Low-overpotential CO₂ reduction by a phosphine-substituted Ru(ii) polypyridyl complex

Abstract

A Ru polypyridyl complex containing a phosphine donor promoted electrocatalytic CO2 reduction at a low overpotential. Mechanistic investigations revealed that the introduction of a phosphine donor at the trans position to the labile ligand is the key to reduce the overpotential for CO2 reduction.

Effect of PDI ligand binding pattern on the electrocatalytic activity of two Ru(II) complexes for CO2 reduction

“…TOF was determined using equation from catalytic CVs: where F is Faraday's constant (96485 C/mol), v is the scan rate employed (0.1 V/s), n p is the number of electrons involved in the non‐catalytic redox reaction ( n p = 1), R is the gas constant (8.314 J/K/mol), T is the temperature (293.15 K), and n cat is the number of electrons involved for the catalytic reaction ( n cat = 2 for the reduction of CO 2 to CO), i p and i cat are determined as the peak currents under Ar and CO 2 , respectively. As for complex 1 , the calculated TOF is 4.4 s −1 ( i cat / i p = 4.7) in MeCN solution at a potential of −1.85 V, which is higher than or comparable to that of many reported ruthenium molecular water oxidation catalysts, and 0.4 s −1 ( i cat / i p = 1.5) in THF solution at a potential of −1.94 V and a scan rate of 100 mV/s. As for complex 2 , the calculated TOFs are 0.3 s −1 ( i cat / i p = 1.2) in MeCN solution at a potential of −2.43 V and 0.2 s −1 ( i cat / i p = 0.9) in THF solution at a potential of −2.21 V at 100 mV/s.…”

“…The PDI in complex 1 adopts an aromatized tridentate η 3 ‐N,N,N‐coordinated mode, which can store multiple electrons in its large delocalized π systems, and cooperates with the central Ru(II) ion for electrocatalysis, whereas the PDI ligand in complex 2 uses a dearomatized η 2 ‐C,N coordination pattern which cannot act as an electron reservoir . In addition, owing to the good π‐acceptor and soft σ‐donor properties, incorporating triphenylphosphine ligand into complex 1 with a central ruthenium ion may also have the influences of enhancing its catalytic activity for the reduction of CO 2 . To further verify this view, the complex [Ru(PDI) 2 ][PF 6 ] 2 (PDI = 2,6‐bis(4‐methoxyphenylmethylimine)pyridine) was prepared according to the literature, in which there is no phosphine ligand, and the binding mode of PDI is η 3 ‐N,N,N, just as in complex 1 .…”

“…In addition, phosphines are an extraordinary type of ligand in transition metal homogeneous catalysis since they can influence electronic structures and promote the chemical reactivity of the catalysis remarkably, as well as making them soluble and stable owing to their good π‐acceptor and soft σ‐donor properties . Previous investigations have proved that transition metal complexes containing phosphine ligands are highly effective catalysts in cross‐coupling reactions, CO 2 reduction, etc., therefore incorporating the phosphine ligand into ruthenium complexes with redox‐active ligand PDI could enhance their catalytic activity for CO 2 reduction.…”

Visible‐Light Photocatalytic Reduction of CO2 to Formic Acid with a Ru Catalyst Supported by N,N′‐Bis(diphenylphosphino)‐2,6‐diaminopyridine Ligands

“…Success in this endeavor requires confronting the inherent stabilitya nd low thermodynamic value of CO 2 and would transform this ubiquitous waste product into av aluable feedstock. [15,16] Recently,p incer ligand-supported catalysts of Fe, Co, Ru, and Ir have been shown to have excellent activity and selectivity for hydrogenation of CO 2 . Furthermore, formic acid has been identified and explored as ap otential carrier of dihydrogen.…”

“…For example, photocatalytic formation of formic acid, at wo-electron reductionp roduct of CO 2 ,w ould yield ac ommodity chemical and al iquid fuel. [15,16] Recently,p incer ligand-supported catalysts of Fe, Co, Ru, and Ir have been shown to have excellent activity and selectivity for hydrogenation of CO 2 . [1,2] Homogeneous catalysts have been developed for CO 2 reduction under both electrochemical and photochemical conditions.…”