Nucleophilic addition of methanol and methanethiol to acetylene in the superbasic system KOH-DMSO: a quantum chemical model

Cluster-continuum models (KOH·nDMSO, n = 1, 5) were used to model the superbasic system “alkali metal hydroxide-dimethyl sulfoxide” within the framework of MP2/6-311++G**/ and B3LYP/6-31G* methods. The KOH molecule surrounded by five DMSO molecules exists as “solvate-loosened” ion pair with elongated K-O distance. It is proposed to consider the “solvate-loosened” ion pair of potassium cation with hydroxide anion in the surroundings of five solvent molecules as the catalytic coordination sphere of the superbasic system KOH-DMSO. Methanol and methanethiol molecules can be incorporated with ease into the first coordination sphere of potassium cation to form methoxide and methanethiolate ions. The possibility of nucleophilic attack of methoxide and methanethiolate ions on acetylene molecule in the first coordination sphere of potassium cation was studied. The model reaction system C₂H₂-CH₃OK-H₂O with one DMSO molecule included explicitly to maintain the “solvate-loosened” [CH₃O]^?...K⁺ ion pair and additional inclusion of solvent effects within the framework of the IEFPCM continuum model is the most preferable for serial calculations.     

<Emphasis Type="Italic">Ab initio</Emphasis> quantum-chemical study of the mechanism of methoxide ion formation in MOH/DMSO/CH<Subscript>3</Subscript>OH systems (M = Li,Na, K)

The profile of the reaction CH₃OH + MOH → CH₃OM + H₂O in the presence of an alkali (MOH, M = Li, Na, K) was investigated by the ab initio quantum-chemical method for the gas phase (with allowance for the solvent) within the continuum model. The proton transfer and the formation of the alkaline methoxide molecule in MOH/DMSO/CH₃OH systems (M = Li, Na, K) in the alkali-methanol pre-reaction complexes can take place without their preliminary dissociation and are barrier-free reactions.     

<Emphasis Type="Italic">AB initio</Emphasis> quantum chemical study of the reaction mechanism of ethynide ion formation in the C<Subscript>2</Subscript>H<Subscript>2</Subscript>/MOH/DMSO system (M = Li,Na, K)

The reaction mechanism of the formation of alkali metal ethynides C₂H₂ + MOH → C₂HM + H₂O (M = Li, Na, K) is studied for the gas phase (MP2/6-311++G**//RHF/6-31+G*) and also with regard to the solvent effect of dimethyl sulfoxide (DMSO) included within the continuum model. Among all acetylene complexes with alkali metal hydroxides considered (C₂H₂·MOH (M = Li, Na, K)), only the complex with KOH is thermodynamically stable in DMSO solution. The formation of this structure results in activation of the acetylene molecule towards electrophilic attack. The formation of alkali metal ethynide in solution is also thermodynamically favorable only in the system with potassium hydroxide of a whole series of metals considered. Further, the ethynide ion can interact in KCCK·HOH systems.     

Anionic Oligomerization of Methyl Methacrylate by Alkali Metal Alkoxides

Abstract

The kinetics of the oligomerization of methyl methacrylate (MMA) by methoxide/methanol solutions was studied using gas chromatography techniques. The effects of the type of the alkali metal, [CH OH]/[monomer] ratio, solvent, and initiator concentration were investigated. The rate of conversion using different alkali metal alkoxides was in the order CH₃OLi < CH₃ONa < CH₃OK, but no oligomers higher than the addition product, RO—MMA (n=1), could be obtained by CH₃OLL DP_n decreased with increasing the [CH₃OH]/[monomer] ratio and with lowering of the initiator concentration. Using DMSO as solvent increased the yields of the higher oligomers. The formation of n=1 was reversible, contrary to the formation of the higher oligomers. Some of the rate constants of the various steps of the oligomerization were estimated by taking into account the reversibility of the initiation reaction and assuming steady-state conditions in the concentration of the various anions present in the system.     

Synthese und Charakterisierung von 2‐O‐funktionalisierten Ethylrhodoximen und ‐cobaloximen

Synthesis and Characterization of 2‐O‐Functionalized Ethylrhodoximes and ‐cobaloximes 2‐Hydroxyethylrhodoxime and ‐cobaloxime complexes L—[M]—CH₂CH₂OH (M = Rh, L = PPh₃, 1 ; M = Co, L = py, 2 ; abbr.: L—[M] = [M(dmgH)₂L] (dmgH₂ = dimethylglyoxime, L = axial base) were obtained by reaction of L—[M]^— (prepared by reduction of L—[M]—Cl with NaBH₄ in methanolic KOH) with BrCH₂CH₂OH. H₂O—[Rh]^—, prepared by reduction of H[RhCl₂(dmgH)₂] with NaBH₄ in methanolic KOH, reacted with BrCH₂CH₂OH followed by addition of pyridine yielding py—[Rh]—CH₂CH₂OH ( 3 ). Complexes 1 and 3 were found to react with (Me₃Si)₂NH forming 2‐(trimethylsilyloxy)ethylrhodoximes L—[Rh]—CH₂CH₂OSiMe₃ (L = PPh₃, 4 ; L = py, 5 ). Treatment of complex 1 with acetic anhydride resulted in formation of the 2‐(acet oxy)ethyl complex Ph₃P—[Rh]—CH₂CH₂OAc ( 6 ). All complexes 1 — 6 were isolated in good yields (55—71 %). Their identities were confirmed by NMR spectroscopic investigations ( 1 — 6 : ¹H, ¹³C; 1 , 4 , 6 : ³¹P) and for [Rh(CH₂CH₂OH)(dmgH)₂(PPh₃)]·CHCl₃·1/2H₂O ( 1 ·CHCl₃·1/2H₂O) and py—[Rh]—CH₂CH₂OSiMe₃ ( 5 ) by X‐ray diffraction analyses, too. In both molecules the rhodium atoms are distorted octahedrally coordinated with triphenylphosphine and the organo ligands (CH₂CH₂OH and CH₂CH₂OSiMe₃, respectively) in mutual trans position. Solutions of 1 in dmf decomposed within several weeks yielding a hydroxyrhodoxime complex “Ph₃P—[Rh]—OH”. X‐ray diffraction analysis exhibited that crystals of this complex have the composition [{Rh(dmg)(dmgH) (H₂O)(PPh₃)}₂]·4dmf ( 7 ) consisting of centrosymmetrical dimers. The rhodium atom is distorted octahedrally coordinated. Axial ligands are PPh₃ and H₂O. One of the two dimethylglyoximato ligands is doubly deprotonated. Thus, only one intramolecular O—H···O hydrogen bridge (O···O 2.447(9)Å) is formed in the equatorial plane. The other two oxygen atoms of dmgH^— and dmg^2—, respectively, act as hydrogen acceptors each forming a strong (intermolecular) O···H′—O′ hydrogen bridge to the H′₂O′ ligand of the other molecule (O···O′ 2.58(2)/2.57(2)Å).     

Spectroscopic characteristics of dimethylsulfoxide molecules coordinated to Mg2+ cation. structure of complexes [Mg(DMSO)i(CH3CN)6-i]2+ from the data of quantum-chemical calculations and IR spectra of Mg(ClO4)2-DMSO-CH3CN Solutions

By the DFT B3LYP/6-31G** method the geometry was optimized and IR spectra were calculated of complexes [Mg(DMSO) _i (CH₃CN)_6-i ]²⁺ (i = 1–6). The values of free energy ΔG in the reaction of ligands substitution in the coordination sphere of the cation were determined. A satisfactory agreement between experimental and calculated values of structural parameters and infrared spectra of free molecules and coordinated to the cation DMSO was obtained. The regularities in the changes of the spectroscopic and structural characteristics of [Mg(DMSO) _i (CH₃CN)_6-i ]²⁺ complexes at varying their composition were revealed. The frequencies and absolute integral intensities of DMSO bands in the IR spectra of pure liquid, solutions in acetonitrile, and in three-component solutions Mg(ClO₄)₂-DMSO-CH₃CN were measured. A correspondence between the calculated change of the frequency and absolute intensity of the IR bands v(C≡N), v(C-C), v(S=O), and v(SC) of the complexes and the corresponding values in the IR spectra of the solutions with different content of components of binary solvent was found.     

Characterization of five [C4H7O]+ Ion structures. Fragmentation of the 2-pentanone molecular ion

The [C₄H₇0]⁺ ions [CH₂?CH? C(?OH)CH₃]⁺ (1), [CH₃CH?CH? C(?OH)H]⁺ (2), [CH₂?C(CH₃)C(?OH)H]⁺ (3), [Ch₃CH₂CH₂C?O]⁺ (4) and [(CH₃)₂CHC?O]⁺ (5) have been characterized by their collision-induced dissociation (CID) mass spectra and charge stripping mass spectra. The ions 1–3 were prepared by gas phase protonation of the relevant carbonyl compounds while 4 and 5 were prepared by dissociative electron impact ionization of the appropriate carbonyl compounds. Only 2 and 3 give similar spectra and are difficult to distinguish from each other; the remaining ions can be readily characterized by either their CID mass spectra or their charge stripping mass spectra. The 2-pentanone molecular ion fragments by loss of the C(1) methyl and the C(5) methyl in the ratio 60:40 for metastable ions; at higher internal energies loss of the C(1) methyl becomes more favoured. Metastable ion characteristics, CID mass spectra and charge stripping mass spectra all show that loss of the C(1) methyl leads to formation of the acyl ion 4, while loss of the C(5) methyl leads to formation of protonated vinyl methyl ketone (1). These results are in agreement with the previously proposed potential energy diagram for the [C₅H₁₀O]⁺˙ system.     

Copper(II) Complexes with N‐(9‐anthracenyl)‐N′‐(3‐pyridyl)urea (L) and a Derivative of L: Synthesis,Structure, and Fluorescent Properties

Three copper(II) complexes, [Cu₂(OAc)₄L₂] · 2CH₃OH ( 1 ), [CuBr₂L′₂(CH₃OH)] · CH₃OH ( 2a ), and [CuBr₂L′₂(DMSO)] · 0.5CH₃OH ( 2b ) {L = N‐(9‐anthracenyl)‐N′‐(3‐pyridyl)urea and L′ = N‐[10‐(10‐methoxy‐anthronyl)]‐N′‐(3‐pyridyl)urea} have been synthesized by the reaction of L with the corresponding copper(II) salts. Complex 1 shows a dinuclear structure with a conventional “paddlewheel” motif, in which four acetate units bridge the two Cu^II ions. In complexes 2a and 2b , the anthracenyl ligand L has been converted to an anthronyl derivative L′, and the central metal ion exhibits a distorted square pyramidal arrangement, with two pyridyl nitrogen atoms and two bromide ions defining the basal plane and the apical position is occupied by a solvent molecule (CH₃OH in 2a and DMSO in 2b ).     

Formation pathways of DMSO2 in the addition channel of the OH‐initiated DMS oxidation: A theoretical study

The production of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO₂) in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been shown to be very sensitive to nitrogen oxides (NO_x) levels. In the present work we have explored the potential energy surfaces corresponding to several reaction pathways which yield DMSO₂ from the CH₃S(O)(OH)CH₃ adduct [including the formation of CH₃S(O)(OH)CH₃ from the reaction of DMSO with OH] and the reaction channels that yield DMSO or/and DMSO₂ from the CH₃S(O₂)(OH)CH₃ adduct are also studied. The formation of the CH₃S(O₂)(OH)CH₃ adduct from CH₃S(OH)CH₃ (DMS‐OH) and O₂ was analyzed in our previous work. All these pathways due to the presence of NO_x (NO and NO₂) and also due to the reactions with O₂, OH and HO₂ are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO₂ (and DMSO) formation yields. In particular, our theoretical results clearly show the existence of NO_x‐dependent pathways leading to the formation of DMSO₂, which could explain some of these experimental results in comparison with experimental measurements carried out in NO_x‐free conditions. Our results indicate that the relative importance of the addition channel in the DMS oxidation process can be dependent on the NO_x content of chamber experiments and of atmospheric conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

Photocatalytic Dissociation of CH3OH on ZnO(0001) Surface

Photocatalysis of CH₃OH on the ZnO(0001) surface has been investigated by using temperature-programmed desorption (TPD) method with a 266 nm laser light. TPD results show that part of the CH₃OH adsorbed on ZnO(0001) surface are in molecular form, while others are dissociated. The thermal reaction products of H₂, CH₃^·, H₂O, CO, CH₂O, CO₂ and CH₃OH have been detected. Experiments with the UV laser light indicate that the irradiation can promote the dissociation of CH₃OH/CH₃O^· to form CH₂O, which can be future converted to HCOO^- during heating or illumination. The reaction between CH₃OH_Znand OH_ad can form the H₂O molecule at the Zn site. Both temperature and illumination promote the desorption of CH₃^· from CH₃O^·. The research provides a new insight into the photocatalytic reaction mechanism of CH3OH on ZnO(0001).     

Binuclear copper(II) and oxovanadium(IV) complexes with 2,6-diformyl-4- tert -butylphenol- bis -(1′-phthalazinylhydrazone). Synthesis,properties and quantum chemical study

Four binuclear transition metal complexes: [Cu₂L(μ-OCH₃)]?·?CH₃OH, [Cu₂H₂L(μ-Cl)Cl₂]?·?(CH₃OH), [Cu₂H₂L(μ-Br)Br₂]?·?(CH₃OH), [(VO)₂H₂L(μ-Cl)]Cl₂?·?(CH₃OH) were synthesized by reaction of the Robson-type binucleating ligand H₃L (2,6-diformyl-4-tert-butylphenol-bis-(1′-phthalazinylhydrazone)) with Cu(II) acetate, CuCl₂, CuBr₂ and VOCl₂, correspondingly. IR and ESR spectra, elemental analysis, conductivity measurements, magnetochemical study and DFT calculations were used to characterize the ligand and isolated complexes. The ligand is a NNONN donor and its degree of deprotonation varies with the metal salt used for reaction (triply deprotonated form L^?3 is observed in reaction with copper(II) acetate, while monodeprotonated form H₂L^? is found in complexes obtained from metal halides). All complexes contain an endogenous phenoxide bridge and an exogenous methoxide, chloride or bromide bridge. Magnetic data reveal existence of antiferromagnetic interactions between the metal ions (experimental 2J values are ?700, ?73, ?50 and ?190?cm^?1, correspondingly). Broken symmetry approach at the UB3LYP/6-31G(d) level was used to theoretically calculate spin-spin coupling between metal centers. Obtained values ?570, ?62, ?53 and ?214?cm^?1 are rather close to experimental ones and reproduce their counterrelation. Spin density distribution in the singlet and triplet states of the complexes is discussed.     

<Emphasis Type="Italic">Ab initio</Emphasis> quantum-chemical study of the reaction mechanisms of acetylene in superbasic media. Noncatalytic vinylation of methanol

The reaction profile of noncatalytic vinylation of methanol with acetylene was studied by ab initio quantum-chemical calculations for the gas phase and by calculations using a combined model that took into account the solvent (DMSO) effect. The reaction occurs via the formation of a prereaction complex of the methoxide ion with acetylene; at this stage, the acetylene molecule is already activated with respect to the proton. The observed stereospecific trans-addition in methanol vinylation in the gas phase and solution is provided by the lower activation barrier corresponding to the E structure of the acetylene molecule in the transition state and barrier-free protonation of the carbanion intermediate.     

Functionalized cyclodiphosphazanes cis-[BuNP(OR)]2 (R=C6H4OMe-o, CH2CH2OMe, CH2CH2SMe, CH2CH2NMe2) as neutral 2e, 4e or 8e donor ligands

Cyclodiphosphazanes having donor functionalities such as cis-[^tBuNP(OR)]₂ (R = C₆H₄OMe-o (2); R = CH₂CH₂OMe (3); R = CH₂CH₂SMe (4); R = CH₂CH₂NMe₂ (5)) were obtained in good yield by reacting cis-[^tBuNPCl]₂ (1) with corresponding nucleophiles. The reactions of 2-5 with [RuCl₂(η⁶-cymene)]₂, [MCl(COD)]₂ (M = Rh, Ir), [PdCl₂(PEt₃)]₂ and [MCl₂(COD)] (M=Pd, Pt) result in the formation of exclusively monocoordinated mononuclear complexes of the type cis-[{^tBuNP(OR)}₂ML_n-κP] irrespective of the reaction stoichiometry and the reaction conditions. In contrast, 2-5 react with [RhCl(CO)₂]₂, [PdCl(η³-C₃H₅)]₂, CuX (X=Cl, Br, I) to give homobinuclear complexes. Interestingly, CuX produces both mono and binuclear complexes depending on the stoichiometry of the reactants and the reaction conditions. The mononuclear complexes on treatment with appropriate metal reagents furnish heterometallic complexes.     

Investigation of electrochemical behavior of secondary products of capture of OH radicals by dimethyl sulfoxide molecules using laser photoemission

Electrode reactions of intermediates formed during capture of OH radicals by dimethyl sulfoxide (DMSO) molecules were studied using laser photoemission in aqueous buffer solutions in the pH range from acidic to basic. The results were compared with characteristics of one-electron reduction of methyl radicals generated via photoemission from methyl halides CH₃X (X = Cl, I). From these experiments, it was concluded that intermediates in these systems were identical since the primary product of capture of OH radicals by DMSO molecules, i.e., adduct (CH₃)₂SO^. (OH), was spontaneously decomposed to form ^.CH₃ with a time as low as <2 × 10^?5 s. Some anomalies were found on time-resolved voltammograms of intermediates in the pH range from weakly basic to weakly acidic and at illumination times of an electrode with UV light T _m ≤ 90–300 ms. These features were presumably caused by rather slow formation of organomercury intermediates as interaction products of the components of the system DMSO—OH radical—mercury electrode.     

Structure and formation of gaseous [C4H6O]+˙ ions: 1—The enolic ions [CH2C(OH)?CHCH2]+˙ and [CH2CH?CHCH(OH)]+˙ and their relationship with their keto counterparts

The [C₄H₆O]^+˙ ion of structure [CH₂?CHCH?CHOH]^+˙ (a) is generated by loss of C₄H₈ from ionized 6,6-dimethyl-2-cyclohexen-1-ol. The heat of formation ΔH_f of [CH₂?CHCH?CHOH]^+˙ was estimated to be 736 kJ mol^?1. The isomeric ion [CH₂?C(OH)CH?CH₂]^+˙ (b) was shown to have ΔH_f, ? 761 kJ mol^?1, 54 kJ mol^?1 less than that of its keto analogue [CH₃COCH?CH₂]^+˙. Ion [CH₂?C(OH)CH?CH₂]^+˙ may be generated by loss of C₂H₄ from ionized hex-1-en-3-one or by loss of C₄H₈ from ionized 4,4-dimethyl-2-cyclohexen-1-ol. The [C₄H₆O]^+˙ ion generated by loss of C₂H₄ from ionized 2-cyclohexen-1-ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH₂?CHCH?CHOH]^+˙ and [CH₂?C(OH)CH?CH₂]^+˙ ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH₃˙ and CO, [CH₂?CHCH?CHOH]⁺˙ and [CH₂?C(OH)CH?CH₂]^+˙ do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C₄H₆O]^+˙ ion [CH₂?C?CHCH₂OH]^+˙ are also reported.     

Coordination chemistry of ester-functionalized cp ligands: synthesis and catalytic activity of [Rh{CpCO2(CHPh)2OH}(NBD)] and [Rh{CpCO2(CH2)3OH}(NBD)]

Two new sodium hydroxyalkoxycarbonylcyclopentadienide salts Na[rac-CpCO₂(CHPh)₂OH] (1) and Na[(2S,3S)-CpCO₂(CHPh)₂OH] (2) were prepared by reaction of NaCp with the five-membered cyclic carbonates cis-4,5-diphenyl-1,3-dioxolan-2-one and (4S,5S)-4,5-diphenyl-1,3-dioxolan-2-one. The reaction of these salts with [Rh(NBD)Cl]₂ gave [Rh{rac-CpCO₂(CHPh)₂OH}(NBD)] (3) and (−)-[Rh{(2S,3S)-CpCO₂(CHPh)₂OH}(NBD)] (4) whose catalytic activity in the hydroformylation of hex-1-ene and styrene has been investigated and compared with that of the previously reported rhodium complexes [Rh{CpCO₂(CHR)₂OH}(NBD)] (R=H, Me). In addition we also discuss some preliminary results regarding the behavior of these complexes in the hydrogenation of the same substrates. The reactivity of NaCp toward the six-membered cyclic carbonate 1,3-dioxan-2-one has also been studied and it has been found that the reaction leads to two cyclopentadienide anions [CpCO₂(CH₂)₃OH]⁻ (5) and [CpCO₂(CH₂)₃OC(O)O(CH₂)₃OH]⁻ (6) in amounts strictly dependent on the carbonate/NaCp stoichiometric ratio.     

Identification of Epoxide Functionalities in Protonated Monofunctional Analytes by Using Ion/Molecule Reactions and Collision-Activated Dissociation in Different Ion Trap Tandem Mass Spectrometers

A mass spectrometric method has been delineated for the identification of the epoxide functionalities in unknown monofunctional analytes. This method utilizes gas-phase ion/molecule reactions of protonated analytes with neutral trimethyl borate (TMB) followed by collision-activated dissociation (CAD) in an ion trapping mass spectrometer (tested for a Fourier-transform ion cyclotron resonance and a linear quadrupole ion trap). The ion/molecule reaction involves proton transfer from the protonated analyte to TMB, followed by addition of the analyte to TMB and elimination of methanol. Based on literature, this reaction allows the general identification of oxygen-containing analytes. Vinyl and phenyl epoxides can be differentiated from other oxygen-containing analytes, including other epoxides, based on the loss of a second methanol molecule upon CAD of the addition/methanol elimination product. The only other analytes found to undergo this elimination are some amides but they also lose O = B-R (R = group bound to carbonyl), which allows their identification. On the other hand, other epoxides can be differentiated from vinyl and phenyl epoxides and from other monofunctional analytes based on the loss of (CH₃O)₂BOH or formation of protonated (CH₃O)₂BOH upon CAD of the addition/methanol elimination product. For propylene oxide and 2,3-dimethyloxirane, the (CH₃O)₂BOH fragment is more basic than the hydrocarbon fragment, and the diagnostic ion (CH₃O)₂BOH₂⁺ is formed. These reactions involve opening of the epoxide ring. The only other analytes found to undergo (CH₃O)₂BOH elimination are carboxylic acids, but they can be differentiated from the rest based on several published ion/molecule reaction methods. Similar results were obtained in the Fourier-transform ion cyclotron resonance and linear quadrupole ion trap mass spectrometer.     

An energy-resolved study of the fragmentation of ionized 1-Penten-3-ol

A detailed energy-resolved study of the fragmentation of CH₂?CHCH(OH)CD₂CD₃ (1-d₅) has been carried out using metastable ion studies and charge exchange techniques, combined with collision-induced dissociation studies to establish the structures of fragment ions. At low internal energies (metastable ions) the molecular ion of 1-d₅ rearranges to the 3-pentanone structure and fragments by loss of C₂H₅ or C₂D₅ leading to the acyl structure, [CH₃CH₂C?O]⁺ or [CD₃CD₂C?O]⁺, for the fragment ion. However, with increasing internal energy of the molecular ion this rearrangement process decreases rapidly in importance and loss of C₂D₅ by direct cleavage, leading to [CH₂?CHCH?OH]⁺, becomes the dominant fragmentation reaction. As a result the [C₃H₅O]⁺ ion seen in the electron impact mass spectrum of 1-penten-3-ol has predominantly the protonated acrolein structure.     

Electron impact ionization of ethylene–methanol heteroclusters: Stable configurations and mechanisms in intracluster ion–molecule reactions

Reactions that proceed within mixed ethylene–methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. The ion abundance ratio, [(C₂H₄)_n(CH₃OH)_mH⁺]/[(C₂H₄)_n(CH₃OH)_m⁺], shows a propensity to increase as the ethylene/methanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope-labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C₂H₄)_n(CH₃OH)_m⁺ and (C₂H₄)_n(CH₃OH)_m–1CH₃O⁺ ions are interpreted as a consequence of the ion–neutral complex and intracluster ion–molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C₂H₄)_n(CH₃OH)_mH⁺ ions with n + m ≤ 3 have particularly stable structures. The result is understood on the basis of ion–molecule condensation reactions, leading to the formation of fragment ions, $ {\rm CH}_2=\!=\mathop {\rm O}\limits^ + {\rm CH}_3 $ and (CH₃OH)H₃O⁺, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C₂H₄)_n(CH₃OH)_mH⁺(n + m ≤ 3) using semi-empirical molecular orbital calculations.     

Probing the Reactivity and Radical Nature of Oxidized Transition Metal-Thiolate Complexes by Mass Spectrometry

Transition metal thiolate complexes such as [PPN]⁺[RuL₃]^- (PPN?=?bis(triphenylphosphoranylidene) ammonium and L?=?diphenylphosphinobenzenethiolate) are known to undergo addition reactions with unsaturated hydrocarbons via the formation of new C-S bonds in solution upon oxidation. The reaction mechanism is proposed to involve metal-stabilized thiyl radical intermediates, a new type of distonic ions such as [RuL₃]⁺ ion in the case of [PPN]⁺[RuL₃]^-. This study presents the reactivity and structure investigation of [RuL₃]⁺ by mass spectrometry (MS) in conjunction with ion/molecule reactions. The addition reactions of [RuL₃]⁺ with alkenes or methyl ketones in the gas phase are indeed observed, in agreement with the proposed mechanism. Such reactivity is also maintained by several fragment ions of [RuL₃]⁺, indicating the preserved thiyl diradical core structure is responsible for the addition reaction. The thiyl radical nature of [RuL₃]⁺ was further verified by the ion/molecule reaction of [RuL₃]⁺ with dimethyl disulfide, in which the characteristic CH₃S? transfer occurs, both at atmospheric pressure and also at low pressure (~mTorr). These results provide, for the first time, clear mass spectrometric evidence of the radical nature of [RuL₃]⁺ (i.e., the distonic ion structure of [RuL₃]⁺), arising from the oxidation of non-innocent thiolate ligands of the complex [PPN]⁺[RuL₃]^-. Similar thiolate complexes, including ReL₃ and NiL₂, were also examined. Although reactions of oxidized ReL₃ or NiL₂ with CH₃SSCH₃ take place at atmospheric pressure, the corresponding reaction did not occur in vacuum. Consistent with these data, the addition of ethylene was not observed either, indicating lower reactivities of [ReL₃]⁺ and [NiL₂]⁺ in comparison to [RuL₃]⁺.