Catalytic ester hydroboration promoted by actinide complexes featuring six-membered N-heterocyclic imine ligands and actinide-alkoxides activation

In the last decade, organoactinide complexes have been active catalysts for the hydroboration of carbonyl moieties, including aldehydes, ketones, amides, isocyanides, and carbonates. The decoration of the metal center by 5, 6, or 7-N-heterocyclic imines increases the electron density at the metal, allowing for remarkable catalytic performances. We report herein the synthesis of a family of thorium and uranium complexes featuring an analogous set of N-heterocyclic iminato ligands built upon a six-membered core ligand framework. The catalytic ability of these complexes was tested in the ester hydroboration reaction, aromatic, aliphatic, and polymeric esters. The reaction was thoroughly investigated, exhibiting an induction period, which was overcome by manipulating the spectator ligands around the metal. Kinetic and thermodynamic studies were conducted to establish the rate law for the reaction and derive the corresponding activation parameters. Deuterium labeling and stoichiometric reactions were performed, and plausible mechanisms were proposed based on the observations.