Experimental verification of diverging mechanisms in the binding of ether, thioether, and sulfone ligands to a dirhodium tetracarboxylate

Article abstract of DOI:10.1002/mrc.2562

Complexation of the oxygen atom in 2-butylphenylethers and sulfur in 2-butylphenylthioethers to a rhodium atom in dirhodium tetracarboxylate Rh ^(II)₂[(R)-(+)-MTPA]₄ is compared. Oxygen atoms complex via electrostatic attra

Full text of DOI:10.1002/mrc.2562

Research Article
Received: 22 August 2009
Accepted: 4 December 2009
Published online in Wiley Interscience: 11 January 2010
(www.interscience.com) DOI 10.1002/mrc.2562
Experimental verification of diverging
mechanisms in the binding of ether, thioether,
and sulfone ligands to a dirhodium
tetracarboxylate
Jens T. Mattiza, Vera J. Meyer and Helmut Duddeck∗
Complexationoftheoxygenatomin2-butylphenylethersandsulfurin2-butylphenylthioetherstoarhodiumatomindirhodium
tetracarboxylate Rh(II)2[(R)-(+)-MTPA]4 is compared. Oxygen atoms complex via electrostatic attraction exclusively leading to
an increase in α effects on C-2 complexation shifts in the sequence OCH3 > F > Br > NO2. However, that trend is opposite in
thioethers. This can be rationalized by an additional highest occupied molecular orbital (HOMO)–LUMO interaction and the
response of this interaction upon complex formation shifts. Thereby, an experimental evidence was found for the existence of
the HOMO–LUMO binding mechanism which has been proposed previously based on theoretical considerations and indirect
spectroscopic evidence. Sulfones hardly bind to Rh(II)2[(R)-(+)-MTPA]4. Diastereomeric dispersion effects at 13C and 1H signals
c
can be observed for all compounds indicating that enantiodifferentiation is easy in all classes of functionalities. Copyright ꢀ
2010 John Wiley & Sons, Ltd.
Keywords: ethers; thioethers; sulfones; dirhodium complex; 1H NMR; 13C NMR; complexation; chiral differentiation
Introduction
and HMBC techniques. The assignment strategies were analogous
1
to those reported for the ethers 1a–1e.[7] 13C and H chemical
Dirhodium complexes as well as their adducts have been in the fo-
cus of interest for many years.[1–3] During the last decade, we have
shown that the enantiomers of many chiral ligands, particularly
those of soft Lewis bases, can be differentiated easily by adding
an equimolar amount of the dirhodium complex Rh(II)2[(R)-(+)-
MTPA]4 (Rh∗,MTPA-H=methoxytrifluoromethylphenylaceticacid
≡ Mosher’s acid; see Scheme 1)[4] to their CDCl3 solution and mon-
itoring the diastereomeric dispersion ꢀν of their 1H (or 13C) NMR
signals at room temperature (dirhodium method).[5] In addition,
the complexation site in the ligand molecules can be identified
from inductive effects on chemical shifts ꢀδ. Recently, we investi-
gated ether ligands where oxygen atoms are attached to aromatic
ring systems and, to our surprise, found that the most significant
complexation shifts are observed at aromatic atoms beyond the
ipso-carbon bound to oxygen.[6] This, however, is not compatible
with the above explanation; rather, itreminds of resonance effects.
In order to gain further insight into the complexation mecha-
nisms of chalcogen ligands, we extended our study to structurally
analogous thioethers (2) and sulfones (3). Although ethers (1) are
hard ligands, thioethers are soft representing a different ligand
category in the dirhodium experiment when compared with the
ethers.[5]
shifts are listed in Table 1. 13C and 1H complexation shifts ꢀδ and
diamagnetic dispersion effects ꢀν provoked by adduct formation
in the presence of an equimolar amount of Rh∗ are collected in
Table 2; NMR data of 1e, which have not been reported before,[7]
are given in the Section on Experimental.
Binding sites and adduct formation
The complexation site of the ligand molecule in the adduct with
the dirhodium complex Rh∗ can be identified by the deshieldings
of nearby 1H and, particularly, 13C nuclei (complexation shifts
ꢀδ).[5] In a qualitative interpretation of positive ꢀδ-values, one
can assume that an increase of the electron-acceptor properties
of the binding atom takes place (inductive effect).[5]
Recently, we investigated ether ligands where oxygen atoms
are attached to aromatic ring systems and found significant com-
plexation shifts at aromatic atoms beyond the ipso-carbon bound
to oxygen.[6] Therefore, we wanted to study this phenomenon,
namely, the fact that complexation shifts seem to be entirely
different if aliphatic or aromatic carbons are involved. Araliphatic
ethers[7] and thioethers (compounds 1 and 2, respectively, in
Scheme 2) were chosen as candidates.
In the present study, we provide experimental evidence of the
existenceoforbitalinteractionwhensulfuratomsarebindingsites.
∗
Correspondence to: Helmut Duddeck, Leibniz University Hannover, Institute of
Organic Chemistry, Schneiderberg 1B, D-30167 Hannover, Germany.
E-mail: duddeck@mbox.oci.uni-hannover.de
Results and Discussion
The complete and unambiguous NMR signal assignment of the
free ligands 2a–2e and 3a–3e (Scheme 2) is straightforward
by applying routine NMR methods, such as DEPT, COSY, HMQC,
Leibniz University Hannover, Institute of Organic Chemistry, Schneiderberg 1B,
D-30167 Hannover, Germany
c
Magn. Reson. Chem. 2010, 48, 192–197
Copyright ꢀ 2010 John Wiley & Sons, Ltd.

Experimental verification of diverging mechanisms
Table 1. 13C and 1H chemical shifts δ of the thioethers 2a–2e, in
ppm; solvent CDCl3
2a
2ba
2c
2d
2e
C-1
20.5
44.8
29.4
11.4
135.5
128.7
131.8
126.5
–
20.5
45.9
29.4
11.4
130.1
135.0
115.8
162.2
–
20.4
45.0
29.4
11.4
134.8
133.3
131.8
120.6
–
20.2
43.2
29.3
11.4
145.1
127.7
123.9
147.3
–
20.5
46.2
C-2
C-3
29.3
C-4
C-1ꢁ
C-2ꢁ/6ꢁ
C-3ꢁ/5ꢁ
C-4ꢁ
11.4
125.2
135.5
114.2
159.3
55.2
Scheme 1. Structure of the dirhodium complex Rh∗.
OCH3
H-1
1.27
3.15
1.23
3.04
1.26
3.13
1.38
3.40
1.21
H-2
H-3b
2.96
1.53/1.66 1.50/1.60 1.52/1.64 1.65/1.75 1.47/1.60
H-4
1.00
7.39
7.27
7.20
–
1.00
7.40
6.99
–
1.00
7.24
7.40
–
1.05
7.36
8.12
–
0.99
7.38
6.83
–
H-2ꢁ/6ꢁ
H-3ꢁ/5ꢁ
H-4ꢁ
OCH3
–
–
–
3.79
a Coupling constants involving 19F: 3J(19F,1H) = 8.9 Hz (H-3ꢁ/5ꢁ);
4J(19F,1H) = 8.7 Hz (H-2ꢁ/6ꢁ); 1J(19F,13C) = 247.1 Hz (C-4ꢁ); 2J(19F,13C)
= 21.7 Hz (C-3ꢁ/5ꢁ); 3J(19F,13C) = 8.1 Hz (C-2ꢁ/6ꢁ); 4J(19F,13C) = 3.4 Hz
(C-1ꢁ); 6J(19F,13C) = 1.0 Hz (C-2).
b Diastereotopic protons; no stereochemical assignment.
attraction for oxygen ligands and an additional HOMO–LUMO
interaction in the case of thioether ligands.
Scheme 2. Structures of 2-butylphenylethers (1) as well as their thioether
(2) and sulfone (3) analogs.
Phenylethers 1a–1e
Ethers form rather weak adducts with Rh∗
and the binding
[7,8]
energy is expected to be based primarily on electrostatic interac-
tion. Orbital [highest occupied molecular orbital (HOMO)–LUMO]
interactiondoesnotcontributesignificantlyifoxygen, asasecond-
row element, is involved; the HOMO–LUMO gap is too large.[9]
We had found that the inductive effect of the ether oxygen
on aliphatic α carbons is enhanced when it is complexed to the
rhodium atom (ꢀδ > 0). This is in accordance with the original
interpretation (see above). However, deshielding complexation
shifts ꢀδ at the aromatic ipso-carbons (also α-positioned) were
minute, whereas ortho- and para-carbon signals were influenced
by the resonance effect of oxygen.[7]
This latter effect can be modulated by remote substituents at
the benzene ring; the modulation of this resonance correlates
linearly with the magnitude of the inductive effect exerted on
the aliphatic α carbon atoms.[7] On the other hand, the 13C
chemical shift modulation at the ortho-carbons (C-2ꢁ/6ꢁ) follows
the resonance effect (σR)[10] of the para-positioned substituent
X: the larger σR, the larger ꢀδ(C-2ꢁ/6ꢁ)[7]; the p-OCH3 analog 1e,
introduced in the present study, fits nicely into that correlation
with a negative slope (Fig. 1; filled squares).
Calculated electrostatic charges at C-2 (density functional with
B3LYP 6-31G∗ basis set; Table 3) are parallel to the ꢀδ(C-2)-
values supporting the dominance of the electrostatic nature in
the binding process and confirming our earlier interpretation.[7]
Phenylthioethers 2a–2e
As shown by Deubel,[9] electrostatic attraction plays an important
role for soft-base ligands but HOMO–LUMO interaction may be
significant too. Apparently, the latter mechanism overrules the
first in the thioethers producing correlations with positive slopes
(Figs 1 and 2; open squares).
A semiquantitative rationalization for this opposite behavior
of complexation shifts at C-2 in correlation with the Hammett
parameters of X is offered in the following. First of all, the HOMOs
are totally different; in contrast to ethers (Fig. 3, left) those of the
thioethers are essential the free electron pairs at sulfur (Fig. 3,
right).[11] Interestingly, this difference is accompanied by a change
in calculated conformations: while the O–C-2 bond is nearly
coplanar with respect to the aromatic ring [1a: torsion angle
φ(C-2/O/C-ipso/C-2ꢁ) = 2◦], the corresponding angle of 2a is φ(C-
2/S/C-ipso/C-2ꢁ) = 73.5◦ so that the free electron pair at sulfur is
situated nearly within the σ-plane of the benzene ring. Thereby,
the thioether-HOMO is easily accessible for adduct formation with
a rhodium atom of Rh∗.
Analogously, the correlation of complexation shifts ꢀδ at the
α-positioned carbons C-2 of 1a–1e shows a negative slope as well
when plotted versus inductive effect parameters (σI) (Fig. 2; filled
squares).
As shown in the Figs 1 and 2, the corresponding correlations
are opposite for the thioethers 2 (open squares) and, generally,
larger ꢀδ-values are observed. This is an evidence for a significant
divergence in adduct formation mechanisms: exclusive dipole
It is well known[12] that σp, the paramagnetic contribution to the
nuclear shielding, dominates the chemical shift of heavier atoms; it
is governed, along with some other structural effects, by the mean
c
Magn. Reson. Chem. 2010, 48, 192–197
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
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J. T. Mattiza, V. J. Meyer and H. Duddeck
Table 2. 13C and 1H complexation shifts ꢀδ (in ppm) and diastere-
omeric dispersions ꢀν (in HZ; integers) of the thioethers 2a–2e, in
ppm; solvent: CDCl3
2a
2b
2c
2d
2e
C-1
−2.5/11
3.4/7
−1.8/4
−0.3/11
−6.1/0
0.1-/1
2.3/3
2.6/0
–
−2.5/10
2.6/3
−1.7/4
−0.3/10
−5.4/0
1.2/2
0.1/1
1.2/0a
–
−2.6/15
3.1/6
−1.8/3
−0.5/13
−6.1/0
−1.4/5
3.5/1
3.1/0
–
−2.5/10
4.4/4
−1.8/4
−0.7/13
−6.0/4
5.5/2
−0.3/1
0.1/0
–
−2.5/11
2.3/5
−1.7/6
−0.3/11
−5.3/5
0.3/4
0.1/2
1.3/0
0.2/1
0.2/4
0.7/0
0.4/1
0/4
C-2
C-3
C-4
C-1ꢁ
C-2ꢁ/6ꢁ
C-3ꢁ/5ꢁ
C-4ꢁ
OCH3
H-1
0.2/4
0.6/1
0.4/0
0/5
0.2/4
0.7/1
0.4/1
0/5
0.2/7
0.6/0
0.4/0
0/5
0.1/9
0.6/1
0.3/1
0/8
H-2
H-3b
Figure 2. Complexationshiftsꢀδ attheα-positionedcarbonsC-2of1a–2e
plotted versus the inductive effect parameters of X (σI). The letters b to e
mark the substituents X (see Scheme 2): b, X = F; c, X = Br; d, X = NO2; e,
X = OCH3.
H-4
H-2ꢁ/6ꢁ
H-3ꢁ/5ꢁ
H-4ꢁ
0.4/0
n.d.c
0.4/2
−0.1/6
–
0.4/1
−0.1/0
–
0.4/0
−0.2/2
–
0.3/2
−0.1/7
–
0.1/1
–
OCH3
–
–
–
−0.1/3
Table 3. Complexation shifts ꢀδ(C-2) and calculateda electrostatic
and Mulliken charges at C-2 for the para-substituted phenylethers
1b–1e
a 1J(19F,13C) = 249.9 Hz (C-4ꢁ), change by complexation: ꢀJ(19F, 13C) =
+2.8 Hz; no significant changes in 19F couplings to other nuclei.
b No stereochemical assignment for the diastereotopic protons; values
are averaged.
X =
NO2
Br
F
OCH3
c ‘n.d.’, not detectable.
Electrostatic charge
Charge (Mulliken)
ꢀδ(C-2), in ppm
0.423
0.060
0.16
0.547
0.142
0.72
0.576
0.142
1.30
0.575b
0.146b
3.29
a Calculated density functionals with B3LYP 6-31G∗ basis set.
b Averaged value for cisoid and transoid conformations; the energy
difference for the two conformations is minute.
in the complex Rh∗, so that its energy is lowered. Thereby, the
HOMO(nS)–LUMO(π∗arom.) transition energy is increased. This
transition energy change becomes even larger if the HOMO en-
ergy is higher and closer to the LUMO(σ∗Rh–Rh) energy. As can
be seen in Table 4, there is a sequence in the calculated HOMO
energies of the thioethers 2 predicting the strongest effect for 2e
(X = OCH3) and the weakest for 2d (X = NO2). So, according to
Eqn (1) the smallest complexation shift is expected for 2e and the
largest for 2d. The group electronegativity of the sulfur atom is
changed correspondingly which, in turn, affects the α-positioned
aliphatic carbon (C-2) in the same direction. This trend is, indeed,
observed as shown in Fig. 2.
Figure 1. Complexation shifts ꢀδ at the ortho-carbons C-2ꢁ/C-6ꢁ of 1a to
2e plotted versus resonance effect parameters of X (σR). The letters b to e
mark the substituents X (see Scheme 2): b, X = F; c, X = Br; d, X = NO2; e,
X = OCH3.
Phenyl sulfones 3a–3e
All 13C and 1H NMR data of the sulfones are listed in Section on
Experimental. Complexation effects are more or less negligible in
the sulfones and so is the modulation by X. This shows that the
oxygen atoms, the only possible binding sites, are too hard for any
effective association to rhodium.
excitation energy ꢂEꢃ and the spatial dimension of the p-orbital in
the valence shell (2p for 13C):
−3
σp ∼ ꢂEꢃ−1r2p
(1)
Enantiodifferentiation by 13C and 1H signal dispersions (ꢀν)
The effect of the mean excitation energy ꢂEꢃ is dominated by
the energetically smallest, i.e. the HOMO(nS)–LUMO(π∗arom.) tran-
sition (Scheme 3). By adduct formation with Rh∗, the HOMO(nS)
of sulfur interacts with the LUMO(σ∗Rh–Rh) of the Rh–Rh bond
As can be seen from the ꢀν data in Table 2, some 1H and 13C signal
splittings of com∗pounds 2 due to the formation of diastereomeric
adducts with Rh can be recognized. Among the 1H NMR signals,
those of the terminal methyl groups (H-1 and H-4) display the
c
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Magn. Reson. Chem. 2010, 48, 192–197

Experimental verification of diverging mechanisms
Table 4. Calculated HOMO energies (E, in kJ/mol) and complexation
shifts ꢀδ(C-2, in ppm) for para-substituted phenylthioethers (2)
X =
H (2a)
NO2 (2d)
Br (2c)
F (2b)
OCH3a (2e)
E(HOMO) −572.0
ꢀδ(C-2)
−36.9b
−21.3b
+11.7b
+13.0b
−1.1c
+1.0c
−0.3c
−0.8c
a Average of values for the cisoid and transoid conformers.
b Relative to the energy of the parent compound with X = H (2a);
calculated density functionals with B3LYP 6-31G∗ basis set.
c Thesevaluesrefertothecorrespondingvalueoftheparentcompound
with X = H (2a).
Figure 3. Highest occupied molecular orbitals (HOMO) of the ether 1a
(left) and the thioether 2a (right); calculated density functionals at the
B3LYP 6-31G∗ level.[11]
.
Figure 4. 1H NMR signals of the terminal methyl groups H-1 of thioether
2d; bottom: free ligand, top: in the presence of an equimolar amount of
Rh∗; the dispersion ꢀν is 9 Hz (at 9.4 T; 400 MHz 1H).
spectrometer. Samples were ca 0.01–0.025 mmol in CDCl3. The
chemical shift reference is internal tetramethylsilane (δ = 0 ppm).
In the standard dirhodium experiment, Rh∗ and equimolar
amounts of the ligands 2a–3d, respectively, were dissolved in
0.7 ml CDCl3; quantities of 10–25 mg of Rh∗ (ca 0.01–0.025 mmol
concentration) were employed. If necessary, the dissolution
process was accelerated by exposing the NMR sample tubes to an
ultrasonic bath for a couple of minutes. In earlier reports on soft-
base ligands, the use of acetone-d6 for increasing the solubility of
Rh∗ has been recommended.[5] This auxiliary, however, has been
avoided in this study because acetone-d6 may be a competitor to
hard-base ligands in the adduct formation.
Note that ꢀν-values are B0 dependent and have no signs
here because racemates have been investigated. In this work, all
dispersion values ꢀν are given as integers in Hz as determined at
B0 = 9.4 T corresponding to 400 MHz 1H and 100.6 MHz 13C.
Infrared (IR) spectra were recorded on a Bruker Vector 22 and
mass spectra on a Micromass LCT.
Scheme 3. Schematic representation of the HOMO–LUMO interaction
between a thioether 2 and the dirhodium complex Rh∗.
most pronounced dispersions that can easily be integrated and
used for chiral differentiation (Fig. 4).
Slight signal dispersions are even observed for the sulfones (see
Section on Experimental), although their affinity to rhodium is
very low.
Experimental
Substances
Spectroscopy
The syntheses of Rh∗ and the ethers 1a–1d[7] have been
[4]
All NMR measurements were performed in analogy to those
described for the corresponding ethers 1; details of the one-
and two-dimensional NMR experiments (DEPT90 and DEPT135,
gradient-selected COSY, HMQC, and HMBC spectra) can be found
in Ref. [7]
1H (400.1 MHz) and 13C (100.6 MHz) NMR measurements were
recorded at room temperature on a Bruker Avance DPX-400
described by us earlier. Ether 1e and some of the thioethers
and sulfones, namely, 1e,[13] 2a,[14] 2d,[15]2e,[16] and 3a,[17] have
been described in the literature; all others are new. In nearly all
cases, complete spectral datasets were not documented properly;
therefore, we collect them in the following (for atom numberings
see Scheme 2).
c
Magn. Reson. Chem. 2010, 48, 192–197
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
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J. T. Mattiza, V. J. Meyer and H. Duddeck
4-Methoxy-1(1-methylpropyloxy)benzene (1e)
4-Methoxy-1(1-methylpropylthio)benzene(2e)
The preparation of 1e followed the procedure described for
1a–1d[7] except that 2-butyl-p-toluenesulfonate was used instead
of 2-bromobutane. The resulting ether 1e was obtained as a
colorless oil; yield 61%. 13C NMR (CDCl3): δ = 9.8 (CH3, C-4,
19.3 (CH3, C-1), 29.2 (CH2, C-3), 55.7 (CH, C-2), 76.2 (CH3, OCH3),
114.6 (CH, C-3ꢁ/5ꢁ), 117.4 (CH, C-2ꢁ/6ꢁ), 152.2 (C, C-1ꢁ), 153.8 ppm
(C, C-4ꢁ); 1H NMR (CDCl3): δ = 0.97 (t, 3H, H-4), 1.26 (d, 3H,
H-1), 1.65 (m, 2H, H-3), 3.76 (s, 1H, OCH3), 4.16 (ddq, 1H, H-2),
6.80 (m, 2H, H-3ꢁ/5ꢁ), 6.85 ppm (m, 2H, H-2ꢁ/6ꢁ); IR (liquid) ν˜: 3048,
2978, 2927, 1576, 1487, 1377, 1221, 1080, 83 cm−1. High-resolution
mass spectrometry ESI-negative calculated for C11H15O2: 179.1072
[M–H]− found: 179.1043 [M–H]−.
Yield: 58%. For NMR data, see Tables 1 and 2; IR (liquid) ν˜: 3060,
2960, 1570, 1325, 1283, 826 cm−1; (70 eV, rel. int. %) m/z 196 (88,
M+), 140 (100, M+-C4H8), 109 (52), 69 (32).
General procedure for the synthesis of the sulfones 3a–3e
The thioethers 2a–2e (0.25 g, 1.48 mmol) were dissolved in 30 ml
dichloromethane. Then, 0.59 g KMnO4 (3.73 mmol) and 0.30 g
CuSO4 (1.85 mmol) were added and the mixture refluxed for
24 h. After cooling to room temperature, the purple solution was
filtered over celite 535 (pH ≥8.5, Merck) and the solid washed with
dichloromethane. The combined, nearly colorless organic phases
were evaporated under reduced pressure to afford yellow, highly
viscous liquids.[19]
General procedure for the synthesis of the thioethers 2a–2e
Racemic thioethers 2a–2e were prepared by nucleophilic sub-
stitution reaction of rac.-2-butyl toluenesulfonate (obtained pre-
viously from toluenesulfochloride and 2-butanol in chloroform
and pyridine at 0 ◦C) and the respective commercially available
thiophenoles.[18]
(1-Methylpropyl)sulfonylbenzene (3a)
Yield: 74%. 13C (CDCl3) δ = 11.0 (CH3, C-4); 12.5 (CH3, C-1); 22.4
(CH2, C-3); 61.4 (CH, C-2); 128.9 (CH, C-2ꢁ/6ꢁ); 129.0 (CH, C-3ꢁ/5ꢁ);
133.4 (C, C-4ꢁ); 137.4 ppm (C, C-1ꢁ); ꢀδ = 0.0 (C-1), 0.1 (C-2, C-3,
C-4), −0.1 (C-1ꢁ), 0.5 (C-2ꢁ/6ꢁ), 0.1 ppm (C-3ꢁ/5ꢁ, C-4ꢁ); ꢀν = 1 (C-1,
C-2, C-3, C-4, C-1ꢁ, C-3ꢁ/5ꢁ), 0 Hz (C-2ꢁ/6ꢁ, C-4ꢁ); 1H (CDCl3) δ = 0.96
(t, 3H, H-4); 1.27 (d, 3H, H-1); 1.44 and 2.01 (ddq, 2H, H-3a/3b); 2.96
(tq, 1H, H-2); 7.56 (m, 2H, H-3ꢁ/5ꢁ); 7.65 (m, 1H, H-4ꢁ); 7.88 ppm (m,
2H, H-2ꢁ/6ꢁ); ꢀδ = 0.0 ppm (all protons); ꢀν = 1 (H-1), 0 Hz (H-2
to H-4ꢁ); IR (liquid) ν˜: 3023, 2934, 2912, 1584, 1336, 1287, 1151,
1020, 688 cm−1; EI-MS (70 eV, rel. int. %) m/z 198 (83, M+), 142
(100, M+-C4H8), 57 (42).
In a solution of 7.0 ml of the respective thiophenol in 6 ml
acetone, 1.06 g K2CO3 (7.6 mmol) was suspended, and then 1.76 g
rac.-2-butyl toluenesulfonate (7.7 mmol) was added. The mixture
was refluxed for 24 h, and acetone was evaporated under reduced
pressure. The residue was dissolved in 10 ml water and extracted
twice with 10 ml toluene. The combined organic phases were
washed twice with 10 ml aqueous sodium hydroxide (10%), dried
over Mg2SO4 followed by evaporation of toluene under reduced
pressure.Theobtainedrawproductwasaslightlyyellowliquidthat
was chromatographed on silica gel with a petrol ether/acetone
mixture (10 : 1) as eluent. It should be noted that purification by
chromatography on silical gel may lead to considerable loses,
probably due to a acid-catalyzed thiophenol elimination.
The phenyl thioethers are slightly yellow, highly viscous liquids.
4-Fluoro-1(1-methylpropylsulfonyl)benzene (3b)
Yield: 76%. 13C (CDCl3) δ = 11.1 (CH3, C-4); 12.6 (CH3, C-1);
6
22.6 (CH2, C-3); 61.8 (C, C-2, JFC = 1.3 Hz); 116.4 (CH, C-3ꢁ/5ꢁ,
3
2JFC = 22.4 Hz); 131.8 (CH, C-2ꢁ/6ꢁ, JFC = 8.0 Hz); 133.5 (C, C-1ꢁ,
4JFC = 3.7 Hz), 165.8 ppm(C, C-4ꢁ, 1JFC = 247.1 Hz);ꢀδ = −0.1(C-
1, C-2ꢁ/6ꢁ), 0.0 (C-2, C-3, C-3ꢁ/5ꢁ, C-4ꢁ), −0.1 (C-4), −0.3 ppm (C-1ꢁ);
ꢀν = 2 (C-1), 0 (C-2, C-2ꢁ/6ꢁ, C-3ꢁ/5ꢁ), −0.1 (C-1ꢁ), 1 Hz (C-3, C-4,); 1H
(CDCl3) δ = 0.99 (t, 3H, H-4); 1.27 (d, 3H, H-1); 1.44 and 2.02 (ddq,
2H, H-3a/3b); 2.94 (tq, 1H, H-2); 7.23 (m, 2H, H-3ꢁ/5ꢁ, 3JFH = 8.5 Hz),
7.89 ppm (m, 2H, H-2ꢁ/6ꢁ, 4JFH = 8.8 Hz); ꢀδ = 0.0 (H-1, H-3, H-4,
H-2ꢁ/6ꢁ), 0.1 ppm (H-2), not detected (H-3ꢁ/5ꢁ); ꢀν = 2 (H-1, H-2,
H-3), 1 Hz (H-4, H-2ꢁ/6ꢁ), not detected (H-3ꢁ/5ꢁ); IR (liquid) ν˜: 3025,
2935, 1578, 1321, 1235, 1212, 1117, 1068, 827, 802 cm−1; EI-MS
(70 eV, rel. int. %) m/z 216 (64, M+), 160 (100, M+-C4H8), 149 (54),
57 (38).
(1-Methylpropyl)thiobenzene (2a)
Yield: 58%. For NMR data, see Tables 1 and 2; IR (liquid) ν˜: 3056,
2963, 2924, 1584, 1479, 1438, 1025, 740, 691 cm−1; EI-MS (70 eV,
rel. int. %) m/z 166 (38, M+), 110 (100, M+-C4H8), 77 (10, C6H5+),
65 (13).
4-Fluoro-1(1-methylpropylthio)benzene (2b)
Yield: 65%. For NMR data, see Tables 1 and 2; IR (liquid) ν˜: 3050,
2964, 1589, 1488, 1219, 828 cm−1; EI-MS (70 eV, rel. int. %) m/z 184
(30, M+), 128 (100, M+-C4H8), 57 (20).
4-Bromo-1(1-methylpropylsulfonyl)benzene (3c)
4-Bromo-4(1-methylpropylthio)benzene (2c)
Yield: 73%. 13C (CDCl3) δ = 11.1 (CH3, C-4); 12.6 (CH3, C-1); 22.5
(CH2, C-3); 61.7 (CH, C-2); 128.9 (C, C-4ꢁ); 130.6 (CH, C-3ꢁ/5ꢁ); 132.4
(CH, C-2ꢁ/6ꢁ); 136.5 ppm (C, C-1ꢁ); ꢀδ = −0.1 (C-1), 0.0 (C-2), 0.0
(C-3), −0.1 (C-4), −0.3 (C-1ꢁ), 0.0 (C-2ꢁ/6ꢁ), 0.0 (C-3ꢁ/5ꢁ), 0.1 ppm
(C-4ꢁ); ꢀν = 2 (C-1), 1 (C-2), 1 (C-3), 1 (C-4), 0 (C-1ꢁ), 0 (C-2ꢁ/6ꢁ),
0 (C-3ꢁ/5ꢁ), 0 Hz (C-4ꢁ); 1H (CDCl3) δ = 0.99 (t, 3H, H-4); 1.27 (d,
3H, H-1); 1.43 and 2.00 (ddq, 2H, H-3a/3b); 2.94 (tq, 1H, H-2); 7.70
(m, 2H, H-2ꢁ/6ꢁ); 7.74 ppm (m, 2H, H-3ꢁ/5ꢁ); ꢀδ = 0.0 (H-1, H-3,
H-4, H-3ꢁ/5ꢁ), 0.1 ppm (H-2); ꢀν = 2 (H-1, H-2, H-3), 1 Hz (H-4,
H-2ꢁ/6ꢁ, H-3ꢁ5ꢁ); IR (liquid) ν˜: 3030, 2962, 1510, 1331, 1250, 846,
763, 705 cm−1; EI-MS (70 eV, rel. int. %) m/z 278/276 (87/85, M+),
222/200 (98/100, M+-C4H8), 141 (48 C6H4S+), 57 (24).
Yield: 54%. For NMR data, see Tables 1 and 2; IR (liquid) ν˜: 3050,
2964, 2924, 1472, 1384, 1091, 1069, 1008, 810 cm−1; EI-MS (70 eV,
rel. int. %) m/z 244/266 (42/41, M+), 188/190 (98/100, M+-C4H8),
109 (68 C6H4S+), 57 (59).
4-Nitro-1(1-methylpropylthio)benzene (2d)
Yield: 62%. For NMR data, see Tables 1 and 2; IR (liquid) ν˜: 3048,
2966,2927,1576,1507,1477,1332,1080,837,741cm−1;(70 eV,rel.
int. %) m/z 211 (98, M+), 155 (100, M+-C4H8), 109 (57, C6H5NO2+),
69 (54).
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2010, 48, 192–197

Experimental verification of diverging mechanisms
4-Nitro-1(1-methylpropylsulfonyl)benzene (3d)
[2] (a) C. Mertis, M. Kravaritoy, M. Chorianopoulou, S. Koinis,
N. Psaroudakis, Top. Mol. Org. Eng. 1994, 11, 321; (b) M. P. Doyle,
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Wiley: New York, 1998; (c) A. Endres, G. Maas, Tetrahedron 2002, 58,
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2155.
Yield: 82%. 13C (CDCl3), δ = 11.0 (CH3, C-4); 12.5 (CH3, C-1); 22.5
(CH2, C-3); 61.7 (CH, C-2); 124.2 (CH, C-3ꢁ/5ꢁ); 130.5 (CH, C-2ꢁ/6ꢁ);
143.4 (C, C-1ꢁ); 150.9 ppm (C, C-4ꢁ). ꢀδ = −0.2 (C-1), 0.0 (C-2), 0.0
(C-3), −0.1 (C-4), −0.4 (C-1ꢁ), 0.1 (C-2ꢁ/6ꢁ), 0.0 (C-3ꢁ/5ꢁ), 0.0 ppm
(C-4ꢁ); ꢀν = 4 (C-1), 2 (C-2), 2 (C-3), 2 (C-4), 0 (C-1ꢁ), 0 (C-2ꢁ/6ꢁ),
1
0 (C-3ꢁ/5ꢁ), 1 Hz (C-4ꢁ); H (CDCl3) δ = 1.01 (t, 3H, H-4); 1.30 (d,
3H, H-1); 1.47 and 2.01 (ddq, 2H, H-3a/3b); 3.02 (tq, 1H, H-2); 8.09
(m, 2H, H-2ꢁ/6ꢁ); 8.41 ppm (m, 2H, H-3ꢁ/5ꢁ); ꢀδ = 0.0 (H-1,H-3, H-4,
H-2ꢁ/6ꢁ), 0.1 ppm (H-2, H-3ꢁ/5ꢁ); ꢀν = 2 (H-1, H-3, H-4), 3 (H-2), 1 Hz
(H-2ꢁ/6ꢁ, H-3ꢁ/5); IR (liquid) ν˜: 3068, 2924, 1522, 1348, 1291, 1131,
1085, 854, 759, 737, 705 cm−1; EI-MS (70 eV, rel. int. %) m/z 244
(20, M+), 188 (40, M+-C4H8), 57 (100).
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J. Shorter), Plenum Press: New York, London, 1978, p 439.
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S. T. Brown, A. T. B. Gilbert, L. V. Slipchenko, S. V. Levchenko,
D. P. O’Neill, R. A. DiStasio Jr, R. C. Lochan, T. Wang, G. J. O. Beran,
N. A. Besley, J. M. Herbert, C. Y. Lin, T. Van Voorhis, S. H. Chien,
A. Sodt, R. P. Steele, V. A. Rassolov, P. E. Maslen, P. P. Korambath,
R. D. Adamson, B. Austin, J. Baker, E. F. C. Byrd, H. Dachsel,
R. J. Doerksen, A. Dreuw, B. D. Dunietz, A. D. Dutoi, T. R. Furlani,
S. R. Gwaltney, A. Heyden, S. Hirata, C.-P. Hsu, G. Kedziora,
R. Z. Khalliulin, P. Klunzinger, A. M. Lee, M. S. Lee, W. Z. Liang,
I. Lotan, N. Nair, B. Peters, E. I. Proynov, P. A. Pieniazek, Y. M. Rhee,
J. Ritchie, E. Rosta, C. D. Sherrill, A. C. Simmonett, J. E. Subotnik,
4-Methoxy-1(1-methylpropylsulfonyl)benzene(3e)
Yield: 67%. 13C (CDCl3), δ = 11.2 (CH3, C-4); 12.6 (CH3, C-1); 22.6
(CH2, C-3); 55.6 (CH3, OCH3); 61.7 (CH, C-2); 114.2 (CH, C-3ꢁ/5ꢁ);
128.8 (C, C-1ꢁ); 131.1 (CH, C-2ꢁ/6ꢁ); 163.6 ppm (C, C-4ꢁ).; ꢀδ = −0.1
(C-1), 0.1 (C-2), 0.0 (C-3), −0.1 (C-4), −0.1 (C-1ꢁ), 0.1 (C-2ꢁ/6ꢁ), 0.1
(C-3ꢁ/5ꢁ), 0.1 (C-4ꢁ) (C-4ꢁ), 0.2 ppm (OCH3); ꢀν = 2 (C-1), 1 (C-2), 1
(C-3), 1 (C-4), 0 (C-1ꢁ), 0 (C-2ꢁ/6ꢁ), 0 (C-3ꢁ/5ꢁ), 0 (C-4ꢁ), 1 Hz (OCH3); 1H
(CDCl3) δ = 0.97 (t, 3H, H-4); 1.26 (d, 3H, H-1); 1.40 and 2.02 (ddq,
2H, H-3a/3b); 2.91 (tq, 1H, H-2); 3.89 (s, 3H, OCH3); 7.02 (m, 2H,
H-3ꢁ/5ꢁ), 7.79 ppm (m, 2H, H-2ꢁ/6ꢁ); ꢀδ = 0 (H-1, H-3, H-4, H-2ꢁ/6ꢁ),
0.1 (H-2), −0.1 ppm (H-3ꢁ/5ꢁ); ꢀν = 2 (H-1, H-3), 0 Hz (H-2, H-4,
H-2ꢁ/6ꢁ, H-3ꢁ/5ꢁ); IR (liquid) ν˜: 3035, 2972, 1594, 1292, 1257, 1132,
1088, 833, 804 cm−1; EI-MS (70 eV, rel. int. %) m/z 242 (78, M+),
186 (100, M+-C4H8), 141 (37), 57 (21).
H. L. Woodcock III,
W. Zhang,
A. T. Bell,
A. K. Chakraborty,
D. M. Chipman, F. J. Keil, A. Warshel, W. J. Hehre, H. F. Schaefer,
J. Kong, A. I. Krylov, P. M. W. Gill, M. Head-Gordon, Phys. Chem.
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Calculations
All molecular calculations were calculated by density functional
methods (B3LYP 6-31G∗ level) using the SPARTAN ‘08 package,
version 1.0.0., Wavefunction Inc., Irvine, CA.[11]
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Acknowledgement
This work was supported by the Deutsche Forschungsgemein-
schaft (grant Du 98/34).
References
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(b) F. A. Cotton, R. A. Walton (Eds) in Multiple Bonds between Metal
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c
Magn. Reson. Chem. 2010, 48, 192–197
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
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