Stimuli-Responsive Multifunctional Iridium(III) Complex Exhibiting Thermo-, Vapochromism, and Double Catalytic Activity

Multifunctional compounds with properties that may be triggered by different external stimuli are highly desirable yet challenging in their design and synthesis. Herein, we report a cyclometalated iridium(III) complex based on bulky 1,2-diphenylphenanthroimidazole (C^N) that can easily change its molecular geometry from trigonal-bipyramidal to octahedral or from a monomeric to dimeric state in response to external stimuli (temperature and solvent variations). The extensive characterization including variable-temperature 1H NMR, single-crystal and powder X-ray diffraction corroborated by density functional theory calculations strongly indicates that the thermochromic behavior of the complex is attributed to the dimer-monomer transformations both in solution and in the solid state. The five-coordinated monomer instantaneously reacts with coordinating solvents (L = CH3CN, CH3OH, pyridine) affording octahedral complexes [Ir(C^N)2(L)Cl]. Binding constants for the formation of the complexes with acetonitrile and methanol were estimated by UV-vis titration. Enabled by the ability to switch between the alternative structural states depending on the medium, the monomer exhibits an unprecedented combination of properties, including a reversible vapochromic behavior and switchable catalytic activity. As illustrative examples, transfer hydrogenation and photoinduced reductive debromination were successfully performed by using the monomer as a catalyst.