Synthesis of Ir^III Hydrido Complexes by Oxidative Addition of Halogenated Theophylline and Adenine Derivatives

Abstract

The Ir III hydrido complexes [ 1 ] and [ 2 ] have been synthesized by the regioselective oxidative addition of the N7–H bond of 8-halogenotheophyllines to [IrCl(coe) 2 ] 2 in the presence of PPh 3 . The use of dppf in this reaction yielded the bimetallic Ir III /Fe II hydrido complexes [ 3 ] and [ 4 ]. X-ray diffraction studies confirmed that complexes [ 1 ]–[ 4 ] feature a theophyllinato ligand coordinated to the metal center in the rarely observed, chelating fashion via the N7 and O1 atoms. In addition, 8-bromoadenine reacts with [IrCl(coe) 2 ] 2 in the presence of PPh 3 to form the Ir III hydrido complex [ 5 ] which features one anionic 8-bromoadeninato and one neutral 8-bromoadenine ligand linked by an intramolecular hydrogen bond. Complex [ 5 ] was characterized by high-resolution mass spectrometry and an X-ray diffraction analysis but could not be analyzed by nuclear magnetic resonance spectroscopy because of its low solubility.

Methanol-Mediated Formation of an Iridium(III) NHC/Azolato Chelate Complex: An Experimental and Theoretical Study

“…Previous work suggested that the synthesis of an iridium­(III) NHC complex bearing a tethered theophylline ligand requires an acetate-assisted C–H activation mechanism, and not a direct C–H oxidative addition, to successfully metalate the C8 position of theophylline due to its electron-poor nature . In addition, treatment of a C8-iodinated theophylline with [IrCl­(coe) 2 ] 2 resulted in the oxidative addition of the N–H bond, keeping the C8–I bond intact . Taken together, the serendipitous installation of a carbonato ligand on iridium in [ 2 ] presented an opportunity to study the metalation of a C8-activated theophylline ligand in the presence one equivalent of an internal base.…”

“…44 In addition, treatment of a C8-iodinated theophylline with [IrCl(coe) 2 ] 2 resulted in the oxidative addition of the N−H bond, keeping the C8−I bond intact. 52 Taken together, the serendipitous installation of a carbonato ligand on iridium in [2] presented an opportunity to study the metalation of a C8activated theophylline ligand in the presence one equivalent of an internal base.…”