Azo-oximate metal-carbonyl to metallocarboxylic acid the intermediate Ir(III) radical congener: quest for co-ligand driven stability of open- and closed-shell complexes.

The redox non-innocent behavior of the diaryl-azo-oxime ligand L1 has been accentuated the synthesis of metastable anion radical complexes of type -[Ir(L)Cl(CO)(PPh)] 2 (CO is to azo group of the ligand) by the oxidative coordination reaction of 1 with Vaska's complex. The stereochemical role of co-ligands the interplay of π-bonding has been found to be decisive in controlling the aptitude of the coordinated redox non-innocent ligand to accept or reject an electron. This has been clarified the isolation of quite a few complexes as well as the failure to synthesize some others. The oxidized analogues of type -[Ir(L)Cl(CO)(PPh)]2+ (CO and azo group of the ligand are ) as well as its isomer -[Ir(L)Cl(CO)(PPh)]3+ (CO and azo group of the ligand are ) have been structurally characterized but the radical anion congener of the latter could not be synthesized. Furthermore, the closed shell complexes [Ir(L)Cl(PPh)] 4 and [Ir(L)Cl(PPh)] 5 have been well characterized by diffraction as well as spectral techniques but their corresponding azo anion radical complexes could not be isolated and this is attributed to the influence of ancillary ligands. The anion radical complexes -[Ir(L)Cl(CO)(PPh)] 2 may be rapidly transformed to the metallocarboxylic acids -[Ir(L)Cl(COH)(PPh)] 6 a proton-coupled electron transfer (PCET) process, thereby demonstrating the role of odd electron over the coordinated ligand framework to trigger metal-mediated carbonyl to carboxylic acid functionalization. Complexes 6 are further stabilized intramolecular -COH⋯ON- (carboxylic acid⋯oximato) H-bonding. The optoelectronic properties as well as the origin of transitions in the complexes were analyzed by TD-DFT and theoretical analysis, which further disclose that the odd electron in -[Ir(L)Cl(CO)(PPh)] 2 is primarily azo-oxime centric with very low contribution from the iridium center.