Synthesis and mechanisms of fluxionality of the clusters [Ir4(CO)11(PH3–nPhn)](n= 1 or 2)

Abstract

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(µ-CO)₃(PH₂Ph)] and [Ir₄(CO)₈(µ-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 ³¹P magnetisation-transfer measurements. It was unambiguously shown that interconversion of the carbonyl-bridged isomers occurs via the all-terminal isomer.