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

Abstract

Magnesium catalysis : A bis-guanidinate magnesium amido complex enables the first example of a substrate-assisted catalytic dihydroboration of nitriles and isocyanides, with the isolation of key intermediates and elucidation of catalytic cycles. The bis-guanidinate amido magnesium( ii ) compound [LMgN(SiMe 3 ) 2 ; L = {(ArHN)(ArN)–CN–C = (NAr)(NHAr)}; [Ar = 2,6-Et 2 -C 6 H 3 ] (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(SiMe 3 ) 2 ·3-Me-C 6 H 4 CN (Mg-2), and the intermediate for isocyanide reduction, LMg-N(SiMe 3 ) 2 ·2,6-Me 2 -C 6 H 3 NC (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.