Synthesis, Structure, and Optical Property of Tris(biaryldiyl)metal Complexes Consisting of Group 9 Elements

We report the synthesis and characterization of tris(biphenyl-2,2'-diyl)metal complexes of trivalent group 9 elements (<b>1</b>_<b>M</b>, M = Co, Rh, Ir) and their nonplanarly π-extended analogs, tris(1,1'-binaphthyl-2,2'-diyl)metal complexes (<b>2</b>_<b>M</b>, M = Rh, Ir). Single crystal X-ray crystallography reveals the distorted octahedral geometry with an approximate <i>C</i>₃ symmetry of trianionic complexes <b>1</b>_<b>M</b> (M = Co, Rh, Ir) and <b>2</b>_<b>M</b> (M = Rh, Ir), which are contacted by three Li⁺ ions in the crystal. Complex <b>1</b>_<b>Ir</b> exhibits yellow luminescence in THF with a photoluminescence quantum yield (<i>Φ</i>_PL) of up to 0.73, along with a distinctive photophysical property, namely, a concentration dependence of the emission wavelength from 530 to 580 nm. This is a characteristic property of <b>1</b>_<b>Ir</b> and has not been observed in its isoelectronic analog, tris(2-phenylpyridinato)iridium(III) (Ir(ppy)₃). The concentration-dependent optical properties originate from the dissociation equilibria of Li⁺ ions from the anionic chromophore. Complex <b>2</b>_<b>Ir</b> also exhibits luminescence at 715 nm in THF, with a notable bathochromic shift from <b>1</b>_<b>Ir</b> through the π-extension. The findings offer insights into the photophysical properties of homoleptic organo-transition metal complexes, providing the foundation for the design of related transition metal complexes.