Synthesis of Secondary, Tertiary and Quaternary 1,3,5-Triazapenta-1,3-dienes and Their CoII, ZnII, PdII, CuII and BF2 Coordination Compounds

The secondary and tertiary 1,3,5-triazapenta-1,3-dienes 2 and 3 are easily obtained by the reaction of N-imidoyl chlorides with amidines or from ethyl N-imidoytimidoates 5 and primary amines. In a new synthetic pathway the compounds 5 were prepared by the reaction of imidoates in their protonated or free form with N-imidoyl chlorides. A quaternary 1,3,5-triazapenta-1,3-diene 4a is obtained by the reaction of the imidoate 5b with pyrrolidine. X-ray diffraction studies of the tertiary 1,3,5-triazapenta-1,3-diene 3c and its protonated form 3c center dot HCl allow the comparison of different patterns of intermolecular hydrogen bonding in the solid state. Two equivalents of a secondary 1,3,5-triazapenta-1,3-diene 2 were treated at room temperature after deprotonation with potassium tent-butoxide with CuCl2, Ni(ClO4)(2) or with Pd(ac)(2) (without deprotonation) to give the corresponding neutral 2:1 chelate complexes (2a)(2)center dot Cu, (2a)(2)center dot Ni and (2b)(2)center dot Pd, respectively. A fluorescent boron complex 2b center dot BF2 was obtained by reacting 2b with boron trifluoride-diethyl ether. From the tertiary triazapentadiene 3c and CoCl2 or ZnCl2 the six-membered 1:1 chelate complexes 3c center dot CoCl2 and 3c center dot ZnCl2, respectively, were obtained. In these cases a proton shift from the terminal nitrogen atom of the free ligand to the central nitrogen atom of the complex was observed. Two equivalents of 3c reacted at room temperature with Cu(ac)(2) or Pd(ac)(2) to form the neutral 2:1 chelate complexes (3c)(2)center dot Cu and (3c)(2)center dot Pd, respectively. A fluorescent 1:1 boron complex 3c center dot BF2 was obtained from 3c and boron trifluoride-diethyl ether. In all cases the triazapentadienes act as neutral or anionic bidentate ligands to form six-membered chelates with the metal ion or the boron centre. Most of the complexes were completely characterized, which included X-ray crystallography. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)