High-pressure NMR studies on the alternating copolymerization of styrene with carbon monoxide catalyzed by a palladium(II)-(R,S)-BINAPHOS complex

The asymmetric copolymerization of styrene with CO catalyzed by Pd-(R,S)-BINAPHOS complexes has been studied using in situ NMR spectroscopy under both diffusion- and reaction-controlled conditions. While a study conducted in a conventional zirconia tube suffered from gas diffusion limitation, use of a high-pressure NMR flow cell allows the observation of potential catalytic intermediates. The formation of Pd-alkyl complexes via 1,2-insertion of styrene into Pd-acyl complexes is confirmed to be the most active catalytic pathway. The 2,1-insertion complexes were found to be quite inactive to further insertion and remarkably stable toward beta-hydride elimination, in contrast to our previous expectations.