Molecules containing actinide-nitrogen multiple bonds are of current interest as simple models for new actinide nitride nuclear fuels, and potential catalytic activation of inert hydrocarbon C-H bonds. Molecules with uranium-nitrogen multiple bonds are now being widely studied, yet thorium nitrogen multiple bonds remain extremely rare. Calculations suggest that thorium nitrogen double bonds should display significant polarity, unlike U=N bonds, but like early transition metal analogues, many of which react with alkanes. Arguments over whether thorium should be considered more like these latter elements than an actinide are receiving increasing attention with reports of new reduced thorium complexes with d-electron configurations, and proposals that a bis(imido) thorium complex should be cis (transition metal–like), rather than trans, as is the norm for uranium.
Sterically protecting cyclopentadienyl-based ligands that enabled the first molecular Th=N bonds to be isolated also constrain their reactivity and flexibility. Here, simple mono(imido), and the first bis(imido) thorium complexes K[Th(=NAr)N"3] and K2[Th(=NAr)2(N")2] are readily made from insertion reactions (Ar = aryl, N" = N(SiMe3)2). X-ray and computational structural analyses show a cis-bis(imido) geometry, and polarised double bonds, in line with the more ‘transition metal-like’ nature, and hinting at the possibility for further reactivity with small inert molecules such as hydrocarbons.
Arnold, Polly L.. (2015). ThBisImido http://dx.doi.org/10.1021/jacs.5b06630, [dataset]. University of Edinburgh.