Electrooxidation of Alcohols Catalyzed by Amino Alcohol Ligated Ruthenium Complexes

Abstract

Ruthenium transfer hydrogenation catalysts physisorbed onto edge-plane graphite electrodes are active electrocatalysts for the oxidation of alcohols. Electrooxidation of CH3OH (1.23 M) in a buffered aqueous solution at pH 11.5 with [(η(6)-p-cymene)(η(2)-N,O-(1R,2S)-cis-1-amino-2-indanol)]Ru(II)Cl (2) on edge-plane graphite exhibits an onset current at 560 mV vs NHE. Koutecky-Levich analysis at 750 mV reveals a four-electron oxidation of methanol with a rate of 1.35 M(-1) s(-1). Mechanistic investigations by (1)H NMR, cyclic voltammetry, and desorption electrospray ionization mass spectrometry indicate that the electroxidation of methanol to generate formate is mediated by surface-supported Ru-oxo complexes.

Energy Production and Storage Promoted by Organometallic Complexes

“…This prompted Brownell and co‐workers to study transfer hydrogenation (TH) catalysts as potentially candidates for alcohol electrooxidation reactions, since catalytic transfer hydrogenation involves the reversible oxidation of alcohols to ketones. They studied two Ru cymene complexes, 1 and 2 (Figure ) for methanol and 2‐propanol electrooxidation …”

“…Ru II ‐cymene complexes 1 and 2 studied in ref . and the proposed mechanism of 2‐propanol electrooxidation.…”

Catalytic Radical Reduction in Aqueous Solution by a Ruthenium Hydride Intermediate

“…[25] Oxidation of M1 red into M1 ox by ABTSC À is expected to be thermodynamically feasible because the ABTSC À /ABTS 2À redox couple occurs at + 0.68 V. [7] Tilset and Norton et al also noted that the deprotonation of M1 ox occurs even if it is thermodynamically unfavorable by 4pK a units,p rovided that the 19 e À Ru I conjugate base (M2 red )i si rreversibly oxidized. [ An anionic h 5 -C 5 H 5 ligand is more electron-donating than an eutral h 6 -cymene,t hus it is more relevant to compare the oxidation of [L n Ru-H] to other Ru complexes with h 6 -cymene ligands rather than M1 red .U nsurprisingly,t he oxidation of M3 red (+ 0.16 V; Scheme 3D)o ccurred at ah igher potential than M1 red , [27] but still well below the ABTSC À /ABTS 2À redox couple.T he difference in oxidation potentials between [L n Ru-H] and M3 red is expected to be smaller than that between M3 red and M1 red ,t herefore ABTSC À should be as ufficiently strong oxidant to oxidize both [L n Ru-H] and [L n Ru-L']. [ An anionic h 5 -C 5 H 5 ligand is more electron-donating than an eutral h 6 -cymene,t hus it is more relevant to compare the oxidation of [L n Ru-H] to other Ru complexes with h 6 -cymene ligands rather than M1 red .U nsurprisingly,t he oxidation of M3 red (+ 0.16 V; Scheme 3D)o ccurred at ah igher potential than M1 red , [27] but still well below the ABTSC À /ABTS 2À redox couple.T he difference in oxidation potentials between [L n Ru-H] and M3 red is expected to be smaller than that between M3 red and M1 red ,t herefore ABTSC À should be as ufficiently strong oxidant to oxidize both [L n Ru-H] and [L n Ru-L'].…”

Multistage Reactive Transmission-Mode Desorption Electrospray Ionization Mass Spectrometry

“…The recent introduction of ambient mass spectrometric techniques [8][9][10][11][12][13][14][15] such as desorption electrospray ionization (DESI) [16] developed by Cooks and co-workers has revolutionized analytical chemistry in the past decade, allowing chemical analyses with minimal sample preparation. A recent advance developed by Zare and co-workers involves using DESI to capture short-lived solution-phase reaction intermediates (<1 ms) [17][18][19][20][21][22][23] at ambient conditions, while minimizing sample preparation times, carry over effects, and experimental complexity compared with ESI configurations. This elegant discovery has opened the possibility for the development of new types of ambient ionization sources and applications for characterizing fast solution-phase processes [4,[24][25][26][27][28][29][30][31][32].…”