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*
