SYNTHETIC, STRUCTURAL, SPECTROSCOPIC AND CALCULATIONAL STUDIES OF A LITHIUM BETA-DIKETINIMATE COMPLEX

Reaction of malonaldehyde bis(phenylimine) monohydrochloride with two equivalents of n-BuLi in the presence of hexamethylphosphoric triamide (HMPA) yielded crystals of [PhN(CH)(3)NPhLi . HMPA](2). The two LiN2C 3 metallacycles of the dimeric molecule are linked by two bridging oxy gens from HMPA. No spectroscopic evidence for dissociative or other eq uilibria was obtained. The lithium projects above the mean plane of th e metallacycles. MNDO calculations on model compounds reproduced bond lengths and angles well, except that all minima were planar, ascribing the envelope conformation to a packing effect. The molecule could bes t be described as a 1,5-diphenyl-1,5-diazapentadienyl lithium complex, the anion having contributions from diketinimato and two equivalent k eteneimine-ene-amido resonance forms. In contrast, the protonated liga nd exists in a localized keteneimine-ene-amine form only.