1005000-68-9Relevant academic research and scientific papers
Ethylene dimerization by cationic palladium(II) alkyl complexes that contain bis(heterocycle)methane ligands
Burns, Christopher T.,Jordan, Richard F.
, p. 6726 - 6736 (2007)
The catalytic ethylene dimerization reactions of (N∧N)PdMe(L) + species that contain bidentate nitrogen donor ligands were studied (N∧N = (1-Me-imidazol-2-yl)2CH2 (a); (1-Me-imidazol-2-yl)2CH(C6H13) (b), 1,1′di(triphenylmethyl)-4,4′-biimidazole (c), (5-Me-pyridin-2-yl) 2CH2 (d), (pyrazol-1-yl)2CH2 (e), (3,5-Me2-pyrazol1-yl)2CH2 (f), (4-Me-C 6H4)N=CMeCMe=N(4-Me-C6H4) (g), and (2,6-iPr2-C6H3)N=CMeCMe=N(2,6- iPr2-C6H3) (h)). (N∧N)PdMe 2 (2a-e,g) and (N∧N)Pd(Me)Cl (3f-h) complexes were converted to [(N∧N)Pd{C(=O)Me}CO][B(C6F5)4)] (7a,c-h), [(N∧N)Pd(Me)(H2C=CH2)][B(C6F 5)4)] (8a-g), and [(N∧N)Pd(Me)(H2C=CH 2)] [SbF6] (8f′). The vco values for 7a,c-f show that there is weak back-bonding in these species, the donor ability of the NAN ligand varies in the order imidazole > pyridine > pyrazole, and variation of the chelate ring size does not strongly affect the electron density at Pd. 8a,c-g and 8f′ dimerize ethylene by an insertion/β-H elimination mechanism. The catalyst resting state is (N∧N)Pd(Et)(H 2C=CH2)+ (9a,c-g). First-order rate constants for ethylene insertion of 8a-g and 8f′ (kinsert,Me) and 9a,c-g (kinsert,Et) were determined by NMR. The kinsert,Et and kinsert,Et values for analogous (N∧N)Pd(R)(H2C=CH 2)+ species are similar. Increasing the electrophilic character and the steric bulk of the (N∧N)Pd unit leads to moderate increases in ethylene insertion rates.
