Lithiation of 3,3‘-Dimethyl-2,2‘-bipyridine and Its Trimethylsilylated Compounds:  X-ray Crystal Structure of [{2-CH(SiMe₃)C₅H₃N}₂{Li(tmeda)}₂] (tmeda = N,N,N‘,N‘-Tetramethylethylenediamine)

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 C 2 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) Å, 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-C5H3NC̄H2 undergoes a 1,6-silyl migration to form the α,α‘-bis-silylated anionic species [2-C̄H(SiMe3)C5H3N−C5H3NCH2(SiMe3)].

Synthesis of Axially Asymmetric N-Functionalized Metal Dialkyls and Bimetallic Complexes: X-ray Structures of Me2M(L‘L‘) (M = Si, Sn; L‘L‘ = (CHSiMe3C5H3N)2) and Me2Sn(L‘L‘)W(CO)4

“…Elemental analyses were performed at MEDAC, Ltd., Department of Chemistry, Brunel University, Uxbridge. Dilithium reagent 1a and 1b were prepared as described in a previous paper …”

“…This is exemplified by the unstable seven-membered platinacycle [Pt{CH 2 (CH 2 ) 4 CH 2 }(PPh 3 ) 2 ], the instability is mainly due to the facile β-hydrogen elimination . Di-Grignard or dilithium reagents derived from (2-chloromethyl)biphenyl and 2,2‘-dimethylbiphenyl have been used as a source of dianion [2-CHRC 6 H 4 ) 2 ] 2- for the preparation of thermally stable metallacyclic derivatives of the type [ML n (2-CHRC 6 H 4 ) 2 ] (R = H or SiMe 3 ; M = Si, Sn, Ti, Zr, Hf, Nb, Ta, and W). − …”