Synthesis and luminescence of a charge-neutral, cyclometalated iridium(III) complex containing N∧C∧N- and C∧N∧C-coordinating terdentate ligands

The first examples of iridium(III) complexes containing a terdentate, NLambdaCLambdaN-coordinated 1,3-di(2-pyridyl)benzene derivative, cyclo-metalated at C2 of the benzene ring, are reported. This mode of binding becomes significant only if competitive cyclometalation at C4/C6 is blocked, and the ligand 1,3-di(2-pyridyl)-4,6-dimethyl-benzene (dpyxH) has been prepared to achieve this condition. The charge-neutral complex [Ir(dpyx)(dppy)], 2, (dppyH(2) = 2,6-diphenylpyridine) has been isolated, containing dpyx and dppy bound to the metal through one and two carbon atoms, respectively. A terpyridyl analogue, [Ir(dpyx)(ttpy)](PF6)(2), 3, (ttpy = 4'-tolylterpyridine) has also been prepared and its X-ray crystal structure determined, confirming the NLambdaCLambdaN binding mode of dpyx. Complex 2 emits strongly in degassed solution at 295 K ( lambda(max) = 585 rim, Phi = 0.21, tau = 3900 ns, in CH3CN). In solution, the excited state can also undergo photodissociation, through cleavage of one of the Ir-C(dppy) bonds.