The Reaction of Diazomethane Derivatives with the Dielement Compounds R2Al-AlR2 and R2Ga-GaR2 [R = CH (SiMe3)2] - Insertion versus Fragmentation

Tetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 reacted with trimethylsilyldiazomethane and bis(trimethylsilyl)diazomethane at room temperature by the insertion of the terminal nitrogen atoms into its aluminium-aluminium bond. As shown by a crystal structure determination, one of the aluminium atoms of each product enhanced its coordination number to four by the interaction with the central nitrogen atom of the C=N-N group, which results in the formation of a three-membered AlN2 heterocycle bearing an exocyclic N=C double bond. The reactions of the corresponding gallium compound (2) containing a gallium-gallium single bond needed more drastic conditions. Mixtures of many unknown products were formed, and only on treatment with trimethylsilyldiazomethane two compounds could be isolated after repeated recrystallization in yields below 10%, which were characterized by crystal structure determinations. One was identified as the trimeric dialkylgallium cyanide (8) with a nine-membered Ga3C3N3 heterocycle, and the other one (9) has a dialkylgallium fragment coordinated by both terminal nitrogen atoms of the chelating ligand NH2-N=C(SiMe3)-NH-. Due to the NMR spectroscopic characterization, 8 seems to be tetrameric in solution with an asymmetric structure containing four different gallium atoms. With this unusual structure, the IR spectrum of tetrameric dimethylgallium cyanide could now completely be interpreted, which was published more than 20 years ago.