Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, United Kingdom.
J Am Chem Soc. 2020 Aug 19;142(33):14169-14177. doi: 10.1021/jacs.0c04732. Epub 2020 Aug 11.
Alkyl-Pd(IV) complexes are frequently invoked in the proposed mechanisms of Pd-catalyzed C(sp)-H functionalization reactions, though few examples of Pd(IV) complexes containing cyclopalladated substrates have been isolated due to the instability of the high-valent Pd(IV) center. Herein, we report the synthesis of stable and isolable OCO pincer-supported alkyl-Pd(IV) complexes containing cyclopalladated alkylamine and oxime frameworks, which represent the first examples of alkyl-Pd(IV) complexes derived from the oxidation of cyclopalladated monodentate -donor substrates. The aminoalkyl-Pd(IV) complexes reacted efficiently with - and -nucleophiles to afford γ-functionalized alkylamine products. A mechanistic study of the nucleophile-mediated reductive elimination was conducted using an oxime-derived Pd(IV) complex, which revealed the intermediacy of a previously unexplored anionic Pd(IV) species.
烷基-Pd(IV) 配合物经常被引入到 Pd 催化的 C(sp)-H 官能化反应的机理中,尽管由于高价态 Pd(IV) 中心的不稳定性,很少有含有环钯化底物的 Pd(IV) 配合物被分离出来。在此,我们报告了稳定且可分离的含有环钯化烷基胺和肟骨架的 OCO 夹持型烷基-Pd(IV) 配合物的合成,这代表了首例由氧化环钯化单齿给体底物得到的烷基-Pd(IV) 配合物。氨基烷基-Pd(IV) 配合物与 - 和 - 亲核试剂反应,有效地得到了 γ-官能化的烷基胺产物。使用肟衍生的 Pd(IV) 配合物进行了亲核试剂介导的还原消除的机理研究,揭示了以前未探索过的阴离子 Pd(IV) 物种的中间体。