Introducing Diradicaloid Thiele's Hydrocarbon Derivatives as Ligand in Transition Metal Chemistry

Thiele's hydrocarbon (TH) derivatives, or p-quinodimethanes, are prototypical members of the organic diradicaloid family, predominantly explored in organic and main-group organometallic chemistry. Herein, we introduce them to transition-metal coordination by employing N-doped TH derivatives as ligands. Pyridine- and pyrazine-substituted p-quinodimethane ligands were synthesized, enabling the formation of mono- and dinuclear rhodium and cyclometalated iridium complexes (Py∙Rh, Pz∙Rh, Py∙Ir, and Pz∙Ir). We show the strong effects that simple metalation, and more importantly, orthometalation can have on the photophysical and electrochemical properties, as well as on singlet-triplet gaps of these diradicaloids. Additionally, the metalated mixed-valent forms are strongly electrochromic NIR absorbing dyes. Spectro-electrochemical studies reveal distinct electronic interactions between the diradicaloid backbone and the metal centers, highlighting the potential of N-doped TH derivatives as versatile redox-active ligands in transition-metal chemistry.