A Simple Preparative Route to Bis(imido)uranium(VI) Complexes by the Direct Reductions of Diazenes and Azides

In clean, one-pot procedures , the uranium complex 1 reductively cleaves azides and azo compounds to generate bis(imido) derivatives [Eq. (a)]. This unusual reaction has not been observed previously in either the actinide series or with a metallocene complex.     

Evidence of a Uranium-Paddlewheel Node in a Catecholate-Based Metal–Organic Framework

The interactions between uranium and non-innocent organic species are an essential component of fundamental uranium redox chemistry. However, they have seldom been explored in the context of multidimensional, porous materials. Uranium-based metal–organic frameworks (MOFs) offer a new angle to study these interactions, as these self-assembled species stabilize uranium species through immobilization by organic linkers within a crystalline framework, while potentially providing a method for adjusting metal oxidation state through coordination of non-innocent linkers. We report the synthesis of the MOF NU-1700 , assembled from U⁴⁺-paddlewheel nodes and catecholate-based linkers. We propose this highly unusual structure, which contains two U⁴⁺ ions in a paddlewheel built from four linkers—a first among uranium materials—as a result of extensive characterization via powder X-ray diffraction (PXRD), sorption, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA), in addition to density functional theory (DFT) calculations.     

Complexes Featuring a cis-[M U M] Core (M=Rh,Ir): A New Route to Uranium-Metal Multiple Bonds

Although examples of multiple bonds between actinide elements and main-group elements are quite common, studies of the multiple bonds between actinide elements and transition metals are extremely rare owing to difficulties associated with their synthesis. Here we report the first example of molecular uranium complexes featuring a cis-[M U M] core (M=Rh, Ir), which exhibits an unprecedented arrangement of two M U double dative bond linkages to a single U center. These complexes were prepared by the reactions of chlorine-bridged heterometallic complexes [{U{N(CH₃)(CH₂CH₂NPⁱPr₂)₂}(Cl)₂[(μ-Cl)M(COD)]₂}] (M=Rh, Ir) with MeMgBr or MeLi, a new method for the construction of species with U−M multiple bonds. Theoretical calculations including dispersion confirmed the presence of two U M double dative bonds in these complexes. This study not only enriches the U M multiple bond chemistry, but also provides a new opportunity to explore the bonding of actinide elements.     

Experimental and Computational Studies on Uranium Diazomethanediide Complexes

Uranium diazomethanediide complexes can be prepared and their synthesis, structure and reactivity were explored. Reaction of the uranium imido compound [η⁵-1,2,4-(Me₃Si)₃C₅H₂]₂U=N(p-tolyl)(dmap) ( 1 ) or [η⁵-1,3-(Me₃C)₂C₅H₃]₂U=N(p-tolyl)(dmap) ( 4 ) with Me₃SiCHN₂ cleanly yields the first isocyanoimido metal complexes [η⁵-1,2,4-(Me₃Si)₃C₅H₂]₂U(=NNC)(μ-CNN=)U(dmap)[η⁵-1,2,4-(Me₃Si)₃C₅H₂]₂ ( 2 ) and {[η⁵-1,3-(Me₃C)₂C₅H₃]₂U[μ-(=NNC)]}₆ ( 5 ), respectively. Both compounds exhibit remarkable thermal stability and were fully characterized. According to density functional theory (DFT) studies the bonding between the Cp₂U²⁺ and [NNC]²⁻ moieties is strongly polarized with a significant 5 f orbital contribution, which is also reflected in the reactivity of these complexes. For example, complex 5 acts as a nucleophile toward alkylsilyl halides and engages in a [2+2] cycloaddition with CS₂, but no reaction occurs in the presence of internal alkynes.     

Laser-induced Fluorescence Spectroscopy of Uranium Monofluoride

The laser-induced fluorescence excitation spectra of uranium monofluoride have been recorded in the range of 17000\begin{document}$ - $\end{document} 19000 cm\begin{document}$^{-1} $\end{document} using two-dimensional spectroscopy. High resolution dispersed fluorescence spectra and time-resolved fluorescence spectroscopy were also recorded. Three rotationally resolved bands were intensively analyzed, and all bands were found to be derived from the ground state X(1)4.5 with a rotational constant of 0.23421 cm\begin{document}$^{-1} $\end{document}. The low-lying electronic states were observed near 435 and 651 cm\begin{document}$^{-1} $\end{document} in the dispersed fluorescence spectra, which were assigned as \begin{document}$ \Omega' $\end{document}=3.5 and 2.5, respectively. The vibrational constants for the X(1)4.5 and X(1)3.5 states were calculated. The branching ratios of the dispersed fluorescence spectra for the [18.62]3.5, [17.72]4.5, and [17.65]4.5 states were reported. Radiative lifetime of 332(9) ns, 825(49) ns, and 433(15) ns for the [18.62]3.5, [17.72]4.5, and [17.65]4.5 states were obtained by fitting the time-resolved fluorescence spectroscopy, respectively. Transition dipole moments were performed using the branching ratios and the radiative lifetimes.     

BN-Butafulvenes and Their Application in the Synthesis of Highly Substituted BN-9,1-Naphthalenes

BN-butafulvenes, mono-BN isosteres of butafulvene and highly strained isomers of azaborines and B-amino boroles, have been synthesized via hydrolysis of the urana-borabicyclic complexes obtained from the reactions of bis(alkynyl)boranes with an uranacyclopropene complex. Their 4-dimethylaminopyridine (DMAP) adducts can further isomerize to 1,2,4,6-multisubstituted BN-9,1-naphthalenes. Both NMR reaction monitoring and theoretical calculations point to a reaction mechanism involving dearomative insertion of DMAP followed by two consecutive 1,2-hydrogen shifts. The photophysical studies of the highly substituted BN-9,1-naphthalenes reveal a notable redshift in both the UV/Vis absorption and emission spectra. The (TD)-DFT calculations corroborate the experimental data, suggesting that the strong π-donating amino substitution at the 1- and/or 6-positions destabilizes the HOMO, and thus leading to a notable decrease of the HOMO–LUMO gap.