SYNTHESIS AND MECHANISMS OF FLUXIONALITY OF THE CLUSTERS [IR4(CO)11(PH3-NPHN)] (N = 1 OR 2)

The carbonyl clusters, [Ir4(CO)11(PH2Ph)] and [Ir4(CO)11(PHPh2)], have been synthesised by replacement of the bromide in [Ir4(CO)11Br] - by the appropriate phosphorus ligand. It is shown that [Ir4(CO)11(PH2Ph)] and [Ir4(CO)11(PHPh2)] exist in solution predominantly as the all-terminal isomers, but there are small concentrations of the two carbonyl-bridged isomers, [Ir4(CO)8(mu-CO)3(PH2Ph)] and [Ir4(CO)8(mu-CO)3(PHPh2)], with the phosphorus ligand axial and equatorial to the bridged face. Carbon-13 magnetisation-transfer measurements were used to demonstrate carbonyl scrambling around the three inequivalent faces of the iridium tetrahedron in [Ir4(CO)11(PH2Ph)], and rates were determined. Interconversion of the three isomers of [Ir4(CO)11(PHPh2)] was demonstrated by P-31 magnetisation-transfer measurements. It was unambiguously shown that interconversion of the carbonyl-bridged isomers occurs via the all-terminal isomer.