“Hidden” Metal–Ligand Cooperation for Additive-Free Formic Acid Dehydrogenation

This study reports a diazadiene ligand containing ruthenium hydride complex for additive-free formic acid dehydrogenation (FADH). Comprehensive experimental data and density functional theory (DFT) analysis highlight the critical role of metal–ligand cooperation (MLC) during the catalysis. These insights offer new perspectives for understanding structure–activity relationship (SAR) in homogenously catalyzed FADH.

Formic acid (FA) is a promising hydrogen (H₂) carrier for reversible hydrogen storage, combining a high storage capacity with safe transportation. Typically, the catalytic release of H₂ from FA requires an external base, limiting the widespread use of FA as a H₂ carrier in the hydrogen economy. Herein, we reveal an additive-free FA dehydrogenation, catalyzed by a new ruthenium hydride complex, made possible with a tetradentate dad-bis-phosphine ligand. Experimental investigations were complemented by density functional theory (DFT) studies to elucidate the molecular mechanism of the process. The comparison of two distinct active species (κ²-NN and η⁴-NCCN coordination mode) by computational studies reveal the crucial role of the back bonding that facilitates FA dehydrogenation, originating from ligand–metal cooperation.