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

Abstract

Mild thermolysis of a toluene solution of [(η⁵-C₅H₅)Mo(CO)₃(C≡CPh)] and [Fe₃(CO)₉(μ₃-E)₂] (E = S, Se) resulted in the formation of mixed-metal clusters, [(η⁵-C₅H₅)₂Mo₂Fe₃(CO)₈(μ₃-E)₂{μ₅-CC(Ph)CC(Ph)}] (E = S, 1; Se, 2), [(η⁵-C₅H₅)₂Mo₂Fe₄(CO)₉(μ₃-E)₂(μ₄-CCPh)₂] (E = S, 3; Se, 4) and [(η⁵-C₅H₅)₂Mo₂Fe₃(CO)₇(μ₃-E)₂{μ₅-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 [(η⁵-C₅H₅)W(CO)₃(C≡CPh)] and [Fe₃(CO)₉(μ₃-E)₂] formed the clusters [(η⁵-C₅H₅)₂W₂Fe₃(CO)₇(μ₃-E)₂(μ₃-η²-CCPh)(μ₃-η¹-CCH₂Ph)] (E = S, 7 or Se, 8) and [(η⁵-C₅H₅)WFe₂(CO)₈(μ-CCPh)] (9). All compounds have been characterised by IR and ¹H and ¹³C NMR spectroscopy. The Se-bridged compounds have been further characterised by ⁷⁷Se NMR spectroscopy. The crystal structures of 1, 3 and 5-9 were elucidated by X-ray diffraction methods.