Synthesis of a sulfido-capped triiron cluster with bridging phosphido ligands and its reactions with alkynes, phosphites and phosphines†

Abstract

Treatment of [Fe(CO)₅] with Ph₂P(SCMe₃) at elevated temperature and pressure afforded, as the major product, the sulfur-capped trinuclear iron cluster [Fe₃(µ₃-S)(µ-PPh₂)₂(µ-CO)(CO)₆] 1, in which two Fe–Fe edges are bridged by phosphido groups and the other by a carbonyl group. Also isolated in low yield from this reaction was the tetranuclear iron complex [{Fe₂(µ-PPh₂)(CO)₆}₂(µ₄-S₂)] 2, which comprises two phosphido-sulfido-bridged diiron fragments linked by an S–S bond. In contrast it has been demonstrated that the reaction of [Fe(CO)₅] with Ph₂P(SPh) gives the discrete dinuclear complex [Fe₂(µ-PPh₂)(µ-SPh)(CO)₆] in which a sulfur–carbon bond has been retained. The reaction of 1 with organo-phosphites and -phosphines results in preservation of the triiron core and monosubstitution of a carbonyl group to give [Fe₃(µ₃-S)(µ-PPh₂)₂(µ-CO)(CO)₅(L)] [L = P(OMe)₃ 3a, P(OPh)₃ 3b, PPhMe₂ 3c or PPh₃ 3d]. On reaction of 1 with terminal alkynes, RCCH [R = Ph or CH₂OH], degradation of the trinuclear framework results to give the metallacyclic-bridged bimetallic complexes [Fe₂(µ-PPh₂CHCRS)(µ-PPh₂CHCR)(CO)₄] [R = Ph 4a or CH₂OH 4b] in which new sulfur–carbon and phosphorus–carbon bonds have formed. In addition, the phosphido-bridged species [Fe₂(µ-PPh₂)(µ-PPh₂CHCPhS)(CO)₅] 5 is isolated as a minor product from the reaction of 1 with PhCCH. The structures of complexes 1, 2, 3c and 4a have been determined by single crystal X-ray diffraction analysis and pathways are postulated for the formation of the various products.