Low-valent germanium and tin hydrides as catalysts for hydroboration, hydrodeoxygenation (HDO), and hydrodesulfurization (HDS) of heterocumulenes

Abstract

The low-valent germanium and tin hydrides, [LMH; L = {(ArHN)(ArN)-CN–C(NAr)(NHAr); Ar = 2,6-Et₂-C₆H₃}; M = Ge; (Ge-1), Sn (Sn-2)] bearing bis-guanidinato anions are employed as catalysts for chemoselective reduction of heterocumulenes via hydroboration reactions. This protocol demonstrates that a wide range of carbodiimides (CDI), isocyanates, isothiocyanates, and isoselenocyanates undergo partial reduction, yielding the corresponding N-boryl formamidine, N-boryl formamide, N-boryl thioformamide, and N-boryl selenoformamide products, respectively. Isocyanates and isothiocyanates are further converted into N-boryl methyl amines through hydrodeoxygenation (HDO) and hydrodesulfurization (HDS) reactions in the presence of catalyst Ge-1. Additionally, catalyst Sn-2 exhibits excellent inter and intra-molecular chemoselectivity over other functional groups. Based on stoichiometric experiments, a plausible catalytic cycle for chemoselective hydroboration of heterocumulenes is proposed.