Fairlamb, Ian J.S. orcid.org/0000-0002-7555-2761 and Lynam, Jason M. orcid.org/0000-0003-0103-9479 (2024) Unveiling Mechanistic Complexity in Manganese-Catalyzed C-H Bond Functionalization Using IR Spectroscopy Over 16 Orders of Magnitude in Time. ACCOUNTS OF CHEMICAL RESEARCH. ISSN 0001-4842
Abstract
Conspectus An understanding of the mechanistic processes that underpin reactions catalyzed by 3d transition metals is vital for their development as potential replacements for scarce platinum group metals. However, this is a significant challenge because of the tendency of 3d metals to undergo mechanistically diverse pathways when compared with their heavier congeners, often as a consequence of one-electron transfer reactions and/or intrinsically weaker metal-ligand bonds. We have developed and implemented a new methodology to illuminate the pathways that underpin C-H bond functionalization pathways in reactions catalyzed by Mn-carbonyl compounds. By integrating measurements performed on catalytic reactions with in situ reaction monitoring and state-of-the-art ultrafast spectroscopic methods, unique insight into the mode of action and fate of the catalyst have been obtained. Using a combination of time-resolved spectroscopy and in situ low-temperature NMR studies, we have shown that photolysis of manganese-carbonyl precatalysts results in rapid (<5 ps) CO dissociation─the same process that occurs under thermal catalytic conditions. This enabled the detection of the key states relevant to catalysis, including solvent and alkyne complexes and their resulting transformation into manganacycles, which results from a migratory insertion reaction into the Mn-C bond. By systematic variation of the substrates (many of which are real-world structurally diverse substrates and not simple benchmark systems) and quantification of the resulting rate constants for the insertion step, a universal model for this migratory insertion process has been developed. The time-resolved spectroscopic method gave insight into fundamental mechanistic pathways underpinning other aspects of modern synthetic chemistry. The most notable was the first direct experimental observation of the concerted metalation deprotonation (CMD) mechanism through which carboxylate groups are able to mediate C-H bond activation at a metal center. This step underpins a host of important synthetic applications. This study demonstrated how the time-resolved multiple probe spectroscopy (TRMPS) method enables the observation of mechanistic process occurring on time scales from several picoseconds through to μs in a single experiment, thereby allowing the sequential observation of solvation, ligand substitution, migratory insertion, and ultimate protonation of a Mn-C bond. These studies have been complemented by an investigation of the “in reaction flask” catalyst behavior, which has provided additional insight into new pathways for precatalyst activation, including evidence that alkyne C-H bond activation may occur before heterocycle activation. Crucial insight into the fate of the catalyst species showed that excess water played a key role in deactivation to give higher-order hydroxyl-bridged manganese carbonyl clusters, which were independently found to be inactive. Traditional in situ IR and NMR spectroscopic analysis on the second time scale bridges the gap to the analysis of real catalytic reaction systems. As a whole, this work has provided unprecedented insight into the processes underpinning manganese-catalyzed reactions spanning 16 orders of magnitude in time.
Metadata
Item Type: | Article |
---|---|
Authors/Creators: |
|
Copyright, Publisher and Additional Information: | Funding Information: We are grateful to all the talented researchers that have contributed to our research program involving Mn(I)–carbonyl chemistry. Key contributions from Drs. Benjamin Moulton, Nasiru Yahaya, Kate Appleby, Benjamin Aucott, Anders Hammarback, Jonathan Eastwood, and Thomas Burden are particularly recognized, as is support by several visiting ERASMUS exchange researchers, summer project students, and undergraduate project students (who are all recognized in our publications in this field since 2016). We have been supported by wonderful collaborations with Profs. Anne Duhme-Klair, Alison Parkin, and Simon Duckett, and aided in many illuminating discussions with Prof. Robin Perutz. We would like to acknowledge the scientific contributions of the CLF (RAL) staff, particularly Prof. Mike Towrie and Drs. Greg Greetham and Ian Clark, as well as colleagues supporting the ULTRA facilities. We thank Syngenta for supporting our efforts in this area, particularly Drs. Alan Robinson and Jean-Philippe Krieger. We thank EPSRC (grant EP/W031914/1), the RSC, STFC, the University of York, and Syngenta for funding. J.M.L. and I.J.S.F. are both supported by Royal Society Industry Fellowships (INF\R1\221057 and INF\R2\202122 respectively. I.J.S.F. and J.M.L. (and a team from York, Syngenta and the Central Laser Facility) were recognized for their work in manganese carbonyl catalysis through the 2021 RSC Horizons Prize. Publisher Copyright: © 2024 The Authors. Published by American Chemical Society. |
Dates: |
|
Institution: | The University of York |
Academic Units: | The University of York > Faculty of Sciences (York) > Chemistry (York) |
Depositing User: | Pure (York) |
Date Deposited: | 15 Mar 2024 10:30 |
Last Modified: | 08 Feb 2025 00:53 |
Published Version: | https://doi.org/10.1021/acs.accounts.3c00774 |
Status: | Published online |
Refereed: | Yes |
Identification Number: | 10.1021/acs.accounts.3c00774 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:210341 |
Download
Description: Unveiling Mechanistic Complexity in Manganese-Catalyzed C−H Bond Functionalization Using IR Spectroscopy Over 16 Orders of Magnitude in Time
Licence: CC-BY 2.5