摘要：

IntroductionThe rich photophysical and electrochemical properties of polypyridyl metal complexes render them of great interest in a wide variety of applications, ranging from photocatalysts to luminescent chemosensors, and from new electroluminescent display materials to devices for the conversion of light to electrical energy.1a–dIridium(iii) complexes with cyclometallating ligands, for example, developed in the 1980s by Watts and others,2have recently enjoyed renewed interest, following the demonstration thattris(2-phenylpyridine)iridium(iii) is able to act as a “triplet harvester” when incorporated into electroluminescent devices, with accompanying large gains in efficiency.1c,3On the other hand, the longer lifetimes and appreciable quantum yields found in iridium(iii) complexes with an N6coordination sphere have sparked interest in their application as luminescent sensors or labels amenable to time-resolved detection procedures.4,5With this latter application in mind, we have been investigating the chemistry and luminescence properties of bis-terpyridyl iridium(iii) complexes.4Their preparation has proved challenging. Successful routes to date involve harsh conditions and laborious purification, reflecting the kinetic inertness of iridium(iii) with respect to ligand substitution processes: temperatures of 160 °C or higher are required.4–7Compared to the more widely-studied ruthenium analogues (typically prepared at about 80 °C), these conditions are very harsh, and represent a hurdle to be overcome in the further development of this chemistry. This is especially important if more delicate functionality is required in the terpyridines, for example, in the case of responsive complexes as chemosensors. In this paper, we report on the possibility of using a simple, bromo-functionalised complex as a synthon in the preparation of larger, potentially more elaborate complexes, by palladium-catalysed cross-coupling with aryl boronic acids. Since the cross-coupling can be achieved under much milder conditions (80–85 °C) than those typically required for the complexation of the terpyridines to the metal (160–200 °C), this strategy could provide an attractive solution to the synthetic problem.Previous work has shown that the luminescence lifetime of [Ir(tpy)2]3+(tpy = 2,2′:6′,2″-terpyridine) is extended upon introduction of simple aryl groups into the 4′-positions of the terpyridine (e.g.4-tolyl; 3,5-di-tert-butylphenyl7). The emission has been assigned to an excited state of predominantly3π–π* character,4–7as opposed to the shorter-lived MLCT states responsible for the luminescence of related cyclometallated compounds.8The complexes prepared during the present exploration of the cross-coupling synthetic strategy incorporate biphenyl-appended terpyridines, and hence offer an opportunity to investigate the effect of extended ligand conjugation on the luminesence properties. Also discussed is the effect of inhibiting conjugation, using a ligand carrying a 4′-mesityl substituent, itself prepared by a cross-coupling procedure.

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