Carbon-carbon coupling and carbon-hydrogen activation reactions in bis(triisopropylphosphine)osmium complexes

摘要

Reaction of the alkenyl complex OsCl(E-CH=CHPh)(CO)(PiPr3)2 (1) with phenyllithium gives OsH-{C6H4-2-(E-CH=CHPh)}(CO)(PiPr 3)2 (2). The structure of 2 (isomer 2a) has been determined by X-ray diffraction: triclinic, P1, a = 9.230(1) Å, b = 10.092(1) Å, c = 18.525(2) Å, α = 88.667(7)°, β = 87.172(7)°. γ = 71.110(6)°, V = 1630.6(3), Z = 2, R (F, Fo ≥ 4σ(Fo)) = 4.01, wR (F2, all reflections) = 9.94%. The geometry around the osmium can be described as a distorted octahedron with the two triisopropylphosphine ligands occupying two relative trans positions. The remaining perpendicular plane is formed by the carbonyl and the 2-(E-1′-styryl)-phenyl ligands mutually trans disposed, the hydride ligand and one olefinic hydrogen of the 2-(E-1′-styryl)phenyl ligand, which shows an agostic interaction with the osmium atom (distance 2.05(7) Å). The solutions of 2 show equilibria between the agostic isomer (2a) and a nonagostic isomer (2b). The thermodynamic magnitudes involved in the equilibrium as well as the activation parameters for the conversion between the two isomers were determined in toluene-d8 by 1H NMR spectroscopy. The values obtained were ΔH° = -1.6 (±0.1) Kcal mol-1 and ΔS° = -9.6 (±0.6) cal K-1 mol-1 for the formation of the agostic isomer, whereas the activation parameters for the breaking of the agostic interaction were ΔH‡ = 7.6 (±0.2) Kcal mol-1 and ΔS† = -1.0 (±0.7) cal K-1 mol-1. 2 reacts with CO to give the octahedral complex OsH{C6H4-2-(E-CH=CHPh)}(CO)2(P iPr3)2 (3). Reactions of 1 with methyllithium and CD3Li give OsH{C6H4-2-(E-CH=CHCH3)}(CO)(P iPr3)2 (4) and OsH{C6H4-2-(E-CH=CHCD3)}-(CO)(P iPr3)2 (4-d3), respectively. The spectra of these complexes indicate that in solution they also show equilibria between agostic and nonagostic isomers. Reactions of 4 with P(OMe)3 and CO afford OsH{C6H4-2-(E-CH=CHCH3)(CO){P(OMe) 3}(PiPr3)2 (5) and OsH{C6H4-2-(E-CH=CHCH3)}(CO)2(P iPr3)2 (6), respectively, in which the incoming ligands coordinate trans to the hydride. 4 and 4-d3 isomerize in solution to give OsH(η3-CH2CHCHPh)-(CO)(PiPr 3)2 (11) and OsD(η3-CD2CHCHPh)(CO)(PiPr 3)2 (11-d3), respectively. Reaction of 11 with CO leads to OsH(η1-CH2CH=CHPh)(CO)2(P iPr3)2 (12). The first order constants kobs and kobs-d3 for the isomerization of 4 and 4-d3 to 11 and 11-d3 were obtained in CDCl3, giving activation parameters of ΔH‡ = 20.8 (±1.7) Kcal mol-1 and ΔS‡ = -2.8 (±2.0) cal K-1 mol-1 for the isomerization of 4 to 11 and a relation kobs/kobs-d3 = 3.6 at 303 K.