EPR studies on carboxylic esters. Part 20. EPR spectra and spin densities in radical anions of isocoumarin, benzocoumarin and their sulfur analogues

Article abstract of DOI:10.3184/030823409X449428

The radical anions of isocoumarin, benzocoumarin and the six corresponding sulfur analogues have been generated by internal electroreduction and studied by EPR spectrosopy. The spin density distributions have been evaluated from the proton hyperfine structure coupling constants and by MO calculations. They are discussed with respect to the spin density distributions in related radical anions.

Full text of DOI:10.3184/030823409X449428

JOURNAL OF CHEMICAL RESEARCH 2009
MAꢀ, 283–286
RESEARCH PAPER 283
EPR studies on carboxylic esters. Part 20. EPR spectra and spin densities in
radical anions of isocoumarin, benzocoumarin and their sulfur analogues
Jürgen Voss*, Gabriele Kupczik and Heidi Stahncke
University of Hamburg, Department of Chemistry – Organic Chemistry, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany
The radical anions of isocoumarin, benzocoumarin and the six corresponding sulfur analogues have been generated
by internal electroreduction and studied by EPR spectrosopy. The spin density distributions have been evaluated
from the proton hyperfine structure coupling constants and by MO calculations. They are discussed with respect to
the spin density distributions in related radical anions.
Keywords: isocoumarin, benzocoumarin, thio-isocoumarins, thio-benzocoumarins, EPR spectroscopy, spin densities
a
Recently we have reported on the radical anions of coumarins
and their sulfur analogues,1 which may be thought of
as cyclic cinnamate esters and thioesters. Their isomeric
counterparts, the isocoumarins, on the other hand, represent
cyclo-conjugated benzoate esters and thioesters, whereas
the corresponding benzoanellated derivatives exhibit a
combination of both these features. Accordingly, this should
be reflected in the spin density distributions. We have
therefore prepared these compounds and studied the EPR
spectra of their radical anions in order to corroborate these
considerations by experimental evidence.
Table 1 Polarographic reduction potentials E /V and peak
½
,2
current ratios iap/icp
b
E /Va
iap/icpb
Compound
½
1
2
3
4
5
6
7
8
a
–1.41
–1.27
–1.07
–0.72
–1.32
–1.16
–0.68
–0.58
0.43
0.43
0.47
0.77
0.90
1.04
c0.72
vs the internal Ag/Ag /AgBr/Br– reference electrode in dry
+
DMF, the potential of which is shifted by –520 mV vs the SCE
Results and discussion
b
according to ref. 3; according to refs 10,11 measured at a
–1 c
The compounds to study, 1–8, were prepared according to
sweep rate of 500 mVs ; no anodic peak observed.
literature procedures (see Experimental).
With the exception of 8, the ratios i /i of the anodic and
ap cp
1
0,11
the cathodic peaks
(Table 1) are well above 0.4. This is, in
general, indicative of the formation of radical anions which
are sufficiently persistent for EPR measurements at ambient
temperature.
X
X
Accordinglyly, we could record well-resolved EPR
spectra with high signal-to-noise ratios as exemplarily
illustrated for the radical anions of isocoumarin 1 (Fig. 1),
thioloisocoumarin 2 (Fig. 2), thionobenzocoumarin 7 (Fig. 3)
and dithiobenzocoumarin 8 (Fig. 4). Fortunately, this even holds
for the dithiobenzocoumarin 8 (see Fig. 4) although 8 does
not exhibit an anodic counter peak in its cyclovoltamogram
Y
Y
1
2
3
4
: X = Y = O
5: X = Y = O
6: X = S, Y = O
7: X = O, Y = S
8: X = Y = S
: X = S, Y = O
: X = O, Y = S
: X = Y = S
Their polarographic half-wave reduction potentials E½
corresponding to the formation of radical anions by single
electron transfer (SET) of 1–8, which we have determined as
described earlier,2 are compiled in Table 1.
A continuous shift of E½ into the positive direction is
observed in the two series 1 → 2 → 3 → 4 and 5 → 6 →
(Table 1). This unexpected result may be due to the different
geometries of the cells and different time-scales of the
cyclovoltammetric and the EPR measurements and is observed
occasionally.
–4
The isocoumarin radical anions and their sulfur analogues
•
•
1
¯ – 4¯ exhibit g-factors close to the values of the respective
7
→ 8 of the compounds. This shift can be explained by the
•
•
benzocoumarin radical anions 5¯ – 8¯ . They are similar
to those found in the coumarin series. Due to the heavy-
enhanced polarisability of sulfur as compared with oxygen
and, in particular, of the thiocarbonyl group versus the
carbonyl group, which facilitates the uptake of an electron
into the molecule. We have observed this effect also in the
2
atom effect of the thiocarbonyl sulfur, i.e. its high spin-orbit
•
•
–
1
coupling constant x = –382 cm , the g-factors of 3¯ , 4¯ ,
•
•
•
•
•
7
¯ and 8¯ are markedly higher than these of 1¯ , 2¯ , 5¯
2
coumarin series and in open-chain esters and their sulfur
•
and 6¯ . The data are, in a semi-quantitative sense, indicative
of significant spin densities in the thiocarbonyl groups of
the thiono and dithio derivatives, although a precise and
5
–9
analogues.
Furthermore, a significant shift in the same
direction occurs between the isocoumarins 1–4 and the
corresponding benzocoumarins 5–8. This effect should be
due to the more extended p-electron system of the latter
with a smaller HOMO–LUMO difference. Remarkably, the
p
conclusive calculation of r (C=S) from the g-factors is not
possible.
The proton hyperfine structure (hfs) coupling constants aH
μ
reduction potentials E of the benzocoumarins are similar to
½
could be determined exactly by use of the autocorrelation
2
E½ of the corresponding coumarin derivatives whereas the
2,12
function
and simulation of the spectra in spite of the fact
E½-values of the isocoumarins deviate significantly. Thus, in
terms of the SET step, the benzocoumarin system is obviously
more closely related to the coumarin than to the isocoumarin
system, each of which formally represents a constituent of the
benzocoumarin system.
that due to the low symmetry of the molecules the number of
different hfs splittings and consequently the number of lines is
•
•
rather large. The coupling constants and g-factors of 1¯ – 8¯
are compiled in Table 2.
In the case of 6¯ , 7¯ and 8¯ several protons appear as
•
•
•
accidentally equivalent. The assignment of the coupling
constants a μ to distinct protons was achieved through
*
Correspondent. E-mail: voss@chemie.uni-hamburg.de
H

2
84ꢀ JOURNALꢀOFꢀCHEMICALꢀRESEARCHꢀ2009
Fig. 1ꢀ Experimentalꢀ(top)ꢀandꢀsimulatedꢀ(bottom)ꢀEPRꢀ
Fig. 2ꢀ Experimentalꢀ(top)ꢀandꢀsimulatedꢀ(bottom)ꢀEPRꢀ
•
•
spectrumꢀofꢀtheꢀisocoumarinꢀradicalꢀanionꢀ(1¯ ).
spectrumꢀofꢀtheꢀthioloisocoumarinꢀradicalꢀanionꢀ(2¯ ).
Fig. 3ꢀ Experimentalꢀ(top)ꢀandꢀsimulatedꢀ(bottom)ꢀEPRꢀ
Fig. 4ꢀ Experimentalꢀ(top)ꢀandꢀsimulatedꢀ(bottom)ꢀEPRꢀ
•
•
spectrumꢀofꢀtheꢀthionobenzocoumarinꢀradicalꢀanionꢀ(7¯ ).
spectrumꢀofꢀtheꢀdithiobenzocoumarinꢀradicalꢀanionꢀ(8¯ ).
comparisonꢀofꢀtheꢀexperimentalꢀdataꢀwithꢀvaluesꢀcalculatedꢀ
asꢀcomparedꢀwithꢀopen-chainꢀbenzoicꢀestersꢀfromꢀwhichꢀtheꢀ
parametersꢀkꢀandꢀhꢀofꢀtheꢀCoulombꢀandꢀresonanceꢀintegralsꢀareꢀ
takenꢀ(seeꢀExperimental).ꢀInꢀfact,ꢀanꢀimprovedꢀagreementꢀforꢀ
p
fromꢀMcLachlanꢀtypeꢀHMOꢀspinꢀdensitiesꢀr ꢀbyꢀapplicationꢀ
μ
H
p
ofꢀtheꢀMcConnellꢀequationꢀa ꢀ=ꢀ–2.7r ꢀ(cf.ꢀTableꢀ3).
μ
μ
p
Onꢀ theꢀ whole,ꢀ theꢀ agreementꢀ betweenꢀ theꢀ theoreticalꢀ
andꢀ experimentalꢀ spinꢀ densitiesꢀ isꢀ quiteꢀ satisfactory.ꢀ Theꢀ
assignmentꢀofꢀtheꢀveryꢀlowꢀvaluesꢀcloseꢀtoꢀzeroꢀisꢀofꢀcourse,ꢀ
somewhatꢀarbitraryꢀbutꢀthisꢀfactꢀdoesꢀnotꢀaffectꢀtheꢀdiscussionꢀ
of the spin density distributions significantly. There are
however some more significant deviations. In particular,
r ꢀwasꢀachievedꢀbyꢀuseꢀofꢀaꢀlowerꢀresonanceꢀintegralꢀkC1-C8aꢀ
8
p
=ꢀ1.1ꢀinsteadꢀofꢀ1.2.ꢀOnꢀtheꢀotherꢀhand,ꢀr ꢀresultsꢀasꢀtooꢀlargeꢀ
6
forꢀtheꢀthiocarbonylꢀderivativesꢀ3ꢀandꢀ4,ꢀwhichꢀcouldꢀalsoꢀbeꢀ
adjustedꢀbyꢀchoiceꢀofꢀlowerꢀresonanceꢀparametersꢀkC1-C8aꢀ=ꢀ0.9ꢀ
(3)ꢀandꢀ1.1ꢀ(4)ꢀandꢀaꢀhigherꢀresonanceꢀparameterꢀkC=Sꢀ=ꢀ1.23ꢀ
insteadꢀofꢀ0.77ꢀforꢀ3ꢀ(cf.ꢀTableꢀ4).ꢀTheꢀhighestꢀspinꢀdensitiesꢀareꢀ
p
p
p
r ꢀ isꢀ overestimatedꢀ forꢀ theꢀ carbonylꢀ derivativesꢀ 1ꢀ andꢀ 2.ꢀ
foundꢀinꢀtheꢀ6-ꢀandꢀ8-positionsꢀwithꢀr ꢀ>ꢀr ,ꢀwhichꢀpositionsꢀ
8
6 8
Thisꢀmayꢀbeꢀdueꢀtoꢀaꢀreducedꢀresonanceꢀinteractionꢀbetweenꢀ
areꢀequivalentꢀtoꢀtheꢀpara-ꢀandꢀortho-positionsꢀinꢀopen-chainꢀ
benzoateꢀestersꢀandꢀthioesters. ꢀConsiderableꢀspinꢀdensitiesꢀ
5
–9
theꢀcarbonylꢀgroupsꢀofꢀ1ꢀandꢀ2ꢀandꢀtheꢀadjacentꢀbenzeneꢀringsꢀ

JOURNALꢀOFꢀCHEMICALꢀRESEARCHꢀ2009ꢀ 285
Table 2ꢀ ProtonꢀhfsꢀcouplingꢀconstantsꢀaHμ/mTꢀandꢀg-factorsꢀofꢀtheꢀradicalꢀanionsꢀof
2
1
3
4
5
4
10
7
6
7
3
9
8
X
X
8
Y
Y
1
– 4
5 – 8
Compoundꢀ
ꢀ
ꢀ
ꢀ
ꢀ
aHμ/mTꢀ
ꢀ
ꢀ
ꢀ
ꢀ
g-factor
ꢀ
ꢀ
1
2
3
4
ꢀ
ꢀ
ꢀ
5
6
7
8
a(3-H)ꢀ
a(4-H)ꢀ
a(5-H)ꢀ
a(6-H)ꢀ
a(7-H)ꢀ
a(8-H)ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0.214ꢀ
0.304ꢀ
0.148ꢀ
0.138ꢀ
ꢀ
0.067ꢀ
0.105ꢀ
0.087ꢀ
0.098ꢀ
ꢀ
0.063ꢀ
0.084ꢀ
0.020ꢀ
0.044ꢀ
ꢀ
0.780ꢀ
0.652ꢀ
0.636ꢀ
0.518ꢀ
ꢀ
0.110ꢀ
0.125ꢀ
0.150ꢀ
0.159ꢀ
ꢀ
0.467ꢀ
0.364ꢀ
0.465ꢀ
0.414ꢀ
ꢀ
ꢀ
ꢀ
2.00335
2.00435
2.00457
2.00644
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a(1-H)ꢀ
a(2-H)ꢀ
a(3-H)ꢀ
a(4-H)ꢀ
a(7-H)ꢀ
a(8-H)ꢀ
a(9-H)ꢀ
a(10-H)ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0.299ꢀ
0.297ꢀ
0.128ꢀ
0.122ꢀ
0.045ꢀ
0.171ꢀ
0.147ꢀ
0.074ꢀ
0.061ꢀ
0.124ꢀ
0.171ꢀ
0.171ꢀ
0.415ꢀ
0.359ꢀ
0.015ꢀ
0.027ꢀ
0.047ꢀ
0.061ꢀ
0.535ꢀ
0.589ꢀ
0.572ꢀ
0.482ꢀ
0.149ꢀ
0.123ꢀ
0.128ꢀ
0.122ꢀ
2.00389
2.00413
2.00476
2.00637
0.047ꢀ
0.047ꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aNotꢀresolved.
Table 3 Experimentalꢀ(rp ꢀ=ꢀaH /–2.7)ꢀandꢀtheoretical ꢀ(HMO)ꢀspinꢀdensitiesꢀrpμꢀinꢀtheꢀiso-ꢀandꢀbenzocoumarinꢀradicalꢀanions
a
μ
μ
2
1
3
4
5
8
4
10
7
6
7
3
9
8
X
X
Y
Y
•
•
•
•
1
¯
– 4¯
5¯ – 8¯
rpμꢀatꢀcentreꢀμ
6ꢀ 7ꢀ
Compoundꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3ꢀ
4ꢀ
0.025ꢀ
–0.037ꢀ
0.039
–0.046ꢀ
0.032
–0.026ꢀ
0.036
–0.032ꢀ
5ꢀ
8ꢀ
ꢀ
1
ꢀ
ꢀ
ꢀ
ꢀ
0.079ꢀ
0.097ꢀ
0.113
0.115ꢀ
0.055
0.056ꢀ
0.051ꢀ
0.057ꢀ
ꢀ
0.023ꢀ
–0.010ꢀ
0.031
–0.027ꢀ
0.007
–0.008ꢀ
0.016
–0.016ꢀ
0.289ꢀ
0.297ꢀ
0.241
0.243ꢀ
0.235
0.247ꢀ
0.192
0.184ꢀ
0.041ꢀ
–0.053ꢀ
0.046
–0.041ꢀ
0.056
–0.057ꢀ
0.059
–0.057ꢀ
0.173ꢀ
0.185ꢀ
0.135
0.137ꢀ
0.172
0.178ꢀ
0.153
0.154
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
ꢀ
3
ꢀ
4
ꢀ
ꢀ
ꢀ
1ꢀ
2ꢀ
3ꢀ
4ꢀ
7ꢀ
8ꢀ
0.006
0.006ꢀ
0.010
–0.006ꢀ
0.027
–0.050ꢀ
0.023ꢀ
–0.045
9ꢀ
10
5
ꢀ
ꢀ
ꢀ
ꢀ
0.111
0.124ꢀ
0.110
0.110ꢀ
0.047
0.064ꢀ
0.045ꢀ
0.060
0.017
–0.023ꢀ
0.017ꢀ
–0.024
0.064
0.080ꢀ
0.054ꢀ
0.078ꢀ
0.027
0.040ꢀ
0.023ꢀ
0.038
0.046
0.046ꢀ
0.017ꢀ
0.034
0.067
0.082ꢀ
0.064
0.086ꢀ
0.154
0.157ꢀ
0.133ꢀ
0.134
0.198
0.198ꢀ
0.218
0.190ꢀ
0.212
0.183ꢀ
0.178ꢀ
0.164
0.055
–0.062
0.046
–0.058
0.047
–0.053
0.045
–0.051
ꢀ
6
ꢀ
b
b
7
ꢀ
ꢀ
ꢀ
–0bꢀ.012ꢀ
0bꢀ.017ꢀ
0.014ꢀ
8
ꢀ
–0.013ꢀ
a
b
ShownꢀinꢀItalics.ꢀ Noꢀcouplingsꢀobserved,ꢀseeꢀTableꢀ2.
exist,ꢀhowever,ꢀalsoꢀinꢀtheꢀ7-position,ꢀwhichꢀmayꢀbeꢀregardedꢀ
canꢀ beꢀ consideredꢀ asꢀ cyclicꢀ cinnamicꢀ acidꢀ derivativesꢀ andꢀ
exhibitꢀ thusꢀ theꢀ highestꢀ spinꢀ densitiesꢀ inꢀ theꢀ 7-ꢀ andꢀ theꢀ
p
asꢀ aꢀ meta-positionꢀ inꢀ aꢀ benzoateꢀ ester.ꢀ Furthermore,ꢀ r ꢀ isꢀ
3
2
significantly non-zero too. This is not unexpected because the
5-positions. ꢀ
p
3
-positionꢀinꢀanꢀisocoumarinꢀcorrespondsꢀwithꢀtheꢀ6-positionꢀ
Inꢀtheꢀbenzocoumarinꢀseries,ꢀtheꢀcalculatedꢀspinꢀdensityꢀr ꢀ
comesꢀoutꢀtooꢀhighꢀforꢀ5ꢀandꢀtheꢀcalculatedꢀr ꢀvaluesꢀareꢀtooꢀ
1
H
p
inꢀaꢀ2H-thiopyrane-2-thione,ꢀandꢀweꢀhaveꢀfoundꢀa ꢀ=ꢀ0.69ꢀmTꢀ
andꢀ r ꢀ =ꢀ 0.256ꢀ forꢀ theꢀ radicalꢀ anionꢀ ofꢀ 5-tert-butyl-2H-
thiopyrane-2-thione. ꢀ Thus,ꢀ theꢀ generalꢀ orderꢀ ofꢀ theꢀ spinꢀ
densitiesꢀinꢀtheꢀradicalꢀanionsꢀofꢀtheꢀisocoumarinsꢀ1–4ꢀisꢀr ꢀ>ꢀ
6
9
p
lowꢀforꢀ6–8ꢀasꢀcomparedꢀwithꢀtheꢀexperimentalꢀvaluesꢀalthoughꢀ
weꢀ usedꢀ Coulombꢀ integralsꢀ forꢀ theꢀ exocyclicꢀ heteroatomsꢀ
[h (5)ꢀ=ꢀ1.65;ꢀh (6)ꢀ=ꢀ0.6;ꢀh (8)ꢀ=ꢀ0.25]ꢀwhichꢀwereꢀslightlyꢀ
6
13
p
6
O
O
S
p
p
p
r ꢀ>ꢀr ꢀªꢀr .ꢀThisꢀspinꢀdensityꢀdistributionꢀisꢀdifferentꢀfromꢀ
differentꢀ fromꢀ theꢀ parametersꢀ givenꢀ inꢀ theꢀ literatureꢀ (cf.ꢀ
8
3
7
theꢀsituationꢀinꢀtheꢀcoumarinꢀradicalꢀanions,ꢀwhichꢀobviouslyꢀ
Tableꢀ 4).ꢀ Moreꢀ spinꢀ densityꢀ isꢀ locatedꢀ inꢀ theꢀ ringsꢀ adjacentꢀ

2
86ꢀ JOURNALꢀOFꢀCHEMICALꢀRESEARCHꢀ2009
Table 4ꢀ Coulombꢀ(k)ꢀandꢀresonanceꢀparametersꢀ(h)ꢀusedꢀforꢀtheꢀMcLachlanꢀtypeꢀMOꢀcalculations
Parameteraꢀ
1
2
3
4
5
6
7
8
k(Cꢀ═ꢀX)ꢀ
1.6ꢀ
1.2ꢀ
1.1ꢀ
1.5ꢀ
2.1ꢀ
1.1ꢀ
0.8ꢀ
1.1ꢀ
0.2ꢀ
1.8ꢀ
1.23ꢀ
0.68ꢀ
0.90ꢀ
0.62ꢀ
1.54ꢀ
0.7ꢀ
0.8ꢀ
1.1ꢀ
0.0ꢀ
2.0ꢀ
1.6ꢀ
1.1ꢀ
1.2ꢀ
1.65ꢀ
2.0ꢀ
1.2ꢀ
0.9ꢀ
1.2ꢀ
0.6ꢀ
2.0ꢀ
0.77ꢀ
0.54ꢀ
1.2ꢀ
0.66
0.65
1.2
0.25
1.9
k(C–Y)ꢀ
bꢀ
k(C–C)
hX(Cꢀ═ꢀX)ꢀ
hY(C–Y)ꢀ
a
0.5ꢀ
1.5ꢀ
b
X =ꢀOꢀforꢀ1,ꢀ2,ꢀ5,ꢀ6; X =ꢀSꢀforꢀ3,ꢀ4,ꢀ7,ꢀ8;ꢀYꢀ=ꢀOꢀforꢀ1,ꢀ3,ꢀ5,ꢀ7;ꢀYꢀ=ꢀSꢀforꢀ2,ꢀ4,ꢀ6,ꢀ8.ꢀ C1–C8aꢀforꢀ1–4;ꢀC6–C6aꢀforꢀ5–8.
toꢀ theꢀ carbonylꢀ orꢀ thiocarbonylꢀ doubleꢀ bondꢀ asꢀ comparedꢀ
withꢀtheꢀotherꢀannelatedꢀbenzeneꢀring.ꢀThus,ꢀtheꢀspinꢀdensityꢀ
Theꢀ
Universityꢀ
ofꢀ
Hamburg,ꢀ
theꢀ
Deutscheꢀ
Forschungsgemeinschaftꢀ andꢀ theꢀ Fondsꢀ derꢀ Chemischenꢀ
Industrie are gratefully acknowledged for financial support.ꢀ
G.ꢀK.ꢀthanksꢀtheꢀFondsꢀderꢀChemischenꢀIndustrieꢀforꢀaꢀgraduateꢀ
scholarship.ꢀ Weꢀ thankꢀ Karinꢀ Grünewald,ꢀ Hamburg,ꢀ forꢀ theꢀ
preparationꢀofꢀ5ꢀandꢀ7.
p
distributionsꢀinꢀtheꢀbenzocoumarinꢀradicalꢀanionsꢀwithꢀr ꢀ>ꢀ
9
•
•
•
p
p
p
p
p
p
r ꢀ>ꢀr ꢀªꢀr ꢀforꢀ5¯ ꢀandꢀ6¯ ,ꢀandꢀr ꢀ>ꢀr ꢀ>ꢀr ꢀforꢀ7¯ ꢀ
1
3
7
9
7
1
•
andꢀ8¯ ꢀresembleꢀthoseꢀinꢀtheꢀisocoumarinꢀradicalꢀanionsꢀifꢀoneꢀ
considersꢀthatꢀtheꢀ6-ꢀandꢀ8-positionsꢀinꢀ1–4ꢀcorrespondꢀwithꢀ
theꢀ9-ꢀandꢀ7-positionsꢀinꢀ5–8.ꢀThisꢀisꢀtoꢀbeꢀexpectedꢀbecauseꢀ
theꢀbenzocoumarinsꢀcanꢀbeꢀregardedꢀasꢀintramolecularꢀphenylꢀ
benzoatesꢀ andꢀ thiobenzoates.ꢀ Considerableꢀ spinꢀ densityꢀ is,ꢀ
however,ꢀ alsoꢀ foundꢀ inꢀ theꢀ secondꢀ ringꢀ sinceꢀ theꢀ benzo-ꢀ
coumarinsꢀmayꢀalsoꢀbeꢀregardedꢀasꢀbiphenylꢀderivativesꢀwithꢀ
anꢀobservedꢀhfsꢀcouplingꢀconstantꢀofꢀe.g.ꢀ0.32ꢀmTꢀforꢀtheꢀ4'-
protonꢀinꢀtheꢀtert-butylꢀbiphenyl-4-carboxylateꢀradicalꢀanion.14
Received 10 January 2009; accepted 2 March 2009
Paper 09/0384 doi: 10.3184/030823409X449428
Published online: 22 May 2009
References
ꢀ
1ꢀ Partꢀ19.ꢀJ.ꢀVoss,ꢀK.ꢀStrey,ꢀT.ꢀMaibom,ꢀM.ꢀKrasmannꢀandꢀG.ꢀAdiwidjaja,ꢀ
Phosphorus, Sulfur, Silicon,ꢀ2009,ꢀ184,ꢀ(accepted).
Experimental
ꢀ 2ꢀ J.ꢀVossꢀandꢀR.ꢀEdler,ꢀJ. Chem. Res.,ꢀ2007,ꢀ226.
ꢀ
ꢀ
ꢀ
ꢀ
3ꢀ H.ꢀGüntherꢀandꢀJ.ꢀVoss,ꢀJ. Chem. Res.,ꢀ1987ꢀ(S)ꢀ68,ꢀ(M)ꢀ775.
4ꢀ J.ꢀVossꢀandꢀF.-R.ꢀBruhn,ꢀLiebigs Ann. Chem.,ꢀ1979,ꢀ1938.
5ꢀ J.ꢀVossꢀandꢀK.ꢀSchlapkohl,ꢀTetrahedron,ꢀ1975,ꢀ31,ꢀ2982.
6ꢀ U.ꢀ Debacher,ꢀ W.ꢀ Schmüserꢀ andꢀ J.ꢀ Voss, J. Chem. Res.,ꢀ 1982ꢀ (S)ꢀ 74,ꢀ
Isocoumarinꢀ(isochromen-1-one,ꢀ1)ꢀwasꢀpreparedꢀfromꢀhomophthalicꢀ
acidꢀ [(2-carboxyphenyl)ethanoicꢀ acid]ꢀ andꢀ ethylꢀ formate.ꢀ Whiteꢀ
1
5
needles,ꢀ m.p.ꢀ 44–46ꢀ°Cꢀ (petroleumꢀ ether),ꢀ lit. :ꢀ 45–46ꢀ°C.ꢀ Thiolo-
isocoumarineꢀ (thioisochromen-1-one,ꢀ 2)ꢀ wasꢀ obtainedꢀ fromꢀ 2-
formylbenzoicꢀacid.ꢀLight-yellowꢀneedles,ꢀm.p.ꢀ78–80ꢀ°Cꢀ(petroleumꢀ
(
M)ꢀ876.
7ꢀ L.ꢀ Prangova,ꢀ T.ꢀ Strelowꢀ andꢀ J.ꢀ Voss,ꢀ J. Chem. Res.,ꢀ 1985ꢀ (S)ꢀ 118,ꢀ
M)ꢀ1401.
8ꢀ L.S.ꢀPrangova,ꢀA.ꢀBöge,ꢀB.ꢀWollnyꢀandꢀJ.ꢀVoss,ꢀJ. Chem. Res.,ꢀ1987ꢀ(S)ꢀ
182,ꢀ(M)ꢀ1601.
ꢀ
ꢀ
16
ether),ꢀlit. :ꢀ78–79ꢀ°C.ꢀThiono-isocoumarinꢀ(isochromene-1-thione,ꢀ3)ꢀ
(
1
7,18
wasꢀ preparedꢀ byꢀ thionationꢀ ofꢀ 1ꢀ withꢀ Lawesson'sꢀ reagent
ꢀ inꢀ
ꢀ Yellowꢀ needles,ꢀ m.p.ꢀ 106–107ꢀ°Cꢀ
:ꢀ 106ꢀ°C.ꢀ Dithio-isocoumarinꢀ (thioisochromene-
-thione,ꢀ 4)ꢀ wasꢀ preparedꢀ byꢀ thionationꢀ ofꢀ 2ꢀ withꢀ Lawesson'sꢀ
1
9,20
tolueneꢀ insteadꢀ ofꢀ P S .
4
10
19,20
(EtOH),ꢀ lit.
ꢀ 9ꢀ L.ꢀ Prangova,ꢀ K.ꢀ Osternackꢀ andꢀ J.ꢀ Voss,ꢀ J. Chem. Res.,ꢀ 1995ꢀ (S)ꢀ 234,ꢀ
(M)ꢀ1551.
ꢀ10ꢀ R.ꢀNicholsonꢀandꢀI.ꢀShain,ꢀAnal. Chem.,ꢀ1964,ꢀ36,ꢀ706.
ꢀ11ꢀ R.ꢀNicholson,ꢀAnal.ꢀChem.,ꢀ1966,ꢀ38,ꢀ1406.
ꢀ12ꢀ F.ꢀSchneiderꢀandꢀM.ꢀPlato,ꢀElektronenspinresonanz,ꢀThiemig,ꢀMünchen,ꢀ
1972,ꢀp.ꢀ182f.
1
17,18
21
reagent
ꢀinꢀtolueneꢀinsteadꢀofꢀP S . ꢀRedꢀneedlesꢀ(68%ꢀyield),ꢀ
4
10
m.p.ꢀ88–89ꢀ°Cꢀ(EtOH).ꢀFound:ꢀC,ꢀ60.66;ꢀH,ꢀ3.33;ꢀS,ꢀ36.10.ꢀCalcdꢀforꢀ
1
13
C H S ꢀ(178.28),ꢀC,ꢀ60.63;ꢀH,ꢀ3.39;ꢀS,ꢀ35.97%.ꢀ Hꢀandꢀ CꢀNMRꢀ
9
6 2
2
1
inꢀ agreementꢀ withꢀ lit. ꢀ Benzocoumarinꢀ (6H-benzo[c]chromen-6-
one,ꢀ 5)ꢀ wasꢀ preparedꢀ byꢀ oxidationꢀ ofꢀ biphenyl-2-carboxylicꢀ acidꢀ
ꢀ13ꢀ R.ꢀRöskeꢀandꢀJ.ꢀVoss,ꢀPhosphorus, Sulfur and Silicon,ꢀ1986,ꢀ26,ꢀ257.
2
2,23
ꢀ14ꢀ S.ꢀ Bruns,ꢀ Dichtefunktional-theoretischeꢀ Berechnungenꢀ derꢀ Strukturenꢀ
undꢀderꢀEPR-HyperfeinstrukturenꢀvonꢀBiarylen,ꢀPhDꢀthesis,ꢀUniversityꢀofꢀ
Hamburg,ꢀGermany,ꢀ2002.
withꢀCrO .ꢀColourlessꢀcrystals,ꢀm.p.ꢀ92ꢀ°Cꢀ(MeOH),ꢀlit.
:ꢀ92.5–
3.5ꢀ°C.ꢀ Thiolo-benzocumarinꢀ (6H-benzo[c]thiochromen-6-one,ꢀ 6)ꢀ
wasꢀ obtainedꢀ byꢀ oxidationꢀ ofꢀ 8ꢀ withꢀ Hg(OAc) .ꢀ Yellowꢀ needles,ꢀ
3
9
2
ꢀ
15ꢀ H.W.ꢀ Johnston,ꢀ C.E.ꢀ Kaslow,ꢀ A.ꢀ Langsjoenꢀ andꢀ R.L.ꢀ Shriner,ꢀ J. Org.
Chem.,ꢀ1948,ꢀ13,ꢀ477.
16ꢀ J.ꢀDijksmanꢀandꢀG.T.ꢀNewbold,ꢀJ. Chem. Soc.,ꢀ1951,ꢀ1213.
2
4,25
m.p.ꢀ 125–127ꢀ°Cꢀ (petroleumꢀ ether),ꢀ lit.
benzocoumarinꢀ (6H-benzo[c]chromene-6-thione,ꢀ 7)ꢀ wasꢀ preparedꢀ
byꢀ thionationꢀ ofꢀ 5ꢀ withꢀ Lawesson'sꢀ reagent
Yellowꢀcrystals,ꢀm.p.ꢀ148–149ꢀ°Cꢀ(EtOH),ꢀlit. :ꢀ150–151ꢀ°C,ꢀlit. :ꢀ
:ꢀ 130–131ꢀ°C.ꢀ Thiono-
ꢀ
1
7,18,23
ꢀ inꢀ toluene.ꢀ
ꢀ17ꢀ J.ꢀVoss,ꢀEncyclopedia of reagents for organic synthesis,ꢀL.A.ꢀPaquetteꢀandꢀ
2
3
26
S.D.ꢀBurkeꢀ(eds),ꢀVol.ꢀ1,ꢀJohnꢀWileyꢀ&ꢀSonsꢀLtd.,ꢀChichester,ꢀ1995,ꢀ534.
1
6
48–150ꢀ°C.ꢀ Dithio-benzocoumarinꢀ (6H-benzo[c]thiochromene-
-thione,ꢀ 8)ꢀ wasꢀ preparedꢀ byꢀ reactionꢀ ofꢀ biphenyl-2-thiol ꢀ withꢀ
ꢀ18ꢀ J.ꢀ Voss,ꢀ Electronic Encyclopedia of reagents for organic synthesis,ꢀ
2
7
“EROS” L.A.ꢀPaquetteꢀandꢀD.ꢀCrichꢀ(eds),ꢀ2ndꢀedn.,ꢀVol.ꢀ1,ꢀJohnꢀWileyꢀ
CSCl ,ꢀ andꢀ subsequentꢀ intramolecularꢀ Friedel–Crafts-acylationꢀ ofꢀ
&ꢀ Sonsꢀ Ltd.,ꢀ Chichester,ꢀ 2006.ꢀ Online:ꢀ http://www.mrw.interscience.
wiley.com/eros/articles/rb170/sect0.html.
2
theꢀintermediateꢀbiphenyl-2-ylꢀchlorodithioformateꢀ[94%,ꢀorangeꢀoil,ꢀ
C H ClS ꢀ(264.80),ꢀCalcdꢀCꢀ58.97,ꢀHꢀ3.43,ꢀClꢀ13.39ꢀSꢀ24.22;ꢀfoundꢀ
1
3
9
2
ꢀ19ꢀ V.ꢀPrey,ꢀB.ꢀKerresꢀandꢀH.ꢀBerbalk,ꢀMonatsh. Chem.,ꢀ1960,ꢀ91,ꢀ774.
ꢀ20ꢀ L.ꢀLegrandꢀandꢀN.ꢀLozac'h,ꢀBull. Soc. Chim. Fr.,ꢀ1964,ꢀ31,ꢀ1787.
ꢀ21ꢀ H.ꢀDuddeckꢀandꢀM.ꢀKaiser,ꢀSpectrochim. Acta,ꢀ1985,ꢀ41A,ꢀ913.
ꢀ22ꢀ G.W.ꢀKenner,ꢀM.A.ꢀMurrayꢀandꢀC.M.B.ꢀTylor,ꢀTetrahedron,ꢀ1957,ꢀ1,ꢀ259.
Cꢀ59.05,ꢀHꢀ3.35,ꢀClꢀ13.31,ꢀSꢀ24.19]ꢀwithꢀAlCl .ꢀRedꢀneedles,ꢀm.p.ꢀ
3
25
28
1
06ꢀ°Cꢀ(petroleumꢀether),ꢀlit. :ꢀ113–114ꢀ°C,ꢀlit. :ꢀ106ꢀ°C.
Theꢀ polarographicꢀ andꢀ cyclovoltammetricꢀ measurements,ꢀ theꢀ
ꢀ
ꢀ
23ꢀ F.M.ꢀDean,ꢀJ.ꢀGoodchildꢀandꢀA.W.ꢀHill,ꢀJ. Chem. Soc., C,ꢀ1969,ꢀ2192.
24ꢀ I.W.J.ꢀStill,ꢀN.ꢀPlavac,ꢀD.M.ꢀMcKinonꢀandꢀM.S.ꢀChauhan,ꢀCan. J. Chem.,ꢀ
1976,ꢀ54,ꢀ280.
generationꢀofꢀtheꢀradicalꢀanionsꢀbyꢀin situꢀelectroreductionꢀinꢀDMFꢀ
atꢀ roomꢀ temperature,ꢀ andꢀ theꢀ recordingꢀ ofꢀ theꢀ EPRꢀ spectraꢀ wereꢀ
performedꢀasꢀdescribedꢀpreviously. ꢀTheꢀg-factorsꢀwereꢀdeterminedꢀ
by direct measurement of the field H ꢀandꢀtheꢀmicrowaveꢀfrequencyꢀ
2
ꢀ25ꢀ J.L.ꢀCharlton,ꢀS.M.ꢀLoosmoreꢀandꢀD.M.ꢀMcKinnon,ꢀCan. J. Chem.,ꢀ1974,ꢀ
o
–
11
–1
52,ꢀ3021.
n ꢀ accordingꢀ toꢀ gꢀ =ꢀ 7.14484∙10 ꢀ n ∙H ꢀ andꢀ correctedꢀ byꢀ usingꢀ
o
o
o
ꢀ
26ꢀ I.ꢀ Jabre,ꢀ M.ꢀ Saquetꢀ andꢀ A.ꢀ Thuillier,ꢀ J. Chem., Res.,ꢀ 1990,ꢀ (S)ꢀ 106,ꢀ
M)ꢀ756.
27ꢀ D.D.ꢀEmrickꢀandꢀW.E.ꢀTruce,ꢀJ. Org. Chem.,ꢀ1960,ꢀ25,ꢀ1103.
28ꢀ L.ꢀBenatiꢀandꢀP.C.ꢀMontevecchi,ꢀJ. Org. Chem.,ꢀ1976,ꢀ41,ꢀ2639.
29ꢀ R.ꢀCannings,ꢀSimple Huckel molecular orbital, SHMO,ꢀiterativeꢀonlineꢀ
programꢀ(http://www.chem.ucalgary.ca/SHMO/).
theꢀ peryleneꢀ radicalꢀ cationꢀ (gꢀ =ꢀ 2.002569)ꢀ asꢀ internalꢀ standard.ꢀ
SpectraꢀsimulationsꢀwereꢀcarriedꢀoutꢀbyꢀusingꢀtheꢀSimfoniaꢀprogramꢀ
(
ꢀ
ꢀ
ꢀ
(
Bruker).
Simpleꢀ HMOꢀ calculationsꢀ wereꢀ performedꢀ byꢀ useꢀ ofꢀ theꢀ onlineꢀ
29
30,31
programꢀShmo. ꢀAnꢀunpublishedꢀfortran-77ꢀprogramꢀhueckel
ꢀ
wasꢀusedꢀforꢀtheꢀMcLachlanꢀtypeꢀcalculations.ꢀTheꢀappliedꢀCoulombꢀ
andꢀ resonanceꢀ parametersꢀ areꢀ compiledꢀ inꢀ Tableꢀ 4.ꢀ Theyꢀ differꢀ
slightlyꢀ fromꢀ theꢀ literatureꢀ dataꢀ forꢀ open-chainꢀ benzoatesꢀ (1ꢀ andꢀ
ꢀ
30ꢀ D.ꢀ Buddensiek,ꢀ Semiempirischeꢀ MO-Rechnungenꢀ undꢀ experimentelleꢀ
UntersuchungenꢀanꢀThioketonenꢀundꢀihrenꢀRadikal-Anionen,ꢀPhDꢀthesis,ꢀ
UniversityꢀofꢀHamburg,ꢀGermany,ꢀpp.ꢀ64,ꢀ200,ꢀ1985.
32
6
5
5
), ꢀ thiolobenzoatesꢀ (2ꢀ andꢀ 6), ꢀ thionobenzoatesꢀ (3ꢀ andꢀ 7) ꢀ andꢀ
ꢀ31ꢀ D.ꢀBuddensiek,ꢀB.ꢀKöpkeꢀandꢀJ.ꢀVoß,ꢀChem. Ber.,ꢀ1987,ꢀ120,ꢀ575.
ꢀ32ꢀ M.ꢀHirayama,ꢀBull. Chem. Soc. Jpn,ꢀ1967,ꢀ40,ꢀ1822.
5
dithiobenzoatesꢀ(4ꢀandꢀ8); ꢀseeꢀabove.