Singular Metal Activation of Diboron Compounds

Abstract

Abstract Organoboron compounds are part of many synthetic routes and target compounds for bio- and medicinal applications. One origin for their preparation was by means of direct interaction between Cl 2 B–BCl 2 and unsaturated organic compounds, but progress toward simple and convenient diboron reagents put tetra(alkoxy)diborons in the spotlight. The less reactive B B bond in tetra(alkoxy)diborons requires transition metal complexes to activate the diboron and transfer the boryl units to unsaturated substrates. Importantly, the mode of activation differs from the metal involved and is also influenced by the ligands modifying the metal center. Oxidative addition and σ-bond metathesis are the most representative modes of activation, and metal complexes become catalytic systems by completing the substrate transformation into the desired organoboron compound. Selectivity is a fundamental issue in the activation and precise delivery of the boryl moiety to the unsaturated substrate. Particularly, asymmetric induction is accomplished by the enantioselective influence of the chiral ligands around the metal centers. Even nanoparticles are known to activate diboron reagents and provide chemoselective diboration processes. The power of diboron reagents in organoboron synthesis is pushing the search of new activation modes, and nowadays, the sole presence of Lewis bases can also play a definitive role to generate Lewis acid–base adducts that directly interact with unsaturated substrates in a fashionable way. Each situation requires the use of the appropriate mode of activation of diboron reagents, and here we collect these singular metal activation modes and analyze their advantages and limitations.