Acceptorless Dehydrogenation of Aliphatics, Amines, and Alcohols with Homogeneous Catalytic Systems

Abstract

The dehydrogenation of saturated substrates is fundamentally essential for producing value-added unsaturated organic molecules both in academia and industry. In recent years, homogeneously catalyzed acceptorless C–C, C–N, and C–O bond desaturations have attracted increasing attention due to high atom economy, environmentally benign nature, and wide availability of the starting materials. This short review discusses the acceptorless dehydrogenation of aliphatics, alcohols, and amines by homogeneous catalytic systems based on two categories of reaction mechanisms: thermal transition-metal-catalyzed two-electron pathway and photoredox catalyzed or electrochemically driven one-electron pathway.1 Introduction2 Catalytic Acceptorless Dehydrogenation of Aliphatics3 Catalytic Acceptorless Dehydrogenation of Amines4 Catalytic Acceptorless Dehydrogenation of Alcohols5 Conclusion

Cobalt-Catalyzed Acceptorless Dehydrogenation of Primary Amines to Nitriles

“…The replacement of the ligated amine of Int1 to imine is exergonic by 1.4 kcal/mol, yielding a Co-imine species Int1′ (9.0 kcal/mol), which is treated as the starting point of the second dehydrogenation process (Figure ). , …”

“…Moreover, harsh reaction conditions (200 °C) were needed to obtain satisfactory yields. In 2013 and 2018, the Szymczak group and the Bera group, respectively, developed ruthenium-catalyzed oxidant-free and hydrogen acceptor-free double dehydrogenation conditions for primary amines (Scheme B). , These reports achieved the ideal acceptorless dehydrogenation of amines and benefited from simple reaction conditions, high atom efficiency, broad amine scope, and the exclusive formation of hydrogen gas as chemical waste.…”

“…In the past 20 years, significant advances toward acceptorless dehydrogenation have been achieved, and the strategy’s sustainability and high atom efficiency render it a green method to introduce unsaturated chemical bonds. , In contrast to the well-explored transition-metal-catalyzed acceptorless dehydrogenation of alcohols, amine dehydrogenation is more challenging and rare . The first report, achieved by Otsuka and co-workers in 1979, found RhH­(P i Pr 3 ) 3 was competent to catalyze the dehydrogenation of benzylamine to benzonitrile in only 27% yield .…”

Ni-catalysed acceptorless dehydrogenative aromatisation of cyclohexanones enabled by concerted catalysis specific to supported nanoparticles

“…In recent years, acceptorless dehydrogenation through hydrogen atom transfer (HAT), which utilises both photoredox catalysts and transition-metal catalysts including non-precious ones, has attracted much attention because of its high site selectivity and mild reaction conditions (Fig. 1b) 15,[32][33][34][35][36][37] . However, the reported photocatalytic systems for acceptorless dehydrogenative aromatisation typically require activated cyclohexane skeletons possessing benzylic, allylic or heteroatom-neighbouring C-H bonds, which have relatively low bond dissociation energies (BDEs) (Fig.…”