title: Cyclometallated iridium and platinum complexes with noninnocent ligands.
abstract: The electronic properties of the cyclometalated (CwedgeN) complexes of iridium and platinum metals with a catechol ligand have been studied experimentally and computationally. The synthesis and characterization of (p-tolylpyridine)Ir(3,5-di-tert-butylcatechol) (abbreviated Ir-sq) and (2,4-diflorophenylpyridine)Pt(3,5-di-tert-butylcatechol) (abbreviated Pt-sq) are reported along with their structural, spectral, and electrochemical properties. Reaction of the 3,5-di-tert-butylcatechol (DTBCat) ligand with the prepared cyclometalated metal complex was carried out in air in the presence of a base. The resulting complexes are air stable and are paramagnetic with the unpaired electron residing mainly on the catechol ligand. The bond lengths obtained from X-ray structure analysis and the theoretical results suggest the semiquinone form of the catechol ligand. Low-energy, intense (approximately 10(3) M-1 cm-1) transitions are observed in the visible to near-infrared region (600-700 nm) of the absorption spectra of the metal complexes. Electrochemically, the complexes exhibit a reversible reduction of the semiquinone form to the catechol form of the ligand and an irreversible oxidation to the unstable quinone form of the ligand. The noninnocent catechol ligand plays a significant role in the electronic properties of the metal complexes. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations on the two open-shell molecules provide the ground-state and excited-state energies of the molecular orbitals involved in the observed low-energy transitions. The spin density in the two complexes resides mainly on the catechol ligand. The intense transition arises from excitation of the beta electron from a HOMO-n (n = 1 or 2 here) to the LUMO, rather than from the excitation of the unpaired alpha electron.
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
authors: Bhavna
authors: B
authors: Hirani
authors: Jian
authors: J
authors: Li
authors: Peter I
authors: PI
authors: Djurovich
authors: Muhammed
authors: M
authors: Yousufuddin
authors: Jonas
authors: J
authors: Oxgaard
authors: Petter
authors: P
authors: Persson
authors: Scott R
authors: SR
authors: Wilson
authors: Robert
authors: R
authors: Bau
authors: William A
authors: WA
authors: Goddard
authors: Mark E
authors: ME
authors: Thompson