Syntheses, characterization, structure and redox properties of new Rh(III) cyclometallates incorporating azoimine ligands

The reaction of 2-(arylazo) aniline, 1 (HL-NH2) [where HL-NH2 is 2-(ArNN)C6H4–NH2; Ar = C6H5 (for HL1-NH2), p-MeC6H4(for HL2-NH2) and p-ClC6H4(for HL3-NH2). H of HL stands for dissociable proton of Ar due to orthometallation], with Rh(PPh3)3Cl (Wilkinson’s catalyst) furnished the cyclometallated azoimine complexes of composition (L-NH)Rh(PPh3)2Cl (2). All the complexes were characterized by spectroscopic technique and confirmed by X-ray structure determination of (L3-NH)Rh(PPh3)2Cl as a representative one. The azoimine chelate ring size of 2 is five membered where the phenyl ring adjacent to the chelate ring is distorted with four longer and two shorter bonds. This structural feature has been attributed to the delocalization of negative charge of the anionic ligands that formed in situ from the precursor (HL-NH2) due to dissociation of an amino proton. The (L-NH)Rh(PPh3)2Cl complexes display an one electron oxidative response in the range of 0.331 to 0.436 V vs. SCE.

Reaction of 2-(arylazo) aniline, HL-NH2, with Wilkinson’s catalyst afforded the new orthometallated complexes of Rh(III) upon oxidative addition. This has relevance with the C–H bond activation in azo compounds by Wilkinson’s catalyst. The electron transfer process of the new Rh(III) cyclometallates have been examined.Figure optionsDownload as PowerPoint slide