Selectivity in multiple methylation of MCl n(Pr 3) m compounds

Abstract

Reaction of RhCl 3L 3 (L = PMe 2Ph or PMePh 2) with excess MeLi or MeMgCl reveals a distinct tendency to stop at the RhMe 2ClL 3 stage. This behaviour is attributed to the concentration of all Cl → Rh π-donation into the single remaining metal-halogen bond, and is shown to be a phenomenon of even broader occurrence and greater potential generality. For cis, mer-RhMe 2ClL 3 containing the bulkier ligand PMePh 2, variable temperature 1H and 31P NMR studies reveal the occurrence of two dynamic processes: hindered rotation about RhP and PC bonds and also dissociation of the unique phosphine trans to one methyl group.