Uranium–nitride chemistry: uranium–uranium electronic communication mediated by nitride bridges

Abstract

Treatment of [UIV(N3)(TrenTIPS)] (1, TrenTIPS = {N(CH2CH2NSiPri3)3}3-) with excess Li resulted in the isolation of [{UIV(-NLi2)(TrenTIPS)}2] (2), which exhibits a diuranium(IV) ‘diamond-core’ dinitride motif. Over-reduction of 1 produces [UIII(TrenTIPS)] (3),...

Progress in the chemistry of molecular actinide-nitride compounds

“…Computational studies show a borderline case where the prospect of direct U-U bonding was raised, but high-level ab initio calculations revealed that if any U-U bonding is present, it is weak, and instead the bridging nitride ligands facilitate the U/U electronic communication. 82 This is consistent with the strong antiferromagnetic coupling measured for the U( 52 Recently, Zhu and co-workers investigated the reactivity of U(IV) azide complexes supported by a phosphorus-substituted Tren ligand, (N(CH 2 CH 2 NP i Pr 2 ) 3 ) 3− = Tren NP ), containing three rigid N-P units. 83 Reaction of the U(IV) complex, [U IV (-Tren NP )Cl], with NaN 3 led to the U(IV)/U(IV) azide complex, [(U IV (Tren NP )) 2 (m-N 3 ) 2 ] (34a).…”

“…The uranium bridged nitrides 30 and 31 are chemically robust, and are reversibly interconverted by oxidation and reduction, respectively, with no evidence of C-H bond activation, which is instead observed with the analogous Th(IV) system (Section 3.1.3) indicating a lower reactivity of the uranium nitride. 78 More recently, the sterically bulkier Tren TIPS (N(CH 2 CH 2 -NSi i Pr 3 ) 3− ) ligand, was utilized to stabilize the bridged U(IV)/ U(IV) bis-nitride complex, [Li 4 (U IV (Tren TIPS )) 2 (m-N) 2 ] (32), 82 which was obtained by reduction of the U(IV) azide precursor, [U IV (Tren TIPS )(N 3 )] (32a) (Scheme 7), with excess metallic lithium (Li), and concomitant formation of the U(III) complex, [U III (Tren TIPS )]. The solid-state structure of complex 32 comprises of a U 2 N 2 diamond-shaped core, with a U/U distance of 3.404(1) Å).…”

“…Attempts to prepare high-valent species by addition of benzo-9-crown-3 ether (B9C3) or AgBPh 4 , resulted in exchange of the Li cation for a proton (H + ), converting complex 32 to the U(IV)/U(IV) nitride-imido complex, [Li 3 (U IV (Tren TIPS )) 2 (m-NH)(m-N)] (33). 82 The U-N nitride bond lengths of 32 (2.153(2) Å) and 33 (2.171(4) Å) are longer than in the U(IV)/U(IV) bridging mononitride complexes (1.95(1)-2.12(1) Å), but are more consistent with the U(V)/U(V) bis-nitride complex, [K 2 ([U V (OSi(O t Bu) 3 ) 3 ] 2 (m-N) 2 )] (9) (2.101(6)-2.022(5) Å). 71 Variable-temperature magnetic data for the U(IV)/U(IV) bridging nitride complexes, 32 and 33, revealed high, lowtemperature magnetic moments, consistent with doubly degenerate ground states, where the effective symmetry of the strong crystal eld of the nitride dominates over the spin-orbit coupled nature of the ground state multiplet of U(IV).…”

Photolysis, Thermolysis, and Reduction of a Uranium Azide Complex Supported by a Double-Layer N–P Ligand

“…Uranium azides are one of the most important precursors for the synthesis of uranium nitrides. The formation of various uranium nitride complexes has been reported by photolysis, − thermolysis, alkali metal reduction, − and Lewis acid dissociation of uranium azides, − which exhibit unique reactivity and redox activity. − These studies show that the steric hindrance and electronic environment of the supported ligand in uranium azide complexes have a major influence on the uranium nitride complex structures. ,, …”

“…They found that a series of terminal and alkali metal-capped U­(V) nitride complexes, [{U V (Tren TIPS )­(μ-N)­(μ-M)} 2 ], could be generated by the reduction of uranium azides with alkali metals . Recently, Liddle and co-workers reported a dinuclear uranium nitride complex [{U V (μ-NLi)­(Tren TIPS )} 2 ] by the reduction of [U IV (N 3 )­(Tren TIPS )] with excess Li . The unique reactivity and electronic structure of these uranium nitrides were fully investigated. − However, when a less bulkier Tren DMBS ({N­(CH 2 CH 2 NSiMe 2 t Bu) 3 } 3- ) ligand was used, the reduction of the corresponding uranium azide complex [{M­(Tren DMBS )­(μ-N 3 )} 4 ] afforded the diuranium­(IV/IV)-nitride [{U­(Tren DMBS )} 2 (μ-N)]­[K­(THF) 6 ] and the mixed-valence diuranium­(IV/V)-nitride [{U­(Tren DMBS )} 2 (μ-N)] complexes .…”