Microwave-Accelerated C,N-Cyclometalation as a Route to Chloro-Bridged Iridium(III) Binuclear Precursors of Phosphorescent Materials: Optimization, Synthesis, and Studies of the Iridium(III) Dimer Behavior in Coordinating Solvents.

We present the results of our research on the use of microwaves as an unconventional heat source for the acceleration of iridium(III) chloro-bridged dimer preparation. The results enabled us to revise and improve known guidelines for the very quick and highly efficient synthesis of iridium(III) dimeric complexes in a very simple isolation manner. According to the developed methodology, the already known dimers containing ligands based on the 2-phenylpyridinato motif, as well as new ones stabilized with functionalized benzo[h]quinolinato and 2-phenoxypyridinato-based ligands, were efficiently synthesized. The scope of the incorporated ligands included compounds equipped with electron-donating (-Me, -OMe, -OPh, -NMe2), electron-withdrawing (-F, -Br, -CF3, -C6F5), and hole-transporting (-NPh2, -C6H4NPh2) groups. The obtained complexes were characterized by NMR, X-ray diffraction, and electrospray ionization mass spectrometry methods, and their behavior was examined in the presence of coordinating solvents such as dimethyl sulfoxide and acetonitrile. Investigation of the interactions between the above-mentioned solvents and dimers enabled us to confirm the ability of the former to cleave µ-chloride bridges, which enriches the knowledge in the field of organometallic chemistry. This knowledge can be particularly useful for the scientists working in the field of iridium-based materials, helping to avoid misinterpretation of the spectroscopic data.

Effect of ß-Ketoiminato Ancillary Ligand Modification on Emissive Properties of New Iridium Complexes.

A series of new bis(benzo[h]quinolinato) Ir(III) complexes with modified ß-ketoiminato ancillary ligands were synthesized, and their electrochemical, photophysical properties were determined with the support of theoretical calculations. Moreover, all the synthesized heteroleptic Ir(III) complexes were examined as dopants of the host-guest type emissive layers in solution-processed phosphorescent organic light emitting diodes (PhOLEDs) of a simple structure. As expected on the basis of voltammetry measurements as well as DFT calculations, all the compounds appeared to be green emitters. Their examination showed that alteration of ß-ketoiminato ligand structure causes frontier orbitals' energy levels to be slightly changed, while significantly affecting photoluminescence and electroluminescence efficiencies of iridium phosphors containing these ligands. It was also found that modification of ancillary ligands might enhance charge trapping on the dopant, thus increasing its efficiency, especially in electroluminescence. From among the iridium complexes studied, the compound bearing 1-naphthyl group bonded to the nitrogen atom of the ancillary ligand proved to be the most efficient emitter. The PhOLED fabricated on the basis of this dopant has reached a luminance level of 16000 cd/m2, current efficiency close to 12 cd/A, and an external quantum efficiency around 3.2%.

Solvent-Free and Efficient Synthesis of Silatranes via an Organocatalytic Protocol under Mild Conditions.

The organocatalytic approach to the formation of silatranyl cages permitted the design of a solvent-free and efficient protocol for the preparation of various organosilatranes. We discovered that amidine derivatives efficiently catalyze the conversion of trialkoxysilanes into organosilatranes, and their catalytic activity is related to the pKBH+ values. NMR studies of equimolar reactions of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) with selected substrates allowed proposing a reliable scheme for the transesterification process and silatranyl cage formation. In addition, green chemistry metrics for the scaled-up synthesis of vinylsilatrane (3k) were appointed. Finally, a scheme for the industrial production of silatrane derivatives with DBU and solvent regeneration was proposed, supported by a catalyst recycling experiment.