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

Abstract

Cyclometallated iridium complexes comprised of two terdentate cyclometallating ligands, of the form [Ir(N⁁C⁁N)(N⁁N⁁C)]⁺, have been explored for the preparation of multimetallic systems by palladium-catalysed cross-coupling reactions. An N⁁N⁁C-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 N₆-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.