Electronic π‑Delocalization Boosts Catalytic Water Oxidation by Cu(II) Molecular Catalysts Heterogenized on Graphene Sheets

• Published in: Journal of the American Chemical Society 2017-09, Vol.139 (37), p.12907-12910
• Main Authors: Garrido-Barros, Pablo, Gimbert-Suriñach, Carolina, Moonshiram, Dooshaye, Picón, Antonio, Monge, Pere, Batista, Victor S, Llobet, Antoni
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.7b06828

A molecular water oxidation catalyst based on the copper complex of general formula [(Lpy)­CuII]2–, 2 2–, (Lpy is 4-pyrenyl-1,2-phenylenebis­(oxamidate) ligand) has been rationally designed and prepared to support a more extended π-conjugation through its structure in contrast with its homologue, the [(L)­CuII]2– water oxidation catalyst, 1 2– (L is o-phenylenebis­(oxamidate)). The catalytic performance of both catalysts has been comparatively studied in homogeneous phase and in heterogeneous phase by π-stacking anchorage to graphene-based electrodes. In the homogeneous system, the electronic perturbation provided by the pyrene functionality translates into a 150 mV lower overpotential for 2 2– with respect to 1 2– and an impressive increase in the k cat from 6 to 128 s–1. Upon anchorage, π-stacking interactions with the graphene sheets provide further π-delocalization that improves the catalytic performance of both catalysts. In this sense, 2 2– turned out to be the most active catalyst due to the double influence of both the pyrene and the graphene, displaying an overpotential of 538 mV, a k cat of 540 s–1 and producing more than 5300 TONs.