Synthesis, structure, and redox properties of diphosphathienoquinones

Article abstract of DOI:10.1002/1521-3773(20020715)41:14<2574::AID-ANIE2574>3.0.CO;2-K

The first diphosphaheteroquinoid compound, which contains two low-coordinate phosphorus atoms and a thienoquinoid skeleton (see picture), was isolated as air-stable orange crystals. Its quinoid nature was confirmed by x-ray crystallography and cyclic volt

Full text of DOI:10.1002/1521-3773(20020715)41:14<2574::AID-ANIE2574>3.0.CO;2-K

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Diphosphaquinone 1 was prepared by dechlorination of 1,4-
bis(chlorophosphanyl)benzene with zinc, but the product was
contaminated with secondary phosphanes because of over-
reduction.[2] To synthesize diphosphaquinones selectively, we
employed 1,6-dehydrochlorination of (chlorophosphanyl)-
phosphanylbenzene or -thiophene precursors 7 as the final
step (Scheme 1). Compounds 7 were prepared by stepwise
introduction of phosphanyl and chlorophosphanyl groups on
the aromatic ring by reaction of the corresponding aryllithium
Synthesis, Structure, and Redox Properties of
Diphosphathienoquinones**
Fumiki Murakami, Shigeru Sasaki, and
Masaaki Yoshifuji*
Although a variety of p-conjugated molecules containing
low-coordinate phosphorus atoms is known,[1] only two stable
phosphaquinoid compounds have been reported: diphospha-
quinone 1 by M‰rkl et al.[2] and
phosphaquinone 2 by us.[3] Di-
R
R
R
R
R
R
R
R
phosphathienoquinones 3 are
expected to be more stable
than 1 and still behave chemi-
cally and physically as a qui-
noid compound, since so-
called heteroquinoid, mole-
cules which contain a hetero-
atom such as sulfur in place of
e
c, d
a, b
H
H
Cl
P
P
P
P
P
Li
Br
Br
X
X
X
X
Mes*
Mes*
Mes*
Mes*
Mes*
7a: X = CH=CH, R = H (39%)
7b: X = S, R = H
7c: X = S, R = Br
1: X = CH=CH, R = H
6a: X = CH=CH, R = H (90%)
6b: X = S, R = H (76%)
6c: X = S, R = Br (57%)
5a: X = CH=CH, R = H
5b: X = S, R = H
5c: X = S, R = Br
3: X = S, R = H (86%)
4: X = S, R = Br (65% from 6c)
Scheme 1. Synthesis of
a
diphosphaquinone and diphosphathienoquinones. a) Mes*PCl2, Et2O, À788C,
b) LiAlH4, Et2O, 0 8C, c) tBuLi (7a, 7b) or nBuLi (7c), Et2O, À788C, d) Mes*PCl2, Et2O, À788C, e) KH,
ˆ
one endocyclic C C bond of
quinoid compounds, generally
have higher stability than their
[18]crown-6, THF, room temperature.
[5]
benzenoid counterparts without losing the inherent properties
of the quinoid system.[4] Here we report a general synthetic
route for diphosphaquinones and diphosphathienoquinones,
and the synthesis, structure, and redox properties of the first
diphosphathienoquinone 4.
with Mes*PCl2 (Mes* ˆ 2,4,6-tri-tert-butylphenyl) and ob-
tained as mixtures of diastereomers. Deprotonation of 7a and
7b with an excess of potassium hydride in the presence of
[18]crown-6 afforded diphosphaquinone 1 and diphospha-
thienoquinone 3 as inseparable 1:1 mixtures of (E)-1 (dP ˆ
261 ppm) and (Z)-1 (dP ˆ 263 ppm) and of (E,Z)-3 (dP ˆ
209 ppm (d, J(P,P) ˆ 264 Hz), 192 ppm (d, J(P,P) ˆ 264 Hz))
and (Z,Z)-3 (dP ˆ 197) isomers. To enhance the preference for
the Z,Z isomer by steric repulsion between the bulky Mes*
and other substituents, bromine atoms were introduced into
the 3- and 4-positions of the thiophene ring, and 7c was
dehydrochlorinated to afford air-stable orange prisms of 4 as a
single Z,Z isomer.
Mes*
Mes*
P
P
O
P
Mes*
R
The 1H NMR spectrum (500 MHz, CD2Cl2) of 4 reflected its
highly symmetrical structure, and only three signals corre-
sponding to aromatic, o-tBu, and p-tBu protons were ob-
served. The 13C NMR spectrum (126 MHz, CD2Cl2) was also
indicative of a symmetrical structure, and three signals
corresponding to the C atoms close to the phosphorus atoms
were observed as a pseudotriplet, typical of an AXX'
pattern.[6] The 31P NMR chemical shifts of diphosphathieno-
quinones (E,Z)-3, (Z,Z)-3, and 4 were observed upfield
relative to those of diphosphaquinones 1 and phosphaquinone
2. The molecular structure of 4 was further studied by X-ray
crystallography (Figure 1) and compared with that of thienyl-
1
2
R
P
Mes*
P
Mes* =
S
Mes*
3: R = H
4: R = Br
[*] Prof. Dr. M. Yoshifuji, Dr. F. Murakami, Dr. S. Sasaki
Department of Chemistry
Graduate School of Science
Tohoku University
Aoba, Sendai 980-8578 (Japan)
Fax :(‡81)22-217-6562
ˆ
phosphane 6c. The two exocyclic P C bonds adopt a Z
E-mail: yoshifj@mail.cc.tohoku.ac.jp
configuration with bond lengths of 1.712(2) and 1.714(2) ä,
which are longer than those of typical sterically protected
phosphaalkenes (ca. 1.68 ä)[7] but comparable to that of
phosphaquinone 2 (1.705(2) ä). The structural change of the
five-membered ring from an ™aromatic∫ thiophene to a
thienoquinoid structure was revealed by comparing 4 with
[**] Financial support by Grant-in-Aid for Scientific Research from the
Ministry of Education, Culture, Sports, Science, and Technology (Nos.
12740335, 08454193, and 09239101) is gratefully acknowledged. F.M.
thanks the Japan Society for the Promotion of Science for a JSPS
Postdoctoral Fellowship. The authors also thank the Instrumental
Analysis Center for Chemistry, Graduate School of Science, Tohoku
University, for the measurement of 500 MHz NMR and mass spectra.
This work was partially carried out in Advanced Instrumental
Laboratory for Graduate Research of Department of Chemistry,
Graduate School of Science, Tohoku University.
À
À
À
À
6c. The single bonds C1 C2, C3 C4, C4 S1, and S1 C1 were
longer than the corresponding values of 6c by 0.049, 0.060,
À
0.031, and 0.024 ä, respectively, while the double bond C2 C3
was shorter by 0.063 ä. The five-membered ring and two
exocyclic phosphorus atoms are planar with a maximum
Supporting information for this article is available on the WWW under
http://www.angewandte.org or from the author.
2574
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
1433-7851/02/4114-2574 $ 20.00+.50/0
Angew. Chem. Int. Ed. 2002, 41, No. 14

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minor contributions.[9] As observed for phosphaquinone 2,
the isotropic and anisotropic hfc constants were much larger
than those of radical anions of typical phosphaalkenes
but very close to those of phosphanyl radicals[10] which
suggests significant localization of an unpaired electron on
the 3p orbital of one phosphorus atom (P1; 69% by
comparison with atomic hfc constants[11]) and considerable
contribution of thiophene-bearing localized phosphorus
radical and anion centers. Further synthetic studies on
phosphathienoquinoid and phosphaquinoid molecules are in
progress.
Figure 1. ORTEP plot of 4 with 50% probability thermal ellipsoids.
Selected bond lengths [ä] and angles [8]: P1-C1 1.712(2), P2-C4 1.714(2),
C1-C2 1.416(3), C2-C3 1.359(3), C3-C4 1.415(3), C4-S1 1.743(2), C1-S1
1.751(2); C5-P1-C1 98.1(1), C23-P2-C4 100.6(1), P1-C1-C2 126.0(2), P1-C1-
S1 126.0(1), C2-C1-S1 108.0(2), C1-C2-C3 115.2(2), C2-C3-C4 114.3(2), C3-
C4-S1 108.8(2), P2-C4-C3 124.7(2), P2-C4-S1 126.4(1), C4-S1-C1 93.6(1),
S1-C1-C2 108.0(2).
Figure 3. EPR spectra obtained at 295 K (a) and 77 K (b) after reduction
of 4 with sodium metal in THF.
deviation from the least-squares plane of 0.0209 ä (C3).
However, two p-tBu groups are located very close to each
other, and the whole diphosphathienoquinoid skeleton is
twisted as a result of steric repulsion between them (C5-P1-
P2-C23 torsion angle 29.78).
Experimental Section
7c: A solution of tert-butyllithium (2.1 mL, 1.50m in n-pentane) was added
to a solution of 6c (669 mg, 1.12 mmol) in diethyl ether (15 mL) at 08C. The
solution was stirred for 20 min at 08C and added to a solution of Mes*PCl2
(417mg, 1.20 mmol) in diethyl ether (15 mL) at À788C. After stirring for
30 min at À788C and 10 h at 208C, the mixture was washed with saturated
NaCl solution, dried over anhydrous MgSO4, and concentrated to afford
crude 7c almost quantitatively. 7c: colorless crystals; 31P NMR (81 MHz,
CDCl3): d ˆ 68.8 (s), À67.4 (d, J(P,H) ˆ 229 Hz), 68.1 (s), À65.8 ppm (d,
J(P,H) ˆ 230 Hz).
In analogy with most other quinoid molecules, 4 was
expected to be reduced stepwise to the dianion via a radical
anion (semiquinone). This was confirmed by cyclic voltam-
metry of 4 (Figure 2), in which the first reversible (1E1/2
ˆ
‡
À1.50 V versus Ag/Ag ) and the second irreversible (2EP ˆ
À2.49 V) redox waves were observed. The first reduction
4: A solution of 7c in THF (10 mL) was added to a suspension of KH
(192 mg, 40 wt% dispersion in mineral oil) and [18]crown-6 (766 mg,
2.90 mmol) in THF (10 mL) at 208C, and the mixture was refluxed for
30 min. Excess KH was decomposed with water (ca. 10 mL) at room
temperature, and the mixture was washed with saturated NaCl solution,
dried over anhydrous MgSO4, and purified by column chromatography
(Al2O3/benzene) and recrystallization from benzene to give 4 (578 mg,
0.729 mmol, 65%). 4: orange plates (benzene), m.p. 173.0 175.08C
(decomp); 1H NMR (500 MHz, CD2Cl2): d ˆ 7.25 (4H, brs, arom.-m),
1.32 (36H, s, C(CH3)3-o) 1.20 ppm (18H, s, C(CH3)3-p); 13C{1H} NMR
1
3
ˆ
(126 MHz, CD2Cl2): d ˆ 172.37 (AXX', J(P,C) ‡ J(P',C) ˆ 73.6 Hz, P C),
154.76 (s, Mes*-o), 151.37(s, Mes*- p), 134.90 (AXX', 1J(P,C) ‡ 5J(P',C) ˆ
54.2 Hz, Mes*-ipso), 128.74 (AXX', 2J(P,C) ‡ 3J(P',C) ˆ 43.3 Hz, quinone-
3), 122.61 (s, Mes*-m), 38.46 (s, C(CH3)3-o), 35.28 (s, C(CH3)3-p), 33.05
Figure 2. Cyclic voltammogram of 4 at 293 K. Conditions: 10À4 m in THF
with 0.1m nBu4NClO4 as a supporting electrolyte; working electrode: glassy
carbon; counter electrode: Pt wire; reference electrode: Ag/0.01m AgNO3
in acetonitrile with 0.1m nBu4NClO4 (E1/2(ferrocene/ferricinium) ˆ
(AXX', J(P,C) ‡ 8J(P',C) ˆ 6.8 Hz, C(CH3)3-o), 31.49 ppm (s, C(CH3)3-p);
4
31P NMR (81 MHz, CD2Cl2): d ˆ 211.2 ppm (s); UV/Vis (hexanes): lmax
(lge) ˆ 466 (4.39), 370 (3.72), 274 nm (3.91); FABMS m/z (%): 794 (56)
0.180 V); scan rate: 50 mVsÀ1
.
‡
‡
‡
‡
[M ‡4], 792 (91) [M ‡2], 790 (45) [M ], 713 (8) [M ‡2 À Br], 711 (5)
‡
‡
[M À Br], 57(62) [ tBu ]; HRMS (70 eV, EI): found: m/z 790.2114; calcd
for C40H58P2SBr2: 790.2101.
potential, which was significantly lower than those of typical
phosphaalkenes (ca. À2.2 V),[8] and the second are very close
Crystal data of 4: C40H58P2SBr2, Mr ˆ 792.71, red prisms from benzene,
crystal dimensions 0.25  0.25  0.20 mm3. Tˆ 115 K, triclinic, space group
2
to that of phosphaquinone 2 (1E1/2 ˆ À1.55 V, EP ˆ À2.45),
≈
P1 (no. 2), a ˆ 11.531(2), b ˆ 18.982(4), c ˆ 10.273(5) ä, a ˆ 95.462(9), b ˆ
but the radical anion of 4 has enhanced stability. The EPR
115.92(3), g ˆ 82.28(2)8, Vˆ 2002(1) ä3, Z ˆ 2, 1calcd ˆ 1.315 gcmÀ3, m ˆ
2.188 mmÀ1, F(000) ˆ 828.00, 6920 reflections measured (2qmax ˆ 51.18),
Rint ˆ 0.030; 6920 observed reflections [I > 0.00s(I)], 639 variable param-
eters. R ˆ 0.037, Rw ˆ 0.043, GOF S ˆ 1.27for observed reflections
[I > 0.00s(I)] and R1 ˆ 0.030 for [I > 2.00s(I)]. The maximum and
minimum peaks on the final difference Fourier map corresponded to 0.34
and À0.43 eäÀ3. CCDC-180101 (4) and -180102 (6c) contain the supple-
mentary crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
.
spectrum of 4 À obtained by reduction of 4 with sodium metal
(Figure 3a) in THF at 293 K consisted of four lines resulting
from hyperfine coupling (hfc) with two nonequivalent 31P
nuclei (a(P1) ˆ 9.3, a(P2) ˆ 2.1 mT, g ˆ 2.007). The EPR
spectrum of the frozen solution at 77 K (Figure 3b) was
interpreted by assuming axial symmetric hfc and g tensors
with a dominant contribution from ak(P1) (27.7 mT) and other
Angew. Chem. Int. Ed. 2002, 41, No. 14
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
1433-7851/02/4114-2575 $ 20.00+.50/0
2575

COMMUNICATIONS
Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge
CB21EZ, UK; fax: (‡44)1223-336-033; or deposit@ccdc.cam.ac.uk).
1) LDA (2.1 equiv), THF, –78 °C, 30 min
2) Ph2FSN (2, 1.1 equiv), THF, –78 °C, 12h
3) 10% HClO4 (aq), RT, 30 min
CH3
Ph
S
Ph
S
Ph
S
N
Ph
HN
CH
NH
ClO4
Received: March 5, 2002 [Z18830]
Ph
Ph
1
3
Ph
S
Ph
S
ion-exchange resin (OH– form)
10% HClO4 (aq), CH3OH, 1h
[1] Multiple Bonds and Low Coordination in Phosphorus Chemistry
(Eds.: M. Regitz, O. J. Scherer), Georg Thieme, Stuttgart, 1990.
[2] G. M‰rkl, R. Hennig, K. M. Raab, Chem. Commun. 1996, 2057 2058.
[3] S. Sasaki, F. Murakami, M. Yoshifuji, Angew. Chem. 1999, 111, 351
354; Angew. Chem. Int. Ed. 1999, 38, 340 343.
1) CH3I/CH3CN, RT, 1h
2) NaClO4/CH3CN, RT
HN
CH
N
Ph
Ph
4
[4] K. Takahashi, Pure Appl. Chem. 1993, 65, 127 134; K. Yui, H. Ishida,
Y. Aso, T. Otsubo, F. Ogura, A. Kawamoto, J. Tanaka, Bull. Chem.
Soc. Jpn. 1989, 62, 1547 1555.
Ph
S
Ph
S
Ph
S
Ph
S
ion-exchange resin (OH– form)
10% HClO4 (aq), CH3OH, 1h
MeN
C
NMe
MeN
CH
NMe
ClO4
Ph
Ph
Ph
Ph
[5] M. Yoshifuji, I. Shima, N. Inamoto, K. Hirotsu, T. Higuchi, J. Am.
Chem. Soc. 1981, 103, 4587 4589; M. Yoshifuji, I. Shima, N. Inamoto,
K. Hirotsu, T. Higuchi, J. Am. Chem. Soc. 1982, 104, 6167.
[6] I. J. Colquhoun, W. McFarlane, J. Chem. Soc. Dalton Trans. 1982,
1915 1921.
[7] R. Appel in Multiple Bonds and Low Coordination in Phosphorus
Chemistry (Eds.: M. Regitz, O. J. Scherer), Georg Thieme, Stuttgart,
1990, pp. 157 219.
[8] M. Geoffroy, A. Jouaiti, G. Terron, M. Cattani-Lorente, Y. Ellinger, J.
Phys. Chem. 1992, 96, 8241 8245.
[9] Tentative assignments: g ˆ 2.007, a(P1) ˆ 9.3, a(P2) ˆ 2.1 mT, g? ˆ
2.010, gk ˆ 2.003, a?(P1) ˆ 0.8, ak(P1) ˆ 27.7, a?(P2) ˆ 2.2, ak(P2) ˆ
1.2 mT.
5
6
Scheme 1. Synthesis of 6.
a-Lithiation of methyldiphenyl-l6-sulfanenitrile (1)[3a] with
lithium diisopropylamide (LDA), followed by treatment with
fluorodiphenyl-l6-sulfanenitrile (2)[3b] and acidification with
perchloric acid afforded 3 in 66% yield. This compound was
further treated with ion-exchange resin IRA-410 (OHÀ form)
to give 4[4 almost quantitatively. The reaction of 4 with
6]
methyl iodide in CH3CN at room temperature and then
treatment with NaClO4 afforded precursor 5, which was
isolated in 26% yield by recrystallization from MeOH and
diethyl ether.[7] The desired compound 6 was prepared in
essentially quantitative yield by passing a methanolic solution
of 5 through a column of the above basic resin.[6] The
compositions of 3 6 were identified by NMR (except for 4)
and IR spectroscopy, as well as elemental analysis, and the
molecular structures of 5 and 6 were determined by X-ray
crystallographic analysis (Figure 1 and 2).[8]
[10] M. Geoffroy, E. A. C. Lucken, C. Mazeline, Mol. Phys. 1974, 28, 839
845; B. fietinkaya, A. Hudson, M. F. Lappert, H. Goldwhite, J. Chem.
Soc. Chem. Commun. 1982, 609 610.
[11] J. R. Morton, K. F. Preston, J. Magn. Reson. 1978, 30, 577 582.
The X-ray structure of 6 indicates the following character-
istic properties (Figure 2). Each sulfur center is associated
with one imido and two phenyl groups, in a pseudo-
tetrahedral arrangement. The bond angles N1-S1-C1 and
Synthesis and Structure of
ˆ ˆ
(MeN)Ph2S C SPh2(NMe)
Takayoshi Fujii, Tomio Ikeda, Toshie Mikami,
Tetsuya Suzuki, and Toshiaki Yoshimura*
ˆ ˆ
(X)R2S C SR2(X) can be regarded as the isoelectronic
‡
ˆ ˆ
carbon analogue of the [(X)R2S N SR2(X)] ion (R ˆ Ar,
alkyl; X ˆ lone pair, NH, O).[1] There has, however, been little
reported on this compound to date.[2] In view of its chemical
properties and structural features, investigation of this com-
pound has posed an interesting challenge. Herein, we report
the first synthesis, isolation, and crystal structure of
ˆ ˆ
(MeN)Ph2S C SPh2(NMe) (6), prepared by the a-proton
abstraction of
a
new type of iminosulfonium ylide
‡
ˆ
À
[(MeN)Ph2S CH SPh2(NMe)] (Scheme 1).
Figure 1. ORTEP drawing of 5 (50% probability thermal ellipsoids for all
non-hydrogen atoms, perchlorate anion is omitted for clarity). Selected
bond lengths [ä] and angles [8]: S1-N1 1.526(2), S1-C1 1.695(2), S1-C2
1.780(3), S1-C3 1.802(3), S2-N2 1.531(2), S2-C1 1.691(2), S2-C4 1.788(3),
S2-C5 1.802(3), N1-C6 1.479(4), N2-C7 1.469(4); N1-S1-C1 123.1(1), N1-S1-
C2 103.4(1), N1-S1-C3 112.5(1), C1-S1-C2 107.8(1), C1-S1-C3 102.4(1), C2-
S1-C3 106.6(1), N2-S2-C1 119.6(1), N2-S2-C4 103.4(1), N2-S2-C5 115.4(1),
C1-S2-C4 110.7(1), C1-S2-C5 102.1(1), C4-S2-C5 104.9(1), S1-N1-C6
117.3(2), S2-N2-C7 118.0(2), S1-C1-S2 118.0(1).
[*] Prof. Dr. T. Yoshimura, Dr. T. Fujii, T. Ikeda, T. Mikami, T. Suzuki
Department of Material Systems Engineering
and Life Science
Faculty of Engineering
Toyama University
Gofuku, Toyama 930-8555 (Japan)
Fax : (‡81)76-445-6850
E-mail: yosimura@eng.toyama-u.ac.jp
2576
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
1433-7851/02/4114-2576 $ 20.00+.50/0
Angew. Chem. Int. Ed. 2002, 41, No. 14