Polypyrazolylborates bidentate

Pyrazolate as a ligand can exhibit various coordination modes, inter alia, monodentate, exo-bidentate, and endo-bidentate. Several review articles have been published in the field.556-559 The use of pyrazole in the modeling of biological systems was also reviewed.560,561 The most common application of pyrazole ligands is to use its exo-bidentate coordination mode linking two metal centers that may be identical or different (compare Section 6.3.4.12.6). Polypyrazolylborates and related ligands are covered in the subsequent section. 

The bonding of polypyrazolylborates to metal is determined primarily by the number of pyrazolyl groups attached to boron. Dipyrazolylborates are necessarily bidentate, and they form with divalent transition metal ions complexes, 1, that are similar to -diketonates but that are always monomeric for steric reasons. The major difference between dipyrazolylborates and -diketonates is that the R2B(pz)2M ring is not planar but is puckered in the boat form as in Structure 2. This results in asym-... 

A good illustration of geometric and conformational stereoisomerism in bidentate polypyrazolylborate complexes is provided by the stable,... 

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