Axially asymmetric metal alkyls. Part 1. Lithium alkyls of 2,2′-dimethylbiphenyl and its trimethylsilylmethylated compounds: Crystal structures of [{Li(Me2NCH2CH2NMe2)} 2{(2-CHRC6H4)2}] for R = H (polymeric) and R = SiMe3 (monomeric)

Lutz M. Engelhardt, Wing Por Leung, Colin L. Raston, Paul Twiss, Allan H. White

Research output: Contribution to journalArticle

43 Citations (Scopus)

Abstract

Metallation of (2-CH2RC6H4)2, with excess Li(tmen)Bun (tmen = NNN′N′-tetramethylethylenediamine) yields the crystalline compounds [{Li(tmen)}2{(2-CHRC6H4)2}][R = H (7) or SiMe3 (9)] whereas for 2-methyl-2′-trimethylsilylmethylbiphenyl, although selectivity is maintained, the crystalline product is a monolithiated species. This difference has been rationalised on the basis of the results of the crystal structure determination of the lithium complexes (7) and (9). The structure of (7) is polymeric (cf. dimeric in benzene by ebullioscopy) with a 'metallacycle' lithium and a lithium bridging methylene groups of different 'metallacycles' (electron-deficient bonding): Li-C (mean) 2.30 Å; Li-C-Li (mean) 159.5, C-Li-C (mean) 106.5°. Compound (9) is best described as a 'contact ion-pair' structure; Li-C(H)SiMe3 contacts, 2.22(1) and 2.19(2) Å. Lithiation of 2-[bis(trimethylsilyl)methyl]-2′-methylbiphenyl results in the formation of (9), via an anionic 1,6-silyl migration.

Original languageEnglish
Pages (from-to)321-330
Number of pages10
JournalJournal of the Chemical Society, Dalton Transactions
Issue number3
DOIs
Publication statusPublished - Mar 1984
Externally publishedYes

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