The importance of understanding (pre)catalyst activation in versatile C-H bond functionalisations catalysed by [Mn2(CO)10]

Jonathan B. Eastwood, Thomas J. Burden, L. Anders Hammarback, Chris Horbaczewskyj, Theo F.N. Tanner, Ian P. Clark, Gregory Greetham, Michael Towrie, Ian J.S. Fairlamb*, Jason M. Lynam*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Mn-catalysed reactions offer great potential in synthetic organic and organometallic chemistry and the success of Mn carbonyl complexes as (pre)catalysts hinges on their stabilisation by strong field ligands enabling Mn(i)-based, redox neutral, catalytic cycles. The mechanistic processes underpinning the activation of the ubiquitous Mn(0) (pre)catalyst [Mn2(CO)10] in C-H bond functionalisation reactions is now reported for the first time. By combining time-resolved infra-red (TRIR) spectroscopy on a ps-ms timescale and in operando studies using in situ infra-red spectroscopy, insight into the microscopic bond activation processes which lead to the catalytic activity of [Mn2(CO)10] has been gained. Using an exemplar system, based on the annulation between an imine, 1, and Ph2C2, 2, TRIR spectroscopy enabled the key intermediate [Mn2(CO)9(1)], formed by CO loss from [Mn2(CO)10], to be identified. In operando studies demonstrate that [Mn2(CO)9(1)] is also formed from [Mn2(CO)10] under the catalytic conditions and is converted into a mononuclear manganacycle, [Mn(CO)4(C^N)] (C^N = cyclometallated imine), a second molecule of 1 acts as the oxidant which is, in turn, reduced to an amine. As [Mn(CO)4(C^N)] complexes are catalytically competent, a direct route from [Mn2(CO)10] into the Mn(i) catalytic reaction coordinate has been determined. Critically, the mechanistic differences between [Mn2(CO)10] and Mn(i) (pre)catalysts have been delineated, informing future catalyst screening studies.

Original languageEnglish
JournalChemical Science
Publication statusAccepted/In press - 2 May 2024

Bibliographical note

Funding Information:
We are grateful to Syngenta, the EPSRC and the Department of Chemistry at the University of York (iCASE studentship to LAH EP/N509413/1, studentships for JBE and TJB) as well as the Royal Society of Chemistry (Research Enablement Grant to support JBE) and the EPSRC (grant number EP/W031914/1) for funding. We thank the STFC for programme access to the ULTRA facility (grant number 1813). JML and IJSF are both supported by Royal Society Industry Fellowships (INF\\R1\\221057 and INF\\R2\\202122 respectively). We are grateful to Mr Matthew McRobie for experimental assistance.

Publisher Copyright:
© 2024 The Royal Society of Chemistry.

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