High-Pressure NMR Studies on the Alternating Copolymerization of Propene with Carbon Monoxide Catalyzed by a Palladium(II) Complex of an Unsymmetrical Phosphine−Phosphite Ligand

When high-pressure NMR techniques are employed, the following two facts are revealed. (1) The cis/trans isomerization from ( SP -4-4)-[Pt(CH 3 )(CO)(L 1 )][BAr 4 ] ( 8a; L 1 = ( R,S )-BINAPHOS; Ar = 3,5-(CF 3 ) 2 C 6 H 3 ) to the more stable SP -4-3 isomer ( 8b ) is faster than CO insertion into either 8a or 8b, the CO insertion being reversible. (2) For the Pd II −L 1 -catalyzed copolymerization of propene and CO, there exist at least two major resting states, most probably acylpalladium, ( SP -4-3)-[Pd(COR)(L 2 )(L 1 )][BAr 4 ] ( 3; L 2 = CH 3 CN, CO), and alkylpalladium, [Pd{CH 2 CH(CH 3 )C( O)R}(L 1 )][BAr 4 ] ( 5a ).