BIFUNCTIONAL LEWIS-ACIDS - SYNTHESIS AND OLEFIN POLYMERIZATION CHEMISTRY OF THE 1,1-DI[BIS(PERFLUOROLPHENYL)BORYL]ALKENES RCH=C[B(C6F5)(2)](2) (R = T-BU, C6H5, C6F5)

The synthesis and characterization, including crystallographic analysi s, of the bifunctional boranes RCH = C[B(C6F5)(2)](2) (R = t-C4H9; 1a; C6H5, 1b; C6F5, 1c) by regioselective hydroboration of the correspond ing 1-boraalkynes using HB(C6F5)(2) are reported herein. Compounds 1a and 1b have been screened as cocatalysts for ethylene polymerization i n the presence of Cp2ZrMe2 (3) under a variety of conditions. NMR spec troscopic Studies indicate that Cp2Zr[eta(2)-(BuC)-C-t=CB(C6F5)(2)] (4 a), Cp2ZrMe(C6F5), the organoborane Me2BC6F5, and methane gas are the final products formed from reaction of 1a with 3 in toluene solution a t room temperature. The stoichiometric mechanism for this transformati on has been elucidated through variable-temperature NMR, studies. Comp lex iia and MeB(C6F5)(2) (7) were prepared independently and screened as ethylene polymerization catalysts and cocatalysts, respectively. Co mpound 4a is inactive for ethylene polymerization, either alone or in the presence of additional 1a. However, the combination of Cp2ZrMe2 an d 7 gives rise to the species [Cp2ZrMe](+)[Me2B(C6F5)(2)](-) (8), whic h although unstable at room temperature in solution (decomposing over a period of 60 min to give Cp2ZrMe(C6F5) and the organoborane Me2BC6F5 ), is active for ethylene polymerization, From a comparison of activit y and MW data, it is concluded that the putative ion pairs formed from 1a (or 1b) and 3 lack sufficient thermal stability at conventional po lymerization temperatures and that the polymerization activity observe d can be interpreted as arising from species 8.