Poly borate complexes, group compounds

Properties of nickel poly(pyrazol-l-yl)borate complexes such as solubility, coordination geometry, etc., can be controlled by appropriate substituent groups on the pyrazol rings, in particular in the 3- and 5-positions. Typical complexes are those of octahedral C symmetry (192)°02-604 and tetrahedral species (193). In the former case, two different tris(pyrazolyl)borate ligands may be involved to give heteroleptic compounds.602,603 Substituents in the 5-position mainly provide protection of the BH group. Only few representative examples are discussed here. 

Table III111-114 contains the physical properties of several poly(pyrazo-lyl)borate complexes found in the literature. Group 2 poly(pyrazolyl)bor-ates are white monomeric complexes that exhibit some volatility. Ca [HB(pz)3]2, which appears to be one of the most volatile of the poly(pyrazolyl)borates, is reported to sublime at 160°C and 10 2 atm.113 The Ba[HB(3,5-Me2pz)3]2 compound is soluble in THF and hot toluene, and the M[HB(pz)3]2 compounds have good solubility in aromatic and chlorinated hydrocarbons. Ca[HB(3,5-Me2pz)3]2 and Sr[HB(3,5-Me2pz)3]2 are also soluble in aromatic and chlorinated hydrocarbons, but less so than their nonmethylated counterparts.114...

During the 40 years of poly(pyrazolyl)borate chemistry, complexes with group 9 metals have provided a particularly fertile area of research. Over 400 publications describe aspects ranging from the synthesis of homoleptic and heteroleptic coordination compounds to the application of complex organometallic molecules in catalysis, and the development of advanced specialist materials. 

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