Effect of Lewis Basic Amine Site on Proton Reduction Activity of NNN‐Co Pincer Complex

Abstract

Electrochemical proton reduction is a promising energy storage method because H 2 molecule has a simple structure with a relatively low potential energy. Current interest in hydrogen catalysts has increased research efforts on synthetic analogs of hydrogenase active sites. In this study, we demonstrated the electrochemical H 2 evolution reactivity of [NNN R -Co(CH 3 CN) 3 ] 2+ (R CH 2 (1b), NCH 3 (2b)) complexes and examined a proton-relay process in the H 2 evolution reaction (HER). Upon one-electron reduction, the Co(II) ion center in a high-spin state dissociated a CH 3 CN ligand, while opening a reaction site. Cyclic voltammograms of the Co complexes indicated quasi-reversible Co(II/I) redox behaviors, and both complexes 1b and 2b showed catalytic H 2 evolution activity. Interestingly, 2b, assisted by a protonrelaying NCH 3 group, exhibited more efficient catalytic activity than 1b.

Two-Electron-Induced Reorganization of Cobalt Coordination and Metal–Ligand Cooperative Redox Shifting Co(I) Reactivity toward CO2 Reduction

“…Previous NNN-pincer type complexes exhibited HER activity, 39,40 S1). The Co−NCCH 3 bonds in [2- 3) (all potentials reported here are vs Fc 0/+ ) and peak to peak separation values (ΔE p ) between 80 and 90 mV at 100 mV/s (Table S2).…”

“…Previous NNN-pincer type complexes exhibited HER activity, , for example, [NNN NCH 3 –Co­(CH 3 CN) 3 ]­(PF 6 ) 2 ([ 1-(CH 3 CN) 3 ]­(PF 6 ) 2 ) showed the turnover frequency (TOF) of ∼10 2 for reduction of acetic acid. However, the enclosure of the Co center with 1,10-phenanthroline (phen) ligand as [NNN NCH 3 –Co­(phen) (CH 3 CN)]­(PF 6 ) 2 ([ 2-CH 3 CN ]­(PF 6 ) 2 ) severely decreased the TOF H2 value of HER to 6 s –1 (Figure S1).…”

“…Electron-induced reorganization of Co coordination complexes: (a) one electron-induced Co–NCCH 3 cleavage, (b) two electron-induced Co–NCCH 3 cleavage and (c) unique Co–N arm cleavage, and the relative reactivities about hydrogen evolution (HER) and CO 2 reduction (CO 2 RR).…”

Metal complexes containing silicon‐based pincer ligands: Reactivity and application in small molecule activation

“…6 Moreover, there has been a series of reports on pincer complexes mimicking the local geometry and reactivity of enzymes. [7][8][9][10][11][12][13] A pincer ligand generally consists of a central monoanionic (or neutral) anchoring donor atom and flanking donor atoms connected through an organic backbone. 14 After the first report of a [PCP]-type pincer ligand by Moulton and Shaw, 15 a number of pincer ligands were synthesized by substituting the donor atoms with N, O, P, S, and so on.…”

“…Metal complexes supported by pincer ligands have already been utilized in various catalytic chemical conversions 6 . Moreover, there has been a series of reports on pincer complexes mimicking the local geometry and reactivity of enzymes 7–13 …”