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]

Two chiral lithium amide complexes derived from alpha-(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 the results in the dimer (S)-{[Ph(Me)CH][PhCH2]NLi . thf}(2) (space group P4(3)2(1)2). 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, P2(1)). 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 H-2 at the benzylic carbons and conversion to an aza-allyl structure, as evidenced by NMR.