19 research outputs found
Metal-Metal Bonding in Uranium-Group 10 Complexes
Heterobimetallic
complexes containing short uranium–group
10 metal bonds have been prepared from monometallic IU<sup>IV</sup>(OAr<sup>P</sup>-κ<sup>2</sup><i>O</i>,<i>P</i>)<sub>3</sub> (<b>2</b>) {[Ar<sup>P</sup>O]<sup>−</sup> = 2-<i>tert</i>-butyl-4-methyl-6-(diphenylphosphino)Âphenolate}.
The U–M bond in IU<sup>IV</sup>(μ-OAr<sup>P</sup>-1κ<sup>1</sup><i>O</i>,2κ<sup>1</sup><i>P</i>)<sub>3</sub>M<sup>0</sup>, M = Ni (<b>3–Ni</b>), Pd (<b>3–Pd</b>), and Pt (<b>3–Pt</b>), has been
investigated by experimental and DFT computational methods. Comparisons
of <b>3–Ni</b> with two further U–Ni complexes
XU<sup>IV</sup>(μ-OAr<sup>P</sup>-1κ<sup>1</sup><i>O</i>,2κ<sup>1</sup><i>P</i>)<sub>3</sub>Ni<sup>0</sup>, X = Me<sub>3</sub>SiO (<b>4</b>) and F (<b>5</b>), was also possible via iodide substitution. All complexes were
characterized by variable-temperature NMR spectroscopy, electrochemistry,
and single crystal X-ray diffraction. The U–M bonds are significantly
shorter than any other crystallographically characterized d–f-block
bimetallic, even though the ligand flexes to allow a variable U–M
separation. Excellent agreement is found between the experimental
and computed structures for <b>3–Ni</b> and <b>3–Pd</b>. Natural population analysis and natural localized molecular orbital
(NLMO) compositions indicate that U employs both 5f and 6d orbitals
in covalent bonding to a significant extent. Quantum theory of atoms-in-molecules
analysis reveals U–M bond critical point properties typical
of metallic bonding and a larger delocalization index (bond order)
for the less polar U–Ni bond than U–Pd. Electrochemical
studies agree with the computational analyses and the X-ray structural
data for the U–X adducts <b>3–Ni</b>, <b>4</b>, and <b>5</b>. The data show a trend in uranium–metal
bond strength that decreases from <b>3–Ni</b> down to <b>3–Pt</b> and suggest that exchanging the iodide for a fluoride
strengthens the metal–metal bond. Despite short U–TM
(transition metal) distances, four other computational approaches
also suggest low U–TM bond orders, reflecting highly transition
metal localized valence NLMOs. These are more so for <b>3–Pd</b> than <b>3–Ni</b>, consistent with slightly larger U–TM
bond orders in the latter. Computational studies of the model systems
(PH<sub>3</sub>)<sub>3</sub>MUÂ(OH)<sub>3</sub>I (M = Ni, Pd) reveal
longer and weaker unsupported U–TM bonds vs <b>3</b>
Differential uranyl(v) oxo-group bonding between the uranium and metal cations from groups 1, 2, 4, and 12; a high energy resolution X-ray absorption, computational, and synthetic study
The uranyl(VI) ‘Pacman’ complex [(UO₂)(py)(H₂L)] A (L = polypyrrolic Schiff-base macrocycle) is reduced by Cp₂Ti(η²-Me₃SiC[triple bond, length as m-dash]CSiMe₃) and [Cp₂TiCl]₂ to oxo-titanated uranyl(V) complexes [(py)(Cp₂OUO)(py)(H₂L)] 1 and [(ClCp₂OUO)(py)(H₂L)] 2. Combination of and synthons with A yields the first –uranyl(V) complex, [(ClCp₂ZrOUO)(py)(H₂L)] 3. Similarly, combinations of and synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(V) complexes [(py)₂(ClMgOUO)(py)(H₂L)] 4, [(py)₂(thf)₂(ICaOUO)(py) (H₂L)] 5; the zinc complexes [(py)₂(XZnOUO)(py)(H₂L)] (X = Cl 6, I 7) are formed in a similar manner. In contrast, the direct reactions of Rb or Cs metal with A generate the first mono-rubidiated and mono-caesiated uranyl(V) complexes; monomeric [(py)₃(RbOUO)(py)(H₂L)] 8 and hexameric [(MOUO)(py)(H₂L)]₆ (M = Rb 8b or Cs 9). In these uranyl(V) complexes, the pyrrole N–H atoms show strengthened hydrogen-bonding interactions with the endo-oxos, classified computationally as moderate-strength hydrogen bonds. Computational DFT MO (density functional theory molecular orbital) and EDA (energy decomposition analysis), uranium M₄ edge HR-XANES (High Energy Resolution X-ray Absorption Near Edge Structure) and 3d4f RIXS (Resonant Inelastic X-ray Scattering) have been used (the latter two for the first time for uranyl(V) in 7 (ZnI)) to compare the covalent character in the –O and O–M bonds and show the 5f orbitals in uranyl(VI) complex A are unexpectedly more delocalised than in the uranyl(V) 7 (ZnI) complex. The –Zn bonds have a larger covalent contribution compared to the Mg–/Ca– bonds, and more covalency is found in the U– bond in 7 (ZnI), in agreement with the calculations
CCDC 1430511: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
Using the phospha-Michael reaction for making phosphonium phenolate zwitterions
The reactions of 2,4-di-tert-butyl-6-(diphenylphosphino)phenol and various Michael acceptors (acrylonitrile, acrylamide, methyl vinyl ketone, several acrylates, methyl vinyl sulfone) yield the respective phosphonium phenolate zwitterions at room temperature. Nine different zwitterions were synthesized and fully characterized. Zwitterions with the poor Michael acceptors methyl methacrylate and methyl crotonate formed, but could not be isolated in pure form. The solid-state structures of two phosphonium phenolate molecules were determined by single-crystal X-ray crystallography. The bonding situation in the solid state together with NMR data suggests an important contribution of an ylidic resonance structure in these molecules. The phosphonium phenolates are characterized by UV-Vis absorptions peaking around 360 nm and exhibit a negative solvatochromism. An analysis of the kinetics of the zwitterion formation was performed for three Michael acceptors (acrylonitrile, methyl acrylate and acrylamide) in two different solvents (chloroform and methanol). Results revealed the proton transfer step necessary to stabilize the initially formed carbanion as the rate determining step. A preorganization of the carbonyl bearing Michael acceptors allowed for reasonable fast direct proton transfer from the phenol in aprotic solvents. In contrast, acrylonitrile not capable of forming a similar preorganization, is hardly reactive in chloroform solution, while in methanol the corresponding phosphonium phenolate is formed
CCDC 1430506: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
CCDC 1430507: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
CCDC 1430513: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures