Dipalladium(I) terphenyl diphosphine complexes as models for two-site adsorption and activation of organic molecules.
Dipalladium(I) terphenyl diphosphine complexes as models for two-site adsorption and activation of organic molecules.
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DOI：
10.1021/ja406696k
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发表时间：
2013-10-23
影响因子：
15
通讯作者：
Agapie T
中科院分区：
文献类型：
--
作者：
Lin S;Herbert DE;Velian A;Day MW;Agapie T
有机分子跨两个金属中心结合的明确模型相对较少。采用对三联苯二膦来负载二钯(I)部分。与之前报道的二钯（I）物质不同，本系统提供了一个单分子半球，用于跨两个金属中心的配体结合，从而能够表征和比较各种饱和和不饱和有机分子的结合。二钯(I)三联苯二膦甲苯封端络合物是在甲苯存在下由二钯(I)六乙腈前体合成的。钯中心显示出与三联苯单元中心环和甲苯中心环的π系统的相互作用。甲苯与苯甲醚、1,3-丁二烯、1,3-环己二烯、噻吩、吡咯或呋喃的交换产生了明确的π键配合物，并通过晶体学、核磁共振 (NMR) 光谱和密度泛函理论对其进行了研究。结构表征表明，二钯单元与二膦中心芳烃的相互作用在该系列中没有显着变化，允许系统比较引入的配体与二钯部分的结合。一些复合物表现出罕见的μ2-η2:η2或μ2-η2:η1（O或S）桥接基序。噻吩和苯并噻吩加合物的氢化被证明在室温下进行。中性配体的相对结合强度通过核磁共振波谱监测的竞争实验来确定。配体取代的相对平衡常数跨越 13 个数量级。这代表了迄今为止对杂环和不饱和配体与双金属位点的相对结合的最全面的分析。通过静电势和分子轨道分析对结合相互作用进行了计算研究。阴离子配体也被证明可以形成 π 结合复合物。
Well-defined models for binding of organic molecules across two metal centers are relatively rare. A paraterphenyl diphosphine was employed to support a dipalladium(I) moiety. Unlike previously reported dipalladium(I) species, the present system provides a single molecular hemisphere for binding of ligands across two metal centers, enabling the characterization and comparison of the binding of a wide variety of saturated and unsaturated organic molecules. The dipalladium(I) terphenyl diphosphine toluene-capped complex was synthesized from a dipalladium(I) hexaacetonitrile precursor in the presence of toluene. The palladium centers display interactions with the π-systems of the central ring of the terphenyl unit and that of the toluene. Exchange of toluene for anisole, 1,3-butadiene, 1,3-cyclohexadiene, thiophenes, pyrroles, or furans resulted in well-defined π-bound complexes which were studied by crystallography, nuclear magnetic resonance (NMR) spectroscopy, and density functional theory. Structural characterization shows that the interactions of the dipalladium unit with the central arene of the diphosphine does not vary significantly in this series allowing for a systematic comparison of the binding of the incoming ligands to the dipalladium moiety. Several of the complexes exhibit rare μ2-η2:η2 or μ2-η2:η1 (O or S) bridging motifs. Hydrogenation of the thiophene and benzothiophene adducts was demonstrated to proceed at room temperature. The relative binding strength of the neutral ligands was determined by competition experiments monitored by NMR spectroscopy. The relative equilibrium constants for ligand substitution span over 13 orders of magnitude. This represents the most comprehensive analysis to date of the relative binding of heterocycles and unsaturated ligands to bimetallic sites. Binding interactions were computationally studied with electrostatic potentials and molecular orbital analysis. Anionic ligands were also demonstrated to form π-bound complexes.
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