Tm ligands

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]

Ligand characteristics, comparison with Tp−

The TmMe anion is a tridentate, tripodal ligand topologically similar to the more common Tp ligands, but the 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]

References

  1. ↑ Mark D. Spicer, John Reglinski "Soft Scorpionate Ligands Based on Imidazole-2-thione Donors" European Journal of Inorganic Chemistry 2009, Issue 12, pp 1553–1574. doi:10.1002/ejic.200801240
  2. ↑ "Synthesis and Characterization of Novel Mononuclear Cadmium Thiolate Complexes in a Sulfur-Rich Environment" S. Bakbak, C. D. Incarvito, A. L. Rheingold, D. Rabinovich, Inorganic Chemistry, 2002, volume 41, p. 998. doi:10.1021/ic0109243
  3. ↑ "Polyazolyl Chelate Chemistry. 13. An Osmaboratrane" M. R. St. J. Foreman, A. F. Hill, A. J. P. White, and D. J. Williams Organometallics, 2004, volume 23, p. 913. doi:10.1021/om0306123. "The Sting of the Scorpion: A Metallaboratrane" A. F. Hill, G. R. Owen, A. J. P. White, and D. J. Williams Angew. Chem., Int. Ed. Engl., 1999, volume 38, p. 2759. doi:10.1002/(SICI)1521-3773(19990917)38:18<2759::AID-ANIE2759>3.0.CO;2-P