Abstract
Low-temperature and selective reductive amination of carbonyl compounds is a highly promising approach to access primary amines. However, it remains a great challenge to conduct this attractive route efficiently over earth-abundant metal-based catalysts. Herein, we designed several Co-based catalysts (denoted as Co@C-N(x), where x represents the pyrolysis temperature) by the pyrolysis of the metal-organic framework ZIF-67 at different temperatures. Very interestingly, the prepared Co@C-N(800) could efficiently catalyze the reductive amination of various aldehydes/ketones to synthesize the corresponding primary amines with high yields at 35 °C. Besides non-noble metal and mild temperature, the other unique advantage of the catalyst was that the substrates with different reduction-sensitive groups could be converted into primary amines selectively because the Co-based catalyst was not active for these groups at low temperature. Systematic analysis revealed that the catalyst was composed of graphene encapsulated Co nanoparticles and atomically dispersed Co-N (x) sites. The Co particles promoted the hydrogenation step, while the Co-N (x) sites acted as acidic sites to activate the intermediate (Schiff base). The synergistic effect of metallic Co particles and Co-N (x) sites is crucial for the excellent performance of the catalyst Co@C-N(800). To the best of our knowledge, this is the first study on efficient synthesis of primary amines via reductive amination of carbonyl compounds over earth-abundant metal-based catalysts at low temperature (35 °C).