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Browsing Natural and Agricultural Sciences by Subject "2,2'-bipyrimidine"

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    Nanoscale model catalysts supported by metal organic frameworks
    (University of the Free State, 2009-11) Young, Cyril; Roodt, Andreas; Bezuidenhout, Ben
    English: The aim of this study was to use square planar platinum(II) and palladium(II) complexes for the synthesis of bridged complexes and as building blocks for the subsequent construction of two dimensional metal organic frameworks. For this purpose, pyrazine, 2,2‟ -bipyrimidine (bpym) and 4,4‟-bipyridine (4,4-bipy) were chosen as rigid bridging ligands. 4,5-Diazafluoren-9-one (Daf) was used as a non-bridging ligand in some of the investigations. The optimum conditions for crystallization of these bridged species were determined in order to co-crystallize the complexes with synthesized crystalline inorganic supports, which consisted of titanium and tungsten oxide. Characterization of the complexes was done by Infrared spectroscopy and Nuclear Magnetic Resonance spectroscopy (NMR). Single crystal X-ray crystallographic structure determinations of the following compounds were completed: cis-[Pd(PPh3)2(Daf)2].-(Trif)2.CH3NO2, cis- [Pd2BpymCl4].DMF and cis-[Pd(PPh3)2(NO3)2].CO(CH3)2 . cis-[Pd(PPh3)2(Daf)2].(Trif)2.CH3NO2 crystallized in the monoclinic space group P2/n with Z =4 in a unit cell with dimensions: a = 15.184(1) Å, b = 17.112(1) Å, c = 22.256(2) Å, α = 90 °, β = 99.676(4) °, γ = 90 ° at 100 K. Least-squares refinement led to a value of the conventional R index of 0.0750 and Rw = 0.1930 for 12345 reflections having I > 2σ(I). The palladium ion is coordinated cis with two phosphorus and two nitrogen atoms. The formal geometry of the palladium center is square planar. In addition there is an interaction between uncoordinated nitrogen atoms of 4,5-diazafluoren-9-one ligand in the axial positions, which results in the formation of a pseudo octahedral structure. A 50% disorder is present on one of the phenyl rings and one of the triflate counter ions. The Rw value is high as the result of one carbon atom and its hydrogen atoms not being located on the disordered acetone solvate. cis-[Pd2BpymCl4].DMF crystallized in the monoclinic space group C2/m with Z = 2 in a unit cell with dimensions: a = 10.73(7) Å, b = 14.24(8) Å, c = 5.938(2) Å, α = 90 °, β = 108.229(4) °, γ = 90 ° at 100 K. Least-squares refinement led to a value of the conventional R index of 0.032 and Rw = 0.0893 for 1110 reflections having I > 2σ(I). The complex consists of two palladium centers linked by the 2,2‟-bipyrimidine ligand. Each palladium atom is coordinated by two chlorido ions, two nitrogen atoms and has a square planar geometry. A 25 % disorder is found on the DMF solvate. cis-[Pd(PPh3)2(NO3)2].CO(CH3)2 crystallized in the monoclinic space group C2/c with Z = 4 in a unit cell with dimensions: a = 40.343(2) Å, b = 9.749(1) Å, c = 19.78(1) Å, α = 90 °, β = 115.514(1) °, γ = 90 ° at 100 K. Least-squares refinement led to a value of the conventional R index of 0.0773 and Rw = 0.1873 for 8638 reflections having I > 2σ(I). The complex consists of a square planar geometry at the palladium center coordinated to two oxygen atoms and two phosphorus atoms in a cis fashion. The high Rw value is a result of one carbon and its hydrogen atoms not being located on the disordered acetone solvate. A preliminary catalytic investigation was attempted using cis-[Pd2BpymCl4].DMF in Heck coupling and the Wacker oxidation process. However, no reproducible results were obtained due to infrastructural and time constraints.