Polypyrazolyl-borates

Ligands of polypyrazolyl-borates (scorpionates) 232 and 233 (E = B) [437-442] are the focus of great interest in modern coordination chemistry ... 

A recent review [440], published 100 years after Werner s coordination theory was first presented, was dedicated to the complex compounds obtained on the basis of polypyrazolyl-borates or scorpionates. Complexes of this kind, an example of which is presented by structure 234, have been obtained with practically all p, /-elements and they can be examined as N-containing analogoues (MN4 coordination unit) of p-diketonates 2 (M04 coordination unit) ... 

Among the coordination compounds obtained on the basis of polypyrazolyl-borates, it is worth emphasizing the copper chelates 235 which are still the only biomimetic model of blue copper proteins, reproducing all their physical (UV-and EPR-spectral) properties [441,446-448], Compound 236 [449] is also an example of complexes of this kind of system ... 

I am very fortunate to have met, interacted with and befriended Jerry Trofimenko. His clever invention, the polypyrazolyl borate ligands have made a major impact on my scientific career and his friendship has enriched my personal life. Jerry will be greatly missed, but his legacy will live forever in the many old, and new disciples of the scorpionates. 

In contrast to the cobalt complexes, on treatment with potassium polypyrazolyl-borates (see below, p. 332), RpFe(CO)4l (Rf = CaFs, i-CsFy) gives only decomposition products." However, n-C3F7 Fe(CO)4l and potassium bispyrazolylborate gives a 63 % yield of the facial (ca. 30%) and meridional (ca. 70%) isomers (23) and... 

Given these correlations, it seems that it should be possible to predictably turn on or off the stereochemical activity of the lead lone pair. To test this idea, Reger and co-workers prepared a series of lead complexes of polypyr-azolyl borate and polypyrazolyl methane ligands in which the number of donor atoms and the size of the ligand was systematically varied (177, 180, 183, 208). For a constant coordination number (6), only the bulkier hgand is holodirected (Fig. 12). This observation is consistent with the idea that the natural (i.e., energetically favored) state for Pb(ll) compounds is one in which the 6s and 6p orbitals are hybridized and the lone pair is stereochemically active, but that sufficient steric repulsion can overcome this effect and make the holodirected structure more stable. 

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