Transition metals-catalyzed amination of biomass feedstocks for sustainable construction of N-heterocycles

Transition metals, which are of diversity in their bonding orbitals, have a variety of significant oxidation states and more complex chemical properties compared to the main group metals. Of particular importance, development of transition metals-mediated catalysis with high activity and stability is a challenging and prospective research hotspot. On the other hand, since the high dependence on petroleum-based raw materials has shown an indelible impact on the environment, it is imminent for the entire society to develop green, renewable, and sustainable energy to achieve the vital goal of reducing carbon emissions. Renewable biomass, the most suitable alternative of organic carbon sources to replace fossil resources, is believed to produce chemicals that can include almost all fossil-based products. The consolidation of biomass and its derived molecules into industrial production can, in principle, enable the sustainable synthesis of high-value-added products such as organonitrogen compounds of N-heterocycles having extensive applications. Importantly, transition metals have partially filled or empty d orbitals, which confer them a distinct catalytic selectivity and superior stability over the main group metals in terms of catalysts preparation like metal–organic frameworks (MOFs), organometallic complexes, and single atoms, especially for sustainable construction of N-heterocycles from biomass feedstocks. This review focuses on the research progress on transition metals catalysis for promoting the selective synthesis of various classes of N-heterocycles by using biomass and its derivatives as substrates or intermediates. The development of transition metals-based heterogeneous and homogeneous catalytic systems and their advantages are highlighted through typical C−N bond-forming coupling reactions. Moreover, the synthesis of N-heterocycles mediated by transition metals-based catalysts is discussed in detail from the perspectives of catalytic modes (thermocatalysis, photocatalysis, and electrocatalysis), catalyst design strategies, structure–activity relationships, and crucial reaction mechanisms. Finally, the current challenges and prospects in N-heterocycles synthesis from biomass feedstocks by transition metals-catalyzed manner are presented to provide interesting guidance for future research, such as precise designing of transition metals-based catalysts and benign broadening of product range of renewable N-heterocycles. This review hopes to provide updated knowledge and perspectives, serving as an important resource to inspire novel ideas and approaches in the field of catalysts design that will facilitate the advancement of sustainable synthesis.