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Cyclooctatetraene Palladium (II) Bromide

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Cyclooctatetraene Palladium (II) Bromide NOTIZEN 269 Cyclooctatetraene Palladium (II) Bromide; This synthesis is complicated by the fact that solvents Synthesis and Characterization such as benzene and toluene precipitate palladium (II) bromide from the nitrile complex. H e r s c h e l F r y e , E r n e s t K u u i a n , a n d J a m e s V ie b r o c k The technique used in the present study consisted University of the Pacific, Stockton, California of first preparing a slurry of 0.5 gram of bis (benzo­ (Z. Naturforschg. 20 b, 269 [1965] ; eingegangen am 7. Dezember 1964) nitrile) palladium (II) bromide with one milliliter of benzonitrile; this mixture was soluble in fifty milli­ Many complexes of transition metal ions with cyclo­ liters of benzene without precipitation of palladium octatetraene have been reported, but there is no record (II) bromide. Addition at room temperature of two of the preparation of cyclooctatetraene palladium (II) milliliters of cyclooctatetraene to the filtered solution bromide. In 1953, J e n s e n 1 prepared cyclooctatetraene caused a color change from brown to cherry red. After platinum (II) chloride from sodium tetrachloroplatinate two hours, dark red crystals of cyclooctatetraene pal­ (II) and cyclooctatetraene using water as solvent; the ladium (II) bromide settled out; these were vacuum method may also be used for the corresponding bro­ filtered, washed with petroleum ether, and vacuum mide. K h a r a s c h , S e y l e r , and M a y o 2 reported pre­ dried in a desiccator. The yield was 70 milligrams, paration of certain olefin-palladium (II) chloride com­ or about 10 per cent. Attempts to increase the yield plexes by means of the reaction of an olefin such as by dilution with petroleum ether resulted in precipita­ cyclohexene, styrene, or ethylene with bis (benzonitrile) tion of palladium(II) bromide; less benzene cannot palladium (II) chloride. This method has been modified be used because the benzonitrile complex would not by K u l j ia n and F r y e 3 and used in the present research then dissolve completely. to prepare bis (benzonitrile) palladium (II) bromide, Cyclooctatetraene palladium (II) bromide is soluble both unreported compounds. in acetone, chloroform, benzene, methanol, and glacial acetic acid; it is insoluble in diethyl ether and reacts Experimental with dimethylformamide, dimethylsulfoxide, and ex­ cess benzonitrile. The compound was characterized by Preparation of bis (benzonitrile) palladium(ll) bromide comparison of the infrared spectrum with that of cyclo­ octatetraene palladium (II) chloride as reported by Two grams of palladium (II) bromide was dissolved F r it z and K e l l e r 4. Carbon-hydrogen data are given in fifty milliliters of aniline free benzonitrile with pro­ in Table I: longed heating at 100 °C. The resulting solution was filtered while hot through a Buchner funnel and calculated found was allowed to cool. Dark brown crystals of bis (benzo­ % C %H % C % H nitrile) palladium (II) bromide were recovered. The 25.94 2.14 25.91 2.20 remaining solution was diluted with either cyclohexane or low boiling petroleum ether to precipitate more Table I. Data on carbon-hydrogen analysis of cycloocta­ crystals. The mixed crystals were vacuum filtered, tetraene palladium (II)-bromide. washed with pretroleum ether, and desiccated at atmo­ spheric pressure over Drierite; reduced pressure tends Table II lists ultraviolet-visible absorption data for to ‘pump off’ benzonitrile. Yield was 3.2 grams, or cyclooctatetraene palladium(II) bromide; data is in­ about 90 per cent. The compound was characterized by cluded for the chloride for comparison: comparison of the infrared spectrum with that of bis (benzonitrile) palladium(II) chloride; no elemental cyclooctatetraene cyclooctatetraene analysis was made of this material. palladium (II) palladium (II) bromide chloride Preparation of cyclooctatetraene palladium(Il) wavelength, bromide millimicrons 432 370 430 357 This compound could not be prepared by the re­ molar absorp­ action of sodium tetrachloropalladate (II) with cyclo­ tivity x io -3 7.4 2.0 7.4 2.3 octatetraene in water; thus a preparation with bis (benzonitrile) palladium (II) bromide was developed. Table II. Ultraviolet-visible spectral data. 1 K. J e n s e n , Acta. chem. scand. 7, 868 [1953]. 3 E. K u l j i a n and H. F r y e , Z. Naturforschg. 19 b, 651 [1964]. 2 M. Kharasch, R. S e y l e r and F. Mayo, J. Amer. diem. Soc. 4 H. F r it z and H. K e l l e r , Chem. Ber. 95, 158 [1962]. 60, 882 [1938]..
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