Metallated ketenimines: Deprotonation of N -isopropyl-diphenylketenimine and subsequent trapping reactions with electrophiles A theoretical and experimental study

Deprotonation of N -isopropyl-diphenylketenimim 1 maybe achieved by surplus strong organic base (2,2,6,6-tetramethylpiperidine, n-butyllithium, potassium tert. butylate in tert. butyhnethyl ether). The resulting organometallic suspension is investigalled by means of fWpingreactions using various eleetrophiles. From the structures of the trapping products obtained the intermediacy of a substituted 1-methyleno-2-azaallyl anion 9 and of a 3-azapentadienyl anion 10 is deduced. Thus, proton sources yield a mixture of the 2-azabutadiene 2 together with two dimenc products, the 3-azahexatriew 3 and the heterocyclus 4 . Methyl iodide leads to the formation of a cross-conjugated dimeric product 5. The 2-azabutadiene derivatives 6 and 7 are the trapping products using trimethylacetyl chloride or dimethyl disulfide, resp., as electrophiles, exiibiting multiple addition to intermediate substituted 3-azapentadienyl anion systems. Quantum chemical calculations (MNDO, PM3, ab initio -methods) are used for the prediction of the gas phase acidities of N -isopropyfformimine and N -isopropylketenimine as model systems; the structures obtained by complete geometry optimizations of the postulated monomeric anions and lithium compounds are discussed.