A Dinculear Rhenium Complex with a Proton Responsive Ligand in the Electrochemical‐Driven CO₂‐Reduction Catalysis

Abstract

Herein, we present a detailed study on a dinuclear Re complex bearing an α‐diimine‐tricarbonyl motif and a proton responsive ligand in the electrochemical CO2 reduction catalysis. The complex exhibits a pyrazole‐pyridine entity as α‐diimine unit and a phenol moiety as internal proton relay, which show non‐innocent behaviour under reductive conditions. Initial two electron reduction leads to NH bond cleavage forming the deprotonated ligand LH−2. Further two electron reduction at considerable negative potential induces OH bond cleavage and ligand reduction. In the presence of CO2, the reduced species reacts with CO2 forming CO. The complex shows a moderate Faraday efficiency and the activity is similar to the mononuclear derivative [Re(bpy)(CO)3(py)]+ (py=pyridine, bpy=2,2′‐bipyridine).

Manganese and Rhenium Tricarbonyl Complexes Equipped with Proton Relays in the Electrochemical CO2 Reduction Reaction

“…[ 47 ] We utilised the dinuclear complex 21 with an pyridine‐pyrazole unit and it was only moderately active and stable (Figure 5). [ 48 ] Initial reduction of 21 at –2.24 V in dmf is a 2e – reduction as proven by coulometry, and leads to a homolytic N–H‐bond rupture similar to that observed in 3 . H 2 is evolved and two pyrazolate units are formed.…”

“…A dinuclear Re(CO) 3 complex with proton relays in plane and axial positions. [48] In fact, none of the complexes with proton relay(s) directly attached at the 6,(6′)-position of the pyridine unit or in the remote position of the ligand (3,3′ or 4,4′) showed an improvement in terms of the overpotential and only a few led to a larger current enhancement under catalytic conditions compared to 1 Cl . This can be attributed to the electron donating character of the proton responsive units in conjugation to the π-system of the bipyridine ligand in all complexes, which led to a decrease in the reduction potentials.…”

“…To solvent [33] [41] 82 (1 % H 2 ) -2.6 -2.40 -thf 5 [37] 95 % (4 % -1.1 vs. pH = 6.9 HCO 2 -) NHE 11 [45] - [48] 40 (traces H 2 ) -2.6 -2.52 10 DMF H 2 O 22 [49] 60 % (5 % H 2 ) -2.6 -2.56 20 DMF H 2 O 23 [50] 65 -2.25 -2.45 dmf 23 [50] 85 (5 % H 2 ) -2.25 -2.27 dmf H 2 O 27 [50] 80 (1 % H 2 ) -2.25 -2.23 dmf H 2 O 26 [50] 105 -2.25 -2.45 dmf 26 [50] 105 (3 % H 2 ) -2.25 -2.36 dmf H 2 O 29 [52] 60 -1.9 MeCN 29 [52] 76 -1.9 MeCN H 2 O 29 [52] 52 -1.9 MeCN MeOH 30 [52] 98 -2.0 MeCN 30 [52] 100 -2.0 MeCN H 2 O 30 [52] 100 -2.0 MeCN MeOH 31 [53] 38 [38] 11.8 % HCO 2 --2.37 -2.4 V 6.7 MeCN 56 % CO 36 [38] -2.12 (E cat/2 ) 9.4 MeCN TFE 39 [54] 89 % ca. -2.5 V MeCN 40 [55] 60 % CO (2.8 M -1.87 (E cat/2 ) 4.7 MeCN H 2 O) 41 [55] 57 % CO (2.8 M -1.89 -1.90 (E cat/2 ) 3.…”

Electrocatalytic CO2 Reduction with Cis and Trans Conformers of a Rigid Dinuclear Rhenium Complex: Comparing the Monometallic and Cooperative Bimetallic Pathways

“…Several bimetallic catalyst designs have been pursued based on flexible alkyl tethers , or hydrogen-bonding interactions, which suffer from a lack of rigidity and variable solution compositions. Other examples feature dinucleating scaffolds that preclude intramolecular bimetallic CO 2 activation and conversion. , Thus, the desirable design parameters surrounding this approach are poorly understood. In this context, we sought to develop catalysts with a rigid dinucleating ligand that positions two rhenium active sites in close proximity with a predictable intermetallic distance and orientation (Scheme ).…”

Dinuclear Re(I) Complexes as New Electrocatalytic Systems for CO2 Reduction

“…From the mechanistic point of view, many studies have provided evidence for the formation of dinuclear intermediates as active species during the catalysis [27][28][29][30][31][32][33][34] and in order to prove this hypothesis different bimetallic catalysts have been synthetized and tested. [35][36][37] However only few examples have been related to catalysts with a rigid bridging ligand that links two rhenium active sites in close proximity with a predictable intermetallic distance and orientation, in order to clearly highlight the contribution of the dinuclear pathway.…”