A molecular mediator for reductive concerted proton-electron transfers via electrocatalysis

Electrocatalytic approaches to the activation of unsaturated substrates via reductive concerted proton-electron transfer (CPET) must overcome competing, often kinetically dominant hydrogen evolution. We introduce the design of a molecular mediator for electrochemically triggered reductive CPET through the synthetic integration of a Brønsted acid and a redox mediator. Cathodic reduction at the cobaltocenium redox mediator substantially weakens the homolytic nitrogen-hydrogen bond strength of a Brønsted acidic anilinium tethered to one of the cyclopentadienyl rings. The electrochemically generated molecular mediator is demonstrated to transform a model substrate, acetophenone, to its corresponding neutral α-radical via a rate-determining CPET.

Solid-State Methylamine VUV Irradiation Study Using Carbon Monoxide as an H Radical Scavenger

Solid-phase methylamine (CH3NH2) was vacuum ultraviolet (VUV) photoprocessed at low temperature (20 K) using a hydrogen flow discharge lamp, which allows irradiation down to 120 nm. Methanimine (CH2=NH), the methylammonium cation (CH3NH3+) and the counterion CN–, as well as the amino radical (NH2), methane (CH4) and ammonia (NH3), were identified as the photoproducts by using FTIR spectroscopy. So far, the branching ratios of the photodissociation pathways of methylamine in the solid phase remain unknown. The methylamine molecule holds two non-equivalent hydrogen atoms on the methyl and the amino group, so we can expect the formation of two distinct radicals via a carbon–hydrogen or a nitrogen–hydrogen bond cleavage, namely CH2NH2 and CH3NH. These radicals are highly reactive and may reform methylamine with hydrogen atom recombination. Their direct infrared spectroscopic detection is therefore tricky. To solve that problem, we use carbon monoxide (CO) as an H radical scavenger, forming the intermediate species HCO. After the irradiation of a CH3NH2 : CO binary ice mixture, formamide (NH2CHO) and N-methylformamide (CH3NHCHO) were identified as the main photoproducts using both infrared and mass spectrometry. We give a rough approximation of the branching ratios, which are in agreement with previous studies in the gas phase.