New ligands for nickel catalysis from diverse pharmaceutical heterocycle libraries.

Ligands are essential for controlling the reactivity and selectivity of reactions catalysed by transition metals. Access to large phosphine ligand libraries has become an essential tool for the application of metal-catalysed reactions industrially, but these existing libraries are not well suited to new catalytic methods based on non-precious metals (for example, Ni, Cu and Fe). The development of the requisite nitrogen- and oxygen-based ligand libraries lags far behind that of the phosphines and the development of new libraries is anticipated to be time consuming. Here we show that this process can be dramatically accelerated by mining for new ligands in a typical pharmaceutical compound library that is rich in heterocycles. Using this approach, we were able to screen a structurally diverse set of compounds with minimal synthetic effort and identify several new ligand classes for nickel-catalysed cross-electrophile coupling. These new ligands gave improved yields for challenging cross-couplings of pharmaceutically relevant substrates compared with those of those of previously published ligands.