Si–Cl σ‑Bond Cleavage by an Fe(0) Complex with Two Steps of One-Electron Transfer toward Hydrosilane Formation from Tetrachlorosilane

Iron catalysts exhibit
unique reactivity that has not been found
in precious metal catalysts. Herein, a new strategy for strong Si–Cl
σ-bond cleavage of tetrachlorosilane (SiCl4) was
successful using [{Fe(PNNP)}2(μ-N2)] (PNNP
= 2,9-bis((diphenylphosphino)methyl)-1,10-phenanthroline). The resulting
oxidative addition product [Fe(SiCl3)(Cl)(PNNP)] was fully
identified, establishing the first example of Si–Cl σ-bond
cleavage using an air-sensitive iron(0) complex. Theoretical study
revealed that Si–Cl σ-bond cleavage occurs with radical
character through two steps of single-electron transfer from [Fe(PNNP)]
to the Si–Cl σ* antibonding orbital, which differs from
usual concerted oxidative addition. This σ-bond cleavage reaction
was successfully applied to HSiCl3 formation from SiCl4 and 1,10-dihydroanthracene via hydrogen atom transfer (HAT).
Thus, we succeeded in performing Si–Cl σ-bond cleavage
using the Fe(0) complex and its application to hydrosilane synthesis
from SiCl4 using a mild hydrogen source. This iron(0) complex
is expected to be active as catalyst for other difficult reaction.