Solid state structures of the chiral lithium amide complexes (S)-[(Ph(Me)CH)(PhCH2)NLi·thf]2 and (R)-[(Ph(Me)CH)(PhCH2)NLi·pmdta]

Abstract

Two chiral lithium amide complexes derived from α-(methylbenzyl)benzylamine have been synthesised and structurally characterised in the solid state by X-ray crystallography. Complexation of (S)-{[Ph(Me)CH][PhCH₂]NLi}_n with thf results in the dimer (S)-{[Ph(Me)CH][PhCH₂]NLi·thf}₂ (space group P4₃2₁2). The dimer is composed of a central four membered (NLi)₂ ring with the Ph(Me)C and Ph(CH₂) moieties adopting a cis orientation relative to the ring rather than the more usual trans. The reaction of (R)-{[Ph(Me)CH][PhCH₂]NLi}_n with the tridentate N donor, pmdta, (N,N,N′,N′,N′′-pentamethyldiethylenetriamine) results in the monomer (R)-{[Ph(Me)CH][PhCH₂]NLi·pmdta} (space group, P2₁). In both structures the amido moiety adopts a similar ‘butterfly-in-flight’ conformation. Heating either the solution or crystals of the monomer results in the loss of H₂ at the benzylic carbons and conversion to an aza-allyl structure, as evidenced by NMR.