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Time-resolved infrared observation of a long-lived transient in the photo-decarbonylation of manganese complex Mn(CO)5C(O)CH3: potential relevance to the CO migratory insertion mechanism
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https://doi.org/10.1021/om00036a010Abstract
Flash photolysis experiments have been carried out at ambient temperature to probe potential reaction intermediates in the carbonylation of the methylmanganese complex CH3Mn(CO)5 (M) togivetheacyl product CH3C(O)Mn(CO)5 (A). Photo-decarbonylation of A gives a long-lived transient C, whose time-resolved infrared spectrum shows but modest sensitivity to the coordinating ability of the solvent such as cyclohexane, perfluoromethylcyclohexane, tetrahydrofuran, and 2,5-dimethyl-THF. Notably, C has an unexpectedly long lifetime (exceeding milliseconds) in each of the solvents investigated. Kinetics studies in cyclohexane show the competing trapping by CO to re-form A and isomerization to M occurs with the respective rate constants kco = 3.8 × 103 M−1 s−1 and 10 s−1. The former value is 3 orders of magnitude less than expected for a solvento complex under these conditions. Thus, it is concluded that TRIR spectra and reactivity patterns of C reflect stabilization of this intermediate by η2-coordination of the acyl group. © 1993, American Chemical Society. All rights reserved.
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