Reduction of N-Cyanomethyl Groups on a Macrocyclic Nickel(II) Complex Using Sodium Borohydride: Synthesis of a Complex Bearing Two N-(2-Aminoethyl) Pendant Arms

There has been a considerable interest in the preparation of various types of aliphatic and aromatic amines, since such compounds can be important chemicals in a variety of industries. Among the methods available for the synthesis of primary amines, reduction of nitriles has been utilized as a fundamental process. In general, however, this method requires relatively strong reducing agents, such as LiAlH4 and Raney nickel, or catalytic hydrogenation and often suffers from a number of drawbacks, such as high temperature or high pressure. Sodium borohydride (NaBH4), a relatively mild reducing agent, is known to be insufficient for the reduction of nitriles to amines, unless a strong Lewis acid or a catalyst is also used. However, some works show that nitriles can be reduced by NaBH4 when they are coordinated to a transition metal ion. For example, [Ru(MeCN)3(triars)] (triars = MeC(CH2AsPh2)3) reacts with NaBH4 in methanol to yield [RuH(MeCH2NH2)2(triars)]. Until now, examples of borohydride reduction of nitriles to amines are limited in number, and the roles of solvents and metal ion on the reaction have remained largely unexplored.