Pietrzak Tomasz, Kubisiak Marcin, Justyniak Iwona, Zelga Karolina, Bojarski Emil, Tratkiewicz Ewa, Ochal Zbigniew, Lewiński Janusz
Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland.
Institute of Physical Chemistry, Polish Academy of Science, Kasprzaka 44/52, 01-224, Warsaw, Poland.
Chemistry. 2016 Dec 5;22(49):17776-17783. doi: 10.1002/chem.201603931. Epub 2016 Oct 27.
Despite the fact that extensive research has been carried out, the oxygenation of alkyl magnesium species still remains a highly unexplored research area and significant uncertainties concerning the mechanism of these reactions and the composition of the resulting products persist. This case study compares the viability of the controlled oxygenation of alkylmagnesium complexes supported by β-diketiminates. The structural tracking of the reactivity of (N,N)MgR-type complexes towards O at low temperature showed that their oxygenation led exclusively to the formation of magnesium alkylperoxides (N,N)MgOOR. The results also highlight significant differences in the stability of the resulting alkylperoxides in solution and demonstrate that [(BDI)Mg(μ-η :η -OOBn)] (in which BDI=[(ArNCMe) CH] and Ar=C H iPr -2,6) can be easily transformed to the corresponding magnesium alkoxide [(BDI)MgOBn] at ambient temperature, whilst [( BDI)Mg(μ-OOtBu)] (in which BDI=[(ArNCMe) CH] and Ar=C H F -2,4,6) is stable under similar conditions. The observed selective oxygenation of (N,N)MgR-type complexes to the corresponding (N,N)MgOOR alkylperoxides strongly contradicts the widely accepted radical-chain mechanism for the oxygenation of the main-group-metal alkyls. Furthermore, either the observed transformation of the alkylperoxide [(BDI)MgOOBn] to the alkoxide [(BDI)MgOBn] as well as the formation of an intractable mixture of products in the control reaction between the alkylperoxide [( BDI)MgOOtBu] and the parent alkylmagnesium [( BDI)MgtBu] complex are not in line with the common wisdom that magnesium alkoxide complexes' formation results from the metathesis reaction between MgOOR and Mg-R species. In addition, a high catalytic activity of well-defined magnesium alkylperoxides, in combination with tert-butyl hydroperoxide (TBHP) as an oxygen source, in the epoxidation of trans-chalcone is presented.
尽管已经进行了广泛的研究，但烷基镁物种的氧化仍然是一个高度未被探索的研究领域，关于这些反应的机理以及所得产物的组成仍存在重大不确定性。本案例研究比较了由β - 二酮亚胺支持的烷基镁配合物可控氧化的可行性。对(N,N)MgR型配合物在低温下与O反应活性的结构追踪表明，它们的氧化仅导致形成烷基过氧化物镁(N,N)MgOOR。结果还突出了所得烷基过氧化物在溶液中的稳定性存在显著差异，并表明[(BDI)Mg(μ - η:η - OOBn)]（其中BDI = [(ArNCMe)CH]且Ar = C6H3iPr - 2,6）在环境温度下可轻松转化为相应的醇盐[(BDI)MgOBn]，而[(BDI)Mg(μ - OOtBu)]（其中BDI = [(ArNCMe)CH]且Ar = C6H2F - 2,4,6）在类似条件下是稳定的。观察到的(N,N)MgR型配合物选择性氧化为相应的(N,N)MgOOR烷基过氧化物，与广泛接受的主族金属烷基氧化的自由基链机理强烈矛盾。此外，烷基过氧化物[(BDI)MgOOBn]向醇盐[(BDI)MgOBn]的观察到的转化以及在烷基过氧化物[(BDI)MgOOtBu]与母体烷基镁[(BDI)MgtBu]配合物的对照反应中形成难以处理的产物混合物，均不符合醇盐镁配合物由MgOOR和Mg - R物种之间的复分解反应形成的普遍认知。此外，还展示了定义明确的烷基过氧化物镁与叔丁基过氧化氢（TBHP）作为氧源在反式查尔酮环氧化反应中的高催化活性。
