Regiochemistry of Nickel-Catalyzed Polymerization of 1,5-Dichlorobenzophenone in the Presence of Coordinating Ligands

The regiochemistry of the nickel-catalyzed polymerization of 2,5-dichlorobenzophenone in the presence of excess zinc and triphenylphosphine with (PBP-B) and without added coligand, 2,2′-bipyridine (PBP-A), has been re-examined. The carbonyl region of the 13 C NMR spectra have been interpreted by analysis of dimeric models for the H–T, H–H and T–T units in the polymer, i.e. 2,3′-bisbenzophenone, 2,2′-bisbenzophenone and 3,3′-bisbenzophenone. Based on the NMR spectral assignments for these model compounds, it has been concluded that PBP-B has few if any H–H units, whereas these units are present in significant amounts in PBP-A. Based on these results, it is proposed that what determines the conjugation length in the UV-vis spectra of PBPs is the occurrence of H–H units along the polymer backbone and not the percentage of H–T units in the chains.