Boron compounds are the workhorses of modern chemical synthesis, but almost all of them are made from boron that acts as an electron acceptor—a limitation that locks chemists out of entire classes of potentially useful molecules. This project aims to break that limitation. The researchers have discovered that bonding boron to magnesium or calcium—elements from a different part of the periodic table—flips boron’s behaviour, making it a potent electron donor instead. That opens the door to synthesising boron-containing molecules that have never been made before. Magnesium and calcium are also cheap, abundant, and non-toxic, which makes the approach practical at scale. If successful, the team plans to make these new reagents commercially available as off-the-shelf chemicals. That could give synthetic chemists—especially those developing pharmaceuticals, electronic materials, and chemical sensors—a fundamentally new set of building blocks. The work is fundamental chemistry, driven by a gap in synthetic capability rather than a specific product. But past breakthroughs in boron chemistry have already earned two Nobel prizes; this one could quietly expand what chemists can build.
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Some of the greatest benefits to human health and well-being have been provided by modern methods of chemical synthesis. Boron compounds provide some of the most widely used reagents in chemistry and are employed in myriad syntheses of pharmaceutical and other high value molecules (e.g. with uses in electronic materials and chemical sensing). Organoborane, boronate ester and boronic acid derivatives, thus, provide some of the most practically useful intermediates in synthetic and medicinal chemistry, to the extent that the application of boron in organic synthesis has been recognised by the award of two Nobel prizes (Brown in 1979 and Suzuki in 2010). Despite these advances, almost all of these compounds are synthesised from starting materials in which boron acts as an electron acceptor (electrophile). This is a natural consequence of boron's position at the top of group 13 in the periodic table and presents a severe limitation to the types and variety of boron compounds that can be made. In this project we will build on our recent discovery (Nature Commun. 2017, 8, 15022) that derivatives in which boron is bonded to a less electronegative group 2 element, magnesium, are easily generated by activation of the B-B bonds of commercially available diboranes. In contrast to the vast majority of available boron reagents, the boron in these compounds reacts as a potent electron donor (nucleophile), providing the potential to allow the synthesis of a wide variety of new boron-containing molecules. In this project, we will apply a multifaceted inorganic/organic synthetic and computational approach to devise, understand and apply a wide array of new and highly reactive boron derivatives of the group 2 metals, primarily magnesium and calcium. The attractiveness of these latter elements is underscored by their negligible toxicity, high natural abundance and resultant low cost. Furthermore, the boron nucleophiles developed in this project will be used in the synthesis of a plethora of unprecedented and previously inaccessible organic and inorganic boron-containing compounds. Our ultimate objective is to ensure that these reagents are available from commercial chemical suppliers and nothing short of establishing previously inaccessible boron nucleophiles as off-the-shelf reagents in the synthetic chemist's larder.
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