Reactivity of [M=O] (3+) (M = Tc, Re) core towards 2-mercapto-1,3-azole ligands. Formation of a new organometallic complex of Re(IV) and X-ray crystal structures

Imidazole-2-thiol derivatives H2L1–3 (H2L1 = 1H-benzoimidazole-2-thiol, H2L2 = 5-methyl-1H-benzoimidazole-2-thiol, and H2L3 = 1H-imidazole-2-thiol) act as neutral monodentate ligands in a number of technetium and rhenium complexes. Disubstituted M(V) (M = Tc, Re) complexes of the type [AsPh4]{[MOCl2(H2Ln)2(H2O)]Cl2} are formed when [MOCl4] react with H2L1–3 in 1:2 stoichiometric ratio. Single crystal X-ray structure determinations were carried out on [AsPh4]{[TcOCl2(H2L1)2(H2O)]Cl2}. The coordination sphere is pseudo-octahedral in which the sulfur atoms of two ligands sit in the equatorial plane and a water molecule is in trans to the TcO multiple bond. All the complexes react with an excess of the corresponding ligand to form tetrasubstituted cationic species {[MO(H2Ln)4]Cl3}. These complexes can be also isolated by reaction of [MOCl4] with an excess of ligand. No complex is obtained with benzothiazole-2-thiol (HL4) and benzoxazole-2-thiol (HL5). Ligand exchange reactions of [ReOCl3(PPh3)2] with HL4,5 have also been investigated. Treating the oxo-precursor with HL4 no product is isolated, while with HL5 the chelate oxo-compound [ReOCl2(L5)(PPh3)] is formed as two isomers. An interesting organometallic complex of Re(IV) [ReCl3(L5*)(PPh3)2] is obtained when a slight excess of HL5 reacts with [ReOCl3(PPh3)2] in refluxing benzene solution and in air. Geometry about the Re atom is approximately octahedral in which the equatorial plane contains three Cl atoms and the carbon atom of the benzoxazole ligand anion, the apical positions are occupied by two PPh3. The reaction with O-ethyl S-hydrogen p-tolyl carbonothioimidate HL6 which contains the same heteroatoms of HL5 does not form an organometallic species, but forms the chelate oxo-Re(V) complex [ReOCl2(L6)(PPh3)]. The solid-state structure has been authenticated by X-ray crystallography.