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Time-Resolved Infrared Observation of a Long-Lived Transient in the Photo-Decarbonylation of Mn(CO)5C(O)CH3: Potential Relevance to the CO Migratory Insertion Mechanism

  • Author(s): Boese, WT
  • Lee, B
  • Ryba, DW
  • Belt, ST
  • Ford, PC
  • et al.
Abstract

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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