Polymerization of Phenylacetylenes Using Rhodium Catalysts Coordinated by Norbornadiene Linked to a Phosphino or Amino Group

The novel rhodium (Rh) catalysts [{nbd-(CH2)4-X}­RhR] (1, X = PPh2, R = Cl; 2, X = NPh2, R = Cl; 3, X = PPh2, R = triphenylvinyl; nbd = 2,5-norbornadiene) were synthesized,
and their catalytic activities were examined for the polymerization
of phenylacetylene (PA) and its derivatives. Rh-103 NMR spectroscopy
together with DFT calculations (B3LYP/6-31G*-LANL2DZ) indicated that
catalyst 1 exists in a mononuclear 16-electron state,
while 2 exists in dinuclear states. Catalyst 1 converted PA less than 1% in the absence of triethylamine (Et3N). Addition of Et3N and extension of the polymerization
time enhanced the monomer conversion. On the other hand, catalysts 2 and 3 quantitatively converted PA in the absence
of Et3N to afford the polymer in good yields. Catalyst 3 achieved two-stage polymerization of PA.