Unsaturated Hetero Chains, VIII First Metal Complexes of Oligonitrile Ligands: Palladium(II) Complexes of NMethoxycarbonyl- and N-Thiobenzoyl-1,3,5,7-tetraazaoctatetraenes

Two mononuclear six-membered chelate PdCl2 complexes 2a, b of the two different types of tetrameric oligonitriles 1a, b have been synthesized. Both contain square-planar palladium(II) with a cis arrangement of the chloride atoms. In complex 2a of the (omega)-amino-substituted N-methoxycarbonyl oligonitrile 1a the metal center is coordinated by the nitrogen atoms N1 and N3. Within the chelate ring alternating bond lengths for the C-N bonds are observed, whereas the non-complexed, more flattened part of the oligonitrile chain shows almost equal C-N bond lengths, indicating strong donor-acceptor interactions involving the terminal amino group and the N3-Pd moiety of the molecule. The complex 2b is derived from the thiobenzoyl ligand 1b bearing a terminal (R)-fenchylidene group. In 2b the sulfur atom S1 and the nitrogen atom N2 are involved in complexation. In contrast to 2a, strong bond-length alternation is observed in 2b for the complexed and the non-complexed part of the ligand. From the NMR spectra of both complexes no indication for a migration of the PdCl2 unit along the chain could be derived.