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首页> 外文期刊>Chemistry: A European journal >Competitive and selective Csp~3-Br versus Csp~2-Br bond activation in palladium-catalysed Suzuki cross-coupling: An experimental and theoretical study of the role of phosphine ligands
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Competitive and selective Csp~3-Br versus Csp~2-Br bond activation in palladium-catalysed Suzuki cross-coupling: An experimental and theoretical study of the role of phosphine ligands

机译：钯催化的Suzuki交叉偶联中竞争性和选择性Csp〜3-Br与Csp〜2-Br键活化的关系：膦配体作用的实验和理论研究

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摘要

Phosphine ligands have been demonstrated to have an effect on reactivity and selectivity in the competitive intramolecular palladium-catalysed Suzuki-Miyaura coupling of dibromo sulfoxide 1a possessing two different hybridised electrophilic carbons. It was found that the bromine bond to the sp~3-hybridised carbon is selectively replaced in the presence of unhindered phosphines such as PPh_3 or xantphos. The use of hindered phosphine ligands such as P(o-tol)_3 and P(1-naphthyl)_3 reversed the selectivity, conducting the cross-coupling at the Csp ~2-Br. Identical trends were observed in external competition experiments carried out with bromomethyl sulfoxide and different substituted bromoarenes. DFT and DFT/MM calculations showed that the selectivity observed is mainly due to the different facility of the ligands to dissociate. Bisphosphine catalysts favour coupling at the sp~3 carbon, whereas monophosphine catalysts prefer the sp~2 carbon. Customised catalysts: Proper selection of the phosphine ligand in the palladium catalyst enables a highly intra- and intermolecular selective Suzuki-Miyaura coupling at either Csp ~3-Br or Csp~2-Br (see figure). DFT and DFT/MM calculations show that the selectivity observed is mainly due to the different facilities of the ligands for dissociation.
机译：在具有两个不同杂交亲电碳的二溴亚砜1a的竞争性分子内钯催化的铃木-宫浦偶合中，已证明膦配体对反应性和选择性有影响。发现在不受阻碍的膦如PPh_3或xantphos的存在下，选择性地取代了与sp_3杂化碳的溴键。使用受阻膦配体（例如P（o-tol）_3和P（1-萘基）_3）会逆转选择性，从而在Csp〜2-Br处进行交叉偶联。在使用溴甲基亚砜和不同取代的溴芳烃进行的外部竞争实验中，观察到了相同的趋势。 DFT和DFT / MM计算表明，观察到的选择性主要是由于配体解离的便利性不同。双膦催化剂有利于在sp〜3碳上偶联，而单膦催化剂优选在sp〜2碳上偶联。定制的催化剂：在钯催化剂中正确选择膦配体可以在Csp〜3-Br或Csp〜2-Br上实现高度的分子内和分子间选择性Suzuki-Miyaura偶联（见图）。 DFT和DFT / MM计算表明，观察到的选择性主要是由于配体离解的便利性不同。

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