Control of the "Superexchange" Interaction through Diphenyl Sulfide 4,4'-Diyl Magnetic Coupler by Changing the Oxidation State and Conformation of the Sulfur Atom

Article abstract of DOI:10.1021/ja9643984

The exchange interaction between two triplet carbene centers through diphenyl sulfide 4,4'-diyl, its sulfoxide and sulfone analogs, and thiaxanthene 2,7-diyl coupling units was studied.Thse dicarbenes were generated by photolysis of the corresponding bisd

Full text of DOI:10.1021/ja9643984

8058
J. Am. Chem. Soc. 1997, 119, 8058-8064
Control of the “Superexchange” Interaction through Diphenyl
Sulfide 4,4′-Diyl Magnetic Coupler by Changing the Oxidation
State and Conformation of the Sulfur Atom
Kenji Matsuda, Takehiro Yamagata, Tomoo Seta, Hiizu Iwamura,* and
Kenzi Hori†
Contribution from the Institute for Fundamental Research in Organic Chemistry,
Kyushu UniVersity, Fukuoka 812-81, Japan
ReceiVed December 23, 1996X
Abstract: The exchange interaction between two triplet carbene centers through diphenyl sulfide 4,4′-diyl, its sulfoxide
and sulfone analogs, and thiaxanthene 2,7-diyl coupling units was studied. These dicarbenes were generated by
photolysis of the corresponding bisdiazo precursors in MTHF matrices at cryogenic temperatures. From the temperature
dependence of the ESR signals it was found that the dicarbene jointed through the sulfide group has a quintet ground
state; it serves as a ferromagnetic coupler. On the other hand, as the oxidation state or the geometry of the sulfur
atom was changed to sulfoxide, sulfone, and thiaxanthene groups, antiferromagnetic interaction was observed between
the two diphenylcarbene units. The magnitude of the exchange interaction J/k was determined to be 11, -30, -92,
and -21 K for diphenyl sulfide, sulfoxide, sulfone 4,4′-diyl, and thiaxanthene 2,7-diyl couplers, respectively. In the
ESR spectra of sterically unconstrained sulfide and its analogs the isolated triplet signals were rather strong. In the
thiaxanthene analog, however, this ratio of the isolated triplet signals to those of the other spin multiplicities was
smaller. The isolated triplets were attributed to the conformation where the two phenyl rings were perpendicular to
each other. It was demonstrated that the magnetic interaction could be tailored from ferro- to antiferromagnetic
coupling by changing the oxidation state or geometry of the sulfur atom.
Introduction
through m-phenylene and 1,3,5-benzenetriyl units. Since chains
and networks consisting of carbon atoms only have a number
of limitations from a preparative point of view, the introduction
of heteroatoms such as nitrogen, oxygen, and sulfur is considered
to be of help in expanding the scope of the structural variation.
However, the role of heteroatoms in coupling the spins in
polymer 1, for example, is not as clearly understood as in
hydrocarbons. The role of bridging heteroatom ligands in
effecting the magnetic coupling in bi- and polynuclear magnetic
metal complexes is interpreted in terms of “super-
exchange”.5 Our naive question was if we might be able to
interpret the coupling in organic polyradicals containing hetero-
atoms in a similar fashion via the filled π orbital localized on
the sulfur atom.
The design and synthesis of polyradicals having high-spin
ground states are subjects of great importance for deepening
our understanding of chemical bonds and developing potential
organic magnetic materials.1-4 In such systems, the control of
topological symmetry in alternant hydrocarbon polyradicals,
namely, connectivity of the radical centers through π-cross-
conjugated chains and networks, is a guiding principle for
aligning electron spins in parallel. Some of the highlights in
these studies include poly(trityl radicals) (S ) 4)3g and poly-
carbenes (S ) 9)2j,l in which the open shell centers are joined
† Current address: Department of Applied Chemistry and Chemical
Engineering, Faculty of Engineering, Yamaguchi University, Tokiwadai,
Ube 755 Japan.
Diphenyl ether 4,4′-diyl unit in dicarbene 2 is reported by
Itoh et al.6 to couple two carbene centers antiferromagnetically.
This was explained in terms of the superexchange or hyper-
X Abstract published in AdVance ACS Abstracts, August 1, 1997.
(1) For reviews see: (a) Iwamura, H. AdV. Phys. Org. Chem. 1990, 26,
179. (b) Dougherty, D. A. Acc. Chem. Res. 1991, 24, 88. (c) Iwamura, H.;
Koga, N. Acc. Chem. Res. 1993, 26, 346. (d) Kurreck, H. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 1409. (e) Miller, J. S.; Epstein A. J. Angew. Chem.,
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Miller, J. S.; Epstein, A. J. Chem. Eng. News 1995, Oct. 2, 30. (h) Kahn,
O. Molecular Magnetism; VCH: New York, 1993.
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1994, 33, 2091. (h) Rajca, A.; Rajca, S.; Desai, S. R. J. Am. Chem. Soc.
1995, 117, 806.
(4) Magnetic interaction through coupler: (a) Murata, S.; Iwamura, H.
J. Am. Chem. Soc. 1991, 113, 5547. (b) Matsumoto, T.; Ishida, T.; Koga,
N.; Iwamura, H. J. Am. Chem. Soc. 1992, 114, 9952. (c) Doi, T.; Ichimura,
A. S.; Koga, N.; Iwamura, H. J. Am. Chem. Soc. 1993, 115, 8928. (d) Jacobs,
S. J.; Shultz, D. A.; Jain, R.; Novak, J.; Dougherty, D. A. J. Am. Chem.
Soc. 1993, 115, 1744. (e) Mitsumori, T.; Inoue, K.; Koga, N.; Iwamura, H.
J. Am. Chem. Soc. 1995, 117, 2467.
(2) Polycarbens: (a) Teki, Y.; Takui, T.; Itoh, K.; Iwamura, H.;
Kobayashi, K. J. Am. Chem. Soc. 1983, 105, 3722. (b) Sugawara, T.;
Bandow, S.; Kimura, K.; Iwamura, H.; Itoh, K. J. Am. Chem. Soc. 1984,
106, 6449. (c) Teki, Y.; Takui, T.; Yagi, H.; Itoh, K.; Iwamura, H. J. Chem.
Phys. 1985, 83, 539. (d) Sugawara, T.; Bandow, S.; Kimura, K.; Iwamura,
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Fujita, I.; Teki, Y.; Takui, T.; Kinoshita, T.; Itoh, K;. Miko, F.; Sawaki,
Y.; Iwamura, H.; Izuoka, A.; Sugawara, T. J. Am. Chem. Soc. 1990, 112,
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S0002-7863(96)04398-3 CCC: $14.00 © 1997 American Chemical Society

“Superexchange” Interaction through Diphenyl Sulfide 4,4′-Diyl
J. Am. Chem. Soc., Vol. 119, No. 34, 1997 8059
Scheme 1a
Figure 1. ESR spectra of the photoproducts of 4d in 10 mM MTHF
matrix (9.42 GHz) (a) at 9.7 K and (b) at 34.1 K. Signals denoted Ti,
Tt, and Q are assigned to isolated triplet, thermally populated triplet,
and quintet signals, respectively.
a Reagents and conditions: (a) PhCOCl, CCl4, 44%; (b) H2O2,
acetone, 40%; (c) t-BuOCl, CH2Cl2, 46%; (d) N2H4, N2H4‚HCl, DMSO;
(e) BaMnO4, CH2Cl2, or HgO, CH2Cl2, 29-58%, two steps; (f)
PhCOCl, PhNO2, 40%.
conjugation on the oxygen atom. On the other hand Kaise, Yabe
et al.7 found that two triplet nitrene centers appeared to be
coupled ferromagnetically in dinitrene 3. Sulfur is on the third
row of the periodic table and so is able to have high oxidation
states. Effect of the oxidation state and/or geometry of the sulfur
atom in diphenyl sulfide 4,4′-diyl coupler has now been studied.8
Figure 2. ESR spectra of the photoproducts of 5d in 10 mM MTHF
matrix (9.41 GHz) (a) at 9.7 K and (b) at 34.1 K. Signals denoted Ti,
Tt, and Q are assigned to isolated triplet, thermally populated triplet,
and quintet signals, respectively.
Results and Discussion
showed from the correlation signal between positions 1 and 9
that the benzoyl substituents were at the 2,7-positions (see
Supporting Information). For diazo compounds 4d-7d IR
spectra showed absorptions at about 2040 cm-1, confirming the
presence of diazo groups. Moreover the sulfoxide group in 5d
and sulfone group in 6d were confirmed by absorptions at 1050
cm-1 and 1154, 1312 cm-1, respectively. UV-vis spectra
showed n-π* absorption maxima at 502-524 nm and slightly
blue-shifted as the oxidation state of the sulfur atom increased.
Diazo compounds 4d-7d were rather stable and could be kept
in a refrigerator for weeks.
Synthesis of the Precursors. Diazo precursors 4d-7d were
synthesized according to Scheme 1. Diphenyl sulfide was
treated with benzoyl chloride to give bis(p-benzoylphenyl)
sulfide 4k.9 Oxidation of sulfide 4k with hydrogen peroxide
or tert-butyl hypochlorite afforded bis(p-benzoylphenyl) sulf-
oxide 5k or sulfone 6k.10 The diketone of thiaxanthene 7k was
synthesized from thiaxanthone. Ketones 4k-7k were converted
to the corresponding hydrazones and then to the corresponding
diazo compounds 4d-7d (Scheme 1).
ESR Measurement of the Dicarbenes. Photolyses of diazo
compounds 4d-7d were carried out in 2-methyltetrahydrofuran
(MTHF) solid solutions in an ESR cavity at 9 K by using light
(λ > 420 nm) from a high-pressure mercury lamp for 60-150
min. ESR spectra of dicarbenes 4c-7c are shown in Figures
1-4. The observed spectral patterns did not change from initial
to later stages of the irradiation and were found to consist of
three sets of signals due to an isolated triplet, a thermally
populated triplet, and a quintet species. From the resonance
field, the signal around 90 mT (marked Ti) was assigned to the
-z transition of an isolated triplet species. The signal around
280 mT (marked Q) was assigned to the quintet of the interacting
dicarbene in reference to those of the corresponding biphenyl
dicarbenes.11 The additional signal (marked Tt) beside the
Diazo compounds were characterized by NMR, IR, and UV-
vis spectroscopy. 1H and 13C NMR spectra were fully assigned.
HH-COSY and relay shift correlation spectrum of 7k clearly
(7) Nimura, S.; Kikuchi, O.; Ohana, T.; Yabe, A.; Kaise, M. Chem. Lett.
1994, 1679.
(8) A preliminary report on the sufide and sufoxide isomers appeared
in: Matsuda, K.; Yamagata, T.; Iwamura, H. Chem. Lett. 1995, 1085.
(9) Dilthey, W.; Neuhaus, L.; Reis, E.; Schommer, W. J. Prakt. Chem.
1930, 124, 114.
(10) Walling, C.; Mintz, M. J. J. Org. Chem. 1967, 32, 1286.

8060 J. Am. Chem. Soc., Vol. 119, No. 34, 1997
Matsuda et al.
a)
Figure 3. ESR spectra of the photoproducts of 6d in 10 mM MTHF
matrix (9.41 GHz) (a) at 9.7 K and (b) at 34.1 K. Signals denoted Ti
and Tt are assigned to isolated triplet and thermally populated triplet,
respectively.
b)
c)
Figure 4. ESR spectra of the photoproducts of 7d in 10 mM MTHF
matrix (9.41 GHz) (a) at 13.3 K and (b) at 43.9 K. Signals denoted Ti,
Tt, and Q are assigned to isolated triplet, thermally populated triplet,
and quintet signals, respectively.
Table 1. Resonance Magnetic Field for Dicarbenes 4c-7c
ESR resonance field (mT)
compd
Ti (-z)a
Tt (-z)
Q
4c
5c
6c
7c
85
94
89
92
112
114
120
78
264
284
not obsd
285
Figure 5. Plots of the intensities of the ESR signal at (a) 85 mT (Ti)
due to the isolated triplet, (b) 264 mT (Q) due to the ground state
quintet, and (c) 112 mT (Tt) due to the thermally populated triplet of
4c vs reciprocal of temperature. The fitting of a theoretical curve for
thermally populated triplet signals was performed in the temperature
range where the dicarbene was chemically intact and the isolated triplet
signals obeyed Curie-Weiss law.
a Signals denoted Ti, Tt, and Q are assigned to isolated triplet,
thermally populated triplet, and quintet signals, respectively. For the
assignment of the signals, see text.
isolated triplet signals was assigned to the thermally populated
triplet signals due to the interacting dicarbene. These kinds of
thermally populated triplet signals are reported in the interacting
bis(trimethylenemethane)-type tetraradical.4d While the intensity
of the isolated triplet signals was strong in the ESR spectra of
the dicarbenes 4c-6c, that of dicarbene 7c was very weak. The
meaning of this observation will be discussed later. In the ESR
spectra of the dicarbenes 5c-7c, one more signal was observed
around 100 mT. This signal was tentatively assigned to a
forbidden band (∆ms ) 2) due to the thermally populated triplet
species. The resonance fields of 4c-7c are summarized in
Table 1.
The plots of the ESR signal intensity vs reciprocal temperature
are shown in Figures 5-8. The signals due to the isolated
triplets obeyed Curie-Weiss laws in the temperature ranges 10-
50 K for dicarbene 4c and 6c and 20-50 K for 5c and 7c,
respectively. The quintet and thermally populated signals
showed different behavior depending upon the dicarbene species.
The quintet signal due to 4c obeyed a Curie-Weiss law, but
the thermally populated triplet signal grew in, reached a
maximum intensity at ca. 45 K, and then decreased as the
temperature was increased (Figure 5). For 5c, the thermally
populated triplet signal showed maximum intensities at ca. 50
K, whereas quintet signal grew up to 50 K (Figure 6). For 6c,
neither thermally populated triplet nor thermally populated
quintet signals were observed up to 37 K. However, the
thermally populated triplet signal appeared above 39 K and
started to increase with increasing temperature (Figure 7). For
7c, the isolated signal was very small compared to the other
carbenes described above. Therefore the temperature depen-
dence of the isolated triplet signal was measured on the y
transition (469 mT). The position of the thermally populated
signal shifted to the lower field. The behavior of the temperature
dependent signals was similar to the case of 5c, the thermally
populated triplet signal showed maximum intensities at ca. 30
K, and the quintet signal intensity increased to 50 K (Figure
8). From these observations, 4c was concluded to have quintet
ground states: ferromagnetic interaction between two carbenes,
while 5c, 6c, and 7c have singlet ground states: antiferromag-
netic interaction between the two carbenes.
Effect of Oxidation State on Sulfur Atom in Super-
exchange Interaction. According to the theory of two weakly
interacting robust triplets,6,12 for which spin Hamiltonian is given
by eq 1, antiferromagnetic interaction (J < 0) leads to a ground
singlet state with excited triplet and quintet states that are higher
in energy by -2J and -6J, respectively, from the ground state,
where J is the exchange integral of two electrons, one on each
(11) Teki, Y.; Fujita, I.; Takui, T.; Kinoshita, T.; Itoh, K. J. Am. Chem.
Soc. 1994, 116, 11499.
(12) Itoh, K. Pure Appl. Chem. 1978, 50, 1251.

“Superexchange” Interaction through Diphenyl Sulfide 4,4′-Diyl
J. Am. Chem. Soc., Vol. 119, No. 34, 1997 8061
Figure 7. Plots of the intensities of the ESR signal at (a) 89 mT (Ti)
due to the isolated triplet and (b) 120 mT (Tt) due to the thermally
populated triplet of 6c vs reciprocal of temperature. The fitting of a
theoretical curve for thermally populated triplet signals was performed
in the temperature range where the dicarbene was chemically intact
and the isolated triplet signals obeyed Curie-Weiss law.
Correlation between the Ground States and Their Ge-
ometry. In order to understand the relationship between the
ground states of the carbenes and the geometry around the
bridging fragment, the geometries of 4d, 5d, and 7d which are
parent molecules of the observed carbenes, were optimized by
using ab initio molecular orbital (MO) calculations on the
GAUSSIAN94 program.15 The 3-21G* basis sets were used
to optimize geometries since higher basis sets handle such big
molecules containing four phenyl rings with some difficulty.16
We chose the parent diazo compounds to estimate the confor-
mations of the carbenes, because the carbenes were safely
assumed to take the conformers very similar to those of the
parent diazo compounds in the temperature range where
photolyses of the diazo compounds were carried out and the
carbenes were studied; in this temperature region no effect of
the annealing on the resonance fields was observed, and the
temperature dependence on the signal intensities was reversible.
Figure 9 displays the optimized structures. It is quite
interesting that the Ph-C(N2)-Ph fragments of the parent
molecules exhibit almost the same geometry since there are no
differences in bond lengths and angles except for the Ph-S-
Ph moiety. The change in the Ph-S-Ph angles causes a distinct
difference between 4d and 5d, i.e., the geometrical relationship
of the phenyl group bridged by the S atom. In order to clarify
Figure 6. Plots of the intensities of the ESR signal at (a) 94 mT (Ti)
due to the isolated triplet, (b) 284 mT (Q) due to the thermally populated
quintet, and (c) 111 mT (Tt) due to the thermally populated triplet of
5c vs reciprocal temperature. The fitting of a theoretical curve for
thermally populated triplet signals was performed in the temperature
range where the dicarbene was chemically intact and the isolated triplet
signals obeyed Curie-Weiss law.
of the carbene centers. When a ferromagnetic interaction (J >
0) is operative, a quintet ground state with excited triplet and
singlet states higher in energy by 4J and 6J, respectively, is
observed. The observed data were analyzed in terms of the
Bleaney-Bowers-type thermal distribution among the three
states:13 for 4c,
H ) -2JS1‚S2
(1)
3 exp(-4J/kT)
5 + 3 exp(-4J/kT) + exp(-6J/kT)
C
T
I(Tt) )
(2)
and for 5c, 6c, and 7c,
(14) Takui, T.; Endoh, M.; Okamoto, M.; Satoh, K.; Shichiri, T.; Teki,
Y.; Kinoshita, T.; Itoh, K. Mat. Res. Soc. Symp. Proc. 1990, 173, 63.
(15) The Gaussian 94 calculation were performed at the Institute for
Molecular Science, Okazaki, Japan. Gaussian 94, Revision C.2; Frisch, M.
J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson, B. G.; Robb,
M. A.; Cheeseman, J. R.; Keith, T.; Petersson, G. A.; Montgomery, J. A.;
Raghavachari, K.; Al-Laham, M. A.; Zakrzewwski, V. G.; Ortiz, J. V.;
Foresman, J. B.; Cioslowski, B. B.; Stefanov, A.; Nanayakkara, A.;
Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.;
Anders, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J.;
Binkley, J. S.; Defrees, D. J.; Baker, J; Stewart, J. P.; Head-Gordon, M.;
Gonzalez, C.; Pople, J. A. Gaussian, Inc.: Pittsburgh, PA, 1995.
(16) We also optimized H(N2)C-C6H5-X-C6H5-C(N2)H (X ) S, SO)
at the 6-31G* level of theory and obtained similar results. The dihedral
angles for X ) S and SO were calculated to be 88.3° and 105.0°,
respectively.
3 exp(2J/kT)
C
T
I(Tt) )
(3)
1 + 3 exp(2J/kT) + 5 exp(6J/kT)
Fitting of the observed intensity data for thermally populated
triplets to these equations in the temperature ranges where the
dicarbenes were chemically intact and the isolated triplet signals
obeyed Curie-Weiss laws gave exchange integral J/k values
of 11, -30, -92, and -21 K for 4c-7c, respectively (Figures
5-8). The fitting of the thermally populated quintet signal for
5c and 7c could not be accurately performed because of the
decomposition of the carbenes.
(13) Bleaney, B.; Bowers, K. D. Proc. R. Soc. London, 1982, A214, 451.

8062 J. Am. Chem. Soc., Vol. 119, No. 34, 1997
Matsuda et al.
a)
b)
c)
Figure 9. Optimized structure of 4d, 5d, and 7d. The 3-21G* basis
sets were served to optimize geometries.
Table 2. Total Energies and Geometrical Parametersa in the
Optimized Geometries of 4d, 5d, and 7d
4d
5d
7d
total energy
S-C
-1601.59057 -1675.98846 -1639.25940
1.781
1.286
1.778
1.287
1.775
1.286
C-N
CSC
101.8
98.8
98.6
dihedral angle 1b
torsion anglec
dihedral angle 2d
93.3
+61.3
59.3
104.1
-99.8
59.7
132.2
-39.0
59.1
Figure 8. Plots of the intensities of the ESR signal at (a) 469 mT (Ti)
due to the isolated triplet, (b) 285 mT (Q) due to the thermally populated
quintet, and (c) 78 mT (Tt) due to the thermally populated triplet of 7c
vs reciprocal of temperature. The fitting of a theoretical curve for
thermally populated triplet signals was performed in the temperature
range where the dicarbene was chemically intact and the isolated triplet
signals obeyed Curie-Weiss law.
a Energies in Haretree unit, lengths and angles in Å and deg units.
b Dihedral angles of the two phenyl planes connected with the S atom.
c The angles between two phenyl rings and CSC plane. Plus and minus
signs correspond to con- and disrotations, respectively. d The average
dihedral angles of the two phenyl planes in the Ph-C(N2)-Ph fragments.
these differences, we used the dihedral angle and torsion angle
(Table 2). Torsion angle is defined as the angle between the
phenyl ring and the CSC plane. Plus and minus signs
correspond to con- and disrotations, respectively. The two
phenyl rings in 4c are in conrotation and takes an almost
perpendicular geometry; the torsion angle is calculated to be
+61.3°. This geometry is considered to be related to the
exchange interaction.
The two phenyl rings are disrotated in the optimized geometry
of 5d and 7d; torsion angles were calculated to be -99.8° and
-39.0° for 5d and 7d, respectively. We can consider a kind
of the conjugative interaction as shown schematically in Scheme
2. This kind of resonance structure stabilizes the singlet ground
state. The semiempirical PM3-CI calculation of the dinitrene
3 showed7 that the energy gaps between singlet and quintet states
are dependent on the torsion angle of two phenyl rings. Fang
et al. have described the correlation between torsion angle and
the magnetic interaction.17
The adjacent phenyl rings may also help to stabilize the singlet
states of 5c and 7c. Considering this effect, it is highly likely
that the opposite magnetic interaction was observed between
two carbenes in 4c and 5c.
Observed Strong Isolated Triplet Signals. For dicarbenes
4c-6c strong signals assigned to isolated triplet species were
observed. Such signals are also observed for oxygen-linked
dicarbene 2. Itoh et al. explained this phenomenon in terms of
a monocarbene due to incomplete photolysis.6 We measured
the ESR spectra of the carbenes under different conditions of
photolysis for various specimens and on different concentration
of the sample. However, there was no evidence for a trans-
formation from monocarbene to dicarbene even under prolonged
irradiation. Therefore the signals are assigned to the dicarbenes.
The calculated structure of 4c and 5c showed that the two
phenyl rings were perpendicular to each other; the dihedral angle
was nearly 90° (Table 2). It is suggested that the isolated triplet
signals should be attributed to the conformers where the two
phenyl rings were perpendicular to each other. When the two
diphenylcarbene units are connected by the vinylene double
bond,18 isolated triplet signals are in fact very small when
The magnitude of this singlet ground state stabilization should
not be very large because the rings do not take the coplanar
geometry shown in Figure 9. However, this is large enough to
reverse the ordering of the small singlet-quintet energy gap.
(17) Fang, S.; Lee, M.-S.; Hrovat, D. A.; Borden, W. T. J. Am. Chem.
Soc. 1995, 117, 6727.
(18) Murata, S.; Sugawara, T.; Iwamura, H. J. Am. Chem. Soc. 1987,
109, 1266.

“Superexchange” Interaction through Diphenyl Sulfide 4,4′-Diyl
J. Am. Chem. Soc., Vol. 119, No. 34, 1997 8063
with dichloromethane, washed with aqueous hydrochloric acid, aqueous
sodium carbonate, and water, dried, and concentrated. Column
chromatography (silica, hexane:dichloromethane ) 7:3) gave sulfide
4k (4.87 g, 44%) as a white solid: mp 169.0-169.9 °C; IR (KBr) ν
3050, 1650, 1590 cm-1; 1H NMR (270 MHz, CDCl3) δ 7.45-7.53 (m,
8H, Ar-H), 7.61 (t, J ) 7.3 Hz, 2 H, Ar-H), 7.76-7.82 (m, 8 H, Ar-
H); 13C NMR (67.8 MHz, CDCl3) δ 128.3, 129.9, 130.3, 130.9, 132.5,
136.3, 137.2, 140.3, 195.6. Anal. Calcd for C26H18O2S: C, 79.16; H,
4.60; S, 8.13. Found: C, 79.40; H, 4.82; S, 8.25.
Scheme 2
Bis(p-benzoylphenyl) Sulfoxide (5k). To a stirred solution of
sulfide 4k (197 mg, 0.50 mmol) in 2 mL of acetone and 5 mL of
dichloromethane was added 0.1 mL of 30% solution of hydrogen
peroxide in water and stirred at room temperature for 2 weeks. The
reaction mixture was poured into aqueous sodium sulfate and extracted
with dichloromethane, washed with water, dried, and concentrated.
Column chromatography (silica, hexane:dichloromethane ) 7:3) gave
sulfoxide 5k (82.9 mg, 40%) as a white solid: mp 162.3-162.9 °C;
IR (KBr) ν 3050, 1650, 1590, 1060 cm-1; 1H NMR (270 MHz, CDCl3)
δ 7.49 (t, J ) 7.5 Hz, 4 H, Ar-H), 7.62(t, J ) 6.6 Hz, 2 H, Ar-H),
7.76-7.83 (m, 8H, Ar-H), 7.90 (d, J ) 8.4 Hz, 4 H, Ar-H); 13C NMR
(67.8 MHz, CDCl3) δ 124.4, 128.4, 130.0, 130.8, 133.0, 136.6, 140.2,
149.1, 195.3. Anal. Calcd for C26H18O3S: C, 76.08; H, 4.42; S, 7.81.
Found: C, 75.88; H, 4.45; S, 8.00.
compared to analogs having a sulfide coupler. The two phenyl
rings of thiaxanthene 7c are fixed to an envelope form as the
thiaxanthene ring should shallow boat form; a dihedral angle
was 132.2°. In the ESR spectrum of 7c, isolated triplet signal
was weaker compared to those of 4c-6c. This observation
supports the interpretation about the origin of the isolated triplet
signal.
Bis(p-benzoylphenyl) Sulfone (6k). To a stirred solution of sulfide
4k (2.5 g, 6.33 mmol) in 30 mL of dichloromethane was added tert-
butylhypochlorite (13.7 g, 126 mmol) and stirred for 2 weeks. The
reaction mixture was concentrated in Vacuo and purified by column
chromatography (silica, dichloromethane) to give sulfone 6k (1.24 g,
46%) as a white powder: mp 200.2-201.0 °C; IR (KBr) ν 3090, 3060,
Conclusions
Four dicarbenes possessing diphenyl sulfide, sulfoxide, and
sulfone 4,4′-diyl and thiaxanthene 2,7-diyl coupling units were
photochemically generated. From the temperature dependence
of the ESR signal intensity the exchange coupling constants
J/k were determined: 11 K in diphenyl sulfide 4,4′-diyl: -30
K sulfoxide: -92 K sulfone: -21 K thiaxanthene 2,7-diyl.
Thiaxanthene derivative 7c has an additional methylene bridge
meta to the carbene centers. However the superexchange
interaction through this meta-methylene moiety is estimated to
be very small and therefore we may neglect the effect of the
methylene group.14 It was demonstrated that the superexchange
interaction could be controlled by changing the oxidation state
or either geometry of the sulfur atom. Unlike alternant
hydrocarbon systems, the spin systems which include heteroatom
cannot be predicted by the topological symmetry alone. In the
case of the interaction through sulfur atom, the geometry played
an important role in determining the value of the exchange
interaction.
1
1670, 1319, 1170 cm-1; H NMR (270 MHz, CDCl3) δ 7.50 (t, J )
7.3 Hz, 4 H, Ar-H), 7.64 (t, J ) 7.6 Hz, 2 H, Ar-H), 7.78 (d, J ) 6.9
Hz, 4 H, Ar-H), 7.91 (d, J ) 8.3 Hz, 2 H, Ar-H), 8.10 (d, J ) 8.3 Hz,
4 H, Ar-H); 13C NMR (67.8 MHz, CDCl3) δ 127.9, 128.6, 130.1, 130.6,
133.4, 136.2, 142.1, 143.9, 207.0. Anal. Calcd for C26H18O4S: C,
73.22; H, 4.25. Found: C, 73.26; H, 4.23.
Bis[p-(r-hydrazinobenzyl)phenyl] Sulfide (4h). To a solution of
sulfide 4k (103 mg, 0.26 mmol) in 1.5 mL of anhydrous hydrazine
and 6.0 mL of dry DMSO was added hydrazine monohydrochloride
(140 mg, 2.0 mmol). After stirring at 90 °C under argon atmosphere
for 0.5 h, the reaction mixture was poured into water. The mixture
was extracted with ether, washed with water, dried, and concentrated
to give bishydrazone 4h (111 mg) as a colorless oil: IR (KBr) ν 3400,
3060, 1590, 1570 cm-1; 1H NMR (270 MHz, CDCl3) δ 5.38-5.52 (m,
4 H, NH2), 7.13-7.57 (m, 18 H, Ar).
Bis[p-(r-hydrazinobenzyl)phenyl] Sulfoxide (5h). To a solution
of sulfoxide 5k (101 mg, 0.25 mmol) in 1.5 mL of anhydrous hydrazine
and 6.0 mL of dry DMSO was added hydrazine monohydrochloride
(150 mg, 2.2 mmol). After stirring at 90 °C under argon atmosphere
for 18 h, the reaction mixture was poured into water. The mixture
was extracted with ether, washed with water, dried, and concentrated
to give bishydrazone 5h (112 mg) as a white oil: IR (KBr) ν 3380,
Experimental Section
A. Materials. 1H and 13C NMR spectra were recorded on a JEOL
GX-270 and JEOL EX-270 instruments. IR spectra were obtained on
a Hitachi I-5040 spectrometer. UV-vis spectra were recorded on a
Hitachi U-3300 spectrophotometer. Melting points are not corrected.
Benzoyl chloride and dimethyl sulfoxide (DMSO) were distilled
under reduced pressure from calcium hydride. 2-Methyltetrahydrofuran
(MTHF) used in the magnetic measurements was purified by successive
distillation from lithium aluminum hydride under a nitrogen atmosphere
and from sodium-benzophenone ketyl under a dry nitrogen atmosphere.
All reactions were performed under an atmosphere of dry nitrogen
unless otherwise specified. Anhydrous magnesium sulfate was used
as the drying agent.
All reactions were monitored by thin-layer chromatography carried
out on 0.2-mm E. Merck silica gel plates (60F-254) using UV light as
a detector. Column chromatography was performed on silica gel
(Wakogel C-200, 200 mesh) or neutral alumina (ICN, activity grade
IV).
1
3050, 1570, 1550, 1040 cm-1; H NMR (270 MHz, CDCl3) δ 5.30-
5.59 (m, 4 H, NH2), 7.13-7.91 (m, 18 H, Ar).
Bis[p-(r-hydrazinobenzyl)phenyl] Sulfone (6h). To a solution of
sulfone 6k (2.0 g, 4.7 mmol) in 30 mL of anhydrous hydrazine and
100 mL of dry DMSO was added hydrazine monohydrochloride (5.0
g, 73 mmol). After stirring at 110 °C under argon atmosphere for 24
h, the reaction mixture was poured into water. The mixture was
extracted with ether, washed with water, dried, concentrated, and
column chromatography (silica, dichloromethane:diethyl ether ) 7: 3)
to give bishydrazone 6h (1.16 g) as a white solid: IR (KBr) ν 3413,
1318, 1152 cm-1; 1H NMR (270 MHz, CDCl3) δ 5.30-5.70 (m, 4 H,
NH2), 7.20-8.23 (m, 18 H, Ar).
Bis[p-(r-diazobenzyl)phenyl] Sulfide (4d). To a solution of
bishydrazone 4h (43 mg, 0.10 mmol) in 6 mL of dichloromethane was
added barium manganate (90 mg) in the dark and stirred 3 h at room
temperature with monitoring the reaction by the thin layer chromatog-
raphy (alumina). Filtration, concentration, and purification by chro-
matography (alumina act. IV, hexane:dichloromethane ) 2:1) gave
bisdiazo compound 4d (24 mg, 58%, 2 steps) as a deep red viscous
oil: IR (KBr) ν 2920, 2040, 1590 cm-1; UV-vis (CH2Cl2) λmax(ꢀ) 292
Bis(p-benzoylphenyl) Sulfide (4k).9 To a stirred slurry of aluminum
trichloride (8.6 g, 64.5 mmol) in 35 mL of carbon tetrachloride was
added benzoyl chloride (7.2 mL, 62 mmol) at 5 °C. Diphenyl sulfide
(4.7 mL, 28 mmol) was added to the mixture at 5 °C dropwise for 2 h.
After the mixture was stirred for 24 h at 20 °C, the reaction mixture
was poured into aqueous hydrochloric acid. The mixture was extracted

8064 J. Am. Chem. Soc., Vol. 119, No. 34, 1997
Matsuda et al.
(29700), 523 (244) nm; 1H NMR (270 MHz, CDCl3) δ 7.20-7.25 (m,
6 H), 7.27-7.32 (m, 4 H), 7.35-7.43 (m, 8 H).
extracted with ether, washed with water, dried, and concentrated.
Column chromatography (silica, dichloromethane:Et2O ) 3:1) gave
bishydrazone 7h (180 mg, 84%) as a white powder: IR (KBr) ν 3391,
3281, 1580 cm-1; 1H NMR (270 MHz, CDCl3) δ 3.76-3.98 (m, 2 H,
CH2), 5.42 (bs, 4 H, NH2), 7.10-7.65 (m, 16 H, Ar).
2,7-Bis(r-diazobenzyl)thiaxanthene (7d). To a solution of bishy-
drazone 7h (30 mg, 0.07 mmol) in 10 mL of dichloromethane was
added yellow mercury oxide (200 mg) in the dark and the solution
was stirred for 16 h at room temperature with monitoring of the reaction
by thin layer chromatography (alumina). Filtration, concentration, and
purification by chromatography (alumina act. IV, pentane) gave
bisdiazo compound 7d (10 mg, 34%) as a deep red solid: IR (NaCl)
ν 3058, 3027, 2926, 2031, 1593 cm-1; UV-vis (CH2Cl2) λmax(ꢀ) 297
(32 000), 335 (sh), 524 (230) nm; 1H NMR (270 MHz, CDCl3) δ 3.83
(s, 2 H), 7.11-7.46 (m, 16 H); 13C NMR (67.8 MHz, CDCl3) δ 37.8,
60.6, 121.8, 122.9, 123.6, 124.1, 125.9, 126.5, 127.5, 127.7, 129.3,
135.3.
B. ESR Measurement. Photolyses of diazo compounds 4d-7d
were carried out in MTHF matrices at 9 K in an ESR cavity. The
light was obtained from a High-Pressure Mercury lamp by combina-
tion of a Kenko L-42 sharp cut filter and an quartz water filter. A
Bruker ESP 300 spectrometer was used to obtain X-band ESR Spectra.
Temperatures were controlled by an Air Products LTD-3-110 cryogenic
temperature controller. The cryostat was maintained at high vacuum
by a diffusion/rotary pump set.
The ESR intensities for I-1/T plots in the temperature range 9-70
K were measured at appropriate power attenuation calibrated to exclude
saturation effects. The temperatures were stepped up from 9 to 70 K
with intervals of ca. 2 K. For the analysis of the intensity, the
temperature region where the isolated triplet signal obeyed Curie-
Weiss law was used.
Bis[p-(r-diazobenzyl)phenyl] Sulfoxide (5d). To a solution of
bishydrazone 5h (43 mg, 0.10 mmol) in 6 mL of dichloromethane was
added barium manganate (90 mg) in the dark and stirred 3 h at room
temperature with monitoring the reaction by the thin layer chromatog-
raphy (alumina). Filtration, concentration, and purification by chro-
matography (alumina act. IV, hexane:dichloromethane ) 7:3) gave
bisdiazo compound 5d (24 mg, 39%, two steps) as a deep red viscous
oil: IR (KBr) ν 3060, 2040, 1590, 1050 cm-1; UV-vis (CH2Cl2) λmax(ꢀ)
295 (56900), 333 (64600), 509 (174) nm; 1H NMR (270 MHz, CDCl3)
δ 7.22-7.34 (m, 10 H), 7.42 (t, J ) 7.5 Hz, 4 H), 7.61 (t, J ) 8.8 Hz,
4 H).
Bis[p-(r-diazobenzyl)phenyl] Sulfone (6d). To a solution of
bishydrazone 6h (300 mg, 0.66 mmol) in 50 mL of dichloromethane,
50 mL of benzene, and 50 mL of hexane was added barium manganate
(2 g) in the dark, and the solution was stirred 18 h at room temperature
with monitoring the reaction by the thin layer chromatography
(alumina). Filtration, concentration, and purification by chromatography
(alumina act. IV, hexane:dichloromethane ) 9:1) gave bisdiazo
compound 6d (170 mg, 29%, two steps) as a red powder: IR (KBr) ν
2043, 1586, 1154, 1312 cm-1; UV-vis (CH2Cl2) λmax(ꢀ) 232 (27 000),
286 (23 000), 356 (36 000), 502 (310) nm; 1H NMR (270 MHz, CDCl3)
δ 7.23-7.36 (m, 10 H), 7.45 (t, J ) 7.4 Hz, 4 H), 7.87 (d, J ) 8.6 Hz,
4 H); 13C NMR (67.8 MHz, CDCl3) δ 63.4, 123.5, 126.5, 127.0, 127.4,
128.2, 129.3, 136.4, 137.2.
2,7-Dibenzoylthiaxanthene (7k). To a stirred slurry of aluminum
trichloride (2.0 g, 15 mmol) in 5 mL of nitrobenzene was added benzoyl
chloride (1.8 mL, 15 mmol) at 5 °C. Thiaxanthene (1.0 g, 5.0 mmol)
was added to the mixture at 5 °C dropwise. After the solution was
stirred for 24 h at 20 °C, the reaction mixture was poured into aqueous
hydrochloric acid. The mixture was extracted with dichloromethane,
washed with aqueous hydrochloric acid, aqueous sodium carbonate and
water, dried, and concentrated. Column chromatography (silica,
dichloromethane) gave sulfide 7k (0.82 g, 40%) as a white solid: mp
Acknowledgment. The authors thank the Computer Center,
Institute for Molecular Science at the Okazaki National Research
Institutes for the use of the NEC HSP computer and the Library
Program GAUSSIAN94. This work was supported by a Grant-
in-Aid for Scientific Research (B) (No. 06453035) from the
Ministry of Education, Science, and Culture, Japan.
1
175.5-176.5 °C; IR (KBr) ν 3058, 1647, 1593 cm-1; H NMR (270
MHz, CDCl3) δ 3.98 (s, 2 H, CH2), 7.45-8.96 (m, 16H, Ar-H); 13C
NMR (67.8 MHz, CDCl3) δ 38.6, 126.4, 128.3, 128.6, 129.5, 129.8,
132.4, 135.0, 136.2, 137.4, 138.3, 195.7. Anal. Calcd for C27H18O2S:
C, 79.78; H, 4.46. Found: C, 79.73; H, 4.51.
Supporting Information Available: 2D-HHCOSY and
relay shift correlation NMR spectrum of NMR spectra of the
ketone 6k (2 pages). See any current masthead page for
ordering and Internet access instructions.
2,7-Dibenzoylthiaxanthene Dihydrazone (7h). To a solution of
thiaxanthene 7k (200 mg, 0.49 mmol) in 3 mL of anhydrous hydrazine
and 12 mL of dry DMSO was added hydrazine monohydrochloride
(260 mg, 3.8 mmol). After stirring at 90 °C under argon atmosphere
for 2 h, the reaction mixture was poured into water. The mixture was
JA9643984