W. Leung, Kathleen S. M. Poon, T. Mak
Jul 23, 1996
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Journal
Organometallics
Abstract
Metalation of 3,3‘-dimethyl-2,2‘-bipyridine and its trimethylsilyl derivatives (2-RCH2C5H3N)2 (R = H, SiMe3) using appropriate stoichiometries of BunLi/tmeda yields the corresponding mono- and dilithiated compounds. Deprotonation was found to occur selectively at the α-methyl carbon, as established by quenching the lithiated compounds with Me3SiCl or D2O and analyzing the products by NMR spectroscopy. The C2 molecular structure of the dilithium compound [{2-CH(SiMe3)C5H3N}2{Li(tmeda)}2] (2a) has been determined by X-ray structure analysis, which shows that each lithium atom is C,N-chelated by the α-carbon atom and the nitrogen atom of the other pyridine ring within the molecule. The Li−Cα and the Li−Npyridyl distances are 2.274(10) and 2.046(9) A, respectively, and the torsion angle between the pyridine rings is 50.7°. In the lithiation of the gem-bis-silylated derivative 2-CH(SiMe3)2C5H3N-C5H3NCH3, the anionic species 2-CH(SiMe3)2C5H3N-C5H3NCH2 undergoes a 1,6-silyl migration to form the α,α‘-bis-silyla...