Iron-molybdenum-oxo complexes as initiators for olefin autoxidation with O-2

The reaction between [(TPA) Fe(MeCN)(2)](OTf)(2) and [nBu(4)N](Cp MoO3) yields the novel tetranuclear complex [(TPA) Fe(mu-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 O-2 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 [nBu(4)N](Cp MoO3) as well as Cp-2 Mo2O5, were found to be inactive, too. Reactivity studies in the absence of cyclooctene revealed that 1 reacts both with O-2 and PhIO via loss of the Cp ligands to give the triflate salt 2 of the known cation [((TPA)Fe)(2)(mu-O)(mu-MoO4)](2+). The cobalt analogue 4 reacts with O-2 in a different way yielding [((TPA)Co)(2)(mu-Mo2O8)](OTf)(2), 5, featuring a Mo2O84- structural unit which is novel in coordination chemistry. The compound [(TPA) Fe(mu-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 Cp-2 .