Improving the Efficiency of Synthesis and Demonstrating the Utility of Difunctionalized Tris-Cyclometallated Iridium Intermediates

Two key reactions in the synthesis of a difunctionalized tris-cyclometallated iridium complex [Ir(ppy-Br)2fppy] (3), which is an important intermediate for the synthesis of more sophisticated iridium complexes, were investigated to improve performance. The first reaction is the formation of a monomeric iridium complex [Ir(ppy)2fppy] (2), and the second reaction is the bromination of complex 2 to yield the bifunctional complex 3. The performance of these reactions during our previous work was suboptimal (e.g., formation of side products, reproducibility issues). A response surface methodology (RSM) investigation of the first reaction provided information to avoid the failures we experienced previously. Investigation of the second reaction showed us that its reaction time could be shortened from 18 h to 3 min and the reaction temperature decreased from 90 °C to 0 °C. This enabled controllable synthesis of the desired complex 3 with an improved yield (87%). Furthermore, investigation of the second reaction led to the identification of conditions for the synthesis of the monobrominated complex [[Ir(ppy)(ppy-Br)(fppy)] (5). Finally, complexes 3 and 5 were modified via Suzuki–Miyaura coupling and reduction to yield complexes 7 and 9, to demonstrate their value as intermediates for further transformations. The photophysical properties of complexes 7 and 9 were investigated and compared with those of their parent structure, complex 10.