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Synthesis and substitution reactions of Mo(η6-PhPMePh)(PMePh2)3. The crystal and molecular structure of Mo(η6-PhPMePh)(CNCMe3)(PMePh2)2
Luck, Rudy L.,Morris, Robert H.,Sawyer, Jeffery F.
, p. 247 - 255 (2008/10/08)
The complex Mo(η6-PhPMePh)(PMePh2)3, 1, is readily prepared in one step by reducing a mixture of Mo2Cl10 and 8 mol of PMePh2 in THF with magnesium under argon. There is evidence for molybdenum complexes in oxidation states IV, II, and 0 as intermediates in the high-yield reduction process. Complex 1 reacts with 1 mol of the strongly coordinating ligands L = P(OMe)3, CNCMe3, and CO at 25°C to give monosubstituted complexes Mo(η6-PhPMePh)(L)(PMePh2)2, 2-4, respectively. Use of excess ligand results in disubstituted products. Only ligands that are sterically smaller than PMePh2 including N2, PMe2Ph, PMe3, and C2H2 react with 1; PPh3 and P(C6H11)3 do not react. Carbon monoxide uptake kinetics indicate that dissociation of a σ-bonded ligand from 1 is the rate-determining step for these reactions; rate = k1[1], k1(303 K) = (1.5 ± 0.1) × 10-3 s-1, ΔH? = 28.8 ± 1.6 kcal mol-1, and ΔS? = 23 ± 5 eu. The σ-bonded PMePh2 ligands in 2-4 are diastereotopic and give ABX or AB 31P NMR spectra. The 31P chemical shift of the η6-PhPMePh ligand is sensitive to the electronic and/or steric properties of the σ-bonded ligands. Compound 3, Mo(η6-PhPMePh)(CNCMe3)(PMePh2)2, has been studied by X-ray crystallography. It crystallizes in the monoclinic space group P21 with cell dimensions a = 9.256 (3) A?, b = 11.497 (3) A?, c = 18.782 (10) A?, β = 103.92 (4)°, V = 1940 A3, and Dcalcd = 1.33 g cm-3 for Z = 2. The structure was solved by the heavy-atom method and refined by least-squares and Fourier methods to final residuals R = 0.0635 (Rw = 0.0785) for 2755 observed (I > 2σ(I)) reflections. The geometry about the molybdenum is distorted octahedral. Principal dimensions are Mo-P = 2.416 (3) and 2.420 (3) A?, Mo-C(isocyanide) = 1.984 (13) A?, and Mo-C(arene) = 2.24 (1)-2.32 (1) A?. Angles in the MoP2(CNCMe3) tripod indicate that the bulky phosphines have moved from ideal octahedral positions toward the CNCMe3 ligand to minimize steric repulsions. The CNCMe3 ligand is nonlinear (C-N-C = 150 (1)°) and is the closest ligand in the tripod to the PMePh group on the η6 ring.
