Bis-Cyclometalated Iridium Complexes with Chelating Dicarbene Ancillary Ligands

5 years ago

Bis-Cyclometalated Iridium Complexes with Chelating Dicarbene Ancillary Ligands

Hanah Na, Thomas S. Teets, Ayan Maity, Rakib Morshed

In this work, we report that covalent postsynthetic modification can be used for the preparation of a class of bis-cyclometalated iridium complexes featuring Chugaev-type chelating dicarbene ligands. Bis-cyclometalated iridium complexes with electron-deficient aryl isocyanide ancillary ligands react with hydrazine to form neutral dicarbene complexes. The neutral iridium carbene complexes have a basic site that can be protonated by strong acid, permitting access to complexes in two protonation states and allowing an additional layer of control over the key properties. These new Chugaev-type iridium complexes exhibit blue phosphorescence at both room temperature and 77 K. Compared to their bis-isocyanide precursors, the electrochemical and photophysical properties of these new complexes are substantially perturbed, demonstrating the concept that the electronic structure and excited state dynamics can be controlled by ancillary ligand modification. Furthermore, the emission spectra and excited-state dynamics are dependent on the protonation state of the dicarbene ancillary ligand, and we note an ∼2-fold increase in emission quantum yield when the ancillary ligand is protonated. This study demonstrates that ligand-based reactivity can be an alternative method for elaborating the structures of bis-cyclometalated iridium complexes and gives access to structures not readily obtainable by other means.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00428

DOI: 10.1021/acs.organomet.7b00428