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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Flexible, linear, tetranuclear palladium complexes supported by tetraphosphine ligands with electron-withdrawing groups
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Flexible, linear, tetranuclear palladium complexes supported by tetraphosphine ligands with electron-withdrawing groups

机译：具有吸电子基团的四膦配体支撑的柔性线性四核钯配合物

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摘要

A linearly ordered tetraphosphine containing electron-withdrawing substituent groups on the outer phosphorus atoms, meso-bis[{di(3,5- difluorophenyl)phosphinomethyl}phenylphosphino]methane (dpmppmF2), was prepared and reacted with [Pd_2(RNC)_6](PF_6)_2 and Pd(dba)_2 to afford tetranuclear palladium complexes, [Pd_4(μ-dpmppmF_2)_2(RNC)_3](PF_6)_2 (R = 2,6-xylyl (Xyl) (1), 2,4,6-mesityl (2), 2,6-diisopropylphenyl (3) and tert-butyl (4)), which involve an asymmetric {(RNC)Pd_4(CNR)_2}~(2+) core supported by two dpmppmF2 ligands in anti-arrangement. Each terminal of the Pd_4 chain was capped by terminal isocyanide and a semi-bridging RNC is introduced into one terminal Pd site. Mechanistic investigation suggested that the dipalladium(i) complex, [Pd_2(μ- dpmppmF_2)_2(RNC)_2](PF_6)_2 (R = Xyl (6)), was a key intermediate to trap Pd0 species by the uncoordinated outer phosphine pendants with electron-withdrawing groups. Variable-temperature UV-vis and ~(31)P{~1H}, ~1H NMR spectroscopic studies demonstrated that the tetrapalladium complexes are quite fluxional in the solution state at high temperature (>20 °C) relating to a symmetric structure of [Pd_4(μ-dpmppmF_2)_2(RNC)_2](PF_6)_2, and the asymmetric solid state structures are retained even in the solution at low temperature (<-60 °C). Theoretical calculations with DFT methods on the asymmetric (R = Xyl (1)) and symmetric (R = Xyl (1′)) structures suggested that contribution of Pd0→PdI-Pd0-PdI with 60 cluster valence electrons (CVEs) would be dominant in 1, while the symmetric structure of 1′ can be recognized as Pd~I-Pd~0-Pd~0-Pd~I with 58 CVEs. The new tetraphosphine dpmppmF_2 was proven very effective in organizing dynamically flexible tetrapalladium chains.
机译：制备了在外部磷原子上具有吸电子取代基的线性有序四膦，内消旋双[{di（3,5-二氟苯基）膦基甲基}苯基膦基]甲烷（dpmppmF2），并与[Pd_2（RNC）_6]反应（PF_6）_2和Pd（dba）_2，得到四核钯配合物[Pd_4（μ-dpmppmF_2）_2（RNC）_3]（PF_6）_2（R = 2,6-二甲苯基（Xyl）（1），2， 4,6-间苯二甲酰基（2），2,6-二异丙基苯基（3）和叔丁基（4）），其中包含由两个dpmppmF2支撑的不对称{（RNC）Pd_4（CNR）_2}〜（2+）核配体的反排列。 Pd_4链的每个末端都被末端异氰酸酯封端，并且半桥状RNC被引入一个末端Pd位点。机理研究表明，二钯铝（i）络合物[Pd_2（μ-dpmppmF_2）_2（RNC）_2]（PF_6）_2（R = Xyl（6））是通过不配位的外膦捕获Pd0物种的关键中间体带有吸电子基团的侧链。可变温度紫外可见光谱和〜（31）P {〜1H}，〜1H NMR光谱研究表明，在高温下（> 20°C），四钯配合物在溶液状态下具有相当的流动性，与[[] Pd_4（μ-dpmppmF_2）_2（RNC）_2]（PF_6）_2甚至在低温（<-60°C）的溶液中也保留了不对称固态结构。使用DFT方法对不对称结构（R = Xyl（1））和对称结构（R = Xyl（1'））进行的理论计算表明，具有60个簇价电子（CVE）的Pd0→PdI-Pd0-PdI的贡献将占主导地位。在图1中，具有58个CVE的1'的对称结构可以被识别为Pd〜I-Pd〜0-Pd〜0-Pd〜I。事实证明，新的四膦dpmppmF_2在组织动态柔性四钯链方面非常有效。

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