Rotation of coordinated acetylide ligands on the triangular surface of trinuclear heterometallic clusters

Article abstract of DOI:10.1021/om00160a018

Convenient and widely applicable synthetic routes to the trinuclear heterometallic acetylide complexes LMM′₂(CO)₈(C≡CR) have been developed. These routes involve the reaction of metal acetylides LM(CO)₃(C≡CR) (L = Cp and Cp*; M = W and Mo; R = Ph, C₅H₄F, C₅H₄OMe, ^tBu, and ⁿPr) with Os₃(CO)₁₀(NCMe)₂ and with Ru₃(CO)₁₂. For the WOs₂ derivatives prepared (1-3), the acetylide ligand adopts an asymmetric arrangement in which the acetylide C-C vector is coordinated to one of the W-Os bonds. For all the WRu₂ derivatives (4-9), the acetylide ligand adopts both the asymmetric (with its C-C bond orthogonal to one of the W-Ru bonds) and the symmetric arrangement (with its C-C bond orthogonal to the unique Ru-Ru bond) and undergoes rapid interconversion in solution. For the MoRu₂ derivatives (10, 11), the acetylide favors the asymmetric form in both solution and the solid state; however, when the substituent R and the ligand L are replaced by a bulky tert-butyl group and Cp* ligand, respectively (13), the symmetric form becomes the dominant species. The dynamic ¹³C NMR studies suggest that the acetylide ligand of the WOs₂ derivatives is static but, in the asymmetric MoRu₂ derivatives (10, 11), the acetylide is fluxional and undergoes migration from one Mo-Ru edge to the other. The preference of the site selectivity for the acetylide ligand has also been studied by variation of the transition-metal atoms (M and M′), the accessory ligand (L), and the substituent (R). The structures of the complexes CpWOs₂(CO)₈(C≡CPh) (1), CpWRu₂(CO)₈(C≡CPh) (4), and CpMoRu₂(CO)₈(C≡CPh) (10) have been determined by single-crystal X-ray diffraction studies. Crystal data for 1: space group P2₁/c; a = 8.332 (3) ?, b = 14.543 (4) ?, c = 17.819 (5) ?, β = 94.46 (3)°, Z = 4; final R = 0.068, R_w = 0.090, and GOF = 1.768. Crystal data for 4: space group P2₁/n; a = 12.476 (1) ?, b = 13.216 (4) ?, c = 13.395 (4) ?, β = 97.99 (2)°, Z = 4; final R = 0.029, R_w = 0.027, and GOF = 1.583. Crystal data for 10: space group P2₁/c; a = 12.770 (4) ?, b = 8.188 (4) ?, c = 21.313 (4) ?, β = 91.26 (2)°, Z = 4; final R = 0.030, R_w = 0.031, and GOF = 2.34.