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Issue 2, 2014
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Iron–molybdenum-oxo complexes as initiators for olefin autoxidation with O2

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Abstract

The reaction between [(TPA)Fe(MeCN)2](OTf)2 and [nBu4N](Cp*MoO3) yields the novel tetranuclear complex [(TPA)Fe(μ-Cp*MoO3)]2(OTf)2, 1, with a rectangular [Mo–O–Fe–O–]2 core containing high-spin iron(II) centres. 1 proved to be an efficient initiator/(pre)catalyst for the autoxidation of cis-cyclooctene with O2 to give cyclooctene epoxide. To test, which features of 1 are essential in this regard, analogues with zinc(II) and cobalt(II) central atoms, namely [(TPA)Zn(Cp*MoO3)](OTf), 3, and [(TPA)Co(Cp*MoO3)](OTf), 4, were prepared, which proved to be inactive. The precursor compounds of 1, [(TPA)Fe(MeCN)2](OTf)2 and [nBu4N](Cp*MoO3) as well as Cp2*Mo2O5, were found to be inactive, too. Reactivity studies in the absence of cyclooctene revealed that 1 reacts both with O2 and PhIO via loss of the Cp* ligands to give the triflate salt 2 of the known cation [((TPA)Fe)2(μ-O)(μ-MoO4)]2+. The cobalt analogue 4 reacts with O2 in a different way yielding [((TPA)Co)2(μ-Mo2O8)](OTf)2, 5, featuring a Mo2O84− structural unit which is novel in coordination chemistry. The compound [(TPA)Fe(μ-MoO4)]2, 6, being related to 1, but lacking Cp* ligands failed to trigger autoxidation of cyclooctene. However, initiation of autoxidation by Cp* radicals was excluded via experiments including thermal dissociation of Cp2*.

Graphical abstract: Iron–molybdenum-oxo complexes as initiators for olefin autoxidation with O2

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Publication details

The article was received on 27 Aug 2013, accepted on 01 Oct 2013 and first published on 23 Oct 2013


Article type: Paper
DOI: 10.1039/C3DT52349G
Citation: Dalton Trans., 2014,43, 806-816
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    Iron–molybdenum-oxo complexes as initiators for olefin autoxidation with O2

    J. P. Falkenhagen, C. Limberg, S. Demeshko, S. Horn, M. Haumann, B. Braun and S. Mebs, Dalton Trans., 2014, 43, 806
    DOI: 10.1039/C3DT52349G

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