Trispyrazolylborate

The Tp ligands are usually prepared from the reaction of pyrazole with potassium borohydride:[3] Intermediates include the monopyrazolylborate ([H3B(C3N2H3)]−) and the bispyrazolylborate ([H2B(C3N2H3)2]−).

Illustrative of the synthetic routes to TpR− complexes, MnBr(CO)5 and KTp react as follows: Electronically related compounds are known, such as CpMn(CO)3 and [(9-ane-S3)Mn(CO)3]+.

The labile acetonitrile complex Mo(CO)3(MeCN)3 reacts with KTp to give the anion [MoTp(CO)3]−, which can be crystallised as its tetraethylammonium salt (see figure): Protonation, allylation, and nitrosylation of this salt gives the corresponding neutral hydride, allyl, and nitrosyl (see figure) derivatives.

In bioinorganic chemistry, some of the first crystallizable copper dioxygen complexes were obtained using this ligand platform, including examples of the Cu2(μ-η2,η2-O2) bonding mode.

Models for hemerythrin, an enzyme with a diiron active site, and xanthine oxidase, a molybdoenzyme, have been examined.

Idealized structure of a Tp ligand bound to a metal center ML n
Two of several resonance structures of trispyrazolylborate
Structure of the piano stool complex Tp Bn,Me Mo(CO) 2 NO.
Structure of the anionic piano stool complex [Tp Me Mo(CO) 3 ] − together with the counterion [NEt 4 ] + .