Nordic Consortium for CO2 Conversion

A nice collaboration between UiT and Helsinki University  on the mechanism of carbamate formation from CO₂ and amines. Congratulations to all authors!

Abstract:
Capture of CO₂ by amines is an attractive synthetic strategy for the formation of carbamates. Such reactions can be mediated by superbases, such as 1,1,3,3,-tetramethylguanidine (TMG), with previous implications that zwitterionic superbase–CO₂ adducts are able to actively transfer the carboxylate group to various substrates. Here we report a detailed investigation of zwitterionic TMG–CO₂, including isolation, NMR behavior, reactivity, and mechanistic consequences in carboxylation of aniline-derivatives. Our computational and experimental mechanistic analysis shows that the reversible TMG–CO₂ zwitterion is not a direct carboxylation agent. Instead, CO₂ dissociates from TMG–CO₂ before concerted low energy carboxylation occurs, where the role of the TMG is to deprotonate the amine as it is attacking a free CO₂. This insight is significant, as it opens a rational way to design new synthesis strategies. As shown here, nucleophiles otherwise inert towards CO₂ can be carboxylated, even without a CO₂ atmosphere, using TMG–CO₂ as a stoichiometric source of CO₂. We also show natural abundance 15N NMR is sensitive for zwitterion formation, complementing variable-temperature NMR studies.

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For a list of publications by members of NordCO₂, see our Publications page 🙂

NordCO₂ PI Sascha Ott and postdoctoral fellow Maxime Laurans have prepared a new manuscript which has been accepted for publication. Congratulations to both!

Abstract:
Photoelectrochemical CO₂ reduction is a promising approach for renewable fuel generation and to reduce greenhouse gas emissions. Owing to their synthetic tunability, molecular catalysts for the CO₂ reduction reaction can give rise to high product selectivity. In this context, a RuII complex [Ru(HO-tpy)(6-mbpy)(NCCH₃)]₂⁺ (HOtpy = 4’-hydroxy-2,2’:6’,2’’-terpyridyne; 6-mbpy = 6-methyl-2,2’-bipyridine) was immobilized on a thin SiOx layer of a p-Si electrode that was decorated with a bromide-terminated molecular layer. Following characterisation of the assembled photocathodes by X-ray photoelectron spectroscopy and ellipsometry, PEC experiments demonstrate electron transfer from the p-Si to the Ru complex through the native oxide layer under illumination and a cathodic bias. A state-of-the-art photovoltage of 570 mV was determined by comparison with an analogous n-type Si assembly. While the photovoltage of the modified photocathode is promising for future photoelectrochemical CO₂ reduction and the p-Si/SiOx junction seems to be unchanged during the PEC experiments, a fast desorption of the molecular Ru complex was observed. An in-depth investigation of the cathode degradation in comparison with reference materials highlights the role of the hydroxyl functionality of the Ru complex to ensure its grafting on the substrate. In contrast, an essential role of the bromide function on the Si substrate designed to engage with the hydroxyl group of the Ru complex in an SN2-type reaction could not be established.

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You can find a list of publications by NordCO₂ on our Publications page.

NordCO₂ PI Mårten S. G. Ahlquist and collaborators have recently published an article presenting DFT calculations for the steps of the mechanism of the Ir/Co-catalyzed photocarboxylation of alkynes. Their work highlights the importance of electron transfer during the rate limiting step of the reaction.

Abstract:
Photocarboxylation of alkyne with carbon dioxide represents a highly attractive strategy to prepare functionalized alkenes with high efficiency and atomic economy. However, the reaction mechanism, especially the sequence of elementary steps (leading to different reaction pathways), reaction modes of the H-transfer step and carboxylation step, spin and charge states of the cobalt catalyst, etc., is still an open question. Herein, density functional theory calculations are carried out to probe the mechanism of the Ir/Co-catalyzed photocarboxylation of alkynes. The overall catalytic cycle mainly consists of four steps: reductive-quenching of the Ir catalyst, hydrogen transfer (rate-determining step), outer sphere carboxylation, and the final catalyst regeneration step. Importantly, the cobalt catalyst can facilitate the H-transfer by an uncommon hydride coupled electron transfer (HCET) process. The pivotal electron delivery effect of the Co center enables a facile H-transfer to the α-C(alkyne) of the aryl group, resulting in the high regioselectivity for β-carboxylation.

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You can find a list of publications by NordCO₂ on our Publications page.