NITROGEN DERIVATES OF OXALIC-ACID AS NEW COMPLEXING AGENTS

Heterocycles with a exocyclic 1,4-diaza-1,3-diene structure 5 a - d have sigma-bonding and pi-backbonding properties similar to the diazadienes (DAD) 1. The investigations of the molybdenum complexes 11 and 12 of the ligands 5 show a dominant sigma-interaction and only a small pi-backbonding, comparable with the compound (CO)4Mo(iPYC) 14, a complex of pyridinecarbaldehyde isopropylimine (iPYC). The oxalamidine (TPOA) 4 (precursor of the heterocycles 5 a - d) are present in a s-trans (E/E)-form with two stable intramolecular 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.