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

Interaction of [NbCl5] with the diphenol 2,2′-CH3CH[4,6-(But)2C6H2OH]2 (LH2) affords, after work-up, the red crystalline complex [NbCl(NCMe)L2] (1). Under similar conditions, [NbOCl3] and the sulfur-bridged diphenol 2,2′-S[4,6-(But)2C6H2OH]2 (LSH2) afford the orange complex [NbCl(LS)2] (2). Crystal structure determinations of 1 · 2MeCN and 2 reveal monomeric 6- and 7-coordinate complexes, respectively. The polymerization behaviour of 1 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–L2)Cl2]2 (3), {Nb[(But-L2)H]2Cl(NCMe)} (4) and [Nb(But-L2)Cl2] (5), derived from the linear-linked aryloxide trimers 2,6-bis(4,6-dimethylsalicyl)-4-tert-butylphenol [(Me–L2)H3] and 2,6-bis(4-methyl-6-tert-butylsalicyl)-4-tert-butylphenol [(But-L2)H3]. The crystal structure of the acetonitrile solvate of 3 · 4MeCN, is also reported.