Nucleophilic Alkaline Earth Boryls: From Conception and Theory to Application

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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.