Polypyrazolylborates: Scorpionates

Polypyrazolylborates, also known as scorpionates because of certain specific features of their coordination chemistry, are a large class of user-friendly ligands, capable of being fine-tuned through appropriate substitution on the pyrazolyl rings. They have had significant impact on many areas of coordination and organometallic chemistry. They were particularly useful in modeling a number of enzymes, involving numerous metals, not just in matching or approaching their spectroscopic features, but also exhibiting some of their catalytic activity. Key features of the ligands and examples of their use in modeling biologically active compounds are briefly presented. Recently, a number of analogous scorpionate ligands has been developed, which contain a tetrasubstituted borate anion, with soft donor functionalities on the substituents, such as thioethers or disubstituted phosphines. Some of them form six-membered rings when coordinated to a metal ion, and others form flexible eight-membered rings.