Nitrogen ligand-containing Rh catalysts for the polymerization of substituted acetylenes

Article abstract of DOI:10.1016/j.molcata.2006.01.072

The present study deals with the application of Rh complexes possessing a phenoxy-imine ligand (1 and 2), a β-diiminate ligand (3 and 4), and ammonia ligands (5) as catalysts in the polymerization of substituted acetylenes (6a-h). All the catalysts (1-5) were effective for the polymerization of monosubstituted acetylenes (6a-e) and afforded polymers in moderate to high yields with high molecular weights (M_n = 15,000-93,000), and the presence of cocatalyst was not a strict requisite in the present polymerization systems in contrast to conventional [Rh(nbd)Cl]₂ and [Rh(cod)Cl]₂ catalysts. In the case of phenoxy-imine catalysts, the nbd-bearing one (1) was more active than the cod-bearing counterpart (2) in accordance to the general behavior of Rh catalysts, while the opposite trend was observed for β-diiminate catalysts (3 and 4). Catalyst 2 exhibited the highest activity among all the catalysts examined in the polymerization of phenylacetylene (6a) and afforded the highest molecular weight poly(6a) (M_n = 93,000) in almost quantitative yield. Introduction of electron-donating groups at meta and para positions of 6a (monomers 6b-d) resulted in the decrease of polymer yields. Et₃N and n-C₄H₉Li exerted cocatalytic effects when combined with 1-5 in the polymerization of 6a, resulting in the increase of both polymer molecular weight and yield.

Full text of DOI:10.1016/j.molcata.2006.01.072

Journal of Molecular Catalysis A: Chemical 254 (2006) 124–130
Nitrogen ligand-containing Rh catalysts for the polymerization
of substituted acetylenes
Irfan Saeed, Masashi Shiotsuki, Toshio Masuda∗
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura Campus, Kyoto 615-8510, Japan
Available online 2 May 2006
Abstract
The present study deals with the application of Rh complexes possessing a phenoxy-imine ligand (1 and 2), a ␤-diiminate ligand (3 and 4), and
ammonia ligands (5) as catalysts in the polymerization of substituted acetylenes (6a–h). All the catalysts (1–5) were effective for the polymerization
of monosubstituted acetylenes (6a–e) and afforded polymers in moderate to high yields with high molecular weights (Mn = 15,000–93,000), and the
presence of cocatalyst was not a strict requisite in the present polymerization systems in contrast to conventional [Rh(nbd)Cl]2 and [Rh(cod)Cl]2
catalysts. In the case of phenoxy-imine catalysts, the nbd-bearing one (1) was more active than the cod-bearing counterpart (2) in accordance to the
general behavior of Rh catalysts, while the opposite trend was observed for ␤-diiminate catalysts (3 and 4). Catalyst 2 exhibited the highest activity
among all the catalysts examined in the polymerization of phenylacetylene (6a) and afforded the highest molecular weight poly(6a) (Mn = 93,000)
in almost quantitative yield. Introduction of electron-donating groups at meta and para positions of 6a (monomers 6b–d) resulted in the decrease
of polymer yields. Et3N and n-C4H9Li exerted cocatalytic effects when combined with 1–5 in the polymerization of 6a, resulting in the increase
of both polymer molecular weight and yield.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Coordination polymerization; Transition metal catalyst; Rhodium complex; Substituted polyacetylene; Phenoxy-imine ligand; ␤-Diiminate ligand
1. Introduction
On the other hand, heteroatom-containing chelate ligands as
exemplified by phenoxy-imine and ␤-diiminate ligands are well
known to form single-site catalysts, which manifest unparalleled
activity and unique features in olefin polymerization [10,11].
These ligands not only offer the advantage of high polymeriza-
tion activity but also allow the detailed modification of ligand
framework to impart characteristic features to the polymeriza-
tion catalysts. As far as Rh catalysts are concerned, there are
few reports discussing the activity of the Rh catalysts bear-
ing heteroatom-containing chelate ligands [12], and there is
no example dealing with phenoxy-imine or ␤-diiminate con-
taining Rh catalysts. Here we report that the Rh complexes,
possessing nitrogen- and oxygen-containing ligands including
phenoxy-imines and ␤-diiminates, catalyze the polymerization
of substituted acetylenes without any cocatalyst (Chart and
Scheme 1).
Design and development of transition metal catalysts for the
polymerization of substituted acetylenes has been a subject of
immense research activity in the last few years. Research in this
field is stimulated by potential applications of polyacetylenes
as functional materials in electronics, optoelectronics, gas sep-
aration materials, humidity sensor and related fields due to
their unique physical and chemical characteristics [1]. Conse-
quently, a wide variety of transition metal catalysts from groups
4–10 have been developed for the polymerization of substituted
acetylenes and applied to a wide range of monomers [2–4].
Stability in a variety of solvents, unprecedented tolerance to
functional groups, and precise control of the stereochemistry
of propagation are the features that make Rh(I)-based catalysts
attractive for polymerization of acetylenes. Rh catalysts have
successfully been applied to the polymerization of monosubsti-
tuted acetylenes [5] such as phenylacetylene [6], propiolic esters
[7,8], and N-propargylamides [9].
2. Experimental
2.1. Materials
∗
Monomers 6a and 6g were purchased from Aldrich (Japan)
Corresponding author. Tel.: +81 75 3832589; fax: +81 75 3832590.
E-mail address: masuda@adv.polym.kyoto-u.ac.jp (T. Masuda).
and Wako (Japan), respectively, and were distilled under
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.01.072

I. Saeed et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 124–130
125
2.1.1. [2-[(Phenylimino)methyl]phenolato]
(η4-cycloocta-1,5-diene)rhodium(I) (1)
To a mixture of [Rh(cod)Cl]2 (49.3 mg, 0.1 mmol) and
2-[(phenylimino)methyl]phenol (39.5 mg, 0.2 mmol), CH2Cl2
(2 mL) was added. The reaction mixture was stirred for 10 min at
room temperature and then a solution of KOH (180 mg, excess)
in water (2 mL) was added to the reaction mixture and the sus-
pension was stirred for 8 h at room temperature. After CH2Cl2
(10 mL) and H2O (10 mL) were added to the flask, the organic
layer was separated and dried over anhydrous MgSO4. After
filtration, CH2Cl2 was evaporated to dryness to give a bright
yellow residue, which was purified by recrystallization from
CH2Cl2/CH3OH to give 1 (68 mg, 84%) as bright yellow solid;
m.p. 231.0–232.0 ◦C. IR (KBr, cm−1): 3029, 2918, 2891, 2810,
1632, 1589, 1537, 1452, 1392, 1371, 1344, 1190, 1151, 771,
1
715, 561. H NMR (400 MHz, CDCl3, 25 ◦C; the results are
slightly different from the reported results [19b]) δ: 7.98 (s, 1H,
HCN), 7.34 (m, 3H, Ar), 7.22 (d, 1H, J = 6.8 Hz, Ar), 7.16 (d,
1H, J = 8.0 Hz, Ar), 7.04 (d, 2H, J = 7.6 Hz, Ar), 6.90 (d, 1H,
J = 8.4 Hz, Ar), 6.57(t, 1H, J = 7.2 Hz, Ar), 4.60(brs, 2H, olefinic
of cod), 3.21 (brs, 2H, olefinic of cod), 2.38 (brs, 4H, CHH of
cod), 1.81 (brs, 4H, CHH of cod). 13C NMR (100 MHz, CDCl3,
25 ◦C) δ: 166.71 (Ar), 165.47 (HCN), 152.23 (Ar), 135.44 (Ar),
135.18 (Ar), 128.52 (Ar), 125.94 (Ar), 123.26 (Ar), 121.94 (Ar),
118.49 (Ar), 114.67 (Ar), 84.63 (d, JRh–C = 11.5 Hz, olefinic of
cod), 72.96 (d, JRh–C = 11.5 Hz, olefinic of cod), 31.36 (CH2 of
cod), 29.00 (CH2 of cod).
Chart 1. Structures of catalysts 1–5.
2.1.2. [2-[(Phenylimino)methyl]phenolato]
(η4-2,5-norbornadiene)rhodium(I) (2)
This compound was prepared by the same method as for 1 by
using [Rh(nbd)Cl]2 instead of [Rh(cod)Cl]2. Yellow solid; yield
83%, m.p. 188.0–189.0 ◦C. IR (KBr): 3072, 3010, 2987, 2915,
1612, 1591, 1537, 1477, 1454, 1446, 1367, 1344, 1307, 1170,
1136, 807, 771, 715. 1H NMR (400 MHz, CDCl3, 25 ◦C) δ: 8.04
(s, 1H, HCN), 7.33 (m, 3H, Ar), 7.18 (m, 2H, Ar), 6.93 (m, 3H,
Ar), 6.61 (t, 1H, J = 7.0 Hz, Ar), 4.39 (brs, 2H, olefinic of nbd),
3.66 (brs, 2H, bridgehead of nbd), 3.04 (brs, 2H, bridgehead of
nbd), 1.26 (d, 1H, J = 8.0 Hz, bridging CH2 of nbd), 1.14 (d, 1H,
J = 8.0 Hz, bridging CH2 of nbd). 13C NMR (100 MHz, CDCl3,
25 ◦C) δ: 166.76 (Ar), 163.09 (HCN), 151.98 (Ar), 135.46 (Ar),
134.99 (Ar), 128.46 (Ar), 125.68 (Ar), 122.66 (Ar), 121.81 (Ar),
118.59 (Ar), 114.99 (Ar), 62.02 (d, 1JRh–C = 9.9 Hz, olefinic of
reduced pressure before use. Monomer 6b was donated
by Fuji Photo Film (Japan), 6h by Shin-Etsu Chemical
(Japan), 6d by NOF Co., Ltd., which were used as received.
Monomer 6c was obtained commercially from Wako (Japan)
and was used as received. Monomer 6e [13], and 6f [14]
were synthesized according to the literature methods. Sol-
vents used for polymerization were purified before use by
the standard procedures. Et3N (Wako, Japan) and n-BuLi
(1.6 mol/L in hexane solution; Kanto Kagaku, Japan) as addi-
tives were purchased and employed without further purifica-
tion. N,Nꢀ-(1,3-Propanediylidene)bis(benzenamine) hydrochlo-
ride [15], 2-[(phenylimino)methyl]phenol [16], [Rh(nbd)Cl]2
[17], [Rh(cod)Cl]2 [17], and Rh complex 5 [18] were synthe-
sized according to the methods described in the literature. Rh
complexes 1–4 were synthesized as shown in Scheme 2 by mod-
ifying the reported procedures [19].
2
nbd), 61.33 (d, JRh–C = 6.5 Hz, bridgehead of nbd), 52.06 (d,
1JRh–C = 11.6 Hz, olefinic of nbd), 48.04 (bridging CH2 of nbd).
2.1.3. [N,Nꢀ-(1,3-Propanediylidene)bis(benzenaminato)]
(η4-cycloocta-1,5-diene) rhodium (I) (3)
A 50 mL two-necked flask was equipped with a three-
way stopcock, a magnetic stirring bar, and flushed with
dry argon. [Rh(cod)Cl]2 (170 mg, 0.35 mmol) and N,Nꢀ-(1,3-
propanediylidene)bis(benzenamine) (188 mg, 0.72 mmol) were
placed in the flask followed by the addition of CH2Cl2 (7 mL)
and THF solution of tetra-n-butylammonium fluoride (0.1 mL,
1 M solution) to give a yellow homogeneous solution. Then,
KOH (500 mg, 8.9 mmol) in water (5 mL) was added to the reac-
tion flask to form a suspension. The contents of the flask were
Scheme 1. Polymerization of monosubstituted acetylenes with catalysts 1–5.

126
I. Saeed et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 124–130
stirred at room temperature for 10 h. CH2Cl2 (10 mL) and water
(15 mL) were added to the reaction mixture, and the organic
layer was separated by separatory funnel and dried over anhy-
drous MgSO4.
typical polymerization procedure is as follows: a toluene solu-
tion (2.0 mL) of monomer (2.5 mmol) was added to a toluene
solution (3.0 mL) of the Rh catalyst (10.0 ␮mol). The reaction
system was kept at 30 ◦C for 24 h. Formed polymers were iso-
lated by precipitation in a large amount of methanol, filtered by
glass filter, and dried under vacuum to constant weight.
After filtration, CH2Cl2 was evaporated under reduced pres-
sure to concentrate the organic layer, and ethanol (30 mL) was
added to precipitate 3. The yellow precipitate was filtered under
air on a glass filter and dried under vacuum to give the desired
product (277 mg, 93%) as yellow solid; m.p. 225.0–227.0 ◦C.
IR (KBr, cm−1): 3044, 3009, 2972, 2937, 2895, 2847, 1600,
1589, 1537, 1493, 1466, 1371, 1344, 1307, 1246, 1149, 760,
783. 1H NMR (400 MHz, CDCl3, 25 ◦C) δ: 7.30–7.01 (m, 12H,
HCN and Ph), 4.89 (t, 1H, J = 7.2 Hz, NCHCHCHN), 3.69 (brs,
4H, olefinic of cod), 2.20 (brs, 4H, CHH of cod), 1.66 (brs, 4H,
CHH of cod). 13C NMR (100 MHz, CDCl3, 25 ◦C) δ: 154.16
(HCN), 129.28 (ipso C of Ph), 128.16 (Ph), 125.75 (Ph), 124.78
(Ph), 90.25 (NCHCHCHN), 77.85 (d, JRh–C = 12.3 Hz, olefinic
of cod), 30.08 (CH2 of cod). Anal. Calcd. for C23H25N2Rh: C,
63.89%; H, 5.83%; N, 6.48%. Found: C, 63.73%; H, 5.71%; N,
6.37%.
2.4. Following the polymerization of 6a with catalysts 2
and 3 by 1H NMR
Rh catalyst 2 (1.6 mg, 4.0 ␮mol) was added to toluene-d8
1
(0.7 mL) under argon and H NMR spectrum was recorded.
Monomer 6a (10.2 mg, 0.1 mmol) was added to toluene-d8 solu-
tion of catalyst 2 under argon in NMR tube and 1H NMR
spectrum was recorded instantaneously. After initiation of the
reaction, 1H NMR spectra were recorded at an interval of 3 min
during first 30 min and then over an interval of 30 min during the
rest of the experiment. In a similar way, polymerization of 6a
with catalyst 3 was monitored by adding 6a (10.2 mg, 0.1 mmol)
to solution of Rh catalyst 3 (2.0 mg, 4.0 ␮mol) in toluene-d8
(0.7 mL) under argon and following the same procedure.
2.1.4. [N,Nꢀ-(1,3-Propanediylidene)bis(benzenaminato)]
(η4-2,5-norbornadiene) rhodium (I) (4)
3. Results and discussion
This compound was prepared by the same method as for
3 by using [Rh(nbd)Cl]2 instead of [Rh(cod)Cl]2. Pale yel-
low solid; yield 83%, m.p. 190.0–191.0 ◦C. IR (KBr, cm−1):
3046, 2992, 2953, 1593, 1581, 1514, 1479, 1456, 1402, 1352,
1315, 794, 771, 738, 700. 1H NMR (400 MHz, CDCl3, 25 ◦C)
δ: 7.43 (dd, 2H, J = 6.6 Hz, J = 2.2 Hz, HCN), 7.28 (m, 4H,
Ph), 7.10 (t, 2H, J = 7.6 Hz, Ph), 6.98 (d, 4H, J = 8.4 Hz, Ph),
4.99 (t, 1H, J = 6.8 Hz, NCHCHCHN), 3.40 (brs, 2H, bridge-
head of nbd), 3.28 (brs, 4H, olefinic of nbd), 1.06 (brs, 2H,
bridging CH2 of nbd). 13C NMR (100 MHz, CDCl3, 25 ◦C) δ:
154.30 (HCN), 151.85 (ipso C of Ph), 127.87 (Ph), 124.87 (Ph),
3.1. Synthesis of Rh catalysts 1–5
Catalyst 1 was synthesized in 84% yield by modification of
a reported method, which involves the use of toxic thallium
salts of 2-[(phenylimino)methyl] phenol ligand [19a,19b]. An
obvious advantage of the present modified method is the use of
nontoxic reagents under mild reaction conditions, and still the
product yield is appreciably high. Synthesis of catalyst 2 was
also carried out using the same procedure as for 1 and the yield
was also very high (83%). Catalysts 3 and 4 were synthesized
according to the literature method. Catalysts 1–4 were stable
towards air and moisture; exposure of a small amount of each
catalyst to air for 24 h showed practically no change in 1H NMR
spectra (Scheme 2).
2
124.39 (Ph), 91.02 (NCHCHCHN), 61.55 (d, JRh–C = 6.6 Hz,
bridgehead of nbd), 57.31 (d, 1JRh–C = 9.9 Hz, olefinic of nbd),
3
48.04 (d, JRh–C = 3.3 Hz, bridging CH2 of nbd). Anal. Calcd.
for C22H21N2Rh: C, 63.47%; H, 5.08%; N, 6.73%. Found: C,
63.27%; H, 4.91%; N, 6.65%.
3.2. Polymerization of 6a–h with Rh catalysts 1–5
2.2. Instruments
The obtained Rh complexes bearing a phenoxy-imine ligand
(1 and 2), a ␤-diiminate ligand (3 and 4), and ammonia ligands
(5) were examined for the polymerization of monosubstituted
acetylenes. Catalysts 1 and 2 showed moderate to high activity
for the polymerization of various monosubstituted acetylenes
(6a–e) in the absence of any cocatalyst (Table 1). Polymerization
of 6a proceeded smoothly with catalyst 1 to give high molecular
weightpoly(6a)(Mn = 52,000)in77%yield. Itisnoteworthythat
the conventional catalysts, [(nbd)RhCl]2 and [(cod)RhCl]2, do
not polymerize monomer 6a in toluene unless some cocatalysts
such as Et3N are added [20]. Polymerization of both 6b and 6c
afforded polymers in low yields of 29 and 14%, respectively.
The resulting polymers precipitated during polymerization due
to their insolubility in toluene [21], which may have resulted in
the lower activity of catalyst 1 for the polymerization of 6b and
6c. Polymerizationof6dhavingelectron-donatingtrimethylsilyl
The number- and weight-average molecular weights (Mn and
Mw, respectively) and polydispersity indices (Mw/Mn) of poly-
mers were measured by GPC at 40 ◦C with a Jasco PU-980/RI-
930 chromatograph; eluent THF, columns KF-805 (Shodex) ×3,
molecular weight range up to 4 × 106, flow rate 1 mL/min, cal-
1
ibrated with polystyrene standards. H and 13C NMR spectra
were recorded on a JEOL EX-400 spectrometer. Infrared spectra
were recorded on a Shimadzu FTIR-8100 spectrometer. Ele-
mental analyses were performed at the Microanalytical Center
of Kyoto University. Melting points were determined by Yanaco
MP-50859 melting point apparatus.
2.3. Polymerization
All the polymerizations were carried out under Ar atmo-
sphere in a Schlenk tube equipped with a three-way stopcock. A

I. Saeed et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 124–130
127
Scheme 2. Synthesis of catalysts 1–4.
group at para position afforded the polymer in moderate yield
of 53% (run 4, Table 1). N-Propargylamide 6e also afforded
the corresponding polymer in 45% yield. Catalyst 2, an nbd
analogue of 1, displayed higher activity in the polymerization
of 6a–e: the yields of the polymers generally improved even in
the case of the insoluble polymers derived from 6b and 6c. The
molecular weights of the polymers from 6a, 6d, and 6e were
higher than those with catalyst 1 and the PDIs were slightly
smaller. It should be noted that catalyst 2 polymerized 6a in
an almost quantitative yield and the formed polymer has the
highest molecular weight (Mn = 93,000) among all the catalysts
examined in this study. These results indicate that the nbd ligand
serves to stabilize active species during propagation, eventually
leading to higher molecular weight of the polymers. Aliphatic
monomers 6f–h did not give any methanol-insoluble product
with either of catalysts 1 and 2.
cocatalysts (Table 2). Monomer 6a polymerized with cod cata-
lyst 3 to give a high molecular weight polymer (Mn = 62,000) in
93% yield. In the polymerization of 6b and 6c, the correspond-
ing polymers formed in low yields probably because of their
insolubility similarly to the case of phenoxy-imine catalysts 1
and 2. Compared to phenoxy-imine catalyst 1, ␤-diiminate cat-
alyst 3 afforded poly(6d) and poly(6e) in high yields without
any significant difference of molecular weights. The yields of
the polymers were lower than those of catalyst 3 in each case in
the polymerization of monomers 6a–e with catalyst 4, an nbd
analogue of 3: especially, monomer 6e afforded almost no poly-
mer by catalyst 4. Besides, aliphatic monomers 6f–h did not
polymerize with either of catalysts 3 and 4.
Comparison of activity of 1 and 2 reveals that nbd catalyst
2 is obviously more active than cod catalyst 1 with regard to
polymer yields, molecular weights, and PDIs. In the case of ␤-
diiminate catalysts, the tendency is opposite, i.e., cod catalyst
3 displayed higher activity than nbd catalyst 4. This observa-
tion indicates that the mechanism of polymerization would be
different between phenoxy-imine (1 and 2) and ␤-diiminate cat-
alysts (3 and 4). As far as the reported examples of nbd Rh
catalysts are concerned, it is generally believed that nbd retains
its coordination to Rh metal during propagation resulting in sta-
bilization of the active species leading to an efficient propagation
[22]. The lower activity of the cod analogues is explained by its
weaker ligation to the Rh atom, which results in the decomposi-
tion of active species during propagation. In the case of present
phenoxy-imine catalysts 1 and 2, it is assumed that the diene
ligands do not dissociate from the Rh center, but either O or N
atom of the phenoxy-imine ligand dissociates, which is followed
by the coordination of monomer to the Rh metal leading to the
formation of active species. In order to clarify this mechanism,
the polymerization of 6a by nbd phenoxy-imine catalyst 2 was
␤-Diiminate Rh complexes 3 and 4 also showed catalytic
activity in the polymerization of 6a–e in the absence of any
Table 1
Polymerization of 6a–e with catalysts 1 and 2a
Run
Catalyst
Monomer
Polymerb
Yield (%)
c
c
Mn
Mw/Mn
1
2
3
4
5
1
6a
6b
6c
6d
6e
77
29
14
53
45
52000
2.8
Insoluble
Insoluble
34000
Insoluble
Insoluble
2.9
19000
1.7
6
7
8
9
10
2
6a
6b
6c
6d
6e
97
57
32
85
51
93000
2.6
Insoluble
Insoluble
67000
Insoluble
Insoluble
2.4
50000
1.6
1
monitored by the H NMR spectroscopy (see Section 2). The
a
In toluene, 30 ◦C, 24 h; [M]o = 0.50 M, [Rh] = 2.0 mM.
Methanol-insoluble product.
Determined by GPC (THF, PSt).
b
c
signal due to imine proton of catalyst 2 which appeared as a
doublet peak at 7.641 ppm (3JRh–H = 1.6 Hz), remained almost

128
I. Saeed et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 124–130
Table 2
Table 4
Polymerization of 6a–e with catalysts 3 and 4a
Effect of Et3N and n-BuLi on the polymerization of 6a with catalysts 1–5a
Run
Catalyst
Monomer
Polymerb
Yield (%)
Run
Cocatalystb
Catalyst
Polymerc
Yield (%)
c
c
d
d
Mn
Mw/Mn
Mn
Mw/Mn
1
2
3
4
5
3
6a
6b
6c
6d
6e
93
25
16
70
54
62000
2.1
1
2
3
4
5
Et3N
1
2
3
4
5
Quant.
Quant.
Quant.
Quant.
78
73000
277000
80000
427000
240000
2.0
2.7
1.9
2.2
1.7
Insoluble
Insoluble
38000
Insoluble
Insoluble
2.3
15000
2.7
6
7
8
9
10
4
6a
6b
6c
6d
6e
68
10
7
51
69000
Insoluble
Insoluble
41000
–
1.8
6
7
8
9
10
n-BuLi
1
2
3
4
5
97
Quant.
24
93
68
57000
164000
73000
100000
300000
2.6
2.5
2.1
2.2
1.7
Insoluble
Insoluble
2.5
Trace
–
a
a
In toluene, 30 ◦C, 24 h; [M]o = 0.50 M, [Rh] = 2.0 mM.
Methanol-insoluble product.
Determined by GPC (THF, PSt).
In toluene, 30 ◦C, 24 h; [M]o = 0.50 M, [Rh] = 2.0 mM.
[Cocat]/[Rh] = 1.
Methanol-insoluble product.
b
c
b
c
d
Determined by GPC (THF, PSt).
unchanged during 3 h polymerization and free nbd was also
not detected in the reaction mixture. This result indicates that
the active species is formed by the dissociation of O atom of
the phenoxy-imine ligand with the subsequent coordination of
monomer to the Rh metal.
the polymerization system. Attempts to polymerize 6f–h were
unsuccessful like the former cases. It is noteworthy that catalyst
5 is the most active for the polymerization of propargylamide 6e
among the present catalysts to afford higher molecular weight
polymer (Mn = 83,000) in 89% yield. The polydispersity index
(3.9) was somewhat broader than those with other catalysts.
In contrast, the diene ligands of ␤-diiminate catalysts 3 and
4 would dissociate in an early stage during the formation of
propagating species. When the polymerization of 6a by cod
1
␤-diiminate catalyst 3 was monitored by the H NMR spec-
3.3. Effect of Et3N and n-BuLi on the activity of catalysts
troscopy (see Section 2), a characteristic double-doublet peak at
7.194 ppm (3JH–H = 6.8 Hz, 3JRh–H = 2.0 Hz), which is assigned
to the ␤-diiminate ligand coordinating to Rh metal of 3 gradually
disappeared. A new double-doublet peak appeared at 7.329 ppm
1–5
As described above, the present catalysts 1–5 do not need any
cocatalysts to accomplish the polymerization of 6a–e, but some
oftheresultsarestillunsatisfactorywithrespecttopolymeryield
and molecular weight. Thus, the effects of Et3N and n-BuLi on
the catalytic performance of catalysts 1–5 in the polymerization
of 6a were examined (Table 4). Obviously, Et3N in conjunction
with all the catalysts showed positive cocatalytic effects for both
polymer yield and their molecular weight. For instance, in the
case of catalyst 5, the polymer yield improved from 48 to 78%,
and molecular weight from Mn = 37,000 to 240,000. Further, the
activity of 2 and 4, which contain an nbd ligand, also increased in
the presence of Et3N to achieve quantitative yield of polymers
as well as the increase of molecular weights. Cod-containing
catalysts 1 and 3 also manifested the improved catalytic activ-
ity with Et3N, as is evident from the quantitative yields of the
obtained polymers, but the magnitude of increase in molecular
weight was not so large as that of catalysts 2 and 4. The effects
of n-BuLi were similar to those of Et3N except for catalyst 3
which showed diminished activity in the presence of n-BuLi.
3
(3JH–H = 7.6 Hz, JRh–H = 1.0 Hz), which retained its double-
doublet peak shape and was downfield shifted. Although the
dissociated cod could not be detected in the NMR analysis, this
result at least indicates that in the newly formed Rh species,
␤-diiminate ligand remains coordinated to the Rh metal during
propagation (Table 2).
A cationic Rh catalyst 5, which contains ammonia ligands,
was also examined in the polymerization of monosubstituted
acetylenes (6a–h) (Table 3). Monomer 6a polymerized in the
absence of any cocatalyst in moderate yield (48%) to give a
polymer with Mn = 37,000. Due to its ionic nature, catalyst 5 is
sparingly soluble in toluene, and thus the lower yield of the
polymers would be the outcome of heterogeneous nature of
Table 3
Polymerization of 6a–e with catalyst 5a
Run
Catalyst
Monomer
Polymerb
Yield (%)
c
c
Mn
Mw/Mn
3.4. Stereochemistry of the formed polymers
1
2
3
4
5
5
6a
6b
6c
6d
6e
48
51
42
23
89
37000
2.0
Insoluble
Insoluble
27000
Insoluble
Insoluble
2.1
Rh catalysts are known to polymerize monosubstituted
acetylenes in a stereospecific fashion to produce polymers with
cis-transoidal main chain structure. The H NMR spectra of
1
83000
3.9
poly(6a)s obtained from catalysts 1–5 displayed a sharp peak
around 5.84 ppm due to cis-olefinic proton of the main chain.
The cis contents (calculated by the integration ratio of olefinic
a
In toluene, 30 ◦C, 24 h; [M]o = 0.50 M, [Rh] = 2.0 mM.
Methanol-insoluble product.
Determined by GPC (THF, PSt).
b
c

I. Saeed et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 124–130
129
proton to the ring protons) of poly(6a)s were in the range of
90–100% manifesting a high level stereoregularity in the poly-
merization. These results also indicate that the stereochemistry
of the formed polymer is not affected by the change in the lig-
ands around the Rh metal. A change in environment around the
Rh metal does not influence the stereochemical outcome of the
polymerization.
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4. Conclusions
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In this paper, it is demonstrated that Rh catalysts 1–5 having
phenoxy-imine, ␤-diiminate, and ammonia ligands were active
for the polymerization of monosubstituted acetylenes (6a–e)
without requirement of any cocatalyst. In the case of Rh cat-
alysts bearing phenoxy-imine ligand, nbd catalyst 2 displayed
higher activity than its cod analogue 1. In contrast, Rh catalysts
having ␤-diiminate ligand showed opposite tendency, i.e., cod
catalyst 3 was more active than its corresponding nbd catalyst
4. Although the mechanism for the formation of active species
during propagation could not be completely elucidated, the dis-
sociation of diene ligands from Rh metal center appears to be an
important step during initiation in the case of catalysts 3 and 4.
Et3N and n-BuLi manifested positive cocatalytic effects in the
polymerization of 6a, and both polymer molecular weight and
polymer yield increased in their presence.
[7] (a) M. Kozuka, T. Sone, Y. Sadahiro, M. Tabata, T. Enoto, Macromol.
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Acknowledgements
This work was supported by a Grant-in-Aid for Scientific
Research from Japan Society for Promotion of Science. Thanks
are also due to Shin-Etsu Chemical Co. Ltd., Japan and Fuji Film
Co. Ltd., Japan for the donation of trimethylsilylacetylene and
3-ethynylaniline, respectively.
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