Regiospecific coupling of coordinated acetylide and disubstituted alkynes. X-ray structures of CpWOs₂(CO)₇[C(Tol)C(Tol)CCⁿBu] and CpWOs₂(CO)₇[C(CF₃)C(CF₃)CCPh]

Treatment of the acetylide complexes CpWOs₂(CO)₈(C≡CR), Cp = C₅H₅, R = Ph, (1) and R = ⁿBu, (2), with Me₃NO in acetonitrile followed by reaction with various disubstituted alkynes, C₂R′₂, in refluxing toluene to give two isomeric trinuclear complexes, CpWOs₂(CO)₇[C(R′)C(R′)CCR], R = Ph, R′ = Tol, (3); R = ⁿBu, R′ = Tol, (4); R = Ph, R′ = CO₂Et, (5); R = ⁿBu, R′ = CO₂Et, (6); R = Ph, R′ = CF₃, (7) by acetylide-alkyne coupling is described. The structure of each isomeric complex consists of a WOs₂ triangle and a coordinated C₄ hydrocarbyl fragment, established by single-crystal X-ray diffraction studies on 4 and 7. The possible mechanism for the formation of these two coupling products is discussed. Crystal data for 4: space group P2₁/c; a = 14.21(1), b = 10.80(1), c = 21.46(2) Å, β = 97.82°, Z = 4; final R = 0.0541, R_w = 0.0469 and GOF = 2.228. Crystal data for 7: space group P2₁/c; a = 10.446(6), b = 18.08(1), c = 14.437(8) Å, β = 105.66(4)°, Z = 4; final R = 0.0595, R_w = 0.0512 and GOF = 3.307.