Understanding light-driven H2 evolution through the electronic tuning of aminopyridine cobalt complexes

Arnau Call; Federico Franco; Noufal Kandoth; Sergio Fernández; María González-Béjar; Julia Pérez-Prieto; Josep M Luis; Julio Lloret-Fillol

doi:10.1039/c7sc04328g

Understanding light-driven H₂ evolution through the electronic tuning of aminopyridine cobalt complexes

Chem Sci. 2017 Dec 19;9(9):2609-2619. doi: 10.1039/c7sc04328g. eCollection 2018 Mar 7.

Authors

Arnau Call¹, Federico Franco¹, Noufal Kandoth¹, Sergio Fernández¹, María González-Béjar², Julia Pérez-Prieto², Josep M Luis³, Julio Lloret-Fillol^{1

4}

Affiliations

¹ Institute of Chemical Research of Catalonia (ICIQ) , The Barcelona Institute of Science and Technology , Avinguda Països Catalans 16 , 43007 Tarragona , Spain . Email: jlloret@iciq.es.
² Instituto de Ciencia Molecular (ICMol) , Universidad de Valencia , C/Catedrático José Beltrán 2, Paterna , E46980 Valencia , Spain.
³ Institut de Química Computacional i Catàlisi (IQCC) , Departament de Química , Universitat de Girona , Campus Montilivi , E17071 Girona , Catalonia , Spain.
⁴ Catalan Institution for Research and Advanced Studies (ICREA) , Passeig Lluïs Companys, 23 , 08010 , Barcelona , Spain.

Abstract

A new family of cobalt complexes with the general formula [Co^II(OTf)₂(^Y,XPy^Metacn)] (1^R , ^Y,XPy^Metacn = 1-[(4-X-3,5-Y-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, (X = CN (1^CN ), CO₂Et (1^CO2Et ), Cl (1^Cl ), H (1^H ), NMe₂ (1^NMe2 )) where (Y = H, and X = OMe when Y = Me (1^DMM )) is reported. We found that the electronic tuning of the ^Y,XPy^Metacn ligand not only has an impact on the electronic and structural properties of the metal center, but also allows for a systematic water-reduction-catalytic control. In particular, the increase of the electron-withdrawing character of the pyridine moiety promotes a 20-fold enhancement of the catalytic outcome. By UV-Vis spectroscopy, luminescence quenching studies and Transient Absorption Spectroscopy (TAS), we have studied the direct reaction of the photogenerated [Ir^III(ppy)₂(bpy˙^-)] (PS_Ir ) species to form the elusive Co^I intermediates. In particular, our attention is focused on the effect of the ligand architecture in this elemental step of the catalytic mechanism. Finally, kinetic isotopic experiments together with DFT calculations provide complementary information about the rate-determining step of the catalytic cycle.