Carbon−Carbon Coupling and Carbon−Hydrogen Activation Reactions in Bis(triisopropylphosphine)osmium Complexes

Abstract

Reaction of the alkenyl complex OsCl(E-CHCHPh)(CO)(PiPr3)2 (1) with phenyllithium gives OsH{C6H4-2-(E-CHCHPh)}(CO)(PiPr3)2 (2). The structure of 2 (isomer 2a) has been determined by X-ray diffraction: triclinic, P1, a = 9.230(1) A, b = 10.092(1) A, c = 18.525(2) A, 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) A). 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 p...