Bis-guanidinate magnesium amide-catalyzed hydroboration of nitriles and isocyanides via a substrate-assisted pathway

Abstract

The bis-guanidinate amido magnesium(II) compound [LMgN(SiMe₃)₂; L = {(ArHN)(ArN)–CN–C = (NAr)(NHAr)}; [Ar = 2,6-Et₂-C₆H₃] (Mg-1) has been employed as a pre-catalyst for the dihydroboration of nitriles, and as a catalyst for the dihydroboration of isocyanides, affording N,N-bis(boryl)amines and N,C-di(boryl)amines in good yields. The protocol introduces the first examples of nitrile and isocyanide reduction via a substrate-assisted pathway. The active catalyst for nitrile hydroboration, LMg-N(SiMe₃)₂·3-Me-C₆H₄CN (Mg-2), and the intermediate for isocyanide reduction, LMg-N(SiMe₃)₂·2,6-Me₂-C₆H₃NC (Mg-3), were isolated and thoroughly characterized by multinuclear NMR spectroscopy and single-crystal X-ray diffraction. Based on these findings, plausible mechanistic cycles for both nitrile and isocyanide dihydroboration reactions have been proposed.