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(L-1)] were synthesized and characterized by spectroscopic methods and X-ray crystallography. The monomeric, five-coordinate compounds are air-stable and bind (L-1)(2-) tridentate in the equatorial coordination sphere. Dimeric products of the compositions [{ReOCl(L-2)}(2)O] and [ReOCl(L-3)](2) were isolated during reactions with HL2 and H2L3. While dimerization in [{ReOCl(L-2)}(2)O] is established via an oxo bridge, the metal atoms in [ReOCl(L-3)](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.