Acid-base Complexes Research Articles

Hydrogen atom transfer from 1,2- and 1,3-diols to the cumyloxyl radical. The role of structural effects on metal-ion induced C-H bond deactivation.

Strong C-H bond deactivation toward HAT has been observed in the reactions of the cumyloxyl radical with 1,2- and 1,3-diols, following addition of Li+ and Ca2+. Weaker effects have been observed with Mg2+. The role of the substrate structure and of the metal ion in the formation of Lewis acid-base complexes is discussed.

Complexation Chemistry in N,N-Dimethylformamide-Based Molecular Inks for Chalcogenide Semiconductors and Photovoltaic Devices.

Molecular inks based on dimethyl sulfoxide, thiourea (TU), and metal salts have been used to form high optoelectronic quality semiconductors and have led to high power conversion efficiencies for solution-processed photovoltaic devices for Cu2ZnSn(S,Se)4 (CZTS), Cu2Zn(Ge,Sn)(S,Se)4 (CZGTS), CuIn(S,Se)2 (CIS), and Cu(In,Ga)(S,Se)2 (CIGS). However, several metal species of interest, including Ag(I), In(III), Ge(II), and Ge(IV), either have low solubility (requiring dilute inks) or lead to precipitation or gelation. Here, we demonstrate that the combination of N,N-dimethylformamide (DMF) and TU has the remarkable ability to form intermediate-stability acid-base complexes with a wide number of metal chloride Lewis acids (CuCl, AgCl, ZnCl2, InCl3, GaCl3, SnCl4, GeCl4, and SeCl4), to give high-concentration stable molecular inks. Using calorimetry, Raman spectroscopy, and solubility experiments, we reveal the important role of chloride transfer and TU to stabilize metal cations in DMF. Methylation of TU is used to vary the strength of the Lewis basicity and demonstrate that the strength of the TU-metal chloride complex formed after DMF evaporation is critical to prevent volatilization of metal containing species. Further, we formulated a sulfur-free molecular ink which was used to deposit crystalline CuInSe2 without selenization that sustains high quasi-Fermi level splitting under constant illumination. Finally, we demonstrate the ability of the DMF-TU molecular ink chemistry to lead to high-photovoltaic power conversion efficiencies and high-open-circuit voltages for solution-processed CIS and CZGTS with power conversion efficiencies of 13.4% and 11.0% and Voc/ Voc,SQ of 67% and 63%, respectively.

Switching the Spin State of Pentafluorophenylnitrene: Isolation of a Singlet Arylnitrene Complex.

The chemistry of arylnitrenes is dominated by their triplet ground states and excited open-shell singlet states. This results in radical-type reactions and unwanted rearrangements, which diminish the use of arylnitrenes as intermediates in organic synthesis. While the closed-shell singlet states of arylnitrenes are expected to undergo useful chemical transformations (comparable to the closed-shell singlet states of carbenes), these states are too high in energy to be chemically accessible. When triplet pentafluorophenylnitrene is interacting with the Lewis acid BF3 under the conditions of matrix isolation, a Lewis acid-base complex consisting of the closed-shell singlet state of the nitrene and two molecules of BF3 is formed. Although the closed-shell singlet state of pentafluorophenylnitrene is calculated (CCSD(T)) to lie more than 25 kcal/mol above its triplet ground state, the reaction with BF3 results in switching the spin state from triplet to singlet. The formation of the singlet complex was monitored by IR, UV-vis, and EPR spectroscopy. DFT, CCSD(T), and CASPT2 calculations confirm the experimental findings.

Ultrasensitive Colorimetric and Ratiometric Detection of Cu2+: Acid-Base Properties, Complexation, and Binding Studies.

Herein, we report the synthesis and characterization of a chemosensor, 5-(diethylamino)-2-(2,3-dihydro-1H-perimidin-2-yl)phenol (HL), synthesized from a condensation between 4-(diethylamino)salicylaldehyde and 1,8-diaminonaphthalene. Upon investigation of the sensing properties of HL, it was found that this sensor may be employed for simple yet efficient detection of Cu2+ in aqueous methanol solutions. The selective and ratiometric response to Cu2+ yielded an outstandingly low limit of detection of 3.7 nM by spectrophotometry and is also useful as a naked-eye sensor from 2.5 μM. The system was studied by spectrophotometric pH titrations to determine Cu2+ binding constants and complex speciation. Binding of Cu2+ to HL occurs in 1:1 stoichiometry, in good agreement with high-resolution electrospray ionization mass spectrometry (ESI-HRMS) results, Cu2+ titrations, and Job’s plot experiments, while the coordination geometry was tentatively assigned as square pyramidal by spectroscopic studies.

Surface Chemistry during Atomic-Layer Deposition of Nickel Sulfide from Nickel Amidinate and H2S

Atomic-layer deposition (ALD) of metal-sulfide thin films has recently been developing very fast, and many new metal-sulfide ALD processes have emerged during the past several years. Surface chemistry plays a key role in ALD, but it remains yet to be investigated for many recently developed sulfide ALD processes. We herein report our study on the surface chemistry of the ALD of nickel sulfide from bis(N,N′-di-tert-butylacetamidinato)nickel(II) and H2S, using the in situ characterization techniques of X-ray photoelectron spectroscopy, low-energy ion scattering, quartz crystal microbalance, and quadrupole mass spectrometry. The surface chemistry is found to deviate from the conventional ligand-exchange ALD scheme, and a formation of a nonvolatile acid–base complex from acidic surface sulfhydryl and basic amidine is suggested during the H2S half-cycle. Since the precursors used herein are fairly representative, the findings should be of valuable reference for many other metal-sulfide ALD processes.

Hierarchical porous hyper-cross-linked polymers modified with phenolic hydroxyl groups and their efficient adsorption of aniline from aqueous solution

Herein two hierarchical porous hyper-cross-linked polymers modified with phenolic hydroxyl (OH) groups were synthesized and their adsorption was comparatively evaluated using aniline as the adsorbate. The results reveal that the phenolic OH groups are helpful for the equilibrium adsorption due to the increased polar matching by formation of acid-base complex and hydrogen bonding, and the hierarchical porosity is favorable for the kinetic adsorption because the three dimensional continuous mesopores facilitate the rapid diffusion of aniline. The original aniline solution is optimum for the adsorption and the molecular state of aniline is preferable. The maximum equilibrium capacity is predicted to be 184.8 mg/g by the Langmuir model, and the enthalpy change, Gibbs free energy change, and entropy change are calculated to be negative. The adsorption can reach equilibrium within 60 min, the kinetic data obey the pseudo-second-order rate equation and the first step of the adsorption is mainly controlled by the intra-particle diffusion model.

Ammonia Borane Acid–Base Complex: An Experiment Involving 1H and 11B NMR Spectroscopy and the Gas Laws

An experiment involving a moisture-sensitive synthesis and spectroscopic characterization suitable for the advanced inorganic laboratory course is presented. The acid–base complex ammonia borane (AB) is synthesized from the heterogeneous reaction between sodium borohydride and finely ground ammonium sulfate in tetrahydrofuran solvent. AB is isolated as a fluffy white solid. The 1H and 11B NMR spectra of AB, separately measured in the solvents D2O and CD3CN, provide an excellent opportunity to introduce some of the basic concepts of multinuclear NMR spectroscopy. The triplet and quartet peaks observed for the NH3 and BH3 groups in the 1H spectrum measured in CD3CN can be used to discuss the nature of JNH and JBH coupling. The former coupling is rarely observed because the quadrupolar 14N in nonspherical structures experiences rapid relaxation and large J coupling, leading to broad peaks for −NH and −NH2 protons. Although such coupling due to 11B is more commonly observed, a comparison of the 1H NMR spectra...

Chemical Conditions in the Boundary Layer Surrounding Phytoplankton Cells Modify Cadmium Bioavailability.

In this study we tested the hypothesis that metal uptake by unicellular algae may be affected by changes in metal speciation in the boundary layer surrounding the algal cells. The freshwater alga Chlamydomonas reinhardtii was preacclimated to different N nutrition regimes; changes in N nutrition are known to change the nature of extracellular metabolites (e.g., reactive oxygen species "ROS", and OH-) and thus boundary layer chemical conditions. Specifically, at a constant bulk free Cd2+ concentration, Cd uptake by N-starved algae in cysteine-buffered solution was significantly higher than that in NTA-buffered solution. This enhancement was likely due to an increase of the free Cd2+ concentration in the boundary layer, resulting from localized cysteine oxidation by ROS released from these algae. On the other hand, Cd uptake was markedly lower when the free Cd2+ concentration near cell surface decreased as a result of an increase in the boundary layer pH of nitrate-acclimated algae or enhanced localized metal complexation. The results imply that redox, acid-base and metal complexation processes in the boundary layer differ from those in bulk water, even under chemically stable bulk conditions, and the boundary layer effect may well be of significance to phytoplankton acquisition of other trace metals.

Some aspects of the adsorption of glyphosate and its degradation products on montmorillonite.

The most worldwide used herbicide is glyphosate, phosphonomethylglycine (PMG). Consequently, a significant amount of PMG, its metabolites (sarcosine, SAR, and aminomethylphosphonic acid, AMPA) and the degradation product, methylphosphonic acid (MPA), reaches the soil, which acts as final sink. Because clays are one of the most reactive components of soils, expansive clays such as montmorillonite (Mt) are used to retain agriculture contaminants with some success. In this work, as a preliminary step for the evaluation of the risk that PMG, SAR, AMPA, and MPA occurrence could have on the environment, their adsorption on Mt surface was performed. The adsorption process was analyzed at constant adsorbate concentrations and two pH values to take into account the different protonation states of the amino group. DTA, XRD, zeta potential measurements, and XPS were used to identify the interactions or association mechanisms with the clay surface, the entry of adsorbates into the Mt interlayer, and electric charge changes on the Mt surface, and evaluate the acid-base surface complex constants, respectively. The interlayer thickness in acid media indicated that adsorbates are able to enter the interlayer in planar form. Besides, for the Mt-PMG sample, some PMG molecules could be also inserted as a bilayer or with a tilt angle of 52.4° in the interlayer. However, in alkaline media, the interlayer thickness indicated that the adsorbate arrangement differed from that of acidic media where PMG and MPA could have more than one orientation. The surface complex deprotonation constants were determined for the =NH+2⇆ =NH+H+ process, being 3.0, 5.0, and 7.3 for PMG, AMPA, and SAR, respectively.

Bonding inside and outside Fullerene Cages.

Concrete crystallographic results of endohedral metallofullerenes (EMFs) disclose that the bonding within the metallic clusters and the interactions between the metal ions and the cage carbon atoms, which are closely associated with the coordination ability of the metal ions, play essential roles in determining the stability, the molecular structure, and the chemical behavior of the hybrid EMF molecules, in addition to the previously recognized charge transfer from metal to cage. For the carbide cluster metallofullerenes, a "size effect" between the encapsulated metallic cluster and the fullerene cage has been suggested. Thus, through the geometric effect, a series of giant fullerenes (C90-C104) have been stabilized by encapsulating a large La2C2 cluster, which adopts different configurations in accordance with cage size and shape. Interestingly, the crystallographic analysis of La2C2@ D5(450)-C100 has led to the direct observation of the axial compression of short carbon nanotubes caused by the internal stress. Additionally, the defective C2(816)-C104 cage is viewed to be a precursor that can transform into the other three ideal tubular fullerene cages, presenting crystallographic evidence for the top-down formation mechanism of fullerenes. Structural characterization of Y2C2@C108 confirms a linear carbide cluster inside the large cage, indicative of a geometric effect of cage size on the bonding behavior of the internal cluster. Apart from the carbide realm, direct metal-metal bonding is observed between the two seemingly repulsive Lu2+ ions in Lu2@C82-86, adding new insights into current coordination chemistry. Meanwhile, the bonding state between the metal ions inside the cage (e.g., in La2@ I h(7)-C80) and even the configuration of the internal metallic cluster (e.g., in Sc3C2@ I h(7)-C80) can be readily controlled by exohedral radical addition, illuminating their future applications as single molecule magnets and in electronics. In addition, observation of the unexpected dimerization between two paramagnetic Y@ Cs(6)-C82 molecules suggests a spin-induced bonding behavior, which depends closely on the cage geometry. In contrast, synergistic effect of both electronic and geometric parameters has led to the formation of the unprecedented [6,6,6]-Lewis acid-base adduct of Sc3N@ I h(7)-C80. However, introduction of an oxygen atom gives rise to the corresponding normal carbene adducts for both Sc3N@ I h(7)-C80 and Lu3N@ I h(7)-C80, presenting an unexpected way of steric hindrance release. Remarkably, the Lewis acid-base complexation is demonstrated to be a facile way toward isomerically pure metallofullerene derivatives with surprisingly high regioselectivity and quantitative conversion yield for Sc2C2@ C3 v(8)-C82. This Account aims to give an advanced summary of the recent achievements in research of EMFs, focusing mainly on the interplay between the internal metallic species and the surrounding cages through bond formation or cleavage. Perspectives suggesting the future developments of EMFs are also given in the last section.

Synchrotron infrared microspectroscopy reveals the response of Sphagnum cell wall material to its aqueous chemical environment

Environmental contextSphagnum moss is a widespread species in peatlands globally and responsible for a large fraction of carbon storage in these systems. We used synchrotron infrared microspectroscopy to characterise the acid-base properties of Sphagnum moss and the conditions under which calcium uptake can occur (essential for plant tissue integrity). The work allows a chemical model for Sphagnum distribution in the landscape to be proposed. AbstractSphagnum is one the major moss types responsible for the deposition of organic soils in peatland systems. The cell walls of this moss have a high proportion of carboxylated polysaccharides (polygalacturonic acids), which act as ion exchangers and are likely to be important for the structural integrity of the cell walls. We used synchrotron light source infrared microspectroscopy to characterise the acid-base and calcium complexation properties of the cell walls of Sphagnum cristatum stems, using freshly sectioned tissue confined in a flowing liquid cell with both normal water and D2O media. The Fourier transform infrared spectra of acid and base forms are consistent with those expected for protonated and deprotonated aliphatic carboxylic acids (such as uronic acids). Spectral deconvolution shows that the dominant aliphatic carboxylic groups in this material behave as a monoprotic acid (pKa=4.97–6.04). The cell wall material shows a high affinity for calcium, with a binding constant (K) in the range 103.9–104.7 (1:1 complex). The chemical complexation model developed here allows for the prediction of the chemical environment (e.g. pH, ionic content) under which Ca2+ uptake can occur, and provides an improved understanding for the observed distribution of Sphagnum in the landscape.

Biomimetic silica deposition promoted by sub-5 μm complexes of dicarboxylic acids/polyethyleneimine microballs: a new approach to tuning silica structures using messenger-like dicarboxylic acids

Acid–base complexes prepared from sub-5 μm polyethyleneimine microballs and dicarboxylic acids promoted silica deposition to give silica microballs with different morphological surface structures which were controlled by the structures of the acids.

Fast kinetics studies of the Lewis acid-base complexation of transient stannylenes with σ- and π-donors in solution.

The Lewis acid-base complexation chemistry of dimethyl- and diphenylstannylene (SnMe2 and SnPh2, respectively) in hexanes solution has been studied by laser photolysis methods. Complexation of the two stannylenes with a series of nine O-, S-, and N-donors (including cyclic and acyclic dialkyl ethers and sulfides, a primary, secondary, and tertiary amine, ethyl acetate and acetone), two alkenes, and an alkyne proceeds rapidly and reversibly to generate the corresponding stannylene-donor Lewis pairs, which have been detected in each case by time-resolved UV-vis absorption spectroscopy. The complexes exhibit UV-vis absorption maxima in the range of λmax ∼ 310-405 nm depending on the donor and substitution at tin. Bimolecular rate constants for complexation (kC), which could be determined for 14 of the 24 Lewis pairs that were studied, were found to fall within a factor of four of the diffusional limit in all cases, with SnMe2 showing consistently higher reactivity than SnPh2. Equilibrium constants for complexation (KC) could be measured for all but one of the stannylene-π- and O-donor pairs, the values corresponding to (gas phase) binding free energies in the range of +1.1 to -3.9 kcal mol-1. Comparison of the experimental equilibrium constants for complexation of SnMe2 and SnPh2 with methanol and diethyl ether to those measured previously for the homologous silylenes and germylenes indicates that Lewis acidity decreases in the order SiR2 > SnR2 > GeR2 for both the dimethyl- and diphenyltetrylene series, the diphenyl derivatives exhibiting significantly stronger Lewis acidity in all three cases. The experimental trends in the binding energies and UV-vis spectra of the complexes are reproduced well by density functional theory (DFT) calculations, which have been carried out at the (TD)ωB97XD/def2-TZVP level of theory. The experimental data also show evidence of a reaction between tetramethyldistannene (Me2Sn[double bond, length as m-dash]SnMe2, 4a) and amine donors, which is suggested to afford the corresponding amine-stabilized stannylidenestannylene structure. The mechanistic proposal is supported by DFT calculations of the complexation of 4a and SnMe2 with model O-, S- and N-donors.

Substantiation for Oxywater Zwitterions and Singlet Oxygen Atoms Generation from Hydrogen Peroxide Molecules in Aqueous Solutions

Hydrogen peroxide is widely used as an oxidant. The results of thermodynamic calculations indicate the impossibility of spontaneous generation of hydroxyl and hydroperoxyl radicals from hydrogen peroxide in aqueous solutions. Hydrogen peroxide spontaneously decomposes in ferrous, ferric, and cupric Fenton reaction systems. Ferric xylenol orange and ferric pyridoxine complexes are oxidized rapidly and spontaneously by this oxidant. Hydrogen peroxide in aqueous solutions spontaneously oxidizes the sulfur atoms of hyposulfite anions and benzylpenicillin molecules. Thus, a hydrogen peroxide molecule generates another intermediate that differs from hydroxyl and hydroperoxyl radicals. Theoretical modeling shows that hydrogen peroxide can participate in the proton transfer reactions. Its isomerization to oxywater zwitterion with subsequent oxywater intramolecular disproportionation is a process that is very suitable for explaining all events of hydrogen peroxide decomposition and oxidative reactivity in aqueous systems. The oxywater zwitterion is a bipolar ion in which the opposite charges are localized on neighboring oxygen atoms. This determines the displacement of electron density from the negatively charged atom to the positively charged atom. As a result, the interoxygen bond heterolytically dissociates with liberation of a water molecule and formation of an oxygen atom (oxene) in a singlet quantum state. This atom has a vacant atomic orbital. The S-oxidation of benzylpenicillin and hyposulfite occurs via targeting of electron pairs of the sulfur atoms by the vacant atomic orbitals of the singlet oxygen atoms. We substantiate an oxene-mediated pathway of hydrogen peroxide disproportionation. A singlet oxygen atom interacts with a second hydrogen peroxide molecule through targeting the unshared electron pair of the oxygen atom by a vacant atomic orbital. The process may be called O-oxidation of hydrogen peroxide; it results in trioxidane (dihydrogen trioxide) formation. Hydrogen trioxide rapidly decomposes and produces water and singlet dioxygen. We have suggested a mechanism of the electron spin rotation during the singlet dioxygen quenching into the triplet quantum state. We have assumed the formation of a dimeric associate from singlet dioxygen antipodes by orbital parameter. Two simultaneous redox reactions (the electron exchange interaction) result in generation of two triplet dioxygen molecules. The first triplet molecule has +1 total electron spin, and the second one has –1 total electron spin. For Fenton reaction systems, the zwitterionization of hydrogen peroxide in Lewis acid-base complexes with metal ions is followed by intramolecular disproportionation of oxywater. The singlet oxene remains in complex with a metal ion. Ferrous iron ion changes its oxidation state to ferric due to rapid and inevitable one-electron transfer within the iron(II)-oxene complex. The ferric-oxyl complex is known as alpha-oxygen complex. In our opinion, the classic Fenton reaction occurs through alpha-complex formation. We maintain such view that is alternative to widespread conceptions of the hydroxyl radical generation or oxoferryl(IV) formation. We have reproduced electro-Fenton reactions of transition metal ions with electrogenerated hydrogen peroxide and presumably observed voltammetric signals for the singlet oxene atoms and oxyl radical anions (alpha-oxygen particles). The oxywater-oxene concept is successfully applicable to explain the catalytic activity of redox-inactive substances. We have used our oxywater-oxene concept for explanation of hydroperoxide monooxygen and dioxygen oxidative functionalization mechanisms in organic synthesis.

Theoretical insight into the role of urea in the hydrolysis reaction of NO2 as a source of HONO and aerosols

Environmental contextUrea is an important component of dissolved organic nitrogen in rainfall and aerosols, but the sources and the mechanisms of its production are not well understood. This computational study explores the effects of urea and water on the hydrolysis of NO2 and urea nitrate production. The results will aid our interpretation of the role of urea in the formation of atmospheric secondary nitrogen contaminants and aerosols. AbstractThe effects of urea on the hydrolysis reaction 2NO2 + mH2O (m = 1–3) have been investigated by theoretical calculations. The energy barrier (−2.67 kcal mol−1) of the urea-promoted reaction is lower than the naked reaction by 14.37 kcal mol−1. Urea also has a better catalytic effect on the reaction than methylamine and ammonia. Urea acts as a catalyst and proton transfer medium in this process, and the produced HONO may serve as a source of atmospheric nitrous acid. In addition, the subsequent reactions include clusters of nitrite, urea, and nitric acid. Then urea nitrate (UN), which is a typical HNO3 aerosol, can be formed in the subsequent reactions. The production of the acid-base complex (UN-2) is more favourable with an energy barrier of 0.10 kcal mol−1, which is 3.88 kcal mol−1 lower than that of the zwitterions NH2CONH3+NO3− (UN-1). The formation of zwitterions and the hydrolysis reaction are affected by humidity. The multi water-promoted hydrolysis reactions exhibit better thermodynamic stability when the humidity is increased. The extra water molecules act as solvent molecules to reduce the energy barrier. The natural bond orbital (NBO) analysis is employed to describe the donor-acceptor interactions of the complexes. The hydrogen bond interaction between the urea carbonyl and nitric acid of UN-2 is the strongest. The potential distribution maps of the urea nitrate and hydrate are examined, and the result shows that they tend to form zwitterions.

Further Evidence of the Relative Stability Evaluation of Lewis Acid Base Complexes

Further Evidence of the Relative Stability Evaluation of Lewis Acid Base Complexes

Aluminabenzene-Rh and -Ir Complexes: Synthesis, Structure, and Application toward Catalytic C-H Borylation.

Aluminabenzene-rhodium and -iridium complexes were synthesized, in which the aluminum atom played as a proximal Lewis acidic site. Based on their structural analysis, aluminabenzene ligand could coordinate to Rh and Ir as a η5-pentadienyl ligand. The Lewis acidic character of aluminum atom in aluminabenzene ligand was confirmed by treatment with 4-dimethylaminopyridine to form the corresponding Lewis acid-base complexes. In addition, the α-selective C-H borylation of triethylamine with the aluminabenzene-ligated iridium catalyst was demonstrated.

Kinetic Analysis of Copper(I)/Feringa-Phosphoramidite Catalyzed AlEt3 1,4-Addition to Cyclohex-2-en-1-one

ReactIR studies of mixtures of AlEt3 (A) and cyclohex-2-en-1-one (CX) in Et2O indicate immediate formation of the Lewis acid–base complex CX·A at −40 °C (K = 12.0 M–1, ΔG°react = −1.1 kcal mol–1). Copper(I) catalysts, derived from precatalytic Cu(OAc)2 (up to 5 mol %) and (R,S,S)-P(binaphtholate){N(CHMePh)2} (Feringa’s ligand (L), up to 5 mol %) convert CX·A (0.04–0.3 M) into its 1,4-addition product enolate (E) within 2000 s at −40 °C. Kinetic studies (ReactIR and chiral GC) of CX·A, CX, and (R)-3-ethylcyclohexanone (P, the H+ quenching product of enolate E) show that the true catalyst is formed in the first 300 s and this subsequently provides P in 82% ee. This true catalyst converts CX·A to E with the rate law [Cu]1.5[L]0.66[CX·A]1 when [L]/[Cu] ≤ 3.5. Above this ligand ratio inhibition by added ligand with order [L]−2.5 is observed. A rate-determining step (rds) of Cu3L2(CX·A)2 stoichiometry is shown to be most consistent with the rate law. The presence of the enolate in the active catalyst best accou...

Cover Feature: Design of Boronic Acid–Base Complexes as Reusable Homogeneous Catalysts in Dehydrative Condensations between Carboxylic Acids and Amines (Asian J. Org. Chem. 9/2017)

Cover Feature: Design of Boronic Acid–Base Complexes as Reusable Homogeneous Catalysts in Dehydrative Condensations between Carboxylic Acids and Amines (Asian J. Org. Chem. 9/2017)

Zwitterionic Alkali-Metal Silanides of Tripodal Ligand Geometry: Synthesis, Structure, and Lewis Acid-Base Chemistry.

A unique family of zwitterionic alkali-metal silanides of general formula [Si(SiMe2OR)3M] (M-3), where M = Li, Na, K and R = CH2CH3 (M-3b), CH(CH3)2 (M-3c), CH2CH(CH3)2 (M-3d), CH2CH2OSCH3 (M-3g), CH2CH2N(CH3)2 (M-3h), have been synthesized and their structures fully characterized. Compounds M-3 were prepared from reactions of the corresponding alkali-metal alkoxides, R'OM (R' = But, Bui; M = Li, Na, K) with the silanes Si(SiMe2OR)4 (2a-h), where R = CH2CH3 (b), CH(CH3)2 (c), CH2CH(CH3)2 (d), CH2CH2OSCH3 (g), CH2CH2N(CH3)2 (h), via selective Si-Si bond cleavage. Analysis of the X-ray data of Li-3a-e,g, Li-h, Li-4, Na-3a-c,e,f,h, and K-3b,d,e,g revealed two major structural motifs in the solid state: infinite chain type and monomeric zwitterions. The reaction of Si(SiMe2OCH2CH3)3Li (Li-3b) with BPh3 in THF gave the zwitterionic Lewis acid-base complex Ph3BSi(SiMe2OCH2CH3)3Li·THF (Li-5b). Reactions of W(CO)6 with Li-3b-d and Na-3b,c resulted in the formation of the zwitterionic silyl tungstenate complexes (CO)5WSi[SiMe2OCH2CH3]3Li (Li-6b), (CO)5WSi[SiMe2OCH(CH3)2]3Li (Li-6c), (CO)5WSi[SiMe2OCH2CH(CH3)2)]3Li (Li-6d), (CO)5WSi(SiMe2OCH2CH3)3Na (Na-6b), and (CO)5WSi[SiMe2OCH(CH3)2]3Na (Na-6c), respectively. The solid-state structures of Li-5b and Na-6b were determined by X-ray crystallography.