Surprising Syntheses of Reduced-Arene Inverse Sandwich Complexes of Thorium: (Cp″₂Th)₂(μ–η⁶:η⁶-C₆H₅R) [R = H, Me; Cp″ = C₅H₃(SiMe₃)₂]

In efforts to generate [Cp″3ThIIIMe]1– [Cp″ = C5H3(SiMe3)2] from potassium graphite (KC8) and Cp″3ThIVMe in the presence of benzene and 18-crown-6 or 2.2.2-cryptand, the dark red reduced benzene inverse sandwich complex (Cp″2Th)2(μ–η6:η6-C6H6), 1, was unexpectedly isolated and crystallographically characterized. Surprisingly, 1 can also be synthesized by the addition of MeLi to Cp″3ThIII in the presence of benzene and a chelate even though Cp″3ThIII and (Cp″3ThII)1– are stable in the presence of arenes. The crystal structure of 1 reveals a twisted boat with distortion from planarity of the bridging C6 moiety with torsion angles of 9.37(4), 10.10(8), and −19.02(4)°. Complex 1 exhibits an axial EPR signal at 77 K with g|| = 1.97 and g⊥ = 1.89, characteristic of a Th(III) 6d1 ion, and a magnetic moment of 2.54 μB at 298 K. When toluene is present during the reduction of Cp″3ThIVMe with KC8, a dark maroon solution is generated that has physical and spectroscopic properties consistent with the formation of the analogous reduced toluene complex (Cp″2Th)2(μ–η6:η6-C7H8), 2. Complex 2 can also be made by the addition of MeLi to Cp″3ThIII in the presence of toluene and a chelate.