Dipyridylketone: A Versatile Ligand for Cationic Heteroleptic Cyclometalated Iridium Complexes

The interest in cyclometalated iridium(III) complexes is continuously renewed due to their high emission quantum yields, long lifetimes, high thermal- and photo-stabilities, and tunable photoemission properties [1-3, and references therein]. The standard synthesis of these class of cationic Ir complexes is based on the direct reaction of the dimer [Ir(ppy)2(μ-Cl)]2 with N,N’ dipyridyl molecules. However, when the employed ligand contains a potentially coordinating group (like a terminal amino group), the synthesis could give rise to several side reaction products with low reaction yields. To circumvent the problem we reported a new synthetic procedure involving first the reaction of 2,2’-dipyridylketone (L1) with the dimer [Ir(ppy)2(μ-Cl)]2 that easily affords the complex IrL1 (having low emission quantum yield) as pure product in high yield [1], then the reactivity of the carbonyl moiety in IrL1 is used to get several derivatives with higher emission quantum yields [2]. The strategy can be applied to several reactions, but with some limitations. For example, the amino derivatives Ir(L5-L11) should be obtained following the classical synthesis only [3]. The complexes have been characterized by spectroscopy (NMR, UV-Vis and Fluorescence emissions), electrochemistry, and their photophysical properties rationalized by means of DFT and TD-DFT calculations. 1. G.Volpi, C.Garino, L.Salassa, J.Fiedler, K.I.Hardcastle, R.Gobetto, C.Nervi, Chem. Eur. J. 2009, 15, 6415-6427. 2. G.Volpi, C.Garino, E.Breuza, R.Gobetto, C.Nervi, Dalton Trans., 2012, 41, 1065–1073. 3. G.Volpi, C.Garino, C.Nervi, Dalton Trans., 2012, DOI:10.1039/C2DT30399J.