Reactions of the triosmium complex Os₃(CO)₁₀(μ-Br)(CH=CHPh) with benzyl isonitrile and triphenylphosphine. Crystal structure and solut fluxionality of the ethenyl derivatives

Reaction of Os₃(CO)₁₀(μ-Br)(CH=CHPh) (1) with benzyl isonitrile in toluene at 85°C gave a trinuclear complex Os₃(CO)₉(CNCH₂Ph)(μ-Br)(CH=CHPh) (2). In contrast, the analogous reaction with triphenylphosphine at 110°C produced dinuclear complexes Os₂(CO)₅(PPh₃)(μ-Br)(CH=CHPh) (4). The ethenyl group of complex 2 is static; however, variable temperature NMR studies indicate that the ethenyl groups of 3 and 4 undergo rapid π → σ,σ → π rearrangement (reversible flipping of the vinyl group) in solution. The structures of 2 and 3 were also determined by single-crystal X-ray diffraction. Crystal data for 2: space group P2₁/c; a = 9.977(2), b = 22.779(6), c = 25.323(5) Å, β = 95.08(2)°, Z = 8 ; final R = 0.038, R_w = 0.037 for 3445 reflections with I ≥ 3σ(I). Crystal data for 3: space group P1‾; a = 10.749(2), b = 13.101(3), c = 13.208(3) Å, α = 118.73(2), β = 105.4992), γ = 97.62(2)°; Z = 2; final R = 0.027, R_w = 0.026 for 4211 reflections with I ≫ 2σ(I).