Highly active [Pd(AcO)2(dppp)] catalysts for CO-C2H4 copolymerization in H2O-CH3COOH solvent [dppp= 1,3-bis(diphenylphosphino)propane]

In MeOH, [Pd(AcO)2(dppp)] becomes an efficient catalyst for the perfectly alternated CO-C2H4 copolymerization when used in combination of a relatively large amount of CH3COOH (CH3COOH/Pd, ca. 2.0×104). Under 4.56 MPa (CO/C2H4 = 1/1), at 90 °C, 7.5 kg polyketone/g Pd∗h are obtained. A significantly higher productivity is obtained in H2O-CH3COOH, in place of MeOH (27.5 kg polymer/g Pd∗h under 4.56 MPa (CO/C2H4 = 1/1), 90 °C, H2O=37% (mol/mol)). Under these conditions the catalyst undergoes only a minor deactivation with time as after 3 h the productivity decreases only by ca. 10%. The NMR analysis shows that [Pd(AcO)2(dppp)] in CH3COOH-H2O yields a perfectly alternated polyketone of ca. 8000 g/mol bearing only ketonic end groups. During the course of the copolymerization reaction CO2 forms in significant amount. These findings suggest that the insertion of C2H4 into PdH bond starts the catalytic cycle, and that alternating insertions of the monomers followed by protonolysis of a PdC bond of a Pd-CH2-CH2-(CO-C2H4)n-H growing chain yields the polymer with only keto ending groups and a Pd-OH species; a reaction closely related to the WGS reproduces the starting Pd-hydride; deprotonation of this species to inactive Pd(0) is prevented by the acid.