Electrocatalytic reduction of CO2 to CO in the presence of a mononuclear polypyridyl ruthenium(II) complex

Abstract

Crystallographic data for [Ru(tptz)(CH 3 CN)Cl 2 ]•CH 3 CN•0.68H 2 O have been deposited with the Cambridge Crystallographic Data Centre, CCDC 1446155.

A new polypyridyl‐based Ru (II) complex as a highly efficient electrocatalyst for CO2 reduction

“…In the CO 2 saturated solution of the complex, the first and second reduction waves are nearly unchanged with respect to the solution saturated with N 2 , while the third reduction wave is replaced by a new reduction wave with an intense current at E pc = −1.58, which is related to the electrocatalytic CO 2 reduction. These results compare well with those reported previously for similar polypyridyl ruthenium complexes …”

“…The asymmetric unit of the compound consists of one complex cation, [Ru (Me 4 phen) 2 (CH 3 CN) 2 ] 2+ , two NO 3 − counter anions, and one ethanol solvent molecule. The Ru–N bond lengths are all in a normal range of 2.021(5)–2.058(5) Å (Table S1) which is usually observed for similar Ru (II) complexes . Further, the N−O bond distances of two NO 3 ¯ anions fall in the 1.203(11)–1.232(11) Å range.…”

“…The synthetic strategy to prepare cis ‐[Ru (Me 4 phen) 2 (CH 3 CN) 2 ](NO 3 ) 2 was based on the synthesis of a new polypyridyl ruthenium (II) complex as an electrocatalyst which has a number of coordinating solvent molecules in its inner coordination sphere to increase the probability of the substitution of a CO 2 molecule in the electrocatalytic cycle. The rate‐limiting step for the electrocatalytic CO 2 reduction is the substitution of CO 2 molecule for a coordinating monodentate ligand such as a coordinating solvent, which is a good leaving group . In this respect, the reaction of Me 4 phen with RuCl 3 · x H 2 O in a 2:1 molar ratio in the presence of AgNO 3 in refluxing ethanol–acetonitrile (1:2 v/v) mixture under N 2 atmosphere in the dark resulted in cis ‐[Ru (Me 4 phen) 2 (CH 3 CN) 2 ](NO 3 ) 2 in high yield (Scheme ).…”

“…As can be seen, [Ru II (Me 4 phen) 2 (CH 3 CN) 2 ] 2+ undergoes two initial sequential one‐electron Me 4 phen‐based reductions [steps ( I ) and ( II )] to give [Ru II (Me 4 phen –• ) 2 (CH 3 CN) 2 ], Int 2 , followed by the substitution of CO 2 for CH 3 CN [step ( III )]. This reaction proceeds along with an intramolecular two‐electron transfer from the Me 4 phen‐moiety to the coordinating CO 2 ligand to give an intermediate as the metallocarboxylate ( Int 3 ), [Ru II (Me 4 phen) 2 (CH 3 CN)(CO 2 2− )], which promotes the reduction of CO 2 . Meyer et al .…”

“…A large number of polypyridyl complexes of transition metals including rhenium, osmium, manganese and ruthenium have been widely used as homogeneous and heterogeneous electrocatalysts for CO 2 reduction to CO. In recent years, synthesis and the electrocatalytic and photocatalytic activity of Dy (III), Gd (III), Re(I), and Ru (II) complexes containing different ligands have been reported for the reduction of CO 2 to CO. These complexes exhibit the preferable catalytic activity for CO formation as a desired product.…”