Iridium(III) Complexes Formed by O−H and/Or C−H Activation of 2-(Arylazo)phenols

Reaction of 2-(arylazo)phenols with [Ir(PPh3)3Cl] in refluxing ethanol in the presence of a base (NEt3) affords complexes of three different types, viz. [Ir(PPh3)2(NO−R)(H)Cl] (R = OCH3, CH3, H, Cl and NO2), [Ir(PPh3)2(NO−R)(H)2] and [Ir(PPh3)2(CNO−R)(H)]. Structures of the [Ir(PPh3)2(NO−Cl)(H)Cl], [Ir(PPh3)2(NO−Cl)(H)2] and [Ir(PPh3)2(CNO−Cl)(H)] complexes have been determined by X-ray crystallography. In the [Ir(PPh3)2(NO−R)(H)Cl] and
[Ir(PPh3)2(NO−R)(H)2] complexes, the 2-(arylazo)phenolate ligands are coordinated to the metal center as monoanionic
bidentate N,O-donors, whereas in the [Ir(PPh3)2(CNO−R)(H)] complexes, they are coordinated to iridium as dianionic
tridentate C,N,O-donors. In all three products formed in ethanol, the two PPh3 ligands are trans. Reaction of
2-(arylazo)phenols with [Ir(PPh3)3Cl] in refluxing toluene in the presence of NEt3 affords complexes of two types,
viz. [Ir(PPh3)2(CNO−R)(H)] and [Ir(PPh3)2(CNO−R)Cl]. Structure of the [Ir(PPh3)2(CNO−Cl)Cl] complex has been
determined by X-ray crystallography, and the 2-(arylazo)phenolate ligand is coordinated to the metal center as a
dianionic tridentate C,N,O-donor and the two PPh3 ligands are cis. All of the iridium(III) complexes show intense
MLCT transitions in the visible region. Cyclic voltammetry shows an Ir(III)−Ir(IV) oxidation on the positive side of
SCE and an Ir(III)−Ir(II) reduction on the negative side for all of the products.