The coupling of a simple microreactor to an atmospheric pressure ion source, such as electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI), allows the investigation of reactions in solution by mass spectrometry. The tris(p-bromophenyl)aminium hexachloroantimonate (1(*)(+)SbCl(6)(-))-initiated reactions of phenylvinylsulfide (2) and cyclopentadiene (3) and of trans-anethole (5) and isoprene (6) and the dimerization of 1,3-cyclohexadiene (8) to give the respective Diels-Alder products were studied. These preparatively interesting reactions proceed as radical cation chain reactions via the transient radical cations of the respective dienophiles and of the respective Diels-Alder addition products. These radical cations could be detected directly and characterized unambiguously in the reacting solution by ESI-MS-MS. The identity was confirmed by comparison with MS-MS spectra of the authentic radical cations obtained by APCI-MS and by CID experiments of the corresponding molecular ions generated by EI-MS. In addition, substrates and products could be monitored easily in the reacting solution by APCI-MS.
Electrospray ionization mass spectrometry (ESI-MS) is a novel tool for the investigation of chemical reactions in solution and for the direct detection and identification of reactive intermediates. The tributyltin hydride mediated addition of tert-butyl iodide to dimethyl 2-cyclohexyl-4-methyleneglutarate (2) in the presence of Lewis acids was investigated by ESI-MS using a microreactor coupled on-line to an ESI mass spectrometer. For the first time we have been able to show that transient radicals in radical chain reactions can be detected unambiguously under steady-state conditions in the reaction solution and can be characterized by ESI-MS/MS and accurate mass determination. The detection of different heterodimer radical complexes by ESI-MS/MS has provided new insights into the mechanism of Lewis acid controlled radical chain reactions. Dimeric chelate complexes of glutarates, such as 2 and 3, and Lewis acids, like Sc(OTf)3, MgBr2OEt2 and LiClO4, were observed as well as higher aggregates with additional equivalents of Lewis acid. Evidence for a dynamic equilibrium of the complexes in solution was found by NMR spectroscopy. The ESI-MS investigation of the chelation of glutarate 2 with various Lewis acids has led to the conclusion that the tendency for Lewis acids to form dimeric chelate complexes and higher aggregates has an important effect on the stereoselective outcome of the radical reactions.
This paper focuses on complexes of the N-heterocyclic carbene (NHC) 1-Np, which contains a 1,1Ј-ferrocenediyl backbone and neopentyl substituents at the N atoms flanking the divalent C atom. 1-Np is a ring-expanded NHC with a ring size of six atoms. The square-planar group 10 metal com-trans-[PdCl 2 (1-Np) 2 ] and trans-[NiCl 2 (1-Np)(PPh 3 )] have been prepared by the reaction of 1-Np with trans-[PdCl 2 (PhCN) 2 ], [PdCl 2 (PPh 3 ) 2 ], cis-[PdCl 2 (COD)] (COD = cycloocta-1,5diene) and [NiCl 2 (PPh 3 ) 2 ], respectively. In addition, the carbene-borane adduct 1-Np-BF 3 has been obtained by serendipity. All new compounds have been structurally characterised by single-crystal X-ray diffraction, which demonstrates the pronounced trans influence of 1-Np. 1-Np has been com- [a]
Microwave (MW) irradiation was successfully employed to convert aromatic and heteroaromatic aldehydes and ketones efficiently to the corresponding dibromoolefins. Exemplified by the successful dibromoolefination of traditionally inert pyridyl‐flanked carbonyls, MW activation significantly broadens the scope of this valuable transformation, although some limitations especially with electron‐rich aromatic ketone derivatives remain.
Neodymium-di-(2-ethylhexyl) phosphoric acid (DEHPA) species forming in the organic phase during solvent extraction of neodymium with solutions of DEHPA have been studied. Two samples were prepared: one with a low molar ratio of neodymium to DEHPA, which is liquid and clear, and the other with a high molar ratio of neodymium to DEHPA (complete loading), which has the consistency of a gel. Electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometric investigations show numerous compounds, in addition to the generally assumed species dimeric DEHPA and Nd(DEHPиDEHPA) 3 , in the liquid sample. The nuclear magnetic resonance (NMR) spectroscopic investigation of pure DEHPA and of a completely loaded sample confirm the formula of pure DEHPA and of the organic part of Nd(DEHP) 3 . Furthermore, chemical analysis of a dried, completely loaded sample also proves the existence of the species Nd(DEHP) 3 . Results of X-ray powder diffraction measurements of this sample agree well with literature data.
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