Ethylene Polymerization with Thermally Robust Vanadium(III) Tris(2-pyridyl)borate Complexes
Jin Qian, Robert J. Comito
Abstract
Despite the useful selectivity offered by vanadium catalysts for olefin polymerization, their implementation under practical conditions remains limited by poor productivity and thermal stability. This report describes phenyl tris(2-pyridyl)borate (Tpy – ) complexes of vanadium(III) that are amenable to ethylene polymerization at temperatures approaching industrial conditions (>100 °C). We developed metal tris(2-pyridyl)borate precursors TpyLi, TpyK, and TpyAg, which undergo smooth metathesis with VCl 3 (THF) 3 to provide solvated complexes TpyVCl 2 (DMF) and TpyVCl 2 (THF). In contrast, soft deprotonation of TpyH with triethylamine and VCl 3 (THF) 3 gave the anionic complex [TpyVCl 3 ][Et 3 NH], our optimal precatalyst. Thus, [TpyVCl 3 ][Et 3 NH] polymerizes ethylene with low dispersity (∼2) and a moderate molecular weight (∼350000) at temperatures up to 135 °C. This work advances the use of tris(2-pyridyl)borates, an emerging ligand class, in catalysis and provides a platform for vanadium catalysis in demanding applications.