Spin-spin interaction between phenoxyl radicals through σ-π system

Article abstract of DOI:10.1016/j.jorganchem.2003.09.004

Compounds having two p-phenoxyl radicals bridged by a 1,2-diphenylenedisilanylene unit in m, p- and p,p- fashions were synthesized and the intramolecular spin-spin interaction was examined by Curie plots of ESR signal intensities due to the Δ M_S=±2 transition at low temperature. It was found that bridging two phenoxyl radicals at meta and para positions of the bridge led to triplet ground state or degeneracy of triplet/singlet states. In contrast, two phenoxyl radicals put at both para positions interacted in an antiferromagnetic fashion through the diphenylenedisilanylene bridge, to realize singlet ground state.

Full text of DOI:10.1016/j.jorganchem.2003.09.004

Journal of Organometallic Chemistry 688 (2003) 192ꢀ199
/
www.elsevier.com/locate/jorganchem
Spinꢀ
/
spin interaction between phenoxyl radicals through sꢀp system
/
Toshiyuki Iida, Joji Ohshita *, Nobuaki Ohta, Kenji Komaguchi, Yoshiteru Itagaki,
Masaru Shiotani, Atsutaka Kunai *
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
Received 24 June 2003; received in revised form 4 September 2003; accepted 4 September 2003
Abstract
Compounds having two p-phenoxyl radicals bridged by a 1,2-diphenylenedisilanylene unit in m,p- and p,p- fashions were
synthesized and the intramolecular spinꢀspin interaction was examined by Curie plots of ESR signal intensities due to the DMSꢁ
/
/
9
/
2 transition at low temperature. It was found that bridging two phenoxyl radicals at meta and para positions of the bridge led to
triplet ground state or degeneracy of triplet/singlet states. In contrast, two phenoxyl radicals put at both para positions interacted in
an antiferromagnetic fashion through the diphenylenedisilanylene bridge, to realize singlet ground state.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Spin state; Phenoxyl radical; sꢀp Conjugation
/
1. Introduction
sꢀp Conjugated organosilicon compounds are of
great interest, regarding their potential utilities as novel
functional materials [1]. For example, it has been
demonstrated that polymers composed of a regularly
alternating arrangement of an organosilicon unit and a
p-system can be used as precursors of organic semi-
conductors, photo-conductors, and hole-transport ma-
terials.
On the other hand, several approaches have been
examined to obtain organic high-spin molecules based
on p-conjugated systems as spin couplers [2,3]. Recent
example includes applications of phenylene [3b,c],
thienylene [3d], pyridylene [3e], pyrrole-1,2,5-triyl
[3f,g], triazine-2,4,6-triyl [3h], ethynylenephenylene [3i],
phenylenevinylene [3j] and anthryleneethynylene [3k], to
the high spin couplers.
al that bridging phenylnitrenes by a disilanylene unit at
the meta and para positions gives rise to the successful
high-spin coupling of the nitrenes [4].
/
Recently, we synthesized di- and monosilanylene
bridged phenyl nitroxides (Chart 1, nꢁ1, 2) and found
/
that they exhibit relatively large spin exchange integrals
at 298 K and triplet state is involved in this systems by
the ESR studies [5]. We also carried out ESR and
SQUID measurements of the silanylene-bridged phenyl
nitroxides (nꢁ
ingly, the disilanylene unit bridging the phenyl nitrox-
ides at meta and para positions works as
/
1ꢀ3) at low temperature [6]. Interest-
/
a
ferromagnetic spin coupler, while bridging two phenyl
nitroxides by a disilanylene unit at both para positions
leads to an antiferromagnetic coupling. In contrast,
mono- and trisilanylene bridges play only an ambiguous
role in the spin-spin coupling. However, the nitroxide
units may not retain the coplanarity with the adjacent
phenylene group, which suppresses the delocalization of
the radical center into the whole molecular system, in
particular at low temperature. In this paper, we report
the synthesis of silicon-bridged phenoxyl radicals, in
which the radical centers are anticipated to be deloca-
lized to the conjugated system than that in phenyl
nitroxides. Their spin states were studied by temperature
dependent ESR measurements.
However, only a little is known for sꢀ
/
p systems as
spin couplers. It has been demonstrated by Iwamura et
* Corresponding authors. Tel.: ꢂ
5494.
E-mail
akunai@hiroshima-u.ac.jp (A. Kunai).
/
81-824-24-7727; fax: ꢂ
/
81-824-22-
Ohshita),
addresses:
jo@hiroshima-u.ac.jp (J.
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.09.004

T. Iida et al. / Journal of Organometallic Chemistry 688 (2003) 192ꢀ
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193
radicals 3a and 3b once formed undergo intramolecular
coupling with loss of the silanylene moiety, which would
be converted to unidentified silanols and siloxanes by
interaction with excess PbO2.
2.2. Preparation of diphenylenedisilanylene-bridged
phenoxyl radicals
Chart 1.
2. Results and discussion
Next, we prepared 1,2-diphenylenedisilanylene-
bridged phenoxyl radicals (6pp and 6mp), as shown in
Scheme 2. Thus, similar to the preparation of 2a and 2b,
silyl-protected hydroxybiphenyl units were introduced
to a disilane core to give 4pp and 4mp. Deprotection of
the silyl capping groups by hydrolysis gave the expected
precursors (5pp and 5mp). When precursors 5pp and
5mp were treated with excess PbO2 in 2-methylTHF
(MTHF), the colorless solutions rapidly turned purple.
The resulting mixtures were stirred vigorously until the
2.1. Preparation of mono- and disilanylene-bridged
phenoxyl radicals
Precursors of phenoxyl radicals (2a and 2b) were
obtained as shown in Scheme 1. Thus, 3,5-di-tert-butyl-
4-(trimethylsiloxy)phenyllithium reacted with 1,2-di-
chlorotetramethyldisilane or dichlorodimethylsilane to
afford silicon-bridged silyl-protected phenol derivatives
(1a and 1b). Deprotection of the phenol unit by treating
1a and 1b with methyllithium then water gave precur-
sors 2a and 2b [7]. However, attempted preparation of
silanylene-bridged phenoxyl radicals 3a and 3b by
oxidation of 2a and 2b with PbO2 failed and no ESR
active species were found to be formed in the mixtures.
Even when the ESR measurements of the reaction
mixtures were performed at low temperature, immedi-
ately after the interaction of 2a and 2b with PbO2, no
signals could be detected at all. The oxidation reactions
always gave diphenoquinone as the sole isolable pro-
duct, as shown in Scheme 1. Although the reaction
mechanism is not clear yet, it seems likely that phenoxyl
OꢀH stretching absorptions disappeared in the IR
/
spectra. Spin densities of the resulting samples were
determined by ESR spectrometries to be 60 and 40% for
6pp and 6mp, respectively.
2.3. ESR spectra of phenoxyl radicals 6pp and 6mp
Phenoxyl radicals 6pp and 6mp thus prepared are
labile to an extent and removal of the solvent gave ESR
silent sticky liquid. They decomposed gradually even in
solutions. In fact, standing the solution of 6pp in MTHF
at room temperature over night led to a decrease of the
spin density to 27%.
Scheme 1.

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T. Iida et al. / Journal of Organometallic Chemistry 688 (2003) 192ꢀ199
/
Scheme 2.
After filtration of Pb salts, the filtrates were subjected
to the following ESR studies without purification. The
1 for 6mp. The signal of DMSꢁ
/
92 were doubly
/
integrated to give Curie Plots (Fig. 2). As shown in
Fig. 2, the plots for 6pp deviated from linearity in the
low temperature region, indicating that 6pp has singlet
ground state. In contrast, the signal intensity of 6mp was
proportional to the reciprocal of absolute temperature.
This indicates that 6mp has triplet ground state or
singlet and triplet at degenerated states.
ESR spectra of phenoxyl radicals 6pp and 6mp in
MTHF showed a sharp singlet signal in the DMSꢁ
1 (g :2) region at room temperature, which was a little
broadened by lowering the temperature. At 77 K, a
signal due to DMSꢁ 2 forbidden transition ascribed
to triplet species was observed at g :4, as shown in Fig.
/
9
/
/
/
9
/
/
Fig. 1. ESR signals of 6mp (a) due to the DMSꢁ
room temperature, and (b) the DMSꢁ 2 transition at 77 K.
/
9
/
1 transition at
Fig. 2. Curie plots for the ESR signals at DMSꢁ
/
9/2 of (m) 6pp and
/
9
/
(k) 6mp.

T. Iida et al. / Journal of Organometallic Chemistry 688 (2003) 192ꢀ
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195
˚
bond distances in 8mp (1.28 and 1.29 A) are much
2.4. MO calculations
˚
shorter than in 7mp (1.39 A), as expected. Bond
distances in the phenylene rings of 7mp range from
˚
1.39 to 1.41 A, indicating that no evident deformation is
In order to ensure the spin state of compound 6mp, we
carried out ab initio MO calculations on model mole-
cules (phenol 7mp and diradical 8mp in Chart 2), having
hydrogens in place of t-butyl groups of 5mp and 6mp,
respectively. Both the geometry optimization and the
energy calculations for 7mp were performed at the
RB3LYP/6-31G level, while for 8mp, the geometries
were optimized on the triplet states at the level of
UB3LYP/6-31G and the energy calculations of both
singlet and triplet states were performed at the level of
involved. In contrast, the phenoxyl units in 8mp possess
˚
˚
C(H) (1.42 A)
˚
C(H) (1.37 A) bonds, in
long C(O)ꢀ
bonds, and short C(H)ꢀ
/
C(H) (1.44 A) and C(C)ꢀ
/
/
accordance with the spin delocalization. However,
such deformation is not clear in the Si-attached inner
phenylene rings, whose CꢀC bond distances are all in
/
˚
the range of 1.39ꢀ
/
1.41 A. The phenyleneꢀphenylene
/
˚
bonds in 8mp are a little shortened by about 0.1 A, as
compared with those in 7mp.
UB3LYP/6-31ꢂG(d) on the optimized geometries.
/
From the calculations, compound 8mp was found to
have triplet ground state with the singlet-triplet energy
gap of 3.12 cal molꢃ1, agreeing with the experimental
results described above.
In addition, the spin densities of triplet states of 8mp
were calculated. In these calculations, both the geometry
optimization and energy calculations were performed at
2.5. Crystal structure of 2b
The crystal structure of 2b was determined by a single
crystal X-ray diffraction study. The ORTEP drawing of
2b is depicted in Fig. 4. All bond distances and angles
are in the normal range. As can be seen in Fig. 4, the
phenylene rings are located in an anti form with respect
the level of UB3LYP/6-31ꢂG(d). The optimized geo-
/
to the Siꢀ
/
Si bond (C1ꢀ
/
Si1ꢀ
/
Si1*ꢀ
/
C1*ꢁ180.08). The
/
metry of 8mp obtained from the calculations processes a
little twisted biphenylene units with the torsion angles of
29.9 and 31.98 for p,p- and m,p-biphenylene units,
angle between the Siꢀ/Si bond and the mean plane of the
attached phenylene ring is 77.58. These bonding features
around the disilane unit almost retained in the optimized
structure of 7mp, in which Siꢀ
are about 858. Other structural parameters of 2b also
closely resemble those of 7mp derived from the calcula-
tions, indicative of the reliability of the MO calculations
on 7mp.
respectively. The Siꢀ
with respect to the adjacent phenylene rings with the
angles of 86.2 and 85.18, respectively, to allow the sꢀ
/
Si bond is almost perpendicular
/
Siꢀ
/
CꢀC dihedral angles
/
/
p
type orbital interaction. Fig. 3 represents the Mulliken
spin densities on the heavy atoms of 8mp, derived from
the calculations. As shown in Fig. 3, the aromatic
carbons carry fairly high spin densities with the mini-
mum absolute value of 0.032 for the Si-attached m-
phenylene carbon, indicating the delocalization of the
phenoxyl spins over the respective p-electron systems. It
is also found that spins lie also on the two silicon atoms
to an extent, although the Mulliken spin densities on the
3. Conclusion
In conclusion, we demonstrated that the substitution
mode of the phenylene units play a vital role on the
spinꢀ
/
spin interaction through the sꢀ
/
p
systems.
silicons are a little low. Interestingly, the spinꢀ
interaction in 8mp is understood by using simple spin
polarization upꢀdown rule, that is, all spin signs in the
/
spin
Although we could not carry out the SQUID measure-
ments on 6pp and 6mp, due to their thermally unstable
properties, it seems to be highly likely that the dis-
ilanylene bridge behaves as like an ethenylene linkage,
which couples p- and m-phenoxyl radicals in a ferro-
magnetic fashion and p-, p- ones in an antiferromag-
netic way [8]. The MO calculations also predicted that
the disilanylene bridge may be able to couple spins,
similar to ethenylene linkage.
/
molecule are alternately arranged, as is observed in
ethenylene-bridged phenoxyl radicals [8].
When optimized structures of 7mp and 8mp are
compared at the level of RB3LYP/6-31G and
UB3LYP/6-31G, respectively, it is found that the OꢀC
/
4. Experimental
4.1. General
All reactions were carried out under an inert atmo-
sphere. The work-up process mentioned below includes
hydrolysis of the reaction mixture with aqueous ammo-
nium chloride, separation of the organic layer, extrac-
Chart 2.

196
T. Iida et al. / Journal of Organometallic Chemistry 688 (2003) 192ꢀ199
/
Fig. 3. Spin densities and optimized geometry of 8mp derived from MO calculations at the UB3LYP/6-31ꢂG(d) level.
/
tion of the aqueous layer with ether or chloroform,
drying the combined organic layer and extracts with
anhydrous magnesium sulfate, and evaporation of the
solvent. Diethyl ether and THF were dried over
spectra were measured on Brucker ESP 300E, JEOL
JES-RE1X and JFS-FE1X spectrometers, using MTHF
as the solvent (10 mM), at the temperature range of 6ꢀ
/
80 K and room temperature (r.t.).
sodiumꢀpotassium alloy and MTHF was dried over
/
sodium. They were distilled just before use. (4-Bromo-
2,6-di-tert-butylphenoxy)trimethylsilane was prepared
as reported in the literature [9]. 3,5-Di-tert-butyl-4-
trimethylsiloxyphenyllithium and 3- and 4-(3,5-di-tert-
butyl-4-trimethylsiloxyphenyl)phenyllithium were pre-
pared by treating the corresponding aryl bromides
with one equivalent of n-butyllithium. For oxidation
of precursors leading to phenoxyl radicals, freshly
prepared PbO2 must be used [10]. Commercially avail-
able PbO2 did not react with the precursors at all. ESR
4.2. Preparation of 1a and 1b
To a solution of 3,5-di-tert-butyl-4-trimethylsiloxy-
phenyllithium in diethyl ether was added 0.42 g (2.80
mmol) of 1,2-dichlorotetramethyldisilane at ꢃ78 8C
/
and the resulting mixture was stirred at r.t. for 2 h.
After work up of the reaction mixture, the crude
product was recrystallized from acetone/chloroform
(10/1) to give 1.40 g (93% yield) of 1b as the colorless
solids: m.p. 186.5ꢀ
188.0 8C; MS m/z 670 [Mꢂ]; 1H-
/
Fig. 4. ORTEP drawing of compound 2b. Protons are omitted for clarity. Thermal ellipsoids are drawn at 50% probability. Selected bond distances
˚
(A) and bond angles (8): Si1ꢀ
1.394(4); C6ꢀC1, 1.392(4); O1ꢀ
C3, 123.7(3); C2ꢀC3ꢀC4, 116.5(3); O1ꢀ
/
Si1*, 2.345(2); Si1ꢀ
C4, 1.385(3); Si1*ꢀ
C4ꢀC3, 118.1(3); O1ꢀ
/
C1, 1.883(3); C1ꢀ
Si1ꢀC1, 109.9(1); Si1ꢀ
C4ꢀC5, 119.4(3); C3ꢀ
/
C2, 1.393(4); C2ꢀ
C1ꢀC2, 119.3(2); Si1ꢀ
C4ꢀC5, 122.5(2); C4ꢀ
/
C3, 1.391(4); C3ꢀ
C1ꢀC6, 123.6(2); C6ꢀ
C5ꢀC6, 117.2(3); C5ꢀ
/
C4, 1.410(4); C4ꢀ
C1ꢀC2, 117.1(2); C1ꢀ
C6.
/
C5, 1.404(4); C5ꢀ
/
C6,
/
/
/
/
/
/
/
/
/
/
/C2ꢀ
/
/
/
/
/
/
/
/
/
/
/
/

T. Iida et al. / Journal of Organometallic Chemistry 688 (2003) 192ꢀ
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197
NMR (CDCl3) d 0.30 (s, 12H), 0.38 (s, 18H), 1.35 (s,
36H), 7.27 (s, 4H); 13C-NMR (CDCl3 at 25 8C) d ꢃ
3.12, 3.93, 31.28, 31.37, 35.08, 129.41, 131.50, 131.56,
139.66, 153.68; 13C-NMR (CDCl3 at 45 8C) d ꢃ
3.13,
3.89, 31.44, 35.14, 129.47, 131.56, 139.81, 153.73; 29Si-
NMR (CDCl3) d 21.95, 13.42. Anal. Calc. for
Calc. for C28H40O2: C, 82.30; H, 9.87. Found: C, 82.32;
H, 9.92%.
Oxidation of 2a, similar to above gave diphenoqui-
none in 98% yield.
/
/
ꢃ
/
4.5. Preparation of 4pp
C38H70O2Si4: C, 67.98; H, 10.51. Found: C, 67.87; H,
10.61%.
Compound 1a was obtained similar to above, using
dichlorodimethylsilane instead of dichlorotetramethyl-
disilane as the starting substance: 93% yield (after
1,2-Dichlorotetramethyldisilane (0.76 g, 2.80 mmol)
was added to a solution of 4-(3,5-di-tert-butyl-4-tri-
methylsiloxyphenyl)phenyllithium in diethyl ether at ꢃ
/
78 8C and the resulting mixture was stirred at r.t. for 2 h.
After work-up of the reaction mixture, the crude
product was recrystallized from hexane to give 1.78 g
recrystallization from acetoneꢀ
m.p. 174ꢀ
176 8C; MS m/z 612 [Mꢂ]; 1H-NMR
(CDCl3) d 0.41 (s, 18H), 0.50 (s, 6H), 1.37 (s, 36H),
7.38 (s, 4H); 13C-NMR (CDCl3) d ꢃ
1.76, 3.96, 31.25,
31.29, 35.12, 129.17, 131.87, 139.64, 154.11; 29Si-NMR
(CDCl3) d ꢃ10.47, 11.93. Anal. Calc. for C36H64O2Si3:
/chloroform (10/1)):
/
(56% yield) of 4pp as the colorless solids: m.p. 179.0ꢀ
/
1
/
181.5 8C; MS m/z 822 [Mꢂ]; H-NMR (CDCl3) d 0.36
(s, 12H), 0.42 (s, 18H), 1.44 (s, 36H), 7.44 (d, 4H, Jꢁ
7.85 Hz), 7.48 (s, 4H), 7.51 (d, 4H, Jꢁ
7.85 Hz); 13C-
NMR (CDCl3) d ꢃ3.70, 3.96, 31.31, 35.29, 124.55,
126.18, 132.78, 134.29, 136.69, 141.02, 141.83, 152.96;
29Si-NMR (CDCl3) d ꢃ
22.02, 13.99. Anal. Calc. for
/
/
/
C, 70.52; H, 10.52. Found: C, 70.39; H, 10.53%.
/
/
4.3. Preparation of 2a and 2b
C50H78O2Si4: C, 72.92; H, 9.55. Found: C, 72.67; H,
9.56%.
Methyllithium (3.64 ml, 4.15 mmol) in diethyl ether
(1.14 M) was added to a solution of 1b (1.27 g, 1.89
4.6. Preparation of 4mp
mmol) in 40 ml of THF at ꢃ30 8C. The mixture was
/
stirred over night at r.t. After work-up of the mixture,
the crude product was recrystallized from hexane to give
1,2-Dichlorotetramethyldisilane (0.60 g, 3.20 mmol)
was added to a solution of 3-(3,5-di-tert-butyl-4-tri-
0.56 g (57% yield) of 2b as the colorless solids: m.p.
1
methylsiloxyphenyl)phenyllithium in diethyl ether at ꢃ
78 8C and the resulting mixture was stirred at r.t. for 2 h,
then again cooled down to ꢃ78 8C. To this was added
/
160.5ꢀ
/
164.0 8C; MS m/z 526 [Mꢂ]; H-NMR (CDCl3)
d 0.31 (s, 12H), 1.38 (s, 36H), 5.18 (s, 2H, OH), 7.19 (s,
4H); 13C-NMR (CDCl3) d ꢃ
2.94, 30.36, 34.29, 128.37,
130.73, 134.87, 154.42; 29Si-NMR (CDCl3) d ꢃ
21.67;
IR 3630.3 cmꢃ1 (Oꢀ
H). Anal. Calc. for C32H54O2Si2: C,
72.94; H, 10.33. Found: C, 72.85; H, 10.39%.
/
/
4-(3,5-di-tert-butyl-4-trimethylsiloxyphenyl)phenyl-
lithium and the resulting mixture was stirred at r.t. for 2
h. After work-up of the reaction mixture, the crude
product was subjected to silica gel chromatography,
/
/
Compound 2a was obtained from 1a in a similar
fashion to above: 55% yield (after recrystallization from
eluting with hexaneꢀethyl acetate (50/1) to give 1.51 g
/
(72% yield) of 4mp as the colorless solids: m.p. 135.1ꢀ
/
hexane): m.p. 189ꢀ
(CDCl3) d 0.50 (s, 6H), 1.42 (s, 36H), 5.26 (s, 2H, OH),
7.35 (s, 4H); 13C-NMR (CDCl3) d ꢃ
1.75, 30.31, 34.34,
128.07, 130.97, 134.89, 154.80; 29Si-NMR (CDCl3) d ꢃ
8.73; IR 3635.6, 3619.2 cmꢃ1 (Oꢀ
H). Anal. Calc. for
/
191 8C; MS m/z 468 [Mꢂ]; 1H-NMR
1
136.58C; MS m/z 822 [Mꢂ]; H-NMR (CDCl3) d 0.37
(s, 6H), 0.38 (s, 6H), 0.43 (s, 18H), 1.43 (s, 18H), 1.44, (s,
/
18H), 7.35 (d, 1H, Jꢁ
Hz), 7.44 (d, 2H, Jꢁ7.62 Hz), 7.45 (s, 2H), 7.46 (s, 2H),
7.50 (d, 1H, Jꢁ7.25 Hz), 7.50 (d, 2H, Jꢁ7.62 Hz), 7.64
(s, 1H); 13C-NMR (CDCl3) d ꢃ
3.74, ꢃ3.62, 3.96, 4.00,
/
7.25 Hz), 7.36 (t, 1H, Jꢁ7.25
/
/
/
/
/
/
C30H48O2Si: C, 76.86; H, 10.32. Found: C, 76.76; H,
10.27%.
/
/
31.23, 31.27, 35.24, 35.27, 124.55, 124.68, 126.18,
127.21, 127.96, 132.03, 132.47, 132.74, 133.26, 134.24,
135.27, 136.60, 139.38, 140.94, 141.05, 141.83, 152.80,
4.4. Oxidation of 2a and 2b
152.93; 29Si-NMR (CDCl3) d ꢃ
/
21.97, ꢃ21.52, 13.87,
/
PbO2 (0.26 g, 1.09 mmol) was added to a solution of
2b (0.05 g, 0.09 mmol) in 9.5 ml of MTHF at r.t. The
mixture was stirred for 30 min. After Pb salts were
filtered and the solvent was evaporated, the residue was
subjected to silica gel chromatography, eluting with
13.96.
4.7. Preparation of 5pp and 5mp
Potassium carbonate (0.18 g ) in 1 ml of water was
added to a solution of 4pp (0.10 g, 0.12 mmol) in 5 ml of
THF. The mixture was stirred over night at r.t. After
work-up of the resulting mixture, the crude product was
recrystallized from hexane to give 0.08 g (90% yield) of
hexaneꢀethyl acetate (10/1) to give 0.03 g (80% yield) of
/
tetra-tert-butyldiphenoquinone: m.p. 210ꢀ212 8C; MS
/
1
m/z 408 [Mꢂ]; H-NMR (CDCl3) d 1.35 (s, 36H), 7.69
(s, 4H); 13C-NMR (CDCl3) d 29.57, 36.01, 125.99,
136.11, 150.42, 186.46; IR 1601.8 cmꢃ1 (Cꢀ
/O). Anal.
5pp as the colorless solids: m.p. 242ꢀ244 8C; MS m/z
/

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T. Iida et al. / Journal of Organometallic Chemistry 688 (2003) 192ꢀ199
/
1
678 [Mꢂ]; H-NMR (CDCl3) d 0.36 (s, 12H), 1.48 (s,
36H), 5.25 (s, 2H OH), 7.39 (s, 4H), 7.44 (d, 4H, Jꢁ7.85
Hz), 7.49 (d, 4H, Jꢁ
7.85 Hz); 13C-NMR (CDCl3) d ꢃ
Table 1
Crystal data, experimental conditions, and summary of structural
refinement for 2b
/
/
/
3.72, 30.34, 34.47, 123.95, 126.27, 132.39, 134.28,
136.15, 136.60, 142.16, 153.53; 29Si-NMR (CDCl3) d
Compound
2b
C
Molecular formula
Molecular weight
Crystal system
Space group
32H54O2Si2
526.95
Triclinic
ꢃ
/
21.99; IR 3637.5 cmꢃ1 (Oꢀ
H). Anal. Calc. for
C44H62O2Si2: C, 77.81; H, 9.20. Found: C, 77.86; H,
/
¯
P1 (no. 2)
9.29%
Compound 5mp was prepared in a similar fashion to
above as the colorless solids: 90% yield (after purifica-
Unit cell dimensions
˚
a (A)
˚
9.726(2)
14.402(3)
6.320(1)
93.74(2)
102.17(2)
104.29(2)
832.2(3)
1
b (A)
˚
c (A)
tion by silica gel column chromatography): m.p. 118.5ꢀ
/
1
120.0 8C; MS m/z 678 [Mꢂ]; H-NMR (CDCl3) d 0.36
(s, 6H), 0.37 (s, 6H), 1.46 (s, 18H), 1.47, (s, 18H), 5.24 (s,
a (8)
b (8)
g (8)
3
˚
1H, OH), 5.25(s, 1H, OH), 7.34 (t, 1H, Jꢁ
7.35 (d, 1H, Jꢁ6.77 Hz), 7.35 (s, 2H), 7.37 (s, 2H) 7.43
(d, 2H, Jꢁ8.09 Hz), 7.47 (d, 2H, Jꢁ8.09 Hz), 7.48 (d,
1H, Jꢁ
6.77 Hz), 7.60 (s, 1H); 13C-NMR (CDCl3) d ꢃ
3.75, ꢃ3.62, 30.31, 30.34, 34.43, 34.46, 123.96, 124.10,
/6.77 Hz),
V (A )
/
Z
Dcalc (g cmꢃ3
F000
)
1.051
290.00
/
/
/
/
Crystal size (mm3)
Crystal color
0.3ꢄ
Colorless
1.30
/
0.3ꢄ0.1
/
/
m (cmꢃ1
Diffractometer
Temperature (K)
)
126.28, 127.28, 127.96, 131.98, 132.37, 132.60, 132.92,
134.24 (two carbons), 136.13, 136.52, 139.44, 141.43,
Rigaku AFC-7R
296
142.19, 153.40, 153.53; 29Si-NMR (CDCl3) d ꢃ
/
21.92,
˚
Wavelength (A)
21.49; IR 3640.4 cmꢃ1 (Oꢀ
C44H62O2Si2: C, 77.81; H, 9.20. Found: C, 77.86; H,
9.26%.
/H). Anal. Calc. for
0.71069 (Mo Ka)
Graphite crystal
ꢃ
/
Monochromator
Scan type
Scan speed (deg minꢃ1
v ꢀ2u
8
/
)
Scan width (8)
No. of unique reflns
65
3819
2004(I ]3s(I))
12.29
None
0.046
0.046
/
2u 555
/
4.8. Preparation of 6pp and 6mp
No. of observed reflections
Reflections/parameter ratio
Corrections
/
Phenoxyl radicals 6pp and 6mp were obtained from
5pp and 5mp, respectively, by oxidation with PbO2 in
large excess, similar to attempted preparation of 3a,b
described above. After filtration of PbO2, the filtrate
was directly subjected to the ESR measurements. ESR
R
a
Rw
a
2 ꢃ1
Weighting scheme is (s(Fo)2ꢂ
/
0.0004jFoj )
.
data: gꢁ
/
2.0051 for 6pp and gꢁ2.0055 for 6mp.
/
94 Fourier techniques [13]. The non-hydrogen atoms
were refined anisotropically. Neutral atom scattering
factors were taken from Cromer and Waber [14].
Anomalous dispersion effects were included in Fcalc
[15]; the values for Df? and Dfƒ were those of Creagh
and McAuley [16]. The values for the mass attenuation
coefficients are those of Creagh and Hubbel [17]. All
calculations were performed using the TEXSAN [18]
crystallographic software package of Molecular Struc-
ture Corporation.
4.9. MO calculational method
MO calculations were carried out on the density
functional theory (DFT) at GAUSSIAN-98 program
[11]. For calculations of the singlet state of phenoxyl
radical 8mp, attempted geometry optimization at the
level of UB3LYP/6-31G failed. In these calculations, we
obtained geometries with unusual spin densities or did
not succeed to find out geometries with energy mini-
mum. Therefore, we carried out the singlet state energy
calculations using the optimized geometries of the triplet
state molecule of 8mp. Calculations using a keyword of
Guessꢁ
/
Mix led to successful results with ꢁSꢂ2ꢁ
/1.
5. Supplementary material
Other calculations on 7mp and the triplet molecule of
8mp were readily performed as described in the section
of results and discussion.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 212529 for compound 2b.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
4.10. X-ray crystallographic analysis of 2b
The crystal date and refinement parameters are
summarized in Table 1. The structure was solved by
Cambridge CB2 1EZ, UK (Fax: ꢂ44-1223-336033; e-
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
/
SIR-92 direct methods [12] and expanded using DIRDIF
-

T. Iida et al. / Journal of Organometallic Chemistry 688 (2003) 192ꢀ
/199
199
(h) P.M. lahti, Y. Liao, M. Julier, F. Palacio, Syn. Met. 122 (2001)
485;
Acknowledgements
(i) H. Nishide, T. Maeda, K. Oyaizu, E. Tsuchida, J. Org. Chem.
64 (1999) 7129;
This work was supported in part by NEDO (project
no. 01A26005a). We thank Sankyo Kasei Co. Ltd. for
financial support, and Shin-Etsu Chemical Co. Ltd. for
the gift of chlorosilanes. We also thank Prof. N. Koga
(Kyushu University) for the valuable suggestions.
(j) H. Nishide, T. Ozawa, M. Miyasaka, E. Tsuchida, J. Am.
Chem. Soc. 123 (2001) 5942;
(k) T. Kaneko, T. Makino, H. Miyaji, M. Teraguchi, T. Aoki, M.
Miyasaka, H. Nishide, J. Am. Chem. Soc. 125 (2003) 3554.
[4] T. Doi, A. Ichimura, N. Koga, H. Iwamura, J. Am. Chem. Soc.
115 (1993) 8928.
[5] J. Ohshita, T. Iida, N. Ohta, K. Komaguchi, M. Shiotani, A.
Kunai, Org. Lett. 4 (2002) 403.
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