TmMe is the abbreviation for anionic tridentate ligand used in coordination chemistry. TmMe is an example of scorpionate ligand. The sodium salt of this anion is prepared by the reaction of molten methimazole (1-methylimidazole-2-thione) with sodium borohydride. Salts of the TmMe anion are known also for lithium and potassium, and a variety of organic substituents are known in place of the methyl group, the class being abbreviated TmR anions (R = alkyl, aryl).[1]
The TmMe anion is a tridentate, tripodal ligand topologically similar the more common Tp ligands, but two two classes of ligands differ in several ways. TmMe has three "soft" sulfur donor atoms, whereas Tp- has three nitrogen donor atoms. The thioamide sulfur is highly basic, as found for other thioureas. The TmR anion simulates the environment provided by three facial thiolate ligands but without the 3- charge of a facial trithiolate.[2]
The large 8-membered SCNBNCSM chelate rings in M(TmMe) complexes are more flexible than the 6-membered CNBNCM rings in M(Tp) complexes. This flexibility enables the formation of boron-metal bonds, after loss of the B-H bond. This degradation of the coordinated TmMe anion gives a dehydrogenated boranamide B(mt)3 where mt = methimazolate.[3]