Probing Mn Precatalyst Activation through Time-Resolved Spectroscopy: A Quantitative Evaluation of the Effects of CO and PPh<sub>3</sub> as Coligands on Ultrafast Dynamics and C–C Bond Formation
An investigation into the effect of a phosphine coligand on the activation of precatalysts for manganese-catalyzed C-H bond functionalization is reported. Although simple precatalysts [MnBr(CO)<sub>5</sub>] and [Mn<sub>2</sub>(CO)<sub>10</sub>] are used extensively in these reactions, there is a dearth of alternate precatalyst structures, which has hindered the development of structure-activity relationships. In this work, the effect of substituting a carbonyl ligand for a phosphine ligand is reported. Investigation of the photochemical activation of the precatalyst <i>fac</i>-[Mn(inpy)(CO)<sub>3</sub>(PPh<sub>3</sub>)] (inpy = cyclometalated 1-(pyridin-2-yl)-1<i>H</i>-indole) <b>3</b> by time-resolved infrared spectroscopy (TRIR) reveals that light-induced dissociation of a CO ligand occurs preferentially over loss of the phosphine. The ultrafast dynamics of the initially formed solvent complex [Mn(inpy)(CO)<sub>2</sub>(toluene)(PPh<sub>3</sub>)] <b>9</b> are described, as is the slower substitution of the coordinated solvent by added pyridine to give [Mn(inpy)(CO)<sub>2</sub>(NC<sub>5</sub>H<sub>5</sub>)(PPh<sub>3</sub>)] <b>10</b>. Replacing the pyridine with phenylacetylene again results in the substitution of the metal-bound toluene to give the alkyne complex [Mn(inpy)(η<sup>2</sup>-HC<sub>2</sub>Ph)(CO)<sub>2</sub>(PPh<sub>3</sub>)] <b>12</b>. The alkyne undergoes a migratory insertion reaction into the Mn-C bond on a microsecond time scale with a very similar first-order rate constant to [Mn(inpy)(CO)<sub>4</sub>], <b>2</b>, demonstrating that this key step in Mn-catalyzed reactions is not affected by the presence of the phosphine ligand.
Authors
- Partha Malakar (ORCID: https://orcid.org/0000-0001-6874-7010)
- Stefan Flesch (ORCID: https://orcid.org/0000-0002-4220-236X)
- Leticia M. Pardo (ORCID: https://orcid.org/0000-0002-5079-1184)
- Jonathan B. Eastwood (ORCID: https://orcid.org/0000-0001-5586-7697)
- Jason M. Lynam (ORCID: https://orcid.org/0000-0003-0103-9479)
- Ian P. Clark (ORCID: https://orcid.org/0000-0002-0105-4743)
- Gerard P. McGlacken (ORCID: https://orcid.org/0000-0002-7821-0804)
- Shobhna Choudhary (ORCID: https://orcid.org/0000-0001-7629-5368)
- Gregory M. Greetham (ORCID: https://orcid.org/0000-0002-1852-3403)
- Adrian C. Whitwood (ORCID: https://orcid.org/0000-0002-5132-5468)
- Richard J. Gammons (ORCID: https://orcid.org/0000-0002-0572-5575)
- Ian J. S. Fairlamb (ORCID: https://orcid.org/0000-0002-7555-2761)
- Katrina Mackey
- Eimear Courtney (ORCID: https://orcid.org/0000-0002-8619-3872)
- Benjamin R. O’Donoghue
Institutions
- Rutherford Appleton Laboratory (GB)
- University College Cork (IE)
- Analytical Engineering (United States) (US)
- University of York (GB)
Publication Details
- Journal
- Inorganic Chemistry
- Published
- 2025-08-12
- DOI
- https://doi.org/10.1021/acs.inorgchem.5c01443
- Citations
- 3
- Primary Topic
- Catalytic C–H Functionalization Methods
- Type
- article
- Field-Weighted Citation Impact
- 2.81
Funders
- Royal Society
- Royal Society of Chemistry
- Science Foundation Ireland
- Irish Research Council
- Engineering and Physical Sciences Research Council
- Science and Technology Facilities Council