Synthesis,\nStructure, and Optical Property of Tris(biaryldiyl)metal\nComplexes Consisting of Group 9 Elements

We\nreport the synthesis and characterization of tris(biphenyl-2,2′-diyl)metal\ncomplexes of trivalent group 9 elements (<b>1</b><sub><b>M</b></sub>, M = Co, Rh, Ir) and their nonplanarly π-extended\nanalogs, tris(1,1′-binaphthyl-2,2′-diyl)metal complexes\n(<b>2</b><sub><b>M</b></sub>, M = Rh, Ir). Single crystal\nX-ray crystallography reveals the distorted octahedral geometry with\nan approximate <i>C</i><sub>3</sub> symmetry of trianionic\ncomplexes <b>1</b><sub><b>M</b></sub> (M = Co, Rh, Ir)\nand <b>2</b><sub><b>M</b></sub> (M = Rh, Ir), which are\ncontacted by three Li<sup>+</sup> ions in the crystal. Complex <b>1</b><sub><b>Ir</b></sub> exhibits yellow luminescence in\nTHF with a photoluminescence quantum yield (<i>Φ</i><sub>PL</sub>) of up to 0.73, along with a distinctive photophysical\nproperty, namely, a concentration dependence of the emission wavelength\nfrom 530 to 580 nm. This is a characteristic property of <b>1</b><sub><b>Ir</b></sub> and has not been observed in its isoelectronic\nanalog, tris(2-phenylpyridinato)iridium(III) (Ir(ppy)<sub>3</sub>).\nThe concentration-dependent optical properties originate from the\ndissociation equilibria of Li<sup>+</sup> ions from the anionic chromophore.\nComplex <b>2</b><sub><b>Ir</b></sub> also exhibits luminescence\nat 715 nm in THF, with a notable bathochromic shift from <b>1</b><sub><b>Ir</b></sub> through the π-extension. The findings\noffer insights into the photophysical properties of homoleptic organo-transition\nmetal complexes, providing the foundation for the design of related\ntransition metal complexes.