Inverse palladocenes

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.