Kamata Keigo, Hirano Tomohisa, Kuzuya Shinjiro, Mizuno Noritaka
Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
J Am Chem Soc. 2009 May 27;131(20):6997-7004. doi: 10.1021/ja901289r.
The reaction of peroxotungstates (H(2)WO(4) + H(2)O(2)) with H(2)SeO(4) gave the novel selenium-containing dinuclear tungsten species, (TBA)(2)[SeO(4){WO(O(2))(2)}(2)] (I, TBA = (n-C(4)H(9))(4)N), which was characterized by elemental analysis, IR, Raman, UV-vis, (77)Se NMR, (183)W NMR, and CSI-MS. Various kinds of homoallylic and allylic alcohols were efficiently epoxidized to the corresponding epoxy alcohols in high yields with 1 equiv. H(2)O(2) with respect to the substrates. Compound I showed the highest catalytic activity for H(2)O(2)-based epoxidation of homoallylic and allylic alcohols among selenium and tungsten complexes. The turnover frequency reached up to 150 h(-1) in a 10 mmol-scale epoxidation of cis-3-hexen-1-ol and this value was the highest among those reported for the transition-metal catalyzed epoxidation of homoallylic alcohols with H(2)O(2). The kinetic, mechanistic, computational studies showed that the stabilization of the transition-state by the hydrogen bonding between I and the substrates results in the high reactivity for the I-catalyzed epoxidation of homoallylic and allylic alcohols. The nature of the hetero atoms in the di- and tetranuclear peroxotungstates with XO(4)(n-) ligands (X = As(V), P(V), S(VI), Si(IV), etc.) was crucial in controlling the Lewis acidity of the peroxotungstates, which significantly affects their electrophilic oxygen transfer reactivity. All the data of the structural, kinetic, spectroscopic, and computational comparison show that the dimeric peroxotungstate unit, {WO(O(2))(2)}(2), in I is activated by the SeO(4)(2-) ligand.
过氧钨酸盐（H₂WO₄ + H₂O₂）与H₂SeO₄反应生成了新型含硒双核钨物种(TBA)₂[SeO₄{WO(O₂)₂}₂]（I，TBA = [(n-C₄H₉)₄N]⁺），通过元素分析、红外光谱、拉曼光谱、紫外可见光谱、⁷⁷Se核磁共振、¹⁸³W核磁共振和串联质谱对其进行了表征。相对于底物，1当量的H₂O₂能将各种高烯丙基醇和烯丙基醇高效地环氧化为相应的环氧醇。在硒和钨配合物中，化合物I对基于H₂O₂的高烯丙基醇和烯丙基醇环氧化反应表现出最高的催化活性。在顺式-3-己烯-1-醇的10 mmol规模环氧化反应中，周转频率高达150 h⁻¹，该值是报道的过渡金属催化高烯丙基醇与H₂O₂环氧化反应中的最高值。动力学、机理和计算研究表明，I与底物之间的氢键对过渡态的稳定作用导致了I催化高烯丙基醇和烯丙基醇环氧化反应的高反应活性。具有XO₄ⁿ⁻配体（X = As(V)、P(V)、S(VI)、Si(IV)等）的双核和四核过氧钨酸盐中杂原子的性质对于控制过氧钨酸盐的路易斯酸性至关重要，这显著影响了它们的亲电氧转移反应活性。所有结构、动力学、光谱和计算比较的数据表明，I中的二聚过氧钨酸根单元{WO(O₂)₂}₂被SeO₄²⁻配体活化。
