Niobium-based ethylene polymerization procatalysts bearing di- and triphenolate ligands

Interaction of [NbCl5] with the diphenol 2,2'-CH3CH[4,6-(Bu-t)(2)C6H2OH](2) (LH2) affords, after work-up, the red crystalline complex [NbCl(NCMe)L-2] (1). Under similar conditions, [NbOCl3] and the sulfur-bridged diphenol 2,2'-S[4,6-(Bu-t)(2)C6H2OH](2) ((LH2)-H-s) afford the orange complex [NbCl(L-S)(2)] (2). Crystal structure determinations of I (.) 2MeCN and 2 reveal monomeric 6- and 7-coordinate complexes, respectively. The polymerization behaviour of I and 2 towards ethylene, in the presence of alkylaluminium co-catalysts has been examined and has been compared with that of the known niobium aryloxides [Nb(Me-L-2)Cl-2/(2) (3), {Nb[(Bu-t-L-2)H](2)Cl-(NCMe)} (4) and [Nb(Bu-t-L-2)Cl-2] (5), derived from the linear-linked aryloxide trimers 2,6-bis(4,6-dimethylsalicyl)-4-tert-butylphenol [(Me-L 2)H-3] and 2,6-bis(4-methyl-6-tert-butylsalicyl)-4-tert-butylphenol [(Bu-t-L-2)H-3]. The crystal structure of the acetonitrile solvate of 3 (.) 4MeCN, is also reported. (c) 2005 Elsevier B.V. All rights reserved.