Synthesis, structure and mechanism of formation of chalcogen-stabilised mixed-metal clusters featuring acetylide bridging and acetylide coupling

Mild thermolysis of a toluene solution of [(eta(5)-C5H5)Mo(CO)(3)(C=CPh)] and [Fe-3(CO)(9)(mu(3)-E)(2)] (E = S, Se) resulted in the formation of mixed-metal clusters, [(eta(5)-C5H5)(2)Mo2Fe3(CO)(8)(mu(3)-E)(2){eta(5)-CC(Ph)CC(Ph)}] (E = S, 1; Se, 2), [(eta(5)-C5H5)(2)Mo2Fe4(CO)(9)(mu(3)-E)(2)(mu(4)-CCPh)(2)] (E = S, 3; Se, 4) and [(eta(5)-C5H5)(2)Mo2Fe3(CO)(7)(mu(3)-E)(2){mu(5)-CC(Ph)C(Ph)C}] (E = S 5; E = Se 6) which feature head-to-tail coupling of two acetylide groups, two acetylide groups which remain uncoupled and a tail-to-tail coupling of two acetylide groups, respectively, on the chalcogen-bridged Fe/Mo cluster framework. Under similar conditions, the reaction of [(eta(5)-C5H5)W(CO)(3)(C=CPh)] and [Fe-3(CO)(9)(mu(3)-E)(2)] formed the clusters [(eta(5)-C5H5)(2)W2Fe3(CO)(7)(mu(3)-E)(2)(mu(3)-eta(2)-CCPh)(mu(3)-eta(1)-CCH2Ph)] (E = S, 7 or Se, 8) and [(eta(5)-C5H5)WFe2(CO)(8)(mu-CCPh)] (9). All compounds have been characterised by IR and H-1 and C-13 NMR spectroscopy. The Se-bridged compounds have been further characterised by Se-77 NMR spectroscopy. The crystal structures of 1, 3 and 5-9 were elucidated by X-ray diffraction methods