In search of tris(trimethylsilylcyclopentadienyl) thorium.

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, (C5tBu2H3)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 HC[triple bond, length as m-dash]CPh to afford products expected from Cp'3Th, namely, Cp'3ThCl, Cp'3ThI, and Cp'3Th(C[triple bond, length as m-dash]CPh), 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.