Intercluster Compound between a Tetrakis{triphenylphosphinegold(I)}oxonium Cation and a Keggin Polyoxometalate (POM): Formation during the Course of Carboxylate Elimination of a Monomeric Triphenylphosphinegold(I) Carboxylate in the Presence of POMs

The preparation and structural characterization of a novel intercluster compound, [{Au(PPh3)}4(μ4-O)]3[α-PW12O40]2·4EtOH (1), constructed between a tetrakis{triphenylphosphinegold(I)}oxonium cation and a saturated α-Keggin polyoxometalate (POM) are described. The tetragold(I) cluster oxonium cation was formed during the course of carboxylate elimination of a monomeric phosphinegold(I) carboxylate complex, i.e., [Au((R,S)-pyrrld)(PPh3)] [(R,S)-Hpyrrld = (R,S)-2-pyrrolidone-5-carboxylic acid], in the presence of the free acid form of a Keggin POM, H3[α-PW12O40]·7H2O. The liquid−liquid diffusion between the upper water/EtOH phase containing the Keggin POM and the lower CH2Cl2 phase containing the monomeric gold(I) complex gave a pure crystalline sample of 1 in good yield (42.1%, 0.242 g scale). Complex 1 was formed by ionic interaction between the tetragold(I) cluster cation and the Keggin POM anion. As a matter of fact, the POM anion in 1 can be exchanged with the BF4− anion using an anion-exchange resin (Amberlyst A-27) in BF4− form. By using other Keggin POMs, such as H4[α-SiW12O40]·10H2O and H3[α-PMo12O40]·14H2O, the same tetragold(I) cluster cation was also formed, i.e., in the forms of [{Au(PPh3)}4(μ4-O)]2[α-SiW12O40]·2H2O (2) and [{Au(PPh3)}4(μ4-O)]3[α-PMo12O40]2·3EtOH (3). Compounds 1−3, as dimethyl sulfoxide-soluble, EtOH- and Et2O-insoluble dark-yellowish white solids, were characterized by complete elemental analysis, thermogravimetric and differential thermal analyses, Fourier transform IR, X-ray crystallography, and solid-state (CPMAS 31P and 29Si) and solution (31P{1H} and 1H) NMR spectroscopy. The molecular structures of 1 and 2 were successfully determined. The tetragold(I) cluster cation was composed of four PPh3AuI units bridged by a central μ4-oxygen atom in the geometry of a trigonal pyramid or distorted tetrahedron.

本文报道了一种新型簇间化合物[{Au(PPh3)}4(μ4-O)]3[α-PW12O40]2·4EtOH（1）的制备与结构表征，该化合物由四(三苯基膦合金(I))氧鎓阳离子与饱和α-型Keggin结构多金属氧簇（polyoxometalate, POM）构建而成。该四核金(I)氧鎓阳离子是在Keggin型多金属氧簇的自由酸形式H3[α-PW12O40]·7H2O存在下，由单核膦合金(I)羧酸根配合物[Au((R,S)-pyrrld)(PPh3)]（其中(R,S)-Hpyrrld对应(R,S)-2-吡咯烷酮-5-羧酸）发生羧酸根消除反应过程中生成的。将含有Keggin型多金属氧簇的上层水/乙醇相与含有单核金(I)配合物的下层二氯甲烷相进行液液扩散，以42.1%的产率（0.242 g规模）得到纯净的化合物1的晶体样品。化合物1通过四核金(I)簇阳离子与Keggin型多金属氧簇阴离子之间的离子相互作用形成。事实上，可采用BF4-型阴离子交换树脂（Amberlyst A-27）将化合物1中的多金属氧簇阴离子与BF4-阴离子进行交换。使用其他Keggin型多金属氧簇，如H4[α-SiW12O40]·10H2O和H3[α-PMo12O40]·14H2O，同样可得到该四核金(I)簇阳离子对应的产物，即[{Au(PPh3)}4(μ4-O)]2[α-SiW12O40]·2H2O（2）与[{Au(PPh3)}4(μ4-O)]3[α-PMo12O40]2·3EtOH（3）。化合物1~3为可溶于二甲基亚砜（dimethyl sulfoxide）、不溶于乙醇与乙醚的深淡黄色固体，通过全元素分析、热重-差热分析、傅里叶变换红外光谱（Fourier transform IR）、X射线晶体学，以及固体交叉极化魔角旋转31P、29Si核磁共振与溶液相31P{1H}、1H核磁共振光谱进行了完整表征，其中化合物1与2的分子结构已成功解析。该四核金(I)簇阳离子由四个PPh3AuI单元构成，中心以μ4-氧原子桥联，其几何构型为三角锥或畸变四面体。