The efficacy of m-nitrobenzyl alcohol (NBA) as a solvent (matrix) for fast atom bombardment (FAB) mass spectrometry of a group of pyrazolate-bridged dirhodium A-frame complexes has been assessed. Although NBA is frequently used to mitigate the formation of artifacts in FAB/MS of organometallics and other materials susceptible to bombardment-induced reactions, substantial evidence indicates that such reactions cause the formation of artifacts in the spectra obtained here. Parallel absorption spectroscopic studies have established that NBA is capable of inducing both oxidation and reduction reactions independent of ion bombardment, depending on analyte reduction half-wave potential (E1/2). From the known electrochemistry of the complexes studied, it can be estimated that 1020 mV > E1/2 > 500 mV for the reaction of NBA serving as a reducing agent, while 500 mV > E1/2 > 424 mV for the reduction potential of NBA. However, in the presence of bombardment the former E1/2 must be at least as low as 356 mY, and the latter E1/2 must be at least as high as 1188 mY. The kinetics of redox reactions involving NBA, and therefore their influence on the appearance of FAB mass spectra, will be highly sample-dependent. However, this study illustrates an important potential role for redox reactions when NBA is used as a solvent, especially in the presence of bombardment in FAB/MS. Although analyte reaction products could be identified, substantial efforts aimed at identifying NBA oxidation and reduction products did not yield any definitive results due to the complexity of product mixtures.
4597The chemical reactivity of the compounds is much greater than the corresponding chlorine analogues. Both N-bromo derivatives react with AgCl, forming the respective silver salts and BrCl, and with chloroform, liberating BrCl. As expected, their reactivity does not approach that of BrOSOzF with covalent chlorides: BrOSOZF reacts rapidly with CFCl, at 22 OC, whereas solutions of the new N-bromo compounds appear to be stable a t 22 O C .Characterization of the new compounds is given in the experimental section, with the IR, N M R , Raman, and mass spectra being similar t o those of t h e respective a n a l o g u e s (CF3S0z)zNCI'1~1Z and (FS02)zNC1.'3.'7*18 Assignment of frequencies to vN-x in this series is not obvious.
Fast atom bombardment (FAB) and collision-induced dissociation (CID) tandem mass spectra of a series of novel pyrazolato-bridged dirhodium A-frame compounds provide structure confirmation and useful information concerning the structural dependence of lability, based upon fragmentation pathways. CID mass spectra indicate that FAB matrixand beam-induced reduction chemistry can alter the energy and/or the structure of the precursor molecules.However, it appears that FAB matrixand beam-induced oxidation chemistry does not do so delectably.limit the amount of structural information that can be gained from FAB mass spectra. Collision-induced dissociation (CID) MS14•15 coupled with FAB ionization has proven useful in providing structural information for organic compounds like peptides16 and
The μ‐chloro‐Rh(I),Rh(I) complexes (I) react with the corresponding pyrazolates or triazolate to give the dirhodium(I) A‐frame complexes (IIa) and (IIc).
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