Schiff base chemistry of the {ReO}3+ core: structural characterization of the unusual ‘3+2’ complex [ReO(η3-OC6H4–CHNC6H4-2-S)(η2-OC6H4CNC6H4-2-S)]

The reaction of [ReOCl3(PPh3)2] with salicylaldehyde-2-mercaptoanil (1) in methanol yields [ReO(OCH3)(PPh3)(η3-OC6H4CHNC6H4S)] (3). Reaction of 3 with 2-(2-hydroxyphenyl)benzothiazole (2) produces [ReO(η3-OC6H4CHNC6H4S)(η2-OC6H4)] (4) in good yield. Compound 4 may also be prepared directly from the reaction of [ReOCl3(PPh3)2] with excess 1, after prolonged reaction times in the presence of atmospheric oxygen. The structure of 3 exhibits a distorted octahedral Re(V) center coordinated to a terminal oxo-group, a methoxy ligand, a triphenylphosphine ligand, and the N, O and S donors of the tridentate Schiff base ligand. The octahedral geometry of 4 is defined by the terminal oxo-group, the N, O and S donors of the tridentate Schiff base ligand, and the N and O donors of the bidentate 2-(2-hydroxophenyl)benzothiazole ligand. Oxidation and cyclization of the Schiff base salicylaldehyde-2-mercaptoanil to produce 2-(2-hydroxyphenyl)benzothiazole is precedented and in this instance may be driven by the formation of the robust ‘3+2’ complex 4.