Molecular polypyridine-based metal complexes as catalysts for the reduction of CO₂

Abstract

Polypyridyl transition metal complexes represent one of the more thoroughly studied classes of molecular catalysts towards CO reduction to date. Initial reports in the 1980s began with an emphasis on 2nd and 3rd row late transition metals, but more recently the focus has shifted towards earlier metals and base metals. Polypyridyl platforms have proven quite versatile and amenable to studying various parameters that govern product distribution for CO reduction. However, open questions remain regarding the key mechanistic steps that govern product selectivity and efficiency. Polypyridyl complexes have also been immobilized through a variety of methods to afford active catalytic materials for CO reductions. While still an emerging field, materials incorporating molecular catalysts represent a promising strategy for electrochemical and photoelectrochemical devices capable of CO reduction. In general, this class of compounds remains the most promising for the continued development of molecular systems for CO reduction and an inspiration for the design of related non-polypyridyl catalysts.

A Bioinspired Nickel(bis-dithiolene) Complex as a Homogeneous Catalyst for Carbon Dioxide Electroreduction

“…1,2,7 Surprisingly there is a very limited contribution of Ni complexes so far, the prototype being Ni(cyclam) 2+ , a catalyst with excellent activity in aqueous solutions and highly selective for CO production, developed in the 80's by Sauvage and collaborators and revisited by several groups recently. 8 , and Ni(terpy) 2 ] 2+ (bipy, phen, terpy = bipyridine, phenanthroline, and terpyridine respectively) which catalyze the selective conversion of CO 2 into CO, albeit with large overpotential requirements and low Faradaic yields; 1,15 (ii) Ni complexes supported by N-heterocyclic carbeneamine ligands and displaying high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO 2 to CO; 16 (iii) very recently, a Ni complex bearing a S 2 N 2 -type tetradentate ligand which was found to selectively catalyze CO 2 reduction to CO in a visible-light-driven photocatalytic system. 17 In the quest for new Ni-based molecular catalysts for CO 2 electro-reduction, we were intrigued by the possibility to explore Ni complexes supported by bioinspired ligands, with a specific interest for those ligands providing a sulfur-rich environment to the metal ion.…”

“…3 As a consequence, during the last 40 years a number of molecular complexes have been studied for their catalytic activity for CO 2 electroreduction into CO/HCOOH. 1,2 However, the best catalysts so far are based on expensive noble metals, such as rhenium, iridium, rhodium and ruthenium. 4,5 There are exceptions, notably the Fe-porphyrin systems developed by Savéant, Costentin and Robert, 6 but also some cobalt, iron and manganese complexes.…”

“…1,2 First, their activity (reaction rates and overpotentials) can be finely tuned via simple modifications of the electronic properties of the organic ligands. Second, they are in general quite selective.…”

Organic, Organometallic and Bioorganic Catalysts for Electrochemical Reduction of CO2

“…Covering all of the reported polypyridine complexes would exceed the space and scope of this Review, therefore we focus on rhenium‐ and manganese‐containing complexes. However, we encourage interested readers to refer to one of the latest review articles summarizing the polypyridine ligands used for CO 2 reduction 13. Among the polypyridine complexes, Re‐containing complexes are of wide interest.…”

Recent Advances in Transition-Metal-Mediated Electrocatalytic CO2 Reduction: From Homogeneous to Heterogeneous Systems

“…(1) metal catalysts with macrocyclic ligands [17]; and (2) metal catalysts with polydentade ligands [18]. It should be noted that this section focuses mainly on introducing recent literature about transition metal centered homogeneous catalysts for CO 2 electroreduction and thus may omit old literature and other types of CO 2 activation reactions.…”