Luminescent complexes of iridium(III) containing N∧C∧N-coordinating terdentate ligands

A family of bis-terdentate iridium(III) complexes is reported which contain a cyclometalated, N boolean AND C boolean AND N-coordinating 1,3-di(2-pyridyl)benzene derivative. This coordination mode is favored by blocking competitive cyclometalation at the C-4 and C-6 positions of the ligand. Thus, 1,3-di(2-pyridyl)-4,6-dimethylbenzene (dpyxH) reacts with IrCl(3)(.)3H(2)O to generate a dichlorobridged dimer [Ir(dpyx-N,C,N)Cl(mu-Cl)](2), 1. This dimer is cleaved by DMSO to give [Ir(dpyx)(DMSO)Cl-2], the X-ray crystal structure of which is reported here, confirming the N boolean AND C boolean AND N coordination mode of dpyx. The dimer 1 can also be cleaved by a variety of other ligands to generate novel classes of mononuclear complexes. These include charge-neutral bis-terdentate complexes of the form [Ir(N boolean AND C boolean AND N)(C boolean AND N boolean AND C)] and [Ir(N boolean AND C boolean AND N)(C boolean AND N boolean AND O)], by reaction of 1 with C boolean AND N boolean AND C-coordinating ligands ( e. g., 2,6-diphenylpyridine and derivatives) and C boolean AND N boolean AND O-coordinating ligands (based on 6-phenylpicolinate), respectively. Treatment of 1 with terpyridines leads to dicationic complexes of the type [Ir(N boolean AND C boolean AND N)(N boolean AND N boolean AND N)](2+), while 2-phenylpyridine gives [Ir(dpyx-N boolean AND C boolean AND N)(ppy-C,N)Cl]. All of the charge-neutral complexes are luminescent in fluid solution at room temperature. Assignment of the emission to charge-transfer excited states with significant MLCT character is supported by DFT calculations. In the [Ir(N boolean AND C boolean AND N)(C boolean AND N boolean AND C)] class, fluorination of the C boolean AND N boolean AND C ligand at the phenyl 2' and 4' positions leads to a blue-shift in the emission and to an increase in the quantum yield (lambda(max) = 547 nm, phi = 0.41 in degassed CH3CN at 295 K) compared to the nonfluorinated parent complex (lambda(max) = 585 nm, phi = 0.21), as well as to a stabilization of the compound with respect to photodissociation through cleavage of mutually trans Ir-C bonds. [Ir(dpyx-N boolean AND C boolean AND N)(ppy-C,N)Cl] is an exceptionally bright emitter: phi = 0.76, lambda(max) = 508 nm, in CH3CN at 295 K. In contrast, the [Ir(N boolean AND C boolean AND N)(C boolean AND N boolean AND O)] complexes are much less emissive, shown to be due to fast nonradiative decay of the excited state, probably involving reversible Ir-O bond cleavage. The [Ir(N boolean AND C boolean AND N)(N boolean AND N boolean AND N)](2+) complexes are very feeble emitters even at 77 K, probably due to the almost exclusively interligand charge-transfer nature of the lowest-energy excited state in these complexes.