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

摘要

The preparation and structural characterization of a novel intercluster compound, [{Au(PPh_3)}_4(μ_4-O)] _3[α-PW_(12)O_(40)]_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)(PPh_3)] [(R,S)-Hpyrrld = (R,S)-2-pyrrolidone-5- carboxylic acid], in the presence of the free acid form of a Keggin POM, H _3[α-PW_(12)O_(40)]·7H_2O. The liquid-liquid diffusion between the upper water/EtOH phase containing the Keggin POM and the lower CH_2Cl_2 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 BF_4- anion using an anion-exchange resin (Amberlyst A-27) in BF4- form. By using other Keggin POMs, such as H_4[α-SiW~(12)O _(40)]·10H_2O and H_3[α-PMo _(12)O_(40)]·14H_2O, the same tetragold(I) cluster cation was also formed, i.e., in the forms of [{Au(PPh _3)}_4(μ_4-O)]_2[α-SiW _(12)O_(40)]·2H_2O (2) and [{Au(PPh _3)}_4(μ_4-O)]_3[α-PMo _(12)O_(40)]_2·3EtOH (3). Compounds 1-3, as dimethyl sulfoxide-soluble, EtOH- and Et_2O-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 ~(31)P and ~(29)Si) and solution (~(31)P{~1H} and ~1H) NMR spectroscopy. The molecular structures of 1 and 2 were successfully determined. The tetragold(I) cluster cation was composed of four PPh_3Au~I units bridged by a central μ4-oxygen atom in the geometry of a trigonal pyramid or distorted tetrahedron.