Design and Synthesis of Tris-Heteroleptic Cyclometalated Iridium(III) Complexes Consisting of Three Different Nonsymmetric Ligands Based on Ligand-Selective Electrophilic Reactions via Interligand HOMO Hopping Phenomena

In
this article we report on the successful synthesis and isolation
of cyclometalated Ir complexes having three different nonsymmetric
ligands based on ligand-selective electrophilic reactions via interligand
HOMO (highest occupied molecular orbital) hopping phenomena. It was
hypothesized that the electrophilic substitution reactions of bis-heteroleptic
Ir complexes having 8-benzenesulfonamidoquinoline as an ancillary
ligand, 5a and 7, would proceed at the 5
position of the quinoline ring of these Ir complexes to afford 18 and 19, because their HOMOs are localized
on the quinoline rings, as predicted by density functional theory
(DFT) calculations. In these products, the HOMO is transferred to
one of two ppy ligands, in which the phenyl group is trans to the Ir–N (1 position of quinoline) bond, and hence, the
iodination or formylation of 18 and 19 occurs
at the 5′ position of the ppy ligand to provide 20a, 23, and 24. Furthermore, we carried out
the functionalization of 20a using cross-coupling reactions
to obtain tris-heteroleptic Ir complexes containing three different
ligands in good yields with negligible diastereomer formation. Photochemical
properties, especially dual emission, and response to pH change, of
new dual-emissive tris-heteroleptic cyclometalated Ir complexes, 21–24, are also reported.