Photochemical Synthesis of a Stable Terminal Uranium(VI) Nitride

Abstract

Terminal uranium nitrides have so far proven impossible to isolate by photolysis of azides. Here we report the second ever example of an isolated terminal uranium­(VI) nitride. We show that the terminal nitride [NBu4]­[U­(OSi­(OtBu)3)4(N)], 3, can be prepared upon photolysis with UV light of the U­(IV) azide analogue. This is achieved by careful tailoring of the azide precursor and of the reaction conditions. Complex 3 is stable under ambient conditions but reacts readily with electrophiles (H+ and CO).

Exceptional uranium(VI)-nitride triple bond covalency from 15N nuclear magnetic resonance spectroscopy and quantum chemical analysis

“…We used coordinates from geometry optimisation (see Supplementary Table 1) at the BP86 level 39 , noting the computed U ≡ N bond length of 1.7795 Å compares well to the crystallographically determined distance of 1.799(7) Å 39 . To give context to the U ≡ N bond length distance in 1/1*, the corresponding distances in [U V (N)(Tren TIPS )][Na(12C4) 2 ] and [U VI (N) {OSi(OBu t ) 3 } 4 ][NBu n 4 ] are 1.825(15) and 1.769(2) Å, respectively 38,40 . We then calculated 15 N nitride δ iso values from single point energy calculations with a range of functionals, corrected for the solvent (THF, since that is the most accurately determined δ iso for 1*) and reference (MeNO 2 = 0 at the same functional level).…”

“…In 2012, the Liddle group reported [U V (N)(Tren TIPS )][Na(12C4) 2 ] (Tren TIPS = N(CH 2 CH 2 NSiPr i 3 ) 3 , 12C4 = 12-crown-4 ether) 38 , and in 2013 disclosed its oxidation to give [U VI (N)(Tren TIPS )] (1) 39 . In 2020 the Mazzanti group 40 reported [U VI (N){OSi(O-Bu t ) 3 } 4 ][NBu n 4 ]. Prior quantum chemical modelling of 1 suggested a highly covalent U ≡ N triple bond rivalling, if not exceeding the covalency in group 6 nitride triple bonds 39,41 , which would be a significant result if experimentally confirmed given the dominance of 5f-over 6d-orbital participation in this bond, and exceptional chemical shielding tensors have thus been predicted for uraniumnitride linkages 25 .…”

Synthesis of a heterobimetallic actinide nitride and an analysis of its bonding

“…The study of actinide–nitrogen multiple bonding has had a considerable impact on our understanding of covalency and f orbital participation in the actinides. 1–7 Notable advances in this area include the discovery of the first terminal actinide nitride by Liddle, 8–11 the synthesis of the uranium poly(imido) complexes by Bart, 12–14 and the isolation of a trans bis(nitrido) uranium complex by Kraus. 15 These studies have revealed the remarkable ability of high valent uranium to engage its 5f orbitals in bonding.…”

Photochemical Synthesis of Transition Metal-Capped Uranium(VI) Nitride Complexes

“…1) by the photolysis of an anionic U(IV) azide analogue. 40 This remains the only example of the successful isolation of a mono-U(VI) nitride complex via a photolysis route. These results demonstrate that U(VI) nitrides are accessible under photochemical conditions but require an appropriate ligand framework and specific reaction conditions to capture this transient mono-U(VI) nitride intermediate.…”

“…[30][31][32] Although several examples of mono-U(V) nitrides have been reported, 33 -39 mono-U(VI) nitrides are extremely rare. [37][38][39][40] For instance, the Cummins group reported a borane-capped U(V) nitridoborate complex [N(n-Bu) 4 ][(C 6 F 5 ) 3 BNU(N[t-Bu]Ar) 3 ] (Ar = 3,5-Me 2 C 6 H 3 ), which could be converted to a U(VI) nitride complex [(C 6 F 5 ) 3 BNU(N[t-Bu]Ar) 3 ] by chemical oxidation. 37 Liddle and co-workers reported that a U(III) complex [U(Tren TIPS )] {Tren TIPS = [N(CH 2 CH 2 NSi i Pr 3 ) 3 ] 3-} could react with NaN 3 , leading to a terminal U(V) nitride complex [UN(Tren TIPS )][Na(12-crown-4) 2 ], which could be further oxidized to the U(VI) nitride complex [U(N)(Tren TIPS )] by iodine.…”