Early transition metal complexes bearing a C-capped tris(phenolate) ligand incorporating a pendant imine arm: synthesis, structure, and ethylene polymerization behavior

The ligand 3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-(2,6-diisopropyl)phenylimine] (L1H3) was reacted with MCl4 (M = Ti, Zr) or MCl5 (M = Nb, Ta) to give complexes of the type [MCl2(L1H2)2] (M = Ti (1); Zr (2)), [NbCl3(L1H)] (3), or [TaCl4(L1H2)] (4), respectively. Single crystal X-ray diffraction of 1−4 revealed common “iminium” species resulting in zwitterionic complexes. Reaction of [V(Np-tol)(On-Pr)3] with L1H3 afforded [{(VNp-tol)(L1H)}2(µ-On-Pr)2] (5), and a second complex [(VO)2(µ-O)(L3H)2] (6) (L3H being derived from 3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-p-tolylimine]). The condensation reaction between 3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-butyl-2-hydroxybenzaldehyde] (L0H3) and o-phenylenediamine (1,2-diaminobenzene) afforded two products: a pseudo-16-membered hydrogen bonded macrocyclic structure {1,2-bis-3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-benzyldiimine]} (L5H6), or the benzimidazolyl bearing ligand (L6H3). The reaction of L5H6 or L6H3 with [VO(On-Pr)3] under varying conditions produced the complexes [(VO)(L5H4)] (7), [(VO)2(L5H)] (8), or [VO(L6H2)2] (9). L0H3 was reacted with a number of anilines to give the proligands {3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-R-imine]}, where R = NC6H5 (L2H3), NC6H4-Me (L3H3), and NC6H2-Me3 (L4H3). Reactions of these ligands with [VO(On-Pr)3] formed bischelating complexes of the form [(VO)(L2−4H2)2] (10, 11, and 12, respectively). The reaction of L1H3 with trimethylaluminum led to a bis-aluminum complex {(AlMe2)[AlMe(NCMe)]L1} (13). The ability of complexes 1−12 to polymerize ethylene in the presence of an organoaluminum cocatalyst was investigated. Procatalysts 1 and 2 were found to produce negligible activities in the presence of dimethylaluminum chloride (DMAC) and the reactivator ethyltrichloroacetate (ETA), whereas 3 and 4 were found to be completely inactive for polymerization using a variety of different organoaluminum cocatalysts. Using the combination of DMAC and ETA, complexes 5−12 were found to be highly active catalysts; in all cases, the polymer formed was of high molecular weight linear polyethylene.