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

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.