Stannylenes Bearing an Amino-Linked NHC Ligand as Efficient Catalysts for Hydroboration of Carbonyls and Imines.

We designed and synthesized a series of three-coordinated stannylenes featuring an amino-linked NHC ligand, specifically tailored for the hydroboration of carbonyl compounds and imines. To fine-tune the catalytic performance both sterically and electronically, various substituents (chloro, triflate, and bis(trimethylsilyl)amino groups) were introduced at the tin center, generating structurally diverse stannylenes. The molecular structures of these stannylenes were confirmed by multinuclear NMR spectroscopy and single-crystal X-ray diffraction analysis. The hydroboration of carbonyl compounds catalyzed by these stannylenes proceeded under mild reaction conditions, affording the corresponding boryl esters in excellent yields with high chemoselectivity. Notably, bis(trimethylsilyl)aminostannylene exhibited outstanding catalytic efficiency, enabling hydroboration with a minimal catalyst loading of 0.01 mol% for aldehydes and 0.1 mol% for ketones, and was tolerant of a wide range of substrates, including sterically hindered and electronically diverse carbonyl compounds. Furthermore, in the hydroboration of imines, the reaction proceeded efficiently with just 5 mol% catalyst, furnishing the corresponding borylamines in high yields. Based on stoichiometric experiments, we propose a plausible catalytic cycle for stannylene-mediated hydroboration.