), 8.10 (td, ³J(¹H,¹H) = 7.8 Hz, ⁴J(¹H,¹H) = 1.4 Hz 1H, pyma), 7.98 (d, ³J(¹H,¹H) = 7.6 Hz, 1H, pyma), 7.65–7.40 (m, 6H, pyma), 3.36 (tt, ³J(¹H,¹H) = 9.2 Hz, ³J(¹H,¹H) = 6.2 Hz, 1H, meso-C₃H₅), 3.16 (dd, ³J(¹H,¹H) = 6.2 Hz, ⁴J(¹H,¹H) = 3.3 Hz, 1H, syn-C₃H₅), 2.48 (dd, ³J(¹H,¹H) = 6.2 Hz, ⁴J(¹H,¹H) = 3.3 Hz, 1H, syn-C₃H₅), 1.31 (d, ³J(¹H,¹H) = 9.2 Hz, 1H, anti-C₃H₅), 1.02 (d, ³J(¹H,¹H) = 9.2 Hz, 1H, anti-C₃H₅). FTIR (ATR, cm⁻¹): 1929 vs [ν_a(CO)], 1845 vs [ν_s(CO)]. Single crystals of 6-allyl suitable for X-ray diffraction analysis were prepared by overlayering of the CH₂Cl₂ solution with hexane.

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(NCMe)₂][BF₄] (8-BF₄)

[(η³-C₃H₅)(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂] (7; 500 mg, 1.49 mmol) was dissolved in CH₂Cl₂ (50 mL), cooled at 0 °C and treated with acetonitrile (5 mL) and then with HBF₄·Et₂O (1.49 mmol). The reaction mixture was stirred for one hour at room temperature. Afterwards, the solvent was vacuum evaporated. The crude product was washed with ether and recrystallized from the mixture CH₂Cl₂/ether and vacuum dried. Yield: 608 mg (88%, 1.31 mmol). Orange powder. Mp: 150–160 °C (dec.). Anal. calcd for C₁₇H₁₇BF₄MoN₂O₂: C, 44.00; H, 3.69; N, 6.04. Found: C, 43.88; H, 3.73; N, 6.12. ¹H NMR (CD₂Cl₂; 400 MHz; δ (ppm)): 7.23 (s, 2H, C₉H₅, H^5,6), 6.00 (d, ³J(¹H,¹H) = 2.6 Hz, 2H, C₉H₅, H^1,3), 5.01 (t, ³J(¹H,¹H) = 2.6 Hz, 1H, C₉H₅, H²), 2.36 (s, 6H, CH₃CN), 1.97 (s, 6H, CH₃). FTIR (ATR, cm⁻¹): 1970 vs [ν_a(CO)], 1897 vs [ν_s(CO)], 1040 vs [ν(BF)]. Single crystals of 8-BF₄ suitable for X-ray diffraction analysis were prepared by overlayering of the MeCN solution with Et₂O.

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(bpy)][(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂Cl₂] (4b-9)

[{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 100 mg, 0.15 mmol) was dissolved in CH₂Cl₂ (50 mL) and treated with bpy (23 mg, 0.15 mmol). The solution was stirred at room temperature overnight. The precipitate was decanted. The product was washed with ether, CH₂Cl₂ and vacuum dried. Yield: 85 mg (69%, 0.10 mmol). Red powder. Mp: 140–150 °C (dec.). Anal. calcd for C₃₆H₃₀Cl₂Mo₂N₂O₄: C, 52.90; H, 3.70; N, 3.43. Found: C, 52.82; H, 3.79; N, 3.51. FTIR (ATR, cm⁻¹): 1950 vs [ν_a(CO)], 1930 vs [ν_a(CO)], 1875 vs [ν_s(CO)], 1837 vs [ν_s(CO)].

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(phen)][(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂Cl₂] (5b-9)

Steps of the synthesis followed the procedure for the compounds 4b-9. Reagents: [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 100 mg, 0.15 mmol) and phen (27 mg, 0.15 mmol). Yield: 95 mg (75%, 0.11 mmol). Red powder. Mp: 140–150 °C (dec.). Anal. calcd for C₃₈H₃₀Cl₂Mo₂N₂O₄: C, 54.24; H, 3.59; N, 3.33. Found: C, 54.38; H, 3.62; N, 3.10. FTIR (ATR, cm⁻¹): 1954 vs [ν_a(CO)], 1926 vs [ν_a(CO)], 1867 vs [ν_s(CO)], 1824 vs [ν_s(CO)]. Single crystals of 5b-9·CH₂Cl₂ suitable for X-ray diffraction analysis were prepared by overlayering of the CH₂Cl₂ solutions of the starting materials.

Synthesis of [Me₄N][(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂Cl₂] (Me₄N-9)

[{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 100 mg, 0.15 mmol) was dissolved in acetone (50 mL) and treated with [Me₄N]Cl (82 mg, 0.75 mmol). The solution was stirred at room temperature overnight. The volatiles were vacuum evaporated. The residuum was dissolved in CH₂Cl₂ and filtered over short pad of Celite. The volatiles were vacuum evaporated. The crude product was washed with ether and recrystallized from the mixture CH₂Cl₂/ether and vacuum dried. Yield: 220 mg (83%, 0.50 mmol). Red powder. Mp: 140–150 °C (dec.). Anal. calcd for C₁₇H₂₃Cl₂MoNO₂: C, 46.38; H, 5.27; N, 3.18. Found: C, 46.12; H, 5.32; N, 3.23. ¹H NMR (CDCl₃; 400 MHz; δ (ppm)): 6.90 (s, 2H, C₉H₅, H^5,6), 5.76 (d, ³J(¹H,¹H) = 2.8 Hz, 2H, C₉H₅, H^1,3), 4.87 (t, ³J(¹H,¹H) = 2.8 Hz, 1H, C₉H₅, H²), 3.32 (s, 12H, (CH₃)₄N)), 2.29 (s, 6H, (CH₃)₂C₉H₅)). FTIR (ATR, cm⁻¹): 1936 vs [ν_a(CO)], 1922 vs [ν_a(CO)], 1820 vs [ν_s(CO)].

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)Cl] (10a)

Method A: steps of the synthesis followed the procedure for the compounds 4a. Reagents: [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 200 mg, 0.30 mmol) and 2,9-Me₂-phen (125 mg, 0.60 mmol). Yield: 315 mg (97%, 0.58 mmol). Method B: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)][BF₄] (10b-BF₄; 100 mg, 0.20 mmol) was dissolved in acetone (50 mL) and treated with [Me₄N]Cl (220 mg, 2.01 mmol; alternatively 2.01 mmol of NaCl or KCl could be used). The solution was stirred for 48 h. The volatiles were vacuum evaporated. The residuum was dissolved in CH₂Cl₂ and filtered over short pad of Celite. The volatiles were vacuum evaporated. The crude product was washed with ether and recrystallized from the mixture CH₂Cl₂/ether and vacuum dried. Yield: 105 mg (97%, 0.19 mmol). Dark red powder. Mp: 150–160 °C (dec.). Anal. calcd for C₂₇H₂₃ClMoN₂O₂: C, 60.18; H, 4.30; N, 5.19. Found: C, 59.96; H, 4.42; N, 5.27. ¹H NMR (CDCl₃; 400 MHz; δ (ppm)): 8.30 (d, ³J(¹H,¹H) = 8.2 Hz, 2H, C₁₂H₆N₂), 7.88 (s, 2H, C₁₂H₆N₂), 7.65 (d, ³J(¹H,¹H) = 8.2 Hz, 2H, C₁₂H₆N₂), 6.21 (s, 2H, C₉H₅, H^5,6), 5.84 (t, ³J(¹H,¹H) = 3.7 Hz, 1H, C₉H₅, H²), 4.57 (d, ³J(¹H,¹H) = 3.7 Hz, 2H, C₉H₅, H^1,3), 3.07 (s, 6H, (CH₃)₂C₁₂H₆N₂), 2.09 (s, 6H, (CH₃)₂C₉H₅). ¹³C NMR (CD₂Cl₂; 126 MHz; δ (ppm)): 231.0 (2C, CO), 162.3, 146.1, 145.9, 129.6, 125.7 (5 × 1C_q), 138.9, 127.1, 126.7, 125.7 (4 × 2C C₁₂H₆N₂ and C₉H₅), 103.5 (1C, C² of C₉H₅), 69.5 (2C, C^1,3 of C₉H₅), 28.9 (2C, C₁₂H₆N₂(CH₃)₂), 17.8 (2C, C₉H₅(CH₃)₂). FTIR (ATR, cm⁻¹): 1927 vs [ν_a(CO)], 1848 vs [ν_s(CO)]. Single crystals of 10a·CH₂Cl₂ suitable for X-ray diffraction analysis were prepared by overlayering of the CH₂Cl₂ solution with hexane. Single crystals of 10a·CHCl₃ suitable for X-ray diffraction analysis were prepared by overlayering of the CHCl₃ solution with ether.

Synthesis of [(η³-C₃H₅)Mo(CO)₂(2,9-Me₂-phen)Cl] (10-allyl)

Steps of the synthesis followed the procedure for the compounds 6-allyl. Reagents: [(η³-C₃H₅)Mo(CO)₂(NCMe)₂Cl] (200 mg, 0.64 mmol) and 2,9-Me₂-phen (135 mg, 0.64 mmol). Yield: 260 mg (93%, 0.60 mmol). Dark orange powder. Mp: 150–160 °C (dec.). Anal. calcd for C₁₉H₁₇ClMoN₂O₂: C, 52.25; H, 3.92; N, 6.41. Found: C, 52.38; H, 3.86; N, 6.49. ¹H NMR (acetone-d⁶; 400 MHz; δ (ppm)): 8.60 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 8.07 (s, 2H, C₁₂H₆N₂), 7.93 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 3.27 (s, 6H, CH₃), 2.69 (d, ³J(¹H,¹H) = 6.2 Hz, 2H, syn-C₃H₅), 2.63 (tt, 1H, meso-C₃H₅), 1.13 (d, ³J(¹H,¹H) = 9.0 Hz, 2H, anti-C₃H₅). FTIR (ATR, cm⁻¹): 1929 vs [ν_a(CO)], 1836 vs [ν_s(CO)]. Single crystals of 10-allyl suitable for X-ray diffraction analysis were prepared by overlayering of the CH₂Cl₂ solution with hexane.

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)][BF₄] (10b-BF₄)

Steps of the synthesis followed the procedure for the compounds 4b-BF₄. Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(NCMe)₂][BF₄] (8-BF₄; 500 mg, 1.08 mmol) and 2,9-Me₂-phen (224 mg, 1.08 mmol). Yield: 505 mg (96%, 1.03 mmol). Red powder. Mp: 160–170 °C (dec.). Anal. calcd for C₁₉H₁₇BF₄MoN₂O₂: C, 46.75; H, 3.51; N, 5.74. Found: C, 46.92; H, 3.35; N, 5.78. ¹H NMR (CD₂Cl₂; 400 MHz; δ (ppm)): 8.50 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 7.96 (s, 2H, C₁₂H₆N₂), 7.86 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 6.27 (d, ³J(¹H,¹H) = 2.9 Hz, 2H, C₉H₅, H^1,3), 6.04 (s, 2H, C₉H₅, H^5,6), 5.45 (t, ³J(¹H,¹H) = 2.9 Hz, 1H, C₉H₅, H²), 3.60 (s, 6H, (CH₃)₂C₁₂H₆N₂), 1.74 (s, 6H, (CH₃)₂C₉H₅). ¹³C NMR (CD₂Cl₂; 101 MHz; δ (ppm)): 252.5 (2C, CO), 166.5, 146.2, 132.9, 131.5, 121.0 (5 × 1C_q), 140.2, 130.0, 127.3, 127.3 (4 × 2C C₁₂H₆N₂ and C₉H₅), 90.6 (1C, C² of C₉H₅), 79.9 (2C, C^1,3 of C₉H₅), 32.8 (2C, C₁₂H₆N₂(CH₃)₂), 18.6 (2C, C₉H₅(CH₃)₂). FTIR (ATR, cm⁻¹): 1946 vs [ν_a(CO)], 1867 vs [ν_s(CO)]. Single crystals of 10b-BF₄·0.5(Me₂-phen·HBF₄) suitable for X-ray diffraction analysis were prepared by overlayering of the crude product in CH₂Cl₂ with hexane.

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)Br] (10c)

Steps of the synthesis followed the procedure for the compounds 10a (Method B). Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)][BF₄] (10b-BF₄; 100 mg, 0.20 mmol) and KBr (240 mg, 2.02 mmol). Yield: 90 mg (94%, 0.19 mmol). Dark red powder. Mp: 160–170 °C (dec.). Anal. calcd for C₁₉H₁₇BrMoN₂O₂: C, 47.42; H, 3.56; N, 5.82. Found: C, 47.30; H, 3.62; N, 5.95. ¹H NMR (CDCl₃; 400 MHz; δ (ppm)): 8.30 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 7.89 (s, 2H, C₁₂H₆N₂), 7.65 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 6.21 (s, 2H, C₉H₅, H^5,6), 5.83 (t, ³J(¹H,¹H) = 3.7 Hz, 1H, C₉H₅, H²), 4.61 (d, ³J(¹H,¹H) = 3.7 Hz, 2H, C₉H₅, H^1,3), 3.04 (s, 6H, (CH₃)₂C₁₂H₆N₂), 2.08 (s, 6H, (CH₃)₂C₉H₅). ¹³C NMR (CD₂Cl₂; 101 MHz; δ (ppm)): 230.1 (2C, CO), 162.6, 146.2, 145.9, 129.7, 125.8 (5 × 1C_q), 138.8, 127.1, 126.6, 125.9 (4 × 2C C₁₂H₆N₂ and C₉H₅), 103.6 (1C, C² of C₉H₅), 68.6 (2C, C^1,3 of C₉H₅), 30.1 (2C, C₁₂H₆N₂(CH₃)₂), 17.8 (2C, C₉H₅(CH₃)₂). FTIR (ATR, cm⁻¹): 1936 vs [ν_a(CO)], 1863 vs [ν_s(CO)]. Single crystals of 10c suitable for X-ray diffraction analysis were prepared by overlayering of the CH₂Cl₂ solution with Et₂O.

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)I] (10d)

Steps of the synthesis followed the procedure for the compounds 10a (Method B). Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)][BF₄] (10b-BF₄; 100 mg, 0.20 mmol) and KI (330 mg, 1.99 mmol). Yield: 100 mg (95%, 0.19 mmol). Brown powder. Mp: 160–170 °C (dec.). Anal. calcd for C₁₉H₁₇IMoN₂O₂: C, 43.20; H, 3.24; N, 5.30. Found: C, 43.44; H, 3.34; N, 5.43. ¹H NMR (CDCl₃; 400 MHz; δ (ppm)): 8.29 (d, ³J(¹H,¹H) = 8.2 Hz, 2H, C₁₂H₆N₂), 7.91 (s, 2H, C₁₂H₆N₂), 7.65 (d, ³J(¹H,¹H) = 8.2 Hz, 2H, C₁₂H₆N₂), 6.21 (s, 2H, C₉H₅, H^5,6), 5.84 (s-br, 1H, C₉H₅, H²), 4.69 (d, ³J(¹H,¹H) = 3.4 Hz, 2H, C₉H₅, H^1,3), 3.00 (s, 6H, (CH₃)₂C₁₂H₆N₂), 2.07 (s, 6H, (CH₃)₂C₉H₅). ¹³C NMR (CD₂Cl₂; 126 MHz; δ (ppm)): 229.0 (2C, CO), 162.9, 146.3, 145.8, 129.8, 125.9 (5 × 1C_q), 138.8, 127.2, 126.5, 125.9 (4 × 2C C₁₂H₆N₂ and C₉H₅), 104.3 (1C, C² of C₉H₅), 67.5 (2C, C^1,3 of C₉H₅), 30.5 (2C, C₁₂H₆N₂(CH₃)₂), 17.9 (2C, C₉H₅(CH₃)₂). FTIR (ATR, cm⁻¹): 1932 vs [ν_a(CO)], 1861 vs [ν_s(CO)].

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)(NCO)] (10e)

Steps of the synthesis followed the procedure for the compounds 10a (Method B). Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)][BF₄] (10b-BF₄; 100 mg, 0.20 mmol) and KOCN (160 mg, 1.97 mmol). Yield: 80 mg (90%, 0.18 mmol). Dark red powder. Mp: 160–170 °C (dec.). Anal. calcd for C₂₀H₁₇MoN₃O₃: C, 54.19; H, 3.87; N, 9.48. Found: C, 54.01; H, 3.89; N, 9.32. ¹H NMR (CDCl₃; 400 MHz; δ (ppm)): 8.34 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 7.94 (s, 2H, C₁₂H₆N₂), 7.71 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 6.20 (s, 2H, C₉H₅, H^5,6), 5.88 (t, ³J(¹H,¹H) = 3.7 Hz, 1H, C₉H₅, H²), 4.68 (d, ³J(¹H,¹H) = 3.7 Hz, 2H, C₉H₅, H^1,3), 3.02 (s, 6H, (CH₃)₂C₁₂H₆N₂), 2.08 (s, 6H, (CH₃)₂C₉H₅). FTIR (ATR, cm⁻¹): 2195 vs [ν(CN)], 1930 vs [ν_a(CO)], 1851 vs [ν_s(CO)].

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)(NCS)] (10f)

Steps of the synthesis followed the procedure for the compounds 10a (Method B). Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-phen)][BF₄] (10b-BF₄; 100 mg, 0.20 mmol) and KSCN (200 mg, 2.06 mmol). Yield: 90 mg (98%, 0.19 mmol). Red powder. Mp: 150–160 °C (dec.). Anal. calcd for C₂₀H₁₇MoN₃O₂S: C, 52.29; H, 3.73; N, 9.15, S, 6.98. Found: C, 52.09; H, 3.65; N, 9.00, S, 7.12. ¹H NMR (CDCl₃; 400 MHz; δ (ppm)): 8.42 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 7.96 (s, 2H, C₁₂H₆N₂), 7.73 (d, ³J(¹H,¹H) = 8.3 Hz, 2H, C₁₂H₆N₂), 6.21 (s, 2H, C₉H₅, H^5,6), 5.79 (t, ³J(¹H,¹H) = 3.7 Hz, 1H, C₉H₅, H²), 4.77 (d, ³J(¹H,¹H) = 3.7 Hz, 2H, C₉H₅, H^1,3), 3.04 (s, 6H, (CH₃)₂C₁₂H₆N₂), 2.08 (s, 6H, (CH₃)₂C₉H₅). FTIR (ATR, cm⁻¹): 2063 vs [ν(CN)], 1925 vs [ν_a(CO)], 1849 vs [ν_s(CO)].

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(3,4,7,8-Me₄-phen)Cl] (11a)

Steps of the synthesis followed the procedure for the compounds 4a. Reagents: [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 50 mg, 76 μmol) and 3,4,7,8-Me₄-phen (35 mg, 0.15 mmol). Yield: 50 mg (93%, 88 μmol). Red powder. Mp: 140–150 °C (dec.). Anal. calcd for C₂₅H₂₁ClMoN₂O₂: C, 61.44; H, 4.80; N, 5.64. Found: C, 61.28; H, 4.87; N, 5.55. ¹H NMR (CD₂Cl₂; 400 MHz; δ (ppm); 11a and 11b-Cl in the ratio 1 : 3): 9.13 (s, 2H of b, C₁₂H₄N₂), 8.59 (s, 2H of a, C₁₂H₄N₂), 8.17 (s, 2H of b, C₁₂H₄N₂), 8.14 (s, 2H of a, C₁₂H₄N₂), 6.32 (d, ³J(¹H,¹H) = 2.8 Hz, 2H of b, C₉H₅, H^1,3), 6.28 (s, 2H of b, C₉H₅, H^5,6), 6.22 (t, ³J(¹H,¹H) = 3.7 Hz, 1H of a, C₉H₅, H²), 6.21 (s, 2H of a, C₉H₅, H^5,6), 5.70 (t, ³J(¹H,¹H) = 2.8 Hz, 1H of b, C₉H₅, H²), 4.93 (d, ³J(¹H,¹H) = 3.7 Hz, 2H of a, C₉H₅, H^1,3), 2.82 (s, 6H of b, (CH₃)₄C₁₂H₄N₂), 2.76 (s, 6H of a, (CH₃)₄C₁₂H₄N₂), 2.66 (s, 6H of b, (CH₃)₄C₁₂H₄N₂), 2.58 (s, 6H of a, (CH₃)₄C₁₂H₄N₂), 2.16 (s, 6H of a, (CH₃)₂C₉H₅), 1.88 (s, 6H of b, (CH₃)₂C₉H₅). FTIR (ATR, cm⁻¹): 1922 vs [ν_a(CO)], 1839 vs [ν_s(CO)].

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-4,7-Ph₂-phen)Cl] (12a)

Steps of the synthesis followed the procedure for the compounds 10a (Method B). Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-4,7-Ph₂-phen)][BF₄] (12b-BF₄; 30 mg, 40 μmol) and [Me₄N]Cl (44 mg, 0.40 mmol). Yield: 27 mg (97%, 39 μmol). Purple powder. Mp: 170–180 °C (dec.). Anal. calcd for C₃₉H₃₁ClMoN₂O₂ : C, 67.78; H, 4.52; N, 4.05. Found: C, 67.89; H, 4.47; N, 4.19. ¹H NMR (CD₂Cl₂; 500 MHz; δ (ppm)): 7.94 (s, 2H, C₁₂H₄N₂), 7.66 (s, 2H, C₁₂H₄N₂), 7.62–7.55 (m, 10H, C₆H₅), 6.21 (s, 2H, C₉H₅, H^5,6), 6.07 (t, ³J(¹H,¹H) = 3.7 Hz, 1H, C₉H₅, H²), 4.70 (d, ³J(¹H,¹H) = 3.7 Hz, 2H, C₉H₅, H^1,3), 3.07 (s, 6H, (CH₃)₂C₁₂H₄N₂), 2.10 (s, 6H, (CH₃)₂C₉H₅). ¹³C NMR (CD₂Cl₂; 126 MHz; δ (ppm)): 231.1 (2C, CO), 161.5, 151.2, 146.7, 146.1, 136.9, 127.8, 125.7 (7 × 1C_q), 130.1, 129.4 (2 × 4C C₆H₅), 129.8, 127.1, 125.7, 124.8 (4 × 2C C₁₂H₄N₂, C₆H₅ and C₉H₅), 103.8 (1C, C² of C₉H₅), 69.4 (2C, C^1,3 of C₉H₅), 30.1 (2C, C₁₂H₄N₂(CH₃)₂), 17.8 (2C, C₉H₅(CH₃)₂). FTIR (ATR, cm⁻¹): 1939 vs [ν_a(CO)], 1862 vs [ν_s(CO)].

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(2,9-Me₂-4,7-Ph₂-phen)][BF₄] (12b-BF₄)

Steps of the synthesis followed the procedure for the compounds 4b-BF₄. Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(NCMe)₂][BF₄] (8-BF₄; 50 mg, 0.11 mmol) and 2,9-Me₂-4,7-Ph₂-phen (36 mg, 0.11 mmol). Yield: 78 mg (98%, 0.11 mmol). Red powder. Mp: 150–160 °C (dec.). Anal. Calcd for C₃₉H₃₁BF₄MoN₂O₂ : C, 63.09; H, 4.21; N, 3.77. Found: C, 63.25; H, 4.14; N, 3.89. ¹H NMR (CD₂Cl₂; 500 MHz; δ (ppm)): 7.94 (s, 2H, C₁₂H₄N₂), 7.82 (s, 2H, C₁₂H₄N₂), 7.66–7.52 (m, 10H, C₆H₅), 4.31 (d, ³J(¹H,¹H) = 2.8 Hz, 2H, C₉H₅, H^1,3), 6.11 (s, 2H, C₉H₅, H^5,6), 5.49 (t, ³J(¹H,¹H) = 2.8 Hz, 1H, C₉H₅, H²), 3.63 (s, 6H, (CH₃)₂C₁₂H₄N₂), 1.79 (s, 6H, (CH₃)₂C₉H₅). ¹³C NMR (CD₂Cl₂; 126 MHz; δ (ppm)): 252.4 (2C, CO), 166.0, 152.1, 147.1, 135.7, 133.0, 121.3 (6 × 1C_q), 130.0, 129.8 (2 × 4C C₆H₅), 130.7, 129.8, 127.6, 124.9 (4 × 2C C₁₂H₄N₂, C₆H₅ and C₉H₅), 91.1 (1C, C² of C₉H₅), 79.8 (2C, C^1,3 of C₉H₅), 33.1 (2C, C₁₂H₄N₂(CH₃)₂), 18.8 (2C, C₉H₅(CH₃)₂). FTIR (ATR, cm⁻¹): 1944 vs [ν_a(CO)], 1893 s [ν_s(CO)], 1877 s [ν_s(CO)].

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(4,4′-Me₂-bpy)][Cl] (13b-Cl)

Steps of the synthesis followed the procedure for the compounds 4a. Reagents: [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂] (2; 50 mg, 76 μmol) and 4,4′-Me₂-bpy (28 mg, 0.15 mmol). Yield: 75 mg (96%, 0.15 mmol). Red powder. Mp: 130–140 °C (dec.). Anal. calcd for C₂₅H₂₃ClMoN₂O₂: C, 58.32; H, 4.50; N, 5.44. Found: C, 58.45; H, 4.61; N, 5.52. ¹H NMR (CD₂Cl₂; 400 MHz; δ (ppm)): 8.84 (d, ³J(¹H,¹H) = 5.4 Hz, 2H, C₁₀H₆N₂), 8.72 (s, 2H, C₁₀H₆N₂), 7.32 (d, ³J(¹H,¹H) = 5.4 Hz, 2H, C₁₀H₆N₂), 6.60 (s, 2H, C₉H₅, H^5,6), 6.16 (s-br, C₉H₅, H^1,3), 5.55 (s-br, 1H, C₉H₅, H²), 2.62 (s, 6H, (CH₃)₂C₁₀H₆N₂), 1.96 (s, 6H, (CH₃)₂C₉H₅). FTIR (ATR, cm⁻¹): 1962 vs [ν_a(CO)], 1877 vs [ν_s(CO)].

Synthesis of [(η³-4,7-Me₂C₉H₅)Mo(CO)₂(6,6′-Me₂-bpy)Cl] (14a)

Steps of the synthesis followed the procedure for the compounds 10a (Method B). Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(6,6′-Me₂-bpy)][BF₄] (14b-BF₄; 30 mg, 53 μmol) and [Me₄N]Cl (58 mg, 0.53 mmol). Yield: 27 mg (99%, 52 μmol). Purple powder. Mp: 170–180 °C (dec.). Anal. calcd for C₂₅H₂₃ClMoN₂O₂: C, 58.32; H, 4.50; N, 5.44. Found: C, 58.39; H, 4.56; N, 5.45. ¹H NMR (CD₂Cl₂; 400 MHz; δ (ppm)): 8.09 (d, ³J(¹H,¹H) = 7.8 Hz, 2H, C₁₀H₆N₂), 7.91 (dd, ³J(¹H,¹H) = 7.8 Hz, ³J(¹H,¹H) = 7.6 Hz, 2H, C₁₀H₆N₂), 7.40 (d, ³J(¹H,¹H) = 7.6 Hz, 2H, C₁₀H₆N₂), 6.18 (s, 2H, C₉H₅, H^5,6), 6.09 (t, ³J(¹H,¹H) = 3.7 Hz, 1H, C₉H₅, H²), 4.55 (d, ³J(¹H,¹H) = 3.7 Hz, 2H, C₉H₅, H^1,3), 2.79 (s, 6H, (CH₃)₂C₁₀H₆N₂), 2.05 (s, 6H, (CH₃)₂C₉H₅). FTIR (ATR, cm⁻¹): 1930 vs [ν_a(CO)], 1852 vs [ν_s(CO)].

Synthesis of [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(6,6′-Me₂-bpy)][BF₄] (14b-BF₄)

Steps of the synthesis followed the procedure for the compounds 4b-BF₄. Reagents: [(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(NCMe)₂][BF₄] (8-BF₄; 50 mg, 0.11 mmol) and 6,6′-Me₂-bpy (20 mg, 0.11 mmol). Yield: 60 mg (98%, 0.11 mmol). Red powder. Mp: 160–170 °C (dec.). Anal. calcd for C₂₅H₂₃BF₄MoN₂O₂: C, 53.03; H, 4.09; N, 5.95. Found: C, 53.10; H, 4.12; N, 5.92. ¹H NMR (CD₂Cl₂; 400 MHz; δ (ppm)): 8.15 (d, ³J(¹H,¹H) = 8.0 Hz, 2H, C₁₀H₆N₂), 7.99 (dd, ³J(¹H,¹H) = 8.0 Hz, ³J(¹H,¹H) = 7.6 Hz, 2H, C₁₀H₆N₂), 7.52 (dd, ³J(¹H,¹H) = 7.6 Hz, ⁴J(¹H,¹H) = 1.0 Hz, 2H, C₁₀H₆N₂), 6.55 (s, 2H, C₉H₅, H^5,6), 6.19 (d, ³J(¹H,¹H) = 2.9 Hz, 2H, C₉H₅, H^1,3), 5.31 (t, ³J(¹H,¹H) = 2.9 Hz, 1H, C₉H₅, H²), 3.35 (s, 6H, (CH₃)₂C₁₀H₆N₂), 1.84 (s, 6H, (CH₃)₂C₉H₅). FTIR (ATR, cm⁻¹): 1947 vs [ν_a(CO)], 1870 vs [ν_s(CO)].

X-ray crystallography

The X-ray data for the crystals of the compounds 3, 4b-BF₄, 5b-9·CH₂Cl₂, 6a, 6-allyl, 8-BF₄, 10a·CH₂Cl₂, 10a·CHCl₃, 10-allyl, 10b-BF₄·0.5(phen·HBF₄) and 10c and were obtained at 150 K using an Oxford Cryostream low-temperature device on a Nonius KappaCCD diffractometer with Mo Kα radiation (λ = 0.71073 Å) and a graphite monochromator. Data reductions were performed with DENZO-SMN.⁶⁴ The absorption was corrected by integration methods⁶⁵ and only in cases of 5b-9·CH₂Cl₂ and 6a it was performed analytically using SADABS software.⁶⁶ Structures were solved by direct methods (Sir92)⁶⁷ and refined by full-matrix least squares based on F² (SHELXL).⁶⁸ Thermal ellipsoids of C13 and C14 atoms in 5b-9·CH₂Cl₂, of F1, F3 and F4 atoms in 8-BF₄ and of F1 atom in 10b-BF₄·0.5(phen·HBF₄) were treated with standard ISOR instruction implemented in SHELXL97 software.⁶⁸ Hydrogen atoms were mostly localized on a difference Fourier map. However, to ensure uniformity of the treatment of the crystal, all hydrogen atoms were recalculated into idealized positions (riding model) and assigned temperature factors U_iso(H) = 1.2[U_eq(pivot atom)] or 1.5U_eq for the methyl moiety with C–H = 0.96, 0.97, and 0.93 Å for methyl, methylene, and hydrogen atoms in aromatic rings or the allyl moiety, respectively.

Acknowledgements

This work was supported by Ministry of Education of the Czech Republic (Project no. SG350004).

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Footnote

† CCDC 1044572–1044582. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ra01450f

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