Diao Tianning, Stahl Shannon S
Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706.
Polyhedron. 2014 Dec 14;84:96-102. doi: 10.1016/j.poly.2014.06.038.
Palladium-catalyzed acetoxylation of allylic C-H bonds has been the subject of extensive study. These reactions proceed via allyl-palladium(II) intermediates that react with acetate to afford the allyl acetate product. Benzoquinone and molecular oxygen are two common oxidants for these reactions. Benzoquinone has been shown to promote allyl acetate formation from well-defined π-allyl palladium(II) complexes. Here, we assess the ability of O to promote similar reactions with a series of "unligated" π-allyl palladium(II) complexes (i.e., in the absence of ancillary phosphorus, nitrogen or related donor ligands). Stoichiometric and catalytic allyl acetate formation is observed under aerobic conditions with several different alkenes. Mechanistic studies are most consistent with a "pull" mechanism in which O traps the Pd intermediate following reversible C-O bond-formation from an allyl-palladium(II) species. A "push" mechanism, involving oxidatively induced C-O bond formation, does not appear to participate. These results and conclusions are compared with benzoquinone-promoted allylic acetoxylation, in which a "push" mechanism seems to be operative.
钯催化的烯丙基C-H键乙酰氧基化反应一直是广泛研究的主题。这些反应通过烯丙基钯（II）中间体进行，该中间体与乙酸盐反应生成乙酸烯丙酯产物。苯醌和分子氧是这些反应中两种常见的氧化剂。已表明苯醌能促进由明确的π-烯丙基钯（II）配合物形成乙酸烯丙酯。在此，我们评估氧气与一系列“未配位”的π-烯丙基钯（II）配合物（即在没有辅助磷、氮或相关供体配体的情况下）发生类似反应的能力。在有氧条件下，使用几种不同的烯烃观察到了化学计量和催化量的乙酸烯丙酯生成。机理研究与“拉”机制最为一致，即氧气在烯丙基钯（II）物种可逆形成C-O键后捕获钯中间体。涉及氧化诱导C-O键形成的“推”机制似乎并未参与。将这些结果和结论与苯醌促进的烯丙基乙酰氧基化反应进行了比较，在后者中“推”机制似乎起作用。
