Anion 1a Research Articles

The Transition (vs ΔpKa) from Triple Ions to Free Cations in Poor Protic Ionic Liquids Made from Weak Acids

In mixtures of amines with carboxylic acids, the limited ionicity at 1:1 stoichiometric mixtures is due to insufficient ionization and/or ion pairing in low-dielectric environments. Higher conductivities have historically been seen at 5:1 acid:base mixing ratios, where simulations have revealed large (and thus more stable) ions: homoassociated anions (AH)2A−(HA)3 and cationic triple ions B+(AH)A− (HA)2B+. Recent work in understanding the Gibbs energies for degree-of-ionization equilibria hints that there may be an onset, for systems with an acid-base pKa difference increasing towards 10, for the formation of free (unpaired) protonate-amine ions BH+. The speed (gradual? sudden?) of such an onset with increasing ΔpKa is explored in this work, with the aim of better understanding the limited ionicity phenomenon in protic ionic liquids.

BAl4Mg−/0/+: Global Minima with a Planar Tetracoordinate or Hypercoordinate Boron Atom

We have explored the chemical space of BAl4Mg−/0/+ for the first time and theoretically characterized several isomers with interesting bonding patterns. We have used chemical intuition and a cluster building method based on the tabu-search algorithm implemented in the Python program for aggregation and reaction (PyAR) to obtain the maximum number of possible stationary points. The global minimum geometries for the anion (1a) and cation (1c) contain a planar tetracoordinate boron (ptB) atom, whereas the global minimum geometry for the neutral (1n) exhibits a planar pentacoordinate boron (ppB) atom. The low-lying isomers of the anion (2a) and cation (3c) also contain a ppB atom. The low-lying isomer of the neutral (2n) exhibits a ptB atom. Ab initio molecular dynamics simulations carried out at 298 K for 2000 fs suggest that all isomers are kinetically stable, except the cation 3c. Simulations carried out at low temperatures (100 and 200 K) for 2000 fs predict that even 3c is kinetically stable, which contains a ppB atom. Various bonding analyses (NBO, AdNDP, AIM, etc.) are carried out for these six different geometries of BAl4Mg−/0/+ to understand the bonding patterns. Based on these results, we conclude that ptB/ppB scenarios are prevalent in these systems. Compared to the carbon counter-part, CAl4Mg−, here the anion (BAl4Mg−) obeys the 18 valence electron rule, as B has one electron fewer than C. However, the neutral and cation species break the rule with 17 and 16 valence electrons, respectively. The electron affinity (EA) of BAl4Mg is slightly higher (2.15 eV) than the electron affinity of CAl4Mg (2.05 eV). Based on the EA value, it is believed that these molecules can be identified in the gas phase. All the ptB/ppB isomers exhibit π/σ double aromaticity. Energy decomposition analysis predicts that the interaction between BAl4−/0/+ and Mg is ionic in all these six systems.

Stimuli-Responsive Supramolecular Coaggregation and Disaggregation of Host-Guest Conjugates Having a Disulfide Linkage.

Water-soluble cationic and anionic cyclophanes (1a and 2a, respectively) having a dabsyl group with a cleavable disulfide linkage were synthesized as a host-guest conjugate covalently bound with both host and guest components. Self-inclusion phenomena but not self-aggregation behaviors were observed for each cyclophane in aqueous media. Each cyclophane includes its own dabsyl moiety (guest component) in its macrocyclic cavity (host component) through hydrophobic interaction. When 1 equiv. of cationic 1a was added to an aqueous solution of anionic 2a, however, supramolecular coaggregates formed spontaneously through host-guest complexation. As regard the supramolecular coaggregates, the existence of larger particles was confirmed by DLS measurements and TEM observation. The hydrophobic interaction between the dabsyl moiety and macrocyclic cavity and electrostatic interactions between 1a and 2a play important roles in the supramolecular coaggregate formation. Each cyclophane having a cleavable disulfide linkage was easily transformed to the corresponding thiols by reducing reagents such as DTT, which was confirmed by MALDI-TOF MS. Disaggregation of the supramolecular coaggregates composed of 1a and 2a was successfully performed upon addition of DTT, with release of the thiol derivative of dabsyl. Such disaggregation of the coaggregates was also conducted by other external stimuli such as salts and competitive guests.

Its Environment Engraves the Geometry of a Molecular Entity: Allyl Coordination within a Dicationic Ruthenium(IV) Complex

The best molecular arrangements for [Ru(η5-C5(CH5)5)(η3-CH2CHCHC6H5)(CH3CN)2]2+ (1) in various environments are determined. The isolated compound 1a serves as a point of reference. On the basis of crystal structure data, solid-state environments are modeled by first placing the cationic compound into the appropriate anionic environment 2a and then completing the unit cell contents by addition of the solvent molecule 3a. Density functional calculations (BP86) augmented by various dispersion corrections (BP86-D2, BP86-D3, BP86-D3(BJ), BP86-dDsC) establish the computational approach for electronic structure and geometry optimization. According to the models considered, intermolecular electrostatic interactions are to a major part responsible for substantial changes in intramolecular arrangements.

Fixation of atmospheric CO2 as novel carbonate-(water)2-carbonate cluster and entrapment of double sulfate within a linear tetrameric barrel of a neutral bis-urea scaffold.

A meta-phenylenediamine-based disubstituted bis-urea receptor L1 with electron-withdrawing 3-chloro and electron-donating 4-methylphenyl terminals has been established as a potential system to fix and efficiently capture atmospheric CO2 as air-stable entrapment of an unprecedented {CO32--(H2O)2-CO32-} cluster (complex 1a) within its tetrameric long straight pillar-like assembly entirely sealed by n-TBA cations via formation of a barrel-type architecture. L1 and its isomeric 4-bromo-3-methyl disubstituted bis-urea receptor L2 have been found to entrap similar kinds of water-free naked sulfate-sulfate double anion (complexes 1b and 2a) by cooperative binding of urea moieties inside the two pairs of the inversion-symmetric linear tetrameric barrel of L1 and L2, respectively. On the other hand, in the presence of excess halides, L1 self-assembles to form hexa-coordinated fluoride complex 1c and tetra-coordinated bromide complex 1d, while L2 self-assembles to form penta-coordinated fluoride complex 2b in the solid state via semicircular receptor architectures and non-cooperative H-bonding interactions of urea moieties.

Salts of novel chelatoborate anions: [R F BX(ox)] − (R F = CF 3 , C 2 F 5 ; X = F, OMe; ox = oxalato) and [R F B(OMe)(cat)] − (R F = CF 3 , C 2 F 5 ; cat = catecholato)

Abstract Tetraethylammonium and tetraphenylphosphonium salts of the oxalatoborate anions [CF 3 B(OCH 3 )(ox)] − ( 1a ), [C 2 F 5 B(OCH 3 )(ox)] − ( 1b ), [CF 3 BF(ox)] − ( 1c ), and [C 2 F 5 BF(ox)] − ( 1d ) have been obtained from easily accessible K[R F B(OCH 3 ) 3 ] and K[R F BF 3 ] (R F = CF 3 , C 2 F 5 ), respectively. In addition, the related catecholatoborate anions [CF 3 B(OCH 3 )(cat)] − ( 2a ) and [C 2 F 5 B(OCH 3 )(cat)] − ( 2b ) have been synthesized starting from K[R F B(OCH 3 ) 3 ] and catechol. Anions 2a and 2b have been isolated as [Ph 4 P] + salts. Two different synthetic strategies have been applied: (i) Reaction of the potassium borate with neat oxalic acid or catechol and (ii) reaction of both components in an ethereal solvent. Salts of all six anions have been obtained via these two different routes except for the [CF 3 BF(ox)] − anion ( 1c ) that was obtained from a reaction in diglyme, only. The new anions have been characterized by multinuclear NMR spectroscopy and by mass spectrometry ((−)-MALDI or (−)-ESI). Furthermore, the tetraphenylphosphonium salts of the chelatoperfluoroalkylborate anions 1a , 1d , and 2a have been characterized by single-crystal X-ray diffraction.

Reactions of Substituted Phenylnitromethane Carbanions with Aromatic Nitro Compounds in Methanol: Carbanion Reactivity, Kinetic, and Equilibrium Studies

ABSTRACTThe feasibility of carrying out nucleophilic addition from electron‐deficient heteroaromatics has been addressed through a detailed investigation of the interaction of a two 7‐substituted‐nitrobenzofurazan (R = OMe 2a; R = Cl 2b) with a series of substituted‐nitroaryl anions (X = 4‐NO2 1a; X = 3‐NO2 1b; X = 4‐CN 1c; X = 4‐Br 1d), all reactions first lead to the quantitative formation of the σ‐adducts 3a–d and 4a–d arising from covalent addition of the nucleophile to the C‐5 carbon. The rate and equilibrium constants for the formation of σ‐adducts 3a–d and 4a–d (k5, K5) together with the rate constants for their decomposition (k−5) have been determined in methanol at 25°C, allowing a determination of intrinsic rate constants, k0 = 0.03, the lower k0 value reflects the very strong salvation by methanol of the negative charge on the nitro group. The discovery of a linear correlation between the E and pKaMeOH parameters allows a calibration of the electrophilicity power of 2a and 2b, E = −11.67 and −10.29, respectively. Applying the general approach to nucleophilicity/electrophilicity recently developed by Mayr et al. through the relationship log k = s(E + N), a successful ranking of our nitroaryl anions 1a–d on the general nucleophilicity scale (N) has been carried out. The N values of 1a–d are found to cover a range from 15.78 to 16.69. The results are compared with previously reported data in water and DMSO.

Acyclic CB[n]-type molecular containers: effect of solubilizing group on their function as solubilizing excipients.

We report the synthesis and X-ray crystal structures of three acyclic CB[n]-type molecular containers (2a, 2h, 2f) that differ in the charge on their solubilizing groups (SO3(−), OH, NH3(+)). The X-ray crystal structures of compounds 2h and 2f reveal a self-folding of the ArOCH2CH2X wall into the cavity driven by π–π interactions, H-bonds and ion–dipole interactions. The need to reverse this self-folding phenomenon upon guest binding decreases the affinity of 2h and 2f toward cationic guests in water relative to 2a as revealed by direct (1)H NMR and UV/Vis titrations as well as UV/Vis competition experiments. We determined the pKa of 6-aminocoumarin 7 (pKa = 3.6) on its own and in the presence anionic, neutral, and cationic hosts (2a: pKa = 4.9; 2h: pKa = 4.1; 2f, pKa = 3.4) which reflect in part the relevance of direct ion–ion interactions between the arms of the host and the guest toward the recognition properties of acyclic CB[n]-type containers. Finally, we showed that the weaker binding affinities measured for neutral and positively charged hosts 2h and 2f compared to anionic 2a results in a decreased ability to act as solubilizing agents for either cationic (tamoxifen), neutral (17α-ethynylestradiol), or anionic (indomethacin) drugs in water. The results establish that acyclic CB[n] compounds that bear anionic solubilizing groups are most suitable for development as general purpose solubilizing excipients for insoluble pharmaceutical agents.

Synthesis of Silaoxazolinium Salts Bearing Weakly Coordinating Anions: Structures and Catalytic Activities in the Aldol Reaction

The synthesis and structures of silaoxazolinium salts 2 and their application to the catalytic Mukaiyama aldol reaction are described. The reaction of (N-amidomethyl)dimethylchlorosilane (1a) or (N-amidomethyl)bis(trimethylsilyl)chlorosilane (1b) with metal salts of weakly coordinating anions such as Na[TFPB] (TFPB = B[3,5-(CF3)2C6H3]4–) and Cs[CB11H12] (CB11H12– = carba-closo-dodecaborate) gave the corresponding five-membered-ring silaoxazolinium salts 2 in high yields (93–97%). The structures of a series of silaoxazolinium salts 2 were determined by X-ray crystal analysis as well as 29Si NMR spectra. It was proved that the silicon atoms of silaoxazolinium salts 2a,b are nearly completely free from the coordination of anions, and the geometries of the silicon centers are distorted tetrahedra. The 29Si chemical shifts of salts 2 appeared in the range +31 to +49 ppm, revealing the appreciable silylium cation character of the silicon. The silaoxazolinium salt of TFPB anion 2a exhibited effective catalytic activity for the Mukaiyama aldol reaction of low reactive unactivated ketones such as cyclohexanone and acetophenone, giving the corresponding aldol products in high yields. The catalytic activity is highly dependent on the nature of the counteranions and the substituents on the silicon. DFT calculations of silaoxazolinium cation have disclosed that positive charges of silaoxazolinium cations are mainly located at the silicon atoms, while the nitrogen atoms and oxygen atoms are negatively charged.

Bridgehead Hydrogen Atoms Are Important: Unusual Electrochemistry and Proton Reduction at Iron Dimers with Ferrocenyl-Substituted Phosphido Bridges

The diphosphido-bridged diiron clusters syn-[{μ2-P(CH2Fc)H}2Fe2(CO)6] (2a) and anti-/syn-[{μ2-P(CH2Fc)Me}2Fe2(CO)6] (3), containing covalently linked ferrocenyl (Fc) groups, were synthesized in order to explore the effect of having a redox-active ligand bound to a Fe2P2 core as in the covalently linked Fe4S4-{μ2-S(Cys)}-Fe2S2 cofactor of [FeFe]-hydrogenases. The X-ray crystal structure of 2a shows an Fe–Fe bond length of 2.630(1) Å and confirms that the two P–H bonds of the bridging 1°-phosphido groups are parallel and are separated by 2.683(2) Å. Cyclic voltammetry and spectroelectrochemistry studies revealed that 2a, unusually, undergoes one-electron reduction at −2.18 V (vs Fc+/Fc) to give the anion [{μ2-P(CH2Fc)}{μ2-P(CH2Fc)H}Fe2(CO)6]– ([2a – H]–), which was independently obtained by deprotonation of 2a with excess 1,8-diazabicycloundec-7-ene (DBU). The reduction proceeds through the radical anion 2a′•– intermediate, which was detected by X-band EPR spectroscopy in situ during electrolysis. The formation of [2a – H]– from the 2a′•– radical formally equates to loss of a hydrogen atom from the bridging P–H group. The result suggests that a new low-energy route for evolution of molecular hydrogen is available in Fe2E2 dimers with bridgehead hydrogen atoms—i.e. dimers with hydrogen directly bonded to the bridging nonmetal atoms (E = P, S). In contrast to the one-electron reduction behavior of 2a, the mixture of dimers 3 exhibited a two-electron reduction at −2.11 V (vs Fc+/Fc) that afforded 32–. Both dimers catalyze the reduction of protons from p-toluenesulfonic acid, with 2a exhibiting higher catalytic currents at lower overpotential.

Synthesis and Photophysical Properties of Cyclometalated Platinum(II) 1,2-Benzenedithiolate Complexes and Heterometallic Derivatives Obtained from the Addition of [Au(PCy3)]+ Units

The cyclometalated compounds [Pt(C^N)(HC^N)Cl] [HC^N = 2-phenylpyridine (Hppy; 1a), 1-(4-tert-butylphenyl)isoquinoline (Htbpiq; 1b)] react with 1,2-benzenedithiol, t-BuOK, and Bu(4)NCl in a 1:1:2:1 molar ratio in CH(2)Cl(2)/MeOH to give the complexes Bu(4)N[Pt(C^N)(bdt)] [bdt = 1,2-benzenedithiolate; C^N = ppy (Bu(4)N2a), tbpiq (Bu(4)N2b)]. In the absence of Bu(4)NCl, the same reactions afford solutions of K2a and K2b, which react with [AuCl(PCy(3))] to give the neutral heterometallic derivatives [Pt(C^N)(bdt){Au(PCy(3))}] [C^N = ppy (3a), tbpiq (3b)]. The cationic derivatives [Pt(C^N)(bdt){Au(PCy(3))}(2)]ClO(4) [C^N = ppy (4a), tbpiq (4b)] are obtained by reacting 3a and 3b with acetone solutions of [Au(OClO(3))(PCy(3))]. The crystal structures of 3b and 4b reveal the formation of short Pt···Au metallophilic contacts in the range 2.929-3.149 Å. Complexes 3b, 4a, and 4b undergo dynamic processes in solution that involve the migration of the [Au(PCy(3))](+) units between the S atoms of the dithiolate. Complexes Bu(4)N2a and 2b display a moderately solvatochromic band in their electronic absorption spectra that can be ascribed to a transition of mixed ML'CT/LL'CT character (M= metal; L = bdt; L' = C^N; CT = charge transfer), while their emissions are assignable to transitions of the same orbital parentage but from triplet excited states. The successive addition of [Au(PCy(3))](+) units to the anions 2a and 2b results in an increase in the absorption and emission energies attributable to lower highest occupied molecular orbital energies. Additionally, the characteristics of the absorption and emission spectra of the heterometallic derivatives indicate a gradual loss of LL'CT character in the involved electronic transitions, with a concomitant increase of the L'C and ML'CT contributions.

Change of the coordination type for the phospholyl ligand under nucleophilic attack of H 2O on phosphorus atom in 2,5-diphenylphosphacymantrene promoted by aliphatic amines

η 5-2,5-Diphenylphosphacymantrene ( 1) in benzene or CH 2Cl 2 solution does not react with amines. However, with amines NHEt 2, NEt 3, NEt(i-Pr) 2 in excess and in the presence of small amounts of water 1 reacts to form anionic complexes [(CO) 3Mn(η 4-Ph 2H 2C 4P( O)H] − A +, where cation A = H 2 NEt 2 + ( 2a), HNEt 3 + ( 2b), HN(Et) ( Pr i ) 2 + ( 2c). Probably, first an unstable intermediate with Р–ОН bond is formed as a result of the attack by the activated H 2O molecule at the P atom. Afterwards, the rapid rearrangement occurs with migration of H from O to P which leads to the ligand 2,5-diphenyl-1- Н-phosphol-1-oxide, Ph 2H 2C 4P( O)H. Salts 2а– с have been characterized by 1H, 31P, 13C NMR- and IR-spectra and the structures of 2a and 2c established by single crystal X-ray diffraction analyses. The phosphoryl ligand in anions 2a and 2c has the “envelope” conformation and is η 4-coordinated with Mn(CO) 3. The phosphorus atom is not involved in the coordination with Mn because the Mn–P distances (2.7670(4) and 2.7732(8) Å) are greater than the sum of covalent radii of P and Mn.

Heptaphosphanortricyclenes with Oligosilyl Substituents: Syntheses and Reactions

AbstractThree new nortricyclic P7R3 derivatives with R = (SiMe3)2MeSi– (2), (SiMe3)2PhSi– (3), and cyclo‐Si6Me11– (4) were synthesized from red phosphorus, sodium/potassium alloy, and a chlorooligosilane, and their structures were elucidated with X‐ray diffraction. Reactions of 2 and 3 and of tri(hypersilyl)heptaphosphane 1 [hypersilyl = (SiMe3)3Si–] with KOtBu and LiOtBu were performed, which led to different results depending on the size of the substituent. With KOtBu, Si–P bonds were cleaved in 2 and 3, and the mono‐ and dianions [P7R2]– [R = (SiMe3)2MeSi: 2a; R = (SiMe3)2PhSi: 3a] and [P7R]2– [R = (SiMe3)2MeSi: 2b] formed. Crystals of the [K+.18‐crown‐6]+ salt of 2b suitable for X‐ray diffraction could be grown successfully. Compound 1 reacted in an unprecedented way with KOtBu at –60 °C. An Si–Si bond was cleaved, and a transient silyl anion formed, which immediately rearranged into a transient heptaphosphanide anion [Hyp2P7]– (1a) under expulsion of bis(trimethylsilyl)silylene. The silylene immediately inserted into a P–P bond of the basal P3 ring of 1a, thereby forming two new isomeric anions {Hyp2P7[Si(SiMe3)2]}–, 1b and 1c. The structure of 1c could be elucidated by X‐ray crystallography, whereas 1b was characterized by 31P NMR spectroscopy. The proposed reaction mechanism could be further confirmed by performing the reaction between 1 and KOtBu in the presence of a large excess amount of dimethylbutadiene, which trapped the silylene. Just the formation of anion 1a was observed in that case. Anion 1a was also obtained quantitatively when KOtBu was replaced by LiOtBu. Compound 1a reacted with trifluoroacetic acid to give Hyp2P7H (1d), which was successfully crystallized and examined by X‐ray diffraction. It is the first structural example of a stable and neutral nortricyclic P7 derivative, R2P7H. All compounds were chracterized further by 31P and 29Si NMR spectroscopy and elemental analyses.

Cubane‐Like Bismuth‐Iron Cluster: Synthesis, X‐ray Crystal Structure and Theoretical Characterization of the [Bi4Fe8(CO)28]4– Anion

AbstractThe reaction of cyclo‐Bi4[Si(SiMe3)3]4 (1) with Na2[Fe(CO)4] in the presence of nBu4NCl leads to the formation of the cage compound [nBu4N]4[Bi4Fe8(CO)28] (2). According to X‐ray single‐crystal structure analysis, the faces of the tetrahedral Bi4 core are capped by Fe(CO)3 moieties in a μ3 fashion to give a cubanoid Bi4Fe4 framework. The four Fe(CO)4 fragments are μ1‐coordinated to bismuth, each. With 12 skeletal electron pairs the [Bi4Fe8(CO)28]4– anion (2a) is a Bi4Fe4 cubane. The negative charge is localized within cluster 2a according to the NBO analysis of its derivatives. The strength of metal–ligand interactions Bi–μ3‐Fe(CO)3 is responsible for the size of the cluster's cubic core. NICS computations at the cage centers of considered molecules show that 2a has paratropic character, whereas removal of four μ1‐Fe(CO)4 fragments from latter causes spherical aromaticity of the modified clusters [Bi4Fe4(CO)12]4– (2aa) and [Bi4Fe4(CO)12]2+ (2ab), mediated by a Bi4 cluster π orbital.

Ferracarborane Benzene Complexes [(η-9-L-7,8-C2B9H10)Fe(η-C6H6)]+ (L = SMe2, NMe3): Synthesis, Reactivity, Electrochemistry, Mössbauer Effect Studies, and Bonding

The benzene complexes [(η-9-L-7,8-C2B9R2H8)Fe(η-C6H6)]+ (3a: L = SMe2, R = H; 3b: L = SMe2, R = Me; 3c: L = NMe3, R = H) were prepared by photochemical reaction of [(η5-C6H7)Fe(η-C6H6)]+ with carborane anions [9-L-7,8-C2B9R2H8]− (1a−c) followed by treatment of the (η-9-L-7,8-C2B9R2H8)Fe(η5-C6H7) (2a−c) ferracarboranes formed with HCl. Visible light irradiation of 3a with tBuNC or P(OMe)3 in acetonitrile results in replacement of the benzene ligand, giving the tris(ligand) derivatives [(η-9-SMe2-7,8-C2B9H10)Fe(ligand)3]+ (4, 5). The unsymmetrical carborane complex (η-9-SMe2-7,8-C2B9H10)Fe(η-9-NMe3-7,8-C2B9H10) (6) was obtained by photochemical reaction of 3a with 1c. The structures of 2a, 3aBPh4, and 6 were determined by X-ray diffraction. Temperature-dependent Mössbauer spectroscopy has been used to elucidate the hyperfine parameters and metal atom vibrational amplitudes in a number of these complexes. The redox activity of the ferracarboranes 2a,c and 3a,c has been investigated by electrochemical techniques and compared with that of the related cyclopentadienyl complexes. Electrochemistry gives evidence that the conversion of 2a−c to 3a−c can also be triggered by a two-electron oxidation followed by deprotonation. DFT calculations of the redox potentials and the respective geometrical changes were performed. Data on electrostatic potentials at iron nuclei suggest that anions 1a,c are stronger donors than Cp− in cationic complexes, but weaker donors in the neutral derivatives.

Nucleophilicities of the Anions of Arylacetonitriles and Arylpropionitriles in Dimethyl Sulfoxide

The rates of the reactions of the colored para-substituted phenylacetonitrile anions 1a-c and the phenylpropionitrile anions 2a-c with Michael acceptors (3a-u) were determined by UV-vis spectroscopy in DMSO at 20 degrees C. The reactions follow second-order kinetics, and the corresponding rate constants k(2) obey the linear-free-energy relationship log k(2)(20 degrees C) = s(N + E), from which the nucleophile-specific parameters N and s of the carbanions 1a-c and 2a-c have been derived. With nucleophilicity parameters from 19 < N < 29, they are among the most reactive nucleophiles which we have so far parametrized. In DMSO, the nucleophilicity of the tert-butoxide anion is comparable to that of the p-cyanophenylacetonitrile anion 1b.

Inter‐ and Intramolecular C–H···O Bonding in the Anions of 1,3‐Indandione Derivatives

AbstractDerivatives of a series of 1,3‐indandione (1) self‐condensation products (2–4) and their anions (2a–4a) were investigated by NMR and UV/Vis spectroscopy and quantum mechanical calculations. These compounds exhibit a number of unusual features in their NMR spectra. Parent compound 1 is nearly not ionized in DMSO, whereas 3 is ionized completely. In contrast, derivatives 2 and 4 undergo partial ionization in DMSO and interaction between the neutral and anionic species affords the anionic intermolecular complexes, which exhibit both temperature‐ and concentration‐dependent NMR spectra. The NMR spectra of pure salts 2a and 3a are concentration independent, but temperature dependent. Charge delocalization in anions 2a and 3a gives rise to restricted rotation over the partial double bonds connecting the indane fragments. Energies of barriers to rotation were estimated from the temperature dependence of the 13C NMR spectra. The intramolecular aromatic C–H···O hydrogen bonding found previously in 2–4 is also observed in corresponding anions 2a–4a.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

The Sixteen CB11HnMe12-n- Anions with Fivefold Substitution Symmetry: Anodic Oxidation and Electronic Structure

The 15 symmetrically methylated derivatives of the CB11H12(-) anion (1a) have been synthesized and found to vary greatly in ease of oxidation. Cyclic voltammetry in liquid SO2 yielded fully reversible oxidation potentials for five of those that have no adjacent unsubstituted vertices in positions 7-12; three others showed some indication of reversibility. The anions 1a-16a and the Jahn-Teller distorted neutral radicals 1r-16r have been characterized by ab initio and density functional theory calculations. In the state average CASSCF(13,12)/6-31+G* approximation, the ground state potential energy surface of 1r contains five symmetry-related pairs of minima. The computational results account for the reversible redox potentials very well when the solvent is included explicitly (RI-DFT(BP)/TZVP, COSMO). For display and for a semiquantitative understanding of methyl substituent effects in terms of perturbation theory, the molecular orbitals of 1a have been expressed in the symmetry-adapted cluster basis. The results serve as an underpinning for a set of additive empirical increments for redox potential prediction. Relative to the usual hydrogen standard, a single methyl group facilitates oxidation by approximately 50, 70, 70, and 10 mV in positions 1, 2, 7, and 12, respectively. This electron donor effect on the redox potential is due to a contribution, whereas those of (inductive and direct field) type are negligible.

Systematic Study of the Interaction Between VIV Centres and Lanthanide Ions MIII in Well Defined {VIV 2MIII}{AsIIIW9O33}2 Sandwich Type Clusters: Part 1

A new type of heteropolytungstate is reported that contains in a triangular arrangement one lanthanide f element and two d transition metals in form of heteroatoms. The first example in this series is the monoclinic Na3K5[((VO)2Dy(H2O)4K2(H2O)2Na(H2O)2)(α-B-AsW9O33)2] · 23H2O (1) which was prepared from an acidified aqueous solution of Na2WO4 · 2H2O, As2O3 and VOSO4 · 5H2O to which Dy3+ ions were added. The single crystal X-ray structure analysis shows that the anion 1a consists of two [α-B-AsIIIW9O33]9− trilacunary Keggin type units linked by two VO2+, one Dy3+ as well as two K+ and one Na+ ion, resulting in a sandwich-type structure with idealized C 2v symmetry. The complete magnetochemical analysis shows very interesting magnetic properties, which will be considered in the full series together with the properties of the homologous compounds in due course.

Dimethylsulfide-dicarbaborane chemistry. Isolation and characterisation of isomers [9-(SMe2)-nido-7,8-C2B9H10-X-Me] (where X = 1, 2, 3 and 4) and some related compounds. An unusual skeletal rearrangement

Oxidative coupling by FeCl(3) of the [nido-7,8-C(2)B(9)H(11)-9-Me](-) anion 1a with SMe(2) yields a mixture of four isomers of 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-X-Me, where X = 1, 2, 3 and 4 (compounds 2a, 2b, 2c and 2d respectively). On high dilution of the reaction mixture, the 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-10-Me 2e isomer is also isolated in a low yield. The isomers are separated by HPLC, and are identified and characterised by NMR spectroscopy and by single-crystal X-ray diffraction analyses of 2c and 2d. The formation of the products implies an unexpected cluster rearrangement, which is discussed in terms of dsd and vertex-flip reaction pathways. Two additional isomers, 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-5-Me 2f and 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-6-Me 2g occur when [nido-7,8-C(2)B(9)H(11)-5-Me](-) 1b is used as the starting substrate, in a reaction in which no cluster rerarrangement is observed. The corresponding bromide, [nido-7,8-C(2)B(9)H(11)-5-Br](-) 1c, behaves similarly, forming only 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-5-Br 2h and 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-6-Br 2i.