Selective Reductive Amination of 5-Hydroxymethylfurfural under Hypobaric H2 by a Durable Carbon-Coated Magnetic Ni Catalyst

The synthesis of primary amines from renewable biobased carbonyl compounds via reductive amination has received much attention. Modifying the surface structure of a heterogeneous catalyst may offer prospects to address selectivity maneuvering in this complex amination process. In this work, a metal–organic framework (MOF)-derived carbon-coated strategy was adopted to prepare the Ni@C catalysts with different thicknesses of carbon shells. This type of Ni catalyst achieved 98% yield of (5-(aminomethyl)furan-2-yl)methanol (AMF) at 100 °C under 2 bar of H 2 from reductive amination of 5-hydroxymethylfurfural (HMF, an important cellulose-derived platform molecule) with NH 3 ·H 2 O. In comparison, a Ni-NiO catalyst obtained by reducing NiO with H 2 would mainly overhydrogenate AMF to (5-(aminomethyl)tetrahydrofuran-2-yl)methanol (THAMF, 52% in yield) as a byproduct. The modification of the electronic structure of Ni 0 active sites with a carbon shell was elucidated, demonstrating electron-rich Ni 0 sites for H 2 activation. Moreover, different HMF adsorption modes on Ni-NiO and Ni@C surfaces were illustrated, significantly affecting the product distribution. Subsequently, distinctive NH 3 ·H 2 O activation processes were proposed for both Ni catalysts to understand selective conversion of the Schiff base (i.e., the critical reaction intermediate). The developed Ni@C catalyst with suitable carbon thickness, abundant Ni 0 centers, and defective carbon species showed high AMF yield under mild reaction conditions, facile separation–regeneration, and satisfying reusability. In addition, this Ni catalyst can also provide a relatively good substrate scope toward bioamine synthesis via reductive amination.