Axially asymmetric metal alkyls. Part 6. Lithiation of 2,2′-dimethyl-1,1′-binaphthyl and its trimethylsilylated compounds, and of 2,2′,6,6′-tetramethyl-1,1′-biphenyl (asymmetric induction): X-ray crystal structures of monomeric [{Li(Me2NCH2CH2NMe2)} 2{(2-CH2C10H6)2}].

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

Research output: Contribution to journalArticlepeer-review

44 Citations (Scopus)

Abstract


The compound [{Li(tmen)}2{(2-CH2C10H6) 2}], (6) (tmen = N,N,N′,N′-tetramethylenediamine), has been prepared via metallation, and structurally characterized using X-ray diffraction data. It is monomeric with two different lithium centres, one bridging the ipso-carbon atoms at 2.13(5) and 2.23(5) Å, the other interacting with one ipso-carbon at 2.36(5) Å and its adjacent ring carbon at 2.51(5) Å, such that one ipso carbon is bridging the lithium centres. 7Li N.m.r. data are consistent with this structure in toluene, below ca. -28 °C. Treatment of (6) with AsMe2I then Mel yielded the arsonium salt [(2-Me3AsCH2C10H6) 2]I2, and with SiMe3Cl it gave (2-Me3SiCH2C10H6)2. This afforded [2-(Me3Si)2CHC10H6]2 on treatment with LiBun(tmen) then SiMe3Cl. Metallation of 2,2′,6,6′-Tetramethyl-1,1′-biphenyl using LiBun(pmdien) (pmdien = N,N,N′,N′,N″-pentamethyldiethylenetriamine) in diethyl ether yielded a monolithiated species [{Li(pmdien)}{2-CH2-6-Me(C6H3) 2-2′,6′-Me2}] (13), also structurally characterized; the lithium centre is attached to only the ipso-carbon of the hydrocarbyl group at 2.14(2) Å. Treatment of the same biphenyl with LiBun(sp) [sp = (-)sparteine] in Et2O yielded a dilithiated species based on the asymmetrical chiral dianion, (2-CH2-6-MeC6H3)22-. The degree of asymmetric induction in the metallation step was estimated to be ca. 40% using a 1H n.m.r.-chiral lanthanide shift reagent technique on the diol (2-HOCH2CH2-6-MeC6H3)2, formed by carboxylation then esterification and reduction of the dilithiated species.

Original languageEnglish
Pages (from-to)2403-2409
Number of pages7
JournalJournal of the Chemical Society, Dalton Transactions
Issue number9
DOIs
Publication statusPublished - Sep 1988
Externally publishedYes

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