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((NCN)-C-boolean AND-N-boolean AND)((NNC)-N-boolean AND-C-boolean AND)](+), have been explored for the preparation of multimetallic systems by palladium-catalysed cross-coupling reactions. An (NNC)-N-boolean AND-C-boolean AND-coordinating ligand carrying a boronate ester group has been prepared and complexed to iridium to give a boronic acid appended complex of this type, 3. This complex has been subjected to cross-coupling with a bromo-substituted bis-terpyridyl iridium complex to give a dinuclear iridium compound 6, in which one of the two iridium centres is N-6-coordinated and the other has an N4C2-coordination sphere. Meanwhile, a bromo-substituted complex 4 has been coupled with a boronic acid-appended ruthenium complex, to give a dinuclear heterometallic complex 8 that can be activated to a second coupling by in situ bromination, offering access to a linear Ir-Ir-Ru trimetallic assembly 11. The electrochemical and luminescence properties of these systems are investigated. In the case of 8 and 11, 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 6, an excited state with significant bridge character appears to play a key role in determining the emission properties.