Multi-electron redox reactivity of a thorium(ii) hydride synthon

Abstract

Molecular thorium complexes are dominated by stable tetravalent thorium, while subvalent thorium and the relevant synthons are very limited. Herein, we report that hydrogenolysis of the half-sandwich penta-arylcyclopentadienyl-supported thorium tribenzyl complex [(Cp^Ar5)Th(p-CH₂–C₆H₄–Me)₃] (1) (Cp^Ar5 = C₅Ar₅, Ar = 3,5-ⁱPr₂–C₆H₃) affords the double-sandwich bimetallic hydride complex [(Cp^Ar5)Th(μ-H)]₂ (2), in which one of the five aryl groups in the Cp^Ar5 ligand is selectively reduced to a puckered di-anionic 1,4-cyclohexadienyl. Complex 2 can be regarded as a thorium(II) hydride synthon, and exhibits unique redox-active reactivity towards various substrates. Complex 2 not only serves as the six-electron transfer reagent in the reduction of Te and N₃SiMe₃, leading to the formation of [(Cp^Ar5)Th(THF)]₂(μ-Te)₃ (3) and [(Cp^Ar5)Th(μ-N₃)(μ-NSiMe₃)]₂ (4), but also promotes the four-electron reductive coupling of CS₂ and benzonitrile accompanied by Th–H addition, resulting in the isolation of [(Cp^Ar5)Th(μ-η²:η²-CS₃)(μ-S)(μ-η⁴:η¹-SCHCHS)Th(Cp^Ar5)] (5) and [(Cp^Ar5)Th(PhCN)₂(μ-NCH₂Ph){η¹,κ³-NC(Ph)C(Ph)NC(Ph)NC(Ph)N}Th(Cp^Ar5)] (6) respectively.