The two donor modules of an annelated pyridyl–mesoionic carbene ligand (aPmic) have different σ- and π-bonding characteristics leading to its electronic asymmetry. A Pd(II) complex 1 featuring aPmic catalyzes the oxidation of a wide range of terminal olefins to the corresponding methyl ketones in good to excellent yields in acetonitrile. The catalytic reaction is proposed to proceed via syn-peroxypalladation and a subsequent rate-limiting 1,2-hydride shift, which is supported by kinetic studies. The electronic asymmetry of aPmic renders a well-defined coordination sphere at Pd. The favored arrangement of reactants on the metal center features an olefin trans to the pyridyl module and a ^tbutylperoxide trans to the carbene. This arrangement gains added stability by the π-delocalization paved by the compatible orbitals on Pd, the pyridyl module, and the olefin that is perpendicular to the Pd(aPmic) plane. The π-interactions are absent in an alternate arrangement wherein the olefin is trans to the carbene. Density functional theory studies reveal the matching orbital overlaps responsible for the preferred arrangement over the other. This work provides an orbital description for the electronic asymmetry of aPmic.

中文翻译：

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电子不对称的退火吡啶基-中碳卡宾支架：在Pd（II）催化的Wacker型烯烃氧化中的应用

吡啶基-Mesoionic卡宾配体（aPmic）的两个供体模块具有不同的σ键和π键特性，导致其电子不对称。具有aPmic的Pd（II）配合物1可以催化多种末端烯烃氧化为相应的甲基酮，在乙腈中的产率高至优异。提出催化反应通过顺过氧化钯和随后的限速1，2-氢化物转移进行，这得到动力学研究的支持。aPmic的电子不对称性在Pd处提供了定义明确的协调范围。反应物在金属中心的优先排列，其特征是烯烃转化为吡啶基模块，^t过氧化丁基可转化为卡宾。这种布置通过在Pd，吡啶基组件和垂直于Pd（aPmic）平面的烯烃上的相容轨道铺平了π-离域作用，从而增加了稳定性。在另一种排列方式中不存在π-相互作用，其中烯烃被转化为卡宾。密度泛函理论研究表明，相配的轨道重叠比其他轨道重叠更为可取。这项工作为aPmic的电子不对称提供了轨道描述。