Bis(carbene)pyridine Complexes of the Early to Middle Transition Metals: Survey of Ethylene Oligomerization and Polymerization Capability
摘要:
Bis(carbene)pyridines of the type 2,6-bis(1-(alkyl/aryl)imidazol-2-ylidene)pyridine have been complexed to Ti, V, Cr, Fe, and Co and single-crystal X-ray structures obtained for two of the complexes (M = Cr, Fe). The structures confirm the tight chelate bite angles (ca. 76-79degrees) enforced by this ligand. All complexes have been evaluated as catalysts for ethylene oligomerization and polymerization in combination with a variety of cocatalysts. While Ti and V complexes of this ligand give rise to highly active ethylene polymerization catalysts, Cr complexes produce exceptionally active Schulz-Flory oligomerization catalysts in combination with MAO. In contrast, complexes of Fe and Co: are inactive, and possible reasons for this are suggested.
A variety of chiral and achiral imidazoliumsalts is synthesized. Methylene-, ethylene-, propylene- and pyridinyl-bridged bis(imidazolium) halides are used to generate the respective free chelating carbenes. The synthesis of palladium complexes of general formula [cis-CH 2 NC(H)=C(H)N(R)C} 2 PdX 2 ] with these chelating N-heterocyclic carbene ligands is reported. Structural proofs of complexes 28
Bis(carbene)pyridine Complexes of Cr(III): Exceptionally Active Catalysts for the Oligomerization of Ethylene
作者:David S. McGuinness、Vernon C. Gibson、Duncan F. Wass、Jonathan W. Steed
DOI:10.1021/ja037217o
日期:2003.10.1
Pincer-heterocyclic carbene complexes of Cr(III), of the form [2,6-(1-alkylimidazol-2-ylidene)pyridine]CrCl3, have been prepared and evaluated as catalysts for the oligomerization of ethylene to alpha-olefins. In combination with methylaluminoxane cocatalyst, exceptionally high activities are obtained, ranging up to ca. 40 000 g mmol-1 bar-1 h-1.