Synthesis and oxidation of Cp*Ir-III compounds: functionalization of a Cp* methyl group

Cp*IrCl2](2) (1) and new Cp*Ir-III(L-L) X complexes (L-L = N-O or C-N chelating ligands; X = Cl, I, Me) have been prepared and their reactivity with two-electron chemical oxidants explored. Reaction of 1 with PhI(OAc)(2) in wet solvents yields a new chloro-bridged dimer in which each of the Cp* ligands has been singly acetoxylated to form [(CpIrCl2)-Ir-OAc-Cl-III](2) (2) (Cp-OAc = eta(5)-C5Me4CH2OAc). Complex 2 and related carboxy-and alkoxy-functionalized Cp-OR complexes can also be prepared from 1 plus (PhIO)(n) and ROH. [(CpIrCl2)-Ir-OAc-Cl-III](2) (2) and the methoxy analogue [(CpIrCl2)-Ir-OMe-Cl-III](2) (3) have been structurally characterized. Treatment of [Cp*IrCl2](2) (1) with 2-phenylpyridine yields Cp*Ir-III(ppy)Cl(4Cl) ( ppy = cyclometallated 2-phenylpyridyl) which is readily converted to its iodide and methyl analogues Cp*Ir-III(ppy)I (4I) and Cp*Ir-III(ppy)Me (4Me). Cp*Ir-III complexes were also prepared with N-O chelating ligands derived from anthranilic acid (2-aminobenzoic acid) and a-aminoisobutyric acid (H2NCMe2COOH), ligands chosen to be relatively oxidation resistant. These complexes and 1 were reacted with potential two-electron oxidants including PhI(OAc)(2), hexachlorocyclohexadienone (C6Cl6O), N-fluoro-2,4,6-trimethylpyridinium (Me(3)pyF(+)), [Me3O]BF4 and MeOTf (OTf = triflate, CF3SO3). Iridium(V) complexes were not observed or implicated in these reactions, despite the similarity of the potential products to known Cp*Ir-V species. The carbon electrophiles [Me3O]BF4 and MeOTf appear to react preferentially at the N-O ligands, to give methyl esters in some cases. Overall, the results indicate that Cp* is not inert under oxidizing conditions and is therefore not a good supporting ligand for oxidizing organometallic complexes.