Synthesis and characterisation of derivatives of [HIr 4(CO) 10(μ-PPh 2)] with mono and diphosphines; X-ray molecular structures of [HIr 4(CO) 8(PPh 3) 2(μ-PPh 2)] and [HIr 4(CO) 8{Ph 2P(CH 2) nPPh 2}(μ-PPh 2)] ( n=1 and 4)

Abstract

The reactions of the cluster compound [HIr 4(CO) 10(μ-PPh 2)] ( 1) with a series of phosphines, PMe 3 and PPh 3, and diphosphines, Ph 2P(CH 2) nPPh 2 ( n=1, dppm, n=2, dppe and n=4, dppb) and cis-PPh 2CHCHPPh 2 (dppen), have been investigated. Reaction of 1 with PMe 3 yielded the mono and di-substituted derivatives [HIr 4(CO) 10− n (PMe 3) n (μ-PPh 2)] ( 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 PMe 3 ligand. In contrast, analogous kinetic isomers were not detected during the synthesis of the PPh 3 derivative [HIr 4(CO) 9(PPh 3)(μ-PPh 2)] ( 4). According to 1H and 31P-NMR data, compounds [HIr 4(CO) 8(L) 2(μ-PPh 2)] (L=PMe 3 3 and PPh 3 5) 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 [HIr 4(CO) 8(dppm)(μ-PPh 2)] ( 6) and [HIr 4(CO) 8(dppen)(μ-PPh 2)] ( 7), respectively, with dppb, both the dimeric compound [{HIr 4(CO) 9(μ-PPh 2)} 2(dppb)] ( 8a) and the monomeric species [HIr 4(CO) 8(dppb)(μ-PPh 2)] ( 8b) are formed, and with dppe, only the dimeric compound [{HIr 4(CO) 9(μ-PPh 2)} 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 [Ir 4(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.