Selective C-O Cleavage and C=O Deoxygenation of Carbamates and Polyurethane Catalyzed by Organoactinide Complexes.

Abstract

The remarkable ability of actinide complexes to activate carbamates is presented in this study, exemplified by the carbamate hydroboration using various Th and U complexes. The activation mode involves the selective catalytic cleavage of the C-O bond and the deoxygenation of the double C=O bond, utilizing pinacolborane (HBpin) as a hydride source. The broad scope of the organoactinides allows us to perform the activation reaction with diverse structural and functional carbamates, offering a flexible strategy for the synthesis of complex amines and amino alcohols. For example, the synthesis of (-) ephedrine and other bioactive analog molecules was achieved in a one-pot, two-step reaction utilizing commercially available carbamate derivatives, including multigram-scale reactions. Additionally, the capability of actinide catalysts to facilitate late-stage modifications of drugs has been extensively studied, and various pharmaceutical compounds have been examined. Notably, we also present the homogeneous catalytic depolymerization of a polyurethane polymer, recycling it to its valuable diamine [Me-N(H)-R-N(H)-Me] through hydroboration followed by hydrolysis. The use of an organic-f-lanthanide compound is also presented as a comparison to the actinides to show their industrial applicability. To understand the reactivity of the actinide complexes, stoichiometric reactions, together with kinetic experiments, thermodynamic measurements, and deuterium labeling studies were performed, allowing us to propose a mechanistic pathway. Computational DFT calculations further substantiate the proposed mechanism.