Uranium-mediated oxidative addition and reductive elimination

This Perspective article summarises the emerging research topic of uranium-mediated oxidative addition and reductive elimination.</p

Synthesis and Characterisation of Lanthanide N-Trimethylsilyl and -Mesityl Functionalised Bis(iminophosphorano)methanides and -Methanediides

We report the extension of the series of {BIPMTMSH}− (BIPMR = C{PPh2NR}2, TMS = trimethylsilyl) derived rare earth methanides by the preparation of [Ln(BIPMTMSH)(I)2(THF)] (Ln = Nd, Gd, Tb), 1a–c, in 34–50% crystalline yields via the reaction of [Ln(I)3(THF)3.5] with [Cs(BIPMTMSH)]. Similarly, we have extended the range of {BIPMMesH}− (Mes = 2,4,6-trimethylphenyl) derived rare earth methanides with the preparation of [Gd(BIPMMesH)(I)2(THF)2], 3, (49%) and [Yb(BIPMMesH)(I)2(THF)], 4, (26%), via the reaction of [Ln(I)3(THF)3.5] with [{K(BIPMMesH)}2]. Attempts to prepare dysprosium and erbium analogues of 3 or 4 were not successful, with the ion pair species [Ln(BIPMMesH)2][BIPMMesH] (Ln  = Dy, Er), 5a–b, isolated in 31–39% yield. The TMEDA (N',N',N",N"-tetramethylethylenediamine) adducts [Ln(BIPMMesH)(I)2(TMEDA)] (Ln = La, Gd), 6a–b, were prepared in quantitative yield via the dissolution of [La(BIPMMesH)(I)2(THF)] or 3 in a TMEDA/THF solution. The reactions of [Ln(BIPMMesH)(I)2(THF)] [Ln  = La, Ce, Pr, and Gd (3)] or 6a–b with a selection of bases did not afford [La(BIPMMes)(I)(S)n] (S = solvent) as predicted, but instead led to the isolation of the heteroleptic complexes [Ln(BIPMMes)(BIPMMesH)] (Ln = La, Ce, Pr and Gd), 7a–d, in low yields due to ligand scrambling

An inverted-sandwich diuranium μ-η5:η5-cyclo-P5 complex supported by U-P5 δ-bonding

Reaction of [U(TrenTIPS)] [1, TrenTIPS=N(CH2CH2NSiiPr3)3] with 0.25 equivalents of P4 reproducibly affords the unprecedented actinide inverted sandwich cyclo-P5 complex [{U(TrenTIPS)}2(μ-η5:η5-cyclo-P5)] (2). All prior examples of cyclo-P5 are stabilized by d-block metals, so 2 shows that cyclo-P5 does not require d-block ions to be prepared. Although cyclo-P5 is isolobal to cyclopentadienyl, which usually bonds to metals via σ- and π-interactions with minimal δ-bonding, theoretical calculations suggest the principal bonding in the U(P5)U unit is polarized δ-bonding. Surprisingly, the characterization data are overall consistent with charge transfer from uranium to the cyclo-P5 unit to give a cyclo-P5 charge state that approximates to a dianionic formulation. This is ascribed to the larger size and superior acceptor character of cyclo-P5 compared to cyclopentadienyl, the strongly reducing nature of uranium(III), and the availability of uranium δ-symmetry 5f orbitals

Synthesis and characterization of an f‑block terminal parent imido [U=NH] complex: a masked uranium(IV) nitride

Deprotonation of [U(TrenTIPS)(NH2)] (1) [TrenTIPS = N(CH2CH2NSiPri3)3] with organoalkali metal reagents MR (M = Li, R = But; M = Na−Cs, R = CH2C6H5) afforded the imido-bridged dimers [{U-(TrenTIPS)(μ-N[H]M)}2] [M = L −Cs (2a−e)]. Treatmentof 2c (M = K) with 2 equiv of 15 crown-5 ether (15C5) afforded the uranium terminal parent imido complex [U(TrenTIPS)(NH)][K(15C5)2] (3c), which can also be viewed as a masked uranium(IV) nitride. The uranium−imido linkage was found to be essentially linear, and theoretical calculations suggested σ2π4 polarized U−N multiple bonding. Attempts to oxidize 3c to afford the neutral uranium terminal parent imido complex [U(TrenTIPS)(NH)] (4) resulted in spontaneous disproportionation to give 1 and the uranium−nitride complex [U(TrenTIPS)(N)] (5); this reaction is a new way to prepare the terminal uranium−nitride linkage and was calculated to be exothermic by −3.25 kcal mol−1

Synthesis and characterisation of halide, separated ion pair, and hydride cyclopentadienyl iron bis(diphenylphosphino)ethane derivatives

Treatment of anhydrous FeX₂ (X = Cl, Br, I) with one equivalent of bis(diphenylphosphino)ethane (dppe) in refluxing THF afforded analytically pure white (X = Cl), light green (X = Br), and yellow (X = I) [FeX₂(dppe)]n (X = Cl, I; Br, II; I, III). Complexes I–III are excellent synthons from which to prepare a range of cyclopentadienyl derivatives. Specifically, treatment of I–III with alkali metal salts of C₅H₅ (Cp, series 1), C₅Me₅ (Cp*, series 2), C₅H₄SiMe₃ (Cp′, series 3), C₅H₃(SiMe₃)₂ (Cp′′, series 4), and C₅H₃(But)₂ (Cptt, series 5) afforded [Fe(Cp†)(Cl)(dppe)] 1Cl–5Cl, [Fe(Cp†)(Br)(dppe)] 1Br–5Br, and [Fe(Cp†)(I)(dppe)] 1I–5I (Cp† = Cp, Cp*, Cp′, Cp′′, or Cptt). Dissolution of 1I–5I in acetonitrile, or treatment of 1Cl–5Cl with Me₃SiI in acetonitrile (no halide exchange reactions were observed in other solvents) afforded the separated ion pair complexes [Fe(Cp†)(NCMe)(dppe)][I] 1SIP–5SIP. Attempts to reduce 1Cl–5Cl, 1Br–5Br, and 1I–5I with a variety of reductants (Li-Cs, KC₈, Na/Hg) were unsuccessful. Treatment of 1Cl–5Cl with LiAlH₄ gave the hydride derivatives [Fe(Cp†)(H)(dppe)] 1H–5H. This report provides a systematic account of reliable methods of preparing these complexes which may find utility in molecular wire and metal–metal bond chemistries. The complexes reported herein have been characterised by X-ray diffraction, NMR, IR, UV/Vis, and Mössbauer spectroscopies, cyclic voltammetry, density functional theory calculations, and elemental analyses, which have enabled us to elucidate the electronic structure of the complexes and probe the variation of iron redox properties as a function of varying the cyclopentadienyl or halide ligand

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

From Europe PMC via Jisc Publications RouterHistory: ppub 2021-09-01, epub 2021-09-24Publication status: PublishedFunder: RCUK | Engineering and Physical Sciences Research Council (EPSRC); Grant(s): EP/M027015/1, EP/K024000/1, EP/S033181/1Funder: European Research Council; Grant(s): 612724Determining the nature and extent of covalency of early actinide chemical bonding is a fundamentally important challenge. Recently, X-ray absorption, electron paramagnetic, and nuclear magnetic resonance spectroscopic studies have probed actinide-ligand covalency, largely confirming the paradigm of early actinide bonding varying from ionic to polarised-covalent, with this range sitting on the continuum between ionic lanthanide and more covalent d transition metal analogues. Here, we report measurement of the covalency of a terminal uranium(VI)-nitride by 15N nuclear magnetic resonance spectroscopy, and find an exceptional nitride chemical shift and chemical shift anisotropy. This redefines the 15N nuclear magnetic resonance spectroscopy parameter space, and experimentally confirms a prior computational prediction that the uranium(VI)-nitride triple bond is not only highly covalent, but, more so than d transition metal analogues. These results enable construction of general, predictive metal-ligand 15N chemical shift-bond order correlations, and reframe our understanding of actinide chemical bonding to guide future studies