Reactions of M(CCCCR)(CO)3Cp [M= Mo, W; R= H, Fe(CO)2Cp, M(CO)3Cp] with cobalt carbonyls:: X-ray structures of {Cp(OC)8Co2M(μ3-C)}CC{(μ3-C)Co2M′(CO)8Cp} (M = M′ = Mo, W; M= Mo, M′ = W)

Reactions of Co-2(CO)(8) with complexes M(C=CC=CR)(CO)(3)Cp [M = Mo, W; R = H, Fe(CO)(2)Cp] are described. Simple adducts containing a Co-2(CO)(6) group attached to the least sterically-hindered C=C triple bond are formed. In contrast, when R = M(CO)(3)Cp (M = Mo, W), bis-cluster complexes {Cp(OC)(8)Co2M(mu(3)-C)}C=C{(mu(3)-C)Co2M'(Co)(8)Cp} (M = M' = Mo, W; M = Mo, M' = W) were obtained. All three complexes were structurally characterised. Important features are the presence of both distal and proximal Cp groups in each molecule, and the formal oxidation of the -C=C-C=C- chain in the precursor to =C-C=C-C= system in the products. Extended Huckel and Density Functional Theory calculations have been used to rationalise the observed structures of the M3C4M3 complexes. The reaction between Co-2(mu-dppm)(CO)(6) and {W(CO)(3)Cp}(2)(mu-C-4) gave the simple adduct Co-2(mu-dppm){mu-[Cp(OC)(3)W]C2C=C[W(CO)(3)Cp]}(CO)(4). (C) 1999 Elsevier Science S.A. All rights reserved.