Crystalline alkyl-lithiums from α-trimethylsilyl-substituted o-xylenes; X-ray crystal structure of [{o-C6H4(CHSiMe3)2}{Li(tmeda)}2](tmedaMe2NCH2CH2NMe2)

Abstract

Reaction of [o-C₆H₄(CHRR′)(CHR″R‴)](R,R′,R″,R‴H or SiMe₃) With LiBuⁿ in n-hexane in the presence of Me₂NCH₂CH₂NMe₂(tmeda) or MeN (CH₂CH₂NMe₂)₂(pmdeta) results in selective lithiation of the α-carbon in a manner dependent on the nature of the associated substituents and the tertiary amine to afford novel crystalline lithium alkyls; a single-crystal X-ray structure determination of [{o-C₆H₄(CHSiMe₃)₂}{Li(tmeda)}₂] shows each lithium to interact with both the α-and adjacent ring carbon atoms from opposite sides of the o-xylidene plane.