# Selective NH3-to-N2H4 conversion electrocatalysed by ruthenium(ii)-cymene complexes

## TL;DR

This paper reports ruthenium complexes that efficiently convert ammonia to hydrazine through selective electrocatalysis.

## Contribution

The study introduces ruthenium(ii)-cymene complexes with modified ligands that enable selective NH3-to-N2H4 conversion with high turnover numbers.

## Key findings

- Electrochemical studies show that methylated ligands significantly lower the oxidation potential of the complexes.
- Controlled potential coulometry reveals a turnover number of up to 453.2 for the [4-NH3]PF6 complex.
- Kinetic and theoretical studies identify two pathways for N–N bond formation during the catalytic process.

## Abstract

A series of ruthenium(ii)-cymene complexes [(η6-p-cymene)Ru(pp)Cl] (1–4) and corresponding NH3-ligated complexes [(η6-p-cymene)Ru(pp)(NH3)]PF6 ([1-NH3]PF6 to [4-NH3]PF6), where cymene = 4-isopropyltoluene and pp− = pyridylpyrrole ligand, have been designed and synthesized. Structural modifications of pp− ligands are accomplished through the use of an increasing number of electron-donating methyl groups on the pyrrole unit. Solid-state structural analysis shows that these complexes have a typical piano-stool structure. Electrochemical studies of these complexes illustrate that the introduction of a methyl group to the pp− ligand can greatly decrease the oxidation potential of Ruiii/ii from 0.49 V vs. Cp2Fe+/0 for [1-NH3]PF6 to 0.16 V vs. Cp2Fe+/0 for [4-NH3]PF6. Controlled potential coulometry experiments show that these complexes exhibit selective catalysis for the oxidation of NH3 to N2H4 with a turnover number of up to 453.2 at Eapp 0.8 V vs. Cp2Fe+/0 for the [4-NH3]PF6 complex. Kinetic and theoretical thermodynamic studies show that the pathway of bimolecular coupling of Ruii-aminyl species and the pathway of ammonia nucleophilic attack of Ruiv-imide (generated from the disproportionation of Ruiii-amide) are involved in N–N formation.

NH3-ligated complexes [(η6-p-cymene)Ru(pp)(NH3)]PF6 display good catalytic performance for selective conversion NH3 to N2H4.