3.1 The general fragmentation patterns of diaryliodonium
cations
Firstly, we studied some representative diaryliodonium salts
(1 ~4 , structures were shown inScheme 2 ). These diaryliodonium salts could be easily ionized
by loss of OTf– to give diaryliodonium cations
[M –OTf]+ in the form of
[Ar1-I+-Ar2]
and their ESI-MS/MS were 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
[Ar1-I+-Ar2]
cations: 1) Reductive elimination10-13,36 to give
diaryl coupling product ions
[Ar1-Ar2]+• by
loss of an iodine atom, followed by the generation of further fragment
ions from these species. Such gas-phase reductive elimination
rearrangement reaction was similar to our previous finding of the
process from [CF3-I+-Ph] atm/z 273 to [PhCF3]+• atm/z 146 by loss of an iodine atom in ESI-MS/MS of
[CF3-I+-Ph];362) The C–I bond cleavage to produce aryl cations
[Ar1]+ or
[Ar2]+, which might further give
[Ar1+H2O]+ or
[Ar2+H2O]+ and
[Ar1+N2]+ or
[Ar2+N2]+ adduct
ions,41 along with their respective fragment ions.
This type fragmentation has also be found in the in ESI-MS/MS of
[CF3-I+-Ph], in which C–I bond
cleavage of [CF3-I+-Ph] atm/z 273 gave rise to [Ph]+ at m/z 77
or [PhI]+• at m/z 204 by loss of
CF3.36
Taking the MS/MS of [1 –OTf]+ as an
illustrative example, we observed that the reductive elimination of
[Ph-I+-Ph] gave diaryl coupling product ion
biphenyl+• at m/z 154 rather than
I+• at m/z 127. This divergence could be
attributed to the significantly higher ionization energy of iodine
(10.45 eV) compared to biphenyl (8.16 eV).42Meanwhile, C–I bond cleavage of [Ph-I+-Ph]
produced [Ph]+ at m/z 77, along with
[Ph+H2O]+ at m/z 95 and
[Ph+N2]+ at m/z 105.
Notably, we did not observe the formation of
[PhI]+• at m/z 204, which could be
attributed to the higher ionization energy of PhI (8.72 eV) in
comparison to the phenyl radical (8.32 eV).42Therefore,
[Ar1-I+-Ar2]
predominantly formed diaryl coupling product ions and aryl cations in
ESI-MS/MS. The two principal fragmentation pathways of
[Ar1-I+-Ar2]
originating from diaryliodonium salts
(1 ~4 ) were depicted in Scheme
3 . The structural assignments for fragment ions were supported by
accurate mass measurements (see in Table
S1 ~S3 ).