Living polymerization of bulky aryl isocyanide with arylrhodium complexes

Article abstract of DOI:10.1021/om0509692

Well-defined arylrhodium complexes Rh(Ar)(nbd)(PPh₃) (Ar = Me₂C₆H₃, 2,4,6-Pr₃ⁱC ₆H₂, 2-PhC₆H₄, 2-Me-1-naphthyl, 9-anthracenyl, C(Ph)=CPh₂

Full text of DOI:10.1021/om0509692

1270
Organometallics 2006, 25, 1270-1278
Living Polymerization of Bulky Aryl Isocyanide with Arylrhodium
Complexes
Kiyotaka Onitsuka,* Mari Yamamoto, Tomoko Mori, Fumie Takei, and
Shigetoshi Takahashi
The Institute of Scientific and Industrial Research, Osaka UniVersity, 8-1 Mihogaoka,
Ibaraki, Osaka 567-0047, Japan
ReceiVed NoVember 11, 2005
Well-defined arylrhodium complexes Rh(Ar)(nbd)(PPh3) (Ar ) Me2C6H3, 2,4,6-Pri3C6H2, 2-PhC6H4,
2-Me-1-naphthyl, 9-anthracenyl, C(Ph)dCPh2; nbd ) 2,5-norbornadiene) that were prepared from the
reaction of [Rh(nbd)Cl]2 with LiAr and PPh3 effectively initiated the living polymerization of aryl
isocyanides possessing bulky substituents at the ortho position in the presence of PPh3 to give poly-
(isocyanide)s with narrow polydispersity indexes in good yields. The bulky aryl groups on the Rh complex
were essential to achieving high initiator efficiency, whereas the bulky substituents on aryl isocyanides
were required for the formation of high molecular weight polymers. The living nature of the present
system was confirmed by kinetic studies as well as the formation of block copolymers. The polymerization
rate was dependent not on the concentration of monomers, but on the concentration of PPh3.
isocyanides have been prepared so far. As Pd-Pt µ-ethynediyl
complexes do not initiate the polymerization of ortho-substituted
aryl isocyanide due to steric reasons, a new polymerization
method should be developed.
Introduction
Polyisocyanides have been the focus of intense research
efforts due to their unique helical structures.1 More than 30 years
have passed since the discovery that some transition metal
complexes serve as efficient catalysts or initiators for the
polymerization of isocyanides.2 However, it is difficult to control
the molecular weights and the sequences of the resulting
polyisocyanides because these are not living polymerization
systems. In 1990s, three examples of living polymerization were
independently discovered. π-Allylnickel complexes are effective
for the living polymerization of alkyl isocyanides,3 whereas
methylpalladium complexes initiate the living polymerization
of 1,2-diisocyanobenzene.4 We showed that Pd-Pt µ-ethynediyl
complexes promote the living polymerization of aryl isocya-
nides.5 Poly(aryl isocyanide)s adopt a stable helical conformation
even in solution when they have the appropriate chiral side
groups.6 Because the stability of the helical conformation of
polyisocyanides is affected by the bulkiness of the side groups,
poly(aryl isocyanide)s prepared from monomers with a bulky
substituent at the ortho position of the phenyl ring are attractive
targets for the investigation of the steric effect on the stability
of the helical conformation. However, no such type of poly-
On the other hand, we are interested also in the chemistry of
aryl isocyanides having alkynyl and alkenyl groups at the ortho
position, because we expect an intramolecular tandem reaction
of the isocyano group and the unsaturated hydrocarbons. In the
reactions of palladium complexes, the isocyano group showed
much higher reactivity than the unsaturated hydrocarbons due
to its stronger coordination ability.7 As the rhodium complex
is known to be a good catalyst for the polymerization of
phenylacetylene, we examined the reactions of 2-alkynylphenyl
isocyanide with organorhodium complexes.8,9 Contrary to our
expectations, only the isocyano group reacted to produce
polyisocyanide even in the reactions of aryl isocyanide having
a bulky alkynyl group. Thus, we extended our finding to the
precise synthesis of poly(aryl isocyanide)s having bulky sub-
stituents. We present herein the living polymerization of aryl
isocyanides that have bulky substituents at the ortho position,
(6) (a) Takei, F.; Yanai, K.; Onitsuka, K.; Takahashi, S. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 1554. (b) Ramos, E.; Bosch, J.; Serrano, J. L.;
Sierra, T.; Veciana, J. J. Am. Chem. Soc. 1996, 118, 4703. (c) Amabilino,
D. B.; Ramos, E.; Serrano, J.-L.; Veciana, J. AdV. Mater. 1998, 10, 1001.
(d) Takei, F.; Onitsuka, K.; Takahashi, S. Polym. J. 1999, 31, 1029. (e)
Takei, F.; Yanai, K.; Onitsuka, K.; Takahashi, S. Chem. Eur. J. 2000, 6,
983. (f) Takei, F.; Onitsuka, K.; Takahashi, S. Polym. J. 2000, 32, 524. (g)
Takei, F.; Hayashi, H.; Onitsuka, K.; Takahashi, S. Polym. J. 2001, 33,
310. (h) Takei, F.; Hayashi, H.; Onitsuka, K.; Kobayashi, N.; Takahashi,
S. Angew. Chem., Int. Ed. 2001, 40, 4092. (i) Ishikawa, M.; Maeda, K.;
Yashima, E. J. Am. Chem. Soc. 2002, 124, 7448. (j) Hida, N.; Takei, F.;
Onitsuka, K.; Shiga, K.; Asaoka, S.; Iyoda, T.; Takahashi, S. Angew. Chem.,
Int. Ed. 2003, 42, 4349. (k) Ishikawa, M.; Maeda, K.; Mitsutsuji, Y.;
Yashima, E. J. Am. Chem. Soc. 2004, 126, 732.
(7) (a) Onitsuka, K.; Segawa, M.; Takahashi, S. Organometallics 1998,
17, 4335. (b) Onitsuka, K.; Yamamoto, M.; Suzuki, S.; Takahashi, S.
Organometallics 2002, 21, 581.
(8) (a) Kishimoto, Y.; Eckerle, P.; Miyatake, T.; Ikariya, T.; Noyori, R.
J. Am. Chem. Soc. 1994, 116, 12131. (b) Kishimoto, Y.; Miyatake, T.;
Ikariya, T.; Noyori, R. Macromolecules 1996, 29, 5054. (c) Kishimoto, Y.;
Eckerle, P.; Miyatake, T.; Kainosho, M.; Ono, A.; Ikariya, T.; Noyori, R.
J. Am. Chem. Soc. 1999, 121, 12035.
(1) (a) Drenth, W.; Nolte, R. J. M. Acc. Chem. Res. 1979, 12, 30. (b)
Nolte, R. J. M. Chem. Soc. ReV. 1994, 23, 11. (c) Suginome, M.; Ito, Y.
AdV. Polym. Sci. 2004, 171, 77.
(2) (a) Yamamoto, Y.; Takizawa, T.; Hagihara, N. Nippon Kagaku Zasshi
1966, 87, 1355. (b) Otsuka, S.; Nakamura, A.; Yoshida, T. J. Am. Chem.
Soc. 1969, 91, 5932. (c) Yamamoto, Y.; Yamazaki, H. Inorg. Chem. 1977,
16, 3182. (d) Nolte, R. J. M.; Zwikker, J. W.; Reedijk, J.; Drenth, W. J.
Mol. Catal. 1978, 4, 423.
(3) (a) Deming, T. J.; Novak, B. M. Macromolecules 1991, 24, 6043.
(b) Deming, T. J.; Novak, B. M. Macromolecules 1993, 26, 7092. (c)
Deming, T. J.; Novak, B. M. J. Am. Chem. Soc. 1993, 115, 9101.
(4) (a) Ito, Y.; Ihara, E.; Murakami, M.; Shiro, M. J. Am. Chem. Soc.
1990, 112, 6446. (b) Ito, Y.; Ihara, E.; Murakami, M. Angew. Chem., Int.
Ed. Engl. 1992, 31, 1509.
(5) (a) Onitsuka, K.; Joh, T.; Takahashi, S. Angew. Chem., Int. Ed. Engl.
1992, 31, 851. (b) Onitsuka, K.; Yanai, K.; Takei, F.; Joh, T.; Takahashi,
S. Organometallics 1994, 13, 3862. (c) Ohshiro, N.; Shimizu, A.; Okumura,
R.; Takei, F.; Onitsuka, K.; Takahashi, S. Chem. Lett. 2000, 786. (d)
Onitsuka, K.; Yabe, K.-i.; Ohshiro, N.; Shimizu, A.; Okumura, R.; Takei,
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10.1021/om0509692 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 02/02/2006

LiVing Polymerization of Bulky Aryl Isocyanide
Organometallics, Vol. 25, No. 5, 2006 1271
Scheme 1
Scheme 2
with well-defined organorhodium complexes. The preliminary
results have been reported elsewhere.10
Mn ) 9000 and Mw/Mn ) 1.17 (Scheme 2). Polymer 3aa50 was
soluble in common organic solvents such as toluene, ether, and
dichloromethane and was purified by reprecipitation with
methanol. The IR spectrum of 3aa50 showed an absorption band
at 1613 cm-1, which is characteristic of ν(CdN) of poly(aryl
isocyanide)s.1 In the 13C NMR spectrum of 3aa50, a relatively
sharp resonance due to the imino carbons of the polymer
backbone was observed at δ 155.1 with a half-bandwidth of 33
Hz. These data indicate that 3aa50 has high stereoregularity of
the imino groups despite the low reaction temperature, in sharp
contrast to poly(aryl isocyanide)s prepared by a nickel catalyst,
which have low stereoregularity of the imino groups.12 The 1H
NMR spectrum of 3aa50 displayed a small singlet at δ 2.35
assignable to the methyl protons at the polymer end originating
from the 2,6-xylyl ligand of 1a, suggesting that the polymeri-
zation proceeded via multiple and successive insertions of 2a
into the Rh-C bond of 1a. However, no information of the
other polymer end was obtained.
When the polymerization was performed at 0 °C, the
conversion of 2a was low (12%). Although the polymerization
also proceeded at 30 °C, a polymer with a slightly low molecular
weight (Mn ) 7800) and a slightly large polydispersity (Mw/Mn
) 1.25) was obtained, compared with that prepared at 20 °C.
The reactions in benzene and DMF gave polymer 3aa with
similar molecular weight. However, the conversion of the
monomer was 67% and the molecular weight of the resulting
polymer was low (Mn ) 4700, Mw/Mn ) 1.27) when dichlo-
romethane was used as the solvent. It should be noted that NiCl2‚
6H2O, which is a standard catalyst for the polymerization of
isocyanides,1 including ortho-substituted aryl isocyanides such
as o-tolyl and 2,6-dichlorophenyl isocyanides, was not effective
for the polymerization of 2a.
Results and Discussion
Arylrhodium complexes Rh(Ar)(nbd)(PPh3) (1) (nbd )
norbornadiene) were synthesized by reacting [Rh(nbd)Cl]2 with
aryllithium reagent, which was prepared from the corresponding
aryl bromide and n-butyllithium, in the presence of PPh3
(Scheme 1).9 The rhodium complexes with bulky aryl groups
were fairly stable and soluble in common organic solvents,
whereas the phenylrhodium complex was unstable.11 Complexes
1a-e were fully characterized by spectral analyses. For example,
the 13C NMR spectrum of 1a showed a signal at δ 177.5
assignable to the ipso carbon of the aryl group, which appeared
as a double doublet due to coupling with the 103Rh and 31P nuclei
(JRh-C ) 35, JP-C ) 13 Hz). The 31P NMR spectrum of 1a
showed a doublet at δ 30.3 with JRh-P ) 191 Hz. The molecular
structure of 1d was determined by X-ray crystallography. As
shown in Figure 1, 1d adopts a square planar geometry around
the rhodium atom. The plane of the naphthyl group is essentially
perpendicular to the coordination plane of the rhodium atom to
minimize steric repulsion with PPh3. The structural parameters
of 1d are similar to those of 1a.10
Polymerization of 2-{(trimethylsilyl)ethynyl}phenyl isocya-
nide (2a) with complex 1a (ArNC/1a ) 50) in the presence of
PPh3 (PPh3/1a ) 10) in THF at 20 °C for 2 h led to the
quantitative formation of a yellow-brown polymer (3aa50) with
We examined the effect of additives and present the repre-
sentative results in Table 1. The polymerization without PPh3
resulted in the incomplete consumption of the monomer and
the production of polymer as well as oligomers. When ligands
were added to the system instead of PPh3, the polymerization
was depressed. Such N-donor ligands as DMAP and bipyridine
were less effective for the present polymerization than PPh3.
These results suggest that the addition of PPh3 is essential for
the smooth polymerization of 2a.
The polymerization of 2a using some rhodium complexes
was performed (Table 2). Organorhodium complexes 1b, 1c,
1d, and 1e, having bulky aryl groups, initiated the polymeri-
zation of 2a to give polymers 3ba, 3ca, 3da, and 3ea,
respectively. However, monomer 2a was not completely con-
sumed when the reaction was performed with 1 mol % of
(10) Yamamoto, M.; Onitsuka, K.; Takahashi, S. Organometallics 2000,
19, 4669.
(11) Takesada, M.; Yamazaki, H.; Hagihara, N. Nippon Kagaku Zasshi
1968, 89, 1122.
(12) (a) Green, M. M.; Gross, R. A.; Schilling, F. C.; Zero, K.; Crosby,
C., III. Macromolecules 1988, 21, 1839. (b) Takei, F.; Onitsuka, K.;
Takahashi, S. Macromolecules 2005, 38, 1513.
Figure 1. Molecular structure of 1d. Hyrdrogen atoms are omitted
for clarity. Selected bond distances (Å) and angles (deg): Rh(1)-
P(1) ) 2.296(2); Rh(1)-C(1) ) 2.052(7); Rh(1)-C(12) ) 2.179-
(7); Rh(1)-C(13) ) 2.211(7); Rh(1)-C(17) ) 2.181(7); Rh(1)-
C(18) ) 2.180(7); P(1)-Rh(1)-C(1) ) 94.3(2).

1272 Organometallics, Vol. 25, No. 5, 2006
Onitsuka et al.
Table 1. Effects of Additives on Polymerization of
2-{(Trimethylsilyl)ethynyl}phenyl Isocycanide 2a with
Complex 1a
Chart 1
(3ac: Mn ) 2400, Mw/Mn ) 1.07; 3ad0: Mn ) 7300, Mw/Mn
) 1.07) were not as high as that of 3aa. In contrast, no
polymerization took place on treatment of 2,6-xylyl isocyanide
with 1a. Alkyl isocyanides such as cyclohexyl and tert-butyl
isocyanides did not polymerize with 1a at all. From these results,
we hypothesized that the rhodium complexes having bulky aryl
groups were effective for the polymerization of aryl isocyanides
that had bulky substituents at one of the two ortho positions.
To confirm this hypothesis, we prepared aryl isocyanides (8)
that had tert-butyl groups at the 2-position via the route shown
in Schemes 3 and 4. Treatment of 2-tert-butylaniline (4) with
iodine in aqueous NaHCO3 resulted in the selective iodation at
the 4-position to give 2-tert-butyl-4-iodoaniline (5). After
N-formylation by reacting with HCO2H/Ac2O to give formamide
derivative (6), the alkoxycarbonyl group was introduced by
carbonylation using a palladium catalyst to give the correspond-
conv
(%)
polymer/
Mw/Mn oligomerb
a
a
entry
additive
m
n
Mn
1
2
3
4
5
6
7
8
0
50
78
7200
9000
1.31
1.17
1.49
1.60
1.33
1.28
1.49
1.03
1.28
1.17
1.21
1.24
95/5
PPh3
P(C6H4Me-p)3
P(C6H4OMe-p)3 10 100
P(C6H4Me-o)3
PCy3
PMePh2
P(OPh)3
dppe
10 50 100
100/0
100/0
100/0
94/6
80/20
100/0
100/0
100/0
76/24
91/9
10 100
86 12 900
81 12 800
10 100
10 50
10 50
10 50
1
1
69
83
94
24
27
49
41
74
9400
5000
8700
1100
1700
4700
5100
5600
9
50
50
10
11
12
BINAP
DMAP
bipyridine
10 50
50
1
94/6
i
ing ester (7). Dehydration with POCl3 and Pr2NH produced
a Determined by GPC using polystyrene standards. b Mn’s of oligomers
were approximately 1200 based on GPC analysis.
desired monomers (8a-d) (Scheme 3). To synthesize 2-tert-
butyl-4-octyloxyphenyl isocyanide (8e), the octyloxy group was
introduced by reacting 5 with sodium octyloxide in the presence
of CuI to give 2-tert-butyl-4-octyloxyaniline (9), which was
converted into 8e via N-formylation and dehydration by a similar
procedure (Scheme 4).
rhodium complexes. Triphenylvinylrhodium complex (1f) showed
similar activity for the polymerization of 2a.9 In contrast, the
reaction with phenylrhodium complex (1g) gave polymer (3ga)
along with a significant amount of oligomers. Despite the small
feed ratio of 2a/1g and the formation of oligomers, the Mn value
of the resulting polymer 3ga was large, suggesting that the
initiator efficiency of 1g was low. Methylrhodium complex (1h)
gave a result similar to that by 1g, whereas phenylethynyl-
rhodium complex (1i) weakly initiated the polymerization of
2a. The reactions of several isocyanides with 1a were examined.
In the reaction of 4-(propoxycarbonyl)phenyl isocyanide (2b),
the conversion was low (12%) and polymer (3ab) with low
molecular weight (Mn ) 1200, Mw/Mn ) 1.06) was obtained.
Although 2-(prop-1-ynyl)phenyl and 2-butylphenyl isocyanides
(2c and 2d) were polymerized by 1a with significant conversions
(76% and 73%), the molecular weights of the resulting polymers
As expected, monomers 8a, 8b, and 8e were smoothly
polymerized with organorhodium complexes 1 (Scheme 5). In
all cases, the isocyanide monomers were completely consumed
and polymers 10 with narrow molecular weight distributions
were isolated in good yields (Table 3). No drastic electronic
effect of the monomers on the polymerization rate was observed
in the present system, in sharp contrast to the fact that the
electron-donating groups on the aryl ring suppressed the
polymerization rate in the reaction of aryl isocyanides with
Pd-Pt µ-ethynediyl complexes.
In the 1H NMR spectrum of 3aa100, a small but sharp signal
due to methyl protons at the polymer end that was derived from
Table 2. Polymerization of 2-{(Trimethylsilyl)ethynyl}phenyl Isocyanide 2a with Various Rh Complexes 1
b
b
entry
complex
R
m
n
conv (%)
polymer
yield (%)a
Mn
Mw/Mn
polymer/oligomerc
1
2
3
4
5
6
7
8
1a
1a
1b
1b
1c
1c
1d
1d
1e
1e
1f
2,6,-Xylyl
10
20
10
20
10
20
10
20
10
20
20
20
20
20
20
50
100
50
100
50
100
50
100
50
100
50
100
20
20
50
100
96
100
77
100
96
100
87
100
92
100
94
100
87
42
3aa50
3aa100
3ba50
3ba100
3ca50
3ca100
3da50
3da100
3ea50
3ea100
3fa50
80
92
82
66
90
84
79
71
75
71
83
85
d
9000
18 000
8900
14 100
9500
16 600
11 600
16 000
10 000
17 700
10 900
15 600
7100
1.17
1.39
1.29
1.53
1.26
1.51
1.16
1.41
1.30
1.33
1.25
1.53
1.31
1.41
1.28
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
77/23
64/36
23/77
2,4,6-Pri3C6H2
2-PhC6H4
2-Me-1-naphthyl
9-anthracenyl
C(Ph)dCPh2
9
10
11
12
13
14
15
1f
3fa100
3ga20
3ha20
3ia50
1g
1h
1i
Ph
Me
CtCPh
d
d
10 800
10100
a Isolated yield. b Determined by GPC using polystyrene standards. c Mn’s of oligomers were approximately 1200 based on GPC analysis. d Not isolated.

LiVing Polymerization of Bulky Aryl Isocyanide
Organometallics, Vol. 25, No. 5, 2006 1273
Table 3. Polymerization of 2-tert-Butylphenyl Isocyanide Derivatives 8 with Rh Complexes 1
b
b
entry
complex
isocyanide
n
m
polymer
yield (%)a
Mn
Mw/Mn
1
2
3
4
5
6
7
8
1a
1a
1b
1b
1b
1b
1c
1d
1d
1e
1e
1f
8a
8a
8a
8a
8b
8e
8a
8a
8a
8a
8a
8a
8a
50
75
50
100
50
50
50
50
100
50
100
50
10
20
10
20
10
20
10
20
10
20
20
20
20
10aa50
10aa75
10ba50
10ba100
10bb50
10be50
10ca50
10da50
10da100
10ea50
10ea100
10fa50
83
91
80
82
99
98
82
87
88
85
83
87
87
22 600
27 300
15 200
33 600
16 200
16 600
16 600
17 200
29 300
18 000
37 500
25 800
41 800
1.34
1.46
1.27
1.50
1.29
1.25
1.35
1.36
1.58
1.36
1.43
1.19
1.35
9
10
11
12
13
1f
100
10fa100
a Isolated yield. b Determined by GPC using polystyrene standards.
Scheme 3. Synthesis of
2-tert-butyl-4-(alkoxycarbonyl)Phenyl Isocyanides
Figure 2. Plot of Mn values versus feed ratio of monomer 2a to
initiator 1a for the series of 3aa.
supported by the measurement of the absolute molecular weight
of 10ba50 by a light-scattering method to give Mw ) 20000,
consistent with the Mw(GPC) value of 19 300.
Scheme 4. Synthesis of 2-tert-butyl-4-(octyloxy)Phenyl
Isocyanides
Then, we attempted to confirm the living nature of the present
system by the stepwise addition of the monomer. When 8a was
added to the solution of 10ba50 that was generated from the
reaction of 8a with 1b (2 mol %) in the presence of 10 equiv
of PPh3 in situ, no polymerization took place. This result
suggested that the active Rh species should decompose after
complete consumption of the isocyanide monomer, consistent
with the remarkable decrease in the polymerization rate at high
conversion (more than 80%). However, a large excess of PPh3
stabilized the active Rh species even after the complete
consumption of the isocyanide monomer. Thus, the three-step
addition of 50 equiv of 8a to 1b in the presence of 400 equiv
of triphenylphosphine resulted in the stepwise formation of
10ba50′ (Mn ) 21 300, Mw/Mn ) 1.19), 10ba100′ (Mn ) 38 000,
Mw/Mn ) 1.20), and 10ba150′ (Mn ) 50 900, Mw/Mn ) 1.29),
having narrow molecular weight distributions (Figure 3). A
block copolymer was also prepared by a similar method.
Treatment of 50 equiv of 2-tert-butyl-4-(cyclohexyloxycar-
bonyl)phenyl isocyanide (8c) with 10ba50′′ (Mn ) 18 000,
Mw/Mn ) 1.21) that was generated from the reaction of 8a with
1b (2 mol %) in the presence of 400 equiv of PPh3 in situ
produced AB type block copolymer 11ba50c50 (Mn ) 32 900,
Mw/Mn ) 1.22) quantitatively (Scheme 6).
Scheme 5
the 2,6-xylyl group of 1a was detected. Thus, the absolute Mn
value was determined from the integral ratio of the methyl signal
of the polymer end to the signal of the trimethylsilyl group
derived from 2a. As shown in Figure 2, the Mn(NMR) values
of 3aa were in good agreement with the ideal Mn values
calculated from the feed ratio of 2a/1a, suggesting that the
initiator efficiency of 1a was almost quantitative. As the
Mn(GPC) values of 3aa were very close to the Mn(NMR) values,
the absolute molecular weights of other polymers 3 and 10
should be similar to the Mn(GPC) values. This conclusion was
Next, we performed the trace experiment of the polymeri-
zation of 8a with 1b. Figure 4 shows a linear relationship

1274 Organometallics, Vol. 25, No. 5, 2006
Onitsuka et al.
Figure 3. Multistage polymerization of 8a with 1b that was
supplied three times at intervals of 6 min. Reaction concentration:
[8a]0 ) [8a]added ) 0.25 M; [1b] ) 0.005 M; [PPh3] ) 2.0 M;
THF, 20 °C.
Figure 5. Plot of conversion of monomer 8a as a function of
reaction time initiated by 1b. Initial concentration: [8a] ) 0.25
M; [1b] ) 0.005; [PPh3] ) 0.050 M; THF, 20 °C.
Scheme 7. Mechanisms of Isocyanide Insertion into M-C
Bond
Figure 4. Plot of Mn values as a function of conversion of
monomer 8a initiated by 1b. Initial concentration: [8a] ) 0.25 M;
[1b] ) 0.005 M; [PPh3] ) 0.050 M; THF, 20 °C.
Table 4. Rate Constants for Polymerization of 8a with 1b at
Several Temperaturesa
entry
T (K)
kobsd × 103 (s-1
)
R2 b
Scheme 6
1
2
3
4
298
293
288
283
0.423
0.299
0.206
0.154
0.991
0.996
0.994
0.997
a Initial concentration: [8a] ) 0.25 M; [1b] ) 0.005 M; [PPh3] ) 0.050
M; THF. b Correlation coeffcient for the first-order plot.
the metal center of isocyanide complexes, generating a five-
coordinate intermediate,13 and the other involves simple migra-
tory insertion, which is the rate-determining step, generating a
coordinatively unsaturated intermediate followed by fast coor-
dination of ligand L′.14 Because isocyanide acts as the incoming
ligand L′ in the polymerization, the former obeys the first-order
rate law with respect to isocyanide concentration and the latter
obeys the zero-order rate law.3c Therefore, the present polym-
erization should proceed via the latter mechanism.
Rate constants for the polymerization of 8a with 1b at several
temperatures were measured, and the representative results are
listed in Table 4. The activation parameters were estimated to
be ∆Hq ) 45.4 kJ mol-1, ∆Sq ) -157.3 J K-1 mol-1, and
∆Gq ) 91.5 kJ mol-1 at 20 °C. Since the present polymerization
proceeds without the nucleophilic attack of the ligands, the large
negative value of ∆Sq may seem unusual. However, it should
be derived from the large solvation effect in the transition state,
generating the coordinatively unsaturated intermediate. The large
negative ∆Sq value was also observed in the insertion of
isocyanides with palladium complexes, in which the reaction
rate did not depend on the concentration of the isocyanide.14
between the conversion of 8a and the Mn(GPC) values of 10ba,
suggesting that the present polymerization had a living nature.
When the conversion of 8a was plotted against reaction time, a
linear relationship was found up to 80% conversion (Figure 5),
suggesting that the rate of the present polymerization was
independent of the concentration of isocyanide monomer 2, in
sharp contrast to the fact that the first-order kinetics was
observed in the plot of the polymerization of aryl isocyanides
with Pd-Pt µ-ethynediyl complexes versus monomer concen-
tration. The chain propagation step of isocyanide polymerization
with transition metal complexes involves the successive insertion
of isocyanide into the M-C bonds of iminoacyl complexes,
and two mechanisms have been proposed for the insertion of
isocyanides in d8 organometallic compounds (Scheme 7). One
involves the nucleophilic attack of an incoming ligand (L′) at
(13) (a) Treichel, P. M.; Wagner, K. P.; Hess, R. W. Inorg. Chem. 1973,
12, 1471. (b) Onitsuka, K.; Ogawa, H.; Joh, T.; Takahashi, S.; Yamamoto,
Y.; Yamazaki, H. J. Chem. Soc., Dalton Trans. 1991, 1531.
(14) (a) Otsuka, S.; Ataka, K. J. Chem. Soc., Dalton Trans. 1976, 327.
(b) Campagnaro, A.; Mantovani, A.; Uguagliati, P. Inorg. Chim. Acta 1985,
1985, L15.

LiVing Polymerization of Bulky Aryl Isocyanide
Organometallics, Vol. 25, No. 5, 2006 1275
Table 5. Rate Constants for Polymerization of 8a with 1b at
Several PPh3 Temperaturesa
Scheme 8
entry
[PPh3] (M)
[PPh3]/[Rh]
kobsd × 103 (s-1
)
R2 b
1
2
3
4
5
6
7
0
0
3
10
0.159
0.157
0.242
0.799
1.587
2.152
2.941
0.997
0.992
0.997
0.996
0.997
0.993
0.999
0.015
0.05
0.2
0.5
1.0
2.0
40
100
200
400
a Initial concentration: [8a] ) 0.25 M; [1b] ) 0.005 M; THF, 293 K.
b Correlation coeffcient for the first-order plot.
Scheme 9
Figure 6. Effect of PPh3 on rate constants for polymerization of
8a with 1b. Initial concentration: [8a] ) 0.25; [1b] ) 0.005 M;
THF, 293 K.
The effect of PPh3 addition on the polymerization rate was
examined. Table 5 lists the rate constants (kobsd) at various
concentrations of triphenylphosphine. The polymerization rate
was increased proportionally with increasing concentration of
PPh3 at low concentrations, whereas the rate became smaller
than that expected from the proportional relationship at higher
concentrations (Figure 6a). In contrast, the reciprocal of kobsd
exhibited a linear relationship with the reciprocal of [PPh3] at
high concentrations (Figure 6b).
nucleus, respectively. These spectra suggested that 12ad was
in equilibrium with coordinatively unsaturated species 13ad
through the dissociation and re-coordination of triphenylphos-
phine. This observation may be derived from the steric repulsion
between bulky ligands in 12ad.
From these results, a probable mechanism for the propagation
step in the present polymerization is illustrated in Scheme 9.
The insertion of isocyanides takes place in complexes 12 and
13, but the reaction of 12 generating 15 should be faster than
the reaction of 13 generating 14. Assumption of rapid equilibra-
tion between 12 and 13 (K ) [12]/[13][PPh3]) leads to the
kinetic expression of eq 1, where [Rh] is the total concentration
of the Rh species and should be constant since the present
reaction is a living polymerization.
Since the effect of triphenylphosphine on the polymerization
rate was confirmed, we examined the reaction of organorhodium
1
complexes with isocyanides by means of H and 31P NMR
spectroscopy (Scheme 8). When 1a was treated with 2 equiv
of 2-tert-butyl-4-methoxycarbonylphenyl isocyanide (8d) in
C6D6 at room temperature, approximately 50% of norbornene
was replaced to give isocyanide complex 12ad. The reaction
using 4 equiv of 8d led to an increase in the conversion of 1a
of up to approximately 90%. Similar ligand exchange took place
in the reaction of 1a with 4-(hexyloxycarbonyl)phenyl isocya-
nide (2e) and in the reaction of 1i with 8d, producing isocyanide
complexes 12ae and 12id, respectively. Although we could not
isolate these isocyanide complexes, their interesting features
were observed in the 31P NMR spectra. A broad singlet appeared
at δ 26.0 in the 31P NMR spectrum of 12ad, whereas the 31P
NMR spectra of 12ae and 12id showed doublets at δ 25.8 (J )
96 Hz) and 32.9 (J ) 90 Hz) due to coupling with the 103Rh
k1 + k2K[PPh3]
1 + K[PPh3]
d[ArNC]
-
)
[Rh]
(1)
dt

1276 Organometallics, Vol. 25, No. 5, 2006
Onitsuka et al.
further purification. Complexes 1f,9b 1g,11 1h,15 and 1i8a were
prepared according to methods in the literature. Isocyanide monomer
2a was prepared by a similar method reported by others.16
In the low concentration range of PPh3, the relation K[PPh3] )
[12]/[13] , 1 is assumed to hold. Thus, kobsd is expressed as
follows.
Synthesis of Rh(2,6-Me2C6H3)(nbd)(PPh3) (1a). To a solution
of 2-bromo-1,3-dimethylbenzene (0.13 mL, 1 mmol) in diethyl ether
(5 mL) was slowly added a 1.6 M hexane solution of n-BuLi (0.62
mL, 1 mmol) at -78 °C. The reaction mixture was stirred for 10
min and allowed to warm to room temperature. Then a solution of
[RhCl(nbd)]2 (115 mg, 0.25 mmol) and triphenylphosphine (295
mg, 1.13 mmol) in THF (10 mL) was added at room temperature.
After stirring for 30 min, a small amount of methanol was added
for quenching. The solvent was removed under reduced pressure,
and the residue was purified by alumina column chromatography
with benzene. Concentration of the red fraction followed by
recrystallization from dichloromethane-,/hexane gave red crystals
kobsd ) k1 + k2K[PPh3]
(2)
On the other hand, if the concentration of PPh3 is high, the
relation k2K[PPh3] . k1 should hold because the polymerization
is highly accelerated. Thus, kobsd is expressed as follows.
k1
kobsd
)
+ k2
(3)
K[PPh3]
Accordingly, the following relationship (eq 4) between kobsd and
the concentration of triphenylphosphine is obtained.
1
of 1a (270 mg, 96%). H NMR: δ 7.30-7.18 (m, 15H, Ph), 6.64
(t, J ) 7.3 Hz, 1H, Ar), 6.52 (d, J ) 7.3 Hz, 2H, Ar), 4.96-4.93
(m, 2H, dCH of nbd), 3.80 (s, 2H, CH of nbd), 3.72 (s, 2H, dCH
of nbd), 2.44 (s, 6H, CH3), 1.58 (d, J ) 7.8 Hz, 1H, CH2 of nbd),
1.39 (dd, J ) 7.8, 1.2 Hz, 1H, CH2 of nbd). 13C NMR: δ 177.5
(dd, J ) 35, 13 Hz, Cipso-Rh of Ar), 142.0 (s, Cipso-CH3 of Ar),
133.6 (d, J ) 12 Hz, Ph), 133.4 (d, J ) 34 Hz, Cipso-P of
Ph), 129.1 (s, Ph), 127.8 (d, J ) 9 Hz, Ph), 124.5 (s, Ar), 122.2
(s, Ar), 77.7 (t, J ) 9 Hz, dCH of nbd), 72.1 (d, J ) 7 Hz, dCH
of nbd), 67.1 (s, CH2 of nbd), 51.7 (s, CH of nbd), 25.6 (s,
CH3). 31P NMR: δ 30.3 (d, JP-Rh ) 191 Hz). Anal. Calcd for
C33H32PRh: C, 70.47; H, 5.73; P, 5.51. Found: C, 70.72; H, 5.78;
P, 5.40.
1
kobsd
1
1
k2
)
+
(4)
k2K[PPh3]
Equation 2 is consistent with the results of Figure 6a, whereas
eq 4 is in good agreement with the results of Figure 6b. One
possible reason the insertion of isocyanide in 12 is faster than
that in 13 is that the electron donation by triphenylphosphine
may stabilize the transition state as 14e- species 15 is generated
at the rate-determining step. On the other hand, the highly
unsaturated 12e- species 14 is generated at low concentrations
of triphenylphosphine. When sufficient amounts of isocyanide
monomers exist in the system, 14 is quickly converted into 13
by coordination of the isocyanides before decomposition. In
contrast, 14 decomposes prior to the coordination of the
isocyanides when most of the isocyanide monomers are
consumed. Therefore, the present polymerization loses its living
nature at high conversion. Although the coordination sphere
around the Rh atom of 15 is crowded with bulky ligands,
triphenylphosphine coordinates to 15 at high concentrations after
consumption of the isocyanide monomers to stabilize the active
Rh species. This should be the reason the block copolymers
could be prepared when a large excess of triphenylphosphine
is added.
Syntheses of Rh(2,4,6-Pri3C6H2)(nbd)(PPh3) (1b), Rh(2-
PhC6H4)(nbd)(PPh3) (1c), Rh(2-Me-1-C10H6)(nbd)(PPh3) (1d),
Rh(9-C10H6)(nbd)(PPh3) (1e), and Rh(2,6-Me2C6H3)(nbd)(PPri3)
(1g). These complexes were prepared by the similar method
described above. Yields and spectral data were as follows.
Complex 1b: Yield 85%. 1H NMR: δ 7.34-7.17 (m, 15H, Ph),
6.56 (s, 2H, Ar), 5.12 (s, 2H, dCH of nbd), 4.01 (sep, J ) 6.4 Hz,
2H, CH of Pri), 3.81 (s, 2H, CH of nbd), 3.46 (s, 2H, dCH of
nbd), 2.76 (sep, J ) 6.7 Hz, 1H, CH of Pri), 1.54 (d, J ) 7.6 Hz,
1H, CH2 of nbd), 1.33 (d, J ) 6.3 Hz, 7H, CH2 of nbd and CH3),
1.22 (d, J ) 6.9 Hz, 7H, CH3). 13C NMR: δ 166.1 (dd, J ) 35, 12
Hz, Cipso-Rh of Ar), 153.3 (s, Cipso-C of Ar), 143.5 (s, Cipso-C
of Ar), 134.0 (d, J ) 33 Hz, Cipso-P of Ph), 133.9 (d, J ) 12 Hz,
Ph), 129.1 (s, Ph), 128.0 (d, J ) 9 Hz, Ph), 119.7 (s, Ar), 75.4 (t,
J ) 9 Hz, dCH of nbd), 70.4 (d, J ) 6 Hz, dCH of nbd), 66.6 (s,
CH2 of nbd), 51.4 (s, CH of nbd), 37.3 (s, CH of Pri), 33.9 (s, CH
of Pri), 26.6 (s, CH3), 24.8 (s, CH3), 23.6 (s, CH3). 31P NMR: δ
27.8 (d, JP-Rh ) 191 Hz). Anal. Calcd for C40H46PRh: C, 72.72;
H, 7.02; P, 4.69. Found: C, 72.55; H, 7.24; P, 4.50.
In conclusion, we developed the novel living polymerization
of aryl isocyanides having bulky substituents at the ortho
position by using well-defined Rh complexes with bulky aryl
groups. Kinetic studies provided not only evidence of the living
nature of the present system but also the mechanistic aspects.
Further studies focusing on the properties of polyisocyanides
prepared by this system are in progress.
1
Complex 1c: Yield 74%. H NMR: δ 7.69-7.65 (m, 2H, Ar),
7.32-7.25 (m, 9H, Ph), 7.19-7.13 (m, 7H, Ar and Ph), 7.00 (d, J
) 7.3 Hz, 1H, Ar), 6.93 (t, J ) 8.5 Hz, 1H, Ar), 6.83 (t, J ) 7.2
Hz, 3H, Ar), 6.76 (t, J ) 6.8 Hz, 1H, Ar), 4.84-4.81 (m, 1H, nbd),
3.76-3.75 (m, 3H, nbd), 3.68 (s, 1H, nbd), 3.59-3.58 (m, 1H,
nbd), 1.46 (d, J ) 7.8 Hz, 1H, CH2 of nbd), 1.26 (d, J ) 5.1 Hz,
Experimental Section
General Procedures. All reactions were carried out under argon
atmosphere, but the workup was performed in air. 1H, 13C, and 31
NMR spectra were measured on JEOL JNM-LA400 Bruker
ARX400 spectrometers using CDCl3 as solvent. Chemical shifts
are based on SiMe4 as the internal standard for H and 13C NMR,
and 85% H3PO4 as the external standard for 31P NMR. IR spectra
were recorded on a Perkin-Elmer system 2000 FT-IR. Elemental
analyses were performed by the Material Analysis Center, ISIR,
Osaka University. Molecular weight was measured by a Shimadzu
LC-6AD liquid chromatograph equipped with Shimadzu GPC-805,
-804, and -8025 columns. THF was used as an eluent at a flow
rate of 1.0 mL/min. The average molecular weights (Mn and Mw)
were determined using polystyrene standards.
THF and diethyl ether used for the reactions were distilled over
benzophenone ketyl under argon immediately before use. Pyridine
was distilled over KOH and stored over molecular sieves (MS 4A).
All other chemicals available commercially were used without
P
1H, CH2 of nbd). 13C NMR: δ 172.1 (dd, J ) 34, 14 Hz, Cipso
-
Rh of Ar), 147.9 (s, Cipso-C of Ar), 146.8 (s, Cipso-C of Ar), 136.1
(s, Ar), 134.3 (d, J ) 34 Hz, Cipso-P of Ph), 133.5 (d, J ) 12 Hz,
Ph), 128.9 (d, J ) 1 Hz, Ph), 128.6 (s, Ar), 127.7 (d, J ) 9 Hz,
Ph), 126.7 (s, Ar), 126.0 (s, Ar), 124.6 (s, Ar), 122.1 (s, Ar), 121.4
(s, Ar), 74.0 (d, J ) 6 Hz, dCH of nbd), 72.3 (s, dCH of nbd),
70.9 (d, J ) 14 Hz, dCH of nbd), 64.5 (t, J ) 5 Hz, CH2 of nbd),
55.7 (dd, J ) 19, 7 Hz, dCH of nbd), 50.6 (d, J ) 6 Hz, CH of
nbd), 50.3 (d, J ) 3 Hz, CH of nbd). 31P NMR: δ 26.7 (d, JP-Rh
) 187 Hz). Anal. Calcd for C37H32PRh: C, 72.79; H, 5.28; P, 5.07.
Found: C, 72.99; H, 5.78; P, 5.10.
1
(15) Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1976, 98, 2134.
(16) (a) Suginome, M.; Fukuda, T.; Ito, Y. Org. Lett. 1999, 1, 1977. (b)
Rainier, J. D.; Kennedy, A. R.; Chase. E. Tetrahedron Lett. 1999, 40, 6325.

LiVing Polymerization of Bulky Aryl Isocyanide
Organometallics, Vol. 25, No. 5, 2006 1277
Complex 1d: Yield 26%. 1H NMR: δ 8.80 (d, J ) 7.9 Hz, 1H,
Ar), 7.51 (d, J ) 7.9 Hz, 1H, Ar), 7.23-7.10 (m, 18H, Ar and
Ph), 6.80 (d, J ) 7.9 Hz, 1H, Ar), 5.09-5.08 (m, 1H, dCH of
nbd), 4.88-4.85 (m, 1H, dCH of nbd), 3.94 (s, 2H, CH of nbd),
3.88 (s, 1H, dCH of nbd), 3.80 (s, 1H, dCH of nbd), 2.59 (s, 3H,
CH3), 1.55 (d, J ) 7.9 Hz, 1H, CH2 of nbd), 1.41 (d, J ) 7.9 Hz,
Anal. Calcd for C11H14INO: C, 43.58; H, 4.66; N, 4.62. Found:
C, 43.81; H, 4.64; N, 4.41. In solution, the product consists of two
isomers in a ratio of 7:3 due to restricted rotation of the C-N bond.
Major isomer: 1H NMR: δ 8.37 (d, J ) 11.0 Hz, 1H, CHO), 7.73
(d, J ) 2.2 Hz, 1H, Ar), 7.58 (dd, J ) 8.3, 2.2 Hz, 1H, Ar), 7.30
(br, 1H, NH), 6.84 (d, J ) 8.3 Hz, 1H, Ar), 1.40 (s, 9H, CH3). 13
C
1H, CH2 of nbd). 13C NMR: δ 179.0 (dd, J ) 37, 13 Hz, Cipso
-
NMR: δ 163.4 (CHO), 145.7, 136.4, 136.2, 134.3, 127.5, 92.3 (Ar),
34.8 (CCH3), 30.4 (CH3). Minor isomer: 1H NMR: δ 8.47 (d, J )
1.5 Hz, 1H, CHO), 7.70 (d, J ) 2.2 Hz, 1H, Ar), 7.56 (dd, J )
8.4, 2.2 Hz, 1H, Ar), 7.52 (d, J ) 8.4 Hz, 1H, Ar), 7.16 (br, 1H,
NH), 1.42 (s, 9H, CH3). 13C NMR: δ 159.6 (CHO), 144.7, 135.9,
135.7, 133.6, 129.3, 91.7 (Ar), 34.5 (CCH3), 30.3 (CH3).
Rh of Ar), 140.9 (s, Cipso-C of Ar), 138.3 (s, Cipso-C of Ar), 133.6
(d, J ) 12 Hz, Ph), 133.1 (d, J ) 37 Hz, Cipso-P of Ph), 132.2 (s,
Cipso-C of Ar), 129.2 (d, J ) 1 Hz, Ph), 127.7 (d, J ) 9 Hz, Ph),
127.4 (s, Ar), 127.3 (s, Ar), 123.0 (s, Ar), 122.1 (s, Ar), 121.7 (s,
Ar), 79.9 (t, J ) 9 Hz, dCH of nbd), 77.3 (d, J ) 18 Hz, dCH of
nbd), 73.3 (d, J ) 6 Hz, dCH of nbd), 71.7 (d, J ) 6 Hz, dCH of
nbd), 67.2 (t, J ) 4 Hz, CH2 of nbd), 52.2 (s, CH of nbd), 51.9 (s,
CH of nbd), 25.3 (s, CH3). 31P NMR: δ 31.1 (d, JP-Rh ) 189 Hz).
Anal. Calcd for C24H38PRh: C, 62.61; H, 8.32; P, 6.73. Found: C,
62.71; H, 8.45; P, 6.54.
Syntheses of 2-tert-Butyl-4-(octyloxycarbonyl)phenyl Iso-
caynide (8a). A solution of N-(2-tert-butyl-4-iodophenyl)formamide
(6.06 g, 20 mmol), n-octanol (15.8 mL, 100 mmol), Pd(OAc)2 (90
mg, 0.4 mmol), and triethylamine (5 mL) in benzene (10 mL) was
placed in stainless steel autoclave (100 mL) equipped with a stirring
bar. The reactor was purged with CO gas several times and
pressured with CO to 5 atm. The autoclave was heated at 100 °C
with stirring for 16 h. After cooling of the autoclave to room
temperature, excess gases were vented carefully. The reaction
mixture was concentrated under reduced pressure, and the residue
was dissolved in dichloromethane. The solution was passed through
a short alumina column, and the solvent was evaporated. The
resulting yellow oil was dissolved in dichloromethane (50 mL),
and diisopropylamine (4 mL) was added. After cooling in an ice-
bath, phosphorus oxychloride (1.2 mL, 12.8 mmol) was added
dropwise, and the reaction mixture was stirred at 0 °C for 30 min.
To the mixture was slowly added a 10% aqueous solution of
Na2CO3 at 0 °C, and the reaction mixture was extracted with
dichloromethane. The extract was dried over Na2SO4, and the
solvent was evaporated. Column chromatography on alumina using
a mixture of hexane and dichloromethane (v/v ) 5:1) gave a
colorless oil (2.06 g, 65%). IR (cm-1, neat): 2116 (νCtN), 1723
(νC)Ã). 1H NMR: δ 8.12 (d, J ) 1.9 Hz, 1H, Ar), 7.88 (dd, J )
8.2, 1.9 Hz, 1H, Ar), 7.44 (d, J ) 8.2 Hz, 1H, Ar), 4.32 (t, J ) 6.6
Hz, 2H, OCH2), 1.80-1.73 (m, 2H, CH2), 1.52 (s, 9H, CH3), 1.43-
1.29 (m, 10H, CH2), 0.88 (t, J ) 6.8 Hz, 3H, CH3). 13C NMR: δ
172.1 (CdO), 165.3 (CtN), 145.8, 130.9, 129.9, 128.4, 128.2,
127.8 (Ar), 65.4 (OCH2), 35.0 (CCH3 of But), 31.6 (CH3 of But),
29.1, 29.0, 28.9, 28.5, 25.9, 22.5 (CH2), 13.9 (CH3). Anal. Calcd
for C20H29NO2: C, 76.15; H, 9.27; N, 4.44. Found: C, 75.87; H,
9.01; N, 4.52.
1
Complex 1e: Yield 32%. H NMR: δ 9.07-9.04 (m, 2H, Ar),
7.74 (s, 1H, Ar), 7.71-7.68 (m, 2H, Ar), 7.21-7.03 (m, 19H, Ar
and Ph), 5.04-5.01 (m, 2H, dCH of nbd), 4.06 (s, 2H, dCH of
nbd), 4.05-4.00 (m, 2H, dCH of nbd), 1.57 (d, J ) 7.9 Hz, 1H,
CH2 of nbd), 1.46 (d, J ) 8.0 Hz, 1H, CH2 of nbd). 13C NMR: δ
189.0 (dd, J ) 38, 13 Hz, Cipso-Rh of Ar), 138.4 (s, Cipso-C of
Ar), 135.0 (s, Cipso-C of Ar), 133.4 (d, J ) 12 Hz, Ph), 132.8 (d,
J ) 38 Hz, Cipso-P of Ph), 131.7 (s, Cipso-C of Ar), 129.1 (d, J )
2 Hz, Ph), 128.2 (s, Ar), 127.7 (d, J ) 10 Hz, Ph), 123.9 (s, Ar),
120.9 (s, Ar), 119.6 (s, Ar), 79.8 (d, J ) 9 Hz, dCH of nbd), 79.7
(d, J ) 9 Hz, dCH of nbd), 73.2 (d, J ) 6 Hz, dCH of nbd), 67.4
(s, CH2 of nbd), 52.4 (s, CH of nbd). 31P NMR: δ 30.9 (d, JP-Rh
) 186 Hz). Anal. Calcd for C39H32PRh: C, 73.82; H, 5.08; P, 4.88.
Found: C, 73.56; H, 5.09; P, 5.15.
Complex 1g: Yield 96%. 1H NMR: δ 6.77-6.61 (m, 3H, Ar),
4.46-4.45 (m, 2H, dCH of nbd), 4.38 (s, 2H, dCH of nbd), 3.82
(s, 2H, CH of nbd), 2.72 (s, 6H, CH3 of Ar), 2.00-1.91 (m, 3H,
CH of Pri), 1.51 (d, J ) 7.8 Hz, 1H, CH2 of nbd), 1.44 (d, J ) 7.8
Hz, 1H, CH2 of nbd), 1.14 (d, J ) 7.2 Hz, 9H, CH3 of Pri), 1.11
(d, J ) 7.2 Hz, 9H, CH3 of Pri). 13C NMR: δ 177.5 (dd, J ) 35,
13 Hz, Cipso-Rh of Ar), 142.0 (s, Cipso-C of Ar), 133.6 (d, J ) 12
Hz, Ph), 133.4 (d, J ) 34 Hz, Cipso-P of Ph), 129.1 (s, Ph), 127.8
(d, J ) 9 Hz, Ph), 124.5 (s, Ar), 122.2 (s, Ar), 77.7 (t, J ) 9 Hz,
dCH of nbd), 72.1 (d, J ) 7 Hz, dCH of nbd), 67.1 (s, CH2 of
nbd), 51.7 (s, CH of nbd), 25.6 (s, CH3 of Ar). 31P NMR: δ 30.3
(d, JP-Rh ) 191 Hz). Anal. Calcd for C33H38PRh: C, 70.47; H,
5.73; P, 5.51. Found: C, 70.72; H, 5.78; P, 5.40.
Syntheses of 2-tert-Butyl-4-(pentyloxycarbonyl)phenyl Iso-
caynide (8b). This compound was prepared by a method similar
to that described above using n-pentanol instead of n-octanol in
92% yield. IR (cm-1, neat): 2118 (νCtN), 1723 (νC)Ã). 1H
NMR: δ 8.12 (d, J ) 1.9 Hz, 1H, Ar), 7.88 (dd, J ) 8.2, 1.9 Hz,
1H, Ar), 7.44 (d, J ) 8.2 Hz, 1H, Ar), 4.32 (t, J ) 6.6 Hz, 2H,
OCH2), 1.80-1.73 (m, 2H, CH2), 1.52 (s, 9H, CH3), 1.43-1.29
(m, 10H, CH2), 0.88 (t, J ) 6.8 Hz, 3H, CH3). 13C NMR: δ 172.1
(CdO), 165.3 (CtN), 145.8, 130.8, 130.0, 128.4, 128.2, 127.8 (Ar),
65.4 (OCH2), 35.0 (CCH3 of But), 28.9 (CH3 of But), 28.2, 28.0,
22.2 (CH2), 13.8 (CH3). Anal. Calcd for C17H23NO2: C, 74.69; H,
8.48; N, 5.12. Found: C, 74.46; H, 8.19; N, 5.09.
Syntheses of 2-tert-Butyl-4-iodoaniline (5). An aqueous solution
(50 mL) of 2-tert-butylaniline (7.46 g, 50 mmol) and NaHCO3 (7.5
g, 90 mmol) was cooled in an ice-bath, and I2 (12.7 g, 50 mmol)
was added in several portions. The reaction mixture was allowed
to warm to room temperature and stirred for 6 h. After addition of
water, the reaction mixture was extracted with dichloromethane.
The extract was dried over Na2SO4, and the solvent was removed
under reduced pressure. The residue was purified by alumina
column chromatography with hexane to give a red oil (12.7 g, 92%).
IR (cm-1, neat): 3499, 3392 (νN-H). 1H NMR: δ 7.45 (s, 1H, Ar),
7.28 (d, J ) 8.3 Hz, 1H, Ar), 6.41 (d, J ) 8.3 Hz, 1H, Ar), 3.83
(br, 2H, NH2), 1.38 (s, 9H, CH3).
Syntheses of 2-tert-Butyl-4-octyloxyphenyl Isocaynide (8e). To
a solution of octanol (11.8 mL, 75 mmol) in pyridine (50 mL) was
added NaH (60% dispersion in oil, 3.0 g, 75 mmol) at 0 °C, and
the mixture was stirred at room temperature for 1 h. After addition
of N-(2-tert-butyl-4-iodophenyl)formamide (6.88 g, 25 mmol) and
CuI (2.38 g, 12.5 mmol), the mixture was stirred at 100 °C for 15
h. The mixture was cooled to room temperature, and ice-water was
slowly added. The mixture was extracted with dichloromethane,
and the extract was dried over Na2SO4. Evaporation of the solvent
gave a red oil, which was treated with diisopropylamine and
phosphorus oxychloride by a method similar to that used in the
preparation of 2-tert-butyl-4-(octyloxycarbonyl)phenyl isocaynide
Syntheses of N-(2-tert-Butyl-4-iodophenyl)formamide (6).
2-tert-Butyl-4-iodoaniline (6.88 g, 25 mmol) was dissolved in a
mixture of formic acid (50 mL) and acetic anhydride (18 mL), and
the solution was stirred at 60 °C for 2 h. After removal of the
solvent, the residue was dissolved in dichloromethane, and the
solution was neutralized with aqueous NaHCO3. The organic layer
was separated, and the aqueous layer was extracted with dichlo-
romethane. The combined organic layer was dried over Na2SO4,
and the solvent was evaporated. The resulting solid was purified
by recrystallization from dichloromethane/hexane to give a colorless
solid (5.10 g, 67%). IR (cm-1, KBr): 3359 (νN-H), 1682 (νCdO).

1278 Organometallics, Vol. 25, No. 5, 2006
Onitsuka et al.
Table 6. Summary of Crystallographic Data for Complex 1d
to give the title compound (2.47 g, 34%) as a pale yellow oil. IR
(cm-1, neat): 2115 (νCtN). 1H NMR: δ 7.30 (d, J ) 8.5 Hz, 1H,
Ar), 6.9 (d, J ) 2.7 Hz, 1H, Ar), 6.68 (dd, J ) 8.5, 2.7 Hz, 1H,
Ar), 3.94 (t, J ) 6.3 Hz, 2H, OCH2), 1.80-1.74 (m, 2H, CH2),
1.47 (s, 9H, CH3), 1.34-1.29 (m, 10H, CH2), 0.89 (t, J ) 6.8 Hz,
3H, CH3). 13C NMR: δ 167.7 (CtN), 159.1, 147.1, 131.1, 117.8,
113.8, 110.8 (Ar), 68.0 (OCH2), 34.8 (C of But), 31.6 (CH3 of But),
29.1, 29.02, 29.00, 28.98, 28.90, 25.8, 22.5 (CH2), 13.9 (CH3). Anal.
Calcd for C19H29NO: C, 79.39; H, 10.17; N, 4.87. Found: C, 79.15;
H, 9.88; N, 4.62.
empirical formula
fw
C36H32PRh
598.53
cryst dimens/mm
cryst syst
lattice params
a/Å
b/Å
c/Å
0.30 × 0.10 × 0.10
monoclinic
11.42(2)
14.78(3)
17.18(3)
105.5(1)
2795(7)
P21/n (# 14)
4
â/deg
V/Å3
space proup
Z value
Typical Procedure of Polymerization. Complex 1a (5.6 mg,
0.01 mmol) and triphenylphosphine (26 mg, 0.1 mmol) were
dissolved in THF (1.5 mL), and a THF solution (0.5 mL) of 2a
(100 mg, 0.5 mmol) was added. After stirring at 20 °C for 2 h, the
reaction mixture was poured into 50 mL of methanol. The resulting
precipitate was filtered off and washed with methanol to give a
yellow-brown solid of 3aa50 (80 mg, 80%). Physical data of the
representative polymers are as follows.
D
calcd/g cm-3
1.422
F(000)
1232
6.90
µ(Mo KR)/cm-1
no. reflns measd
total
6760
unique
6446 (Rint ) 0.050)
3621 (I > 3.0σ(I))
343
0.052; 0.076
1.14
no. observations
no. params
residuals: R1; wR2
GOF
1
3aa50: IR (cm-1, KBr): 2150 (νCtC), 1613 (νCdN). H NMR:
δ 8.74 (s, 1H, Ar), 7.92 (d, J ) 7.6 Hz, 1H, Ar), 7.34 (d, J ) 7.6
Hz, 1H, Ar), 6.84 (t, J ) 7.6 Hz, 1H, Ar), 2.35 (s, CH3 of terminal
Ar), -0.31 (s, 9H, SiMe3). 13C NMR: δ 162.7 (CdN), 155.4, 136.8,
127.6, 127.0, 124.1, 113.7 (Ar), 102.0, 97.8 (Ct), -0.45 (SiMe3).
Anal. Calcd for [C12H13NSi]50: C, 72.31; H, 6.57; N, 7.03. Found:
C, 72.70; H, 6.51; N, 7.00.
3ba50: IR (cm-1, KBr): 1721 (νCdÃ), 1638 (νCdN). 1H NMR: δ
8.41 (br, 1H, Ar), 8.09 (br, 1H, Ar), 7.52 (br, 1H, Ar), 4.35 (br,
1H, OCH2), 4.19 (br, 1H, OCH2), 1.72-1.69 (m, 2H, CH2), 1.38-
1.11 (m, 10H, CH2), 1.23 (s, 9H, CH3 of But), 0.83 (t, J ) 6.5 Hz,
3H, CH3). 13C NMR: δ 165.9 (CdO), 159.9 (Ar), 158.0 (CdN),
142.1, 130.8, 127.5, 126.4, 124.4 (Ar), 65.1 (OCH2), 35.6 (C of
But), 31.7 (CH3 of But), 29.7, 29.2, 29.1, 28.8, 25.9, 22.6 (CH2),
14.0 (CH3). Anal. Calcd for [C20H29NO2]50: C, 76.15; H, 9.27; N,
4.44. Found: C, 75.95; H, 9.13; N, 4.17.
3bb50: IR (cm-1, KBr): 1722 (νCdÃ), 1636 (νCdN). 1H NMR: δ
8.44 (br, 1H, Ar), 8.12 (br, 1H, Ar), 7.56 (br, 1H, Ar), 4.39 (br,
1H, OCH2), 4.22 (br, 1H, OCH2), 1.74 (br, 2H, CH2), 1.37 (br,
4H, CH2), 1.26 (s, 9H, CH3 of But), 0.90 (br, 3H, CH3). 13C NMR:
δ 166.0 (CdO), 160.0 (Ar), 158.4 (CdN), 142.2, 132.1, 127.3,
126.4, 124.5 (Ar), 65.1 (OCH2), 35.6 (C of But), 29.7 (CH3 of But),
28.5, 28.2, 22.4 (CH2), 14.0 (CH3). Anal. Calcd for [C17H23NO2]50:
C, 74.69; H, 8.48; N, 5.12. Found: C, 74.50; H, 8.38; N, 4.88.
3bc50: IR (cm-1, KBr): 1623 (νCdN). 1H NMR: δ 7.16 (br, 1H,
Ar), 7.13 (br, 1H, Ar), 6.89 (br, 1H, Ar), 3.81 (br, 2H, OCH2),
1.68 (br, 2H, CH2), 1.38 (br, 2H, CH2), 1.21 (br, 10H, CH2), 1.13
(s, 9H, CH3 of But), 0.80 (br, 3H, CH3). 13C NMR: δ 161.0 (Ar),
155.1 (CdN), 149.3, 143.3, 126.0, 118.4, 108.0 (Ar), 67.9 (OCH2),
35.5 (C of But), 31.8 (CH2), 30.1 (CH3 of But), 29.5, 29.2, 26.2,
22.7 (CH2), 14.1 (CH3). Anal. Calcd for [C19H29NO2]50: C, 79.39;
H, 10.17; N, 4.87. Found: C, 79.19; H, 9.94; N, 4.60.
Block Copolymerization. To a THF solution (1 mL) of 1b (6.6
mg, 10 µmol) and triphenylphosphine (1048 mg, 4 mmol) was
added a THF solution (0.5 mL) of 8a (157.7 mg, 0.5 mmol), and
the reaction mixture was stirred at 20 °C for 5 min. After addition
of a THF solution (0.5 mL) of 8c (142.7 mg, 0.5 mmol), the mixture
was stirred for an additional 5 min at the same temperature. The
reaction mixture was poured into methanol (50 mL), and the
resulting precipitate was filtered and washed with methanol. Drying
in vacuo gave a pale yellow solid of 11ba50c50 (283 mg, 94%). IR
peak, hole/e Å-3
0.88, -0.93
(cm-1, KBr): 1717 (νCdÃ), 1634 (νCdN). 13C NMR: δ 165.3 (Cd
O), 160.1 (Ar), 158.5 (CdN), 141.9, 130.8, 127.4, 126.8, 124.6
(Ar), 73.4 (OCH2), 36.4 (CH2 of octyl), 35.5 (C of But), 31.6 (CH2
of octyl), 29.7 (CH3 of But), 29.1 (CH2 of octyl), 25.4 (CH2 of
octyl), 23.2 (CH2 of Cy), 22.5 (CH2 of octyl), 20.2 (CH3 of octyl),
14.0 (CH3 of octyl). Anal. Calcd for [C38H52N2O4]50: C, 75.96; H,
8.72; N, 4.66. Found: C, 75.71; H, 8.59; N, 4.62.
Typical Procedure for the Kinetic Study. To a solution of 1b
(6.6 mg, 10 µmol), PPh3 (26 mg, 0.1 mmol), and naphthalene
(internal standard, 39.9 mg, 0.31 mmol) in THF (1.5 mL) was added
8a (157.7 mg, 0.5 mmol) in THF (0.5 mL) at 293 K. The reaction
mixture was kept at the same temperature, and the reaction course
was followed by gel permeation chromatography using a UV
detector (254 nm). The conversion of the reaction was determined
by peak integration of the unreacted monomer and naphthalene.
X-ray Diffraction Analyses of Complex 1d. A crystal suitable
for X-ray diffraction was mounted on a glass fiber with epoxy resin.
All measurements were performed on a Rigaku AFC7R automated
four-circle diffractometer using graphite-monochromated Mo KR
radiation (λ ) 0.71069 Å). A summary of crystallographic data is
given in Table 6. Additional information on the collection of the
data and the refinement of the structures is available as the
Supporting Information.
Acknowledgment. This work was partially supported by a
Grant-in-Aid for Scientific Research from the Ministry of
Education, Culture, Sports, Science and Technology. We thank
the members of the Material Analysis Center, ISIR, Osaka
University, for spectral measurements, microanalyses, and X-ray
crystallography.
Supporting Information Available: Details of crystallographic
work (CIF file). This material is available free of charge via the
Internet at http://pubs.acs.org.
OM0509692