Compounds 1a,d were obtained as orange to red solids by
recrystallization in high yields. Compounds 1b,c,e,f could
be isolated by alumina column chromatography as viscous
red oils, but they slowly decomposed by standing them in
the condensed phase. Carbon-bridged phenylnitroxide 2 was
even less stable and could not be isolated. Therefore, these
compounds were subjected to the following ESR experiments
after removal of inorganic salts by filtration without further
purification, which also gave sufficient data without any
signals due to the monoradicals (vide infra). The phenylni-
troxides were characterized by IR spectrometry and elemental
analysis, except for 2.
Scheme 1
The crystal structure of 1a was determined by a single-
crystal Xray diffraction study, and the ORTEP drawing is
depicted in Figure 1.6 As can be seen in Figure 1, the
of σ-π conjugated systems as flexible high-spin couplers.4
We also prepared methylene-bridged phenylnitroxides, for
comparison.
Bridged phenylnitroxides 1a-f were obtained, as shown
in Scheme 1 and Table 1. Thus, di(lithiophenyl)di- and
Figure 1. ORTEP drawing of compound 1a. The thermal ellipsoids
are drawn at 50% probability level. Hydrogen atoms are omitted
for clarity. Selected bond distances (Å) and angles (deg): Si1-
Si2 ) 2.344(4), Si1-C1 ) 1.887(9), Si1-C21 ) 1.87(1), N1-
O1 ) 1.27(1), N1-C4 ) 1.41(1), N1-C7 ) 1.49(1), N2-O2 )
1.28(1), N2-C14 ) 1.41(1), N2-C17 ) 1.47(1), Si2-Si1-C1 )
108.4(3), Si1-Si2-C11 ) 107.4(3), O1-N1-C4 ) 116.1(8), O1-
N1-C7 ) 117.3(7), C4-N1-C7 ) 126.6(8), O2-N2-C14 )
115.3(9), O2-N2-C17 ) 116.5(8), C14-N2-C17 ) 128.1(9).
Table 1. Preparation and ESR Data for Compounds 1, 2, and 3
ESR data
compd
yield/%a
g
hfc/Gc
distance/Åd
phenylnitroxide groups are located in a trans fashion with
respect to the Si-Si bond which possesses a gauche
configuration. The Si-Si bond is almost perpendicular to
1a
1b
1c
1d
1e
1f
2
68
26
21
73
85
95
nib
nib
2.0068
2.0069
2.0069
2.0066
2.0073
2.0077
2.0071
2.0073
5.96
6.37
5.93
5.80
6.11
6.60
6.17
12.22
12.0
10.7
10.6
10.4
10.0
9.1
in 8 mL of THF at -78 °C, and the mixture was stirred at room temperature
for 1 h. The mixture was hydrolyzed with aqueous ammonium chloride
and extracted with ether. The ether layer was dried over anhydrous
magnesium sulfate. After evaporation of the solvent, the crude product was
recrystallized from acetone to give 0.75 g (73 % yield) of 1,2-bis[4-(N-
hydroxy-tert-butylamino)phenyl]-1,1,2,2-tetramethyldisilane as a pale yellow
10.5
3d
a Isolated yield. b ni ) not isolated. c hfc at room temperature. d Intramo-
lecular distance between radicals estimated by the ESR spectrum at 77 K.
1
solid: mp 208-209 °C; MS m/z 444 (M+); H NMR (δ in THF-d8) 0.31
(s, 12H), 1.13 (s, 18H), 7.19 (d, 4H, J ) 8.09 Hz), 7.25 (d, 4H, J ) 8.09
Hz), 7.35 (s, 2H, OH); 13C MNR (δ in THF-d8) -3.54, 26.56, 60.50, 124.69,
133.69, 134.44, 152.47; 29Si NMR (δ in THF-d8) -22.65; IR 3228 cm-1
(O-H); UV (in THF) λmax 265 nm. Anal. Calcd for C24H40N2O2Si2: C,
64.81; H, 9.07; N, 6.30. Found: C, 65.11; H, 9.06; N, 6.25. To a solution
of 50 mg (0.11 mmol) of 1,2-bis[4-(N-hydroxy-tert-butylamino)phenyl]-
1,1,2,2-tetramethyldisilane in 5 mL of ether was added a large excess amount
(100 mg, 0.78 mmol) of Ag2O, and the mixture was stirred for 30 min at
room temperature. The mixture was filtered and the solvent was evaporated;
then the residue was recrystallized from hexane to give 34 mg (68 % yield)
of 1a as a red needle crystal: mp 129-133 °C; MS m/z 442 (M+); λmax (in
cyclohexane) 311.2 nm. Anal. Calcd for C24H38N2O2Si2: C, 65.10; H, 8.65;
N, 6.33. Found: C, 65.12; H, 8.68; N, 6.26. IR spectrum of 1a reveled no
absorptions in the region of O-H stretching.
monosilanes were treated with tert-butylnitroso dimer to
afford the corresponding hydroxylamines. The hydroxy-
lamines were then treated with excess silver oxide until the
O-H stretching absorptions in the IR spectra disappeared.5
(4) Iwamura et al. mentioned that they have synthesized compound 1a
and determined the crystal structure by an Xray diffraction study (ref 3).
However, no detailed description has been given so far.
(5) An illustrative procedure for the preparation of 1 is as follows. To a
solution of 1.0 g (2.33 mmol) of 1,2-bis(4-bromophenyl)-1,1,2,2-tetram-
ethyldisilane in 8 mL of ether was added 3.0 mL (4.80 mmol) of an
n-butyllithium/hexane solution (1.6 M) at -78 °C, and the mixture was
gradually warmed to room temperature over a period of 1 h. To this was
added a solution of 0.52 g (3.04 mmol) of 2-methyl-2-nitrosopropane dimer
(6) Crystal data for 1a: C24H38O2N2Si2, MW ) 442.75, space group P21/c
with a ) 7.459(2) Å, b ) 17.920(2) Å, c ) 20.139(1) Å, â ) 93.22(1)°,
V ) 2687.5(6) Å3, Z ) 4, density (calcd) ) 1.094 g/cm3, F(000) ) 960.00,
µ(Mo KR) ) 1.52 mm-1. A total of 6633 intensity data were collected on
a Rigaku AFC7R diffractometer using a 0.8 × 0.1 × 0.1 mm3 sized crystal;
1884 unique reflections with I > 1σ(I) (reflns/para ) 7.0) were used in
refinement; R ) 7.9, Rw ) 8.3%.
404
Org. Lett., Vol. 4, No. 3, 2002