Inducing Cu Charge Redistribution by Modulating Proximity with Zr(OH)4 for Selective Synthesis of Imines and Secondary Amines with Stoichiometric Benzyl Alcohol and Nitrobenzene

Abstract

The one-pot synthesis of amines from benzyl alcohol (BA) and nitrobenzene (NB) represents a step-economic method. However, reported works typically require more than 3 equiv of BA to complete the transfer hydrogenation of NB, and few studies can achieve selective synthesis of imines and secondary amines. In our previous work, Zr(OH)₄ demonstrated both hydrogenation and dehydrogenation capabilities. Building on this, another component Cu was introduced to enhance its catalytic performance for catalyzing coupling reaction between stoichiometric BA and NB under a H₂ atmosphere. The physical hybrid catalyst Cu + Zr(OH)₄ selectively produced imines, while the supported catalyst Cu/Zr(OH)₄ yielded secondary amines. Characterization and mechanism experiments revealed that modulating the proximity between Cu and Zr(OH)₄ leads to (1) different adsorption abilities of the catalyst for N-benzylideneaniline (NBA) and (2) interactions between Zr(OH)₄ and Cu in close contact, which stabilized the electronic structure of Cu forming more Cu⁺/Cu⁰ ion pairs with strong H₂ activation ability. This work presents a catalyst design strategy and offers an approach for the selective preparation of N-benzylideneaniline and N-benzylaniline.