Flexible, linear, tetranuclear palladium complexes supported by tetraphosphine ligands with electron-withdrawing groups.
Flexible, linear, tetranuclear palladium complexes supported by tetraphosphine ligands with electron-withdrawing groups.
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DOI：
10.1039/c3dt51433a
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发表时间：
2013-10
影响因子：
4
通讯作者：
T. Tanase;Satoko Hatada;Ayaka Mochizuki;Kanako Nakamae;B. Kure;Takayuki Nakajima
中科院分区：
文献类型：
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作者：
T. Tanase;Satoko Hatada;Ayaka Mochizuki;Kanako Nakamae;B. Kure;Takayuki Nakajima
制备了外部磷原子上含有吸电子取代基的线性有序四膦，内消旋双[{二(3,5-二氟苯基)膦甲基}苯基膦]甲烷(dpmppmF2)，并与[Pd2(RNC)6](PF6)2和Pd(dba)2反应得到四核钯配合物， [Pd4(μ-dpmppmF2)2(RNC)3](PF6)2 (R = 2,6-二甲苯基 (Xyl) (1)、2,4,6-基 (2)、2,6-二异丙基苯基 (3) 和叔丁基 (4))，其中涉及由两个 dpmppmF2 配体支持的不对称 {(RNC)Pd4(CNR)2}(2+) 核心反安排。 Pd4 链的每个末端均由末端异氰化物封端，并将半桥接 RNC 引入到一个末端 Pd 位点。机理研究表明，二钯(I)络合物[Pd2(μ-dpmppmF2)2(RNC)2](PF6)2 (R = Xyl (6))是通过具有吸电子基团的不配位外部膦悬垂捕获Pd(0)物质的关键中间体。变温UV-vis和(31)P{(1)H}、(1)H NMR光谱研究表明，四钯配合物在高温(>20℃)溶液状态下具有相当的流动性，与[Pd4(μ-dpmppmF2)2(RNC)2](PF6)2的对称结构有关，并且即使在低温(<-60℃)溶液中也保留了不对称固态结构。用DFT方法对不对称（R = Xyl（1））和对称（R = Xyl（1'））结构的理论计算表明，具有60个团簇价电子（CVE）的Pd（0）→Pd（I）-Pd（0）-Pd（I）的贡献在1中占主导地位，而1'的对称结构可以被认为是Pd(I)-Pd(0)-Pd(0)-Pd(I)，具有 58 个 CVE。事实证明，新型四膦 dpmppmF2 在组织动态柔性四钯链方面非常有效。
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 [Pd2(RNC)6](PF6)2 and Pd(dba)2 to afford tetranuclear palladium complexes, [Pd4(μ-dpmppmF2)2(RNC)3](PF6)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)Pd4(CNR)2}(2+) core supported by two dpmppmF2 ligands in anti-arrangement. Each terminal of the Pd4 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, [Pd2(μ-dpmppmF2)2(RNC)2](PF6)2 (R = Xyl (6)), was a key intermediate to trap Pd(0) species by the uncoordinated outer phosphine pendants with electron-withdrawing groups. Variable-temperature UV-vis and (31)P{(1)H}, (1)H 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 [Pd4(μ-dpmppmF2)2(RNC)2](PF6)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 Pd(0)→Pd(I)-Pd(0)-Pd(I) 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 dpmppmF2 was proven very effective in organizing dynamically flexible tetrapalladium chains.