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

Abstract

The square-planar complex [Ir(C7H4NS2)(CO)(PPh3)2] (1) is obtained in high yield from the reaction of lithium benzothiazole-2-thiolate (L1C7H4NS2) with Yaska’s complex, [IrCl-(COXPPhshl. 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)(PPli3)2]BF4 and the rhodium(I) compound [Rh(CO)(PPh3)2(C7HsNS2)]BF4, respectively. The neutral ligand C7H5NS2 reacts with 1 to give [IrH(C7BLNS2)2(CO)(PPh3)2] (4). Complex 1 adds dihydrogen, methyl iodide, and dioxygen. The dioxygen complex [Ir(C7H4NS2)(02)(C0)(PPh3)2l (7) undergoes an intramolecular oxidation of the carbonyl ligand, catalyzed by water, to yield the carbonato complex [Ir(C7H4NS2)(C03)(PPh3)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 1 1 heterocyclic nitrogen of the benzothiazole-2-thiolate ligand to give [Ir{C(0)NC(S)SC6H4}- (SCLXPPhsti (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.