Preparation of silyl-terminated branched polyethylenes catalyzed by Brookhart's nickel diimine complex activated with hydrosilane/B(CF).

Brookhart's nickel α-diimine complex [(κ-,-BIAN)NiCl] (1) (where BIAN = {Ar-NAceN-Ar}, Ace = acenaphthen-1,2-diyl, and Ar = 2,6-(iPr)-CH) activated with a hydrosilane/B(CF) (SiHB) adduct forms a highly active catalytic system for ethylene polymerization. Under optimal conditions, the activity of the system depends on the nature of hydrosilane and decreases in the order RSiH > PhSiH > PhSiH. The decrease in system activity within the hydrosilane series is correlated with increasing formation of Ni(I) species. In addition to their activation effect, hydrosilanes act as efficient chain termination/chain transfer agents, with the Si/Ni ratio controlling the molecular weight of the resulting polyethylene (PE). The use of EtSiH generated elastomeric, highly branched polymers with a saturated chain-end, while systems using PhSiH and PhSiH led to branched end-functionalized PEs terminated with the hydrosilyl functionality ( br-PE-SiPhH or br-PE-SiPhH).