Abstract
Metallocene research has influenced the development of organometallic chemistry, and the metal-nonmetal inverted half-sandwich structure (inverse metallocene) was very recently discovered. However, additional instances are required to propose the concept inverse metallocene and it remains uncertain whether metal five-membered ring structures analogous to the cyclopentadienyl anion structure exist. Herein we report the synthesis of a series of palladium analogs Pd(8)(PPh)(2)(PPh(3))(2)(Ph(2)P=O)(S-Adm)(5) (Pd(8)-P), Pd(6)(PPh)(PPh(3))(S-Adm)(6) (Pd(6)), Pd(5)(PPh)(S-Adm)(4)[(Ph(2)P)(2)O] (Pd(5)-O), and Pd(5)(PPh)(S-Adm)(4)[(Ph(2)P)(2)CH(2)] (Pd(5)-C), identify their fundamental metal building block named five-membered Pd aromatic ring, and reveal their conjugation‒photothermy correlation. In particular, we report an average NIR-II photothermal conversion efficiency per metal atom of 14.7% and the stability of the five-membered Pd aromatic ring, as illustrated by the fact that Pd(5)-C maintained photothermy performance for >10 heating-cooling cycles even after the ligands were removed. We further demonstrate the great potential of inverse palladocenes in areas such as laser shielding, high-temperature degradation, ignition, and temperature/light control. These results declare the research and application start of a type of materials named inverse palladocenes.