Metallosite selectivity studies in reactions of tetrahedral MCo3 carbonyl clusters (M = Fe, Ru) with cyclohexylphosphine.: Skeletal rearrangements leading to tri- and pentanuclear phosphinidene clusters and crystal structures of RuCo4(μ4-PCy)(μ-CO)2(CO)11 and RuCo2(μ3-PCy)(CO)9

We have studied the metallosite selectivity of substitution reactions at heterometallic tetranuclear clusters of the type HMCo3(CO)(12) (M = Fe, Ru). Monosubstitution with PCyH2 occurs with a different metalloselectivity as a function of M. When M = Fe, substitution of a Go-bound CO ligand occurs whereas when M = Ru, the phosphine ligand is bound to Ru. Introduction of a second substituent (PCyH2 or NMe3) occurs in both cases at cobalt and, in the case of HFeCo3(CO)(11)(PCyH2), at a cobalt that does not carry the PCyH2 substituent. The clusters HMCo3(CO)(11)(PCyH2) (2a, M = Fe; 2b, M = Ru) transform in solution to give the corresponding mu(3)-phosphinidene-capped heterotrinuclear clusters MCo2(mu(3)-PCy)(CO)(9) (4a, M = Fe; 4b, M = Ru). The mu(4)-phosphinidene-capped intermediate RuCo4(mu(4)-PCy)(mu-CO)(2)-(CO)(11) (5b) could be fully characterized, whereas the analogous species could not be isolated when M: = Fe. The transformation of 2a,b was accelerated by addition of Me3NO. This work demonstrates that a reaction which represents a partial cluster fragmentation, with a nuclearity change from 4 to 3, may occur via the intermediacy of a larger cluster, of nuclearity 5. Reactions and products were studied by IR and H-1, P-31{H-1}, and Co-59 NMR spectroscopic methods, and the clusters 4b and 5b have been characterized by X-ray diffraction.