School of Chemistry, Bio21 Institute of Molecular Science and Biotechnology, University of Melbourne , Parkville, Victoria 3010, Australia.
Department of Chemistry, Faculty of Science, Central Tehran Branch, Islamic Azad University , Shahrak Gharb, Tehran 1467686831, Iran.
J Am Chem Soc. 2015 Oct 28;137(42):13588-93. doi: 10.1021/jacs.5b08044. Epub 2015 Oct 15.
Gas-phase studies utilizing ion-molecule reactions, supported by computational chemistry, demonstrate that the reaction of the enolate complexes (CH2CO2-C,O)M(CH3) (M = Ni (5a), Pd (5b)) with allyl acetate proceed via oxidative addition to give M(IV) species (CH2CO2-C,O)M(CH3)(η(1)-CH2-CH═CH2)(O2CCH3-O,O') (6) that reductively eliminate 1-butene, to form (CH2CO2-C,O)M(O2CCH3-O,O') (4). The mechanism contrasts with the M(II)-mediated pathway for the analogous reaction of (phen)M(CH3) (1a,b) (phen = 1,10-phenanthroline). The different pathways demonstrate the marked effect of electron-rich metal centers in enabling higher oxidation state pathways. Due to the presence of two alkyl groups, the metal-occupied d orbitals (particularly dz(2)) in 5 are considerably destabilized, resulting in more facile oxidative addition; the electron transfer from dz(2) to the C═C π* orbital is the key interaction leading to oxidative addition of allyl acetate to M(II). Upon collision-induced dissociation, 4 undergoes decarboxylation to form 5. These results provide support for the current exploration of roles for Ni(IV) and Pd(IV) in organic synthesis.
气相离子-分子反应研究结合计算化学表明，烯醇化物配合物(CH2CO2-C,O)M(CH3)（M=Ni(5a)，Pd(5b)）与烯丙基乙酸酯的反应通过氧化加成进行，生成 M(IV)物种(CH2CO2-C,O)M(CH3)(η(1)-CH2-CH=CH2)(O2CCH3-O,O')（6），该物种还原消除 1-丁烯，生成(CH2CO2-C,O)M(O2CCH3-O,O')（4）。该反应机制与类似的(phen)M(CH3)（1a，b）（phen=1，10-菲咯啉）反应的 M(II)介导途径形成对比。不同的反应途径表明富电子金属中心对更高氧化态途径的显著影响。由于存在两个烷基基团，5 中金属占据的 d 轨道（特别是 dz(2)）会受到相当大的去稳定化，从而更容易进行氧化加成；来自 dz(2)到 C═C π*轨道的电子转移是导致烯丙基乙酸酯与 M(II)发生氧化加成的关键相互作用。在碰撞诱导解离过程中，4 发生脱羧反应形成 5。这些结果为当前对 Ni(IV)和 Pd(IV)在有机合成中的作用的探索提供了支持。
