Mass spectrometry trimers

A structurally related tetrameric macroheterocycle is compound 13 that is prepared in a one-pot synthesis (yield 64%) from salicylaldehyde and (3-aminophenyl)boronic acid in methanol (Fig. 4). Due to its insolubility it has been characterized only by mass spectrometry. If a substitutent is introduced at the imine function (R = Me, Ph), trimeric structures (14 and 15) are... 

Sanders (14) has exploited the strong and selective coordination of phosphine donor groups to Ru(II) to construct hetero-dimetallic porphyrin dimers (17, Fig. 5). An alkyne-phosphine moiety introduced on the periphery of a free base or metalloporphyrin (M = Zn or Ni) spontaneously coordinates to a Ru(II)(CO) porphyrin when the two porphyrins are mixed in a 1 1 ratio. Coordination is characterized by a downfield shift of the 31P resonance (A<531P = 19 ppm). There is no evidence of self-coordination of the zinc porphyrin at 10 6 m in toluene, there is no shift in the Soret band in the UV-Vis absorption spectrum. The Ni-Ru dimer was observed by MALDI-TOF mass spectrometry. Heating the Ru(II)CO porphyrin with 2 equivalents of the phosphine porphyrins led to quantitative formation of trimeric assemblies. 

Let us return to the thermal decomposition of Fe(CO)(l,3-C4H6)2. Once the calibration constant is known, the enthalpy of the net process 9.10 can be calculated as the product of s and the area (A + B). The next step is to correct this value to 298.15 K by using heat capacity data. This exercise is, however, complicated by the cyclobutadiene polymerization. Brown et al. analyzed the reaction products by mass spectrometry and found several oligomers, in particular the dimer (C4H6)2 and the trimer (C4H6)3 [163]. With such a mixture, it is difficult to ascribe the observed enthalpy change to a well-defined chemical reaction. This is discussed in the paper by Brown and colleagues, who were nevertheless able to recommend a value for the standard enthalpy of formation of the iron-olefin... 

Reports of depolymerization studies carried out by Semiyen and co-workers at the University of York, UK, typically used much longer reaction times (24-72 h) for the depolymerization of PET [27], This group also reported that the titanates were ineffective catalysts for depolymerization, but it is not known whether measures to prevent titanate hydrolysis were taken. The York group also reported that the relative proportions of cyclic oligomers (trimer, tetramer, etc.) altered as the dilution ratio was changed. Similar results were seen with PBT. They have also reported fast-atom bombardment mass spectrometry (FAB-MS), LC-MS, GPC and X-ray crystallography data. The most recent work reports characterization of the cyclic oligomers from six ester and ether ester systems [29],... 

Molecular beam mass spectrometry has been used to study penta-fluorides ofNb, Ta, Mo, Re, Os,Ir, Ru, Rh, Pt, Sb, and Bi (139), indicating dimeric, trimeric, and even tetrameric ions (139). Simple fragmentations of the type... 

Mass spectrometry has proved extremely useful in determining the composition of various polyferrocene products such as those formed by trimerization of ferrocenylacetylenes (180), reactions of ferrocenyl-acetylenes with metal carbonyls (175), oxidative coupling of ferrocenyl polyacetylenes (179), and lithiation of ferrocene (186). The 1,12-dimethyl-[l,l]ferrocenophane (XC) shows a very strong molecular ion and fragments [M—Me]+ [M—2 Me]+ and the doubly charged species M2+, [M —Me]2+, and [M —2 Me]2+ (197). 

D. Zhang et al., Chiral resolution of D, L-amino acids by tandem mass spectrometry of Ni(II)-bound trimeric complexes. Int. J. Mass Spectrom. 204, 159-169 (2001)... 

Dendrimer characterization was accomplished by 13C, NMR and FT-IR spectroscopy as well as mass spectrometry using fast atom bombardment (FAB) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) techniques. Molecular ion base peaks were observed in the MALDI-TOF MS of polyester 168 (mlz 18900 (calcd. 19044)) along with minor peaks at 37000 and 54000 mlz corresponding to ionic gasphase dimer and trimer complexes. 

Fig. 23. Asymmetric oligomerzation of propylene. Isomers of trimeric propylene were detected by gas chromatography/mass spectrometry (204).

The rhodium(O) complex reacts instantaneously with hydrogen and abstracts it from several hydrides (Scheme 2). On heating [Rh2(PF3)8] to 170°C, it decomposes forming [Rh3(PF3)9]. The trimer has been characterized by mass spectrometry, but there is the possibility it may be the mixed Rh /Rh° species [Rh3(PF2)(PF3)8].33... 

The ultraviolet photoelectron spectra of diatomic alkali halide molecules are reviewed and interpreted. Data for lithium halide dimers, 112X2> are presented and it is shown that the dimers have significantly larger ionization thresholds than the corresponding monomers. Some historical controversies regarding the presence of dimers and their ionization energies are clarified. Photoionization mass spectrometry is used to determine the adiabatic ionization potential of lithium chloride trimer, in order to probe the trend of I.P. with cluster size. The predictions of Hartree-Fock, Xa and ionic model calculations on this point are presented. 

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