SYNTHETIC, STRUCTURAL, MECHANISTIC, AND THEORETICAL MO STUDIES OF THEALKALI-METAL CHEMISTRY OF DIBENZYLAMINE AND ITS TRANSFORMATION TO 1,3-DIPHENYL-2-AZAALLYL DERIVATIVES

Dibenzylamido anions ((PhCH(2)N-) can be transformed into 1,3-diphenyl -2-azaallyl anions ({PhC(H)-N-C(H>Ph}(-)) by the assistance of PMDETA- ((Me(2)NCH(2)CH(2))(2)NMe) complexed Li+, Na+, or K+ cations. The hea vier alkali-metal cations give only the trans,trans conformation of th e azaallyl anion, in contrast to the lighter Li+ cation, which yields two crystalline conformers, the trans,trans and an unknown species, Ab initio MO geometry optimizations on model Li and Na complexes intimat e that it is the relative tightness of the contact ion pair structures which dictates this distinction with Li+ having more influence on the conformation and stability of the anion than Na+, which forms a much looser contact ion pair more akin to the ''free'' anion, On the basis of kinetic H-1 NMR studies, combined with X-ray crystallographic data, the amido --> azaallyl conversion can be explained in terms of a two- step process involving beta-elimiqation of a metal hydride followed by hydride metalation of the produced imine PhCH(2)N=C(H)Ph. This proces s appears to be initiated by deaggregation of the metallodibenzylamine to an intermediate monomeric structure, accomplished by solvation. Th e nature and degree of solvation required depend on the particular M() cation involved. Three new crystal structures are revealed in the co urse of this study. All are based on familiar four-membered (N-M)(2) r ings, but whereas the sodium complex [{(PhCH(2))(2)NNa.TMEDA}(2)] and the lithium complex [{(PhCH(2))(2)NLi.THF}(2)] are both discrete dimer s, unique [{[(PhCH(2))(2)NLi](2).(dioxane)}infinity], isolated as its toluene hemisolvate, is a polymer composed of linked dimeric units and so is the first dibenzylamido alkali-metal species to have an infinit ely extended structure.