[(thf)Li2{H2CS(NtBu)2}]2: Synthesis, Polymorphism, and Experimental Charge Density to Elucidate the Bonding Properties of a Lithium Sulfur Ylide

Indium Kα radiation from a MetalJet X-ray source: the long way to a successful charge-density investigation

The MetalJet X-ray source provides indium Kα radiation with a wavelength even shorter than Ag radiation. This paper reports on problematic spectral impurities and presents possible countermeasures so that collection of data with excellent quality up to a high resolution is possible. It is demonstrated that these data can be used in the refinement of a multipole model, the results of which are used for a topological analysis to assess the bonding situation in a sulfur ylide compound.

Coordination and Stabilization of a Lithium Ion with a Silylene

Herein, we report the stabilization of lithium-ion as the source of lithium to use as a trans-metalation reagent [{PhC(N^t Bu)₂ Si(^t Bu)Li}₂ I(^t BuN)₂ CPh] (1). The reaction of 3 equivalents of the LSi^t Bu (L=PhC(N^t Bu)₂ ) and lithium iodide at low temperature leads to a silylene stabilized lithium-ion with an additional coordination of amidinate ligand. Compound 1 shows two four membered and one six membered ring as confirmed by QTAIM calculations. Whereas the reaction of the LSiCl with 1.5 equivalents of carbodiimide (CyN)₂ C at room temperature affords compound [PhC(N^t Bu)₂ Si(Cl)(NCy)₂ NCy] (2) with the CN₂ SiN₂ C skeleton containing silicon as a central atom. Both the compounds were fully characterized by NMR, mass spectrometry, X-ray crystallographic analysis, and quantum mechanical calculations.

Isolation and Properties of the Long Elusive Deep Blue Soluble [K3 {(Nt Bu)3 S}2 ]. Cage Radical

The reaction of potassium metal with sulfurtriimide S(Nt Bu)3 (II) gives the long elusive deep blue cage radical [K3 {(Nt Bu)3 S}2 ]. (1_K) that crystallizes at -35 °C from toluene solution. The subsequent physical characterization via X-ray structure analysis, UV/Vis-, and EPR spectroscopy from solution reveals the existence of one unpaired electron delocalized within the whole cage, i.e. coupling with the six nitrogen atoms, as well as the three potassium atoms caped by the two SN3 ligands. The present X-ray structure analysis further supports previous assumptions made on the parent compound 1_Li obtained from [Li4 {(Nt Bu)3 S}2 ] (I) and finally elucidates the structural arrangement of the SN3 caps and alkali metals in such radical cage species.

Structural Motifs of Alkali Metal Superbases in Non-coordinating Solvents

Lochmann-Schlosser superbases (LSB) are a standard reagent in synthetic chemistry to achieve an exchange of a proton on an organic framework with an alkali metal cation, which in turn can be replaced by a wide range of electrophilic groups. In standard examples, the deprotonating reagent consists of an equimolar mixture of n-butyllithium and potassium t-butoxide. However, the nature of the reactive species could not be pinned down either for this composition or for similar mixtures with comparable high reactivity. Despite the poor solubility and the fierce reactivity, some insights into this mixture were achieved by some indirect results, comparison with chemically related systems, or skillful deductions. Recent results, mainly based on new soluble compounds, delivered structural evidence. These new insights lead to advanced and more detailed conclusions about the interplay of the involved components.

Insight into the Bonding and Aggregation of Alkyllithiums by Experimental Charge Density Studies and Energy Decomposition Analyses

In this Article, the organolithiums [((-)-sparteine)Li^tBu] (1), [(ABCO)Li^tBu]₂ (2), and [(ABCO)₂(LiⁱPr)₄] (3) are investigated by means of experimental and theoretical charge density determination to elucidate the nature of the Li-C and Li-N bonds. Furthermore, the valence shell charge concentrations (VSCCs) in the nonbonding region of the deprotonated C_α-atom will provide some insight on the localization of the carbanionic lone pair. Analysis of the electron density (ρ(r_BCP)), Laplacian (∇²ρ(r_BCP)), and the energy decomposition (EDA) confirmed that the Li-C/N bond exhibits astonishingly similar characteristics, to reveal an increasingly polar contact with decreasing aggregate size. This explains former observations on the incorporation of halide salts in organolithium reagents. Furthermore, it could be shown that the bonding properties of the ⁱPr group are similar to those of the ^tBu substituent. The accuracy of fit to all previously determined properties in organolithiums is remarkable.

Experimental charge density study on FLPs and a FLP reaction product

The charge density distribution of the intramolecular frustrated Lewis pair (FLP) Mes2PCH2CH2B(C6F5)2 (1), the phosphinimine HNPMes2CH2CH2B(C6F5)2 (2), as well as a FLP homologue with nitrogen NEt2CHPhCH2B(C6F5)2 (3) were investigated with Bader’s quantum theory of atoms in molecules (QTAIM). The charge densities were derived from both experimental high-resolution X-ray diffraction data (2, 3) and theoretical calculations (1, 3). The QTAIM analysis for the FLPs 1 and 3 showed the prominent B-pnictogen interaction to be weak dative bonds without significant charge-transfer. This holds also true for the B–N–bond of 2. The nitrogen atom is negatively charged, due to a charge transfer from phosphorous and shows features of a sp2-hybridization. The bond is therefore best described as a non-hypervalent Pδ+–Nδ− moiety.

Benchmarking lithium amide versus amine bonding by charge density and energy decomposition analysis arguments

We investigated [{(Me₂NCH₂)₂(C₄H₂N)}Li]₂ (1) by means of experimental charge density calculations based on the quantum theory of atoms in molecules (QTAIM) and DFT calculations using energy decomposition analysis (EDA).

Lithium amides are versatile C–H metallation reagents with vast industrial demand because of their high basicity combined with their weak nucleophilicity, and they are applied in kilotons worldwide annually. The nuclearity of lithium amides, however, modifies and steers reactivity, region- and stereo-selectivity and product diversification in organic syntheses. In this regard, it is vital to understand Li–N bonding as it causes the aggregation of lithium amides to form cubes or ladders from the polar Li–N covalent metal amide bond along the ring stacking and laddering principle. Deaggregation, however, is more governed by the Li←N donor bond to form amine adducts. The geometry of the solid state structures already suggests that there is σ- and π-contribution to the covalent bond. To quantify the mutual influence, we investigated [{(Me₂NCH₂)₂(C₄H₂N)}Li]₂ (1) by means of experimental charge density calculations based on the quantum theory of atoms in molecules (QTAIM) and DFT calculations using energy decomposition analysis (EDA). This new approach allows for the grading of electrostatic Li⁺N^–, covalent Li–N and donating Li←N bonding, and provides a way to modify traditional widely-used heuristic concepts such as the –I and +I inductive effects. The electron density ρ(r) and its second derivative, the Laplacian ∇²ρ(r), mirror the various types of bonding. Most remarkably, from the topological descriptors, there is no clear separation of the lithium amide bonds from the lithium amine donor bonds. The computed natural partial charges for lithium are only +0.58, indicating an optimal density supply from the four nitrogen atoms, while the Wiberg bond orders of about 0.14 au suggest very weak bonding. The interaction energy between the two pincer molecules, (C₄H₂N)₂^2–, with the Li₂²⁺ moiety is very strong (ca. –628 kcal mol^–1), followed by the bond dissociation energy (–420.9 kcal mol^–1). Partitioning the interaction energy into the Pauli (ΔE_Pauli), dispersion (ΔE_disp), electrostatic (ΔE_elstat) and orbital (ΔE_orb) terms gives a 71–72% ionic and 25–26% covalent character of the Li–N bond, different to the old dichotomy of 95 to 5%. In this regard, there is much more potential to steer the reactivity with various substituents and donor solvents than has been anticipated so far.

New Pd(ii) complexes of sulfur ylides; synthesis, X-ray characterization, a theoretical study and catalytic activity toward the Mizoroki–Heck reaction

The reaction of sulfur ylides SMe₂C(H)C(O)R (R = 4-nitrophenyl, phenyl, and 3-nitrophenyl) with [PdCl₂(cod)] gives the new Pd(ii) complexes of type cis- and trans-[PdCl₂(SMe₂C(H)C(O)R)₂] (R = phenyl (1), 3-nitrophenyl (2), and 4-nitrophenyl (3)).

Electron density distribution in tetralithium hypodiphosphate hexahydrate, Li4P2O6·6H2O

Tetralithium hypodiphosphate hexahydrate, Li4P2O6·6H2O, forms a highly symmetrical crystal structure, where hypodiphosphate anions have \bar 3m (D3d) symmetry. Analysis of the charge distribution (experimental and theoretically calculated) shows that the charges of the P atoms are lower than in phosphates and phosphonates, whereas the O charges are similar. Values of both ρc and ∇(2)ρc suggest that the P-P bond is a weak covalent one, while the P-O one is polarized covalent, with topological parameters similar to those of P-O bonds in phosphates or phosphonates. Theoretical calculations show that the hypodiphosphate anion is relatively insensitive to its coordination environment; this is brought about by the vicinity of cationic P atoms. The localization and delocalization indices have been computed and discussed.

Meaningful structural descriptors from charge density

This paper provides a short introduction to the basics of electron density investigations. The two predominant approaches for the modelling and various interpretations of electron density distributions are presented. Their potential translations into chemical concepts are explained. The focus of the article lies on the deduction of chemical properties from charge density studies in some selected main group compounds. The relationship between the obtained numerical data and commonly accepted simple chemical concepts unfortunately is not always straightforward, and often the chemist relies on heuristic connections rather than rigorously defined ones. This article tries to demonstrate how charge density analyses can shed light on aspects of chemical bonding and reactivity resulting from the determined bonding situation. Sometimes this helps to identify misconceptions and sets the scene for new unconventional synthetic approaches.

New chelating ligands based on S-organosulfurdiimides: synthesis and single crystal X-ray structures of their lithium complexes

Three new diimidosulfinates, [TMSCH(2)S(N(t)Bu)(2)Li](2) (1), [2-PyCH(2)S(N(t)Bu)(2)Li](2) (2), and [{PhCH(2)S(N(t)Bu)(2)Li}(2) x THF] (3) (TMS = trimethylsilyl; Py = 2-pyridyl), have been synthesized by the reaction of functionalized alpha-CH(2)-organolithium compounds with bis-tert-butylsulfurdiimide. These new organolithium chelates are characterized by NMR ((1)H, (13)C, (7)Li, and (29)Si) spectroscopy and single-crystal X-ray diffraction analyses. Compounds 1 and 2 crystallize as dimers without donor molecules, whereas one of the lithium atoms in 3 is coordinated by a single THF molecule. The crystal structure of 1 shows significant intramolecular proximity between one methyl group of the trimethylsilyl (TMS) and one lithium atom, which could be described as an electrostatic Li...C interaction. The coordination sphere of each lithium atom in 2 is completed by donation from the nitrogen atom of the pyridyl ring; however, one of the lithium atoms in 3 is coordinated by a THF molecule. In addition, the first mixed sulfurdiimide species containing a diimidosulfinate and a diimidosulfite fragment, [{PhCHS(N(t)Bu)(2)Li(2)(THF)(2)}{MeS(N(t)Bu)(2)Li(THF)}] (4), was isolated by deprotonation of the alpha-CH(2) group in 3. The single-crystal X-ray structure of 4 revealed two different S-bound substituents coexisting in one dimer and two asymmetrically coordinated lithium atoms.