CO-Photolysis-Induced H-Atom Transfer from Mn I O-H Bonds

• Published in: Inorganic chemistry 2019-04, Vol.58 (7), p.4679-4685
• Main Authors: Kadassery, Karthika J, Sethi, Komal, Fanara, Paul M, Lacy, David C
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.9b00322

The formation of TEMPOH from a mixture of [Mn(CO) (μ -OH)] (1) and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) is shown to occur through a light-initiated CO photolysis from 1 (illumination at 300-375 nm). One hypothesis is that the loss of carbon monoxide (CO) causes significant O-H bond weakening to render proton-coupled electron transfer (PCET) to TEMPO favorable. For instance, the ground-state O-H bond dissociation free energy (BDFE ) of 1 (computed with density functional theory and estimated using effective BDFE reagents) is too high to transfer an H-atom to TEMPO. We also demonstrate that TEMPO and 1 interact in the dark through a hydrogen-bonded "precomplex" (1···TEMPO). We suggest that the PCET reaction that forms TEMPOH is the result of a H-atom-transfer reaction that occurs immediately after photolysis of a CO ligand(s).