Electrocatalytic hydrogen generation by a trithiolato-bridged dimanganese hexacarbonyl anion with a turnover frequency exceeding 40 000 s⁻¹

Abstract

An unusual ionic manganese model complex [Mn(bpy)3](+)[(CO)3Mn(μ-SPh)3Mn(CO)3](-)(bpy: 2,2'-bipyridine) has been synthesized, which bears some structural resemblance to the active site of [FeFe] hydrogenase. An overpotential of 0.61 V has been determined for the electrocatalytic proton reduction using this complex in CH3CN with CF3COOH as the proton source. A turnover frequency of 44,600 s(-1) is achieved at high scan rates and in the presence of a large amount of acid.

Dinuclear Manganese Carbonyl Complexes: Electrocatalytic Reduction of Protons to Dihydrogen

“…The TOF values were determined by taking successive CVs of the reaction mixtures with systematic increase in acid concentration, until the TOF was invariant. The data for a few reported Mn complexes has been included in table for a comparison . The overpotential for the complexes, calculated by the method of Evans et al., was found to be 0.83 (for 1 ), 0.79 (for 3 ) and 0.77 V (for 4 ) (Table ) .…”

“…Based on the CVs and mechanism described for reported Mn complexes,, an EECC mechanism can be proposed for the electrocatalytic H 2 production by complexes 1 , 3 and 4 . However, further investigations are needed to explain the proposed mechanism.…”

“…Since the report on the first structure of the [FeFe] hydrogenase enzyme active site, numerous complexes based on earth‐abundant metals cobalt, nickel and iron have been reported as photo‐ and electrocatalysts for the hydrogen evolution reaction (HER) . While several Mn electrocatalysts have been developed for CO 2 reduction, very few catalysts have been developed for HER . This is surprising because: (i) Mn is also considered as one of the most abundant metals on earth, (ii) it is a desirable element for sustainable catalytic transformations, (iii) it has the capability to be stable in different oxidation states thus allowing redox reactions to be carried out in a facile manner, and (iv) the Mn I (CO) 3 moiety is isolobal with the Fe II (CO)(CN) 2 unit present in the [NiFe] H 2 ase active site.…”

“…This is surprising because: (i) Mn is also considered as one of the most abundant metals on earth, (ii) it is a desirable element for sustainable catalytic transformations, (iii) it has the capability to be stable in different oxidation states thus allowing redox reactions to be carried out in a facile manner, and (iv) the Mn I (CO) 3 moiety is isolobal with the Fe II (CO)(CN) 2 unit present in the [NiFe] H 2 ase active site. So far the Mn complexes reported as electrocatalysts include both mononuclear and dinuclear systems (Figure ) . Mostly dinuclear manganese complexes have been investigated as catalysts for the HER.…”

“…Mostly dinuclear manganese complexes have been investigated as catalysts for the HER. These include: [Mn 2 (CO) 8 ( μ ‐SePh) 2 ], [Mn(CO) 4 ( μ ‐SePh) 2 Mn(CO) 3 (Py)], [Mn 2 (CO) 4 ( μ ‐CO)( μ ‐SePh) 2 (PBu 3 ) 2 ], [(Mn(CO) 3 ) 2 ( μ ‐SC 6 H 4 ‐o‐S−S‐C 6 H 4 ‐o‐ μ ‐S)], [(bipy) 3 Mn] + [Mn 2 ( μ ‐SPh) 3 (CO) 6 ] − . The few reported mononuclear systems include: Mn vinylidene and allenylidene complexes, [(Mn=C=C(H)Ph)( η 5 ‐C 5 H 5 )(CO)(PPh 3 )], [(Mn=C=C=CPh 2 )( η 5 ‐C 5 H 5 )(CO) 2 (PPh 3 )], fac ‐[Mn( κ 3 ‐tpa)(CO) 3 ] + OTf − , [Mn(mesbpy)(CO) 3 (MeCN)](OTf), [( κ 4 ‐ Ph2PPr PDI)Mn( μ ‐ η 1 , η 2 ‐CO)K(18‐crown‐6)], [( Ph2PPr PDI)‐Mn(CO)][Br] The reported mononuclear systems show high overpotentials and low activity.…”