Nickel-Catalyzed Hydrophosphonylation and Hydrogenation of Aromatic Nitriles Assisted by Lewis Acid

In this paper, we describe the catalytic hydrophosphonylation of several aromatic nitriles used to synthesize alpha-aminophosphonates (alpha-APs) using commercially available trialkyl phosphites (P(OR)(3), R=Et, iPr, Bu,) and simple and inexpensive nickel chloride (NiCl2.6H(2)O) as the catalytic precursor. The use of triethylborane (Et3B) as a Lewis acid (LA) was mandatory in order to successfully perform H-phosphite moiety incorporation at the CN bond of non-activated benzonitriles (BN) derivatives. Interestingly, when a highly activated BN such as 2,3,4,5,6-pentafluorobenzonitrile (BN-g) was employed, it was possible to perform the reaction in the absence of an LA using milder reaction conditions. Also, we found that using HP(O)(OiPr)(2) as a starting material afforded the aminobisphosphonate derivative with better selectivity than using the method involving P(OiPr)(3) as the initial reagent. Remarkably, when using HP(O)(OiPr)(2) with an excess of Et3B, the reaction's selectivity completely changed to yield N-benzyl- benzylimine (BBI) and 2,4,5-triphenylimidazole.