Iron–molybdenum-oxo complexes as initiators for olefin autoxidation with O<sub>2</sub>
作者:Jan P. Falkenhagen、Christian Limberg、Serhiy Demeshko、Sebastian Horn、Michael Haumann、Beatrice Braun、Stefan Mebs
DOI:10.1039/c3dt52349g
日期:——
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 [MoâOâFeâOâ]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 Mo2O84â 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*.
[(TPA)Fe(MeCN)2](OTf)2与[nBu4N](Cp*MoO3)反应生成了新型四核复合物[(TPA)Fe(δ-Cp*MoO3)]2(OTf)2,即 1,其矩形[MoâOâFeâOâ]2 内核含有高自旋铁(II)中心。事实证明,1 是顺式环辛烯与 O2 自氧化生成环辛烯环氧化物的高效引发剂/(预)催化剂。为了测试 1 在这方面的基本特征,我们制备了具有锌(II)和钴(II)中心原子的类似物,即[(TPA)Zn(Cp*MoO3)](OTf), 3 和[(TPA)Co(Cp*MoO3)](OTf), 4,事实证明它们没有活性。发现 1 的前体化合物 [(TPA)Fe(MeCN)2](OTf)2 和 [nBu4N](Cp*MoO3) 以及 Cp2*Mo2O5 也没有活性。在没有环辛烯的情况下进行的反应研究表明,1 通过失去 Cp* 配体与 O2 和 PhIO 反应,生成已知阳离子[((TPA)Fe)2(δ-O)(δ-MoO4)]2+ 的三盐酸盐 2。钴类似物 4 与 O2 以不同的方式发生反应,生成[((TPA)Co)2(δ-Mo2O8)](OTf)2, 5,其特点是具有配位化学中新颖的 Mo2O84â 结构单元。化合物[(TPA)Fe(δ-MoO4)]2, 6 与 1 有关,但缺少 Cp* 配体,未能引发环辛烯的自氧化反应。不过,通过包括 Cp2* 热解离在内的实验,排除了 Cp* 自由基引发自氧化的可能性。