Synthesis and characterisation of derivatives of [HIr4(CO)10(μ-PPh2)] with mono and diphosphines; X-ray molecular structures of [HIr4(CO)8(PPh3)2(μ-PPh2)] and [HIr4(CO)8{Ph2P(CH2)nPPh2}(μ-PPh2)] (n=1 and 4)

The reactions of the cluster compound [HIr4(CO)10(μ-PPh2)] (1) with a series of phosphines, PMe3 and PPh3, and diphosphines, Ph2P(CH2)nPPh2 (n=1, dppm, n=2, dppe and n=4, dppb) and cis-PPh2CHCHPPh2 (dppen), have been investigated. Reaction of 1 with PMe3 yielded the mono and di-substituted derivatives [HIr4(CO)10−n(PMe3)n(μ-PPh2)] (n=1, 2 and n=2, 3). 1H and 31P-NMR spectroscopy monitoring revealed that the two kinetic isomers 2b and 2c undergo conversion to the thermodynamic isomer 2a through a process, which apparently involves intra-molecular migration of the PMe3 ligand. In contrast, analogous kinetic isomers were not detected during the synthesis of the PPh3 derivative [HIr4(CO)9(PPh3)(μ-PPh2)] (4). According to 1H and 31P-NMR data, compounds [HIr4(CO)8(L)2(μ-PPh2)] (L=PMe33 and PPh35) exist in solution in three isomeric forms 3a–3c and 5a–5c, respectively, at −60 °C. Compound 1 also reacts with diphosphines to give CO substitution products, whose composition depends on the size of the methylene chain. Whilst reaction with dppm and dppen yields only the bi-substituted species [HIr4(CO)8(dppm)(μ-PPh2)] (6) and [HIr4(CO)8(dppen)(μ-PPh2)] (7), respectively, with dppb, both the dimeric compound [{HIr4(CO)9(μ-PPh2)}2(dppb)] (8a) and the monomeric species [HIr4(CO)8(dppb)(μ-PPh2)] (8b) are formed, and with dppe, only the dimeric compound [{HIr4(CO)9(μ-PPh2)}2(dppe)] (9) is obtained. The dppm derivative exists in solution in the form of two inter-converting isomers 6a and 6b that differ with respect to the mode of coordination of the dppm and CO ligands. Isomerisation of 6a–6b is proposed to involve intra-molecular migration of dppm and carbonyl ligands. Structures were proposed for all compounds, on the basis of 1H and 31P[1H]-NMR studies and of correlations previously established for the phosphine and diphosphine derivatives of [Ir4(CO)12]; the molecular structures of compounds 5c, 6a and 8b were established by X-ray diffraction studies which confirmed the structures proposed based on spectroscopic data.