Dehydrogenation through Cooperative Base Metal Catalysis

Introduction

The mild dehydrogenation of unactivated small molecules presents a formidable challenge for synthetic chemists. The Sorensen group has recently reported a dual-catalytic system capable of dehydrogenating alkanes and alcohols at low temperatures with hydrogen gas as the sole byproduct. This system uses inexpensive, earth-abundant metal catalysts tetrabutylammonium decatungstate (900432) and cobaloxime pyridine chloride (341630) and proceeds at room temperature under near-UV irradiation. The system can tolerate some functionality and presents a method to selectively dehydrogenate small molecules.

Comparison of dehydrogenation strategies

 

Fig. 1 Comparison of dehydrogenation strategies

Catalyst structures for dual-catalytic system

Fig. 2 Catalyst structures for dual-catalytic system

 

Advantages

  • Inexpensive, earth-abundant catalysts
  • Stable to air and moisture
  • Mild conditions
  • Functional group tolerance
  • Non-traditional selectivity

Dehydrogenation of Alkanes

Unactivated alkanes may be dehydrogenated with moderate efficiency using the dual-catalytic system. Notably, the system shows some divergent selectivity from late-metal-mediated reactions, especially in its reluctance to form benzene from cyclohexane and the exclusive production of the skipped enone product from ethyl isovalerate.

Dehydrogenation of Alcohols

The oxidation of secondary alcohols with concomitant evolution of hydrogen gas proceeds readily using the cooperative catalyst system, often furnishing high yields of the ketone product. Interestingly, primary alcohols are not suitable substrates for the dehydrogenation reaction likely due to competitive reaction of the aldehyde product with the TBADT catalyst.

 

Thank you to Julian West and Erik Sorensen for contributing this Technology Spotlight!

Materials

     

References

  1. West, J.G.; Huang, D.; Sorensen, E.J. Nat. Commun. 2015, 6, 10093.