Amide‐Based Nonheme Cobalt(III) Olefin Epoxidation Catalyst: Partition of Multiple Active Oxidants CoVO, CoIVO, and CoIII-OO(O)CR
- 29 March 2012
- journal article
- Published by Wiley in Chemistry – A European Journal
- Vol. 18 (19), 6094-6101
- https://doi.org/10.1002/chem.201103916
Abstract
A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl2][Et4N] (1; H2bpc=4,5‐dichloro‐1,2‐bis(2‐pyridine‐2‐carboxamido)benzene), was prepared and then characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy, and X‐ray crystallography. This nonheme CoIII complex catalyzes olefin epoxidation upon treatment with meta‐chloroperbenzoic acid. It is proposed that complex 1 shows partitioning between the heterolytic and homolytic cleavage of an OO bond to afford CoVO (3) and CoIVO (4) intermediates, proposed to be responsible for the stereospecific olefin epoxidation and radical‐type oxidations, respectively. Moreover, under extreme conditions, in which the concentration of an active substrate is very high, the CoOOC(O)R (2) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the OO bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the OO bond of the CoOOC(O)R species might proceed predominantly by heterolytic cleavage, even in the presence of small amounts of protic solvent, to produce a discrete CoVO intermediate as the dominant reactive species. Evidence for these multiple active oxidants was derived from product analysis, the use of peroxyphenylacetic acid as the peracid, and EPR measurements. The results suggest that a less accessible CoVO moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors.Keywords
This publication has 100 references indexed in Scilit:
- Structure and reactivity of a mononuclear non-haem iron(III)–peroxo complexNature, 2011
- Modeling the cis‐Oxo‐Labile Binding Site Motif of Non‐Heme Iron Oxygenases: Water Exchange and Oxidation Reactivity of a Non‐Heme Iron(IV)‐Oxo Compound Bearing a Tripodal Tetradentate LigandChemistry – A European Journal, 2011
- Formation of stable and metastable porphyrin- and corrole-iron(IV) complexes and isomerizations to iron(III) macrocycle radical cationsJournal of Inorganic Biochemistry, 2009
- Iron-oxidation-state-dependent O–O bond cleavage of meta-chloroperbenzoic acid to form an iron(IV)-oxo complexInorganica Chimica Acta, 2008
- Laser Flash Photolysis Generation of High-Valent Transition Metal−Oxo Species: Insights from Kinetic Studies in Real TimeAccounts of Chemical Research, 2008
- Trans-dioxo Manganese(V) PorphyrinsJournal of the American Chemical Society, 2007
- Oxoiron(IV) porphyrin π-cation radical complexes with a chameleon behavior in cytochrome P450 model reactionsJBIC Journal of Biological Inorganic Chemistry, 2005
- Molecular and Electronic Structure of Four‐ and Five‐Coordinate Cobalt Complexes Containing Two o‐Phenylenediamine‐ or Two o‐Aminophenol‐Type Ligands at Various Oxidation Levels: An Experimental, Density Functional, and Correlated ab initio StudyChemistry – A European Journal, 2004
- MCPBA Epoxidation of Alkenes: Reinvestigation of Correlation between Rate and Ionization PotentialJournal of the American Chemical Society, 1998
- Syntheses, Structures, and Reactivities of Cobalt(III)−Alkylperoxo Complexes and Their Role in Stoichiometric and Catalytic Oxidation of HydrocarbonsJournal of the American Chemical Society, 1998