Publications by authors named "Alisa Denisiuk"

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The Impact of a Proton Relay in Binuclear α-Diimine-Mn(CO) Complexes on the CO Reduction Catalysis.

Inorg Chem 2019 Aug 3;58(16):10444-10453. Epub 2019 Jul 3.

Universität Göttingen , Institut für Anorganische Chemie , Tammannstr. 4 , 37077 Göttingen , Germany.

Herein, we describe the redox chemistry of bi- and mononuclear α-diimine-Mn(CO) complexes with an internal proton source in close proximity to the metal centers and their catalytic activity in the electrochemically driven CO reduction reactions. In order to address the impact of the two metal sites and of the proton source, we investigate a binuclear complex with phenol moiety, , a binuclear Mn complex with methoxyphenol unit instead, , and the mononuclear analogue with a phenol unit, . Spectroelectrochemical investigation of the complexes in dmf under a nitrogen atmosphere indicates that and undergo a reductive H formation forming [Mn(HL)(CO)Br] and [Mn(HL)(CO)], respectively, which is redox neutral for the complex and equivalent to a deprotonation of the phenol unit. The reaction likely proceeds via internal proton transfer from the phenol moiety to the reduced metal center forming a Mn-H species. dimerizes during reduction, forming [Mn(L)(CO)], but and do not. Reduction of , , and is accompanied by bromide loss, and the final species represent [Mn(HL)(CO)], [Mn(L)(CO)], and [Mn(HL)(CO)], respectively. and are active catalysts in the electrochemical CO reduction reaction, whereas decomposes quickly under an applied potential. Thus, the second redox active unit is crucial for enhanced stability. The proton relay in alters the kinetics for the 2H/2e reduced products of CO in dmf/water mixtures. For , CO is the only product, whereas formate and CO are formed in similar amounts, 40% and 50%, respectively, in the presence of . Thus, the reaction rate for the internal proton transfer from the phenol moiety to the metal center forming the putative Mn-H species and subsequent CO insertion as well as the reaction rate of the reduced metal center with CO forming CO are similar. The overpotential with regard to the standard redox potential of CO to CO and the observed overall rate constant for catalysis at scan rates of 0.1 V s are higher with than with , that is, the OH group is beneficial for catalysis due to the internal proton transfer.
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August 2019