Facile Synthesis of Rh Anchored Uniform Spherical COF for One-Pot Tandem Reductive Amination of Aldehydes to Secondary Imines

Abstract

The development of transition metal-based heterogeneous catalysts for economical and efficient synthesis of secondary imines remains both desirable and challenging. Herein, for the first time, we present two kinds of Rh nanoparticle anchored uniform spherical COF heterogeneous catalysts with well-defined crystalline structures for the effective one-pot tandem reductive amination of aldehydes on a gram scale. This reaction is carried out using ammonia as a nitrogen source and hydrogen gas as the source of hydrogen, which is not only an atom-economical but also an environmentally friendly process for the selective production of secondary imines. In particular, in the presence of the betterdesigned Rh nanoparticles anchored COF2 catalyst, the starting material aldehydes could be fully converted (99% conversion), and 95% selectivity of N-benzylidene(phenyl)methanamine is obtained under mild reaction conditions (2 MPa of H 2 and 90 °C). Additionally, the Rh/COF2 catalyst is also applied to a variety of substituted aromatic aldehyde compounds, manifesting good yields in corresponding secondary imines. This work not only expands the COF family but also offers economical and effective access to acquire various aromatic amine targets, especially secondary imines.

Size-Tunable Carbon-Doped Ni Nanoparticles for Switchable Reductive Amination of Biomass-Derived Carbonyl Compounds to Primary Amines and Secondary Imines

“…Nitrogen-containing compounds represent a huge market portion in the organic chemical industry, − among which primary amines and secondary imines are key intermediates that have been widely used in the fields of food additives, pharmaceuticals, agrochemicals, lubricants, polymers, fine chemicals, and functional materials. − For the synthesis of primary amines, one of the most attractive approaches is the reductive amination of carbonyl compounds using NH 3 as the nitrogen source and H 2 as the reductant, which can be performed under relatively mild reaction conditions. − Particularly, the carbonyl compounds derived from biomass resources (e.g., furfural, 5-hydroxymethyl furfural, and 5-methyl furfural) allow for the production of primary amines in a sustainable and environmentally benign manner and open new opportunities for transforming renewable biomass into high-value-added nitrogen-containing compounds. 6 However, selective production of primary amines by this approach is very challenging because many side reactions often occur, e.g., reduction of carbonyl compounds to alcohols and overalkylation (condensation of carbonyl compounds with the obtained primary amines). − Especially when the carbonyl compounds contain the reduction-sensitive functional groups (e.g., halogens, aromatic rings, and heterocycles), many byproducts caused by overhydrogenation/hydrogenolysis are obtained, resulting in low yields of the target amines and high costs for purification. − Notably, the secondary imines can be synthesized by the side reaction of overalkylation during reductive aminations, − which, however, are easily overhydrogenated to form the secondary amines. − If the goal is to synthesize the secondary amines, an effective approach is hydrogen-transfer reductive amination of aldehydes with amines over Ni nanoparticles using isopropanol as the hydrogen source . Obviously, selective reductive amination of carbonyl compounds toward primary amines or secondary imines is still a substantial challenge due to the complex reaction networks (taking reductive amination of furfural as an example, , Scheme S1).…”

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

“…The Rh nanoparticle-loaded Rh/COF2 with 3.3 wt% Rh is capable of converting benzaldehyde to N-benzyl-1phenylmethanimine via a one-pot tandem reductive amination in ammonia methanol solution at 2 MPa H 2 with greater than 99% conversion and greater than 95% selectivity, as reported by Ma and co-workers in 2021. 350 3.5.4. Ruthenium-metalated COF catalysts.…”

Selectivity tunable iron nanoparticles from lignocellulosic components for the reductive amination of carbonyl compounds towards switchable products

“…The yields of secondary imines could be satisfactory in all of the above systems, but often required expensive amines, nitryl or nitrile as the starting materials that will inevitably impede the commercial application. On the contrary, Wang et al 14 prepared an Rh-anchored COF matrix by a modified impregnation method, which presents an ideal route to selectively produce secondary imines from benzaldehyde using ammonia as the nitrogen source; unfortunately, the unacceptable cost of noble metals is still the obstacle, let alone the complex procedure for Rh/COF catalysts. As a result, attentions were gradually switched to the simplified preparation of heterogeneous catalysts loaded with transition metals.…”