Selective reagents in chemical ionization mass spectrometry: Tetramethylsilane with ethers

Chemical ionization mass spectra of several ethers obtained with He/(CH₃)₄Si mixtures as the reagent gases contain abundant [M + 73]⁺ adduct ions which identify the relative molecular mass. For the di-n-alkyl ethers, these [M + 73]⁺ ions are formed by sample ion/sample molecule reactions of the fragment ions, [M + 73 ? C_nH_2n]⁺ and [M + 73 ? 2CnH_2n]⁺. Small amounts of [M + H]⁺ ions are also formed, predominantly by proton transfer reactions of the [M + 73 ? 2CnH_2n]⁺ or [(CH₃)₃SiOH₂]⁺ ions with the ethers. The di-s-alkyl ethers give no [M + 73] ⁺ ions, but do give [M + H]⁺ ions, which allow the determination of the relative molecular mass. These [M + H]⁺ ions result primarily from proton transfer reactions from the dominant fragment ion, [(CH₃)₃SiOH₂]⁺ with the ether. Methyl phenyl ether gives only [M + 73]⁺ adduct ions, by a bimolecular addition of the trimethylsilyl ion to the ether, not by the two-step process found for the di-n-alkyl ethers. Ethyl phenyl ether gives [M + 73]⁺ by both the two-step process and the bimolecular addition. Although the mass spectra of the alkyl etherr are temperature-dependent, the sensitivities of the di-alkyl ethers and ethyl phenyl ether are independent of temperature. However, the sensitivity for methyl phenyl ether decreases significantly with increasing temperature.     

Negative Ion Mass Spectral Fragmentation of N-Alkoxycarbonyl-1-Aminoarylmethyl Phosphonic Monoesters under Electrospray Ionization Conditions

Abstract

The negative ion mass spectrometry of N-benzyloxycarbonyl and N-ethoxycarbonyl 1-aminoarylmethylphosphonic methyl, ethyl, and phenyl monoesters was investigated under electrospray ionization conditions. Their fragmentation pathways are proposed and supported by collisional activated dissociation product-ion spectrometry. All of the deprotonated molecules preferentially eliminate a molecule of benzyl alcohol or ethanol first to yield isocyanato-alkylphosphonate anions, which further generate phosphonate ions by the loss of carbon monoxide, phenol or alcohol, carbon monoxide plus arenes. The isocyanato-sulfonate anions can further cyclize to generate 3-aryl-2-phenoxy-1,2,4-oxaphosphazolidine-2,5-dione amide anions, which can undergo rearrangements by the loss of carbon dioxide, metaphosphorous acid phenyl ester, or carbon dioxide plus metaphosphorous acid phenyl ester, respectively, to give rise to nitrogen-containing anions. The title compounds show an obviously different fragmentation in the negative ion mode from that in the positive ion mode under the electrospray ionization conditions.     

Two derivatives of (N‐phenylthioureidoalkyl)phosphonates

The structures of di­phenyl [3‐methyl‐1‐(3‐phenyl­thio­ureido)­butyl]­phosphonate and di­phenyl [2‐methyl‐1‐(3‐phenyl­thio­ureido)­butyl]­phosphonate, both C₂₄H₂₇N₂O₃PS, are reported. In both compounds, the thio­urea moiety adopts a syn–syn conformation (i.e. the S—C—N—C torsion angles are synperi­planar), which enables N—H⋯O hydrogen bonds to be formed between centrosymmetrically related mol­ecules. The geometries around the P atoms can be described as distorted tetrahedral. Some of the functional groups in each structure are disordered. The bulk of the different alkyl substituents between the amide and phosphonate groups influences the molecular conformation and crystal packing. Although the structures of these compounds and two related derivatives appear to be similar, they are not isostructural.     

Abundant Intramolecular Ring Rearrangements of 1-(N-Benzyloxycarbonylamino)arylmethylphosphonate Phenyl monoesters Under Electrospray Ionization Conditions

Abstract

The mass spectrometric behavior of 1-(N-benzyloxycarbonylamino)arylmethyl-phosphonate phenyl monoesters was investigated under positive ion electrospray ionization conditions. All nitrogen-protonated title compounds undergo four- and/or six-membered ring rearrangements to yield nitrogen-containing fragment ions by consecutive or simultaneous loss of a carbon dioxide and phenyl hydrogen phosphonate or phenyl benzylphosphonate or an arylmethylimine. All oxygen-protonated title compounds undergo four- to six-membered ring rearrangements to produce fragment ions by loss of a carbon dioxide plus an arylmethylimine, or phenyl benzylphosphonate, by consecutive or simultaneous loss of benzyl phenyl ether and isocyanic acid. The fragmentation is obviously different from the corresponding methyl and ethyl monoesters, which show a tendency to undergo intramolecular four-membered ring rearrangements only.

GRAPHICAL ABSTRACT      

Collision-induced decompositions of [M – H]− and [M + Li]+ ions from fast atom bombardment of dinucleoside phenylphosphonates

The collision-induced decompositions of the [M – H]^? and [M + Li]⁺ ions of a few dinucleoside phenylphosphonates were studied using fast atom bombardment and linked scanning at constant B/E. Deprotonation takes place on the base or sugar moieties. The [M – H]^? ion decomposes mainly by cleavage on either side of the phosphonate linkage, leading to the formation of mononucleotide fragment ions and also by cleavage of the basesugar bond. Rupture of the 3′-phosphonate bond is preferred. Unlike the normal charged nucleotides, these neutral nucleotides do not eliminate a neutral base from the [M – H]^? ion. However, the mononucleotide fragment ions which can have the charge on the phosphorus oxygen eliminate neutral bases by charge-remote fragmentation. The 4,4′-dimethoxytrityl (DMT)-protected nucleotides show the additional fragmentation of loss of DMT. Li⁺ attachment can occur at several sites in the molecule. As observed for the [M – H]^? ion, the major cleavage occurs on either side of the phosphonate bond in the fully deprotected nucleotides, cleavage of the ester bond on C(3′) being preferred. Cleavage of the 5′-phosphonate bond is not observed in the DMT-protected nucleotides. Many of the fragmentations observed can be explained as arising from charge-remote reactions.     

Rearrangements and fragmentations of phenyl styryl sulfides: 2—labelling studies

Metastable molecular ions of phenyl styryl sulfides may decompose by loss of CH₃^˙, SH^˙, CHS^˙, C₆H₅^˙, C₆H₆ or C₇H₇^˙. Labelling with carbon-13 and deuterium gave information about the mechanisms of these reactions. It appears that extensive rearrangements occur prior to most of these fragmentations. In the case of phenyl β-styryl sulfide both phenyl groups and both vinyl carbon atoms are found in the C₇H₇ fragment in comparable amounts. For phenyl α-styryl sulfide this fragmentation leads more specifically to the loss of the S-phenyl group and the β-vinyl carbon atom. It was concluded that rearrangements occur, partly via symmetric diphenyl ethene sulfide structures, to benzyl phenyl thione ions, from which the fragmentation occurs. For the loss of CHS^˙ an earlier proposed mechanism was confirmed. From both compounds the S-phenyl ring can be lost as C₆H₅^˙ or C₆H₆ as well as the C-phenyl ring. Fragmentation occurs from one of the initial structures as well as from benzyl phenyl thione. Loss of CH₃^˙ is thought to occur after ring closure with formation of dihydrobenzo[b]thiophenes followed by ring opening by rupture of a C? S bond. While phenyl β-styryl sulfide shows a strong tendency towards isomerization to a symmetric structure like 1,2-diphenylethene sulfide, phenyl α-styryl sulfide easily rearranges in an electrocyclic reaction with formation of benzyl phenyl thione.     

Synthesis,structural characterization and computational studies of catena‐poly[chlorido[μ3‐(pyridin‐1‐ium‐3‐yl)phosphonato‐κ3O:O′:O′′]zinc(II)]

Coordination polymers are constructed from two basic components, namely metal ions, or metal‐ion clusters, and bridging organic ligands. Their structures may also contain other auxiliary components, such as blocking ligands, counter‐ions and nonbonding guest or template molecules. The choice or design of a suitable linker is essential. The new title zinc(II) coordination polymer, [Zn(C₅H₅NO₃P)Cl]_n , has been hydrothermally synthesized and structurally characterized by single‐crystal X‐ray diffraction and vibrational spectroscopy (FT–IR and FT–Raman). Additionally, computational methods have been applied to derive quantitative information about interactions present in the solid state. The compound crystallizes in the monoclinic space group C 2/c . The four‐coordinated Zn^II cation is in a distorted tetrahedral environment, formed by three phosphonate O atoms from three different (pyridin‐1‐ium‐3‐yl)phosphonate ligands and one chloride anion. The Zn^II ions are extended by phosphonate ligands to generate a ladder chain along the [001] direction. Adjacent ladders are held together via N—H…O hydrogen bonds and offset face‐to‐face π–π stacking interactions, forming a three‐dimensional supramolecular network with channels. As calculated, the interaction energy between the neighbouring ladders is −115.2 kJ mol⁻¹. In turn, the cohesive energy evaluated per asymmetric unit‐equivalent fragment of a polymeric chain in the crystal structure is −205.4 kJ mol⁻¹. This latter value reflects the numerous hydrogen bonds stabilizing the three‐dimensional packing of the coordination chains.     

Two Trinuclear CuII Complexes: Effect of Phosphonate Ligand on the Magnetic Property and Electrocatalytic Reactivity for Water Oxidation

Two trinuclear copper phosphonate complexes, [Cu₃(pda)₃(tBuPO₃)]?2(Et₃NH) ( 1 ) and [Cu₃(pda)₃(PhPO₃)]?2(Et₃NH) ( 2 ), have been synthesized and investigated by a combination of X‐ray crystallography, PXRD, magneto‐ and electrochemistry, EPR, in situ UV‐vis spectroelectrochemistry and DLS. The two complexes feature almost identical crystal structures, the anions of which are both supported by pda^2? and tBuPO₃^2?/PhPO₃^2? groups, bridging three five‐coordinated Cu^II atoms to form a crown‐like structure. This is the first time that trinuclear copper phosphonate complexes have been isolated and characterized. Magnetic susceptibility measurements reveal that complexes 1 and 2 both display overall ferromagnetic characters, but with different exchange interactions between the metal ions within the two clusters. The electrocatalytic activity for water oxidation of the two complexes was preliminarily investigated, which reveals that both of the two complexes can carry out electrocatalytic water oxidation in a neutral system owing to the introduction of phosphonate ligands into the complexes, with a TOF of about 0.82 s^?1 ( 1 ) and 0.58 s^?1 ( 2 ), respectively. We propose that the presence of phosphonate ligands may affect the magnetic property and catalytic activity of the complexes.     

Three hydrates of the bisphosphonate risedronate,consisting of one molecular and two ionic structures

Three different hydrates of risedronate were obtained by varying the pH of a solution containing the compound. At the pH values used, the N atom of the pyridine group is protonated and the compounds are zwitterionic. Crystals obtained directly from the synthesis resulted in risedronate monohydrate, or [1‐hydroxy‐1‐phosphono‐2‐(pyridinium‐3‐yl)­ethyl]phosphonate monohydrate, C₇H₁₁NO₇P₂·H₂O, (I), in which just one phosphonate group is negatively charged. Recrystallizations at pH values of 2 and 4 yielded risedronate dihydrate, or sodium [1‐hydroxy‐2‐(pyridinium‐3‐yl)­ethane‐1,2‐diyl]­bis­(phosphonate) dihydrate, Na⁺·C₇H₁₀NO₇P₂⁻·2H₂O, (II). Finally, recrystallizations at pH values of 7 and 8 produced risedronate 2.5‐­hydrate, or sodium [1‐hydroxy‐2‐(pyridinium‐3‐yl)­ethane‐1,2‐diyl]­bis­(phosphonate) 2.5‐hydrate, Na⁺·C₇H₁₀NO₇P₂⁻·­2.5H₂O, (III). At these four pH values, both phosphonate groups in (II) and (III) are negatively charged and coordinated to an Na⁺ ion. Crystals of (II), i.e. those grown at pH values of 2 and 4, have isomorphous polymeric ion aggregate structures with geminal phosphonate and alcohol groups coordinated to the same Na⁺ ion. On the other hand, crystals of (III), i.e. those grown at pH values of 7 and 8, have isomorphism polymeric ion aggregate structures with geminal phosphonate and alcohol groups coordinated to different Na⁺ ions.     

The mass spectra of alkyl phenyl tellurides

The mass spectra of several alkyl phenyl tellurides, C₆H₅TeR (R = CH₃, CD₃, C₂H₅, n-C₃H₇, i-C₃H₇ and n-C₄H₉) have been studied with special emphasis on the fragmentation patterns involving cleavage of the alkyl and aryl tellurium–carbon bonds. Each compound exhibited intense parent ions. The rearrangement ions [C₆H₆Te]⁺? and [C₆H₆]⁺? were found in the spectra of phenyl ethyl and higher tellurides. Two other rearrangement ions [HTe]⁺ and [C₇H₇]⁺ were observed in the spectrum of each compound. Examination of the mass spectrum of phenyl methyl-d₃ telluride demonstrated that the [HTe]⁺ ions derive hydrogen from the phenyl group.     

Synthesis and evaluation of new dental monomers with both phosphonic and carboxylic acid functional groups

Novel dental monomers containing both phosphonic and carboxylic acid functional groups were prepared. The monomers were based on t‐butyl α‐bromomethacrylate (t‐BuBMA) and synthesized in three steps: The reaction of o‐hydroxyaryl phosphonates [diethyl (2‐hydroxyphenyl) phosphonate, tetraethyl (2,5‐dihydroxy‐1,4‐phenylene) diphosphonate and tetraethyl 5,5′‐(propane‐2,2‐diyl)bis(2‐hydroxy‐5,1‐ phenylene) diphosphonate] with t‐BuBMA, the hydrolysis of phosphonate groups to phosphonic acid using trimethyl silylbromide, and the hydrolysis of the t‐butyl groups to carboxylic acid with trifluoroacetic acid. The monomers were solids and soluble in water and ethanol. The structures of the monomers were determined by Fourier transform infrared (FTIR), ¹H, ¹³C, and ³¹P nuclear magnetic resonance (NMR) spectroscopy. The copolymerization behaviors of the synthesized monomers with glycerol dimethacrylate were first investigated in bulk using photodifferential scanning calorimetry at 40 °C with 2,2′‐dimethoxy‐2‐phenyl acetophenone as photoinitiator. Then, the solution copolymerization of the monomers with acrylamide in ethanol and water was studied, indicating that the synthesized monomers are incorporated into the copolymers. The acidic nature of the aqueous solutions of these monomers (pH values 1.72–1.87) is expected to give them etching properties important for dental applications. The interaction of the monomers with hydroxyapatite was investigated using ¹³C NMR and FTIR techniques. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1953–1965, 2009     

Ion-Neutral complexes from protonated propyl phenyl ethers. Gas-phase solvolysis versus elimination-readdition

Ion-neutral complexes, well attested as intermediates in the expulsion of alkenes from M⁺? and MH⁺ ions from primary alkyl phenyl ethers, are shown to intervene in the decomposition of the MH⁺ ion of a secondary alkyl phenyl ether, (CD₃)₂CHOPh. Chemical ionization (CI) (methane reagent gas)-mass-analysed ion kinetic energy spectroscopy (MIKES) shows ions of both m/z 96 and 97, indicating that the proton deposited by the CI reagent exchanges with the methyl deuterium atoms. The ratio of daughter ion intensities, as well as the proportions of ions of m/z 95, 96 and 97 from the MH⁺ of CD₃CH₂CD₂OPh, agree with predictions based on the gas-phase solvolysis mechanism, in which [i-Pr⁺ PhOH] complexes form from the protonated parent via simple bond heterolysis. An alternative mechanism, elimination-readdition, would proceed via [propene PhOHD⁺] complexes. This latter mechanism predicts a ratio of daughter ion intensities that is very different from gas-phase solvolysis and which disagrees with experiment. The elimination-readdition pathway is effectively ruled out, while the gas-phase solvolysis mechanism is reinforced.     

Formation of thioacylium ions in the gas phase

A study of the ion chemistry of benzenethioic acid using ion cyclotron resonance techniques shows that a long-lived ion of composition C₇H₅S⁺ is formed from the reaction of the neutral acid with primary fragment ions, m/z 77 (phenyl) and m/z 105 (benzoyl). The product is assigned the thiobenzoyl structure on the basis df its mode of formation from benzoyl cations and tbe neutral acid. Other reactant ions (acetylium and thioacetylium) derived from mixtures of benzenethioic acid with ethanethioic acid or acetate esters similarly lead to thiobenzoyl ions as the major product The significance of these results as support for the thioacetylium structure of C₂H₃S⁺ ions from ethanethioic acid is discussed.     

Rearrangements and fragmentations of phenyl styryl sulfides: 1—Metastable ion spectra

The mass spectra of two isomeric phenyl styryl sulphides show abundant peaks for fragment ions formed after interesting and unusual rearrangements, e.g. loss of CHS^˙ and C₇H₇^˙. Information about these rearrangements was obtained by comparison of the metastable peak intensities and peak shapes with those of four isomers. It appears that isomerization reactions between the phenyl styryl sulfides and the isomers are possible and that most of the metastable ion fragmentations proceed via reacting configurations that are common to two or more of the compounds investigated. The results indicate that an earlier proposed mechanism for the fragmentation of phenyl vinyl sulfides is incomplete and only partly correct for the compounds studied. Metastable ion spectra were obtained using high voltage scans and constant B/E scans: a short comparison of the results obtained with the two methods is given.     

Hydrogen rearrangement in molecular ions of alkyl benzenes: Appearance potentials and substituent effects on the formation of [C7H8]+ ions

The mechanism of the formation of [C₇H₈]⁺ ions by hydrogen rearrangement in the molecular ions of 1-phenylpropane and 1,3-diphenylpropane has been investigated by looking at the effects of CH₃O and CF₃ substituents in the meta and para positions on the relative abundances of the corresponding ions and on the appearance energies. The formation of [C₇H₈]⁺ ions from 1,3-diphenylpropane is much enhanced at the expense of the formation of [C₇H₇]⁺ ions by benzylic cleavage, due to the localized activation of the migrating hydrogen atom by the γ phenyl group. A methoxy substituent in the 1,3-diphenylpropane, exerts a site-specific influence on the hydrogen rearrangement, which is much more distinct than in 1-phenylpropane and related 1-phenylalkanes, the rearrangement reaction being favoured by a meta methoxy group. The mass spectrum of 1-(3-methoxyphenyl)-3-(4-trideuteromethoxyphenyl)-propane shows that this effect is even stronger than the effect of para methoxy groups on the benzylic cleavage. From measurements of appearance potentials it is concluded that the substituent effect is not due to a stabilization of the [C₇H₇X]⁺ product ions. Whereas the [C₇H₇]⁺ ions are formed directly from molecular ions of 1-phenylpropane and 1,3-diphenylpropane, the [C₇H₈]⁺ ions arise by a two-step mechanism in which the s? complex type ion intermediate can either return to the molecular ion or fragment to [C₇H₈]⁺ by allylic bond cleavage. Obviously the formation of this s? complex type ion, is influenced by electron donating substituents in specific positions at the phenyl group. This is borne out by a calculation of the ΔH_f values of the various species by thermochemical data. Thus, the relative abundances of the fragment ions are determined by an isomerization equilibrium of the molecular ions, preceding the fragmentation reaction.     

Use of a hand-portable gas chromatograph-toroidal ion trap mass spectrometer for self-chemical ionization identification of degradation products related to O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX)

The chemical warfare agent O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX) and many related degradation products produce poorly diagnostic electron ionization (EI) mass spectra by transmission quadrupole mass spectrometry. Thus, chemical ionization (CI) is often used for these analytes. In this work, pseudomolecular ([M+H]⁺) ion formation from self-chemical ionization (self-CI) was examined for four VX degradation products containing the diisopropylamine functional group. A person-portable toroidal ion trap mass spectrometer with a gas chromatographic inlet was used with EI, and both fixed-duration and feedback-controlled ionization time. With feedback-controlled ionization, ion cooling (reaction) times and ion formation target values were varied. Evidence for protonation of analytes was observed under all conditions, except for the largest analyte, bis(diisopropylaminoethyl)disulfide which yielded [M+H]⁺ ions only with increased fixed ionization or ion cooling times. Analysis of triethylamine-d₁₅ provided evidence that [M+H]⁺ production was likely due to self-CI. Analysis of a degraded VX sample where lengthened ion storage and feedback-controlled ionization time were used resulted in detection of [M+H]⁺ ions for VX and several relevant degradation products. Dimer ions were also observed for two phosphonate compounds detected in this sample.     

Metal-ion-coordinating properties of various phosphonate derivatives,including 9−[2−(phosphonylmethoxy)ethyl]adenine (PMEA) – an adenosine monophosphate (AMP) analogue with antiviral properties

The stability constants of the 1:1 complexes formed between Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, (in part) Zn²⁺, or Cd²⁺ and (phosphonylmethoxy)ethane (PME^2?) or 9?[2?(phosphonylmethoxy)ethyl]adenine (PMEA^2?) were determined by potentiometric pH titration in aqueous solution (I = 0.1M , NaNO₃; 25°). The experimental conditions were carefully selected such that self-association of the adenine derivative PMEA and of its complexes was negligibly small; i.e., it was made certain that the properties of the monomeric [M(PMEA)] complexes were studied. Recent measurements with simple phosphate monoesters, R–MP^2– (where R is a non-coordinating residue; S. S. Massoud, H. Sigel, Inorg. Chem. 1988 , 27, 1447), were used to show that analogously simple phosphonates (R? PO) – we studied now the complexes of methyl phosphonate and ethyl phosphonate – fit on the same log K/logK vs. pK/ pK straight-line plots. With these reference lines, it could be demonstrated that for all the [M(PME)] complexes with the mentioned metal ions an increased complex stability is measured; i.e., a stability higher than that expected for a sole phosphonate coordination of the metal ion. This increased stability is attributed to the formation of five-membered chelates involving the ether oxygen present in the ? O? CH₂? PO residue of PME^2? (and PMEA^2?); the formation degree of the five-membered [M(PME)] chelates varies between ca. 15 and 40% for the alkaline earth ions and ca. 35 to 65% for 3d ions and Zn²⁺ or Cd²⁺. Interestingly, for the [M(PMEA)] complexes within the error limits exactly the same observations are made indicating that the same five-membered chelates are formed, and that the adenine residue has no influence on the stability of these complexes, with the exception of those with Ni²⁺ and Cu²⁺. For these two metal ions, an additional stability increase is observed which has to be attributed to a metal ion-adenine interaction giving thus rise to equilibria between three different [M(PMEA)] isomers. These equilibria are analyzed, and for [Cu(PMEA)] it is calculated that 17(±3)% exist as an isomer with a sole Cu²⁺-phosphonate coordination, 34(±10)% form the mentioned five-membered chelate involving the ether oxygen, and the remaining 49(±10)% are due to an isomer containing also a Cu²⁺-adenine interaction. Based on various arguments, it is suggested that this latter isomer contains two chelate rings which result from a metal-ion coordination to the phosphonate group, the ether oxygen, and to N(3) of the adenine residue. For [Ni(PMEA)], the isomer with a Ni²⁺-adenine interaction is formed to only 22(±13)%; for [Cd(PMEA)] and the other [M(PMEA)] complexes if at all, only traces of such an isomer are occurring. In addition, the [M(PMEA)] complexes may be protonated leading to [M(H·PMEA)]⁺ species in which the proton is mainly at the phosphonate group, while the metal ion is bound in an adenosine-type fashion to the nucleic base residue. Finally, the properties of [M(PMEA)] and [M(AMP)] complexes are compared, and in this connection it should be emphasized that the ether oxygen which influences so much the stability and structure of the [M(PMEA)] complexes in solution is also crucial for the antiviral properties of PMEA.     

Synthesis and Characterization of Copper(II)–Phosphonate Coordination Chain Array of Metallocages

Reaction of CuCl₂ ·2H₂O and 2,4,6‐tris(phosphorylmethyl)mesitylene (H₆tpmm) in H₂O?DMF solution at room temperature afforded green crystals of [Cu₆(H₂tpmm)₃(H₂O)₉]·3H₂O ( 1 ), which were characterized by Fourier transform infrared (FT‐IR), thermogravimetric (TG) analysis, and powder X‐ray diffraction (PXRD). The solid‐state structure of 1 reveals a one‐dimensional chain array of M₄L₂ ‐metallocages constituted by the connection of two kinds of metallocage units, namely MC‐A (phosphonate/water‐bridged) and MC‐B (phosphonate‐bridged only), via μ₂‐O(phosphonate)? Cu bonds in ABAABA order. The tris‐phosphonate ligand H₆tpmm is partially deprotonated to form H₂tpmm^4?, which displays a cis,cis,cis conformation to bridge six Cu(II) centers via two monodentate phosphonate groups in a η ⁰:η ⁰:η ¹‐bonding mode and one tridentate phosphonate group in a μ₄, η ¹:η ¹:η ²‐bondingng mode.     

Hydrogen-carbon,carbon-carbon double rearrangement induced by proximity effects. 1–formation of methoxybenzyl ions in the electron impact mass spectra of substituted 1,1-bis(dimethoxyphenyl)methanes

The 75 eV electron impact mass spectra of 1,1-bis(dimethoxyphenyl)methanes bearing o-methoxy groups are dominated by intense peaks corresponding, at least formally, to benzyl ions [(CH₃O)₂C₆H₃CH₂]⁺ (b). They arise from ions [((CH₃O)₂C₆H₃)₂CH]⁺ (a), which are in turn formed from molecular ions by loss of an alkyl radical through benzylic cleavage. The analysis of compounds labelled with ²H or ¹³C at methoxy groups led to the determination of the mechanism. Hydrogen migration, as hydride, followed by electrophilic substitution by the methylene carbon of the phenyl methylene ether cation through a six-centred transition state is responsible for the formation of benzylic ions b.     

Mass spectrometry of diaziridines: 1—Rearrangements of the molecular ion of 1-benzyl-3,3-dimethyldiaziridine and identification of some daughter ions using collisional activation

Intense rearrangement processes involving migrations of hydrogen atoms and the phenyl group were observed in the electron impact induced fragmentation of 1-benzyl-3,3-dimethyldiaziridine. The following ions are observed: (i) m/z 146: a two-step fragmentation involving hydrogen transfer followed by loss of NH₂; (ii) m/z 119: C—N¹ bond fission followed by a 1–4 phenyl shift and loss of CH₃N₂; (iii) m/z 106: a process involving reciprocal hydrogen migration between the methyl and benzylic methylene groups; (iv) m/z 58: hydrogen transfer from benzylic methylene and subsequent loss of PhCHN. The origin of these ions has been confirmed by measurements of metastable transitions in 1-benzyl-3,3-dimethyldiaziridine, and on specifically deuterated and substituted diaziridines. The structure of the ions at m/z 119 and m/z 106 has been deduced by means of collisional activation spectrometry.