Eleonore Raabe

Developing potentially useful organometallic Lewis acid catalysts: (η-cyclopentadienyl)zirconium trichloride derivatives

Abstract The organometallic Lewis acid (η-cyclopentadienyl)zirconium trichloride ( 2 ) was obtained from bis(cyclopentadienyl)zirconium dichloride ( 1 ) and chlorine by means of a radical induced metal-Cp bond cleavage. Reaction of 2 with tetrahydrofuran gave the CpZrCl 3 -bis(tetrahydrofuran) adduct 3 ; treatment of either 2 or 3 with excess dimethylformamide furnished CpZrCl 3 (dmf) 2 ( 4 ). (η-Methylcyclopentadienyl)bis(tetrahydrofuran)zirconium trichloride ( 7 ) was prepared by treatment of ZrCl 4 (thf) 2 ( 6 ) with one molar equivalent of the (methylcyclopentadienyl)thallium reagent 5 . Complexes 3, 4 and 7 were characterized by X-ray diffraction studies and their dynamic NMR spectra were recorded. Complex 3 crystallizes in space group P 2 1 / n with cell parameters a 8.155(1), b 13.342(2), c 15.775(1) A, β 104.81(1)°, Z = 4, R = 0.041, R w = 0.056. CpZrCl 3 (dmf) 2 ( 4 ) crystallizes in space group P 2 1 / c with cell parameters a 7.790(1), b 15.445(2), c 13.893(1) A, β 93.94(1)°, Z = 4, R = 0.032, R w = 0.052. Complex 7 crystallizes in space group P 2 1 / n with cell parameters a 10.242(2), b 12.836(2). c 13.683(1) A, β106.37 (1)°, Z = 4, R = 0.037, R w = 0.039. The (cyclopentadienyl)bis(tetrahydrofuran)zirconium trichloride adduct 3 selectively catalyzed the Diels-Alder addition of 2,3-dimethylbutadiene and methacrolein at ambient temperature to give 1,3,4-trimethyl-3-cyclohexenyl-1-carbaldehyde ( 13 ). However, the CpZrCl 3 -Lewis acid catalyzed rearrangement of 13 to 1,3,4-trimethylbicyclo[2.2.1]heptan-2-one ( 14 ) does not take place at a significant rate until ca. 150°C.

Neue methoden zur herstellung von trialkylphosphan-alkadien-eisen(0)-komplexen

Abstract Mono(1,3-diene)tris(PR 3 )iron(0) complexes and bis(1,3-diene)mono(PR 3 )iron(0) complexes can be synthesized by reduction of FeCl 2 with magnesacyclopent-3-ene or activated Mg in the presence of 1,3-dienes and the appropriate PR 3 (R = Me, Et, Pr n , Cy) ligand. How the various substituted bis(1,3-diene)PR 3 Fe 0 complexes can be obtained from the thermally unstable 1,3-butadiene-tris(PR 3 )Fe 0 complexes by addition of 1,3- or 1,5-dienes is shown. The NMR spectra of these complexes indicate that they are square-pyramidal. This geometry was confirmed by a crystal structure analysis of 1,5-COD-1,3-butadiene-iron(0)-PEt 3 . The probable mechanism of formation of these novel iron(0) complexes is discussed and their characteristic properties are described.

1H-benzo[c]pyrazolo[1,2-a]cinnolines: a novel photochromic system

A novel photochromic system based on the pyrazolo[1,2-a]cinnoline structure (type 1,2-system) is described, together with syntheses, spectroscopic properties, and an X-ray analysis.

X-Ray structure and force field calculations of a chiral benzaldehyde Schiff base

The crystal structure of the Schiff base formed from benzaldehyde and (R)-2-aminobutan-1-ol is compared to one obtained from force-field calculations employing a new parameter set; the probable structure of the hydrogen-bonded Schiff base dimer is discussed.