Johannes J. C. Erasmus

Electron density manipulation in rhodium(I) phosphine complexes: structure of acetylacetonatocarbonylferrocenyl- diphenylphosphinerhodium(I)

Abstract The title complex [Rh(acac)(CO)(PPh2Fc)] (acac = acetylacetonato, PPh2Fc = ferrocenyldiphenylphosphine), was obtained in acetone by reaction of the tertiary phosphine with [Rh(acac)(CO)2] and was characterised by IR spectroscopy, 1H and 31P NMR and single crystal X-ray crystallography. This is a rare example illustrating the incorporation of the ferrocenyl moiety in a monodentate tertiary phosphine complex of rhodium(I). It crystallises in the triclinic space group P 1 with two independent molecules in the asymmetric unit and refined to R=2.40% from 5215 reflections. The independent molecules, showing the usual square planar geometry, differ mainly in the rotation mode of the asymmetric phosphine around the Rh-P bond and a slight deviation in the Rh-CO bond from linearity, which was correlated with IR data.

Oxidative addition of methyl iodide to [Rh(PhCOCHCOPh)(CO)(P(OCH2)3CCH3)]: an experimental and computational study

The reaction rate of the oxidative addition and CO insertion steps of methyl iodide with [Rh(PhCOCHCOPh)(CO)(P(OCH2)3CCH3)] are presented. Large negative experimental values for the activation entropy and results from a density functional theory computational chemistry study indicated trans addition of the CH3I to [Rh(PhCOCHCOPh)(CO)(P(OCH2)3CCH3)]. A study of the molecular orbitals gives insight into the flow of electrons during the oxidative addition reaction. CO insertion leads to a square pyramidal [Rh(PhCOCHCOPh)(P(OCH2)3CCH3)(COCH3)(I)] acyl product with the COCH3 moiety in the apical position. The strong electron donation of the P(OCH2)3CCH3 ligand accelerates the oxidation addition step of methyl iodide to [Rh(PhCOCHCOPh)(CO)(P(OCH2)3CCH3)] by ca. 265 times faster (at 35°C) than that of the Monsanto catalyst, but inhibits the CO insertion step.