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 β-hydride elimination, in contrast to our previous expectations.