Neue Komplexbildner auf der Basis stickstoffhaltiger Oxalsäurederivate

Nitrogen Derivates of Oxalic Acid as New Complexing Agents Heterocycles with a exocylic 1,4-diaza-1, 3-diene structure 5a–d have σ-bonding and π-backbonding properties similar to the diazadienes (DAD) 1 . The investigations of the molybdenum complexes 11 and 12 of the ligands 5 show a dominant σ-interaction and only a small π-backbonding, comparable with the compound (CO)₄Mo(iPYC) 14 , a complex of pyridinecarbaldehyde isopropylimine (iPYC). The oxalamidine (TPOA) 4 (precursor of the heterocycles 5a–d ) are present in a s-trans (E/E)-form with two stable intra-molecular hydrogen bridges. 4 reacts with ferrous and cobaltous chloride to the polymer coordination compounds 8 and 9 . According to the diazadiene 1 oxalamadine 4 substitutes two carbonyls in Mo(CO)₆ by formation of (CO)₄Mo(TPOA) 10 . The coordinated ligand 4 shows in the complex 10 a s-cis(E/E)-form with respect to the free ligand and no H-bridges were observed. The crystal structures of TPOA 4 and (CO)₄Mo(TPOA) 10 were determined. Cyclisation reactions on the coordinated oxalamidine are possible.