Potassium-chloride clusters

One of the first published cluster compounds of the heavier group 13 elements was the closo-dodecaaluminate K2[Ali2iBui2] 54 (Figure 2.3-10) [79], which possesses an almost undistorted icosahedron of 12 aluminum atoms with short Al-Al distances (268-270 pm). Up until today, it remained the only homonuclear cluster compound of the elements aluminum to indium which, with respect to structure and cluster electron count, is completely analogous to any boronhydride (see Chapters 1.1.2, 1.1.3, 1.1.5.2, and 2.1.5.6) (in this case doso-[Bi2H12]2 ). Compound 54 was formed in small quantities by the reaction of di(isobutyl)aluminum chloride with potassium and was isolated as dark red crystals (Figure 2.3-10). 

A tetraarylcubane has recently been reported. 2,6-Dimesitylphenyltin(II) chloride reacts with potassium to give, not the expected tetrahedral cluster (ArSn)4 but the highly distorted cubane 18-12 with D2h symmetry. The edges of the cube have rSnSn in the range of 285.3(2)-302.3(2) pm, but the diagonal bonds shown have r 310.7(2) pm.89... 

The potassium hydrate K OH2 was detected by Chupka " in a mass spectrometric study of ions emerging from a heated Knudsen cell containing KCl salt, and water as an impurity. The ion clusters Ar OH2, where M = Li, Na, and K, were also mass spectrometrically observed in a study of ions in flames by Hayhurst and Sugden. " The ions were produced by spraying an aqueous solution of the alkali chlorides in a premixed H2, 02,N2 flame at 1 atm. The authors also attempted to measure the ionic equilibria -h H2O = M OH2. However, their data are inconsistent, which is not surprising, considering the complexity of the experimental conditions and arrangement. 

Other suitable reaction solvents are aqueous tetrahydrofiiran, 1,2-diraethoxyethane or acetonitrile [28]. The same result was obtained by the method G, whereas 4-nitro-chlorobenzene was also coupled, in almost quantitative yield, within 2 h at 100 °C, or 87 h at room temperature. However, in the presence of tetra-n-butylammonium bromide (5 mol%), a soluble source of bromide anions, the SM reactions of aryl bromides have been effected in ethanol at room temperature in the presence of palladium(II) acetate or chloride (2 mol%) and potassium phosphate (2 eq.) as the base, even under exposure to air [55]. Palladium salts are reduced in situ with arylboronic acids to form catalytically active nano-sized palladium clusters (2-5 nm). The latter are stabilized by adsorbtion of one-layer bromide ions at the surface of each palladium-particle. Otherwise, the unstable nano-sized palladium-clusters are aggregated to the micro-sized catalytically inactive palladium black. In this manner, 2-bromonaphthalene (268) was reacted with 2-methoxyphenylboronic acid (269) to fiimish the biaryl 270 in 98% yield [55], respectively. Scheme 17. 

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