Reductive C(sp2)-Si Cross-Couplings by Catalytic Sodium-Bromine Exchange

Abstract

The metal-halogen exchange reaction constitutes one of the most important preparative routes towards polar organometallic reagents such as aryllithium or Grignard reagents. However, despite extensive developments over the past eight decades, this fundamental organometallic elementary step has only been exploited stoichiometrically. Against this background, we demonstrate that the sodium-bromine exchange reaction can be implemented in a catalytic setting as a mean to activate C(sp²)-Br bonds in a transition metal-free manner en route to the regioselective and general preparation of (hetero)aryl silanes. Simply treating structurally diverse (hetero)aryl bromides with N-tert-butyl-N'-silyldiazenes (tBu-N=N-Si) as silylating reagents and inexpensive sodium alkoxides as catalytic promoters yields a range of aromatic organosilicon compounds under ambient conditions. Mechanistic studies provide solid evidence for the involvement of tert-butyl sodium as the C(sp²)-Br metalating agent.

Keywords: Arylsilanes; Diazene; Metal-halogen exchange; Organosodium; Silylation.