Magnesium–Ligand Cooperation in Breaking the O–H and C–H Bonds of Water and Diazoalkane

In our previous paper, we reported that the reaction of a tridentate nacnac ligand with a pendant picolyl group, with KHMDS and MgI 2, resulted in the formation of a homoleptic hexacoordinate magnesium compound. Here, we show that the analogous reaction of the ligand with CH 3 MgBr led to a heteroleptic magnesium bromide species ( 1 ). Attempts to generate the magnesium hydride species from 1 led to the dearomatization of the pyridine ring, and the resulting product was a magnesium hydroxide ( 3 ) presumably generated due to an adventitious amount of water. The reaction of the ligand with n Bu 2 Mg afforded a unique dearomatized magnesium species ( 2 ) in high yield. Theoretical calculations reveal the presence of a nonbonding orbital on the magnesium, susceptible to nucleophilic attack. Indeed, the reaction of 2 with H 2 O/D 2 O cleaves the O–H/D bond via magnesium–ligand cooperation and generates a magnesium hydroxide ( 4 and 5 ). In addition, 2 reacts with Me 3 SiCHN 2 and cleaves the C–H bond to generate another unusual, well-defined magnesium compound with a bridging isocyanide moiety ( 6 ) via migration of the SiMe 3 group from the carbon to the nitrogen atom. The latter can be described as a dimer of magnesium isocyanamide. DFT calculations were performed to understand the electronic structures of the synthesized molecules.