Palladium-catalyzed Suzuki Reaction For Synthesis Of Cyclometalated Ligands And Studies On Photoelectric Properties Of Corresponding Iridium Complexes

Carbon-carbon bond formation is one of the most important processes in organic synthesis. Transition metal-catalyzed cross-coupling reactions have been established as the most versatile and powerful tools for the selective construction of C-C bonds. Among them, palladium-catalyzed Suzuki reaction of aryl halides with nucleophilc organoboron reagents, due to low toxicity with boron compounds, mild reaction conditions, broad groups tolerance and high yields, has been wildly used to synthesize nature products, pharmaceuticals and advance matericals.In this thesis, we have developed two highly efficient catalytic systems, Pd/C/EtOH/H2O/K2CO3and Pd(OAc)2/EtOH/H2O/K2CO3, for the Suzuki reaction under ligand-free and aerobic conditions. Furthermore, the catalytic system Pd(OAc)2/EtOH/H2O/K2CO3was successfully extended to the synthesis of triphenylamine derivatives and carbazole derivatives. A series of iridium complexes containing triphenylamine derivatives or carbazole derivatives as cyclometalated ligands were designed and synthesized. The relationships between photophysical, electrochemical properties of these complexes and the structures of cyclometalted ligands or the type of substituents were systematically investigated. The main contents are as follows:(1) A very simple and general Pd/C-catalyzed Suzuki reaction under ligand-free and aerobic conditions was developed. This ligand-free catalytic system tolerates a broad range of functional groups in both coupling partners. The cross-coupling of aryl bromides with aryl boronic acids could be proceeded smoothly within short reaction times at room temperature, and a variety of heteroaryl halides were coupled with arylboronic acids to give the corresponding heterobiaryls in good to excellent yields at80℃. Control experiments demonstrated that the Pd/C-catalyzed Suzuki reaction was promoted by oxygen. The Pd/C catalyst could be recycled at least ten times without significant loss of catalytic activity.(2) A highly efficient ligand-free catalytic system of Pd(OAc)2/EtOH/H2O/K2CO3for the Suzuki reaction of heteroaryl halides with arylboronic acids was described. Moreover, the catalytic system was successfully applied for the synthesis of triphenylamine derivatives and carbazole derivatives. Heteroaryl halides could be reacted smoothly with4-(diphenylamino)-phenylboronic acid or4-(9H-carbazol-yl)phenylboronic acid or9-phenyl-9H-carbazol-3-yl-boronic acid to afford good to excellent yields within short reaction times. (3) A series of new heteroleptic cyclometalated iridium complexes, Ir1-Ir8, containing4-heteroaryl-substituted triphenylamine derivatives as ligands were synthesized and characterized. A systematical investigation on the effects of diphenylamino, triphenylamino, substituents on pyridiyl ring and the π-conjugation length in the cyclometalated ligands on the photophysical and electrochemical properties of the iridium complexes has been carried out. The study indicates that the introduction of diphenylamino, triphenylamino or-CF3on the2-phenylpyridine frame make these iridium complexes with a better solubility and a great bathochromic shift of the emission color, while the incorporation of substituents such as-CH3or-F group on the pyridyl ring of the ligand does not change significantly the phosphorescence energy and the emission color of the iridium complexes. Among these iridium complexes, Ir5, Ir6and Ir7are excellent orange heteroleptic iridium complexes.(4) Five new heteroleptic cyclometalated iridium complexes, Ir9-Irl3, containing2-[9-(N-phenylcarbazolyl)]pyridine derivatives as ligands have been synthesized and characterized. These iridium complexes are thermally stable and Ir9-Ir12have been characterized by X-ray crystallography. It is well demonstrated that introducing a carbazolyl group on the2-phenylpyridine frame makes the iridium complex with a lower oxidation potential. However, the incorporation of substituent, such as-CH3or-F group on the pyridyl ring of the ligand does not change significantly the phosphorescence energy and the emission color of the iridium complex. The introduction of an electron-withdrawing-CF3group on the pyridyl ring of the ligand results in a great bathochromic shift of the emission color of the iridium complex. Electrophosphorescent OLEDs with outstanding device performance can be fabricated based on Ir13, which exhibits a maximum luminance efficiency of43.2cd A-1, corresponding to an external quantum efficiency of12.6%.