Double Reduction of 4,4'-Bipyridine and Reductive Coupling of Pyridine by Two Thorium(III) Single-Electron Transfers

The redox chemistry of uranium is burgeoning and uranium(III) complexes have been shown to promote many interesting synthetic transformations. However, their utility is limited by their reduction potentials, which are smaller than many non-traditional lanthanide(II) complexes. Thorium(III) has a greater redox potential so it should present unprecedented opportunities for actinide reactivity but as with uranium(II) and thorium(II) chemistry, these have not yet been fully realized. Herein we present reactivity studies of two equivalents of [Th(Cp'')₃ ] (1, Cp''={C₅ H₃ (SiMe₃ )₂ -1,3}) with 4,4'-bipyridine or two equivalents of pyridine to give [{Th(Cp'')₃ }₂ {μ-(NC₅ H₄ )₂ }] (2) and [{Th(Cp'')₃ }₂ {μ-(NC₅ H₅ )₂ }] (3), respectively. As relatively large reduction potentials are required to effect these transformations we have shown that thorium(III) can promote reactions that uranium(III) cannot, opening up promising new reductive chemistry for the actinides.