Preparation, methylation, and coupling reaction of 1,2-dithienyl-3,4- bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutenes

Article abstract of DOI:10.1246/bcsj.77.1377

Sterically protected 1,2-di(2-thienyl)- and 1,2-di(3-thienyl)-3,4-bis[(2,4, 6-tri-t-butylphenyl)phosphinidene]cyclobutenes were prepared and their properties were studied. When the dithienyldiphosphinidenecyclobutenes were allowed to react with butyllithi

Full text of DOI:10.1246/bcsj.77.1377

Ó 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 1377–1383 (2004) 1377
Preparation, Methylation, and Coupling Reaction of 1,2-Dithienyl-
3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutenes
ꢀ
Kozo Toyota, Keita Abe, Keiko Horikawa, and Masaaki Yoshifuji
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578
Received December 8, 2003; E-mail: yoshifj@mail.tains.tohoku.ac.jp
Sterically protected 1,2-di(2-thienyl)- and 1,2-di(3-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclo-
butenes were prepared and their properties were studied. When the dithienyldiphosphinidenecyclobutenes were allowed
to react with butyllithium and then with iodomethane, the corresponding methylthienyl derivatives were obtained. The
structure of (E,E)-1,2-bis(5-methyl-3-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene was analyzed
by X-ray crystallography. Lithiation of the dithienyldiphosphinidenecyclobutenes, followed by treatment with CuCl2,
afforded the corresponding coupling products on the thiophene rings.
Sterically protected 3,4-diphosphinidenecyclobutenes (ab-
breviated as DPCB, 1 in Chart 1),1 are unique ligands,2 because
of the relatively rigid framework that contains the phosphorus–
carbon ꢀ-bonds.3 Various transition metal complexes of DPCB
have been prepared2 and used as homogeneous catalysts;4 how-
ever, there are only limited examples of compounds containing
more than one DPCB unit in a molecule, although we previous-
ly reported the synthesis of a polymeric DPCB derivative 2.5
Although oligomeric DPCB derivatives have not been reported,
they attract interest, from a viewpoint of modern transition met-
al complex chemistry, because they might form the ‘metal as-
sembled complexes’ containing sp2-hybridized phosphorus-
bonded transition metals.
of
1,2-dithienyl-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphini-
dene]cyclobutenes 1a and 1b as promising building blocks con-
taining the DPCB skeleton.6
In a typical preparative method of 3,4-diphosphinidenecy-
clobutenes, alkynylphosphines were used as the starting mate-
rial.1 Thus, first we prepared (thienylethynyl)(2,4,6-tri-t-butyl-
phenyl)phosphines (3a,b), which contain a bulky 2,4,6-tri-t-bu-
ꢀ
tylphenyl substituent (hereafter abbreviated to the Mes group)
as a sterically protecting auxiliary7 (Scheme 1). Reaction of 2-
ethynylthiophene8 with ethylmagnesium bromide, followed by
treatment with chloro(2,4,6-tri-t-butylphenyl)phosphine,9 af-
forded 3a in 44% yield. In some cases, phosphaallene 4a was
formed as a by-product, probably via base-induced allenic rear-
rangement of 3a. Compound 3b was also obtained by a similar
method in 82% yield, starting from 3-ethynylthiophene8b,10 and
chloro(2,4,6-tri-t-butylphenyl)phosphine. In this case, only a
trace amount of phosphaallene 4b was formed.
For the purpose of connecting the DPCB moieties, reactions
under mild conditions are desirable, because the phosphorus–
carbon ꢀ-bonds are essentially reactive and may decompose
under severe reaction conditions. We report here preparations
Chart 1.
Scheme 1.
Published on the web July 9, 2004; DOI 10.1246/bcsj.77.1377

1378 Bull. Chem. Soc. Jpn., 77, No. 7 (2004)
1,2-Dithienyl-3,4-diphosphinidenecyclobutenes
Scheme 2.
Figure 1 shows the UV–vis spectra of 1a and 1b along with
those of the 1,2-diphenyl derivative (1c)1a and 1,2-non-substi-
tuted DPCB (1d).1c The bathochromic effect was observed in
the absorption of the aromatic ring-substituted DPCB (1a–c),
compared with that of 1d. Although the spectrum of 1b was
very similar to that of 1c, the longest absorption band of 1a
showed an apparent red shift (ca. 30 nm), compared to the cor-
responding absorption bands of 1b and 1c. The red shift in 2,20-
bithienyl, compared with either 2,30- or 3,30-bithienyl, is well
documented; this shift also appears in oligothiophenes of high-
er molecular weights.11
Lithiation of 1a with butyllithium (2 molar ratio), followed
by treatment with an excess amount of iodomethane, afforded
the corresponding bis(5-methyl-2-thienyl) derivative 6a in
64% isolated yield (Scheme 3). It should be mentioned that
6a (E,E-form) isomerized relatively easily to the (E,Z)-form
during the isolation process. This isomerization lowered the
isolated yield of 6a. In the case of methylation reaction of
1b, bis(5-methyl-3-thienyl) derivative 6b was obtained regiose-
lectively in 97% yield. Introduction of a substituent at the posi-
tion ꢂ to the bulky cyclobutene group seems to be retarded due
to steric repulsion. The regioselective introduction of substitu-
ents in 1b is promising in the viewpoint of the utilization of (3-
thienyl)DPCB system as a building block for construction of
more extended ꢀ systems.
Fig. 1. UV–vis spectra of 1a–d in hexane.
The ethynylphosphines 3a and 3b thus obtained were con-
verted to the corresponding diphosphinidenecyclobutene 1a
and 1b by the ordinary method1b using t-butyllithium (1 molar
ratio) and 1,2-dibromoethane (0.5 molar ratio) [Scheme 2, 1a:
57% yield, 1b: 63% yield]. In the reaction of 3a, formation of
an intermediate 5a was observed by 31P NMR spectroscopic
monitoring [5a: ꢁP ¼ 80:5]. It should be noted that reactions
of 4a and 4b with t-butyllithium (1 molar ratio) followed by ad-
dition of 1,2-dibromoethane (0.5 molar ratio) also gave 1a and
1b, respectively, in nearly quantitative yields.
The structure of 6b was unambiguously determined by X-ray
crystallography. Figure 2 depicts a molecular structure of 6b in
the crystal.12 In order to release the steric repulsion between the
ꢀ
methyl group and the Mes group, both of the methyl substitu-
ents of the thiophene rings locate apart from the sterically pro-
tecting groups. Atoms P(1), P(2), and C(1)–C(4) lie on almost
ꢀ
the same plane, within ꢁ0:03 A. The interplanar angle between

K. Toyota et al.
Bull. Chem. Soc. Jpn., 77, No. 7 (2004) 1379
Scheme 3.
Fig. 3. UV–vis spectra of 7a,b in hexane.
tween the aromatic planes and the DPCB plane are 84.5(1)ꢂ
and 93.2(1)ꢂ, respectively.
Fig. 2. Molecular structure of 6b, showing the atomic label-
ing scheme with thermal ellipsoids (30% probability). Hy-
drogen atoms are omitted ꢂfor clarity. Some selected bond
Then we tried to combine the two 1,2-dithienyl-3,4-diphos-
phinidenecyclobutenes together. Compounds 1a and 1b were
lithiated with butyllithium and the resulting thienyllithiums
ꢀ
lengths (A) and angles ( ): P(1)–C(3), 1.675(3); P(1)–
C(13), 1.851(3); P(2)–C(4), 1.674(3); P(2)–C(31),
1.851(3); C(1)–C(2), 1.393(4); C(2)–C(3), 1.494(4);
C(3)–C(4), 1.521(4); C(1)–C(4), 1.484(4); C(1)–C(6),
13
were treated with CuCl2 to give compounds 7a and 7b in
23% and 25% yields, respectively. The 31P NMR spectra of
1.451(4);
C(2)–C(10),
1.452(4);
P(1)–C(3)–C(2),
7a and 7b showed an AB pattern (7a: ꢁP ¼ 170:9 and 173.1,
148.8(2); P(1)–C(3)–C(4), 123.4(2); P(2)–C(4)–C(1),
149.5(5); P(2)–C(4)–C(3), 124.1(2); C(3)–P(1)–C(13),
106.8(1); C(4)–P(2)–C(31), 105.5(1); C(1)–C(2)–C(3),
92.1(2); C(1)–C(4)–C(3), 87.6(2); C(2)–C(1)–C(4),
92.8(2); C(2)–C(3)–C(4), 87.4(2).
3
3JPP ¼ 102:3 Hz; 7b: ꢁP ¼ 167:3 and 169.6, JPP ¼ 96:1 Hz).
The large spin–spin coupling constants (3JPP) observed for 7a
ꢀ
and 7b indicated all (E)-geometries around the Mes P=C
moieties.1b,d,f
Figure 3 shows the UV–vis spectra of 7a and 7b. The spec-
ꢀ
trum of 7a showed a red shift of ꢀ–ꢀ transition, compared
the DPCB plane [P(1), P(2), C(1)–C(4)] and one of the thio-
phene rings [S(1), C(5)–C(8)] is 34.2(1)ꢂ, while the angle be-
tween the DPCB plane and the other thiophene ring [S(2),
with those of the isomer 7b and the monomeric 1a (Fig. 1), al-
though the ꢃmax values of 7b were very similar to those of the
monomeric 1b. This may be attributed to the efficient electron
delocalization through the conjugation systems of the ꢂ-linked
bithienyl moiety.14 The delocalization through the bithienyl
part appears to be more effective in 7a (due to linear conjuga-
ꢀ
C(9)–C(12)] is 21.5(1)ꢂ. The two aromatic rings of the Mes
group, [C(13)–C(18)] and [C(31)–C(36)], are almost perpen-
dicular to the DPCB plane, whereas the interplanar angles be-

1380 Bull. Chem. Soc. Jpn., 77, No. 7 (2004)
1,2-Dithienyl-3,4-diphosphinidenecyclobutenes
ꢂ
4a: Pale yellow crystals, mp 133–136 C (decomp); 1H NMR
tion) than in 7b (due to cross conjugation). Semi-empirical cal-
culations (MOPAC, AM1) of 7a showed the p orbitals of the ꢂ-
carbons (carbon atoms bound to the other thiophene ring) are
incorporated into both HOMO and LUMO of 7a, while little
contribution of the corresponding p orbitals at the ꢂ-carbons
is indicated in the case of 7b.
In summary, we have prepared 1,2-dithienyl- and 1,2-bis-
(methylthienyl)-3,4-diphosphinidenecyclobutenes, as well as
compound 7 containing two DPCB moieties within a molecule.
The results described here show that the thienyldiphosphini-
denecyclobutenes are promising building blocks for the
DPCB-based oligomers or polymers. Further studies on prepa-
ration and properties of DPCB oligomers are now in progress.
(400 MHz, CDCl3) ꢁ 1.40 (9H, s, p-t-Bu), 1.74 (18H, s, o-t-Bu),
6.96 (1H, d, 3JPH ¼ 26:4 Hz, P=C=CH), 6.98 (2H, m, thiophene),
7.26 (1H, t, 3JHH ¼ 3:3 Hz, thiophene), and 7.49 (2H, s, m-Mes );
ꢀ
13C{1H} NMR (100 MHz, CDCl3) ꢁ 31.9 (s, p-CMe3), 34.1 (d,
4JPC ¼ 6:9 Hz, o-CMe3), 35.5 (s, p-CMe3), 38.6 (s, o-CMe3),
2
107.1 (d, JPC ¼ 9:3 Hz, P=C=C), 122.7 (s, arom.), 126.9 (s,
1
arom.), 127.0 (s, arom.), 127.7 (s, arom.), 131.1 (d, JPC
ꢀ
¼
66:3 Hz, ipso-Mes ), 138.3 (d, JPC ¼ 13:5 Hz, arom.), 150.4 (s,
ꢀ
2
ꢀ
p-Mes ), 154.4 (d, JPC ¼ 3:3 Hz, o-Mes ), and 239.6 (d,
1JPC ¼ 23:7 Hz, P=C=C); 31P NMR (162 MHz, CDCl3) ꢁ 80.7
3
(d, JPH ¼ 26:4 Hz); UV (hexane) 296 (log " 4.31) and 310 nm
(sh, 4.17); IR (KBr) 1591, 1473, 1400, 1363, 1240, 1205, 1130,
1041, 879, 835, 750, and 704 cmꢃ1; MS (70 eV) m=z (rel intensity)
384 (Mþ; 23), 328 (Mþ ꢃ t-Bu + 1; 100), and 313 (Mþ ꢃ t-Bu ꢃ
Me; 50). Found: m=z 384.2040. Calcd for C24H33PS: M, 384.2041.
(3-Thienylethynyl)(2,4,6-tri-t-butylphenyl)phosphine (3b).
A mixture of (2,4,6-tri-t-butylphenyl)phosphine (3.2 g, 11.6
mmol) and AIBN (65 mg, 0.58 mmol) in carbon tetrachloride
(41 mL) was refluxed for 4 h. The resulting mixture was concen-
trated in vacuo and 40 mL of THF was added to the residual
chloro(2,4,6-tri-t-butylphenyl)phosphine. On the other hand, to a
solution of 3-ethynylthiophene (11 mmol) in THF (20 mL) was
added 11 mmꢂol of ethylmagnesium bromide (0.89 M solution in
hexane) at 0 C. The resulting solution was stirred for 10 min,
warmed to room temperature, and stirred for 20 min. Then the so-
lution was added to the above THF solution of the chlorophosphine
Experimental
Melting points were measured on a Yanagimoto MP-J3 micro
melting point apparatus and were uncorrected. NMR spectra were
recorded on a Bruker Avance-400 or a Bruker AM-600 spectrom-
eter. IR spectra were obtained on a Horiba FT-300 spectrometer.
MS spectra were taken on either a JEOL HX-110 or a Hitachi
M-2500S spectrometer. FT-ICR-MS spectra were measured on a
Bruker APEX III spectrometer. Gel permeation liquid chromatog-
raphy (GPC, Japan Analytical Industry, JAIGEL H1+H2 column)
was also used for the molecular weight determination using a poly-
styrene standard. X-ray diffraction data were collected on a Rigaku
R-AXIS IV diffractometer. Reactions were performed under an ar-
gon atmosphere, unless otherwise specified.
(2-Thienylethynyl)(2,4,6-tri-t-butylphenyl)phosphine (3a).
A mixture of (2,4,6-tri-t-butylphenyl)phosphine15 (2.5 g, 9.0
mmol) and 2,20-azobisisobutyronitrile (AIBN) (42 mg, 0.45 mmol)
in carbon tetrachloride (31 mL) was refluxed for 4 h. The resulting
mixture was concentrated in vacuo and 30 mL of tetrahydrofuran
(THF) was added to the residual chloro(2,4,6-tri-t-butylphenyl)-
phosphine. On the other hand, to a solution of 2-ethynylthiophene
(11 mmol) in THF (10 mL) was added 12 mmol of ethylmagne-
ꢂ
ꢂ
at 0 C. The mixture was stirred at 0 C for 10 min, warmed to
room temperature, and stirred for 2 h. Then the solvent was re-
moved under reduced pressure and the residue was submitted to
a silica-gel column chromatographic treatment to give 3.64 g
ꢀ
(82% yield based on the starting Mes PH2) of the phosphine 3b.
ꢂ
3b: Pale yellow crystals, mp 113–116 C; 1H NMR (400 MHz,
CDCl3) ꢁ 1.36 (9H, s, p-t-Bu), 1.86 (18H, s, o-t-Bu), 6.22 (1H, d,
1JPH ¼ 247:2 Hz, PH), 6.60 (1H, m, thiophene), 6.85 (1H, m, thi-
ꢀ
ophene), 6.97 (1H, m, thiophene), and 7.27 (2H, s, m-Mes );
siumꢂ bromide (0.89 M solution in hexane; 1 M = 1 mol dmꢃ3
)
13C{1H} NMR (100 MHz, CDCl3) ꢁ 31.7 (s, p-CMe3), 34.1 (d,
4JPC ¼ 6:9 Hz, o-CMe3), 35.6 (s, p-CMe3), 39.0 (s, o-CMe3),
87.9 (d, 1JPC ¼ 21:8 Hz, PCꢄC), 98.0 (s, PCꢄC), 123.3 (s, arom.),
at 0 C. The resulting solution was stirred for 10 min, warmed to
room temperature, and stirred for 20 min. Then the solution was
ꢂ
1
ꢀ
added to the above THF solution of the chlorophosphine at 0 C.
ꢂ
125.6 (s, arom.), 126.1 (d, JPC ¼ 25:7 Hz, ipso-Mes ), 129.4 (s,
ꢀ
The mixture was stirred at 0 C for 10 min, warmed to room tem-
arom.), 130.3 (s, arom.), 130.5 (s, arom.), 151.1 (s, p-Mes ), and
ꢀ
perature, and stirred for 2 h. Then the solvent was removed under
reduced pressure and the residue was submitted to a silica-gel col-
umn chromatographic treatment to give 1.53 g of 3a (44% yield
156.0 (d, 2JPC ¼ 10:4 Hz, o-Mes ); 31P NMR (162 MHz, CDCl3)
ꢁ ꢃ100:4 (d, 1JPH ¼ 247:2 Hz); UV (hexane) 254 (log " 4.16) and
268 nm (sh, 4.14); IR (KBr) 3104, 2958, 2927, 2869, 2399, 2362,
2337, 2154, 1594, 1473, 1394, 1361, 1236, 1209, 1187, 1164,
1126, 1079, 1024, 941, 923, 873, 781, and 622 cmꢃ1; MS
(70 eV) m=z (rel intensity) 384 (Mþ; 93), 369 (Mþ ꢃ Me; 24),
ꢀ
based on the starting Mes PH2). In some cases, (2-thienylethenyli-
dene)(2,4,6-tri-t-butylphenyl)phosphine (4a) was obtained as a
by-product.
3a: Pale yellow micro needles, mp 109–113 C (decomp);
327 (Mþ ꢃ t-Bu; 28), 231 (Mes ꢃ Me + 1; 100), and 57 (t-
ꢂ
ꢀþ
1H NMR (400 MHz, CDCl3) ꢁ 1.42 (9H, s, p-t-Bu), 1.77 (18H,
Buþ; 98). Found: m=z 384.2040. Calcd for C24H33PS: M,
384.2041.
(E,E)-1,2-Di(2-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phos-
1
s, o-t-Bu), 6.06 (1H, d, JPH ¼ 249:0 Hz, PH), 6.96–7.27 (3H,
ꢀ
m, thiophene), and 7.62 (2H, s, m-Mes ); 13C{1H} NMR
4
(100 MHz, CDCl3) ꢁ 31.7 (s, p-CMe3), 34.1 (d, JPC ¼ 6:9 Hz,
phinidene]cyclobutene (1a). To a solution of 3a (980 mg,
2.6 mmol) in THF (40 mL) was added 2.6 mmol of t-butyllithium
(1.60 M solution in pentane) at ꢃ78 C. The resulting mixture was
o-CMe3), 35.6 (s, p-CMe3), 39.0 (s, o-CMe3), 93.0 (d,
1JPC ¼ 23:6 Hz, PCꢄC), 95.9 (s, PCꢄC), 123.3 (s, arom.), 124.1
ꢂ
ꢀ
(s, arom.), 125.7 (d, 1JPC ¼ 25:6 Hz, ipso-Mes ), 127.3 (s, arom.),
stirred for 10 min at this temperature. Then the mixture was treated
with 1,2-dibromoethane (1.3 mmol) and the resulting solution was
stirred for 10 min, warmed to room temperature, stirred for 2 h; fi-
nally, the solvent was removed in vacuo. Chromatographic treat-
ment (SiO2/hexane) of the residue affꢂorded 560 mg (57%) of
(E,E)-1a: Orange prisms, mp 214–216 C; 1H NMR (400 MHz,
CDCl3) ꢁ 1.47 (18H, s, p-t-Bu), 1.62 (36H, s, o-t-Bu), 6.00 (2H,
127.7 (s, arom.), 132.6 (d, JPC ¼ 1:6 Hz, arom.), 151.2 (s, p-
Mes ), and 156.1 (d, JPC ¼ 10:8 Hz, o-Mes ); 31P NMR
(162 MHz, CDCl3) ꢁ ꢃ100:1 (d, 1JPH ¼ 249:0 Hz); UV (hexane)
261 (log " 4.13) and 282 nm (4.20); IR (KBr) 2974, 2403, 2156,
1595, 1537, 1464, 926, and 704 cmꢃ1; MS (70 eV) m=z (rel inten-
sity) 384 (Mþ; 48) and 57 (t-Buþ; 100). Found: m=z 384.2042.
Calcd for C24H33PS: M, 384.2041.
ꢀ
2
ꢀ
3
3
d, JHH ¼ 3:7 Hz, 3-thiophene), 6.60 (2H, dd, JHH ¼ 5:0 Hz

K. Toyota et al.
Bull. Chem. Soc. Jpn., 77, No. 7 (2004) 1381
3
3
and JHH ¼ 3:7 Hz, 4-thiophene), 7.10 (2H, d, JHH ¼ 5:0 Hz, 5-
0.260 mmol) in THF (4 mL) was added 0.260 mmol of t-butyl-
ꢂ
thiophene), and 7.50 (4H, s, m-Mes ); 13C{1H} NMR (100 MHz,
lithium (1.45 M solution in pentane) at ꢃ78 C. The reaction mix-
ꢀ
ꢂ
CDCl3) ꢁ 32.1 (s, p-CMe3), 33.6 (s, o-CMe3), 35.5 (s, p-CMe3),
38.8 (s, o-CMe3), 122.5 (s, arom.), 127.3 (s, arom.), 128.2 (s,
arom.), 130.2 (s, arom.), 133.2 (s, arom.), 135.1 (pseudo t,
ture was stirred at ꢃ78 C for 5 min and 0.130 mmol of 1,2-dibro-
moethane was added. The resulting mixture was stirred at this tem-
perature for 10 min then warmed to room temperature and stirred
for 1 h. Evaporation of the solvent under reduced pressure, fol-
lowed by column chromatographic treatment, afforded 98.1 mg
(98%) of 1a. Compound 1b was obtained from 4b, by a similar pro-
cedure, in an almost quantitative yield.
1JPC ¼ 27:5 Hz, ipso-Mes ), 147.5 (d, JPC ¼ 5:7 Hz, P=C–C),
ꢀ
2
ꢀ
ꢀ
150.9 (s, p-Mes ), 155.7 (s, o-Mes ), and 175.5 (d,
1JPC ¼ 17:5 Hz, P=C); 31P{1H} NMR (162 MHz, CDCl3) ꢁ
170.5; UV (hexane) 216 (log " 4.60), 248 (4.37), 341 (4.45), and
428 nm (sh, 3.99); IR (KBr) 1593, 1529, 1475, 1396, 1363,
1240, 1211, 1126, and 906 cmꢃ1; MS (70 eV) m=z (rel intensity)
(E,E)-1,2-Bis(5-methyl-2-thienyl)-3,4-bis[(2,4,6-tri-t-butyl-
phenyl)phosphinidene]cyclobutene (6a). To a solution of (E,E)-
1a (80 mg, 0.10 mmol) in THF (5 mL) was added 0.20 mmol of
butyllithium (1.56 M solution in hexane) at ambient temperature.
The resulting mixture was stirred for 30 min at this temperature.
Then the mixture was treated with an excess amount of iodo-
methane (2.0 mmol) and the resulting solution was stirred for
45 min. Removal of the solvent in vacuo, followed by chromato-
graphic treatment (SiO2/hexane–Et2O) of the residue, afforded
766 (Mþ; 23), 709 (Mþ ꢃ t-Bu; 10), 491 (Mþ ꢃ Mes P + 1;
ꢀ
23), and 275 (Mes Pþ ꢃ 1; 100). Found: C, 73.26; H, 8.43; S,
ꢀ
8.44%. Calcd for C48H64P2S2 H2O: C, 73.43; H, 8.47; S, 8.17%.
ꢅ
(E,E)-1,2-Di(3-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phos-
phinidene]cyclobutene (1b). To a solution of 3b (1.13 g, 2.9
mmol) in THF (40 mL) was added 2.8 mmol of t-butyllithium
(1.60 M solution in pentane) at ꢃ78 C. The resulting mixture was
ꢂ
ꢂ
stirred for 10 min at this temperature. Then the mixture was treated
with 1,2-dibromoethane (1.4 mmol) and the resulting solution was
stirred for 10 min, warmed to room temperature, stirred for 2 h; fi-
nally, the solvent was removed under reduced pressure. Chromato-
graphic treatment (SiO2/hexane) of the residue gave 710 mg (63%
yield based on 3b) of (E,E)-1b. (3-Thienylethenylidene)(2,4,6-tri-
t-butylphenyl)phosphine (4b) was formed as a by-product.
53 mg (64%) of (E,E)-6a: Orange solid, mp 220–223 C (de-
comp); 1H NMR (400 MHz, CDCl3) ꢁ 1.38 (18H, s, p-t-Bu),
1.54 (36H, s, o-t-Bu), 2.28 (6H, s, Me), 5.51 (2H, d,
3
3JHH ¼ 3:3 Hz, thiophene), 6.16 (2H, d, JHH ¼ 3:3 Hz, thio-
ꢀ
phene), and 7.41 (4H, s, m-Mes ); 13C{1H} NMR (100 MHz,
CDCl3) ꢁ 15.9 (thienyl-Me), 32.1 (s, p-CMe3), 33.6 (s, o-CMe3),
35.6 (s, p-CMe3), 38.8 (s, o-CMe3), 122.4 (s, arom.), 126.2 (s, ar-
om.), 131.1 (s, arom.), 131.1 (s, arom.), 135.7 (pseudo t,
(E,E)-1b: Red crystals, mp 249–252 C; 1H NMR (400 MHz,
CDCl3) ꢁ 1.44 (18H, s, p-t-Bu), 1.56 (36H, s, o-t-Bu), 5.63 (2H,
ꢂ
ꢀ
JPC ¼ 29:0 Hz, ipso-Mes ), 142.8 (s, arom.), 147.1 (pseudo t,
4
3
ꢀ
ꢀ
d, JHH ¼ 2:8 Hz, 2-thiophene), 6.59 (2H, dd, JHH ¼ 5:0 Hz
JPC ¼ 5:7 Hz, P=C–C), 150.8 (s, p-Mes ), 155.7 (s, o-Mes ),
5
4
1
2
and JPH ¼ 1:1 Hz, 4-thiophene), 6.91 (2H, dd, JHH ¼ 2:8 Hz
and 175.9 (dd, JPC ¼ 17:4 Hz and JPC ¼ 8:8 Hz, P=C);
31P{1H} NMR (162 MHz, CDCl3) ꢁ 165.3; UV (hexane) 348
(log " 4.53) and 428 nm (4.10); IR (KBr) 1466, 1394, 1362,
1244, 1207, and 800 cmꢃ1; MS (70 eV) m=z (rel intensity) 794
3
ꢀ
and JHH ¼ 5:0 Hz, 5-thiophene), and 7.47 (4H, s, m-Mes );
13C{1H} NMR (100 MHz, CDCl3) ꢁ 32.0 (s, p-CMe3), 33.5 (s,
o-CMe3), 35.6 (s, p-CMe3), 38.8 (s, o-CMe3), 122.6 (s, arom.),
124.3 (s, arom.), 127.2 (s, arom.), 127.9 (s, arom.), 129.9 (d,
(Mþ; 90), 737 (Mþ ꢃ t-Bu; 15), 519 (Mþ ꢃ Mes P; 24), and 57
ꢀ
1JPC ¼ 26:3 Hz, ipso-Mes ), 132.8 (s, arom.), 149.4 (d,
(t-Buþ; 100).
ꢀ
2JPC ¼ 5:6 Hz, P=C–C), 150.9 (s, p-Mes ), 155.7 (s, o-Mes ),
(E,E)-1,2-Bis(5-methyl-3-thienyl)-3,4-bis[(2,4,6-tri-t-butyl-
phenyl)phosphinidene]cyclobutene (6b). To a solution of (E,E)-
1b (100 mg, 0.13 mmol) in THF (5 mL) was added 0.55 mmol of
butyllithium (1.56 M solution in hexane) at ambient temperature.
The resulting mixture was stirred for 30 min at this temperature.
Then the mixture was treated with an excess amount of iodo-
methane (1.3 mmol) and the resulting solution was stirred for
45 min. Removal of the solvent in vacuo, followed by chromato-
graphic treatment (SiO2/hexane–Et2O) of the residue, afforded
ꢀ
ꢀ
and 176.2 (d, JPC ¼ 17:5 Hz, P=C); 31P{1H} NMR (162 MHz,
1
CDCl3) ꢁ 166.6; UV (hexane) 216 (sh, log " 4.66), 248 (4.48),
328 (4.58), and 396 nm (sh, 4.07); IR (KBr) 1576, 1460, 1401,
1359, 1212, 873, and 784 cmꢃ1. Found: C, 75.35; H, 8.63; S,
8.62%. Calcd for C48H64P2S2: C, 75.16; H, 8.41; S, 8.36%.
4b: Colorless crystals, mp 134–135 C (decomp); 1H NMR
(600 MHz, CDCl3) ꢁ 1.30 (9H, s, p-t-Bu), 1.64 (18H, s, o-t-Bu),
ꢂ
3
6.72 (1H, d, JPH ¼ 27:0 Hz, P=C=CH), 7.09 (1H, dd,
3JHH ¼ 5:0 Hz, JPH ¼ 0:9 Hz, 4-thiophene), 7.11 (1H, d,
97 mg (97%) of (E,E)-6b: Yellow crystals, mp 216–223 C (de-
5
ꢂ
4JHH ¼ 2:7 Hz, 2-thiophene), 7.23 (1H, dd, JHH ¼ 5:0 Hz,
comp); 1H NMR (400 MHz, CDCl3) ꢁ 1.43 (18H, s, p-t-Bu),
1.56 (36H, s, o-t-Bu), 2.26 (6H, s, Me), 5.17 (2H, s, thiophene),
3
4JPH ¼ 2:7 Hz, 5-thiophene), and 7.39 (2H, d, JPH ¼ 1:2 Hz, m-
4
ꢀ
ꢀ
Mes ); 13C{1H} NMR (151 MHz, CDCl3) ꢁ 31.3 (s, p-CMe3),
6.43 (2H, s, thiophene), and 7.47 (4H, s, m-Mes ); 13C{1H} NMR
4
33.4 (d, JPC ¼ 6:0 Hz, o-CMe3), 34.9 (s, p-CMe3), 38.1 (s, o-
(100 MHz, CDCl3) ꢁ 15.5 (s, thienyl-Me), 32.1 (s, p-CMe3), 33.5
(s, o-CMe3), 35.6 (s, p-CMe3), 38.8 (s, o-CMe3), 122.6 (s, arom.),
125.9 (s, arom.), 126.1 (s, arom.), 132.6 (s, arom.), 136.0 (d,
2
CMe3), 106.9 (d, JPC ¼ 10:5 Hz, P=C=C), 122.1 (s, arom.),
122.8 (d, JPC ¼ 1:5 Hz, arom.), 125.8 (s, arom.), 127.4 (s, arom.),
1
ꢀ
ꢀ
ꢀ
130.8 (d, JPC ¼ 64:8 Hz, ipso-Mes ), 134.9 (d, JPC ¼ 12:0 Hz,
1JPC ¼ 28:0 Hz, ipso-Mes ), 138.2 (s, arom.), 150.9 (s, p-Mes ),
ꢀ
2
ꢀ
ꢀ
arom.), 149.7 (s, p-Mes ), 153.7 (d, JPC ¼ 4:5 Hz, o-Mes ),
155.6 (m, P=C–C), 155.7 (s, o-Mes ), and 176.7 (m, P=C);
and 240.1 (d, JPC ¼ 24:1 Hz, P=C=C); 31P NMR (162 MHz,
31P{1H} NMR (162 MHz, CDCl3) ꢁ 164.0; UV (hexane) 216
(sh, log " 4.61), 249 (4.43), 331 (4.52), and 406 nm (sh, 4.05);
IR (KBr) 1593, 1533, 1473, 1394, 1363, 1242, 1207, 877, 833,
1
3
CDCl3) ꢁ 75.6 (d, JPH ¼ 27:0 Hz); UV (hexane) 203 (log "
4.69), 236 (4.43), 258 (4.46), and 266 nm (sh, 4.41); IR (KBr)
1589, 1469, 1394, 1361, 1240, 877, 827, 771, 617, and
487 cmꢃ1; MS (70 eV) m=z (rel intensity) 385 (Mþ + 1; 6), 327
and 760 cmꢃ1
Compound 7a.
.
To a solution of (E,E)-1a (200 mg,
(Mþ ꢃ t-Bu; 100), 313 (Mþ ꢃ t-Bu ꢃ Me + 1; 55), 271 (Mþ
ꢃ
ꢃ
0.261 mmol) in THF (1.2 mL) was added ꢂ0.521 mmol of butyl-
2t-Bu + 1; 58), 257 (Mes PCCHþ ꢃ 3Me + 1; 52), 216 (Mþ
lithium (1.58 M solution in hexane) at ꢃ78 C. The resulting mix-
ꢀ
3t-Bu; 42), and 173 (Mes PCþ ꢃ 2t-Bu ꢃ 1; 21). Found: m=z
ture was stirred for 30 min at ꢃ78 C. Then the mixture was treat-
ꢀ
ꢂ
384.2036. Calcd for C24H33PS: M, 384.2041.
Preparation of 1a,b from 4a,b. To a solution of 4a (100 mg,
ed with an anisole (1.2 mL) solution of CuCl2 (0.130 mmol) at
ꢂ
ꢃ78 C and the resulting solution was stirred for 1 h. The solution

1382 Bull. Chem. Soc. Jpn., 77, No. 7 (2004)
1,2-Dithienyl-3,4-diphosphinidenecyclobutenes
was warmed to room temperature and ca. 0.5 mL of 3% hydro-
chloric acid was added. The resulting mixture was extracted with
ether. The organic phase was washed with 15% aqueous ammonia
and dried over MgSO4. Removal of the solvent in vacuo, followed
by gel permeation chromatographic treatment, afforded 22.7 mg
X-ray Crystallographic Analysis of 6b. C50H68P2S2, Mr ¼
795:15, monoclinic, space group P21=n (#14), a ¼ 15:035ð4Þ,
ꢂ
ꢀ
b ¼ 10:848ð2Þ, c ¼ 30:40ð3Þ A, ꢄ ¼ 102:181ð5Þ , V ¼ 4847ð4Þ
ꢀ 3
A , Z ¼ 4, ꢅ ¼ 1:090 g cmꢃ3, ꢆ ¼ 2:06 cmꢃ1; R1 ¼ 0:062,
R ¼ 0:111, RW ¼ 0:144; 5767 unique reflections with 2ꢇ ꢆ
(23%) of 7a. 7a: Dark red powder, mp 156–157 C; 1H NMR
50:0ꢂ were recorded on an imaging plate diffractometer (Mo Kꢂ
ꢂ
ꢂ
(600 MHz, CDCl3) ꢁ 1.30 (18H, s, p-t-Bu), 1.37 (18H, s, p-t-
Bu), 1.54 (36H, s, o-t-Bu), 1.55 (36H, s, o-t-Bu), 5.30 (2H, d,
radiation, graphite monochrometer) at ꢃ120 C. Of these, 5317
with I > 2ꢈðIÞ were used for R1 calculation. The structure was
solved by heavy-atom direct methods and expanded using Fourier
techniques. The non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included but not refined. Crystallographic
data have been deposited at the Cambridge Crystallographic Data
Centre (no. CCDC 224042).
3
3JHH ¼ 3:9 Hz, thiophene), 6.06 (2H, d, JHH ¼ 3:8 Hz, thio-
3
phene), 6.33 (2H, d, JHH ¼ 3:9 Hz, thiophene), 6.58 (2H, dd,
3
3JHH ¼ 5:0 Hz and JHH ¼ 3:8 Hz, thiophene), 7.05 (2H, d,
ꢀ
3JHH ¼ 5:0 Hz, thiophene), 7.38 (4H, s, m-Mes ), and 7.39 (4H,
ꢀ
s, m-Mes ); 13C{1H} NMR (150 MHz, CDCl3) ꢁ 31.6 (s, p-
CMe3), 33.1 (s, o-CMe3), 35.1 (s, p-CMe3), 38.3 (s, o-CMe3),
ꢀ
128.0 (s, thiophene), 129.6 (s, thiophene), 131.6 (s, thiophene),
122.0 (s, m-Mes ), 124.2 (s, thiophene), 126.8 (s, thiophene),
This work was supported in part by some Grants-in-Aid for
Scientific Research (Nos. 13640522, 13304049, and 14044012)
from the Ministry of Education, Culture, Sports, Science and
Technology.
132.0 (s, thiophene), 132.5 (s, thiophene), 134.4 (d,
ꢀ
1
1JPC ¼ 57:4 Hz, ipso-Mes ), 135.0 (d, JPC ¼ 57:4 Hz, ipso-
ꢀ
Mes ), 150.6 (s, p-Mes ), 155.2 (s, o-Mes ), 155.3 (s, o-Mes ),
Mes ), 138.3 (s, thiophene), 146.3 (m, P=C–C), 150.4 (s, p-
ꢀ
ꢀ
ꢀ
ꢀ
1
2
References
174.5 (dd, JPC ¼ 50:6 Hz and JPC ¼ 20:4 Hz, P=C), and 175.1
(dd, JPC ¼ 49:1 Hz and JPC ¼ 21:9 Hz, P=C); 31P{1H} NMR
1
a) R. Appel, V. Winkhaus, and F. Knoch, Chem. Ber., 120,
1
2
3
(162 MHz, CDCl3) ꢁ 170.9 and 173.1 (AB, JPP ¼ 102:3 Hz);
243 (1987). b) M. Yoshifuji, K. Toyota, M. Murayama, H.
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UV (hexane) 248 (log " 4.75), 315 (sh, 4.62), 336 (4.64), 390
(4.56), and 518 nm (4.58); IR (KBr) 2962, 2904, 2868, 1591,
1531, 1475, 1435, 1394, 1362, 1240, 1209, 1126, 877, 798, 758,
and 700 cmꢃ1; MW (GPC, vs the polystyrene standard) 1350.
Found: C, 75.05; H, 8.30; S, 8.49%. Calcd for C96H126P4S4: C,
75.25; H, 8.29; S, 8.37%.
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¨
Compound 7b. To a solution of (E,E)-1b (100 mg, 0.130
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ꢂ
(1.58 M solution in hexane) at ꢃ78 C. The resulting mixture
2
K. Toyota, K. Tashiro, and M. Yoshifuji, Chem. Lett., 1991,
was stirred for 30 min at this temperature. Then the mixture was
treated with an anisole (0.6 mL) solution of CuCl2 (0.065 mmol)
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ꢂ
at ꢃ78 C and the resulting solution was stirred for 1 h. The solu-
tion was warmed to room temperature and ca. 0.5 mL of 3% hydro-
chloric acid was added. The resulting mixture was extracted with
ether. The organic phase was washed with 15% aqueous ammonia
and dried over MgSO4. Removal of the solvent in vacuo followed
by gel permeation chromatographic treatment afforded 24.5 mg
ꢂ
(25%) of 7b. 7b: Yellow powder, mp 168–169 C (decomp);
3
‘‘Multiple Bonds and Low Coordination in Phosphorus
1H NMR (600 MHz, CDCl3) ꢁ 1.34 (18H, s, p-t-Bu), 1.41 (18H,
s, p-t-Bu), 1.51 (36H, s, o-t-Bu), 1.52 (36H, s, o-t-Bu), 5.11 (2H,
Chemistry,’’ ed by M. Regitz and O. J. Scherer, Georg Thieme
Verlag, Stuttgart (1990); K. B. Dillon, F. Mathey, and J. F. Nixon,
‘‘Phosphorus: The Carbon Copy,’’ John Wiley & Sons, Chichester
(1998).
4
s, thiophene), 5.65 (2H, d, JHH ¼ 2:5 Hz, thiophene), 6.50 (2H,
3
4
dd, JHH ¼ 5:1 Hz and JHH ¼ 1:2 Hz, thiophene), 6.65 (2H, d,
4JHH ¼ 1:2 Hz, thiophene), 6.82 (2H, dd, JHH ¼ 5:1 Hz and
4
K. Toyota, K. Masaki, T. Abe, and M. Yoshifuji, Chem.
3
4JHH ¼ 2:5 Hz, thiophene), 7.39 (4H, s, m-Mes ), and 7.42 (4H,
Lett., 1995, 221; S. Ikeda, F. Ohhata, M. Miyoshi, R. Tanaka, T.
Minami, F. Ozawa, and M. Yoshifuji, Angew. Chem., Int. Ed.,
39, 4512 (2000); F. Ozawa, S. Yamamoto, S. Kawagishi, M.
Hiraoka, S. Ikeda, T. Minami, S. Ito, and M. Yoshifuji, Chem.
Lett., 2001, 972; T. Minami, H. Okamoto, S. Ikeda, R. Tanaka,
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(2001); F. Ozawa, H. Okamoto, S. Kawagishi, S. Yamamoto, T.
Minami, and M. Yoshifuji, J. Am. Chem. Soc., 124, 10968 (2002).
ꢀ
s, m-Mes ); 13C{1H} NMR (150 MHz, CDCl3) ꢁ 31.5 (s, p-
CMe3), 31.6 (s, p-CMe3), 33.0 (s, o-CMe3), 33.1 (s, o-CMe3),
ꢀ
35.1 (s, p-CMe3), 35.1 (s, p-CMe3), 38.3 (s, o-CMe3), 122.1 (s,
m-Mes ), 123.5 (s, thiophene), 123.9 (s, thiophene), 126.2 (s, thio-
ꢀ
phene), 126.8 (s, thiophene), 127.4 (s, thiophene), 132.2 (s, thio-
1
phene), 132.8 (s, thiophene), 135.1 (d, JPC ¼ 34:7 Hz, ipso-
ꢀ
phene), 148.1 (m, P=C–C), 149.9 (m, P=C–C), 150.5 (s, p-Mes ),
1
ꢀ
Mes ), 135.4 (d, JPC ¼ 36:2 Hz, ipso-Mes ), 135.3 (s, thio-
ꢀ
155.2 (s, o-Mes ), 155.3 (s, o-Mes ), and 175.8 (dd,
5
N. Yamada, K. Toyota, and M. Yoshifuji, Chem. Lett.,
ꢀ
ꢀ
2001, 248; See, also: M. Yoshifuji, N. Yamada, A. Maack, and
K. Toyota, Tetrahedron Lett., 39, 9481 (1998).
1JPC ¼ 49:6 Hz and JPC ¼ 22:6 Hz, P=C); 31P{1H} NMR
2
3
(162 MHz, CDCl3) ꢁ 167.3 and 169.6 (AB, JPP ¼ 96:1 Hz);
6
A part of this work was reported at the 81st National
UV (hexane) 258 (log " 4.46), 328 (4.93), and 398 nm (sh,
4.44); IR (KBr) 3113, 2956, 2906, 2868, 1593, 1539, 1475,
1396, 1362, 1238, 1207, 1126, 876, 827, 793, 758, 696, and
625 cmꢃ1; MW (GPC, vs the polystyrene standard) 1430.
Meeting of the Chemical Society of Japan, Tokyo, March 26–29,
2002, Abstr., No. 2G2-28.
7
M. Yoshifuji, I. Shima, N. Inamoto, K. Hirotsu, and T.
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8
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`
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G. Markl and P. Kreitmeier, Angew. Chem., Int. Ed. Engl.,
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