- A new and simple 'LEGO' system for the synthesis of branched oligopyridines
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The condensation of carboxamidrazones 1 with 1,2-dicarbonyl compounds 2 is the best method for the synthesis of alkyl, aryl or hetaryl substituted 1,2,4-triazines 3 - 7. These 1,2,4-triazines can be easily transformed to pyridines 8 - 12 by [4+2] cycloaddition with bicyclo[2.2.1]hepta-2,5-diene followed by [4+2] cycloreversions of nitrogen and cyclopentadiene. This reaction sequence offers a new, simple and general access to branched oligopyridines.
- Pabst, Gunther R.,Schmid, Konrad,Sauer, Juergen
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- Palladium(II)complexes of ambidentate and potentially cyclometalating 5-aryl-3-(2′-pyridyl)-1,2,4-triazine ligands
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The 5-aryl-3-(2′-pyridiyl)-1,2,4-triazine ligands under study [5-phenyl-(PyTZPh)L1 5-(3-methoxyphenyl)-(PyTZ3Me-OPh)L2 5-(4-methoxyphenyl)-(PyTZ4MeOPh)L3 5-(4-trifluoromethylphenyl)-(PyTZ4CF3Ph)L4 5-(4-fluorophenyl)-(PyTZ4FPh)L5 and tris-3,5,6-(2′-pyridyl)-1,2,4-triazine (Py3TZ)L6] react with [(COD)PdCl2] (COD = 1,5-cyclooctadiento form complexes [(L1-6)PdCl2] with N,N bidentate binding ligands, also including the potentially N,N,N tridentate ligand L6. This was concluded from an in-depth NMR spectroscopic study of the new complexes and from comparison with Pd-terpy complexes [(R′ terpy)PdCl]Cl [R′terpy = 4′-R′-2,2′:6′,2′′-terpyridine R′ = H or SMe], showing definite tridentate N,N,N coordination, and with the Pd-bpy complexes [(bpy)Pd(Mes)Cl] and [(bpy)PdCl2], show-ing definite bidentate N,N binding. The new ligands and complexes were fully characterised by multinuclear NMR spectroscopy, IR spectroscopy and mass spectrometry. No evidence for the parent triazine complexes is observed in EI-MS instead, cyclometalated complexes (HCl eliminatiowere detected in all cases. TDA/TG experiments support this assumption. Attempts to prepare the cyclometalated derivatives as substances failed, in line with the unfavourable binding mode. Detailed electrochemical measurements reveal ligand-centred reductions at very moderate potentials, in line with UV/Vis absorption spectroscopy and DFT calculations, revealing very low-lying triazine-centred LUMOs. Results from cyclic voltammetry also support the composition of [(Py3TZ)PdCl2].
- Zvirzdinaite, Maryte,Garbe, Simon,Arefyeva, Natalia,Krause, Maren,Von Der Stück, René,Klein, Axel
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p. 2011 - 2022
(2017/12/06)
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