Scorpionates: genesis, milestones, prognosis

doi:10.1016/j.poly.2003.11.013

Polyhedron

Volume 23, Issues 2–3, 22 January 2004, Pages 197-203

https://doi.org/10.1016/j.poly.2003.11.013 Get rights and content

Abstract

The development of the polypyrazolylborate/scorpionate ligand system is traced from its inception, through its early and later stages of development, primarily on the basis of the author’s experiences and contributions.

The development of the polypyrazolylborate/scorpionate ligand system is traced from its inception to the current state, based largely on the author’s experiences and contributions.

Introduction

Polypyrazolylborate/scorpionate chemistry is a very large, and still growing area. Since its inception until now, there have been about 2000 papers published on polypyrazolylborates, and complexes of seventy elements of the periodic table have been reported. A number of reviews of this area exist covering time-spans, or concentrating on certain elements, or unified by some other feature. However, in this article I would like to recount, on a personal basis, some background and little-known details, as to how this whole field came into being, focusing on my personal experiences and contributions.

Section snippets

History

When I joined the Du Pont company at the end of 1959, this was still the heady time of cyanocarbon research, and my initial assignment was to prepare the first percyanoalkane, which I did, synthesizing hexacyanoethane [1]. Shortly thereafter, I developed the first practical synthesis of what was called “cyanoform” [2], and which actually turned out to be dicyanoketeneimine, rather than tricyanomethane [3]. This led to the synthesis of 4-cyanopyrazole, 1, my first direct experience with this

Earliest developments

It was in this search for something novel, that I decided to work on boron–pyrazole chemistry. What made me select this area? Around that time, Fred Hawthorne had published a communication on the reaction of triethylborane with acetylacetone, which yielded a rather stable compound, 4, in which the diethylboryl group had taken the place of the chelated hydrogen bridge [11]. In other words, the diethylboryl cation took on a metalloid role.

I thought that it would be rather interesting to explore

Hiatus and second generation of scorpionates

My work on polypyrazolylborates ended in 1973 when I was transferred from Central Research to other departments, working on olefin polymerization catalysis, market development and, finally, to the International Department: overseas, first to Geneva/Switzerland, then to Warsaw/Poland, as manager of the DuPont office. When the Russians invaded Afghanistan, the Du Pont manager of the Moscow office was pulled back to Warsaw, bumping me all the way to Parkersburg, West Virginia. This was a plant

Non-classical scorpionates

Although polypyrazolylborates are the oldest and classical examples of the scorpionate ligand system, related scorpionate ligands may be derived from them by replacement of either the central boron, or of pyrazole. A number of such examples have been covered [35], and new ones are appearing ever more frequently. Neutral ligands are best exemplified by geminal polypyrazolylalkanes, which were introduced back in 1970, [56] and are currently being studied in detail by Dan Reger.

In recent years a

Prognosis

So where do we go from here? As someone quipped: “predictions are difficult, especially about the future”. Nevertheless, I will venture a guess in what areas is further growth likely to occur. First of all, the “classical” polypyrazolylborates, while mature ligands, still have room for expansion, especially as heteroscoropionates, containing pyrazolyl arms with additional donor atoms, some of which are shown as homoscorpionates below.

The potential of ligands that can range from tridentate to

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Scorpionates: genesis, milestones, prognosis

Abstract

Introduction

Section snippets

History

Earliest developments

Hiatus and second generation of scorpionates

Non-classical scorpionates

Prognosis

Polyhedron

Inorg. Chim. Acta

J. Am. Chem. Soc.

J. Org. Chem.

J. Org. Chem.

J. Org. Chem.

J. Org. Chem.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Coord. Chem.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Chem. Phys.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

Inorg. Chem.

J. Am. Chem. Soc.

Inorg. Chem.

Acta. Crystallogr.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

Angew. Chem. Int. Ed. Engl.

J. Chem. Soc., Chem. Commun.

Inorg. Chem.

Scorpionates: The Coordination Chemistry of Polypyrazolylborate Ligands

Organometallics

J. Am. Chem. Soc.