Transition metal acetylide catalysts for polymerization of alkynes: 2. Effect of ligands on catalytic activity of palladium complexes

Abstract

Single-component and environmentally stable palladium acetylides with the structures of PdL 2(CCR) 2 (L=PPh 3, PBu 3; R= p-C 6H 4CCH, C 6H 5, H, CH 2OH, CH 2OCOCH 3, CH 2OCOC 6H 5, CH 2OCOC 6H 4OH- o) are novel efficient initiating systems for p-diethynylbenzene polymerization. The polymerization proceeds under mild conditions to give soluble π-conjugated polymers with molecular weights as high as 1.8×10 4 in yields as high as 84%. The catalytic property of these acetylides is related to phosphine and alkynyl ligands bonded to the metal atoms. Palladium complexes containing PPh 3 ligand are much more active than that containing PBu 3 ligand. The complexes containing polar alkynyl ligands show higher catalytic activity than the corresponding complexes containing non-polar ligands. For the complexes containing non-polar alkynyl ligands, the greater the conjugation degree of the alkynyl ligand, the higher the catalytic activity of the corresponding complex. For the complexes containing polar alkynyl ligands, the complexes containing ester ligands show higher catalytic activity than the corresponding complex containing alcohol ligand, and the catalytic activity of the complexes containing ester ligands increases with increasing acidity of the corresponding acids.