Rhenium and Technetium Complexes with Tridentate <i>N</i>-[(<i>N</i>′′,<i>N</i>′′-Dialkylamino)(thiocarbonyl)]-<i>N</i>′-substituted Benzamidine Ligands

N-[(Dialkylamino)(thiocarbonyl)]benzimidoyl chlorides react with functionalized amines such as 2-aminophenol, 2-methylaminopyridine, and 2-aminobenzoic acid in clean and high-yield procedures with the formation of the novel tridentate N-[(N′′,N′′-dialkylamino)(thiocarbonyl)]-N′-substituted benzamidine ligands H2L1, HL2, and H2L3. By starting from (NBu4)[MOCl4] (M = Re, Tc) or [ReOCl3(PPh3)2] and H2L1, a series of oxorhenium(V) and oxotechnetium(V) complexes of the composition [MOCl(L1)] were synthesized and characterized by spectroscopic methods and X-ray crystallography. The monomeric, five-coordinate compounds are air-stable and bind (L1)2− tridentate in the equatorial coordination sphere. Dimeric products of the compositions [{ReOCl(L2)}2O] and [ReOCl(L3)]2 were isolated during reactions with HL2 and H2L3. While dimerization in [{ReOCl(L2)}2O] is established via an oxo bridge, the metal atoms in [ReOCl(L3)]2 are connected by the carboxylic group of the ligand, and the product represents the first example of a high-oxidation state rhenium complex displaying such a bonding feature.