Gallium Hydride‐Catalyzed Selective Hydroboration of Unsaturated Organic Substrates

Abstract

The first examples of tetrasubstituted conjugated bis‐guanidinate (CBG) supported monomeric and thermally stable gallium dihalides [LGaX2], (X= Cl (Ga‐Cl), I (Ga‐I)) and dihydride (Ga‐H) [LGaH2] (where L = {(ArHN)(ArN)‐C=N‐C=(NAr)(NHAr)}; Ar = 2,6‐Et2‐C6H3) compounds are reported. The reaction of in situ generated LLi with 1.0 equiv. GaX3 (X= Cl, I) afforded compounds Ga‐Cl and Ga‐I. The reaction between Ga‐Cl and Li[HBEt3] in benzene yielded the dihydride compound Ga‐H. All reported compounds (Ga‐Cl, Ga‐I, and Ga‐H) were characterized by NMR, HRMS, and single‐crystal X‐ray diffraction studies. Ga‐H was probed for the hydroboration of carbodiimides (CDI), isocyanates, and isothiocyanates with HBpin. Compound Ga‐H was also found effective for the catalytic hydroboration of imines, nitriles, alkynes, esters, and formates, affording the corresponding products in quantitative yields. Stoichiometric reactions with a CDI were performed to establish the catalytic cycle.