Acids HX Research Articles

Monohydrides of the Group 13 Elements M=B, Al and Ga: Axial Bi-Nucleophilicity and the Propensity to Form Both H-M⋅⋅⋅HX and M-H⋅⋅⋅HX Hydrogen Bonds (X=F, Cl, Br, I, CN, CCH, CP).

Equilibrium dissociation energies De of the hydrogen-bonded complexes HAl⋅⋅⋅HX and HGa⋅⋅⋅HX (X=F, Cl, Br, I, CN, CCH, and CP) were calculated ab initio at the CCSD(T)-(F12c)/cc-pVDZ-F12 level of theory. The gradients of graphs of De versus the electrophilicity EHX of the Lewis acids HX yielded the nucleophilicities NM-X of the Group 13 atoms M in these diatomic molecules. Molecular electrostatic surfaces potentials reveal that H-Al and H-Ga are bi-nucleophilic and that the H ends of these H-M molecules are more nucleophilic than the M ends for M=Al and Ga, but not when M=boron. Therefore, the complexes M-H⋅⋅⋅HX were investigated using the same approach. It was concluded for M=Al and Ga that, for a given X, the M-H⋅⋅⋅HX complexes were more strongly bound than the corresponding H-M⋅⋅⋅HX complexes for both M=Al and Ga but the reverse order applies for M = boron. The effects of substituting the H atoms in the M-H molecules by F atoms and by methyl groups were investigated to measure the -I and +I inductive effects relative to H, respectively, on the nucleophilicities of the molecules M-H when M is acting as hydrogen-bond acceptor in complexes H-M⋅⋅⋅H-X.

Aromatic bio-oil production from corn stover by FAU + MFI dual-catalyst catalytic fast pyrolysis: A study of two catalyst parameters

The dual-catalyst catalytic fast pyrolysis (CFP) is a promising approach for producing hydrocarbon-rich bio-oil from biomass waste. However, the lack of detailed research on the structural parameters of the first- and second-layered catalysts was lacking and hindered the development of this technology. Herein, dual-catalyst CFP of corn stover was conducted, and the effects of the acidity and porosity of the two-layered catalysts were studied in detail to enhance their synergistic effect. The results demonstrated that for the second-layered catalyst (MFI zeolite), the utilization of a strong acidic ZSM-5(25) facilitated the production of aromatic hydrocarbon (38.8 area%). For the first-layered catalyst (FAU zeolite), the employment of medium acidity and microporous HY(2.6) was advantageous for the production of valuable monocyclic aromatic hydrocarbon (MAHs) with a selectivity of 21.5 area%, which was ∼1.6 times higher than that in the less acidic HX(1.5) + ZSM-5(25) trial. These findings confirmed that the synergy between the two-layered catalysts was dramatically enhanced by using the HY(2.6) + ZSM-5(25) catalyst combination. Finally, a proposed reaction pathway for the dual-catalyst CFP of corn stover was provided to guide the optimization of dual-catalyst CFP technology and the design of pyrolysis catalyst.

Unveiling the correlation between the catalytic efficiency and acidity of a metal-free catalyst in a hydrogenation reaction. A theoretical case study of the hydrogenation of ethene catalyzed by a superacid arising from a superhalogen.

A systematic quantum-chemical study of the hydrogenation of ethene, catalyzed by strong acids HX (X = F, Cl, Br) and superacids HA (A = MgX3, Mg2X5; X = F, Cl, Br) arising from octet superhalogens is explored. Two possible paths are proposed, concerted and stepwise, and the calculated results show that the concerted path is more favorable than the stepwise path. Compared to the hydrogenation reaction without any catalyst, the improvement of the catalytic efficiency of the superacid HA (A = MgX3, Mg2X5) is high, up to 38.8 to 59.4%. Compared to the strong acid HX (X = F, Cl, Br), the barrier energy is significantly reduced and the improvement of the catalytic efficiency of the superacid HA reaches 23.1 to 31.7%. In particular, for HMg2Br5, the barrier energy of the hydrogenation of ethene is only 36 kcal mol-1, which shows that the reaction could proceed under experimental conditions. In addition, the results show that the catalytic efficiency of the superacid HA is related to the acidity of the superacid. In general, the greater the acidity, the lower the barrier energy and the easier the hydrogenation reaction. From the analysis of the bond order, the newly formed C-H bond of the transition state (TS3) in the concerted path, in which the H atom comes from the superacid catalyst, directly affects the barrier energy of the entire reaction. For the more acidic catalyst, this H atom is provided more easily, and then the formed C-H bond in the transition state is stronger. Consequently, this stronger bond leads to a more stable transition state, and hence to a lower energy barrier as well as a higher efficiency of the superacid catalyst. Therefore, a positive correlation between the acidity of the metal-free catalyst and its catalytic efficiency is expected in the hydrogenation reaction.

Solid‐State Fluorescence of Excited‐State Cation–Anion Intermolecular Proton Transfer in 2‐(2‐Hydroxypyridyl)benzothiazole

AbstractA basic pyridyl unit is introduced to the excited‐state intramolecular proton transfer (ESIPT) of 2‐(2‐hydroxyphenyl)benzothiazole fluorescent molecule, forming 2‐(2‐hydroxypyridyl)benzothiazole (1). The formation of the proton‐transferred H1+•X− salts is confirmed in X− = Cl−, Br−, BF4−, and CF3COO− (trifluoroacetate, TFA−) wherein the highly acidic HX species are easily transferred to the pyridyl unit of 1. Normal ESIPT fluorescence is observed in H1+•BF4− crystals as the ESIPT active intramolecular O−H•••N= hydrogen‐bonding conformation (Stokes shift ≈ 8500 cm−1). In contrast, the H1+•Cl−, H1−•Br−, and H1+•TFA− salts exhibit an ESIPT inert structure without any intramolecular O−H•••N= hydrogen‐bonding structure (Stokes shift ≈ 9500 cm−1), which could not be sufficiently explained by normal ESIPT fluorescence. The excited‐state monoprotonated H1+ exhibits an intermolecular cation–anion proton transfer from N−H+•••X− to N•••HX, which transforms the cationic H1+ to neutral 1, and exhibits intense green fluorescence with a large Stokes shift.

Reduced nucleophilicity: an intrinsic property of the Lewis base atom interacting with H in hydrogen-bonds with Lewis acids HX (X = F, Cl, Br, I, CN, CCH, CP)

Equilibrium hydrogen-bond dissociation energies De for the process B⋯HX = B + HX are calculated at the CCSD(T)(F12c)/cc-pVDZ-F12 level for ∼190 complexes B⋯HX. As established earlier, De values for such complexes can be described by the equation De = cNBEA, in which NB and EHX are the nucleophilicity and electrophilicity of the Lewis base B and the Lewis acid HX, respectively, and the constant c = 1 kJ mol-1. Graphs of De as the ordinate and EHX as the abscissa are presented for 26 series of hydrogen-bonded complexes B⋯HX. The Lewis base is fixed and HX is HF, HCl, HBr, HI, HCN, HCCH and HCP in each series. Each plot yields a good straight line, the slope of which is the nucleophilicity NB of B. The Lewis bases are chosen for their simplicity and all have at least one non-bonding electron pair carried by the atom directly involved in the B⋯HX hydrogen bond. The direction of the minimum value σmin of the molecular electrostatic surface potential on the 0.001 e bohr-3 iso-surface in the chosen bases B usually coincides with the axis of a non-bonding electron pair. The gradient of a graph of De/σmin plotted against EHX defines a reduced nucleophilicity ИB = NB/σmin in the sense that ИB appears to be a property only of the atom of B that is directly involved in the B⋯HX hydrogen bond, independent of the remainder of B. For example, the values of the reduced nucleophilicity for the series of isocyanide complexes CH3NC⋯HX, HNC⋯HX and FNC⋯HX are 0.0343(16), 0.0337(18) and 0.0332(18), respectively, while those for the corresponding series of cyanide complexes are 0.0337(23), 0.0329(24) and 0.0333(23).

Mechanistic Pathways for N2O Elimination from trans-R3Sn-O-N═N-O-SnR3 and for Reversible Binding of CO2 to R3Sn-O-SnR3 (R = Ph, Cy)

The rate and mechanism of the elimination of N2O from trans-R3Sn-O-N═N-O-SnR3 (R = Ph (1Ph) and R = Cy (1Cy)) to form R3Sn-O-SnR3 (R = Ph (2Ph) and R = Cy (2Cy)) have been studied using both NMR and IR techniques to monitor the reactions in the temperature range of 39-79 °C in C6D6. Activation parameters for this reaction are ΔH⧧ = 15.8 ± 2.0 kcal·mol-1 and ΔS⧧ = -28.5 ± 5 cal·mol-1·K-1 for 1Ph and ΔH⧧ = 22.7 ± 2.5 kcal·mol-1 and ΔS⧧ = -12.4 ± 6 cal·mol-1·K-1 for 1Cy. Addition of O2, CO2, N2O, or PPh3 to sealed tube NMR experiments did not alter in a detectable way the rate or product distribution of the reactions. Computational DFT studies of elimination of hyponitrite from trans-Me3Sn-O-N═N-O-SnMe3 (1Me) yield a mechanism involving initial migration of the R3Sn group from O to N passing through a marginally stable intermediate product and subsequent N2O elimination. Reactions of 1Ph with protic acids HX are rapid and lead to formation of R3SnX and trans-H2N2O2. Reaction of 1Ph with the metal radical •Cr(CO)3C5Me5 at low concentrations results in rapid evolution of N2O. At higher •Cr(CO)3C5Me5 concentrations, evolution of CO2 rather than N2O is observed. Addition of 1 atm or less CO2 to benzene or toluene solutions of 2Ph and 2Cy resulted in very rapid reaction to form the corresponding carbonates R3Sn-O-C(═O)-O-SnR3 (R = Ph (3Ph) and R = Cy (3Cy)) at room temperature. Evacuation results in fast loss of bound CO2 and regeneration of 2Ph and 2Cy. Variable temperature data for formation of 3Cy yield ΔHo = -8.7 ± 0.6 kcal·mol-1, ΔSo = -17.1 ± 2.0 cal·mol-1·K-1, and ΔGo298K = -3.6 ± 1.2 kcal·mol-1. DFT studies were performed and provide additional insight into the energetics and mechanisms for the reactions.

Synthesis Design of Electronegativity Dependent WO3 and WO3∙0.33H2O Materials for a Better Understanding of TiO2/WO3 Composites’ Photocatalytic Activity

The design of a semiconductor or a composite semiconductor system—with applications in materials science—is complex because its morphology and structure depend on several parameters. These parameters are the precursor type, solvent, pH of the solution, synthesis approach, or shaping agents. This study gives meaningful insight regarding the synthesis design of such WO3 materials. By systematically alternating the precursor (sodium tungstate dihydrate—NWH, or ammonium tungstate hydrate—AMT), subsequently shaping the agents (halide salts—NaX, KX, or hydrohalic acids—HX; X = F−, Cl−, Br−, I−), we have obtained WO3 semiconductors by hydrothermal treatment, which in composite systems can enhance the commercial TiO2 photocatalytic activity. We investigated three sample series: WO3-NWH-NaX/WO3-NWH-KX and, subsequently, WO3-AMT-HX. The presence of W+5 centers was evidenced by Raman and X-ray photoelectron spectroscopy. W+5 and W+6 species affected the band gap values of the NaX and KX series; a higher percentage of W+5 and, subsequently, W+6 caused a redshift, while, regarding the HX series, it led to a blue shift. Increased electronegativity of the halide anions has an unfavorable effect on the composites’ photoactivity. In contrast, in the case of hydrohalic acids, it had a positive impact.

Palladium-Catalyzed Aminocyclization-Coupling Cascades: Preparation of Dehydrotryptophan Derivatives and Computational Study.

Dehydrotryptophan derivatives have been prepared by palladium-catalyzed aminocyclization-Heck-type coupling cascades starting from o-alkynylaniline derivatives and methyl α-aminoacrylate. Aryl, alkyl (primary, secondary, and tertiary), and alkenyl substituents have been introduced at the indole C-2 position. Further variations at the indole benzene ring, as well as the C-2-unsubstituted case, have all been demonstrated. In the case of C-2 aryl substitution, the preparation of the o-alkynylaniline substrate by Sonogashira coupling and the subsequent cyclization–coupling cascade have been performed in a one-pot protocol with a single catalyst. DFT calculations have revealed significant differences in the reaction profiles of these reactions relative to those involving methyl acrylate or methacrylate, and between the reactions of the free anilines and their corresponding carbamates. Those calculations suggest that the nature of the alkene and of the acid HX released in the HX/alkene exchange step that precedes C–C bond formation could be responsible for the experimentally observed differences in reaction efficiencies.

Pseudohalogen Chemistry in Ionic Liquids with Non-innocent Cations and Anions.

Within the second funding period of the SPP 1708 “Material Synthesis near Room Temperature”,which started in 2017, we were able to synthesize novel anionic species utilizing Ionic Liquids (ILs) both, as reaction media and reactant. ILs, bearing the decomposable and non‐innocent methyl carbonate anion [CO3Me]−, served as starting material and enabled facile access to pseudohalide salts by reaction with Me3Si−X (X=CN, N3, OCN, SCN). Starting with the synthesized Room temperature Ionic Liquid (RT‐IL) [nBu3MeN][B(OMe)3(CN)], we were able to crystallize the double salt [nBu3MeN]2[B(OMe)3(CN)](CN). Furthermore, we studied the reaction of [WCC]SCN and [WCC]CN (WCC=weakly coordinating cation) with their corresponding protic acids HX (X=SCN, CN), which resulted in formation of [H(NCS)2]− and the temperature labile solvate anions [CN(HCN)n]− (n=2, 3). In addition, the highly labile anionic HCN solvates were obtained from [PPN]X ([PPN]=μ‐nitridobis(triphenylphosphonium), X=N3, OCN, SCN and OCP) and HCN. Crystals of [PPN][X(HCN)3] (X=N3, OCN) and [PPN][SCN(HCN)2] were obtained when the crystallization was carried out at low temperatures. Interestingly, reaction of [PPN]OCP with HCN was noticed, which led to the formation of [P(CN)2]−, crystallizing as HCN disolvate [PPN][P(CN⋅HCN)2]. Furthermore, we were able to isolate the novel cyanido(halido) silicate dianions of the type [SiCl0.78(CN)5.22]2− and [SiF(CN)5]2− and the hexa‐substituted [Si(CN)6]2− by temperature controlled halide/cyanide exchange reactions. By facile neutralization reactions with the non‐innocent cation of [Et3HN]2[Si(CN)6] with MOH (M=Li, K), Li2[Si(CN)6] ⋅ 2 H2O and K2[Si(CN)6] were obtained, which form three dimensional coordination polymers. From salt metathesis processes of M2[Si(CN)6] with different imidazolium bromides, we were able to isolate new imidazolium salts and the ionic liquid [BMIm]2[Si(CN)6]. When reacting [Mes(nBu)Im]2[Si(CN)6] with an excess of the strong Lewis acid B(C6F5)3, the voluminous adduct anion {Si[CN⋅B(C6F5)3]6}2− was obtained.

Reactivity of Magic-Size Nanoclusters (CdSe)13 and (CdTe)13 with Acids: Rapid, Low-Temperature Formation of Flat Colloidal Nanocrystals

The amine-ligated magic-size nanoclusters [(II-VI)13(n-octylamine)13] (II–VI = CdSe and CdTe) and acids HX (X = OBz, OAc, NO3, Br, and Cl where OBz = benzoate and OAc = acetate) react to afford cry...

Tin based organic-inorganic hybrid semiconductors with reversible phase transition and dielectric anomaly.

Organic-inorganic hybrid materials with perovskite structure have recently attracted tremendous interest due to their structural tunability and rich functional properties, such as phase transition and photoelectric properties. Within this context, two discrete tin-based organic-inorganic hybrid compounds [(FMBA)2SnCl6] (1) and [(FMBA)2SnBr6] (2) were prepared by the reaction of 3-fluoro-N-methylbenzylamine (FMBA) with SnX4 (X = Cl, Br) in the corresponding concentrated halogen acids HX. Differential scanning calorimetry (DSC) and dielectric measurements showed that both compounds underwent reversible phase transition and dielectric anomaly at a phase transition point above 400 K. Crystal structure analyses revealed that the phase transition mainly originated from the order and disorder of a fluorine-substituted organic amine structure at low and high temperatures. Meanwhile, both compounds showed a semiconducting property with optical bandgaps of 4.24 eV for 1 and 2.58 eV for 2. This finding of two Sn(iv)-based metal halides with prominent phase transition and semiconducting behaviors will expand an executable pathway for designing multifunctional perovskite-type switchable materials.

Reactivity of an Unusual Divalent Chromium Aggregate Supported by a Multifunctional Bis(pyrazolate) Pincer Ligand

Reaction of Cr[N(SiMe3)2]2(THF)2 with equimolar bis‐pyrazolylpyridine, H2L, yields a product of empirical formula CrL. The kinetic product is [CrL]2, which transforms into the thermodynamic product, the S4 symmetric tetramer [CrL]4, with aggregation by bridging via half of the pyrazolate β‐nitrogen atoms. Dimeric [CrL]2 reacts with DMAP (4‐dimethylamino pyridine) to form square pyramidal LCr(DMAP)2, which weakly binds a third DMAP at low temperatures; that weak binding is associated with the Jahn–Teller effect which already weakens the axial Cr/DMAP bond in LCr(DMAP)2. To confirm its dimeric character, reaction of [CrL]2 with bis‐triphenyl iminium salt of chloride is shown to give the C2 symmetric anion [L2Cr2Cl]–. Reaction of phenol with [CrL]2 in the presence of adventitious water occurs with oxidation of half of the chromium, forming the hydroxyl‐bridged mixed‐valent species [(HL)(L)Cr2(µ‐OH)(OPh)(OH2)], containing five coordinate Cr(II) and six coordinate Cr(III); this multifunctional molecule exhibits several examples of hydrogen bonding. Wholly analogous mixed valent products [(HL)(L)Cr2(µ‐OH)(RCOO)(OH2)] are formed and characterized for benzoic and naphthoic acids. With naphthol, another mixed valent product, containing CrIICrIII, is obtained and characterized. This proton responsive reactivity is generalized to a number of acids HX, to yield mixed valent chromium aggregates where some protons are on pyrazole, and others have been reduced to H2, which is released; in every case the conjugate base of HX binds to the otherwise unsaturated Cr. Mechanistic aspects of reduction of protons to H2 exhibited here are analyzed for their impact on this conversion using various reduced chromium species.

Bambusurils as a mechanistic tool for probing anion effects.

Bambusuril macrocycles have high affinity towards anions (X−) such as PF6− and SbF6− or BF4− and ClO4−. Therefore, addition of bambusurils to reaction mixtures containing these anions effectively removes the free anions from the reaction process. Hence, comparing reactions with and without addition of bambusurils can demonstrate whether the anions actively participate in the reaction mechanism or not. We show this approach for gold(i) mediated addition of methanol to an alkyne. The reaction mechanism can proceed via monoaurated intermediates (e.g., in catalysis with [(IPr)AuX]) or via diaurated intermediates (e.g., in catalysis with [(PPh3)AuX]). We show that anions X− slightly affect the reaction rates, however the effect stays almost the same even after their encapsulation in the cavity of bambusurils. We also demonstrate that X− affects the overall reaction rate in the very same way as the reaction rate of the protodeauration step. All results are consistent with the indirect effect of X− by the acidity of the conjugated acid HX on the rate-determining step. There is no evidence that a direct involvement of X− would affect the reaction rate.

Reversible Exchange of L-Type and Bound-Ion-Pair X-Type Ligation on Cadmium Selenide Quantum Belts.

CdSe quantum belts of composition {CdSe[n-octylamine]0.53} and protic acids HX (X = Cl, Br, NO3, acetate (OAc), and benzoate (OBz)) react to exchange the L-type amine ligation to bound-ion-pair X-type ligation. The latter ligation has X- anions bound to the nanocrystal surfaces and closely associated LH+ counter-cations (protonated n-octylamine or tri-n-octylphosphine (TOP) to balance the surface charges. The compositions of the exchanged QBs are {CdSe[Br]0.44[n-octylammonium]0.41}, {CdSe[NO3]0.10[TOPH]0.12}, {CdSe[OBz]0.08[n-octylammonium]0.02[TOPH]0.06}, and {CdSe[OAc]0.16[n-octylammonium]0.02[TOPH]0.14}. (The HCl-exchanged QBs are insufficiently stable for elemental analysis.) The bound-ion-pair X-type ligation is fully reversed to L-type n-octylamine ligation in the cases of X = NO3, acetate, and benzoate. The ligand exchanges are monitored by absorption spectroscopy, and the exchanged, bound-ion-pair X-type ligated nanocrystals are characterized by a range of methods.

The Combination of Superhalogens and Brønsted Acids HX (X = F, Cl, Br): An Effective Strategy for Designing Strong Superacids.

A series of 27 composite structures, consisting of superhalogen and Brønsted acid, is designed and systematically studied based on combined ab initio and DFT calculations focusing on their potentials as novel superacids. As indicated by high-level CCSD(T) results, all the composites here fulfill the theoretical criterion for superacid and the acidities of two of them are close to the strongest superacid ever reported. The influences of various factors on the superacid properties of these composites were analyzed in detail. Our results demonstrate that the acidity of these superacids is mainly determined by the superhalogen components while the effect of Brønsted acids, irrespective of their number or type, is relatively mild. Therefore, it is probable to design novel composite superacid with enhanced property through the regulation of the superhalogen component. It is encouraging that MP2 and DFT could also provide reliable results when compared with the high-level CCSD(T) method. The reliability of these low-cost methods implies the capability of theoretical calculations for future composite superacid of enlarged size, and thus it is highly probable that an effective guide to the related experimental research could be provided by the theory.

Relay Catalysis: Manganese(III) Phosphate Catalyzed Asymmetric Addition of β-Dicarbonyls to ortho-Quinone Methides Generated by Catalytic Aerobic Oxidation.

The combination of an in situ formed MnL3 complex (HL = Hacac or R(C═O)CH2CO2R) and a chiral phosphoric acid HX* allows for a fully catalytic, asymmetric synthesis of 4H-chromenes starting from 2-alkyl-substituted phenols. The aerobic oxidation toward a transient ortho-quinone methide was efficiently catalyzed by a manganese(III) species MnL3 while the ensuing Michael addition of β-dicarbonyl compounds proved to be catalyzed by a chiral manganese phosphate MnL2X*.

Iridium Halide Complexes [1,1‐X2‐8‐SMe2‐1,2,8‐IrC2B9H10]2 (X = Cl, Br, I): Synthesis, Reactivity and Catalytic Activity

The reactions of thallium salt Tl[7‐SMe2‐7,8‐C2B9H10] with [(cod)RhCl]2 and [Cp*RuCl]4 are accompanied by room‐temperature polyhedral rearrangement, giving rhoda‐ and ruthenacarboranes 1‐cod‐8‐SMe2‐1,2,8‐RhC2B9H10 (2) and 1‐Cp*‐8‐SMe2‐1,2,8‐RuC2B9H10 (3), respectively. According to DFT calculations, the rearrangement could be attributed to the triangular face rotation mechanism. The reaction of iridium derivative 1‐cod‐8‐SMe2‐1,2,8‐IrC2B9H10 (1) with anhydrous hydrohalic acids HX (X = Cl, Br, I) results in the dimeric halide iridacarboranes [1,1‐X2‐8‐SMe2‐1,2,8‐IrC2B9H10]2 [4a–c; X = Cl (a), Br (b), I (c)]. Bromide 4b reacts with Tl[Tl(η‐7,8‐C2B9H11)] and TlCp giving iridacarboranes 8′‐SMe2‐1,1′‐Ir(2,3‐C2B9H11)(2′,8′‐C2B9H10) (5) and 1‐Cp‐8‐SMe‐1,2,8‐IrC2B9H10 (6). The formation of the latter compound is accompanied by demethylation of the SMe2 substituent. The structures of 2, 3, 5 and 6 were determined by single‐crystal X‐ray diffraction. Iridacarboranes 4b and [1,1‐Br2‐4‐SMe2‐1,2,3‐IrC2B9H10]2 (7) catalyze the dimerization of diphenylacetylene, giving 1,2,3‐triphenylnaphthalene in 20–24 % yields. Compounds 4b and 7 also effectively catalyze the reductive amination reaction between aldehydes (or ketones) and primary (or secondary) amines in the presence of carbon monoxide, giving the corresponding secondary and tertiary amines in high yields (60–85 %).

Zn-containing double complex salts formed by Keggin type polyoxotungstates: Synthesis and crystal structure

Novel double complex salts, [Zn(DMF)6]2[SiW12O40] · 2H2O (I) and [Zn(H2O)2(DMF)4][Zn(DMF)6]2[PW12O40]2 · 6DMF (II) (DMF = N,N-dimethylformamide), were prepared by the reaction of Zn2+ and heteropoly acids Hx[EW12O40] · xH2O (E = P, X = 3, E = Si, X = 4) in DMF. Compounds I and II were studied by X-ray diffraction (СIF files CCDC nos. 1497570 (I) and 1497571 (II)) and IR spectroscopy.

Weak hydrogen bonding and fluorous interactions in the chloride and bromide salts of 4-[(2,2,3,3-tetrafluoropropoxy)methyl]pyridinium.

Neutralization of 4-[(2,2,3,3-tetrafluoropropoxy)methyl]pyridine with hydrohalo acids HX (X = Cl and Br) yielded the pyridinium salts 4-[(2,2,3,3-tetrafluoropropoxy)methyl]pyridinium chloride, C9H10F4NO+·Cl-, (1), and 4-[(2,2,3,3-tetrafluoropropoxy)methyl]pyridinium bromide, C9H10F4NO+·Br-, (2), both carrying a fluorous side chain at the para position of the pyridinium ring. Single-crystal X-ray diffraction techniques revealed that (1) and (2) are isomorphous. The halide anions accept four hydrogen bonds from N-H, ortho-C-H and CF2-H groups. Two cations and two anions form a centrosymmetric dimeric building block, utilizing complimentary N-H...X...H-Csp3 connections. These dimers are further crosslinked, utilizing another complimentary Csp2-H...X...H-Csp2 connection. The pyridinium rings are π-stacked, forming columns running parallel to the a axis that make angles of ca 44-45° with the normal to the pyridinium plane. There are also supramolecular C-H...F-C interactions, namely bifurcated C-H...F and bifurcated C-F...H interactions; additionally, one type II C-F...F-C halogen bond has been observed.

Reactivity of a Molecular Magnesium Hydride Featuring a Terminal Magnesium-Hydrogen Bond.

The reactivity of the molecular magnesium hydride [Mg(Me3TACD·AliBu3)H] (1) featuring a terminal magnesium-hydrogen bond and an NNNN-type macrocyclic ligand, Me3TACD ((Me3TACD)H = Me3[12]aneN4 = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane), can be grouped into protonolysis, oxidation, hydrometalation, (insertion), and hydride abstraction. Protonolysis of 1 with weak Brønsted acids HX such as terminal acetylenes, amines, silanols, and silanes gave the corresponding derivatives [Mg(Me3TACD·AliBu3)X] (X = C≡CPh, 3; HN(3,5-Me2-C6H3), 4; OSiMe3, 5; OSiPh3, 6; Cl, 7; Br, 8). Single-crystal X-ray diffraction of anilide 4 showed a square-pyramidal coordination geometry for magnesium. No correlation with the pKa values of the acids was detected. Oxidation of 1 with elemental iodine gave the iodide [Mg(Me3TACD·AliBu3)I] (9), and oxidation with nitrous oxide afforded the μ-oxo-bridged compound [{Mg(Me3TACD·AliBu3)}2(μ-O)] (10) with a linear Mg-O-Mg core, as characterized by single-crystal X-ray diffraction. The Mg-H bond reacted with benzaldehyde, benzophenone, fluorenone, and CO2 under insertion but not with the olefins 1,1,2-triphenylethylene, tert-butylethylene, and cyclopentene. The unstable formate, prepared also by salt metathesis of iodide 9 with potassium formate, revealed κO,κO' coordination in the solid state. Hydride abstraction with triphenylborane gave the ion pair [Mg(Me3TACD·AliBu3)(thf)][HBPh3] (16), which catalyzed the hydroboration of polar substrates by pinacolborane.