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In Situ Spectroscopic Investigation of the Rhenium‐Catalyzed Deoxydehydration of Vicinal Diols
Author(s) -
Dethlefsen Johannes R.,
Fristrup Peter
Publication year - 2015
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201403012
Subject(s) - rhenium , vicinal , chemistry , alkene , catalysis , diol , photochemistry , infrared spectroscopy , kinetics , polymer chemistry , organic chemistry , physics , quantum mechanics
The mechanism of the CH 3 ReO 3 ‐catalyzed deoxydehydration of a vicinal diol to an alkene driven by oxidation of a secondary alcohol was investigated by time‐resolved, in situ IR spectroscopy and was found to occur in three steps: 1) reduction of the catalytically active methyltrioxorhenium(VII) to a rhenium(V) complex (the rate‐limiting step), 2) condensation of the diol and the rhenium(V) complex to a rhenium(V) diolate, and 3) extrusion of the alkene accompanied by oxidation of the Re center and thus regeneration of CH 3 ReO 3 . The reaction follows zero‐order kinetics initially but, unexpectedly, accelerates towards the end, which is explained in terms of a deactivating pre‐equilibrium, in which the catalytically active CH 3 ReO 3 condenses reversibly with the diol to form an inactive rhenium(VII) diolate. This conclusion is supported by the direct observation of a catalytically inactive species as well as DFT calculations of the IR spectra of the relevant compounds.