LITHIO-DIAZOMETHANE AND LITHIO-(TRIMETHYLSILYL)DIAZOMETHANE - THEORETICAL AND EXPERIMENTAL STUDIES OF THEIR STRUCTURES, REACTIONS AND REACTION-PRODUCTS

The first report of a metalated diazomethane by Eugen Muller and his coworkers appeared in 1933. Then, in a thirty-six years ongoing story, 1-6 this group revealed highly interesting but also puzzling details about the chemistry of metalated diazomethane and metalated substituted diazomethanes: 1. Metalation of diazomethane 1a (the parent compound) to give the corresponding Li (or Na) species followed by protonation led to ''isodiazomethane'' which finally turned out to be N-isocyano amine 1c. Ab initio calculations of the structures and energies of the three non-cyclic CH2N2 isomers 1a-c and of the four non-cyclic lithiated diazomethane isomers 2-Li(I)-2-Li(IV), as well as their dimers, provide an understanding of this reaction sequence. 2. Metalation of mono-substituted diazomethanes RCHN(2), R = Ph, Me, Me(3)Si, e.g. by methyllithium, followed by protonation, resulted in a completely different observation, namely the formation of 4,5-bis-R-substituted 1,2,3-triazoles (e.g. 10) and methylamine 11. In the crystals of lithiated trimethylsilyl-diazomethane 13-Li, which allowed for the first time to determine the crystal structure of a lithiated (substituted) diazomethane, is also present the corresponding Li-triazole 14-Li ([6 13-Li . 2 14-Li . 6 Et(2)O . hexane]). Model calculations traced the pathway of the triazole formation via a nitrenoid (e.g. 9.Li) which is also responsible for the formation of methylamine 11. The completely different chemistry of diazomethane 1a and mono-substituted diazomethanes in the deprotonation-protonation sequence is due to the different structures of the corresponding Li(Na) species and their different reactivities (selectivities).