1005189-86-5Relevant academic research and scientific papers
Ethylene polymerization by sterically crowded palladium(II) complexes that contain bis(heterocycle)methane ligands
Burns, Christopher T.,Jordan, Richard F.
, p. 6737 - 6749 (2008/10/09)
The catalytic ethylene polymerization reactions of (NN)PdMe(L) + species that contain bulky bis(heterocycle)methane ligands were studied (NN = (1-Me-imidazol-2-yl)2CHCH(p-tolyl)2 (1i), (1-Me-imidazol-2-yl)2CHC(p-tolyl)3 (1j), (5-Me-pyridin-2-yl)2CHC(p-tolyl)2)3 (1k), (5-Me-pyridin-2-yl)2CHCH(p-tolyl)2 (1l), (3-Me-pyridin-2-yl)2CHCH(p-tolyl)2 (1m), (5-Me-pyridin-2-yl)2CHCH(m-xylyl)2 (1n), (3-Me-pyridin-2-yl)2CHCH(/n-xylyl)2 (1o), (quinol-2-yl)2CHCH(m-xylyl)2 (1p), and (3-Me-quinol-2-yl)2CHCH(m-xylyl)2 (1q). (NN)PdMe2 (2i,j,q) and (NN)Pd(Me)Cl (3m-o) complexes were converted to (NN)Pd{C(=O)Me}CO+ complexes (7i,j,m-o,q). The vCO values for 7i,j,m-o,q show that there is weak back-bonding in these species. Complexes 2i,j and (NN)Pd(Me)Cl complexes 3l-o were converted to (NN)Pd(Me)(H2C=CH2)+ (8i,j,l-o and 8q (not directly observed)). First-order rate constants for ethylene insertion of 8i,j,l-o were determined by NMR. Increasing the electrophilic character and the steric bulk of the (NN)Pd unit increases the rate of ethylene insertion. In-situ-generated 8j,l-n,q produce low molecular weight polyethylene (Mw ≤ 4200), while 8o produces higher molecular weight polyethylene (Mw = 34 000). Polyethylene produced by 8j,l,m contains 100 branches/103 C, while that from 8n,o,q contains 60 branches/103C.
