Preparation of silyl-terminated branched polyethylenes catalyzed by Brookhart's nickel diimine complex activated with hydrosilane/B(C 6 F 5 ) 3 .

Brookhart's nickel α-diimine complex [(κ 2 - N , N -BIAN)NiCl 2 ] (1) (where BIAN = {Ar-NAceN-Ar}, Ace = acenaphthen-1,2-diyl, and Ar = 2,6-(iPr) 2 -C 6 H 3 ) activated with a hydrosilane/B(C 6 F 5 ) 3 (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 R 3 SiH > Ph 2 SiH 2 > PhSiH 3 . 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 Et 3 SiH generated elastomeric, highly branched polymers with a saturated chain-end, while systems using Ph 2 SiH 2 and PhSiH 3 led to branched end-functionalized PEs terminated with the hydrosilyl functionality ( i.e. br-PE-SiPh 2 H or br-PE-SiPhH 2 ).