Showing papers by "Rita G. Hazell published in 2001"

Catalytic, highly enantioselective Friedel-Crafts reactions of aromatic and heteroaromatic compounds to trifluoropyruvate. A simple approach for the formation of optically active aromatic and heteroaromatic hydroxy trifluoromethyl esters.

Abstract: A new catalytic enantioselective synthetic method for the formation of optically active aromatic and heteroaromatic hydroxy-trifluoromethyl ethyl esters is presented. This catalytic enantioselective Friedel-Crafts reaction of trifluoromethyl pyruvate with aromatic and heteroaromatic compounds is catalyzed by a chiral bisoxazoline copper(II) complex and proceeds in good yield and with high enantiomeric excess. For a series of substituted indoles, the corresponding 3-substituted hydroxy-trifluoromethyl ethyl esters are formed in up to 93% yield and 94% ee. Pyrrole and 2-substituted pyrroles also react with trifluoromethyl pyruvate in a highly enantioselective aromatic electrophilic reaction and up to 93% ee and good yields are obtained. Furanes and thiophenes give the corresponding 2-hydroxy-trifluoromethyl ethyl esters in high enantiomeric excess; however, the yields of the products are only moderate. Various types of aromatic compounds react in this catalytic reaction with trifluoromethyl pyruvate to give the aromatic electrophilic addition product in good yield. To obtain high enantiomeric excess (> 80% ee) it is necessary that aromatic amines are protected with sterically demanding protecting groups such as benzyl or allyl. This prevents coordination of the amine nitrogen atom to the catalyst, as aromatic amines having a N,N-dimethyl group probably coordinate to the catalyst, leading to a significant reduction of the enantioselective properties of the catalyst. On the basis of the experimental results and the absolute configuration of the formed chiral center, the mechanism for the catalytic enantioselective Friedel-Crafts reaction is discussed.

Solid and solution state structures of mono- and di-nuclear iron(III) complexes of related hexadentate and pentadentate aminopyridyl ligands

Abstract: Two mononuclear iron(III) complexes formed with the related ligands N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (tpen) and N-benzyl-N,N′,N′-tris(2-pyridylmethyl)ethylenediamine (bztpen) have been studied. X-Ray crystallography reveals for the complex [Fe(tpen)][ClO4]3 that tpen acts as a hexadentate ligand in the solid state. In methanol or water containing solutions it was shown by EPR and UV-Vis spectroscopy that one pyridyl arm is exchanged by a solvent molecule. In dmf solution only partial exchange of a pyridyl arm was observed. The complex with the related pentadentate ligand bztpen [Fe(bztpen)Cl][ClO4]2 showed exchange of the coordinated chloride with methanol and water, but not with dmf. In water containing solutions both complexes are slowly converted into the dimeric μ-oxo complexes [(tpen)FeIII(Cl)OFeIII(Cl)(tpen)]2+ or [(bztpen)FeIII(Cl)OFeIII(Cl)(bztpen)]2+. This reaction is accelerated by addition of an excess of chloride.

Study of formation of cobalt and zinc phosphates in solvothermal synthesis using piperazine and 2-methylpiperazine as templating molecules. Structure investigations of [C4H8N2H4][(Co0.44(1)Zn0.56(1))2(PO4)(H1.5PO4)2] and of [C5N2H14][(Co0.25(3)Zn0.75(3))(HPO4)2]

Abstract: The compounds [C4H8N2H4][Zn2(PO4)(H1.5PO4)2], [C4H8N2H4][(Co0.44(1)Zn0.56(1))2(PO4)(H1.5PO4)2], [C5N2H14][Zn(HPO4)2] and [C5N2H14][(Co0.25(3)Zn0.75(3))(HPO4)2] were obtained in solvothermal synthesis using piperazine or 2-methylpiperazine as templating molecules. Syntheses were made in Teflon-lined pressure vessels at temperatures up to 190 °C and the crystallization processes were investigated by real time in situ measurements of synchrotron X-ray powder diffraction patterns at temperatures up to 200 °C.