Synthesis of Iridium(III) and Rhodium(III) Complexes Bearing C8-Metalated Theophylline Ligands by Directed C–H Activation

The directed C–H activation at the C8 position of N-donor tethered theophylline with iridium­(III) and rhodium­(III) is presented. The donor strength of the N-tethered donor group has been varied. Proligands bearing a strongly donating imidazolin-2-ylidene or the weaker donating pyridine group were both metalated under similar conditions, suggesting that the electron density at the metal center does not play a significant role in the C–H activation step, which was concluded to proceed via a carboxylate-assisted route. The synthesis and characterization of iridium­(III) and rhodium­(III) complexes bearing chelating CNHC^Cazolato ligands (M = Ir: [4], M = Rh: [5]) and Npyridine^Cazolato ligands (M = Ir: [7], M = Rh: [8]) are reported. In addition, the NHC complexes which are the precursors to the CNHC^Cazolato complexes (M = Ir: [2], M = Rh: [3]) were isolated and characterized.