Cyclometalated Rhodium and Iridium Complexes Containing Masked Catecholates: Synthesis, Structure, Electrochemistry, and Luminescence Properties

Two neutral cyclometalated rhodium and iridium coordination assemblies [(F2ppy)2M(eta-Cat)], M = Rh, (2) and M= Ir, (3) (F2ppy: 2,4-difluorophenylpyridine), displaying a masked catecholate (eta-Cat =eta-O perpendicular to O) are described. The catecholateligand is pi-bonded to an organometallic Cp*Ru(II) moiety. The latter brings stability to the whole system in solution and suppresses the formation of the related paramagnetic semiquinonecomplex. The determination of the molecular structure of theiridium complex [(F2ppy)2Ir(eta-Cat)] (3) corroborates theformation of the target compound and reveals the generation ofa rare two-dimensional (2D) honeycomb supramolecular architecture in the solid state, in which the Delta-enantiomer self-assembleswith the Lambda-enantiomer through encoded pi-pi interactions among individual units. The electrochemistry of complexes2and3wasinvestigated and showed that reduction occurs at very negative potentials (similar to-2.2 V versus saturated calomel electrode (SCE)),while oxidation of the cyclometalated Rh and Ir centers occurs at 0.8 and 0.86 V. In contrast to complexes with 1,2-dioxolenechelates, which are nonemissive, the heterodinuclear diamagnetic complexes2and3were found to be emissive at room temperature both in solution and in the solid state. Moreover, at 77 K in a solid state, both compounds display opposite emission behavior, for instance, complex3displays a blue-shifted emission, while rhodium compound2exhibits red-shifted emission to lower energy