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.