The Role of the ortho-Methoxy Group in Pd(II) Diphosphine Complexes Applied in the Copolymerization of CO and Ethene

Drent et al. have shown that the catalytic CO/ethene copolymerization activity of palladium(II) complexes with diphosphines of the type Ar2P(CH2)nPAr2 depends on the backbone chain length and the substituents on the phosphorous donor atoms.[1] Within the different substituents on the phenyl ring of chelating diphosphines the ortho-methoxy group is one of the most important in this kind of catalysis. Since the role of the ortho-methoxy group has not been fully understood yet, we compare the catalytic activity of palladium(II) complexes with 1,2-bis(diphenylphosphino) ethane (dppe), 1,2-bis(di-(o-methoxyphenyl)phosphino) ethane (MeO-dppe), 1,3-bis(diphenylphosphino) propane (dppp) and 1,3-bis(di-(o-methoxyphenyl)phosphino) propane (MeO-dppp) under identical conditions in the copolymerization of CO and ethene. In addition to catalytic investigations we studied comparable Pd(II) compounds by means of single crystal X-ray structure analyses, IR- as well as high pressure NMR-spectroscopy in order to understand the positive effect induced by the ortho-methoxy moiety. REFERENCE: [1] Drent, E., Budzelaar, P. H. M. Chem. Rev., 1996, 96, 663.