Cis/trans Isomerization of o-Phosphino-Arenesulfonate Palladium Methyl Complexes

Abstract

The cis/trans isomerization of (PO-OMe)PdMe(lut) ([PO-OMe]− = 2-{P(2-OMe-Ph)2}-4-Me-benzenesulfonate) was studied to model the proposed isomerization in chain propagation in ethylene polymerization by (o-phosphino-arenesulfonate)PdR(ethylene) species. Nonequilibrium mixtures of cis-P,C- and trans-P,C-(PO-OMe)PdMe(2,6-lutidine) were generated by the reaction of Na[PO-OMe] and {Pd(μ-Cl)Me(2,6-lutidine)}2 in CD2Cl2 at −25 °C. Kinetic studies revealed lutidine-catalyzed and noncatalyzed isomerization pathways. The lutidine-catalyzed pathway involves five-coordinate (PO-OMe)PdMe(lut)2 intermediates that undergo Berry pseudorotation. Kinetic studies, structure–activity relationships, solvent effects, and density functional theory calculations for the noncatalyzed pathway are most consistent with a mechanism, originally proposed by Nozaki, Morokuma, and co-workers, which proceeds through a five-coordinate transition state with κ3-P,O,O coordination of the [PO]− ligand.