# Molecular Hydrogen Production from Formic Acid by Cationic Phenanthroline Ruthenium Complexes: Experimental and DFT Mechanistic Insights

## TL;DR

Scientists created new ruthenium complexes that efficiently produce hydrogen from formic acid and showed how they work using experiments and computer models.

## Contribution

The study introduces new cationic phenanthroline ruthenium complexes with superior catalytic performance for hydrogen production from formic acid.

## Key findings

- Dinuclear ruthenium complexes achieved 100% formic acid conversion and showed excellent stability through multiple cycles.
- Mechanistic studies revealed the formation of two Ru-monohydride species with distinct geometries involved in hydrogen production.
- DFT calculations showed that the fac-RuHP2 species is energetically more favorable than the mer-RuHP2 species.

## Abstract

A series of new monocationic Ru complexes containing
phenanthroline
derivatives were developed. The monometallic complexes [Ru­(κ2-OAc)­(dppb)­(N,N)]­OAc derivatives were synthesized in high
yield via the reaction between [Ru­(κ2-OAc)2dppb] and the corresponding N,N ligand. Additionally, dinuclear [(dppb)­(κ2-OAc)­(Ru­(μ-N,N--C,N)­Ru­(κ2-OAc)­(dppb)]­OAc complexes were synthesized from equimolar
amounts of the appropriate monometallic complex and [Ru­(κ2-OAc)2dppb]. All complexes were characterized by
NMR, FTIR, UV–vis spectroscopy, and cyclic voltammetry. These
precatalysts display selective catalytic activity toward dehydrogenation
of formic acid for H2 production, with the dinuclear systems
demonstrating superior performance, achieving up to 100% conversion
under optimized conditions. The dinuclear system maintained consistent
TOF50 values through several catalytic cycles, demonstrating
excellent stability. Mechanism investigations revealed the formation
of two Ru-monohydride species, showing a fac-RuHP2 and a mer-RuHP2 arrangement,
respectively, formed via substitution of a κ2-OAc
by a κ2-O2CH followed by a β-elimination,
where both are involved in the mechanisms. DFT calculations of the
species involved in the mechanism showed that fac-RuHP2 is lower in energy than mer-RuHP2. The complexes were additionally applied in the transfer
hydrogenation of CO2 to produce formic acid with 2-propanol.