Germanium-Carbon Versus Germanium-Nitrogen Double-Bond Formation in the Reactions Between Germylenes and Diazo Compounds

The reactions between methyl diazoacetate, HC(N-2)COOMe, and a range of germylenes L2Ge [L = CH3, NH2, OCH3, Ph, CH=CH2, SiH3, (H3Si)(2)N, and (H3Si)(2)CH] have been studied using MNDO calculations. Molecular and electronic structures have been determined for the transoid germaketimines L2Ge=N-N=C(H) COOMe [the primary 1: 1 adducts of L2Ge and HC(N2) COOMe], for their cyclic cisoid isomers L2Ge-N=N-C(H)=C(OMe)-O, and for the germaethenes L2Ge-C(H) COOMe. The intermediate L2GeCH(N-2) COOMe was found to dissociate smoothly along the unique GeC bond when L = NH2, OCH3, or (H3Si)(2)N (so leading to no net reaction) but to undergo facile loss of N-2, forming the germaethene L2Ge-C(H) COOMe, when L = CH3, Ph, CH=CH2, SiH3, or (H3Si)(2)CH. The calculations thus enable the prediction of substantially different patterns of reactivity, and hence different products, in the reactions between diazo compounds and the two closely similar germylenes [(Me3Si)(2)N](2)Ge and [(Me3Si)(2)CH](2)Ge.