Acyclic and cyclic di- and tri(4-oxyphenyl-1,2-phenyleneethynylene)s: Their synthesis and ferromagnetic spin interaction

Article abstract of DOI:10.1021/jo990575i

A new set of π-conjugated and alternant but non-Kekule-type di- and tri(1,2-phenyleneethynylene)s pendantly substituted with phenoxyl radicals at the 4 positions (1a, 2a, and 3a) was synthesized. The synthesis of these acyclic and cyclic compounds was achieved through the head-to-tail coupling of 2-bromo(or -iodo)-4-[3',5'-di-tert-butyl-4'-trimethylsiloxyl(or - hydroxy)phenyl]-1-ethynylbenzenes. The di- and triphenoxyl compounds (1a, and 2a and 3a) were triplet and quartet at the ground state, respectively, which was ascribed to a ferromagnetic coupling effect of the diphenyl ethynylene bridge for the pendant phenoxyls' spins. The cyclic π-conjugation in 3a exhibited a stronger effect on the spin alignment.

Full text of DOI:10.1021/jo990575i

J . Org. Chem. 1999, 64, 7375-7380
7375
Acyclic a n d Cyclic Di- a n d
Tr i(4-oxyp h en yl-1,2-p h en ylen eeth yn ylen e)s: Th eir Syn th esis a n d
F er r om a gn etic Sp in In ter a ction
Hiroyuki Nishide,* Masahiro Takahashi, J unichi Takashima, Yong-J in Pu, and
Eishun Tsuchida
Department of Polymer Chemistry, Waseda University, Tokyo 169-8555, J apan
Received March 31, 1999
A new set of π-conjugated and alternant but non-Kekule´-type di- and tri(1,2-phenyleneethynylene)s
pendantly substituted with phenoxyl radicals at the 4 positions (1a , 2a , and 3a ) was synthesized.
The synthesis of these acyclic and cyclic compounds was achieved through the head-to-tail coupling
of 2-bromo(or -iodo)-4-[3′,5′-di-tert-butyl-4′-trimethylsiloxyl(or -hydroxy)phenyl]-1-ethynylbenzenes.
The di- and triphenoxyl compounds (1a , and 2a and 3a ) were triplet and quartet at the ground
state, respectively, which was ascribed to a ferromagnetic coupling effect of the diphenyl ethynylene
bridge for the pendant phenoxyls’ spins. The cyclic π-conjugation in 3a exhibited a stronger effect
on the spin alignment.
In tr od u ction
pendant-type radical polymers have the following advan-
tages as a high-spin molecule: (i) The spin coupling is
not sensitive to spin defects. (ii) The spins are expected
to interact also among their remote spins. (iii) A chemi-
cally stable radical species can be introduced to the
π-conjugation as the pendant group. To increase such a
high-spin alignment, research on the very high-spin
molecules including the pendant-type ones has recently
focused on a still larger molecule with a higher dimen-
sion, i.e., star-shaped, dendric, macrocyclic, and ladder
homologues.2
On the other hand, novel graphitic carbon allotropes
as a planar and two-dimensionally π-conjugated frame-
work is an area of intense investigation.5 A typical
example is graphyne5e (Chart 3), and its subunits are
acyclic and cyclic tri(1, 2-phenyleneethynylene)s. While
acyclic oligo- and poly(phenyleneethynylene)s with a 1,3-
(meta)- or 1,4-(para)-substitution on the benzene ring
have been well studied,6 only Grubbs and Kratz reported
the synthesis, structure, and π-conjugated property of
acyclic oligo- and poly(1,2-(ortho)-phenyleneethynylene)s.7
Cyclic tri(1,2-phenyleneethynylene), i.e, tribenzotrisdehy-
dro[12]annulene, is well-known and charactized by a
triangular and coplanar π-conjugation.5e,8 The acyclic and
cyclic 1,2-phenyleneethynylenes are expected to be one
of the effective π-conjugated backbones to ferromagneti-
cally connect the pendant radical’s spins and to be the
unit for extending the high-spin part to a (pseudo) two-
Much effort has been continuously expended in syn-
thesizing very high-spin and purely organic molecules
that are expected to display molecular-based and un-
known magnetism caused by intramolecular through-
bond spin ordering.1,2 A π-conjugated and alternant but
non-Kekule´-type organic molecule bears plural radical
centers, and some of its isomers are multiplet at the
ground state. One of the ways to extend these non-
Kekule´-type molecules to very high-spin molecules is to
synthesize a π-conjugated linear polymer bearing pen-
dant radical groups on every monomer unit, which are
substituted on the polymer backbone to satisfy a π-con-
jugated and alternant but non-Kekule´-type structure. For
example, we experimentally examined non-Kekule´-type
stilbene diradicals and a triplet ground state of a meta,-
para′-disubstituted isomer with relative stability;3 we
extended the triplet stilbene diradical to poly[4-(radical
substituted)-1,2-phenylenevinylene]s, such as poly[4-
(3′,5′-di-tert-butyl-4′-oxyphenyl)-1,2-phenylenevinylene]
(Chart 2), and reported a strong ferromagnetic interac-
tion between the pendant radical’s spins through its
π-conjugated backbone, poly(1, 2-phenylenevinylene) for
example, and five spins alignment on average.4 Such
(1) For reviews on high-spin organic molecules, see: (a) Dougherty,
D. A. Acc. Chem. Res. 1991, 24, 88. (b) Iwamura, H.; Koga, N. Acc.
Chem. Res. 1993, 26, 346. (c) Rajca, A. Chem. Rev. 1994, 94, 871. (d)
Nishide, H. Adv. Mater. 1995, 7, 937. (e) Lahti, P. M. Magnetic
Properties of Organic Materials; Marcel Dekker: New York, 1998.
(2) For recent papers on very high-spin organic molecules, see: (a)
Rajca, A.; Lu, K.; Rajca, S. J . Am. Chem. Soc. 1997, 119, 10355. (b)
Rajca, A.; Wongsriratanakul, J .; Rajca, S. J . Am. Chem. Soc. 1997,
119, 11674. (c) Ruiz-Molina, D.; Veciana, J .; Palacio, F.; Rovira, C. J .
Org. Chem. 1997, 62, 9009. (d) Rajca, A.; Wongstriratanakul, J .; Rajca,
S.; Cerny, R. Angew. Chem., Int. Ed. Engl. 1998, 37, 1229. (e) Bushby,
R.; Gooding, D. J . Chem. Soc., Perkin Trans. 2 1998, 1069. (f) Nishide,
H.; Miyasaka, M.; Tsuchida, E. Angew. Chem., Int. Ed. Engl. 1998,
37, 2400. (g) Nishide, H.; Miyasaka, M.; Tsuchida, E. J . Org. Chem.
1998, 63, 7399.
(3) Yoshioka, N.; Lahti, P. M.; Kaneko, T.; Kuzumaki, Y.; Tsuchida,
E.; Nishide, H. J . Org. Chem. 1994, 59, 4272.
(4) (a) Kaneko, T.; Toriu, S.; Kuzumaki, Y.; Nishide, H.; Tsuchida,
E. Chem. Lett. 1994, 2135. (b)Nishide, H.; Kaneko, T.; Nii, T.; Katoh,
K.; Tsuchida, E.; Yamaguchi, K. J . Am. Chem. Soc. 1995, 117, 548. (c)
Nishide, H.; Kaneko, T.; Nii, T.; Katoh, K.; Tsuchida, E.; Lahti, P. M.
J . Am. Chem. Soc. 1996, 118, 9695.
(5) (a) Diederich, F. Nature 1994, 369, 199. (b) Bunz, U. H. F.;
Wiegelmann-Kreiter, J . E. C. Chem. Ber. 1996, 129, 785. (c) Haley,
M. M.; Brand, S. C.; Pak, J . J . Angew. Chem., Int. Ed. 1997, 36, 836.
(d) Baughman, R. H.; Eckhardt, H.; Kertesz, M. J . Chem. Phys. 1987,
87, 6687. (e) Eickmeier, C.; J unga, H.; Matzger, A. J .; Scherhag, F.;
Shim, M.; Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1997, 36,
2103.
(6) (a) Weder, C.; Wrighton, M. S. Macromolecules 1996, 29, 5157.
(b) Sanechika, K.; Yamamoto, T.; Yamamoto, A. Bull. Chem. Soc. J pn.
1984, 57, 752. (c) Trumbo, D. L.; Marvel, C. S. J . Polym. Sci., Polym.
Chem. Ed. 1986, 24, 2311.
(7) Grubbs, R. H.; Kratz, D. Chem. Ber. 1993, 126, 149.
(8) (a) Wolovsky, R,; Sondheimer, F.; Gattatt, P. J .; Calder, I. C. J .
Am. Chem. Soc. 1965, 87, 5720. (b) Campbell, I. D.; Eglington, G.;
Henderson, W.; Raphael, R. A. Chem. Commun. 1996, 87. (c) Staab,
H. A.; Graf, F. Chem. Ber. 1970, 103, 1107. (d) Kloster-J ensen, E.; Wirz,
J . Angew. Chem., Int. Ed. Engl. 1973, 12, 671.
10.1021/jo990575i CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/16/1999

7376 J . Org. Chem., Vol. 64, No. 20, 1999
Nishide et al.
Ch a r t 1
Ch a r t 2
Sch em e 1
Sch em e 2
Ch a r t 3
Scheme 1. 4-(3′,5′-Di-tert-butyl-4′-hydroxyphenyl)ethy-
nylbenzene 6 was prepared via a cross-coupling reaction
of 1-bromo-4-(3′,5′-di-tert-butyl-4′-trimethylsilyloxyphe-
nyl)benzene with trimethylethynylsilane and the follow-
ing elimination of the protecting silyl (TMS: trimethyl-
silyl) groups. A cross-coupling of 6 with the 2-bromo-4-
(3′,5′-di-tert-butyl-4′-trimethylsilyloxyphenyl)toluene 7 (or
1e) and subsequent elimination of the TMS group yielded
1c (or 1e).
dimensional framework. However, to our knowledge,
pendant-type radicals attached to an acyclic or cyclic
oligo(1,2-phenyleneethynylene) have not been reported.
In this paper, we have first synthesized acyclic and cyclic
di- and tri(1,2-phenyleneethynylene)s pendantly 4-sub-
stituted with 3′,5′-di-tert-butyl-4′-oxyphenyl groups and
examined their high-spin state.9
The acyclic tri(4-hydroxyphenyl-1,2-phenyleneethy-
nylene) 2c was synthesized, as shown in Scheme 2. The
vinyl group of 2-bromo-(3′,5′-di-tert-butyl-4′-acetoxyphenyl)-
styrene4b 8 was converted to the ethynyl group via the
addition of bromine and the following elimination of
hydrogen bromide. 9 was stepwisely protected with TMS
groups to give 11, which was cross-coupled with 6.
Elimination of the TMS groups yielded 1e. The cross-
coupling of 1e with 7 and subsequent elimination of the
TMS group gave 2c.
To obtain the cyclic tri(4-hydroxyphenyl-1,2-phenyl-
eneethynylene) or a dehydro[12]annulene symmetrically
annelated with a phenol-bearing benzene 3b, we tried
the cross-coupling of the 2-bromo-4-ethynylbenzene de-
rivatives 9 and 10; however, 3b was not formed. The
bromo substituent in 11 was substituted with iodine,
Resu lts a n d Discu ssion
Syn th esis. A restricted primary structure or complete
head-to-tail linkage of the monomer unit is essential for
a ferromagnetic high-spin state in the pendant-type
oligoradical, which was established for the precursors of
acyclic di- and tri(4-oxyphenyl-1,2-phenyleneethynylene)s,
1b and 2b (Chart 1), through the cross-coupling reactions
in the presence of a palladium-triphenylphosphine cata-
lyst and cuprous iodide.
3,4′-Bis[4′-(3′′,5′′-di-tert-butyl-4′′-hydroxyphenyl)]diphe-
nylethynylenes, 1c and 1e, were prepared as shown in
(9) Our preliminary paper on the cyclic tri(1,2-phenyleneethynylene)
4-substituted with oxyphenyl groups: Pu, Y.-J .; Takahashi, M.;
Tsuchida, E.; Nishide, H. Chem. Lett. 1999, 161.

Di- and Tri(4-oxyphenyl-1,2-phenyleneethynylene)s
J . Org. Chem., Vol. 64, No. 20, 1999 7377
Sch em e 3
Ch a r t 4
Ta ble 1. UV/vis Absor p tion a n d F lu or escen ce Ma xim a
a n d Red ox P oten tia l of th e Hyd r oxy P r ecu r sor s
solution at room temperature and that the radical
generation is not accompanied by a subsequent chemical
side reaction. The redox potentials of the phenolate/
phenoxyl given in Table 1 are ca. 0.01 V for 1c, 2c, and
3b. Differential pulse voltammetry was applied to the
oxidation of these phenol derivatives; however, it gave
only a unimodal current peak. These results indicate that
the diphenylethynylene coupler is too long in the π-con-
jugation and/or steric distance to induce an effect on the
redox reaction.
UV absa
(log ꢀmax
λ
max, nm
)
fluorescenceb
redox potentialc
(V)
compd
λ
em, nm (Φ)
1b
2b
15
3b
16
312 (4.4)
314 (4.5)
272 (4.7)
333 (5.1)
287 (5.4)
361
387
0.01
0.01
500 (0.12)
485 (0.07)
0.01
a
b
Chloroform solution. Benzene solution, λmax ) 420 nm, Φ:
quantum yield normalized with 9,10-diphenylanthracene (Φ )
0.84). c Redox potential in the methylene dichloride solution of 6
ESR Sp ectr a of th e P h en oxyl Ra d ica ls. The phe-
noxyl radicals, 1a , 2a , and 3a , were obtained by hetero-
geneously treating the toluene solutions of 1c, 2c, and
3b with aqueous alkaline K3Fe(CN)6 solution or with
fresh PbO2 powder. The toluene solutions rapidly turned
deep green: The appearance of a new absorption peak
at ca. 640 nm suggests the formation of phenoxyl radicals.
Although the oxidation of 1e did not yield a stable radical
probably due to a radical coupling reaction between the
ethynyl groups of 1e, the methyl-protected derivative 1c
formed a stable radical.
equiv (CH3)4NOH and 0.1
M (CH3)4NBF4 as an alkali and
electrolyte, respectively, vs Ag/AgCl (ref Fc/Fc+ ) 0.58 V).
using n-butyllithium, to improve the reactivity of the
o-halogenoethynylbenzene. The hydroxy and ethynyl
groups of 12 were deprotected to afford 13. A selective
protection of the hydroxy group of 13 yielded 14. The
cuprous acetylide derivative of 14 was condensed in
pyridine to give the annulene derivative 3b.Str u ctu r e.
The acyclic hydroxy precursors, 1c and 2c, were dissolved
well in common solvents such as benzene, THF, and
chloroform. On the other hand, the solvent solubility of
the cyclic precursor 3b was low, probably due to its large
planar aromatic structure. FAB mass spectroscopy of 1c,
2c, and 3b agreed with their calculated values. The
fluorescence of these compounds was attributed to the
diphenyl ethynylene moiety. 13C and 1H NMR peaks
ascribed to the benzene rings and the ethynylene bridge
of 1c, 2c, and 3b supported both the phenylenethynylene
bonds and the head-to-tail linkage structure (for details,
see the Experimental Section). The cyclic precursor 3b
gave 12 absorption peaks in the 13C NMR, which indi-
cates a C3 symmetrical structure of the cyclic 3. In the
1H NMR data, the signals for the nine protons on the
annelated benzene ring of 3b were slightly shifted upfield
(∆δ ) 0.1-0.2) relative to the corresponding monomeric
and acyclic units, which correlates with the paramagnetic
ring current of the cyclic annulene ring.
A preliminary tool to estimate the π-conjugation of the
phenyleneethynylene backbone is the UV absorption and
fluorescence spectroscopic data collected in Table 1. The
absorption and fluorescence maxima of the phenylene-
ethynylene bathochromically shifted from the dimer to
the acyclic and the cyclic trimer. These shifts reflect the
increase in number of the phenyleneethynylene units.
The maxima of 2b and 3b also bathochromically shifted
in comparison with those of 15 and 16, which are ascribed
to the developed π-conjugation due to the three phenol
groups.Electrochemical redox of the pendant but π-con-
jugated phenol with the phenyleneethynylene will give
additional information on the backbone. The cyclic vol-
tammograms of 1c, 2c, and 3b exhibited completely
reversible but simple redox waves ascribed to the phe-
nolate/phenoxyl redox couple, in alkaline dichloromethane
solution under a nitrogen atmosphere. This means that
the phenoxyl radicals are chemically stable even in
The ESR spectra of the monoradicals of 9, 2c, and 3b
[for the latter two; i.e, 2a and 3a with a very low spin
concentration (spin concn ) spin/monomeric phenol
residue unit)] gave a hyperfine structure attributed to
5-6 protons of the phenoxyl ring and the phenylene-
ethynylene backbone (Figure 1), which was in contrast
to the simple three-line hyperfine structure of 2,4,6-tri-
tert-butylphenoxyl or that attributed to an unpaired
electron localized in the phenoxyl ring. The dashed line
in Figure 1a shows a simulation of the hyperfine struc-
ture of the monomeric unit (the monoradical of 9), which
gave the four aH values attributed to the five protons of
the phenoxyl and phenylene rings and to the remote
proton of the ethynyl group. The monoradical of the
corresponding dimer 2c gave a similar hyperfine struc-
ture in the ESR spectrum (Figure 1b). The ESR spectrum
of the monoradical of 3b showed a clearer hyperfine
structure, which was assigned to the two protons of the
phenoxyl ring and three protons of the annulene back-
bone (Figure 1c). These ESR results indicate an ef-
fectively delocalized spin distribution into the phenyl-
enethynylene backbone.
The ESR spectra of 1a , 2a , and 3a showed sharp and
unimodal signals with increasing spin concn; the spectra
in the frozen toluene glass exhibited a ∆Ms ) (2
forbidden transition ascribed to a triplet species at g ) 4
(inset in Figure 2). The ESR signal in the ∆Ms ) (2
region was doubly integrated to give Curie plots (Figure
2). Although the signal intensities are proportional to the
reciprocal of the temperature (1/T) at higher temperature,
the plots deviate upward from linearity in the lower
temperature (<10 K) region, especially for 3a . The
upward deviation of the ∆MS ) (2 transition means an
enhancement of probability of the triplet and/or quartet

7378 J . Org. Chem., Vol. 64, No. 20, 1999
Nishide et al.
F igu r e 3. ømolT vs T plots (O) of the diphenoxyl 1a with spin
concentration ) 0.72 spin/unit and ømolT vs T plots (b) of the
triphenoxyl 2a with spin concentration ) 0.92 spin/unit in
frozen 2-methyltetrahydrofuran. Solid lines are theoretical
curves calculated using equations10 for 1a (2J ) 31 cm-1, θ )
-0.12 K, x1 ) 0.43, x2 ) 0.57) and 2a (2J ) 31 cm-1, θ ) -0.16
K, x1 ) 0.16, x2 ) 0.79, x3 ) 0.05), respectively. Inset:
Normalized plots of magnetization (M/Msat) vs the ratio of
magnetic field and temperature (H/(T - θ)) for the 1a at T )
1.8 (O), 2 (b), 2.5 (0), 3 (9) K. The theoretical curves correspond
to the S ) 1/2 and 2/2 Brillouin functions.
F igu r e 1. ESR spectra of (a) the radical of 9, (b) the
monoradical of 2c, and (c) the monoradical of 3b in toluene at
room temperature. Precursor phenol concentration ) 0.5 unit
mM. (a) Monoradical of 9 with spin concentration ) 0.9, g )
2.0044; the dashed line for the simulation with aHa ) 0.18,
aHb ) 0.17, aHc ) 0.06, and aHd ) 0.05 mT. (b) Monoradical of
2c with spin concentration ) 0.025, g ) 2.0042. (c) Monoradical
of 3b with spin concentration ) 0.0001, g ) 2.0043; dashed
line for the simulation with aHa ) 0.18, aHb ) 0.08 mT.
the acyclic bi- and triradical 2a and 3a by curve fitting
the ømolT vs T data (Figure 3) to the equation derived
from a linear three- or two-spin model based on the
Heisenberg Hamiltonian.10 The resulting parameters are
summarized in the caption of Figure 3. The spin-
exchange constant or stability of the triplet ground-state
2J (or ∆ET-S) values for 1a and 2a were estimated to be
31 and 32 cm-1, respectively. These values were smaller
than those of m,p′-bis(3,5-di-tert-butyl-4-oxyphenyl)stil-
bene (2J ) 50 cm-1).4b,c This result dose not conflict with
the prediction of ∆ET-S using semiempirical AM1 com-
putation for the meta,para′-disubstituted diradicals based
on stilbene (or tolane backbone) by Lahti et al.11 They
explained that the tolane backbone is not as effective as
a ferromagnetic coupler because it lacks the alternativity
of single-double bonds in the π-conjugation at the ethy-
nylene triplet bond bridge.
The M/ Msat plots of 3a with a spin concn ) 0.81 spin/
unit lie almost on the Brillouin curve for S ) 3/2 at 1.8-
20 K, indicating a quartet ground state and a ferromag-
netic spin alignment between the pendant phenoxyl
electrons through the cyclic π-conjugation tribenzotris-
dehydro[12]annulene.
The J value was estimated by curve fitting12 the ømolT
vs T data (inset of Figure 4) to the equation derived from
a triangular three-spin model based on the Heisenberg
Hamiltonian.11 2J was evaluated to be 48 cm-1. This 2J
F igu r e 2. Curie plots for the peak in the ∆Ms ) (2 regions
for the acyclic diphenoxyl 1a (O) with spin concentration )
0.70 spin/unit and the cyclic triphenoxyl 3a (b) with spin
concentration ) 0.70 spin/unit in toluene glass. Precursor
phenol concentration ) 30 unit mM. Inset: ∆Ms ) (2
spectrum for 1a .
ground states in the low temperature and a ferromag-
netic interaction between the phenoxyl spins.
(10) ømolT ) NAg2µB2T{x3{1 + exp[-2J /(kT)] + 10exp[J /(kT)]}/{12-
{1 + exp[-12J /(kT)] + 2exp[J /(kT)]}} + x2/{3 + exp[-2J /(kT)]} + x1/
4}/[k(T - θ), where 2J , θ, x1, x2, and x3 are the effective magnetic
moment, the spin exchange coupling constant, the Weiss constant for
a weak intermolecular magnetic interaction, and the fraction of doublet
(S ) 1/2), the triplet (S ) 1), and the quartet (S ) 3/2), respectively.
x3 ) 0 for a two-spin system. (a) Bleaney, B.; Bowers, K. D. Proc. R.
Soc. London 1952, A214, 451. (b) Vleck, J . H. V. The Theory of Electric
and Magnetic Susceptibilities; Oxford University Press: London, 1932.
(11) (a) Lahti, P. M.; Ichimura, A. S. J . Org. Chem. 1991, 56, 3030.
(b) Lahti, P. M.; Ichimura, A. S. Mol. Cryst. Liq. Cryst. 1989, 176, 125.
(12) ømolT ) NAg2µB2T{x3{2 + 10 exp[3J /(kT)]}/{12{2 + exp[3J /
(kT)]}}} + x2/{3 + exp[-2J /(kT)]} + x1/4}/[k(T - θ)]. (a) Carlin, R. L.
Magnetochemistry; Springer-Verlag: Berlin, 1986. (b) Fujita, J .;
Tanaka, M.; Suemune, H.; Koga, N.; Matsuda, K.; Iwamura, H. J . Am.
Chem. Soc. 1996, 118, 9347.
Ma gn etic P r op er ties. The static magnetic suscepti-
bility (ø) and magnetization (M) of the acyclic diphenoxyl
1a and triphenoxyl 2a and the cyclic triphenoxyl 3a , in
frozen toluene or 2-methyltetrahydrofuran, were mea-
sured using a SQUID magnetometer. For example,
normalized plots of magnetization (M/Msat) for 1a were
presented close to the Brillouin curve for S ) 2/2 at 2-10
K (inset of Figure 3), indicating a triplet ground state of
the diradical 1a .
The spin-exchange coupling constant of the intramo-
lecular spin-alignment through the π-conjugated bond
(positive for a ferromagnetic coupling) was estimated for

Di- and Tri(4-oxyphenyl-1,2-phenyleneethynylene)s
J . Org. Chem., Vol. 64, No. 20, 1999 7379
for C43H52O2 600.9. Anal. Calcd for C43H52O2: C, 86.0; H, 8.7;
O, 5.3. Found: C, 85.9; H, 8.5.
2-Br om o-4-(3′, 5′-d i-ter t-bu tyl-4′-h yd r oxyp h en yl)eth y-
n ylben zen e (9). 2-Bromo-4-(3′,5′-di-tert-butyl-4′-acetoxyphe-
nyl)styrene 8 was prepared according to our previous paper.4b,c
A chloroform solution (16 mL) of bromine (3.0 g, 19 mmol) was
slowly added into a chloroform solution (8 mL) of 8 (8.0 g, 19
mmol) at 0 °C. After being stirred for 5 min at room temper-
ature, the mixture was washed with 5% aqueous sodium sulfite
and extracted with chloroform. The extract was washed with
water, dried over anhydrous sodium sulfate, and evaporated
to afford 11.0 g of 2-bromo-4-(3′,5′-di-tert-butyl-4′-hydroxyphe-
nyl)-1-(1′,2′-dibromoethyl)benzene as a white powder, which
was used in the following reaction without any purification.
A DMSO solution (250 mL) of the dibromide derivative (10 g,
17 mmol) was treated with 70% aqueous sodium hydroxide
for 3 h at 50 °C. The mixture was neutralized with 10%
aqueous ammonium chloride and extracted with ether. The
extract was dried and evaporated. The crude product was
purified using a silica gel column with a chloroform/hexane
(1/5) eluent. Recrystallization from ethanol gave 9 (2.6 g) as
colorless crystals: yield 50%; mp 141 °C; 1H NMR (CDCl3, 270
MHz; ppm) δ 7.75 (d, 1H, Ar), 7.53-7.56 (m, 2H, Ar), 7.45 (d,
2H, Ar), 7.42 (d, 1H, Ar), 5.35 (s, 1H, OH), 3.39 (s, 1H, tC-
H), 1.48 (s, 18H, tert-butyl); 13C NMR (CDCl3, 68 MHz; ppm)
δ 154.34, 144.26, 136.53, 134.14, 130.57, 130.14, 125.80,
125.50, 123.92, 121.85, 82.12, 81.76, 34.49, 30.28; IR (KBr
pellet, cm-1) 3615 (νO-H), 3310 (νtC-H), 2114 (νCtC); MS (EI)
m/e 385 (M+), 387 (M+ + 2) calcd for C22H25OBr 385.34. Anal.
Calcd for C22H25OBr: C, 68.6; H, 6.5; Br, 20.7; O, 4.2. Found:
C, 68.5; H, 6.2; Br, 20.4.
F igu r e 4. M/Ms vs H/(T - θ) plots for the cyclic triphenoxyl
3a with spin concentration ) 0.81 spin/unit in frozen toluene
at 1.8 (O), 2.0 (b), 2.25 (0), 5 (9), 10 (4), 15 (2), 20 (×) K, and
the theoretical Brillouin curves for S ) 1/2, 2/2, and 3/2.
Inset: ømolT vs T plots of the 3a . Solid line is a theoretical
curve calculated using the equation12 for 3a (2J ) 48 cm-1, θ
) -0.052 K, x1 ) 0.07, x2 ) 0.40, x3 ) 0.53).
value of 3a is larger than those estimated above for 1a
and 2a . The strong exchange interaction is probably
ascribed to the coplanarity of the annulene ring and more
effective spin distribution of the pendant phenoxyl radi-
cals through the backbone conjugation of this annulene.
Because the tribenzotrisdehydro[12]annulene can be
further modified into a two-dimensional extension, the
pendant-type and cyclic triradical 3a would become an
effective quartet unit for the purpose of synthesizing a
very high-spin polyradical.
2,4′-Bis(3′′,5′′-d i-ter t-b u t yl-4′′-h yd r oxyp h en yl)-2′-[4′′-
(3′′′,5′′′-d i-ter t-bu tyl-4-h yd r oxyp h en yl)p h en yl]-5-m eth yl-
tola n e (2c). 1e (1.7 g, 2.8 mmol) and 7 (1.3 g, 2.8 mmol) were
reacted according to procedure i and purified using silica gel
column with a chloroform/hexane (1/3) eluent (Rf 0.31) to afford
2b (0.40 g) as a yellow powder, yield 15%. 2b (0.40 g, 0.41
mmol) was deprotected according to procedure ii and purified
using a silica gel column with a chloroform/hexane (1/3) eluent
(Rf 0.26) to afford 2c (0.33 g): yield 88%; 1H NMR (CDCl3,
500 MHz; ppm) δ 7.78-7.22 (m, 16H, Ar), 5.33 (s, 1H, OH),
5.29 (s, 1H, OH), 5.23 (s, 1H, OH), 2.58 (s, 3H, Ar-CH3), 1.49
(s, 54H, tert-butyl); 13C NMR (CDCl3, 125 MHz; ppm) δ 154.1,
153.9, 153.5, 142.1, 141.8, 139.7, 138.5, 136.4, 136.3, 136.2,
132.4, 132.1, 131.7, 131.6, 131.0, 130.3, 130.2, 129.8, 128.3,
127.1, 126.7, 126.5, 126.2, 125.9, 123.9, 123.8, 123.7, 123.5,
Exp er im en ta l Section
Cr oss-Cou p lin g of th e Acetylen ic Com p ou n d s w ith
th e Ar yl Br om id es (P r oced u r e i in Sch em es 1-3). A THF
solution of an aryl bromide (1 equiv) and an acetylenic
compound (1 equiv) were added to a THF solution of tetrakis-
(triphenylphosphine)palladium(0) (0.05 equiv), cuprous iodide
(0.02 equiv), and dry triethylamine (15 equiv). In the coupling
reaction of trimethylsilylacetylene, it was added to the reaction
mixture of an aryl bromide and the catalyst with a syringe.
The reaction mixture was stirred under nitrogen at 70 °C for
17 h and monitored using thin-layer chromatography (TLC).
The mixture was extracted with ether, and the extract was
washed with water, dried over anhydrous sodium sulfate, and
evaporated to give a crude product.
Dep r otection of th e Tr im eth ylsilyl Gr ou p (P r oced u r e
ii in Sch em es 1-3). A methanol/THF (or methylene dichlo-
ride) (1/1) solution of the TMS derivative was stirred after the
addition of aqueous sodium hydroxide (5 equiv) under nitrogen
atmosphere at 50 °C. The reaction was monitored by TLC and
took 3-6 h. The mixture was diluted with water, neutralized
with aqueous ammonium chloride, and extracted with ether.
The extract was washed with water, dried over anhydrous
sodium sulfate, and evaporated to afford the crude acetylenic
derivative.
93.4, 92.9, 92.2, 89.1, 34.5, 30.4, 20.6; IR (KBr pellet, cm-1
)
3636 (νO-H), 2211 (νCtC), 2106 (νCtC); MS (FAB) m/e 904.5 calcd
for C65H76O3 905.3. Anal. Calcd for C65H52O3: C, 86.2; H, 8.5;
O, 5.3. Found: C, 86.0; H, 8.2.
4-[3′,5′-Di-ter t-bu tyl-4′-(tr im eth ylsiloxy)p h en yl]-2-iod o-
[(tr im eth ylsilyl)eth yn yl]ben zen e (12). n-Butyllithium in
hexane (1.6 M, 4.0 mL) was slowly added to a THF solution
(52 mL) of 11 (3.2 g, 6.0 mmol) at 80 °C. After the mixture
was stirred for 15 min, a THF solution (5.5 mL) of iodine (3.1
g, 12 mmol) was added to the mixture. The mixture was stirred
at room temperature for 1 h, washed with a saturated aqueous
sodium sulfite, extracted with ether, and washed with water.
The crude product was purified using silica gel column with a
hexane eluent (Rf 0.21). Recrystallization from ethanol afforded
1
gave 12 (2.24 g) as colorless crystals: yield 64.4%; H NMR
(CDCl3, 500 MHz; ppm) δ 8.01 (q, 1H, Ar), 7.47 (d, J ) 1.0 Hz,
2H, Ar), 7.41 (s, 2H, Ar), 1.45 (s, 18H, tert-butyl), 0.43 (s, 9H,
TMS), 0.29 (s, 9H, TMS); 13C NMR (CDCl3, 125 MHz; ppm) δ
153.7, 143.3, 141.4, 136.8, 132.7, 130.5, 127.4, 126.1, 124.5,
3-(3′,5′-Di-ter t-bu tyl-4′-h ydr oxyph en yl)-6-m eth yl-4′-[3′,5′-
d i-ter t-bu tyl-4′-(tr im eth ylsilyloxy)p h en yl]tola n e (1c). 1b
(0.9 g, 1.34 mmol) was deprotected according to procedure ii.
106.7, 101.7, 98.8, 35.3, 31.2, 3.9, -0.1; IR (KBr pellet, cm-1
2160 (νCtC); MS (EI) m/e 576 calcd for C28H41IOSi2 576.1.
)
The crude product was purified using silica gel with
a
chloroform/hexane (1/5) eluent (Rf 0.18) to afford 1c (0.70 g)
as a white powder: yield 88%; 1H NMR (CDCl3, 500 MHz;
ppm) δ 7.22-7.69 (m, 11H, Ar), 5.30 (s, 1H, OH), 5.25 (s, 1H,
OH), 2.55 (s, 3H, Ar-CH3), 1.50 (s, 36H, tert-butyl); 13C NMR
(CDCl3, 125 MHz; ppm) δ 153.9, 153.5, 142.0, 139.7, 138.2,
136.3, 136.2, 131.9, 131.7, 130.1, 129.8, 128.3, 126.9, 126.8,
123.9, 123.8, 123.4, 121.5, 93.4, 88.9, 34.5, 30.4, 20.4; IR (KBr
pellet, cm-1) 3634 (νO-H), 2209 (νCtC); MS (EI) m/e 600, calcd
2 ,8 ,1 4 -T r i s o x y p h e n y l t r i b e n z o t r i s d e h y d r o [1 2 ]-
a n n u len e (3b). A ethanol solution (20 mL) of 14 (0.90 g, 2.1
mmol) was added to a aqueous ammonium hydroxide solution
(55 mL) of cuprous chloride (0.47 g, 4.7 mmol). The mixture
was stirred at room temperature for 2.5 h to give a suspension
of a yellow precipitation and a blue solution. The precipitation
was collected, washed with successive water and ethanol, and
dried to afford a copper(I) acetylide derivative (0.74 g, yield

7380 J . Org. Chem., Vol. 64, No. 20, 1999
Nishide et al.
71%), which was used in the next procedure without any
purification. The cuprous acetylide derivative (0.16 g, 0.31
mmol) was dissolved in pyridine (6.0 mL), and the solution
was refluxed for 10 h to afford a crude product as a yellow
powder. The crude product was purified using silica gel column
with a chloroform/hexane (3/5) eluent to give 3b (0.030 g) as
a yellow solid: yield 32%; 1H NMR (CDCl3, 500 MHz; ppm) δ
7.52 (d, J ) 1.8 Hz, 3H, Ar), 7.43 (d, J ) 8.3 Hz, 3H, Ar), 7.38
(s, 6H, Ar), 7.35 (dd, J ) 1.8, 8.3 Hz, 3H, Ad), 5.32 (s, 3H,
OH), 1.49 (s, 54H, tert-butyl); 13C NMR (CDCl3, 125 MHz; ppm)
154.2, 142.5, 136.5, 132.5, 130.8, 130.2, 127.3, 126.9, 124.4,
123.8, 93.5, 93.1, 34.6, 30.5; IR (KBr pellet, cm-1) 3640 (νO-H),
2957 (νC-H); MS (FAB) m/e 913.6 (M+) calcd for C66H72O3 913.3.
Anal. Calcd for C66H72O3: C, 86.8; H, 8.0; O, 5.3. Found: C,
86.6; H, 7.9.
Oxid a tion . Aqueous solutions of sodium hydroxide and
potassium ferricyanide (10 and 20 equiv to the phenol group,
respectively) were added successively to a toluene or 2-meth-
yltetrahydrofuran solution (1s20 mM) of the hydroxy precur-
sor (9, 1c, 2c, or 3b) with vigorous stirring at room temper-
ature in a glovebox. The mixture was turned deeply green after
5 min. After the mixture was stirred for 30 min, the organic
layer was separated, washed with water, and dried over
anhydrous sodium sulfate to give the radical solution.
ESR a n d SQUID Mea su r em en ts. ESR spectra were taken
on a J EOL TE-200 ESR spectrometer with a 100 kHz field
modulation. The spin concentration of each sample was
determined both by careful integration of the ESR signal
standardized with that of 2,2,6,6-tetramethyl-1-piperidinyloxy
solution and by analyzing the saturated magnetization at the
SQUID measurement.
magnetometer. The magnetization was measured from 0 to 7
T at 1.8, 2, 2.25, 2.5, 3, 5, 10, 15, and 20 K. The static magnetic
susceptibility was measured from 1.8 to 200 K at a field of 0.5
T.
Oth er Sp ectr oscop ic Mea su r em en ts. The 1H and 13C
NMR, MS, FAB-MS, UV/vis, IR, and fluorescence spectra were
measured using a J EOL Lambda 500 or a J NM-EX270, a
Shimadzu GCMS-QP5050, a J MS-SX-102A, a J ASCO V-500,
a J ASCO FT/IR-410, a Hitachi F-4500 spectrometer, respec-
tively.
Ack n ow led gm en t. This work was partially sup-
ported by a Grant-in-Aid for Scientific Research (Nos.
09305060 and 277/08246101) from the Ministry of
Education, Science and Culture, J apan, and by the
NEDO Project on Technology for Novel High-Functional
Materials.
Su p p or tin g In for m a tion Ava ila ble: Syntheses and char-
acterizations of 4-[3′,5′-di-tert-butyl-4′-(trimethylsilyloxy)phe-
nyl](trimethylsilyl)ethynyl benzene (5), 4-(3′,5′-di-tert-butyl-
4′-hydroxyphenyl)ethynylbenzene (6), 3-(3′,5′-di-tert-butyl-4′-hy-
droxyphenyl)-6-methyl-4′-[3′,5′-di-tert-butyl-4′-(trimethylsilyloxy)phenyl]-
tolane (1b), 2-bromo-4-[3′,5′-di-tert-butyl-4′-(trimethylsilyloxy)-
phenyl]ethynylbenzene (10), 1-[2-bromo-4-[3′,5′-di-tert-butyl-
4′-(trimethylsilyloxy)phenyl]phenyl)]-2-(trimethylsilyl)acetyl-
ene (11), 5-(3′′,5′′-di-tert-butyl-4′′-hydroxyphenyl)-4-[3′′,5′′-
di-tert-butyl-4′′-(trimethylsilyloxy)phenyl]-2-(trimethylsilyl)-
ethynyl tolane (1d ), 5,4′-bis(3,5-di-tert-butyl-4-hydroxyphenyl)-
2-ethynyltolane (1e), and 4-[3′,5′-di-tert-butyl-4′-(trimethylsi-
loxy)phenyl]-2-iodo-ethynylbenzene (14). This material is
available free of charge via the Internet at http://pubs.acs.org.
The 2-methyltetrahydrofuran or toluene solutions of radicals
were immediately transferred to a diamagnetic capsule after
the oxidation. Magnetization and static magnetic susceptibility
were measured with a Quantum Design MPMS-7 SQUID
J O990575I