om050242d_si_001.cif (31.04 kB)

Synthesis and Characterization of the New Alkyl Borates [RB(C6F5)3]- (R = CH2Me, CHMe2, CH2CMe3):  Utilization of [Me3CCH2B(C6F5)3]- as a Weakly Coordinating Counteranion during Zirconocene-Induced Catalysis of Propylene Polymerization

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posted on 06.06.2005, 00:00 by Neda Bavarian, Michael C. Baird
Reactions of alkyllithium compounds RLi (R = Me, Et, i-Pr, Np) with B(C6F5)3 result in the formation of the alkylborate salts Li[RB(C6F5)3]. Metathesis reactions of these with Ph3CCl and chloride salts of (Ph3P)2N+, PMePh3+, and HNMe2Ph+ proceed with varying degrees of success, as shown by NMR spectroscopy and electrospray mass spectrometry, and the compounds [PPN][EtB(C6F5)3], [PMePh3][NpB(C6F5)3], and [HNMe2Ph][NpB(C6F5)3] have been characterized crystallographically. All three anions assume the expected pseudotetrahedral structures with normal B−aryl bond lengths and R−B−aryl and aryl−B−aryl bond angles. The compound [HNMe2Ph][NpB(C6F5)3] reacts with Cp2ZrMe2, (Indenyl)2ZrMe2, and SBIZrMe2 to give propylene polymerization catalysts that are significantly more active and give higher molecular weight polypropylene than do the catalysts obtained using B(C6F5)3. Thus the [NpB(C6F5)3]- anion is for steric reasons more weakly coordinating than is [MeB(C6F5)3]-.