Earth-abundant transition metal catalysts for alkene hydrosilylation and hydroboration

The addition of X3Si–H or X2B–H (X = H, OR or R) across a C–C multiple bond is a well-established method for incorporating silane or borane groups, respectively, into hydrocarbon feedstocks. These hydrofunctionalization reactions are often mediated by transition metal catalysts, with precious metals being the most commonly used owing to the ability to optimize reaction scope, rates and selectivities. For example, platinum catalysts effect the hydrosilylation of alkenes with anti-Markovnikov selectivity and constitute an enabling technology in the multibillion dollar silicones industry. Increased emphasis on sustainable catalytic methods and on more economic processes has shifted the focus to catalysis with more earth-abundant transition metals, such as iron, cobalt and nickel. This Review describes the use of first-row transition metal complexes in catalytic alkene hydrosilylation and hydroboration. Defining advances in the field are covered, noting the chemistry that is unique to first-row transition metals and the design features that enable them to exhibit precious-metal-like reactivity. Other important features, such as catalyst activity and stability, are covered, as are practical considerations, such as cost and safety. Transition-metal-catalysed hydrosilylation and hydroboration reactions are valuable in the synthesis of commodity and fine chemicals, respectively. This Review describes the catalyst design principles that enable us to perform these reactions using catalysts based on earth-abundant metals. Scenarios in which using earth-abundant metals can offer an advantage over using a precious metal are also outlined.