one feature is changed) a great deal of organometallic chemistry has been done using Tp (and more recently Tm) as a co-ligand on the metal. The Tp, Tm, trithia-9-crown-3 (a sulfur version of a small crown ether) and cyclopentadienyl (Cp) ligands related ligands and form related complexes. These ligands donate the same number of electrons to the metal, and the donor atoms are arranged in a fac manner covering a face of a polyhedron. The Tp and Tm ligands are isolobal with the Cp ligands. For example, the Cp manganese tricarbonyl complex is a half sandwich compound, with one face of the Cp ligand binding to the metal atom. The tricarbonyl manganese complex of trithia-9-crown-3 has the three sulfur atoms binding to the metal atom in the same place as the Cp ligand and using the same sort of orbitals for the bonding. While the geometry of the Tp ligands do not allow the formation of simple borane complexes with the metals, the geometry of the Tm ligands (and sometimes their bidentate versions Bm) are such that with late transition metals such as osmium and platinum it is possible to turn the Tm ligand inside out to form a borane to which the metal forms a dative bond. Here is the manganese complex of Tm with (again three carbonyls). Tp class The tris(pyrazolyl)borate ligand is often known as Tp to many inorganic chemists - using different pyrazoles substituted in the 3,4, and 5 positions, a range of different ligands can be formed. In this article we will group all the trispyrazolylborates together. These compounds are usually synthesized by reacting pyrazole with alkali-metal borohydrides, such as sodium borohydride NaBH4, under reflux. H2 is evolved as the borohydride is sequentially converted first to pyrazolylborate [H3B(C3N2H3)], then to bis(pyrazolyl)borate [H2B(C3N2H3)2], and finally to tris(pyrazolyl)borate [HB(C3N2H3)3]. Bulky pyrazolyl borates can be prepared from 3,5-disubstituted pyrazoles, such as the dimethyl derivative. These bulky pyrazolyl borates have proven especially valuable in the preparation of catalysts and models for enzyme active sites. Utilizing scorpionate ligands in the syntheses of metal catalysts may allow simpler and more accurate methods to be developed. Ligands allow for good shielding of the bound metal while strong sigma bonds between the nitrogens and the metal stabilize the metal; these attributes help scorpionate compounds with creating highly symmetrical supramolecular silver complexes and olefin polymerization (with the compound hydrotris(pyrazolyl) borate Mn). Tm class By