Zinc Hydride Catalyzed Chemoselective Hydroboration of Isocyanates: Amide Bond Formation and C=O Bond Cleavage

Herein, a remarkable conjugated bis‐guanidinate (CBG) supported zinc hydride, [{LZnH} 2 ; L={(ArHN)(ArN)−C=N−C=(NAr)(NHAr); Ar=2,6‐Et 2 ‐C 6 H 3 }] ( I ) catalyzed partial reduction of heteroallenes via hydroboration is reported. A large number of aryl and alkyl isocyanates, including electron‐donating and withdrawing groups, undergo reduction to obtain selectively N‐boryl formamide, bis(boryl) hemiaminal and N‐boryl methyl amine products. The compound I effectively catalyzes the chemoselective reduction of various isocyanates, in which the construction of the amide bond occurs. Isocyanates undergo a deoxygenation hydroboration reaction, in which the C=O bond cleaves, leading to N‐boryl methyl amines. Several functionalities such as nitro, cyano, halide, and alkene groups are well‐tolerated. Furthermore, a series of kinetic, control experiments and structurally characterized intermediates suggest that the zinc hydride species are responsible for all reduction steps and breaking the C=O bond.