Solution structure and dynamic behaviour of two isomers of [Fe3(CO)9{P(OR3)}3](R = Me, Et, or Ph) derivatives

Abstract

The reaction between [Fe3(CO)12] and P(OR)3(R = Me, Et, or Ph) in the presence of the bimetallic catalyst [{Fe(CO)2(PPh3)(SEt)}2] affords two 1,2,3-trisubstituted isomers which rapidly interconvert at room temperature on the n.m.r. time-scale. The solution structures and dynamics have been elucidated for both isomers by means of variable-temperature 31P and 13C n.m.r. studies. In polar solvents the major isomer shows a [Fe3(CO)12]-like structure whereas the minor one contains only terminally bonded CO groups. The observation of three equally intense carbonyl resonances in the low-temperature-limiting spectra (R = Me or Et) supports a D3 structure for this isomer. The equilibration of axial CO ligands occurs readily as the temperature is increased; this rearrangement may be ascribed to the motion of the Fe3 triangle inside the polyhedral cloud of ligands or alternatively to an interconversion between a left-hand screw with a right-hand screw.