Surprising Reaction of Non-Nucleophilic Bases with 1-Hydrosiloles: Addition and Not Deprotonation1

Synthesis of 1,1'-Bis(1-Methyl/Chloro-2,3,4,5-Tetraphenyl-1-Silacyclopentadienyl) [Ph4C4Si(Me/Cl)-(Me/Cl)SiC4Ph4] from Silole Anion [MeSiC4Ph4]-•[Li+ or Na+] and Silole Dianion [SiC4Ph4]2-•2[Li+]; Oxidative Coupling of Silole Anion [MeSiC4Ph4]-•[Li+ or Na+] by Ferrous Chloride (FeCl2) and Oxidative Coupling and Chlorination of Silole Dianion [SiC4Ph4]2-•2[Li+] by Cupric Chloride (CuCl2)

A reaction of silole anion {[MeSiC₄Ph₄]⁻•[Li⁺ or Na⁺] (1) with anhydrous ferrous chloride (FeCl₂) in THF (tetrahydrofuran) gives 1,1′-bis(1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadienyl) [Ph₄C₄Si(Me)-(Me)SiC₄Ph₄] (2) with precipitation of iron metal in high yield. Silole dianion {[SiC₄Ph₄]²⁻•2[Li⁺] (3) is added to anhydrous cupric chloride (CuCl₂) in THF at −78 °C, then the dark red solution changes into a greenish solution. From the solution, a green solid is isolated, and stirring it in toluene at room temperature provides quantitatively 1,1′-bis(1-chloro-2,3,4,5-tetraphenyl-1-silacyclopentadienyl) [Ph₄C₄Si(Cl)-(Cl)SiC₄Ph₄] (4) with precipitation of copper metal in toluene. The green solid is suggested to be 1,1′-bissilolyl bisradical [Ph₄C₄Si-SiC₄Ph₄]^2• (8), and lithium cuprous chloride salts {[Li₂Cu^ICl₂]⁺•[Cu^ICl₂]⁻}. Both reactions are initiated by single-electron transfer (SET) from the electron-rich anionic silole substrates (1 and 3) to iron(II) and copper(II).