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

• Published in: Inorganic chemistry 2024-05, Vol.63 (21), p.9676-9686
• Main Authors: Deng, Chong, Liang, Jiefeng, Wang, Yi, Huang, Wenliang
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.4c00458

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, (AdTPBN3)­ThCl (1) and (DtbpTPBN3)­ThCl­(THF) (4) [RTPBN3 = 1,3,5-[2-(RN)­C6H4]3C6H3; 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, [(AdTPBN3)­ThK­(Et2O)2]2 (3), featuring a unique tetraanionic tricyclic core. On the other hand, reduction of 4 with 1 equiv of KC8 in hexanes/1,2-dimethoxyethane (DME) afforded a single C–C coupling product, [(DtbpTPBN3)­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.