Diazoalkane Reduction for the Synthesis of Uranium Hydrazonido Complexes

Abstract

The reactivity of the uranium(III) alkyl Tp*2UCH2Ph (1) toward diazoalkanes is reported. Addition of 1 equiv. N2CPh2 produces 0.5 equiv. bibenzyl, along with Tp*2U(N2CPh2) (2). This species is dynamic in solution at room temperature and rapidly interconverts between the η1‐ and η2 isomers as determined by variable‐temperature 1H NMR spectroscopy. X‐ray crystallographic analysis at low temperature shows exclusively the η2 isomer, which features a short U–N multiple bond analogous to an imido species. The η1 isomer reacts quantitatively with aldehydes and ketones through multiple bond metathesis to produce Tp*2U(O) and the corresponding ketazine. Treatment of 1 with N2CHSiMe3 generates 0.5 equiv. bibenzyl and the η1 isomer Tp*2U(N2CHSiMe3) (3). This species is unstable over the course of hours, and there is no spectroscopic evidence for the η2 isomer. Tp*2U(η1‐N2CHSiMe3) can be trapped by addition of phenylacetylene by a [2+2] cycloaddition to afford the uranium(IV) metallacycle Tp*2U[(N‐N = CHSiMe3)CHCPh] (4). Crystallographic data for 4 are presented.

Synthesis of Terminal Uranium(IV) Disulfido and Diselenido Compounds by Activation of Elemental Sulfur and Selenium

“…Thus, we set out to study the reactivity of elemental sulfur and selenium with Tp* 2 U(CH 2 Ph) ( 1 ) (Tp*=hydrotris(3,5‐dimethylpyrazolyl)borate), as activation could occur either by insertion into the UC bond, by analogy to the work of Evans, or by two electron reduction of the chalcogen. The latter mode of reactivity has been observed for 1 with organoazides21 and diazomethanes,22 producing uranium(IV) imido and hydrazonido derivatives, respectively, by extrusion of bibenzyl. Herein we present the reactivity of 1 toward elemental sulfur and selenium, spectroscopic, magnetic, and crystallographic characterization of the products, as well as a computational analysis of the uranium–chalcogenide bonding.…”

Achievements in uranium alkyl chemistry: celebrating sixty years of synthetic pursuits

“…23 The U-C σ-bond in 6 is easily protonated with terminal alkynes, amines, and thiols to generate the corresponding uranium(III) family, Tp* 2 UX (X = CCPh, CCSiMe 3 , NHPh, NHCH 2 Ph, SPh). 25 In the presence of organoazides or diazoalkanes, 6 reacts to form the oxidized uranium(IV) imido complexes, Tp* 2 UNR (R = Mes, Ph, Ad), 26 or hydrazonido complexes, Tp* 2 U(η 2 -N 2 CPh 2 ) and Tp* 2 U(η 1 -N 2 CHSiMe 3 ), 27 with loss of benzyl radical that subsequently couples and is identified as bibenzyl.…”

“…Others have taken advantage of the strong oxophilicity of uranium with the use of alkoxide ligands. Andersen and coworkers treated U(OCH(CMe 3 ) 2 ) 4 with MeLi (1 equivalent in hexanes) to produce five coordinate LiUCH 3 (OCH(CMe 3 ) 2 ) 4 (27), which features a lithium counterion coordinated to two oxygens. 60 Compound 27 shows a square pyramidal geometry in the solid state, with an apical methyl group displaying a U-C distance of 2.465(7) Å, and dissociates readily in solution, generating MeLi and the tetravalent alkoxide starting material.…”

The synthesis and versatile reducing power of low-valent uranium complexes

“…bipy or benzophenone), these species have been observed to act as two-electron reductants, 157,162,163 sometimes with accompanying radical coupling to the bipy ligand. 69,159 Similar multi-electron reductive behavior has been observed in uranium(III) benzyl, 162,[164][165][166][167][168] hydride, 169,170 and tetraphenylborate species. 171,172 In benzyl and hydride complexes, one reducing equivalent may be provided by oxidative coupling to form half an equivalent (per benzyl or hydride ligand) of bibenzyl or dihydrogen, respectively.…”