Against All Odds, Uranium and Thorium Iminato Complexes Enable the Cleavage of CO Bonds in Isocyanates

The catalytic activity of actinide-based catalysts is presented herein for the hydroboration and deoxygenation of isocyanates with pinacolborane (HBpin). A modified class of ligand systems possessing a five-membered ring core constructing the N-heterocyclic iminato moiety is introduced. All actinide complexes showed very good catalytic activities under mild conditions, with low catalyst loadings achieving almost quantitative yields. A wide number of isocyanates were studied including aliphatic isocyanates, aromatic isocyanates, and diisocyanates yielding to the corresponding borylated N-methyl amines and the borylated formamides, which are easily hydrolyzed toward the free amines and formamides. These organoactinide catalysts exhibited a great functional group tolerance toward methoxy, amido, and halides. The reaction selectivity was thoroughly investigated and exhibited a very good selectivity toward the isocyanate functionality having double or triple unsaturated C–C bonds. Kinetic studies were performed in order to establish the rate order dependency on the concentrations of the organoactinide complex, HBpin, and isocyanate. A proposed mechanism is presented based on experiments affording a more comprehensive understanding of the experimental activity trends and reinforced by the stoichiometric reaction studies, thermodynamic measurements, deuterium-labeling experiments, and theoretical DFT calculations.