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1.
Chem Commun (Camb) ; 55(78): 11727-11730, 2019 Sep 26.
Artigo em Inglês | MEDLINE | ID: mdl-31512685

RESUMO

The multiple reaction monitoring mode of a triple quadrupole mass spectrometer is used to examine the Buchwald-Hartwig amination reaction at 0.1% catalyst loading in real-time using sequential addition of reagents to probe the individual steps in the cycle. This is a powerful new method for probing reactions under realistic conditions.

2.
J Am Soc Mass Spectrom ; 30(9): 1750-1757, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31218572

RESUMO

The abundance of an ion in an electrospray ionization mass spectrum is dependent on many factors beyond just solution concentration. Even in cases where the analytes of interest are permanently charged (under study here are ammonium and phosphonium ions) and do not rely on protonation or other chemical processes to acquire the necessary charge, factors such as cation structure, molecular weight, solvent, and the identity of the anion can affect results. Screening of a variety of combinations of cations, anions, and solvents provided insight into some of the more important factors. Rigid cations and anions that conferred high conductivity tended to provide the highest responses. The solvent that most closely reflected actual solution composition was acetonitrile, while methanol, acetonitrile/water, and dichloromethane produced a higher degree of discrimination between different ions. Functional groups that had affinity for the solvent tended to depress response. These observations will provide predictive power when accounting for analytes that for reasons of high reactivity can not be isolated.

3.
J Chem Inf Model ; 59(4): 1295-1300, 2019 04 22.
Artigo em Inglês | MEDLINE | ID: mdl-30932490

RESUMO

Mass spectrometric data are copious and generate a processing burden that is best dealt with programmatically. PythoMS is a collection of tools based on the Python programming language that assist researchers in creating figures and video output that is informative, clear, and visually compelling. The PythoMS framework introduces a library of classes and a variety of scripts that quickly perform time-consuming tasks: making proprietary output readable; binning intensity vs time data to simulate longer scan times (and hence reduce noise); calculating theoretical isotope patterns and overlaying them in histogram form on experimental data (an approach that works even for overlapping signals); rendering videos that enable zooming into the baseline of intensity vs time plots (useful to make sense of data collected over a large dynamic range) or that depict the evolution of different species in a time-lapse format; calculating aggregates; and providing a quick first-pass at identifying fragments in MS/MS spectra. PythoMS is a living project that will continue to evolve as additional scripts are developed and deployed.

4.
J Mass Spectrom ; 54(5): 466-479, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30980780

RESUMO

Electrospray ionization mass spectrometry (ESI-MS) is a useful technique for solving organometallic and coordination chemistry characterization problems that are difficult to address using traditional methods. However, assigning the ESI mass spectra of such compounds can be challenging, and the considerations involved in doing so are quite different from assigning the mass spectra of purely organic samples. This is a tutorial article for organometallic/coordination chemists using ESI-MS to analyze pure compounds or reaction mixtures. The fundamentals of assigning ESI mass spectra are discussed within the context of organometallic and coordination systems. The types of ions commonly observed by ESI-MS are categorized and described. Finally, a step-by-step guide for the assignment of organometallic and coordination chemistry ESI mass spectra is provided along with two case studies.

5.
Inorg Chem ; 58(1): 747-755, 2019 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-30525532

RESUMO

Kinetic profiles obtained from monitoring the solution-phase substitution chemistry of [Ru(η5-indenyl)(NCPh)(PPh3)2]+ (1) by both electrospray ionization mass spectrometry and 31P{1H} NMR are essentially identical, despite an enormous difference in sample concentrations for these complementary techniques. These studies demonstrate dissociative substitution of the NCPh ligand in 1. Competition experiments using different secondary phosphine reagents provide a ranking of phosphine donor abilities at this relatively crowded half-sandwich complex: PEt2H > PPh2H ≫ PCy2H. The impact of steric congestion at Ru is evident also in reactions of 1 with tertiary phosphines; initial substitution products [Ru(η5-indenyl)(PR3)(PPh3)2]+ rapidly lose PPh3, enabling competitive re-coordination of NCPh. Further solution experiments, relevant to the use of 1 in catalytic hydrophosphination, show that PPh2H out-competes PPh2CH2CH2CO2Bu t (the product of hydrophosphination of tert-butyl acrylate by PPh2H) for coordination to Ru, even in the presence of a 10-fold excess of the tertiary phosphine. Additional information on relative phosphine binding strengths was obtained from gas-phase MS/MS experiments, including collision-induced dissociation experiments on the mixed phosphine complexes [Ru(η5-indenyl)PP'P″]+, which ultimately appear in solution during the secondary phosphine competition experiments. Unexpectedly, unsaturated complexes [Ru(η5-indenyl)(PR2H)(PPh3)]+, generated in the gas-phase, undergo preferential loss of PR2H. We propose that competing orthometallation of PPh3 is responsible for the surprising stability of the [Ru(η5-indenyl)(PPh3)]+ fragment under these conditions.

6.
Dalton Trans ; 47(48): 17291-17298, 2018 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-30480693

RESUMO

Methylalumoxane (MAO) ionizes highly selectively in the presence of octamethyltrisiloxane (OMTS) to generate [Me2Al·OMTS]+ [(MeAlO)16(Me3Al)6Me]-. We can take advantage of this transformation to examine the reactivity of a key component of MAO using electrospray ionization mass spectrometry (ESI-MS), and here we describe the reactivity of this pair of ions with other trialkyl aluminum (R3Al) components. Using continuous injection methods, we found Et3Al to exchange much faster and extensively at room temperature in fluorobenzene (t½âˆ¼2 s, up to 25 exchanges of Me for Et) than iBu3Al (t½âˆ¼40 s, up to 11 exchanges) or Oct3Al (t½âˆ¼200 s, up to 7 exchanges). The exchanges are reversible and the methyl groups on the cation are also observed to exchange with the added R3Al species. These results point to the reactive components of MAO having a structure that deviates significantly from the cage-like motifs studied to date.

7.
Dalton Trans ; 47(46): 16729-16736, 2018 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-30427005

RESUMO

A series of complexes with the formulae [(BIMEt3)SnF4-x][OTf]x with x = 1-4 has been synthesized by successive fluoride abstraction from SnF4 with TMSOTf in the presence of the tetradentate nitrogen donor BIMEt3 (tris ((1-ethyl-benzoimidazol-2-yl)methyl)amine). Single crystal X-ray diffraction and heteronuclear NMR spectroscopic analysis provided insight into these new main group cations. Electrospray ionization mass spectrometric analysis on solutions containing the different salts allowed for successful detection of the cations [(BIMEt3)SnF]3+, [(BIMEt3)SnF2]2+ and [(BIMEt3)SnF3]+.

8.
Chemistry ; 24(21): 5506-5512, 2018 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-29342315

RESUMO

The anions formed from methylalumoxane (MAO) and suitable donors (e.g. octamethyltrisiloxane) are amenable to mass spectrometric (MS) analysis. Their composition as deduced from this data allows direct insight into the chemical transformations of their neutral precursors. One such process is oxidation, which is well-known to be facile for MAO without any clear idea of what actually occurs at a molecular level. Addition of O2 to MAO results in immediate gelation, but MS analysis reveals no corresponding change to the composition of the principal oligomeric anions. A slow (hours) reaction does occur that involves net incorporation of Me2 AlOMe into the oligomeric anions, and the identities of the OMe-containing anions were confirmed by 1 H NMR spectroscopy, MS/MS analysis, and addition of an authentic sample of Me2 AlOMe to MAO. The result tallies with the fact that addition of O2 to MAO produces Me2 AlOMe from free Me3 Al which eventually leads to formation of oxidized MAO oligomers and changes in ion abundance. Aging of the oxygenated MAO results in further growth of the oligomers similar to that of the non-oxidized species. Mass spectrometric analysis therefore reveals useful insights into the environmental history of a given MAO batch.

9.
Inorg Chem ; 57(1): 457-461, 2018 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-29219302

RESUMO

Reduction of red Cp2TiCl2 (Cp = cyclopentadienyl) with zinc dust in acetonitrile produces a blue solution of [Cp2Ti(NCMe)2]+, which when exposed to air rapidly discolors to bright yellow. This behavior makes the blue solution a handy visual indicator for the presence of oxygen, but the chemistry is considerably more complicated than the primary colors suggest at first glance. Real-time mass spectrometric and colorimetric analysis reveals that oxidation from Ti(III) to Ti(IV) produces a host of oxygen-containing complexes, whose appearance parallels the observed color changes.

10.
Analyst ; 142(17): 3278-3284, 2017 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-28792015

RESUMO

Bromobenzyl compounds react selectively with phenols via the Williamson ether synthesis. An imidazolium charge-tagged bromobenzyl compound can be used to reveal phenol impurities in jet fuel by analysis via electrospray ionization mass spectrometry. The complex matrix as revealed by Cold EI GC/MS analysis is reduced to a few simple sets of compounds in the charge-tagged ESI mass spectrum, primarily substituted phenols and thiols. Examination of jet fuels treated by different refinery methods reveals the efficacy of these approaches in removing these contaminants.

11.
Chem Commun (Camb) ; 53(5): 854-856, 2017 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-27991623

RESUMO

A combination of UV-Vis spectroscopy and electrospray ionization mass spectrometry is used for real-time monitoring of Pd2(dba)3 activation with sulfonated versions of PPh3 and Buchwald-type ligands. This provides insight into the effect of ligand and preparation conditions on activation and allows for establishment of rational activation protocols.

12.
Analyst ; 141(19): 5520-6, 2016 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-27390787

RESUMO

A simple chemical derivatization technique was developed for electrospray ionization mass spectrometry (ESI-MS) in which thiols and disulfides may be selectively analyzed in a complex matrix and easily characterized. These reagents enhance detection of thiols and disulfides solely due to the nature of the charge-tag derivatization agent and therefore does not require an isotopically labelled substrate. The charged disulfides readily and exclusively react with thiols in a complex matrix in a short amount of time. Furthermore, the synthesis of these reagents is simple and results in a highly pure and stable reagent. The efficacy of this reaction was demonstrated using on-line monitoring, while the scope and usefulness of the reaction was demonstrated in petroleum fractions.

13.
Chem Sci ; 7(4): 2544-2552, 2016 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-28660025

RESUMO

A series of phosphinophosphonium cations ([R2PPMe3]+; R = Me, Et, i Pr, t Bu, Cy, Ph and N i Pr2) have been prepared and examined by collision-induced dissociation (CID) to determine the fragmentation pathways accessible to these prototypical catena-phosphorus cations in the gas-phase. Experimental evidence for fission of P-P and P-E (E = P, C) bonds, and ß-hydride elimination has been obtained. Comparison of appearance potentials for the P-P bond dissociation fragments [R2P]+ (P-P heterolysis) and [PMe3]+˙ (P-P homolysis) shows that heterolytic P-P cleavage is more sensitive than P-P homolysis towards changes in substitution at the trivalent phosphorus center. The facility of ß-hydride elimination increases with the steric bulk of R in [R2PPMe3]+. A density functional theory (DFT) study modelling these observed processes in gas-phase, counterion- and solvent-free conditions, to mimic the mass spectrometric environment, was performed for derivatives of [R2PPMe3]+ (R = Me, Et, i Pr, t Bu, Ph and N i Pr2), showing good agreement with experimental trends. The unusual observation of both homolytic and heterolytic cleavage pathways for the P-P and P-C bonds reveals new insight into the fundamental aspects of bonding in monocations and undermines the use of simplistic bonding models.

14.
Dalton Trans ; 44(47): 20367-75, 2015 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-26469767

RESUMO

The mechanism of the Sonogashira reaction in methanol was studied in detail using pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS). Several key intermediates were identified and their structures were assigned by MS/MS studies. Cationic and anionic charged-tagged substrates were employed to look into the mechanism of this reaction from variety of angles. A reverse kinetic isotope effect was observed in which the reaction rate is accelerated in deuterated solvents (kH/kD = 0.6). The reaction was found to be zero order with respect to the aryl iodide and first order with respect to the phenylacetylene. A Hammett parameter of ρ = 1.4 indicates that the reaction is more favorable for aryl iodides with para EWGs. No evidence of product inhibition, dimerization of palladium catalyst, or agglomeration were observed. However, catalyst decomposition was inferred from a non-zero intercept in the plot of catalyst loading versus reaction rate. Monitoring the reaction by PSI-ESI-(-)MS on neutral and negatively charged substrates at variety of concentrations and conditions did not reveal any detectable anionic palladium complexes. Likewise no evidence of carbopalladation and relevant intermediates in the absence of a base was observed.

15.
Chemistry ; 21(43): 15174-87, 2015 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-26394809

RESUMO

Complexation of 1,4-phenylenebis(methylene) diisonicotinate, L1, with cis-protected Pd(II) components, [Pd(L')(NO3 )2 ], in an equimolar ratio yielded binuclear complexes, 1 a-d of [Pd2 (L')2 (L1)2 ](NO3 )4 formulation where L' stands for ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bpy), and phenanthroline (phen). The combination of 4,4'-bipyridine, L2, with the cis-protected Pd(II) units is known to yield molecular squares, 2 a-d. However, 2 b-d coexist with the corresponding molecular triangles, 3 b-d. Combination of an equivalent each of the ligands L1 and L2 with two equivalents of cis-protected Pd(II) components in DMSO resulted in the D-shaped heteroligated complexes [Pd2 (L')2 (L1)(L2)](NO3 )4 , 4 a-d. Two units of the D-shaped complexes interlock, in a concentration dependent fashion, to form the corresponding [2]catenanes [Pd2 (L')2 (L1)(L2)]2 (NO3 )8 , 5 a-d under aqueous conditions. Crystal structures of the macrocycle [Pd2 (tmeda)2 (L1)(L2)](PF6 )4 , 4 b'', and the catenane [Pd2 (bpy)2 (L1)(L2)]2 (NO3 )8 , 5 c, provide unequivocal support for the proposed molecular architectures.

16.
Chemistry ; 21(7): 2980-91, 2015 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-25556910

RESUMO

Electrospray-ionization mass spectrometric studies of poly(methylaluminoxane) (MAO) in the presence of [Cp2 ZrMe2 ], [Cp2 ZrMe(Cl)], and [Cp2 ZrCl2 ] in fluorobenzene (PhF) solution are reported. The results demonstrate that alkylation and ionization are separate events that occur at competitive rates in a polar solvent. Furthermore, there are significant differences in ion-pair speciation that result from the use of metallocene dichloride complexes in comparison to alkylated precursors at otherwise identical Al/Zr ratios. Finally, the counter anions that form are dependent on the choice of precursor and Al/Zr ratio; halogenated aluminoxane anions [(MeAlO)x (Me3 Al)y-z (Me2 AlCl)z Me](-) (z=1, 2, 3…︁) are observed using metal chloride complexes and under some conditions may predominate over their non-halogenated precursors [(MeAlO)x (Me3 Al)y Me](-) . Specifically, this halogenation process appears selective for the anions that form in comparison to the neutral components of MAO. Only at very high Al/Zr ratios is the same "native" anion distribution observed when using [Cp2 ZrCl2 ] when compared with [Cp2 ZrMe2 ]. Together, the results suggest that the need for a large excess of MAO when using metallocene dichloride complexes is a reflection of competitive alkylation vs. ionization, the persistence of unreactive, homodinuclear ion pairs in the case of [Cp2 ZrCl2 ], as well as a change in ion pairing resulting from modification of the anions formed at lower Al/Zr ratios. Models for neutral precursors and anions are examined computationally.

17.
Chemistry ; 20(15): 4273-83, 2014 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-24590571

RESUMO

A series of thioether-functionalised imidazolium salts have been prepared and characterized. Subsequent reaction of the thioether-functionalised imidazolium salts with iodomethane affords imidazolium-sulfonium salts composed of doubly charged cations and two different anions. Imidazolium-sulfonium salts containing a single anion type are obtained either by a solvent extraction method or by anion exchange. The imidazolium-sulfonium salts undergo a methyl-transfer reaction on exposure to water, giving rise to a new, singly charged imidazolium salt with iodide introduced at the 2-position of the imidazolium ring. Crystal structures of some of the imidazolium-sulfonium salts were determined by X-ray crystallography providing the topology of the interactions between the dications and the anions. Electrospray ionization mass spectrometry and quantum-chemical calculations were used to rationalise the relative strength of these interactions.

18.
J Mass Spectrom ; 49(1): 1-8, 2014 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-24446256

RESUMO

Electrospray ionization mass spectrometry (ESI-MS) is a soft ionization technique commonly coupled with liquid or gas chromatography for the identification of compounds in a one-time view of a mixture (for example, the resulting mixture generated by a synthesis). Over the past decade, Scott McIndoe and his research group at the University of Victoria have developed various methodologies to enhance the ability of ESI-MS to continuously monitor catalytic reactions as they proceed. The power, sensitivity and large dynamic range of ESI-MS have allowed for the refinement of several homogenous catalytic mechanisms and could potentially be applied to a wide range of reactions (catalytic or otherwise) for the determination of their mechanistic pathways. In this special feature article, some of the key challenges encountered and the adaptations employed to counter them are briefly reviewed.

19.
Chem Commun (Camb) ; 49(98): 11488-90, 2013 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-24175316

RESUMO

The rate of hydrodehalogenation of aryl iodides with a palladium catalyst in methanol exhibits a strong primary kinetic isotope effect from both CD3OD and CH3OD, suggesting that deprotonation plays a major role in the mechanism.

20.
Dalton Trans ; 42(31): 11312-8, 2013 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-23817327

RESUMO

Continuous monitoring using electrospray ionisation mass spectrometry (ESI-MS) shows that Wilkinson's catalyst hydrogenates a charge-tagged alkyne to the corresponding alkene, and at only a marginally slower rate, to the alkane. No rhodium-containing intermediates were observed during the reaction, consistent with the established mechanism which points at the initial dissociation of triphenylphosphine from Rh(PPh3)3Cl as being the key step in the reaction. A numerical model was constructed that the closely matched the experimental data, and correctly predicted the response of the reaction to the addition of excess PPh3.

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