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Chemoselectivity Diversity in the Reaction of LiNC6F5SiMe3 with Nitriles and the Synthesis, Structure, and Reactivity of Zirconium Mono- and Tris[2-(2-pyridyl)tetrafluorobenzimidazolate] Complexes

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journal contribution
posted on 18.10.2010, 00:00 by Sinai Aharonovich, Mark Botoshansky, Robert M. Waymouth, Moris S. Eisen
Unlike the reaction of LiNTMS2·TMEDA (TMS = SiMe3; TMEDA = tetramethylethylenediamine) with 2-cyanopyridine, which results in the nearly exclusive formation of the amidinate, (Me3SiNC6F5)Li·TMEDA (1) reacts with 2-cyanopyridine in toluene to yield quantitatively the lithium pyridyltetrafluorobenzimidazolate complex [C6F4N2C(2-C5H4N)]Li·TMEDA (3). In this work, the reactivity of complex 1 toward aromatic nitriles Ar−CN (Ar = Ph, o-OMeC6H4, C6F5, 2-pyridyl) was examined. Whereas complex 1 fails to react with o-methoxybenzonitrile, its reaction with benzonitrile or pentafluorobenzonitrile gives triphenyl-1,3,5-triazine (4) or the hexacoordinate lithium polymer [LiN(4-NCC6F4)(C6F5)·THF·TMEDA]n (7), respectively. When 1 is reacted with 2-cyanopyridine in tetrahydrofuran (THF), the benzimidazolate coordination polymer {[C6F4N2C(2-C5H4N)]Li·THF}n (5) is obtained. Herein we discuss how this diverse chemoselectivity in the reaction of the examined lithium N-silylated amides LiNRTMS·TMEDA (R = TMS, C6F5) with nitriles is influenced by the electronic properties of the nitrile or amide substituents and by the ability of these substituents to interact with the lithium or silicon atoms. Further, we present the syntheses and structures of zirconium tris(pyridyltetrafluorobenzimidazolate) chloride (10) and zirconium bis(dimethylamido)(pyridyltetrafluorobenzimidazolate) chloride·THF (11) complexes. These complexes, the first prepared zirconium mono- and tris(benzimidazolate)s, were crystallographically characterized and examined in the polymerization of propylene with methyl aluminoxane (1:1000 Zr/Al molar ratio).