Synthesis of Tetracobalt Clusters from Dicobalt Alkne Complexes

The room-temperature reactions of [Co-2(mu-PhCCH)(CO)(6)] or [Co-2(mu-MeCCMe)(CO)(6)] with Ph(2)PC = CPh (L) afford [Co-2(mu-PhCCH)(CO)(5)(eta(1)-L)] or [Co-2(mu-MeCCMe)(CO)(5)(eta(1)-L)] and [CO2(mu-MeCCMe)(CO)(4)n(1)-L)(2)], respectively, in which L is bound via the phosphine functionality. The structure of [Co-2(mu-MeCCMe)(CO)(4)(eta(1)-L)(2)] has been established by X-ray crystallography and comprises two Co(CO)(2)(eta(1)-L) units bridged by a MeC = CMe ligand. Reactions of [Co-2(mu-R(1)CCR(2))(CO)(5)(eta(1)-L)] with [Co-2(CO)(8)] afford [Co-2(mu-R(1)CCR(2))(CO)(5)(mu-eta(1):eta(2)-L)Co-2(CO)(6)] (R(1) = Ph, R(2) = H; R(1) = R(2) = Me), in which L is bound to the Co-2(CO)(6) unit via the alkyne functionality. Pyrolysis of [Co-2(mu-MeCCMe)CO)(5)(mu-eta(1):eta(2)-L)Co-2(CO)(6)] results in phosphorus-carbon bond cleavage and cobalt-cobalt and carbon-carbon bond formation to afford a butterfly cluster [Co-4{mu(4)-eta(3)-PhCCC(Me)=C(Me)C(O)}(mu-PPh(2))(mu-CO)(2)(CO)(6)] whose structure has been established by X-ray diffraction.