Base Hydrolysis of Methyltrioxorhenium. The Mechanism Revised and Extended: A Novel Application of Electrospray Mass Spectrometry

The full kinetic pH profile for the base-promoted decomposition of MTO to CH(4) and ReO(4)(-) was examined with the inclusion of new data at pH 7-10. Spectroscopic and kinetic data gave evidence for mono- and dihydroxo complexes: MTO(OH(-)) and MTO(OH(-))(2). Parallel unimolecular eliminations of methane from these species account for the rate-pH profile; the respective rate constants are MTO(OH(-)), k = 4.56 x 10(-)(5) s(-)(1) and MTO(OH(-))(2), k = 2.29 x 10(-)(4) s(-)(1) at 25 degrees C. Some kinetic data were acquired with electrospray mass spectrometry to monitor the buildup in the concentration of perrhenate ions. Reliable signals for each of the isotopomers of ReO(4)(-) were obtained by this method with initial MTO concentrations of 160mgr;M.