Rhett Kempe

Metallacyclische acyl-carboxylate des nickels: Reaktivität der acylgruppe und synthesepotential bei kreuzkopplungsreaktionen mit alkylhalogeniden

Abstract 2-Cyclohexene-1,2-dicarboxylic acid-anhydride reacts with electron-rich nickel(0) centres to form nickel(0) complexes, whereas the isomeric 4-cyclohexene-1,2-dicarboxylic acid-anhydride reacts with ring opening of the anhydride to yield thermally stable acyl-carboxylato-nickel(II) compounds. The structure of a typical compound with (TMED)Ni 0 as a complex fragment was determined by single crystal X-ray structural analysis, the crystal also containing the product of CO-elimination, the nickelalactone. The cross-coupling reaction of metallacyclic acyl-carboxylato complexes of Ni with Rue5f8X can be used for the formation of side chains of steroids containing γ-ketocarboxylic acids. These compounds are interesting precursors for the preparation of a analogues of vitamin D3 metabolises.

Komplexkatalyse: XLII. Die Kristallstruktur des η3,η2,η2-Dodeca-2(E) 6(E),10(Z)-trien-1-yl-nickel(II)hexafluorophosphats - ein Beitrag zur Klärung der Katalysatorstruktur für die 1,4-cis-Polymerisation des Butadiens

Abstract Single crystals of the title complex could be obtained from a solution of CH2Cl2. The X-ray structure analysis shows an almost planar η3,η2,η2-coordination of the C12-chain around the central nickel atom. The C3-substituted allyl group exhibits the syn- configuration and for the two double bonds an E- and a Z-configuration is found. The quasi-planar arrangement of the C12-chain leaves the nickel atom open for further coordination from one side, and there is an observed weak interaction with the hexafluorophosphate anion. From the structure of the complex, detailed conclusions can be derived concerning the catalyst structure and the mechanism of the 1,4-cis polymerization of butadiene.

Komplexkatalyse: XLI. Die Kristallstruktur des η3,η2-Octa-2(E),7-dien-1-yl-(triphenylphosphin) nickel(II)-tetrafluoroborats, ein Beitrag zur Klärung der Koordinationsverhältnisse in der allylnickelkomplexkatalysierten Butadienpolymerisation

Abstract Single crystals of the title complex suitable for X-ray structure analysis could be obtained from the solution in dichloromethane by crystallization after addition of ether. The nickel is quasi-planar coordinated by the η3-bonded allyl group existing in the syn configuration, by the double bond at the other end of the C 8 -chain, and by the phosphine ligand. There is no coordinative interaction with the tetrafluoroborate anion. Thus, the existence and the structure of stable planar allyl mono(ligand) nickel(II) cations with one chelate coordinated olefinic double bond is proved, and for the mechanism of trans polymerization a sterically plausible explanation for Cue5f8C bond formation can be formulated.

Synthesis of novel N-aroyl- and N-arylsulfonylisothiazole-2-imines by cyclization of thiocyanatovinylaldehyde hydrazones

Abstract The synthesis of N-aroyl- and N-arylsulfonylisothiazole-2-imines 7c - f as well as the corresponding acceptor-substituted 2-aminoisothiazolium sa