Asymmetric hydrogenation of dimethyl itaconate catalysed by rhodium chelates of aminophosphine phosphinites: A kinetic and NMR spectroscopical study

Abstract

The asymmetric hydrogenation of dimethyl itaconate in the presence of cationic seven-membered ring aminophosphine phosphinite rhodium(I)-cyclooctadiene complexes derived from Propranolol (PROPRAPHOS-Rh derivatives) can be described by the Michaelis-Menten kinetics. Variation of the nitrogen substituent in the aminophosphine phosphinite moiety of the rhodium catalyst causes a change in the concentration of the catalyst-substrate complexes. This is especially high in the case of the N-cyclohexyl derivative as follows from the Michaelis constants. 31P NMR spectra of this compound gave signals of three catalyst-substrate complexes due to the different phosphorus donors: one minor- and two major-complexes. A second minor-complex could not be observed. Line-shape analysis indicates the intramolecular interconversion between diastereomeric catalyst-substrate complexes, being in favour of the intermolecular processes as found already for bis(phosphinite) chelates.