In search of tris(trimethylsilylcyclopentadienyl) thorium

Abstract

Reduction of Cp′₃ThCl, Cp′₃ThBr, and Cp′₃ThI (Cp′ = C₅H₄SiMe₃) with potassium graphite generates dark blue solutions with reactivity and spectroscopic properties consistent with the formation of Cp′₃Th. The EPR and UV-visible spectra of the solutions are similar to those of crystallographically-characterized tris(cyclopentadienyl) Th(III) complexes: [C₅H₃(SiMe₃)₂]₃Th, (C₅Me₄H)₃Th, (C₅^tBu₂H₃)₃Th, and (C₅Me₅)₃Th. Density functional theory (DFT) analysis indicates that the UV-visible spectrum is consistent with Cp′₃Th and not [Cp′₃ThBr]¹⁻. Although single crystals of Cp′₃Th have not been isolated, the blue solution reacts with Me₃SiCl, I₂, and HCCPh to afford products expected from Cp′₃Th, namely, Cp′₃ThCl, Cp′₃ThI, and Cp′₃Th(CCPh), respectively. Reactions with MeI give mixtures of Cp′₃ThI and Cp′₃ThMe. Evidence for further reduction of the blue solutions to a Cp′-ligated Th(II) complex has not been observed. The crystal structures of Cp′₃ThMe and (Cp′₃Th)₂(μ-O) were also determined as part of these studies.