Development of a new sterically protecting auxiliary of the metacyclophane type and application to unsymmetrical diphosphenes, 1,3-diphosphaallene and 1,4-diphosphabutatriene

Article abstract of DOI:10.1039/b209666h

A new bulky bromobenzene of the metacyclophane type was converted to an unsymmetrically substituted 1,4-diphos-phabutatriene whose spin-spin coupling constant (³J_PP) turned out to be larger, for the first time, than the ²J

Full text of DOI:10.1039/b209666h

Development of a new sterically protecting auxiliary of the
metacyclophane type and application to unsymmetrical diphosphenes,
1,3-diphosphaallene and 1,4-diphosphabutatriene†
Kozo Toyota, Akitake Nakamura and Masaaki Yoshifuji*
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan.
E-mail: yoshifj@mail.cc.tohoku.ac.jp; Fax: +81-22-217-6562; Tel: +81-22-217-6558
Received (in Cambridge, UK) 3rd October 2002, Accepted 31st October 2002
First published as an Advance Article on the web 15th November 2002
A new bulky bromobenzene of the metacyclophane type was
converted to an unsymmetrically substituted 1,4-diphos-
phabutatriene whose spin–spin coupling constant (3JPP
)
turned out to be larger, for the first time, than the 2JPP value
of the corresponding 1,3-diphosphaallene.
Sterically protected heterocumulenes1–6 containing multiple
bonds of the heavier main-group elements, such as silaallenes2
and phosphaallenes4 attract current attention. Heterocumulenes
containing two or three heavy atoms7–11 have also been of
interest. Utilizing an extremely bulky 2,4,6-tri-tert-butylphenyl
(Mes*) group as a sterically protecting auxiliary,12 we have
reported the preparation of the first 1-phosphaallenes,4a as well
as the first symmetrical7a and unsymmetrical 1,3-diphos-
phaallenes.7e Although Märkl and Kreitmeier prepared the first
symmetrically substituted 1,4-diphosphabutatriene,10a we have
reported an alternative synthesis of the diphosphabutatriene10b,c
as well as the preparation of tungsten complexes of the
diphosphabutatriene.10c However, preparation of an unsymmet-
rically substituted and metal-free 1,4-diphosphabutatriene re-
mained unexplored.
In the course of our study of new sterically demanding groups
and systematic modification of the Mes* group, we have
prepared various bulky bromobenzenes containing the Mes*
framework.13,14 We now report utilization of new bulky arenes
of the metacyclophane type as a sterically protecting auxiliary
and the preparation of unsymmetrically substituted 1,4-diph-
osphabutatrienes for the first time as well as unsymmetrical
diphosphene and 1,3-diphosphaallene.
Scheme 1 Reagents and yield: i, KCN, 18-crown-6, MeCN, H2O, 96%; ii,
MeI, KOH, DMSO, H2O, 60%; iii, DIBAL-H, hexane, C6H6, 81%; iv, 5,
THF, 58% (isomeric mixture); v, H2, PtO2, EtOH, 97%; vi, n-BuLi, THF
then PCl3; vii, Mes*P(H)Li, THF, then DBU, 50% based on 7a; viii, CCl4,
n-BuLi, THF, 20% [64% of (E)-9 was recovered]; ix, t-BuLi, THF, 77%; x,
Mes*PNCNC(Li)Tms, THF; xi, KF, 18-crown-6, toluene, 12% for (E)-12
(based on 7a).
acyclophane derivative 7a. Similarly, 4b14 was converted to 7b,
via 6b [(Z,Z)-6b+(E,Z)-6b = 11+9], in 87% overall yield.‡
Then preparations of low coordinated phosphorus com-
pounds bearing the new sterically protecting group were
examined, as follows. Lithiation of 7a with butyllithium
followed by reaction with PCl3 afforded the corresponding
phosphonous dichloride 8 [31P NMR (162 MHz, C6D6) dP
=
152.4]. Reaction of 8 with Mes*P(H)Li16 followed by dehydro-
chlorination using DBU afforded an unsymmetrical diph-
osphene (E)-9.
The structures of 7a§ and (E)-9§ were unambiguously
determined by X-ray crystallography (Figs. 1 and 2).17 The
–PNP– moiety in (E)-9 is distorted from planarity: the torsion
angle C(1)–P(1)–P(2)–C(22) is 167.7(2)° whereas in Mes*PNP-
Mes*,12a the corresponding torsion angle is 172.2(1)°. This may
be attributable to molecular packing in the crystal, because the
large methylene bridge pushes the aryl substituent of the
neighboring molecules. Interplanar angles between the average
plane of C(1)–P(1)–P(2)–C(22) and average aromatic ring
planes [C(1)–C(6) and C(22)–C(27)] are 73.4(1)° and
68.96(10)°, respectively.
Preparation of 7a starting from 2-bromo-1,3-bis(bromome-
thyl)benzene (1)15 is shown in Scheme 1. The bis-Wittig
When (E)-9 was treated with carbon tetrachloride and
butyllithium,7d 3,3-dichloro-1,2-diphosphirane 10 was obtained
in 20% yield [dP(C6D6) = 265.3 and –63.4, AB, 1JPP = 136.1
Hz], and 64% of (E)-9 was recovered. Reaction of 10 with tert-
butyllithium afforded stable 1,3-diphosphaallene 11: [MS m/z
604 (M+) and 548 (M+2 t-Bu + 1)]. Contrary to the case of 11,
an attempted synthesis of 1-(2,4,6-tri-tert-butylphenyl)-
reaction of 4a using ylide 5 [Ph3PNCH(CH2)5CHNPPh3] gave a
mixture of (Z,Z)-6a and (E,Z)-6a [(Z,Z)-6a+(E,Z)-6a = 9+16].
Catalytic hydrogenation of the mixture afforded a met-
† Electronic supplementary information (ESI) available: Physical data. See
Fig. 1 Molecular structure of 7a, showing the atomic labelling scheme with
http://www.rsc.org/suppdata/cc/b2/b209666h/
thermal ellipsoids (30% probability).
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CHEM. COMMUN., 2002, 3012–3013
This journal is © The Royal Society of Chemistry 2002

1919.2(9) Å3, Z = 4, Dcalc = 1.265 g cm21, m(MoKa) = 21.45 cm21. 3091
Unique reflections with 2q @ 50.0° were collected at 170 K. Of these 2939
with I > 2.0s(I) were used for R1 calculation. The structure was solved by
direct methods. The non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included but not refined. R1 = 0.064, R = 0.133, Rw
= 0.170. CCDC 193389.
Crystal data for (E)-9: C39H62P2, orthorhombic, space group P212121
(#19), a = 15.398(2), b = 23.597(5), c = 10.236(2) Å, V = 3719(1) Å3,
Z = 4, Dcalc = 1.059 g cm21, m(MoKa) = 1.40 cm21. 3205 Unique
reflections with 2q @ 50.0° were collected at 173 K. Of these 2997 with I
> 2.0s(I) were used for R1 calculation. The structure was solved by direct
methods. The non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were included but not refined. R1 = 0.062, R = 0.134, Rw = 0.139.
CCDC 193025.
See http://www.rsc.org/suppdata/cc/b2/b209666h/ for crystallographic
data in CIF or other electronic format.
Fig. 2 Molecular structure of (E)-9, showing the atomic labelling scheme
with thermal ellipsoids (30% probability). Some selected bond lengths (Å)
and angles (°): P(1)–P(2), 2.039(2); P(1)–C(1), 1.861(4); P(2)–C(22),
1.861(4); P(2)–P(1)–C(1), 101.4(1); P(1)–P(2)–C(22), 97.9(1).
1 As a review, see: J. Escudié, H. Ranaivonjatovo and L. Rigon, Chem.
Rev., 2000, 100, 3639.
2 G. E. Miracle, J. L. Ball, D. R. Powell and R. West, J. Am. Chem. Soc.,
1993, 115, 11598.
3 (a) B. E. Eichler, D. R. Powell and R. West, Organometallics, 1998, 17,
2147; (b) N. Tokitoh, K. Kishikawa and R. Okazaki, Chem. Lett., 1998,
811.
4 (a) M. Yoshifuji, K. Toyota, K. Shibayama and N. Inamoto, Tetra-
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Inamoto, Tetrahedron Lett., 1989, 30, 839; (c) M. Yoshifuji, H.
Yoshimura and K. Toyota, Chem. Lett., 1990, 827.
5 (a) G. Märkl, H. Sejpka, S. Dietl, B. Nuber and M. L. Ziegler, Angew.
Chem., Int. Ed. Engl., 1986, 25, 1003; (b) M. Yoshifuji, K. Toyota, H.
Yoshimura, K. Hirotsu and A. Okamoto, J. Chem. Soc., Chem.
Commun., 1991, 124.
3-(2,4,6-triisopropylphenyl)-1,3-diphosphaallene resulted in
formation of the corresponding dimer.18
Finally, 8 was converted to the first unsymmetrically
substituted metal-free 1,4-diphosphabutatriene, in a similar
manner to that reported by Märkl and Kreitmeier.10a Reaction of
Mes*PNCNC(Li)Tms with 8 in THF followed by treatment with
KF and 18-crown-6 under refluxing toluene gave a mixture of
(E)-12 and (Z)-12 [4+1 ratio]. After column chromatographic
treatment (SiO2–hexane), (E)-12 was isolated in 12% yield as
yellow solid [MS m/z 616 (M+)]. 13C{1H} NMR (100 MHz)
spectrum of (E)-12 in CDCl3 showed signals at d = 192.1 (dd,
1JPC = 40.5 Hz and 2JPC = 24.4 Hz) and 192.5 (dd, 1JPC = 40.6
Hz and 2JPC = 22.5 Hz), due to the cumulene carbons.
Table 1 shows 31P NMR chemical shifts and spin–spin
coupling constants (JPP) for 9, 11, 12 together with those for
Mes*PN(C)nNP[W(CO)5]Mes* (13: n = 0,19 14: n = 1,20 15: n
= 210c), and Mes*PNCH–CHNPMes* (16).21 The 3JPP for (E)-
6 M. Bouslikhane, H. Gornitzka, H. Ranaivonjatovo and J. Escudié,
Organometallics, 2002, 21, 1531.
7 (a) M. Yoshifuji, K. Toyota and N. Inamoto, J. Chem. Soc., Chem.
Commun., 1984, 689; (b) H. H. Karsch, F. H. Köhler and H.-U.
Reisacher, Tetrahedron Lett., 1984, 25, 3687; (c) R. Appel, P. Fölling,
B. Josten, M. Siray, V. Winkhaus and F. Knoch, Angew. Chem., Int. Ed.
Engl., 1984, 23, 619; (d) M. Yoshifuji, S. Sasaki, T. Niitsu and N.
Inamoto, Tetrahedron Lett., 1989, 30, 187; (e) M. Yoshifuji, S. Sasaki
and N. Inamoto, J. Chem. Soc., Chem. Commun., 1989, 1732; (f) M.
Gouygou, C. Tachon, R. El Ouatib, O. Ramarijaona, G. Etemad-
Moghadam and M. Koenig, Tetrahedron Lett., 1989, 30, 177.
8 (a) O. I. Kolodiazhnyi, Tetrahedron Lett., 1982, 23, 4933; (b) R. Appel
and W. Paulen, Angew. Chem., Int. Ed. Engl., 1983, 22, 785; (c) L.
Rigon, H. Ranaivonjatovo, J. Escudié, A. Dubourg and J.-P. Declercq,
Chem. Eur. J., 1999, 5, 774; (d) H. Ramdane, H. Ranaivonjatovo, J.
Escudié, S. Mathieu and N. Knouzi, Organometallics, 1996, 15, 3070;
(e) H. Ranaivonjatovo, H. Ramdane, H. Gornitzka, J. Escudié and J.
Satgé, Organometallics, 1998, 17, 1631.
2
and (Z)-12 are larger than the JPP value for 11, due to the p-
conjugation of the two phosphorus–carbon double bonds in the
–PNCNCNP– array of 12, while the p systems in the –PNCNP–
moiety of 11 is perpendicular. These 3JPP values in 12 are even
3
larger than JPP for a 1,4-diphosphabutadiene 16. Coupling
constants for the tungsten complexes 14 and 15 are larger than
those for the compounds 11 and 12, respectively. In contrast, the
1JPP value for the tungsten complexes 13 is smaller than that for
the diphosphene (E)-9, probably because the extreme steric
congestion in 13 might affect the conformation.
Table 1 31P NMR data of some unsymmetrical low-coordinated phosphorus
compounds
9 M. Bouslikhane, H. Gornitzka, J. Escudié, H. Ranaivonjatovo and H.
Ramdane, J. Am. Chem. Soc., 2000, 122, 12880.
10 (a) G. Märkl and P. Kreitmeier, Angew. Chem., Int. Ed. Engl., 1988, 27,
1360; (b) M. Yoshifuji, K. Toyota and H. Yoshimura, Chem. Lett., 1991,
491; (c) S. Ito, K. Toyota and M. Yoshifuji, J. Organomet. Chem., 1998,
553, 135.
11 H. Grützmacher, S. Freitag, R. Herbst-Irmer and G. S. Sheldrick,
Angew. Chem., Int. Ed. Engl., 1992, 31, 437.
12 (a) M. Yoshifuji, I. Shima, N. Inamoto, K. Hirotsu and T. Higuchi, J.
Am. Chem. Soc., 1981, 103, 4587; (b) M. Yoshifuji, I. Shima, N.
Inamoto, K. Hirotsu and T. Higuchi, J. Am. Chem. Soc., 1982, 104,
6167.
13 M. Yoshifuji, J. Organomet. Chem., 2000, 611, 210, and references
cited therein.
Compound
d(PA)a
d(PB)a
JPP /Hz
(E)-9
11
487.4
140.8
174.6
168.5
375.4
132.8
105.3
243.1
497.7
145.5
182.8
173.9
486.3
151.9
181.5
284.5
581.3
23.5
257.1
294.3
561.5
39
(E)-12
(Z)-12
13b
14c
15d
315.1
188
(E,Z)-16e
a In CDCl3, relative to external 85% H3PO4. b Data taken from Ref. 19.
c Data taken from Ref. 20b. d Data taken from Ref. 10c. e Data taken from
Ref. 21.
14 M. Yoshifuji, M. Nakazawa, T. Sato and K. Toyota, Tetrahedron, 2000,
56, 43.
15 F. Vögtle, Chem. Ber., 1969, 102, 1784.
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Nishimoto, J. Am. Chem. Soc., 1983, 105, 2495.
17 C. K. Johnson, Oak Ridge National Laboratory Report, ORNL-TM-
5138, Oak Ridge, TN, 1976.
18 R. Appel and F. Knoll, Adv. Inorg. Chem., 1989, 33, 259.
19 M. Yoshifuji, K. Toyota, T. Sato and N. Inamoto, Sci. Rep., Tohoku
Univ., Ser. 1, 1990, 73, 1.
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Matsuda, T. Sato and N. Inamoto, J. Organomet. Chem., 1986, 311,
C63; (b) C. A. Akpan, P. B. Hitchcock, J. F. Nixon, M. Yoshifuji, T.
Niitsu and N. Inamoto, J. Organomet. Chem., 1988, 338, C35.
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1987, 26, 779.
This work was supported in part by the Grants-in-Aid for
Scientific Research (Nos. 13304049, 14044012, and 13640522)
from the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
Notes and references
‡ The geometries were determined based on vicinal spin–spin coupling
constants between the vinyl protons: in (Z,Z)-6a, 3J = 11.2 Hz, whereas in
(E,Z)-6a, 3J = 16.0 Hz (E) and 11.2 Hz (Z).
§
Crystal data for 7a: C21H33Br, monoclinic, space group P21/n (#14), a
= 11.387(2), b = 10.989(3), c = 15.757(5) Å, b = 103.25(3)°, V =
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