Double C─Si Bond-Activating C─C Bond Formation: Palladium-Catalyzed Synthesis of Silicon-Tethered Fluorenes via Silacycle-to-Palladacycle Si/Pd Exchange.

Organosilanes constitute an important class of compounds in modern organic chemistry, and the reactions involving activation of a carbon─silicon bond under transition-metal catalysis enables straightforward conversion of readily available organosilanes to more complex or useful ones. In this context, herein we developed a palladium-catalyzed synthesis of silicon-tethered fluorenes from diarylsilanes through a palladacycle formation from a silacycle via a two-fold C─Si bond-activating Si/Pd exchange process. The reaction can be conducted in combination with several nucleophiles such as H2O, carboxylic acids, and phenols to provide fluorene-attached silanols, silyl esters, and silyl ethers in a modular fashion. Experimental and theoretical mechanistic investigations were also performed, elucidating a plausible reaction pathway for the formation of a palladacycle from a silacycle, which was found to be significantly accelerated by the assistance of an acetate ligand.