1,2,3-Triphenylphosphirene derivatives of the iridium carbonyl clusters [HIr4(CO)9L(μ-PPh2)] (L = CO, PPh3) resulting from substitution, insertion and hydrometallation processes †

Abstract

1,2,3-Triphenylphosphirene reacts with [HIr4(CO)10(μ-PPh2)] 1, at room temperature, to afford [Ir4(CO)8(μ3-η2-PhPCPhCPh)(μ-PhPCPhCHPh)(μ-PPh2)] 2 which contains the phosphametallacycle (μ3-η2-PhPCPhCPh) and the phosphidoalkenyl (μ-PhPCPhCHPh) ligands arising from insertion and hydrometallation processes respectively. In contrast, the PPh3 derivative of 1, [HIr4(CO)9(PPh3)(μ-PPh2)] 3, reacts selectively at room temperature with the phosphirene to give only CO substitution products, [HIr4(CO)9 − n(PPh3)(η1-PhPCPhCPh)n(μ-PPh2)] (n = 1, 4 and 2, 5) which are the first carbonyl cluster compounds containing intact η1-ligated phosphirene rings. High yield conversion of compound 4 into the phosphametallacycle species [HIr4(CO)7(PPh3)(μ3-η2-PhPCPhCPh)(μ-PPh2)] 6 is achieved under mild thermolytic conditions. An insight into the mechanism of formation of 2 was given by the reaction of the phosphirene ring with the anion [Ir4(CO)10(μ-PPh2)]−1a derived from 1, followed by protonation, which gave [HIr4(CO)8(μ3-η2-PhPCPhCPh)(μ-PPh2)] 7, which is analogous to 6 with a CO ligand replacing PPh3. Quantitative conversion of the hydride phosphametallacycle 7 into the labile phosphidoalkenyl cluster [Ir4(CO)11(μ-PhPCPhCHPh)(μ-PPh2)] 8 is easily achieved in the presence of CO (1 atm, RT, 2 h), as a result of the reductive elimination of a C–H group. Compound 8 undergoes facile CO dissociation and co-ordination of the phosphidoalkenyl CC bond to the metal centre to produce [Ir4(CO)9(μ3-η3-PhPCPhCHPh)(μ-PPh2)] 9. The molecular structures of compounds 2, 4, 6 and 9 were established by X-ray diffraction studies and the structures of all compounds in solution were investigated by a combination of 1H and 31P{1H} NMR studies.