Fast atom bombardment and secondary ion mass spectra of iodonium salts: Interpretation of spectra and implications for sputtering mechanisms

Abstract

Positive ion fast atom bombardment and liquid secondary ion mass spectra of aryl iodonium salts usually contain the intact cation as the base peak in the spectrum, along with lower abundance fragment ions that result from cleavages, rearrangements, and in some cases, combinations of such losses with addition of hydrogen from the matrix. An interesting rearrangement that leads to loss of the central iodine as a neutral atom occurs in source fragmentations as well as in low collision energy collision-activated dissociation. Energy-resolved tandem mass spectrometry is used to establish the relative facilities of the rearrangement and cleavage reactions of the intact cation. Tandem mass spectrometry is also used to identify reduced forms of the intact cation and its fragments. The occurrence of these reactions implicates direct fragmentation in the condensed phase or in a solventsalt cluster in the selvedge immediately above the sample surface.

Gas‐phase Smiles rearrangement of ortho‐nitro‐substituted diaryliodonium cations and their mechanistic insights

“…[M-OTf] + in the form of [Ar 1 -I + -Ar 2 ], and their ESI-MS/MS are shown in Figure 1. According to the previous reports and our studies of these spectra, 13,36,40 we proposed two major fragmentation patterns of [Ar 1 -I + -Ar 2 ] cations: (1) reductive elimination [10][11][12][13]36 to give diaryl coupling product ions [Ar 1 -Ar 2 ] +• by the loss of an iodine atom, followed by the generation of further fragment ions from these species; such gas-phase reductive elimination rearrangement reaction 42 Therefore, [Ar 1 -I + -Ar 2 ] predominantly formed diaryl coupling product ions and aryl cations in ESI-MS/MS. The two principal fragmentation pathways of [Ar 1 -I + -Ar 2 ] originating from diaryliodonium salts (1)(2)(3)(4) are depicted in Scheme 3.…”

“…Chemical structures of some diaryliodonium salts (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16) in this study, Mes, mesitylene.…”

“…13 In 1989, Busch et al employed fast atom bombardment (FAB) and secondary ion mass spectrometry to provide further insights. 9,10 Then, in 1992, the Busch group combined FAB with semiempirical calculations to examine iodonium salts and pointed out that orthohindered iodonium salts lacked the rearrangement process. 11 In 1995, Sam et al made significant contributions by employing electrospray ionization mass spectrometry (ESI-MS) to investigate the oxidation of PhIO in methanol.…”

“…In addition, the aryliodonium salts find widespread usage in photoredox catalysis and serve as cationic photoinitiators in polymerization reactions, contributing to the production of diverse materials such as adhesives, coatings, composites, and dental materials. [8][9][10][11] In 1983, Gross et al pioneered the use of mass spectrometry to investigate the gas-phase reaction between benzene radical cations and alkyl iodides, leading to the proposal of the C 9 H 13 I + intermediate. 12 Six years later, the same group described the six fragmentation processes involving iodonium radical cations.…”

“…For instance, the bis(4‐(1,1‐dimethylethyl)phenyl)iodonium salt is a type of useful ionic photoacid generator. In addition, the aryliodonium salts find widespread usage in photoredox catalysis and serve as cationic photoinitiators in polymerization reactions, contributing to the production of diverse materials such as adhesives, coatings, composites, and dental materials 8–11 …”