Characterization of selected organometallic compounds by electrospray ionization- and matrix-assisted laser desorption/ionization-mass spectrometry using different types of instruments: Possibilities and limitations.

RATIONALE: Organometallic compounds are becoming increasingly important in their industrial application as catalysts. Mass spectrometry is an essential tool for the structural confirmation of such organometallics. Because the analysis of this class of molecules can be challenging, the ionization behavior and structural confirmation of selected transition metal catalysts are described in this work. METHODS: The transition metal catalysts investigated were analyzed using classical vacuum MALDI reflectron TOF-MS as well as intermediate pressure matrix-assisted laser desorption/ionization quadrupole time-of-flight mass spectrometry (MALDI QTOF-MS). Obtained mass spectra were compared with electrospray ionization MS (ESI-MS) already established for organometallic compounds, utilizing a QTOF mass spectrometer here. In addition, various sample preparations, including two selected MALDI matrices (trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile and 2,2':5',2″-terthiophene) with different solvent combinations for MALDI-MS measurements, were investigated in detail with respect to their correct isotope distribution of the molecular ions observed. RESULTS: All investigated organometallic compounds were successfully identified by vacuum and intermediate pressure MALDI-MS. Accurate masses of ions related to molecular ion species (e.g., [M-Cl]+ , [M]+ , and [M + Na]+ ) could be determined by MALDI QTOF-MS measurements with a mass error of less than ±5 ppm for all compounds. Both investigated MALDI matrices performed equally on both instruments. The impact of the analyte/matrix solvent mixtures turned out to be crucial for a successful analysis of the investigated compounds. In contrast, ESI QTOF-MS yielded masses of ions related to molecular ion species in favorable cases. CONCLUSIONS: The use of MALDI-MS for the structural confirmation of organometallic compounds is still not widely used. Nevertheless, this work showed that this analytical technique does have some benefits. The analysis of neutral catalysts proves to be quite useful, concluding that this technique provides a complement and/or an alternative to ESI-MS.

Fluorescence signal of proteins in birch pollen distorted within its native matrix: Identification of the fluorescence suppressor quercetin-3-O-sophoroside.

The properties of biogenic aerosol strongly depend on the particle's proteinaceous compounds. Proteins from primary biological aerosol particles (PBAPs) can cause allergic reactions in the human respiratory system or act as ice and condensation nuclei in clouds. Consequently, these particles have high impact on human health and climate. The detection of biogenic aerosol is commonly performed with fluorescence-based techniques. However, many PBAPs (i.e., pollen of birch, mugwort, or ragweed) show weak or rather low fluorescence signals in the particular protein region (λex ~ 255-280 nm, λem ~ 280-350 nm). We hypothesize that the fluorescence signal of proteins present in birch pollen is being distorted within its native matrix. In this study, we conducted in vitro quenching experiments and employed UV/Vis spectroscopy, capillary zone electrophoresis (CZE), liquid chromatography (LC), electrospray ionization mass spectrometry (ESI-MS), and multistage MS (MS2 and MS3) to target major components in birch pollen washing water (BPWW) possibly quenching the fluorescence activity of proteins and thus explaining the lack of corresponding protein fluorescent signals. We identified quercetin-3-O-sophoroside (Q3OS, MW 626 g mol-1) to be the main UV/Vis absorbing component in BPWW. Our results point out that Q3OS suppresses the fluorescence of proteins in our samples predominantly due to inner filter effects. In general, when applying fluorescence spectroscopy to analyze and detect PBAPs in the laboratory or the atmosphere, it is important to critically scrutinize the obtained spectra.

Manganese-Catalyzed Dehydrogenative Silylation of Alkenes Following Two Parallel Inner-Sphere Pathways.

We report on an additive-free Mn(I)-catalyzed dehydrogenative silylation of terminal alkenes. The most active precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate which undergoes rapid Si-H bond cleavage of the silane HSiR3 forming the active 16e- Mn(I) silyl catalyst [Mn(dippe)(CO)2(SiR3)] together with liberated butanal. A broad variety of aromatic and aliphatic alkenes was efficiently and selectively converted into E-vinylsilanes and allylsilanes, respectively, at room temperature. Mechanistic insights are provided based on experimental data and DFT calculations revealing that two parallel reaction pathways are operative: an acceptorless reaction pathway involving dihydrogen release and a pathway requiring an alkene as sacrificial hydrogen acceptor.

The influence of the specific growth rate on the lipid composition of Sulfolobus acidocaldarius.

Archaeal lipids are constituted of two isoprenoid chains connected via ether bonds to glycerol in the sn-2, 3 position. Due to these unique properties archaeal lipids are significantly more stable against high temperature, low pH, oxidation and enzymatic degradation than conventional lipids. Additionally, in members of the phylum Crenarchaeota condensation of two (monopolar) archaeal diether lipids to a single (bipolar) tetraether lipid as well as formation of cyclopentane rings in the isoprenoid core strongly reduce permeability of the crenarchaeal membranes. In this work we show that the Crenarchaeum Sulfolobus acidocaldarius changes its lipid composition as reaction to a shift in growth rate caused by nutrient limitation. We thereby identified a novel influencing factor for the lipid composition of S. acidocaldarius and were able to determine the effect of this factor on the lipid composition by using MALDI-MS for the semi-quantification of an archaeal lipidome: a shift in the specific growth rate during a controlled continuous cultivation of S. acidocaldarius from 0.011 to 0.035 h-1 led to a change in the ratio of diether to tetraether lipids from 1:3 to 1:5 and a decrease of the average number of cyclopentane rings from 5.1 to 4.6.

Study of metabolism and identification of productive regions in filamentous fungi via spatially resolved time-of-flight secondary ion mass spectrometry.

Filamentous fungi are well-established production hosts that feature a strong interconnection between morphology, physiology, and productivity. For penicillin production in Penicillium chrysogenum, industrial processes frequently favor a pellet morphology comprising compact hyphal agglomerates. Inherently these tightly packed entanglements lead to inactive, degrading sections within the pellet's core because of limitations. Optimal process design requires detailed knowledge of the nature of the limitations and localization of productive zones in the biomass, which is generally obtainable through modeling and complex analytical methods such as oxygen microelectrode and histological investigations. Methods that combine physiological and morphological insight are crucial yet scarce for filamentous fungi. In this study, we used time-of-flight secondary ion mass spectrometry in combination with oxygen and glucose tracer substrates, requiring little effort for sample preparation and measurement. Our method is capable of analyzing oxygen and substrate uptake in various morphological structures by the use of 18O as a tracer. In parallel, we can assess productive biomass regions through identification of penicillin mass fragments to simultaneously study oxygen diffusion, substrate incorporation, and productive biomass sections.

Investigations of the generality of quaternary ammonium salts as alkylating agents in direct C-H alkylation reactions: solid alternatives for gaseous olefins.

C-H alkylation reactions using short chain olefins as alkylating agents could be operationally simplified on the lab scale by using quaternary ammonium salts as precursors for these gaseous reagents: Hofmann elimination delivers in situ the desired alkenes with the advantage that the alkene concentration in the liquid phase is high. In case a catalytic system did not tolerate the conditions for Hofmann elimination, a very simple spatial separation of both reactions, Hofmann elimination and direct alkylation, was achieved to circumvent possible side reactions or catalyst deactivation. Additionally, the truly catalytically active species of a rhodium(i) mediated alkylation reaction could be identified by using this approach.

In-depth analysis of crocetin ester glycosides from dried/processed stigmas of Crocus sativus L. by HPLC-ESI-MSn (n = 2, 3).

INTRODUCTION: Saffron stigmas from Crocus sativus L. (Iridaceae) are used as a drug in folk medicine, as a food additive and as a dying agent for at least 3500 years. Despite this long-term use the chemical composition of saffron seems still to be not fully known. OBJECTIVE: An analytical strategy for detailed investigations of aqueous saffron extract is developed based on reverse-phase high-performance liquid chromatography electrospray ionisation (HPLC-ESI) multistage mass spectrometry (MSn ) for crocins. METHODS: Commercially available stigmas are analysed by reverse-phase HPLC in combination with ESI/three-dimensional (3D)-ion trap mass spectrometry (MS) and MSn (n = 2 and 3). Sodium chloride is added to the analyte solution ready for injection to promote abundant [M + Na]+ adduct ions of crocins, being ideal precursor ions for low-energy collision-induced dissociation (CID)-MS2/3 . RESULTS: This strategy allows the detailed structural elucidation of known as well as previously unknown crocin derivatives (molecular mass of the aglycon, oligosaccharide chain length and linkage determination). The two isomeric trisaccharide substituents neapolitanose and gentiotriose are distinguished based on linkage-specific cross-ring cleavage for the first time. Furthermore, crocins containing up to six hexose units are also observed. Five novel crocin ester glycosides shifted by a mass difference of -40 Da indicate the presence of the here newly described C17 -aglycon, termed norcrocetin (crocetin = C20 ). CONCLUSIONS: These findings indicate the action of at least two different carotenoid cleavage dioxygenases (CCD2 and tentatively CCD4) during biosynthesis of this new bis-apocarotenoid aglycon (norcrocetin) and the existence of even higher glycosylated crocin derivatives at trace level.

A laser desorption ionization/matrix-assisted laser desorption ionization target system applicable for three distinct types of instruments (LinTOF/curved field RTOF, LinTOF/RTOF and QqRTOF) with different performance characteristics from three vendors.

RATIONALE: We have developed a target system which enables the use of only one target (i.e. target preparation set) for three different laser desorption ionization (LDI)/matrix-assisted laser desorption ionization (MALDI) mass spectrometric instruments. The focus was on analysing small biomolecules with LDI for future use of the system for the study of meteorite samples (carbonaceous chondrites) using devices with different mass spectrometric performance characteristics. METHODS: Three compounds were selected due to their potential presence in meteoritic chondrites: tryptophan, 2-deoxy-d-ribose and triphenylene. They were prepared (with and without MALDI matrix, i.e. MALDI and LDI) and analysed with three different mass spectrometers (LinTOF/curved field RTOF, LinTOF/RTOF and QqRTOF). The ion sources of two of the instruments were run at high vacuum, and one at intermediate pressure. Two devices used a laser wavelength of 355 nm and one a wavelength of 337 nm. RESULTS: The developed target system operated smoothly with all devices. Tryptophan, 2-deoxy-d-ribose and triphenylene showed similar desorption/ionization behaviour for all instruments using the LDI mode. Interestingly, protonated tryptophan could be observed only with the LinTOF/curved field RTOF device in LDI and MALDI mode, while sodiated molecules were observed with all three instruments (in both ion modes). Deprotonated tryptophan was almost completely obscured by matrix ions in the MALDI mode whereas LDI yielded abundant deprotonated molecules. CONCLUSIONS: The presented target system allowed successful analyses of the three compounds using instruments from different vendors with only one preparation showing different analyser performance characteristics. The elemental composition with the QqRTOF analyser and the high-energy 20 keV collision-induced dissociation fragmentation will be important in identifying unknown compounds in chondrites.

Formation of Mono Oxo Molybdenum(IV) PNP Pincer Complexes: Interplay between Water and Molecular Oxygen.

The synthesis of cationic mono oxo MoIV PNP pincer complexes of the type [Mo(PNPMe-iPr)(O)X]+ (X = I, Br) from [Mo(PNPMe-iPr)(CO)X2] is described. These compounds are coordinatively unsaturated and feature a strong Mo≡O triple bond. The formation of these complexes proceeds via cationic 14e intermediates [Mo(PNPMe-iPr)(CO)X]+ and requires both molecular oxygen and water. ESI MS measurements with 18O labeled water (H2 18O) and molecular oxygen (18O2) indicates that water plays a crucial role in the formation of the Mo≡O bond. A plausible mechanism based on DFT calculations is provided. The X-ray structure of [Mo(PNPMe-iPr)(O)I]SbF6 is presented.

Manganese-Catalyzed Aminomethylation of Aromatic Compounds with Methanol as a Sustainable C1 Building Block.

This study represents the first example of a manganese-catalyzed environmentally benign, practical three-component aminomethylation of activated aromatic compounds including naphtols, phenols, pyridines, indoles, carbazoles, and thiophenes in combination with amines and MeOH as a C1 source. These reactions proceed with high atom efficiency via a sequence of dehydrogenation and condensation steps which give rise to selective C-C and C-N bond formations, thereby releasing hydrogen and water. A well-defined hydride Mn(I) PNP pincer complex, recently developed in our laboratory, catalyzes this process in a very efficient way, and a total of 28 different aminomethylated products were synthesized and isolated yields of up to 91%. In a preliminary study, a related Fe(II) PNP pincer complex was shown to catalyze the methylation of 2-naphtol rather than its aminomethylation displaying again the divergent behavior of isoelectronic Mn(I) and Fe(II) PNP pincer systems.

Processed stigmas of Crocus sativus L. imaged by MALDI-based MS.

The processed, i.e. dried under certain conditions, stigmas of Crocus sativus L. are one of the most expensive plant parts used commercially. For the color, aroma and biological activity a very complex mixture of glycolipids termed crocins are responsible. Therefore studying structural composition and distribution in the commercial plant material is of great interest. We showed successfully the application of a MALDI-based mass spectrometric imaging (MSI) approach for stigmas towards different crocin species. MSI opens up the investigation of processed plant materials in various fields allowing studying the processing in detail as well as adulteration attempts (which are quite frequent due to the price of the material). Furthermore, we could demonstrate that a similar number of crocins present in stigmas could be detected by MALDI MSI compared to the classical approach of analyzing the solvent-extract of stigmas by MALDI-MS.

Inositol-phosphodihydroceramides in the periodontal pathogen Tannerella forsythia: Structural analysis and incorporation of exogenous myo-inositol.

BACKGROUND: Unique phosphodihydroceramides containing phosphoethanolamine and glycerol have been previously described in Porphyromonas gingivalis. Importantly, they were shown to possess pro-inflammatory properties. Other common human bacteria were screened for the presence of these lipids, and they were found, amongst others, in the oral pathogen Tannerella forsythia. To date, no detailed study into the lipids of this organism has been performed. METHODS: Lipids were extracted, separated and purified by HPTLC, and analyzed using GC-MS, ESI-MS and NMR. Of special interest was how T. forsythia acquires the metabolic precursors for the lipids studied here. This was assayed by radioactive and stable isotope incorporation using carbon-14 and deuterium labeled myo-inositol, added to the growth medium. RESULTS: T. forsythia synthesizes two phosphodihydroceramides (Tf GL1, Tf GL2) which are constituted by phospho-myo-inositol linked to either a 17-, 18-, or 19-carbon sphinganine, N-linked to either a branched 17:0(3-OH) or a linear 16:0(3-OH) fatty acid which, in Tf GL2, is, in turn, ester-substituted with a branched 15:0 fatty acid. T. forsythia lacks the enzymatic machinery required for myo-inositol synthesis but was found to internalize inositol from the medium for the synthesis of both Tf GL1 and Tf GL2. CONCLUSION: The study describes two novel glycolipids in T. forsythia which could be essential in this organism. Their synthesis could be reliant on an external source of myo-inositol. GENERAL SIGNIFICANCE: The effects of these unique lipids on the immune system and their role in bacterial virulence could be relevant in the search for new drug targets.

Sustainable Synthesis of Quinolines and Pyrimidines Catalyzed by Manganese PNP Pincer Complexes.

This study represents the first example an environmentally benign, sustainable, and practical synthesis of substituted quinolines and pyrimidines using combinations of 2-aminobenzyl alcohols and alcohols as well as benzamidine and two different alcohols, respectively. These reactions proceed with high atom efficiency via a sequence of dehydrogenation and condensation steps that give rise to selective C-C and C-N bond formations, thereby releasing 2 equiv of hydrogen and water. A hydride Mn(I) PNP pincer complex recently developed in our laboratory catalyzes this process in a very efficient way. A total of 15 different quinolines and 14 different pyrimidines were synthesized in isolated yields of up to 91 and 90%, respectively.

Divergent Coupling of Alcohols and Amines Catalyzed by Isoelectronic Hydride Mn(I) and Fe(II) PNP Pincer Complexes.

Herein, we describe an efficient coupling of alcohols and amines catalyzed by well-defined isoelectronic hydride Mn(I) and Fe(II) complexes, which are stabilized by a PNP ligand based on the 2,6-diaminopyridine scaffold. This reaction is an environmentally benign process implementing inexpensive, earth-abundant non-precious metal catalysts, and is based on the acceptorless alcohol dehydrogenation concept. A range of alcohols and amines including both aromatic and aliphatic substrates were efficiently converted in good to excellent isolated yields. Although in the case of Mn selectively imines were obtained, with Fe-exclusively monoalkylated amines were formed. These reactions proceed under base-free conditions and required the addition of molecular sieves.

A Cobalt(I) Pincer Complex with an η(2) -C(aryl)-H Agostic Bond: Facile C-H Bond Cleavage through Deprotonation, Radical Abstraction, and Oxidative Addition.

The synthesis and reactivity of a Co(I) pincer complex [Co(ϰ(3) P,CH,P-P(CH)P(NMe) -iPr)(CO)2](+) featuring an η(2)-C(aryl)-H agostic bond is described. This complex was obtained by protonation of the Co(I) complex [Co(PCP(NMe) -iPr)(CO)2]. The Co(III) hydride complex [Co(PCP(NMe) -iPr)(CNtBu)2(H)](+) was obtained upon protonation of [Co(PCP(NMe) -iPr)(CNtBu)2]. Three ways to cleave the agostic C-H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C-H bond cleavage) and reformation of [Co(PCP(NMe) -iPr)(CO)2]. Second, C-H bond cleavage is achieved upon exposure of [Co(ϰ(3)P,CH,P-P(CH)P(NMe) -iPr)(CO)2](+) to oxygen or TEMPO to yield the paramagnetic Co(II) PCP complex [Co(PCP(NMe) -iPr)(CO)2](+). Finally, replacement of one CO ligand in [Co(ϰ(3) P,CH,P-P(CH)P(NMe) -iPr)(CO)2](+) by CNtBu promotes the rapid oxidative addition of the agostic η(2) -C(aryl)-H bond to give two isomeric hydride complexes of the type [Co(PCP(NMe) -iPr)(CNtBu)(CO)(H)](+).

Collision-induced dissociation of aminophospholipids (PE, MMPE, DMPE, PS): an apparently known fragmentation process revisited.

A new type of low-mass substituted 4-oxazolin product ions of [M + H](+) precursor ions of aminophospholipids (glycerophosphatidylethanolamine, glycerophosphatidyl-N-methylethanolamine, glycerophosphatidyl-N,N-dimethylethanolamine, glycerophosphatidylserine) resulting from high-energy collision-induced dissociation (matrix-assisted laser desorption/ionization time-of-flight/reflectron time-of-flight mass spectrometry) and low-energy collision-induced dissociation (e.g., electrospray ionization quadrupole reflectron time-of-flight mass spectrometry) with accurate mass determination is described; these were previously misidentified as CHO-containing radical cationic product ions. The mechanism for the formation of these ions is proposed to be via rapid loss of water followed by cyclization to an 11-membered-ring transition state for the sn-1 fatty acid substituent and to a ten-membered-ring transition state for the sn-2 fatty acid substituent, and via final loss of monoacylglycerol phosphate, leading to substituted 4-oxazolin product ions. The minimum structural requirement for this interesting skeletal rearrangement fragmentation is an amino group linked to at least one hydrogen atom (i.e., ethanolamine, N-methylethanolamine, serine). Therefore, N,N-dimethylethanolamine derivates do not exhibit this type of fragmentation. The analytical value of these product ions is given by the fact that by post source decay and particularly high-energy collision-induced dissociation achieved via matrix-assisted laser desorption/ionization time-of-flight/reflectron time-of-flight mass spectrometry, the sn-2-related substituted 4-oxazolin product ion is always significantly more abundant than the sn-1-related one, which is quite helpful for detailed structural analysis of complex lipids. All other important product ions found are described in detail (following our previously published glycerophospholipid product ion nomenclature; Pittenauer and Allmaier, Int. J. Mass. Spectrom. 301:90-1012, 2011).

On the Question of Site-Selective Ligand Exchange in Carboxylate-Substituted Metal Oxo Clusters.

Reaction of [Ti4Zr4O6(OBu)4(OMc)16] (OMc = methacrylate) with acetylacetone (acacH) resulted in dissection of the cluster and formation of [Ti(OBu)2(acac)2] and the smaller cluster [Ti2Zr4O4(OMc)16]. In contrast, the same reaction with [Zr6O4(OH)4(OOCR)12]2·6RCOOH (R = Et, CH2CH=CH2) led to site-selective substitution of two carboxylate ligands and formation of isostructural [Zr6O4(OH)4(OOCR)12-x (acac) x ]2·6RCOOH (x ≤ 1).

Ultrahigh-performance liquid chromatography/electrospray ionization linear ion trap Orbitrap mass spectrometry of antioxidants (amines and phenols) applied in lubricant engineering.

RATIONALE: For the qualification and quantification of antioxidants (aromatic amines and sterically hindered phenols), most of them applied as lubricant additives, two ultrahigh-performance liquid chromatography (UHPLC) electrospray ionization mass spectrometric methods applying the positive and negative ion mode have been developed for lubricant design and engineering thus allowing e.g. the study of the degradation of lubricants. METHODS: Based on the different chemical properties of the two groups of antioxidants, two methods offering a fast separation (10 min) without prior derivatization were developed. In order to reach these requirements, UHPLC was coupled with an LTQ Orbitrap hybrid tandem mass spectrometer with positive and negative ion electrospray ionization for simultaneous detection of spectra from UHPLC-high-resolution (HR)-MS (full scan mode) and UHPLC-low-resolution linear ion trap MS(2) (LITMS(2)), which we term UHPLC/HRMS-LITMS(2). RESULTS: All 20 analytes investigated could be qualified by an UHPLC/HRMS-LITMS(2) approach consisting of simultaneous UHPLC/HRMS (elemental composition) and UHPLC/LITMS(2) (diagnostic product ions) according to EC guidelines. Quantification was based on an UHPLC/LITMS(2) approach due to increased sensitivity and selectivity compared to UHPLC/HRMS. Absolute quantification was only feasible for seven analytes with well-specified purity of references whereas relative quantification was obtainable for another nine antioxidants. All of them showed good standard deviation and repeatability. CONCLUSIONS: The combined methods allow qualitative and quantitative determination of a wide variety of different antioxidants including aminic/phenolic compounds applied in lubricant engineering. These data show that the developed methods will be versatile tools for further research on identification and characterization of the thermo-oxidative degradation products of antioxidants in lubricants.

A complete series of halocarbonyl molybdenum PNP pincer complexes - Unexpected differences between NH and NMe spacers.

In the present study a complete series of seven-coordinate neutral halocarbonyl Mo(II) complexes of the type [Mo(PNPMe-Ph)(CO)2X2] (X = I, Br, Cl, F), featuring the new PNP pincer ligand N,N'-bis(diphenylphosphino)-N,N'-methyl-2,6-diaminopyridine (PNPMe-Ph), were prepared and fully characterized. The synthesis of these complexes was accomplished by different methodologies depending on the halide ligands. For X = I and Br, [Mo(PNPMe-Ph)(CO)2I2] and [Mo(PNPMe-Ph)(CO)2Br2] were obtained by reacting [Mo(PNPMe-Ph)(CO)3] with stoichiometric amounts of I2 and Br2, respectively. Alternatively, these complexes were obtained upon treatment of [MoX2(CO)3(CH3CN)2] (X = I, Br) with 1 equiv. of PNPMe-Ph. On the other hand, in the case of X = Cl, [Mo(PNPMe-Ph)(CO)2Cl2] was afforded by the reaction of [Mo(CO)4(µ-Cl)Cl]2 with 1 equiv. of PNPMe-Ph. The equivalent procedure also worked for X = Br. Finally, addition of 1 equiv. of 1-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate to [Mo(PNPMe-Ph)(CO)3] yielded the analogous fluorine complex [Mo(PNPMe-Ph)(CO)2F2]. The modification of the ligand scaffold by introducing a Me group instead of H changed the properties of the PNP-Ph ligand significantly. While in the present case exclusively neutral seven-coordinate complexes of the type [Mo(PNPMe-Ph)(CO)2X2] were obtained, with the parent PNP-Ph ligand, i.e., featuring NH spacers, cationic seven-coordinate complexes of the type [Mo(PNP-Ph)(CO)3X]X were afforded. DFT calculations indicated that the reactions are under thermodynamic control. The structures of representative complexes were determined by X-ray single crystal analyses.

Electrospray Ionization Tandem Mass Spectrometric Study of Selected Phosphine-Based Ligands for Catalytically Active Organometallics.

Selected organometallic compounds are nowadays extensively used as highly efficient catalysts in organic synthesis. A great variety of different ligand systems exists, of which phosphine-based ligands are a significant subgroup. While mass spectrometry, predominantly electrospray ionization mass spectrometry (ESI-MS), is a standard analytical technique for the identification of new ligands and their metal complexes, there is little information on the behavior of phosphine-based ligands/molecules by electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) at low collision energies (<100 eV) in the literature. Here, we report a study on the identification of typical product ions occurring in tandem mass spectra of selected phosphine-based ligand systems by ESI-CID-MS/MS. The influence on the fragmentation behavior of different backbones (pyridine, benzene, triazine) as well as different spacer groups (amine, methylamine, methylene), which are directly linked to the phosphine moiety, is investigated by tandem mass spectrometry. In addition, possible fragmentation pathways are elaborated based on the assigned masses in the tandem mass spectra with high-resolution accurate mass determination. This knowledge may be particularly useful in the future for the elucidation of fragmentation pathways for coordination compounds by MS/MS, where the studied compounds serve as building blocks.