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

Single-component and environmentally stable palladium acetylides with the s tructures of PdL2(C equivalent to CR)(2) (L = PPh3, PBu3; R = p-C6H4C equiv alent to CH. C6H5, H, CH2OH, CH2OCOCH3, CH2OCOC6H5, CH2OCOC6H4OH-o) are nov el efficient initiating systems forp-diethynylbenzene polymerization. The p olymerization proceeds under mild conditions to give soluble rr-conjugated polymers with molecular weights as high as 1.8 x 10(4) in yields as high as 84%. The catalytic property of these acetylides is related to phosphine an d alkynyl ligands bonded to the metal atoms. Palladium complexes containing PPh3 ligand are much more active than that containing PBu3 ligand. The com plexes containing polar alkynyl ligands show higher catalytic activity than the corresponding complexes containing non-polar ligands. For the complexe s containing non-polar alkynyl ligands, the greater the conjugation degree of the alkynyl ligand, the higher the catalytic activity of the correspondi ng complex. For the complexes containing polar alkynyl ligands, the complex es containing eater ligands show higher catalytic activity than the corresp onding complex containing alcohol ligand, and the catalytic activity of the complexes containing ester ligands increases with increasing acidity of th e corresponding acids. (C) 2001 Elsevier Science B.V. All rights reserved.