Synthesis and crystal structures of palladium(II) complexes of macrobicyclic azathiaether ligands

The macrobicyclic azathioether ligands L-1 and L-2 were investigated regarding their capability to form complexes with divalent palladium. L-1 represents a cyclophane-like ligand system comprising two 4-tert-butyl-2,6-bis(aminomethyl)thiophenolate units, which are linked by an ethylene and two 3-aza-1,5-pentylene units to give two seventeen-membered dithia-triaza crowns fused at the common ArSCH2CH2SAr fragment. L-2 is the hexa-N-methylated derivative of L-1. Treatment of L-1 and L-2 with two equivalents of [PdCl2(CH3CN)(2)] gave the new complexes [(L-1)Pd2Cl](+) (1) and [(L-2)Pd2Cl](2+) (2), respectively, which were isolated as perchlorate salts and characterized by elemental analysis, IR and NMR spectroscopy and by X-ray crystallography. In 1, L-1 acts as a septadentate ligand to give two distorted square-planar PdN3S and PdN3Cl units, respectively The structure of 2 shows L-2 to be hexacoordinate, yielding two distorted square-planar PdN2SCl units leaving two NMe groups dangling. NMR spectroscopic studies reveal that both complexes retain their solid-state structures in solution. The reaction of L-2 with one equivalent of [PdCl2(CH3CN)(2)] is accompanied by a bond cleavage reaction of one of the two aliphatic thioether bonds to afford the dinuclear complex [(L-3)Pd2Cl2]Cl (3.Cl) of the ring-opened 24-membered hexaaza-vinylthioether/thiophenolate derivative (L-3)(-). The crystal structure determination of 3-Cl reveals two distorted-square planar PdN2ClS units which are bridged by the thiophenolate sulfur atom of (L-3)(-). The vinyl-thioether moiety and the two remaining amine donors of (L-3)(-) do not interact with the two palladium ions. The X-ray structure analysis of the free macrocycle L-2 demonstrates that the C-S bond lengths become elongated upon coordination to the palladium(II) ions.