Preparation of sterically protected 3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]-1,2-bis[4-(4-vinylphenyl)butyl]c yclobutene and its polymers

Article abstract of DOI:10.1246/cl.2001.248

Two new sterically protected 3,4-diphosphinidenecyclo-butenes, i.e., 1,2-bis[4-(4-methylphenyl)butyl]-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene] cyclobutene, and 3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]-1,2-bis[4-(4-vinylphenyl)butyl]c yclobutene, were prepared. Copolymerization of the latter with styrene was studied. Treatment of [6-(4-vinylphenyl)hex-1-ynyl](2,4,6-tri-t-butylphenyl)phosphine with butyllithium and 1,2-dibromoethane afforded a polymer of the latter cyclobutene.

Full text of DOI:10.1246/cl.2001.248

248
Chemistry Letters 2001
Preparation of Sterically Protected 3,4-Bis[(2,4,6-tri-t-butylphenyl)phosphinidene]-
1,2-bis[4-(4-vinylphenyl)butyl]cyclobutene and Its Polymers
Naoki Yamada,# Kozo Toyota, and Masaaki Yoshifuji*
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578
(Received November 27, 2000; CL-001071)
Two new sterically protected 3,4-diphosphinidenecyclo-
butenes, i.e., 1,2-bis[4-(4-methylphenyl)butyl]-3,4-bis[(2,4,6-tri-t-
butylphenyl)phosphinidene]cyclobutene, and 3,4-bis[(2,4,6-tri-t-
butylphenyl)phosphinidene]-1,2-bis[4-(4-vinylphenyl)but-
yl]cyclobutene, were prepared. Copolymerization of the latter
with styrene was studied. Treatment of [6-(4-vinylphenyl)hex-1-
ynyl](2,4,6-tri-t-butylphenyl)phosphine with butyllithium and 1,2-
dibromoethane afforded a polymer of the latter cyclobutene.
In solid phase synthesis and more recently combinatorial
chemistry, polystyrene and the related polymers have been attrac-
tive to the synthetic organic chemists.1 Polymers having special
functionalities, such as polymer–metal complexes, have also been
of interest in materials science.2 However, to the best of our
knowledge, there have been no studies on polymers containing
phosphorus atom(s) in low coordination states.3,4 We have report-
ed syntheses of sterically protected 3,4-diphosphinidenecy-
clobutene–metal complexes 1, utilizing an extremely bulky 2,4,6-
tri-t-butylphenyl substituent (abbreviated to the Mes* group) as
sterically protecting auxiliary.5 Introduction of the diphos-
phinidenecyclobutene moieties into polymeric structures is inter-
esting from the viewpoint of synthetic chemistry as well as mate-
rials chemistry. We report here the preparation of polymers con-
taining the 3,4-diphosphinidenecyclobutene moieties, as well as
preparations of 1,2-bis(4-arylbutyl)-3,4-bis[(2,4,6-tri-t-
butylphenyl)phosphinidene]cyclobutenes.
noted that reaction of 4b9 and lithium acetylide–ethylenediamine
complex resulted in the formation of a trace amount of 6b.
Lithiation of the phosphine 3a (6.86 mmol) with t-butyllithi-
um (6.88 mmol) in THF followed by treatment with 1,2-dibro-
moethane (3.47 mmol) afforded (E,E)-2a [δP (CDCl3) = 149.7]
(ca. 40% yield) and a trace amount of (E,Z)-2a [δP (CDCl3) =
154.0 and 170.8, AB, 3JPP = 9.7 Hz]. An attempted purification of
(E,E)-2a using silica-gel column chromatography and recycling
gel-permeation column chromatography (GPC) failed. Thus, the
crude diphosphinidenecyclobutene (E,E)-2a was allowed to react
with PdCl2(MeCN)2 in THF to give the corresponding
dichloropalladium complex 1a in pure form (36% yield based on
Mes*PH2): Red prisms, mp 162–164 °C; δP (CDCl3) = 143.9;
FAB-MS m/z 1000 (M+–2Cl–1) and 893 (M+–Pd–2Cl–2).
Although the FAB-MS spectrum of 1a did not give the molecular
ion peak, the structure of 1a was unambiguously confirmed by X-
ray crystallography.10 Figure 1 is an ORTEP11 drawing of the
molecular structure of 1a.
In a typical preparative method of the ligand 2, alkynylphos-
phines 3 were used as starting materials. Thus, we prepared [6-(4-
methylphenyl)hex-1-ynyl](2,4,6-tri-t-butylphenyl)phosphine (3a)
and (2,4,6-tri-t-butylphenyl)[6-(4-vinylphenyl)hex-1-ynyl]phos-
phine (3b) as follows. 4-Bromotoluene was treated in THF with
butyllithium and 1,4-dibromobutane to give 1-(4-bromobutyl)-4-
methylbenzene (4a)6 (76% yield). When 1,4-diiodobutane was
used instead of 1,4-dibromobutane, the corresponding iodide 5a
was obtained.7 Reaction of 4a (or 5a) with lithium acetylide–eth-
ylenediamine complex afforded 6-(4-methylphenyl)hex-1-yne
(6a).7 Then the alkyne 6a was metallated in THF using EtMgBr
and the resulting acetylide was allowed to react with
Mes*P(H)Cl8 (prepared from Mes*PH2) to form the phosphine
3a: 31P NMR (81 MHz, C6D6) δP = –101.4 (d, 1JPH = 244.5 Hz).
The phosphine 3b was also prepared by a method similar to that
for 3a, starting from 4-bromostyrene, via 5b and 6b.7 3b: 31P
1
NMR (CDCl3) δP = –100.9 (d, JPH = 220.8 Hz). It should be
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
249
3
The phosphine 3b was converted to (E,E)-2b [δP (CDCl3) =
150.2], by the reaction of 3b with t-butyllithium and 1,2-dibro-
moethane, in 4% isolated yield (based on 3b) after treatment with
GPC (JAIGEL H1+H2 column).12 Then preparation of a polymer
of 2b was attempted. Treatment of (E,E)-2b with t-butyllithium
(12 mol%) afforded not a polymer but dimeric products13 in a
trace amount, however, treatment of a mixture of (E,E)-2b (254
mg, 0.276 mmol) and styrene (273 mg, 2.62 mmol) with t-butyl-
lithium (0.014 mmol) in THF at –78 °C afforded a copolymer
(90.0 mg after GPC; δP (CDCl3) = 149.6 and 149.9 (1:1); Mn =
2900, MW/Mn = 1.3, determined by GPC using polystyrenes as
standard).
Interestingly, when 3b (778 mg, 1.69 mmol) was treated with
n-butyllithium (1.69 mmol) and 1,2-dibromoethane (0.85 mmol)
in THF at –78 °C, a polymer of 2b was obtained in ca. 70% yield
based on 3b (Mn = 12000, MW/Mn = 72).14 31P NMR spectrum of
the polymer showed a relatively broad signal at δP (CDCl3) =
151.0, indicating (E,E)-configuration about the phosphorus–car-
bon double bond. The polymer was soluble in several solvents
such as chloroform and THF.
Hz, CH2), 3.28 (2H, t, J = 6.7 Hz, CH2), and 7.20 (4H, br. t,
arom.); 13C{1H} NMR (50 MHz, CDCl3) δ = 7.0 (CH2), 21.2
(Me), 32.4 (CH2), 33.0 (CH2), 34.4 (CH2), 128.3 (arom.), 129.1
(arom.), 135.3 (arom.), and 138.7 (arom.). Found: m/z 274.0216
(M+). Calcd for C11H15I, 274.0178. 5b: 68% yield; colorless oil;
1H NMR δ = 1.76–2.03 (4H, m, CH2), 2.71 (2H, t, J = 7.3 Hz,
3
CH2), 3.26 (2H, t, 3J = 6.7 Hz, CH2), 5.32 (1H, dd, 3J = 11.7 Hz,
2J = 0.9 Hz, CH=CHH’), 5.83 (1H, dd, 3J = 17.6 Hz, 2J = 0.9 Hz,
3
3
CH=CHH’), 6.86 (1H, dd, J = 10.9 Hz, J =17.6 Hz, CH=CH2),
3
3
7.20 (2H, d, J = 8.1 Hz, arom.), and 7.41 (2H, d, J = 8.1 Hz,
arom.); 13C{1H} NMR δ = 7.0 (CH2), 32.2 (CH2), 33.0 (CH2),
34.5 (CH2), 113.1 (CH=CH2), 126.3 (arom.), 128.6 (arom.), 135.4
(arom.), 136.7 (CH=CH2), and 141.5 (arom.). Found: m/z
286.0222 (M+). Calcd for C12H15I, 286.0178.
6a: 78% yield either from 4a or 5a; colorless oil; 1H NMR δ
= 1.60–1.86 (4H, m, CH2), 2.03 (1H, t, 4J = 2.7 Hz, C≡CH), 2.30
3
4
(2H, dt, J = 6.9 Hz, J = 2.7 Hz, CH2), 2.42 (3H, s, Me), 2.69
(2H, t, 3J = 7.5 Hz, CH2), and 7.18 (4H, br. s, arom.); 13C{1H}
NMR δ = 18.4 (CH2), 21.1 (Me), 28.1 (CH2), 30.6 (CH2), 35.0
(CH2), 68.5 (C≡CH), 84.4 (C≡CH), 128.3 (arom.), 129.1 (arom.),
135.2 (arom.), and 139.2 (arom.). Found: m/z 172.1251 (M+).
1
Calcd for C13H16, 172.1252. 6b: 41% yield; colorless oil; H
4
NMR δ = 1.53–1.84 (4H, m, CH2), 1.97 (1H, t, J = 2.6 Hz,
C≡CH), 2.23 (2H, dt, 3J = 6.9 Hz, 4J = 2.6 Hz, CH2), 2.64 (2H, t,
3J = 7.5 Hz, CH2), 5.21 (1H, dd, 3J = 10.9 Hz, 2J = 1.0 Hz,
CH=CHH’), 5.73 (1H, dd, 3J = 17.6 Hz, 2J = 1.0 Hz,
CH=CHH’), 6.72 (1H, dd, 3J = 10.9 Hz, 3J =17.6 Hz, CH=CH2),
3
3
7.16 (2H, d, J = 8.1 Hz, arom.), and 7.35 (2H, d, J = 8.1 Hz,
arom.); 13C{1H} NMR δ = 18.4 (CH2), 28.1 (CH2), 30.5 (CH2),
35.2 (CH2), 68.7 (C≡CH), 84.4 (C≡CH), 113.0 (CH=CH2), 126.3
(arom.), 128.7 (arom.), 135.3 (arom.), 136.8 (CH=CH2), and
142.0 (arom.). Found: m/z 184.1256 (M+). Calcd for C14H16,
184.1252.
G. Märkl and P. Kreitmeier, Angew. Chem., Int. Ed. Engl., 27,
1360 (1988).
T. Onozuka, M. Shindo, H. Kiba, and Y. Aosaki, Japan. Kokai
Tokkyo Koho JP, 07108179 (1995); Chem. Abstr., 123: 179001
(1995).
When the polymer was treated with PdCl2(MeCN)2 in THF,
a brown solid was precipitated. The solid was insoluble in com-
mon solvents. Further studies on the properties of the polymer of
2b and their derivatives are in progress.
8
9
This work was supported by Grants-in-Aid for Scientific
Research on Priority Area (Nos. 09239104 and 12020205) from
the Ministry of Education, Science, Sports and Culture, Japan.
10 Recrystallized from CH2Cl2. 1/2[C62H88Cl2P2Pd]·CH2Cl2, Mr =
621.25. Monoclinic, space group C2/c (#15), a = 23.821(1), b =
11.2078(4), c = 26.4565(5) Å, β = 108.450(1)°, V = 6700.2(4)
Å3, Z = 8, Dcalc = 1.232 gcm–3, µ (Mo Kα) = 5.99 cm–1. 7342
Unique reflections with 2θ ≤ 55.0°. Of these, 4546 with I>
3.0σ(I) were used for R1 calculation. The structure was solved
by heavy-atom Patterson methods. Non-hydrogen atoms except
for C(10)–C(12) and C(14)–C(16) were refined anisotropically.
Hydrogen atoms except for those on C(10)–C(12) and
C(14)–C(16) were included but not refined. R1 = 0.068, R =
0.068, Rw = 0.091. Crystallographic data have been deposited at
the Cambridge Crystallographic Data Centre (no. CCDC-
156637).
11 C. K. Johnson, ORTEP-II, Oak Ridge National Laboratory
Report, ORNL-TM-5138, Oak Ridge, TN, 1976.
12 A side reaction seems to have taken place, in which one of the
vinyl groups of (E,E)-2b was attacked by t-BuLi. (E,E)-2b: pale
yellow oil; 1H NMR (600 MHz, CDCl3) δ = 0.88 (4H, br. t, 3J
= 7.5 Hz, CH2), 1.03 (4H, t, 3J = 7.6 Hz, CH2), 1.11 (4H, tt, 3J =
7.8 Hz, CH2), 1.31 (18H, s, p-t-Bu), 1.52 (36H, s, o-t-Bu), 2.35
References and Notes
#
Fellowships of the Japan Society for the Promotion of Science
for Japanese Junior Scientists.
1
N. K. Terrett, “Combinatorial Chemistry,” Oxford University
Press, Inc., New York (1998).
2
3
E. Tsuchida and H. Nishide, Adv. Polym. Sci., 24, 1 (1977).
“Multiple Bonds and Low Coordination in Phosphorus
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
5
M. Yoshifuji, I. Shima, N. Inamoto, K. Hirotsu, and T. Higuchi,
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Yoshifuji, K. Toyota, K. Shibayama, and N. Inamoto,
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3
3
(4H, t, J = 7.4 Hz, CH2), 5.19 (2H, d, J = 10.9 Hz, =CHH'),
5.69 (2H, d, J = 17.7 Hz, =CHH'), 6.68 (2H, dd, J = 17.7 Hz
3
3
3
and 10.9 Hz, CH=), 6.98 (4H, d, J = 8.0 Hz, arom.), 7.28 (4H,
d, 3J = 8.0 Hz, arom.), and 7.32 (4H, m-Mes*).
13 1H NMR spectrum, molecular weight measurement (by GPC),
and MALDI-TOF MS indicate formation of a mixture of prod-
ucts, whose molecular weights correspond to [2×(E,E)-2b+n(t-
Bu)+nH; n = 1–5], however, attempted separation and character-
ization have been unsuccessful because of the low yield.
14 A MALDI-TOF MS showed only weak signals less than 12000,
including those corresponding to dodecamer (Found: m/z 11030;
Calcd: 11024) and undecamer (Found: m/z 10107; Calcd:
10105).
6
7
E. Bosies, A. Eswein, F. Grams, and H.-w. Krell, Ger. Offen.
DE, 19548624 (1997); Chem. Abstr., 127: 121746 (1997).
5a: 28% yield; colorless oil; 1H NMR (200 MHz, CDCl3) δ
= 1.76–2.00 (4H, m, CH2), 2.44 (3H, s, Me), 2.70 (2H, t, 3J = 7.3