Significant O–H Bond Weakening in CpMn(CO)<sub>2</sub>(CH<sub>3</sub>OH): Evidence for the Generation of the CpMn(CO)<sub>2</sub>(CH<sub>3</sub>O) Radical upon H Atom Abstraction by O<sub>2</sub>
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Abstract
The
UV–visible photolysis of CpMn(CO)<sub>3</sub> in methanol
generates CpMn(CO)<sub>2</sub>(CH<sub>3</sub>OH), which upon H atom
abstraction using either O<sub>2</sub>, dpph, or H<sub>2</sub>O<sub>2</sub> gives the CpMn(CO)<sub>2</sub>(CH<sub>3</sub>O) radical complex.
The radical with a lifetime of 10 to 20 min has been mainly characterized
using FTIR and ESR spectroscopy and chemical oxidation studies. Together
with density functional theory calculations, it is shown that the
O–H bond is significantly weakened in the CpMn(CO)<sub>2</sub>(CH<sub>3</sub>OH) complex compared to free methanol. NBO spin density
analysis suggests that the bond cleavage is facilitated by the formation
of the CpMn(CO)<sub>2</sub>(CH<sub>3</sub>O) radical in which the
electron spin is localized at the metal center rather than at the
oxygen atom
