Probing the Chemistry, Electronic Structure and Redox Energetics in Organometallic Pentavalent Uranium Complexes

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• 作者：Christopher R. Graves ; Anthony E. Vaughn ; Eric J. Schelter ; Brian L. Scott ; Joe D. Thompson ; David E. Morris ; Jaqueline L. Kiplinger
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：December 15, 2008
• 年：2008
• 卷：47
• 期：24
• 页码：11879-11891
• 全文大小：435K
• 年卷期：v.47,no.24(December 15, 2008)
• ISSN：1520-510X

文摘

A series of organometallic pentavalent uranium complexes of the general formula (C₅Me₅)₂U(=N-2,6-ⁱPr₂-C₆H₃)(Y) (Y = monoanionic, non-halide ligand) have been prepared using a variety of routes. Utilizing the direct oxidation of (C₅Me₅)₂U(=N-2,6-ⁱPr₂-C₆H₃)(THF) (2) with the appropriate copper(I) salt yielded the triflate (Y = OTf (OSO₂CF₃), 11), thiolate (Y = SPh, 12), and acetylide (Y = CCPh, 13) complexes, while a salt metathesis route between the U^V-imido (C₅Me₅)₂U(=N-2,6-ⁱPr₂-C₆H₃)(I) (10) and various alkali salts gave the diphenylamide (Y = NPh₂, 14), aryloxide (Y = OPh, 15), alkyl (Y = Me, 16), and aryl (Y = Ph, 17) complexes. Paired with 13, the isolation of 16 and 17 shows that U^V can support the full range of carbon anions (sp, sp², and sp³), and these are, to the best of our knowledge, the first examples of pentavalent uranium complexes with anionic carbon moieties other than carbocyclic (C₅R₅, C₇H₇, C₈H₈) ligands. Finally, both protonolysis and insertion pathways afforded the U^V-imido ketimide complex (C₅Me₅)₂U(=N-2,6-ⁱPr₂-C₆H₃)(N=CPh₂) (18). The complexes have been isolated in good yield and characterized using various combinations of ¹H NMR spectroscopy, elemental analysis, mass spectrometry, single crystal X-ray diffraction, cyclic voltammetry, UV-visible-NIR absorption spectroscopy, and magnetic susceptibility measurements. All (C₅Me₅)₂U(=N−Ar)(X) (X = F, Cl, Br, I) and (C₅Me₅)₂U(=N−Ar)(Y) complexes exhibit U^VI/U^V and U^V/U^IV redox couples by voltammetry. The potential separation between these couples remains essentially constant at 1.50 V, but both processes shift in tandem in potential by 700 mV across the series of X/Y ligands. No significant differences between μ_eff values or temperature dependencies in the magnetic susceptibility were observed for these complexes regardless of the identity of the ancillary X/Y ligand. However, an excellent linear correlation was observed between the chemical shift values of C₅Me₅ ligand protons in the ¹H NMR spectra and the oxidation potentials of (C₅Me₅)₂U(=N-2,6-ⁱPr₂-C₆H₃)(X/Y), suggesting that there is a common origin, overall σ-/π-donation from the ancillary X/Y ligand to the metal, contributing to both observables. Combined, these data confer the following trend in increasing σ/π-donating ability of the X/Y ligand to the U^V metal center: OTf < I < Br < Cl < SPh < CCPh < F < [OPh Me Ph] NPh₂ < N=CPh₂. These (C₅Me₅)₂U(=N-2,6-ⁱPr₂-C₆H₃)(X/Y) complexes also show distinct hallmarks of a covalent bonding interaction between the metal and the imide ligand that is modulated to varying degrees by the interaction between the X/Y ancillary ligand and the U^V metal center. These signatures of covalency include stabilization of multiple metal oxidations states [U^VI, U^V, and U^IV] and enhanced intensities in the intraconfiguration (f-f) transitions. Of particular note in this regard is the more than 20-fold enhancement in the f-f intensities observed for Y = CCPh and N=CPh₂, which is a clear reflection of the covalent metal-ligand bonding interactions sustained by the acetylide and ketimide ligands in these pentavalent systems.