Oxidation of substrates by an iridium dioxygen complex: Intramolecular oxidation of carbon monoxide and activation of a carbonyl group by attack of a heterocyclic nitrogen

Article abstract of DOI:10.1021/om00010a044

The square-planar complex [Ir(C₇H₄NS₂)(CO)(PPh₃)₂] (1) is obtained in high yield from the reaction of lithium benzothiazole-2-thiolate (LiC₇H₄NS₂) with Vaska's complex, [IrCl-(CO)(PPh₃)₂]. Coordination of the new ligand in 1 and in the homologous rhodium complex should occur through the sulfur atom, as shown by their protonation reactions with HBF₄, which give the hydridoiridium(III) complex [IrH(C₇H₄NS₂)(CO)(PPh₃) ₂]BF₄ and the rhodium(I) compound [Rh(CO)(PPh₃)₂(C₇H₅NS ₂)]BF₄, respectively. The neutral ligand C₇H₅NS₂ reacts with 1 to give [IrH(C₇H₄NS₂)₂(CO)(PPh ₃)₂] (4). Complex 1 adds dihydrogen, methyl iodide, and dioxygen. The dioxygen complex [Ir(C₇H₄NS₂)(O₂)(CO)(PPh ₃)₂] (7) undergoes an intramolecular oxidation of the carbonyl ligand, catalyzed by water, to yield the carbonate complex [Ir(C₇H₄NS₂)(CO₃)(PPh ₃)₂] (8). Labeling studies show that the reaction is multistep and oxygen from water is incorporated into the carbonate ligand. Sulfur dioxide is oxidized by complex 7, but in addition, activation of the carbonyl group occurs by attack of the heterocyclic nitrogen of the benzothiazole-2-thiolate ligand to give [Ir{C(O)NC(S)SC₆H₄}-(SO₄)(PPh₃) ₂] (11). In 8 both benzothiazole-2-thiolate and carbonate anions act as N,S- and O,O-chelating ligands. The structure of 11 shows a C,S-chelating ligand, obtained by an unprecedented incorporation of the carbonyl group of 7 into the benzothiazole-2-thiolate through the heterocyclic nitrogen, in addition to a chelating sulfato ligand.