Efficient incorporation of polar comonomers in copolymerizations with ethylene using a cyclophane-based Pd(II) α-diimine catalyst

Polar olefins were copolymerized with ethylene using a cyclophane-based palladium(II) alpha-diimine catalyst. The incorporation levels of both methyl acrylate and tert-butyl acrylate are unusually high compared to what is obtained with the corresponding acyclic catalyst. Mechanistic studies by low-temperature NMR spectroscopy revealed that the differences between the insertion barriers for ethylene and MA (Delta Delta G) are similar for the acyclic and cyclophane catalysts. The equilibration of comonomers, fast on experimental time scales for the acyclic catalyst, was too slow to be measured for the cyclophane catalyst. These results suggest that ligand substitution is significantly retarded by the bulky cyclophane ligand. The reduction of the rate of monomer exchange with respect to monomer insertion reduces the catalyst's ability to discriminate between comonomers, hence resulting in the high incorporation levels of acrylates in copolymerizations with ethylene.