Two-Electron Oxidative Atom Transfer at a Homoleptic, Tetravalent Uranium Complex

Abstract

A tetrahomoleptic, pseudotetrahedral U4+ imidophosphorane complex, [U­(NP­(pip)3)4], 1-U­(PN), is reported. This complex can be oxidized by two electrons with either mesityl azide or nitrous oxide. This two-electron atom/group transfer oxidation is the first example observed at a homoleptic, tetravalent uranium complex. The mesityl imido compound [U­(NMes)­(NP­(pip)3)4], 2-U­(PN)­NMes, exhibits a unique square pyramidal geometry in contrast to the expected trigonal bipyramidal geometry of the oxo complex [U­(O)­(NP­(pip)3)4], 2-U­(PN)­O. The bonding driving the structural dichotomy of these structures and the absence of a structurally observable inverse trans-influence in 2-U­(PN)­NMes were examined by DFT and natural bonding orbital analysis.

Divergent uranium- versus phosphorus-based reduction of Me3SiN3 with steric modification of phosphido ligands

“…The byproduct, SiMe 4 , was observed in the crude NMR spectra for both 4 and 5. The formation of 5 using the U VI/IV redox couple is rare 16,[18][19][20][21] and nearly all examples involve forming bis(imido) 17,22 complexes or uranyl functionalization 23,58 as the U V/III redox is far more common, 59 especially with azide reduction. Complex 5 is unusual as nearly all bis(imido) actinide complexes have a nitrogen-carbon, silicon, or hydrogen linkage.…”

“…15 This twoelectron reduction typically is done by the metal centre to form a U(V) imido. There are limited examples of U(IV) oxidation to U(VI), [16][17][18][19][20][21][22][23] all of them involving oxo-or imido-delivering agents. Our group has taken the approach of examining the reactivity of An(IV), An ¼ Th, U, complexes with so donor ligands, such as phosphorus, which also has a rich chemistry with organic azides.…”

Continuous Shape Measures Study of the Coordination Spheres of Actinide Complexes – Part 1: Low Coordination Numbers

“…The second family, less numerous, has the general formula [MXY 4 ], being Y most commonly the silanolate anion {O t Bu} 3 SiO À . The coordination trigonal bipyramids of most of the members of this family are found to be distorted between 11 and 48 % toward the square pyramid, whereas one compound with the less common phosphinimido ligands, [(MesN)U(N=P{pip} 3 ) 4 ], [53] has two crystallographically independent uranium atoms, with an intermediate Berry (66 % square pyramidal) and a practically square pyramidal (97 %) shape, respectively (Figure 9a). Finally, the small family of homoleptic [MY 5 ] compounds comprises [U(N=C t Bu 2 ) 5 ] 0,À 1 , [54] [U(CH 2 SiMe 3 ) 5 ] À , [50] [Th-(CH 2 t Bu) 5 ] À , [51] [U(Piperidine) 5 ] À , [55] and [U(NH(C 6 H 5 i Pr 2 ) 5 ] À , [56] all of them within the 13-42 % range of the Berry pathway.…”

“…The deviation of the two axial donor atoms toward the equatorial plane seems to be associated to the presence of bidentate ligands. In particular, 70 % of the members of this family have two or more chelate rings, and [U(NP{pip} 3 ) 4 (NMes)], [53] a square pyramid with monodentate ligands only; (b) [U(BMes 2 ) 3 (OPPh 3 ) 2 ], [58] a square pyramid with one bidentate ligand; (c) [U 2 (OÀ Si{O t Bu} 3 )(k 2 -OÀ Si{O t Bu} 3 )(μ-OÀ Si{O t Bu} 3 )], [61] and edge-capped tetrahedron, and (d) [UI 2 (thf) 2 (N{Si i Pr 3 )], [38] a trigonal bipyramid with a rocking distortion.…”

“…Figure 9. Shapes of several representative five-coordinate compounds: (a) [U(NP{pip} 3 ) 4 (NMes)],[53] a square pyramid with monodentate ligands only; (b) [U(BMes 2 ) 3 (OPPh 3 ) 2 ],[58] a square pyramid with one bidentate ligand; (c) [U 2 (OÀ Si{O t Bu} 3 )(k 2 -OÀ Si{O t Bu} 3 )(μ-OÀ Si{O t Bu} 3 )],[61] and edge-capped tetrahedron, and (d) [UI 2 (thf) 2 (N{Si i Pr 3 )],[38] a trigonal bipyramid with a rocking distortion.…”