A Robust Zintl Cluster for the Catalytic Reduction of Pyridines, Imines and Nitriles

Despite p-block clusters being known for over a century, their application as catalysts to mediate organic transformations is underexplored. Here, the boron functionalized [P ₇] cluster [(BBN)P ₇] ²⁻ ([1] ²⁻; BBN = 9-borabicyclo[3.3.1]nonane) is applied in the dearomatized reduction of pyridines, as well as the hydroboration of imines and nitriles. These transformations afford amine products, which are important precursors to pharmaceuticals, agrochemicals, and polymers. Catalyst [1] ²⁻ has high stability in these reductions: recycling nine times in quinoline hydroboration led to virtually no loss in catalyst performance. The catalyst can also be recycled between two different organic transformations, again with no loss in catalyst competency. The mechanism for pyridine reduction was probed experimentally using variable time normalization analysis, and computationally using density functional theory. This work demonstrates that Zintl clusters can mediate the reduction of nitrogen containing substrates in a transition metal-free manner.