Teaming up main group metals with metallic iron to boost hydrogenation catalysis

Hydrogenation of unsaturated bonds is a key step in both the fine and petrochemical industries. Homogeneous and heterogeneous catalysts are historically based on noble group 9 and 10 metals. Increasing awareness of sustainability drives the replacement of costly, and often harmful, precious metals by abundant 3d-metals or even main group metals. Although not as efficient as noble transition metals, metallic barium was recently found to be a versatile hydrogenation catalyst. Here we show that addition of finely divided Fe-0, which itself is a poor hydrogenation catalyst, boosts activities of Ba-0 by several orders of magnitude, enabling rapid hydrogenation of alkynes, imines, challenging multi-substituted alkenes and non-activated arenes. Metallic Fe-0 also boosts the activity of soluble early main group metal hydride catalysts, or precursors thereto. This synergy originates from cooperativity between a homogeneous, highly reactive, polar main group metal hydride complex and a heterogeneous Fe-0 surface that is responsible for substrate activation. Elemental iron turns alkaline-earth metal complexes into highly active catalysts for the hydrogenation of alkenes, alkynes, imines and arenes. The proposed mechanism combines homogeneous catalysis by a soluble main group metal hydride complex with heterogeneous catalysis at the iron surface.

Automated summary

The addition of metallic iron can enhance the hydrogenation activity of barium, allowing for rapid hydrogenation of various compounds. Moreover, iron also boosts the activity of soluble early main group metal hydride catalysts, resulting in highly active catalysts for the hydrogenation of different unsaturated compounds. This synergy between homogeneous and heterogeneous catalysis highlights the potential of using elemental iron to improve catalytic processes.