Reduction of Thorium Tris(amido)arene Complexes: Reversible Double and Single C-C Couplings.

The reduction chemistry of thorium complexes is less explored compared to that of their uranium counterparts. Here, we report the synthesis, characterization, and reduction chemistry of two thorium(IV) complexes, ( Ad TPBN 3 )ThCl ( 1 ) and ( Dtbp TPBN 3 )ThCl(THF) ( 4 ) [ R TPBN 3 = 1,3,5-[2-(RN)C 6 H 4 ] 3 C 6 H 3 ; R = 1-adamantyl (Ad) or 3,5-di- tert -butylphenyl (Dtbp); THF = tetrahydrofuran], supported by tripodal tris(amido)arene ligands with different N -substituents. Reduction of 1 with excessive potassium in n -pentane yielded a double C-C coupling product, [( Ad TPBN 3 )ThK(Et 2 O) 2 ] 2 ( 3 ), featuring a unique tetraanionic tricyclic core. On the other hand, reduction of 4 with 1 equiv of KC 8 in hexanes/1,2-dimethoxyethane (DME) afforded a single C-C coupling product, [( Dtbp TPBN 3 )Th(DME)] 2 ( 5 ), with a dianionic bis(cyclohexadienyl) core. The solid- and solution-state structures of dinuclear thorium(IV) complexes 3 and 5 were established by X-ray crystallography and NMR spectroscopy. In addition, reactivity studies show that 3 and 5 can behave as thorium(II) and thorium(III) synthons to reduce organic halides. For instance, 3 and 5 are able to reduce 4 and 2 equiv of benzyl chloride, respectively, to regenerate 1 and 4 with concomitant formation of dibenzyl. Reversible C-C couplings under redox conditions provide an alternative approach to exploiting the potential of thorium arene complexes in redox chemistry.