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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Theoretical study on intramolecular allene-diene cycloadditions catalyzed by PtCl_2 and Au(i) complexes
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Theoretical study on intramolecular allene-diene cycloadditions catalyzed by PtCl_2 and Au(i) complexes

机译：PtCl_2和Au（i）配合物催化分子内烯丙二烯环加成反应的理论研究

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摘要

The intramolecular [4C+3C] cycloaddition reaction of allenedienes catalysed by PtCl_2 and several Au(i) complexes has been studied by means of DFT calculations. Overall, the reaction mechanism comprises three main steps: (i) the formation of a metal allyl cation intermediate, (ii) a [4C(4π)+3C(2π)] cycloaddition that produces a seven-membered ring and (iii) a 1,2-hydrogen migration process on these intermediates. The reaction proceeds with complete diastereochemical control resulting from a favoured exo-like cycloaddition. Allene substituents have a critical influence in the reaction outcome and mechanism. The experimental observation of [4C+2C] cycloadducts in the reaction of substrates lacking substituents at the allene terminus can be explained through a mechanism involving Pt(iv)-metallacycles. With gold catalysts it is also possible to obtain [4C+2C] cycloaddition products, but only with substrates featuring terminally disubstituted allenes, and employing π-acceptor ligands at gold. However the mechanism for the formation of these adducts is completely different to that proposed with PtCl_2, and consists of the formation of a metal allyl cation, subsequent [4C+3C] cycloaddition and a 1,2-alkyl shift (ring contraction). Electronic analysis indicates that the divergent pathways are mainly controlled by the electronic properties of the gold heptacyclic species (L-Au-C 2), in particular, the backdonation capacity of the metal center to the unoccupied C_2 (pπ-orbital) of the intermediate resulting from the [4C+3C] cycloaddition. The less backdonation, (i.e. using P(OR)_3Au~+ complexes), the more favoured is the 1,2-alkyl shift.
机译：通过DFT计算研究了PtCl_2和几种Au（i）配合物催化的烯丙二烯类的分子内[4C + 3C]环加成反应。总体而言，反应机理包括三个主要步骤：（i）金属烯丙基阳离子中间体的形成;（ii）产生七元环的[4C（4π）+ 3C（2π）]环加成反应;和（iii） 1,2-氢在这些中间体上的迁移过程。由于有利的exo样环加成反应，反应进行了完全的非对映化学控制。丙二烯取代基对反应结果和机理具有关键影响。可以通过涉及Pt（iv）-金属环的机理来解释[4C + 2C]环加合物在烯丙基末端缺少取代基的底物反应中的实验观察结果。使用金催化剂，也可能获得[4C + 2C]环加成产物，但仅使用具有末端双取代的烯基并在金上使用π受体配体的底物。但是，这些加合物的形成机理与PtCl_2所提出的机理完全不同，包括形成金属烯丙基阳离子，随后的[4C + 3C]环加成反应和1,2-烷基转移（环收缩）。电子分析表明，发散途径主要受金七环类（L-Au-C 2）的电子性质控制，特别是金属中心对中间体的未占据C_2（pπ-轨道）的背胶能力由[4C + 3C]环加成反应得到。较少的回授（即使用P（OR）_3Au〜+络合物），1,2-烷基移位越受青睐。

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