CHARACTERIZATION OF BIO-RELATED VANADIUM AND ZINC - COMPLEXES CONTAINING TETRADENTATE DITHIOLATE-DISULFIDE, DITHIOLATE-DIAMINE AND DITHIOLATE-AMINE-AMIDE LIGANDS

The reaction of [VCl3(PMe(2)Ph)(3)] with HSS'S'SH (where the HS are th iophenolate and the S' thioether functions, respectively), H-2-1, yiel ds [VCl(mu-SS'S'S)](2) (3) with one of the thiolate groups of each of the two ligands in the bridging mode. Reaction of Na-2-1 with [VOCl2(t hf)(2)] leads to a polymeric product of composition [VO(SS'S'S)](x) (4 ). The products obtained from the reaction between [VOCl2(thf)(2)] and NaSNNSNa, Na-2-2, (S is thiophenolate, N the amine function) depend o n subtle changes in the diamine backbone of this ligand: If the amine functions are linked by -CH2CH2- (2a), the tetranuclear V-IV complex [ V(SNNS)mu-O](4) (5) is formed alongside the V-III complex [VCl(SNNS)]. If the backbone is -CH(Me)CH(Me)- (2b), [VO(SNNS)] (7) and the dinucl ear, asymmetrically ore-bridged V-IV complex [{(SNN-S)(thf)V}mu-O{V(SN N-S)}] (8) are obtained. In 8, one amine of each of the two ligands is deprotonated to the amide group. In either case, the complexation is accompanied by oxidation of the thiolates to disulfides, leading to th e generation of teraazatetrathio-cycloeicosanes (6a/b). Compounds 5 an d 8 . 2THF have been structurally characterized by X-ray analyses. The connectivities have further been established for 3 . 2CH(2)Cl(2) and for 6b, which exhibits the same conformation as formally characterized 6a. The cluster compound 5 is stabilized by an extended intramolecula r N-H...O and N-H...S) hydrogen-bonding network. In 7 . 2THF, one of t he THFs of crystallization is hydrogen-bonded to the NH of the penta-c oordinated {VO(SNN-S)} moiety; further, there is an intramolecular hyd rogen bond between one of the thiolates of this tetragonal-pyramidal h alf of the molecule and the NH of the octahedral {VO(SNN-S)thf} half. The generation of the ligand 2b from its precursor compound, the zinc complex [Zn(SNNS)] (9) leads to the structural characterization of 9 . CH3OH with a large SZnS bite angle and a strong hydrogen bond between the methanolic OH and one of the thiolate sulfurs. The relevance of t hese compounds in biological systems is discussed.