Ion–molecule reaction in the gas phase 3—nucleophilic substitution of 17ξ-R-5α,14β-androstane-14,17ξ-diols under [NH4]+ chemical ionization conditions1

Under Ammonia chemical Ionization conditions the source decompositions of [M + NH₄]⁺ ions formed from epimeric tertiary steroid alchols 14 OH_β, 17OH_α or 17 OH_β substituted at position 17 have been studied. They give rise to formation of [M + NH₄? H₂O]⁺ dentoed as [MH_sH]⁺, [M_sH? H₂O]⁺, [M_sH? NH₃]⁺ and [M_sH? NH₃? H₂O]⁺ ions. Stereochemical effects are observed in the ratios [M_sH? H₂O]⁺/[M_sH? NH₃]⁺. These effects are significant among metastable ions. In particular, only the [M_sH]⁺ ions produced from trans-diol isomers lose a water molecule. The favoured loss of water can be accounted for by an S_N2 mechanism in which the insertion of NH₃ gives [M_sH]⁺ with Walden inversion occurring during the ion-molecule reaction between [M + NH₄]⁺ + NH₃. The S_N1 and S_Ni pathways have been rejected.     

Cp*rhodium complexes with salicyloxazolines: Diastereoselective synthesis, configurational stability and use as asymmetric catalysts for a Diels-Alder reaction

Reaction of [RhCl₂Cp*]₂ (Cp* = η-C₅Me₅) with salicyloxazolines in the presence of NaOMe gives complexes [RhCl(R-saloxaz)Cp*] (1-4) which have been fully characterised. The diastereoselectivity of complexation depends on the substituents and the absolute configuration at the metal centre is unstable in solution. Treatment of 2 with 4-methylpyridine and NaSbF₆ in methanol at reflux gave [Rh(4-Mepy){(S)-ⁱPr-saloxaz}Cp*][SbF₆] (5) whilst [Rh(OH₂)(Me₂-saloxaz)Cp*][SbF₆] (6) was prepared by reaction of 1 with AgSbF₆. Three complexes, [RhCl(Me₂-saloxaz)Cp*] (1), [RhCl{(S)-ⁱPr-saloxaz}Cp*] (2), and [Rh(OH₂)(Me₂-saloxaz)Cp*][SbF₆] (6) have been characterised by X-ray crystallography. Some of the complexes, after treatment with AgSbF₆, have been tested as enantioselective catalysts for the Diels-Alder reaction of methacrolein with cyclopentadiene.     

Reaction of [Xe-F]+ with HI

The reaction behavior of [XeF][AsF₆] in solution toward hydrogen iodide, HI, was investigated, and Xe, HF, and [I₄][AsF₆]₂ were identified as the final reaction products. The reaction enthalpy of the gas-phase reaction ([XeF]⁺ + HI → [XeI]⁺ (¹Σ) + HF) was calculated at the optimized MP4(SDQ) geometries at the QCISD(TQ) level to be: ΔH0298 [QCISD(TQ)/LANL2DZ//MP4(SDQ)/LANL2DZ] = −63.3 kcal mol⁻¹. The [XeI]⁺ cation is bound only in the ¹Σ singlet state, and the triplet state (³Π) was shown to be essentially unbound at all levels of theory applied and very close in energy to the singlet state at equilibrium structure. According to the ab initio calculations, [XeI]⁺ can react with HI in a thermodynamically and spin-symmetry allowed reaction to yield the [XeI]⁺ (¹Σ) cation that may, after interconversion into the unbound triplet state, immediately dissociate into xenon (¹S) and I⁺ (³P). © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 473–478, 1997     

Ion–molecule reaction in the gas phase 4—Stereospecific nucleophilic substitution under ammonia chemical ionization conditions from diastereomeric methyl and benzyl ethers of 3-hydroxy steroids

The ammonia chemical ionization (CI/[NH₄⁺]) mass spectra of a series of diastereomeric methyl and benzyl ethers derived from 3-hydroxy steroids (unsaturated in position 5 and saturated) have been studied. The adduct ions [M+NH₄]⁺ and [MH]⁺ and the substitution product ions [M+NH₄? ROH]⁺ (thereafter called [M_sH]⁺) are characterized by an inversion in their relative stabilites in relation to their initial configuration. [M+NH₄]_α⁺ and [MH]_α⁺ formed from the α-Δ⁵-steroid isomers are stabilized by the presence of a hydrogen bond which is not possible for the β-isomers. This stereochemical effect has also been observed in the mass analysed ion kinetic energy (MIKE) spectra of [M+NH₄]⁺ and [MH]⁺. The MIKE spectra of [M_sH]⁺ indicate that those issued from the β-isomers are more stable than the one originating from the α-isomers. This behavior is also observed in the first field free region (HV scan spectra) for [MH]⁺, [M_sH]⁺ and [M+NH₄]⁺ which are precursors of the ethylenic carbocations (base peak in the conventional CI/[NH₄]⁺ spectra). Mechanisms, such as S_N1 and S_Ni, have been ruled out for the formation of [M_sH]⁺, but instead the data support an S_N2 mechanism during the ion-molecule reaction between [M+NH₄]⁺ and NH₃.     

Solvent effects on the asymmetric Pauson-Khand-type reaction by rhodium

The reaction efficiency and enantioselectivity of an asymmetric Pauson-Khand-type reaction catalyzed by cationic rhodium are heavily dependent on the solvent. Coordinating solvents, such as THF, provide a faster reaction and better stereoselectivity than non-coordinating solvents, such as toluene. These beneficial effects can be attributed to a significant increase in the more reactive catalytic species of [Rh(bisphosphane ligand)^∗(solvent)_n]⁺ (3) than of [Rh(bisphosphine ligand)^∗CO(solvent)]⁺(4) and [Rh(bisphosphine ligand)∗(CO)₂]⁺ (5) in a coordinating solvent.     

Electrophilic reactivity of the zwitterionic titanocene monohalides Cp[η-C5H4B(C6F5)3]TiX (X = Cl, Br): Reactions with water and methanol

The paper reports new data evidencing for a high electrophilicity of the positively charged titanium atom in the previously described zwitterionic titanocene monochloride Cp[η⁵-C₅H₄B(C₆F₅)₃]TiCl (1) and titanocene monobromide Cp[η⁵-C₅H₄B(C₆F₅)₃]TiBr (2), containing a B(C₆F₅)₃ group in one of the C₅ rings. It has been established that on a contact of a toluene solution of these zwitterions with water vapour at 20 °C under Ar, a rapid protolytic cleavage of the otherwise inert B-C₆F₅ bond in the tris(pentafluorophenyl)borane moiety occurs to afford pentafluorobenzene and the corresponding halogenide hydroxide complex of titanocene Cp[η⁵-C₅H₄B(C₆F₅)₂]TiX(μ-OH), where X = Cl (3), Br (4). An X-ray diffraction study of the complexes has shown that the hydroxide group in 3 and 4 is bonded via the oxygen atom both to the titanium and boron atoms. Under similar conditions, the interaction of zwitterion 1 with methanol gives rise to pentafluorobenzene and the chloride methoxide complex of titanocene Cp[η⁵-C₅H₄B(C₆F₅)₂]TiCl(μ-OCH₃). It has been suggested that the driving force of the protolysis of the B-C₆F₅ bond in 1 and 2 is a sharp increase in the acidity of water or methanol molecule as a result of their complexation with the positively charged titanium centre in the starting zwitterion.     

The formation of aryloxenium ion in the reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine with strong acids

The reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine (1) with conc. H₂SO₄ affords 4-nitropyrocatechol and that with conc. sulfonic acids (RSO₃H where R = Me, CF₃) affords 2-hydroxy-5-nitrophenyl-R-sulfonates in yields of 80?C85%. These reactions are assumed to proceed through an intermediate (phenoxy)oxodiazonium ion [NO₂C₆H₄O-N=N=O]⁺, which eliminates the N₂O molecule to form the aryloxenium ion [NO₂C₆H₄O]⁺. The latter reacts with acid anions at the ortho-carbon atom of the phenyl ring. The thermodynamical parameters of the elementary reactions resulting in the formation of the (phenoxy)oxodiazonium ion [NO₂C₆H₄O-N=N=O]⁺ and aryloxenium ion [NO₂C₆H₄O]⁺ were calculated in the B3LYP/6?311+G(d) study of the combined molecular system (nitrohydroxylamine 1 + [H₃SO₄]⁺). The reaction of nitrohydroxylamine 1 with aqueous solutions of strong acids (??70% H₂SO₄, CF₃SO₃H) affords mainly 4-nitrophenol. It appears that the mechanism of this reaction does not involve the formation of the aryloxenium ion.     

Ruthenium(II) and iron(II) complexes of N-pyridyl substituted imidazolin-2-ylidenes

N-mesityl-N′-pyridyl-imidazolium chloride 1a and the corresponding bromide salt 1b have been deprotonated with NaH in THF giving the free N-heterocyclic carbene N-mesityl-N′-pyridyl-imidazolin-2-ylidene 2 in 80% yield (starting from 1a). Imidazolium salt 1a reacts with RuCl₃ · xH₂O to give a racemic mixture of dinuclear di-μ-chloro bridged ruthenium complexes [(κ²-2)₂Ru(μ-Cl)₂Ru(κ²-2)₂]²⁺ [3a]²⁺. The carbene carbon atoms as well as the halides are arranged in cis-positions to each other whereas the nitrogen atoms adopt a trans-configuration. The di-μ-bromo bridged derivative [(κ²-2)₂Ru(μ-Br)₂Ru(κ²-2)₂]²⁺ [3b]²⁺ was obtained from RuCl₃ · xH₂O and 1b. The bridging halide ligands can be removed by the reaction with silver or sodium salts of bidentate Lewis acids. Complex [3a]²⁺ reacts with silver pyridylcarboxylate to give a racemic mixture of the mononuclear complex [4]⁺. Reaction of [3a]²⁺ with the sodium salt of l-proline resulted in a diastereomeric mixture of complexes [5]⁺. The free N-heterocyclic carbene 2 reacts with [FeCl₂(PPh₃)₂] to give after anion exchange with NaBPh₄ cis/cis/trans coordinated [Fe(κ²-2)₂(MeCN)₂](BPh₄)₂ [6](BPh₄)₂. The molecular structures of [3b](PF₆)₂, [4]PF₆ and [6](BPh₄)₂ · H₂O are reported.     

Metal complexes of anionic 3-borane-1-alkylimidazol-2-ylidene derivatives

Addition of BH₃·thf to 1-alkylimidazoles (alkyl=methyl, butyl) and 1-methylbenzimidazole leads to BH₃ adducts, which are deprotonated by BuLi to yield the organolithium compounds (L)Li⁺(1b–d)⁻. In the solid state (thf)Li⁺1b⁻ is dimeric. The acyl–iron complexes (thf)₃Li⁺(3b,d)⁻ are formed from (thf)Li⁺(1b,d)⁻ and Fe(CO)₅. (L)Li⁺(1a–c)⁻ react with [CpFe(CO)₂X], however, the only complex obtained is [CpFe(CO)₂1a] (5a). The analogous reaction of (L)Li⁺1a⁻ with the pentadienyl complex [(C₇H₁₁)Fe(CO)₂Br] yields the corresponding iron compound 6a. Their compositions follow from spectroscopic data. Treatment of Cp₂TiCl with (L)Li⁺1a⁻ leads to [Cp₂Ti1a] (7a), which could not be oxidized with PbCl₂ to give the corresponding Ti(IV) complex. The compounds [Li(py)₄]⁺9a⁻ and [Li(L)₄]⁺(10b–d)⁻ are obtained when (L)Li⁺1⁻ are reacted with VCl₃ and ScCl₃. The X-ray structure analysis of the vanadium complex reveals a distorted tetrahedron of the anion [V(1a)₄]⁻ with two smaller and four larger CVC angles. The scandium compound [Li(dme)₂⁺10c⁻] has a different structure: the distorted tetrahedron of the anion [Sc(1c)₄]⁻ contains two larger (140.2 and 142.9°) and four smaller CScC angles (93.9–98.7°). This arrangement allows the formation of four bridging BHSc 3c,2e bonds to give an eight-fold coordination. The anion 10c⁻ is formally a 16e complex.     

Synthesis and property of BrCCH- and BrCCBr-coordinated tetrairon clusters

The reaction of (η⁵-C₅H₄Me)₄Fe₄(HCCH)₂ (1) with 1 equiv. of N-bromosuccinimide (NBS) gives the one-electron oxidized form in 83% yield. Further treatment of [1]⁺ with NBS results in the stepwise bromination of four acetylenic protons to give [(η⁵-C₅H₄Me)₄Fe₄(HCCH)(HCCBr)]⁺ ([2]⁺), [(η⁵-C₅H₄Me)₄Fe₄(HCCBr)₂]⁺ ([3a]⁺), [(η⁵-C₅H₄Me)₄Fe₄(HCCBr)(BrCCBr)]⁺ ([4]⁺), and [(η⁵-C₅H₄Me)₄Fe₄(BrCCBr)₂]⁺ ([5]⁺) in moderate yields, with the isomer of [3a]⁺, [(η⁵-C₅H₄Me)₄Fe₄(HCCH)(BrCCBr)]⁺ ([3b]⁺), formed as a minor product. These compounds are characterized by analytical and spectroscopic techniques, and the molecular structures of [2](PF₆), [4](TFPB), and [5](TFPB) are established by X-ray diffraction analysis [TFPB = tetrakis{bis(3,5-trifluoromethyl)phenyl}borate]. The compounds are confirmed to retain the butterfly core of four iron atoms as in [1](TFPB). The bromoacetylene part in [2]⁺ exhibits high reactivity toward various nucleophiles: Cluster[2]⁺ is moisture-sensitive and is converted to a mixture of [(η⁵-C₅H₄Me)₄Fe₄(HCCH)(μ₃-CH)(μ₃-CO)]⁺ ([6]⁺) and [1]⁺. Reactions of [2]⁺ with ZnR₂ (R = Me, Et) give [(η⁵-C₅H₄Me)₄Fe₄(HCCH)(HCC-R)]⁺ in good yields (R = Me ([9]⁺, 88%), Et ([10]⁺, 91%)). Accordingly, treatment of [2]⁺ with HC CMgBr and LiS^pTol leads to the introduction of the ethynyl and thiolate groups to give [(η⁵-C₅H₄Me)₄Fe₄(HCCH)(HCC-CCH)]⁺ ([11]⁺, 95%) and [(η⁵-C₅H₄Me)₄Fe₄(HCCH)(HCC-S^pTol)]⁺ ([12]⁺, 78%), respectively. Substitution of the bromo group in [2]⁺ with pyridine affords [(η⁵-C₅H₄Me)₄Fe₄(HCCH)(HCC-Py)]²⁺ ([13]²⁺) in 90% yield. The reaction with 4,4′-bipyridyl (bpy) requires the severer conditions (70 °C, 2 days), probably due to the relative low basicity of bpy, giving [(η⁵-C₅H₄Me)₄Fe₄(HCCH)(HCC-bpy)]²⁺ ([14]²⁺) in 54% yield. The substitution reaction with 4,4′-bipyridyl is strongly accelerated by treatment with silver salt to give [14]²⁺ in 90% yield. The products derived from [2]⁺ and nucleophiles are unequivocally determined by elemental, spectroscopic, and X-ray diffraction analyses.     

Influence of arenechromium tricarbonyl on the redox behavior of copper in new heteropentanuclear complexes prepared from functionalized phenanthroline tweezer ligands

Novel mixed [Cu(4a–c)₂]CF₃SO₃ pentanuclear copper(I)/chromium(0) complexes containing tweezer ligands that contain, within the same molecule, a 2,9-disubstituted-1,10-phenanthroline and two arene-chromium subunits. The mononuclear copper(I) complexes [Cu(5a–c)₂] CF₃SO₃ have been prepared from the chromium free ligand species 5a–c, obtained by quantitative photochemical decomplexation of the parent species 4a–c. Cyclic voltammetry showed that in these complexes copper(I) can be reversibly oxidized to copper(II) in CH₂Cl₂. The Cu^II/I couples are more positive in the presence of the four surrounding redox-active arenechromium subunits, revealing an electron-withdrawing effect. Complexes [Cu(4c)₂]⁺, [Cu(5c)₂]⁺ form new species (1 : 1 ligand copper stoichiometry) upon addition of excess [Cu(CH₃CN)₄]⁺, which were identified electrochemically and by FAB⁺ mass spectroscopy.     

A heteronuclear compound of ruthenium and silver containing bridging tris(pyridyl)methanoate ligands

The reaction of [{Ru(η⁶-C₆H₆)Cl(μ-Cl)}₂] with Py₃COH in ethanol results in the formation of the cation [Ru(η⁶-C₆H₆)(N,N′,O,-(C₅H₄N)₃CO)]⁺ which is isolated as its hexafluorphosphate salt 1. The cation acts as a ligand towards other transition metal ions. With Ag⁺ the hetero-trinuclear complex [{Ru(η⁶-C₆H₆)((C₅H₄N)₃CO)}₂Ag][PF₆]₃ 2 is formed, while reaction with [Pd(PhCN)₂Cl₂] gives the bimetallic [Ru(η⁶-C₆H₆)((C₅H₄N)₃CO)PdCl₂][PF₆] 3. Both compounds were fully characterised by spectroscopic methods and the trinuclear complex was additionally characterised by X-ray diffraction.     

Isolation of fac-[Re(CO)3(HMPA)3][BF4]. Structural characterization of a key cationic intermediate in the exchange reaction between [Re(CO)6][BF4] and acetylferrocene. Implications in radiopharmaceutical chemistry

[Re(CO)₆][BF₄] reacts with HMPA to form [Re(CO)₃(HMPA)₃][BF₄] (4), whose structure was determined by X-ray crystallography and proves to be a key intermediate in the ligand exchange reaction between three CO and Cp; and may be related to other cations such as [Re(CO)₃(H₂O)₃]⁺, [Re(CO)₃(CH₃CN)₃]⁺, [Re(CO)₃(DMSO)₃]⁺, obtained by different ways, and important in the field of organometallic radiopharmaceuticals.     

Chemistry of strained polycyclic compounds—V : The stereospecific cationic cage expansion reaction of 4-homocubane carbinols to 1,3-bishomocubane bridgehead alcohols

The cationic rearrangement of four homocubane bridgehead carbinols viz dimethyl 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonyl-9-one ethylene ketal) carbinol 2, diphenyl 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonyl-9-one ethylene ketal) carbinol 3, 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7] nonyl-9-one ethylene ketal) carbinol 4 and 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonyl) carbinol 16, has been studied undervarious conditions.Exclusive migration of the C₄C₇ (or the equivalent C₃C₄ bond) in the homocubane skeleton was observed leading to 1,3-bishomocubane bridgehead alcohols. Relief of cage constraint governs the selective course of these cage expansions.     

Crystal structures of two syn bent tetraalkylhydrazines,their radical cations,and a dication

The crystal structures of 2,7-diazatetracyclo[6.2.2.2^3,6.0^2.7]tetradec-4-ene, 2, its cation radical nitrate salt 2⁺, NO₃^-, 2,7-diazatetracyclo[6.2.2.2^3,6.0^3,7]tetradecane, 3, its dication dihexafluorophosphate salt 3²⁺(PF₆^-)₂, and a low quality structure of the monocation radical tosylate salt of 3 are reported and compared with MNDO calculations of these structures. Cations 2⁺ and 3⁺ are found to be significantly syn bent at nitrogen, and the dication 3²⁺ has a longer N-N distance than its azo analogue, 2,3-diazabicyclo [2.2.2]oct-2-ene (11).     

Ring transformation of cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium ion to the corresponding pyrrole derivatives via troponeimine intermediates: photo-induced autorecycling oxidizing reactions of some amines

Ring transformation of 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]furan- 8(7H),10(9H)-dionylium tetrafluoroborate 4⁺·BF₄⁻ to 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrrole-8(7H),10(9H)-dionylium tetrafluoroborate 6a-d⁺·BF₄⁻ consists of the reaction of 4⁺·BF₄⁻ with amines and subsequent exchange of the counter-ion using aq. HBF₄. Reactions of 4⁺·BF₄⁻ with aniline and 4-substituted anilines afforded the corresponding pyrrole derivatives 6a-c⁺·BF₄⁻ directly in good yields. On the other hand, reaction of 4⁺·BF₄⁻ with benzylamine gave the troponeimine intermediate 9, which was not converted to 6d⁺·BF₄⁻ and reverted to 4⁺·BF₄⁻ by adding HBF₄; however, it was converted to 6d⁺·BF₄⁻ upon treatment with (COCl)₂ or SOCl₂, followed by exchange of the counter-ion. In a search for the characteristics of 9, inspection and comparison of the X-ray crystal analyses, NMR and UV-vis spectra, and CV measurement of 9 and N,N-disubstituted troponeimine derivatives 12 were carried out to suggest the remarkable structure of 12 having ionic C-O bonding between the imine-carbon atom and the oxygen atom of the barbituric acid moiety in the solid state. Thus, characteristics of 9 were ascribed to the sterically hindered and favorable conformation of N-protonated troponeimine intermediates. Furthermore, novel photo-induced oxidation reactions of a series of 4⁺·BF₄⁻, 5⁺·BF₄⁻, and 6a,e⁺·BF₄⁻ towards some amines under aerobic conditions were carried out to give the corresponding imines in 455-8362% yields [based on compounds 4⁺, 5⁺, and 6a,e⁺], suggesting the oxidation reaction occurs in an autorecycling process. Mechanistic aspects of the amine-oxidation reaction are also postulated.     

Osmium dimethyl sulfoxide complexes: Synthesis and properties of [H(dmso)2][OsIII(dmso)2Br4]

The reaction of H₂[OsBr₆] with DMSO in ethanol solution resulted in DMSO complex [H(dmso-O)₂][Os^III(dmso-S)₂Br₄] (1) described previously as an intermediate product in the reaction of K₂[OsBr₆] with DMSO and characterized by EAS and ESR spectra. The coordination of DMSO molecules was established by IR and ¹H and ¹³C NMR spectroscopy. The oxidation state of osmium and trans arrangement of DMSO molecules in the anion were established by ESR. The behavior of complex 1 in solutions was studied by EAS, ESR, and mass-spectrometry: a displacement of Br^? ions accompanied by the reduction of osmium to oxidation state +2 occurs in DMSO, a solvation with displacement of DMSO molecules is observed at the first stage in water and methanol (rate constants 2.3 × 10^?4 and 1.7 × 10^?3 s^?1, respectively), the sequential substitution of DMSO molecules and osmium oxidation to form [Os^IVBr₆]_2? ions takes place in 4 mol/L HBr.     

Study of selected ions in the ammonia desorption chemical ionization mass spectra of peracetylated gentiobiose and two isotopically labelled peracetylated gentiobioses

The ammonia desorption chemical ionization (NH₃-DCI) mass spectra of peracetylated gentiobiose (1) and two isotopically labelled gentiobioses (2 and 3) were examined. Compound 2 is labelled with trideuteroacetyl groups in the non-reducing moiety and 3 with trideuteroacetyl groups in the reducing moiety. It is shown that the [M + NH₄ – 42]⁺ ion is not formed direct from [M + NH₄]⁺ by loss of ketene but appears to be formed by way of a nucleophilic acyl substitution reaction resulting in a neutral species which complexes with NH₄⁺. The disaccharides undergo cleavage at either side of the glycosidic oxygen joining the two sugar residues, a process which is accompanied by addition of H or CH₃CO to afford neutral species which complex with NH₄⁺. The structures of the ions resulting from H transfer have been inferred by comparison of their mass-analysed ion kinetic energy (MIKE) spectra with MIKE spectra of the [M + NH₄]⁺ ions of compounds of established structure. A ring fragmentation reaction of 1, 2 and 3 is reported.     

Unexpected product formed by the reaction of [2,6-(MeOCH2)2C6H3]Li with SbCl3: Structure of Sb-O intramolecularly coordinated organoantimony cation

Reaction of [2,6-(MeOCH₂)₂C₆H₃]Li (1) with SbCl₃ in 1:1 molar ratio yielded except the intended product [2,6-(MeOCH₂)₂C₆H₃]SbCl₂ (2) unexpected complex 3 consisting of antimony anion [Sb₆Cl₂₂]⁴⁻ compensated by four intramolecularly coordinated organoantimony cations [2,6-(MeOCH₂)₂C₆H₃]₂Sb⁺. Compound 3 is labile in CH₂Cl₂(CHCl₃) solution and decomposes to compound 2 and SbCl₃. Both compounds were characterized by the help of ¹H and ¹³C NMR spectroscopy, ESI-mass spectrometry and in the case of 3 by single crystal X-ray diffraction techniques.     

The structure and dissociation pathways of protonated methanol: An ab initio molecular orbital study

Ab initio molecular orbital calculations with moderately large polarization basis sets and including valence-electron correlation have been used to examine the structure and dissociation mechanisms of protonated methanol [CH₃OH₂]⁺. Stable isomers and transition structures have been characterized using gradient techniques. Protonated methanol is found to be the only stable isomer in the [CH₅O]⁺ potential surface. There is no evidence for a tightly-bound complex, [HOCH₂]⁺…?H₂, analogous to the preferred structure [CH₃]⁺…?H₂ of [CH₅]⁺. Protonated methanol is found to possess a pyramidal arrangement of bonds at the oxygen atom with a barrier to inversion of 8kJ mol^?1. The lowest energy fragmentation pathways are dissociation into methyl cation and water (predicted to require 284 kJ mol^?1 with zero reverse activation energy) and loss of molecular hydrogen (endothermic by 138 kJ mol^?1 but with a reverse activation barrier of 149 kJ mol^?1). The results offer a possible explanation as to why production of [CH₂OH]⁺ from the reaction of methyl cation with water is not observed. Other dissociation processes examined include loss of a hydrogen atom to yield the methylenoxonium radical cation or methanol radical cation (requiring 441 and 490 kJ mol^?1, respectively) and loss of a proton to yield neutral methanol (requiring 784 kJ mol^?1).