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(CH3)(CO)(L-1)][BAr4] (8a; L-1 = (R,S)-BINAPHOS; Ar = 3,5-(CF3)(2)C6H3) 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)][BAr4] (3; L-2= CH3CN, CO), and alkylpalladium, [Pd{CH2CH(CH3)C(=O)R}(L-1)][BAr4] (5a).