Cyclometallated, bis-terdentate iridium complexes as linearly expandable cores for the construction of multimetallic assemblies.

Cyclometallated iridium complexes comprised of two terdentate cyclometallating ligands, of the form [Ir(Ninsertion markCinsertion markN)(Ninsertion markNinsertion markC)](+), have been explored for the preparation of multimetallic systems by palladium-catalysed cross-coupling reactions. An Ninsertion markNinsertion markC-coordinating ligand carrying a boronate ester group has been prepared and complexed to iridium to give a boronic acid appended complex of this type, . This complex has been subjected to cross-coupling with a bromo-substituted bis-terpyridyl iridium complex to give a dinuclear iridium compound , in which one of the two iridium centres is N(6)-coordinated and the other has an N(4)C(2)-coordination sphere. Meanwhile, a bromo-substituted complex has been coupled with a boronic acid-appended ruthenium complex, to give a dinuclear heterometallic complex that can be activated to a second coupling by in situ bromination, offering access to a linear Ir-Ir-Ru trimetallic assembly . The electrochemical and luminescence properties of these systems are investigated. In the case of and , the behaviour can be rationalised in terms of a supramolecular description: efficient energy transfer occurs from the Ir terminus to the Ru. In contrast, for compound , an excited state with significant bridge character appears to play a key role in determining the emission properties.