Syntheses and structures of bulky monophosphine-ligated methylpalladium complexes: Application to homo- and copolymerization of norbornene and/or methoxycarbonylnorbornene

Article abstract of DOI:10.1021/om060347w

Several new bulky monophosphine-ligated methylpalladium complexes were synthesized. Treatment of Pd(cod)MeCl (cod = cyclooctadiene) with bulky phosphines, P^tBu₃, or P(o-tol)₃ afforded monophosphine-ligated methylpalladium

Full text of DOI:10.1021/om060347w

4588
Organometallics 2006, 25, 4588-4595
Syntheses and Structures of Bulky Monophosphine-Ligated
Methylpalladium Complexes: Application to Homo- and
Copolymerization of Norbornene and/or
Methoxycarbonylnorbornene
Makoto Yamashita, Ikuko Takamiya, Koichiro Jin, and Kyoko Nozaki*
Department of Chemistry and Biotechnology, Graduate School of Engineering, The UniVersity of Tokyo,
7-3-1 Hongo, Bunkyo-ku, 113-0033 Tokyo, Japan
ReceiVed April 18, 2006
Several new bulky monophosphine-ligated methylpalladium complexes were synthesized. Treatment
of Pd(cod)MeCl (cod ) cyclooctadiene) with bulky phosphines, PtBu3, or P(o-tol)3 afforded monophos-
phine-ligated methylpalladium chloride complexes 1a and 1b, which were isolated as crystalline solids
in excellent yields. The structures depended on the shape of the ligand: a mononuclear three-coordinate
structure for 1a and a chloride-bridged dinuclear structure for 1b. Absorption of chloride from
methylpalladium chloride complexes 1a and 1b afforded the corresponding methylpalladium triflate
complexes 2a and 2b, which were structurally characterized by NMR spectroscopy and X-ray
crystallography. In the presence of NaB[3,5-(CF3)2C6H3]4, 1a and 1b catalyzed the addition homopo-
lymerization of norbornene or methoxycarbonylnorbornene. The activity of the catalyst was found to be
dependent on the structure of the complexes and the counteranions. The catalyst system 1a-NaB[3,5-
(CF3)2C6H3]4 was also active for the copolymerization of norbornene and methoxycarbonylnorbornene
to form a block-type copolymer. The obtained copolymer has the highest ester content probably due to
the two vacant sites on the palladium. The molecular weight distribution reached the narrowest value,
indicating the long lifetime of the catalyst.
plexes: (1) solvent-coordinated dicationic palladium, [Pd-
(NCMe)4]X2 (X ) BF4, SbF6),3 (2) cationic allylpalladium [(η3-
allyl)Pd]X2 (X ) counteranion),4,5 (3) olefin-coordinated cationic
norbornylpalladium,6,7 (4) PPh3-ligated cationic methylpalladium
complex, where the active catalyst was assumed to be “[(Ph3P)-
PdMe]B[3,5-(CF3)2C6H3]4”,8,11 (5) phosphine-ligated cationic
allylpalladium complex [(η3-allyl)Pd(PR3)]B(C6F5)4 (R ) alkyl,
aryl),9 and (6) cationic cyclooctadiene methylpalladium complex
[(cod)PdMe]B[3,5-(CF3)2C6H3]4.10
Introduction
Late transition metal catalysts, such as nickel and palladium,
are active for the addition polymerization of norbornenes.1
Recently, the less oxophilic character of the late transition metal
has been considered to be effective for the polymerization of
heteroatom-functionalized monomers.2 However, the rate of
polymerization of functionalized norbornene3-11 is apparently
slower than that of the unsubstituted norbornene. This decelera-
tion may be due to the coordination of functional group to the
metal center to form a strong chelate.8,11 The examples of nickel
and palladium catalysts that can polymerize methoxycarbonyl-
norbornene are classified into the following types of com-
Over the past few years, bulky monophosphines are widely
known as the ligands that develop active catalyst systems in
palladium-catalyzed reactions.12-50 For example, the palladium-
* To whom correspondence should be addressed. E-mail: nozaki@
chembio.t.u-tokyo.ac.jp.
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10.1021/om060347w CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/17/2006

Bulky Monophosphine-Ligated Methylpalladium Complexes
Organometallics, Vol. 25, No. 19, 2006 4589
catalyzed coupling reactions of aryl halides with organometallic
species or amines were accelerated using bulky monophosphines
as ligands.24,30,34,51-53 Various bulky monophosphine-ligated
palladium complexes, LPd(R)X [L ) monophosphine, R ) aryl,
allyl, X ) halogen or heteroatom], were isolated as reaction
intermediates.37,51-53 In contrast to the intensive studies of aryl
or allyl complexes, corresponding alkyl complexes have never
been isolated54 until we have recently reported the syntheses of
methylpalladium complexes bearing a monodentate phosphine
ligand.55 Thus, we became interested in the structures and
catalytic properties of monophosphine-ligated alkylpalladium
complexes for the polymerization of functionalized norbornene.
Bulky monophosphine-ligated arylpalladium complexes,
(R3P)Pd(Ar)X,51-53 were reported to have a formal vacant site
to form a T-shape, three-coordinate structure around the
palladium atom. The vacant site may be useful for the
polymerization of methoxycarbonylnorbornene in the following
two points. (1) A large monomer, norbornene, can coordinate
to the vacant site to lead to a high catalytic activity. (2) The
monomer can approach the metal center even in the presence
of an intramolecularly coordinated functional group, such as
an ester group.
Here we report the syntheses and full structural characteriza-
tions of bulky monophosphine-ligated methylpalladium com-
plexes and their applications to homo- and copolymerization
of norbornene and/or methoxycarbonylnorbornene.
Results and Discussion
Syntheses of Monophosphine-Ligated Methylpalladium
Chloride Complexes 1a and 1b. The syntheses of monophos-
phine-ligated methylpalladium chloride complexes are shown
in Scheme 1. Simple ligand exchange reactions of Pd(cod)MeCl
(cod ) cyclooctadiene)56,57 with bulky phosphines tBu3P or (o-
tol)3P gave the corresponding methylpalladium chloride com-
plexes 1a and 1b, which were isolated as crystalline solids in
excellent yields.
(24) Yin, J.; Rainka, M. P.; Zhang, X.-X.; Buchwald, S. L. J. Am. Chem.
Soc. 2002, 124, 1162-1163.
Scheme 1. Syntheses of Methylpalladium Chloride
Complexes (1a and 1b)
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Single crystals of 1a and 1b suitable for X-ray crystal-
lographic analysis were obtained from a CCl4 solution of 1a or
a CHCl3 solution of 1b diffused by hexane at 0 °C. The crystal
structures of the complexes 1a and 1b are presented in Figures
1 and 2, respectively. Selected bond lengths and angles are
shown in Table 1. The X-ray crystallography revealed that
complex 1a has a three-coordinate T-shape structure stabilized
by a weak C-H agostic interaction between the palladium atom
and a C-H bond of the tert-butyl group. This is the first example
of a three-coordinate alkylpalladium complex. An electron-
donating methyl ligand was located trans to the formal vacant
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1
reported aryl palladium complex Pd(PtBu3)PhBr.52 In the H
NMR spectrum at room temperature, the tert-butyl groups of
1a were all equivalent, indicating free rotation of both the Pd-P
and P-C bond on the NMR time scale. In contrast to 1a,
complex 1b has a Cl-bridged dinuclear structure where half of
the molecule is in the unit cell. Despite the bulkiness of the
ligands, bond lengths and angles around the central palladium
atom in 1b are similar to those of usual Cl-bridged dinuclear
complexes.58-62 One of the two Pd-Cl bonds, Pd(1)-Cl(1), is
shorter than Pd(1)-Cl(1*). Thus, one can expect the longer Pd-
(1)-Cl(1)* bond cleavage in 1b to lead to the equilibrium
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A. L. J. Chem. Soc., Dalton Trans. 2002, 4726-4731.

4590 Organometallics, Vol. 25, No. 19, 2006
Yamashita et al.
Scheme 2. Syntheses of Methylpalladium Triflate
Complexes (2a and 2b)
Figure 1. ORTEP drawing of 1a (all hydrogen atoms except for
H5 are omitted for clarity).
Figure 3. ORTEP drawing of 2a (all hydrogen atoms except for
H5 are omitted for clarity).
Figure 2. ORTEP drawing of 1b (all hydrogen atoms are omitted
for clarity).
Table 1. Selected Bond Distances (Å) and Angles (deg) for
Complexes 1a and 1b
1a
1b
Pd(1)-C(1)
1.985(5)
2.245(3)
2.336(3)
2.029(5)
2.249(4)
2.416(4)
2.455(4)
87.70(19)
85.77(19)
172.27(4)
Pd(1)-P(1)
Pd(1)-Cl(1)
Pd(1)-Cl(1)*
C(1)-Pd(1)-Cl(1)
C(1)-Pd(1)-P(1)
P(1)-Pd(1)-Cl(1)
Figure 4. ORTEP drawing of 2b (all hydrogen atoms are omitted
for clarity).
92.98(16)
97.50(16)
169.40(5)
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Complexes 2a and 2b
between the dinuclear complex and the corresponding mono-
nuclear complex LPd(Me)Cl, which has a three-coordinate
structure similar to that of 1a as reported for the equilibrium in
[(o-tol)3PPd(p-tol)Br]2.63 In 1b, it was indicated that free rotation
of both the Pd-P and P-C bond is inhibited, because the three
methyl signals of the ligand are inequivalent and broadened in
its 1H NMR spectrum, as was observed for [(o-tol)3PPd(p-tol)-
Br]2.63 Lowering the temperature of the CD2Cl2 solution of 1b
to -80 °C resulted in three clearly separated peaks for the
methyl group of the o-tol groups and two separated peaks for
the methyl group on the palladium.
2a
2b
Pd(1)-C(1)
2.002(2)
2.2277(6)
2.1640(15)
2.013(2)
Pd(1)-P(1)
2.2157(7)
2.1889(14)
2.2391(14)
89.46(7)
86.09(7)
175.49(4)
Pd(1)-O(1)
Pd(1)-O(2)*
C(1)-Pd(1)-O(1)
C(1)-Pd(1)-P(1)
O(1)-Pd(1)-P(1)
86.07(9)
97.16(8)
175.33(4)
AgOTf in CH2Cl2 formed corresponding methylpalladium
triflate complexes 2a and 2b in excellent to moderate yields
(Scheme 2).
Synthesis of Monophosphine-Ligated Methylpalladium
Triflate Complexes 2a and 2b. To compare the counteranion
effect for the structure and reactivity, methylpalladium triflate
complexes were also synthesized. Treatment of 1a and 1b with
The crystal structures of complexes 2a and 2b are presented
in Figures 3 and 4, respectively. Selected bond lengths and
angles are shown in Table 2. It was found that 2a has a
mononuclear structure stabilized by a C-H bond agostic
interaction, like 1a. There was no significant difference of the
(63) Paul, F.; Joe, P.; Hartwig, J. F. Organometallics 1995, 14, 3030-
3039.
1
bond lengths and angles between 1a and 2a. From H NMR

Bulky Monophosphine-Ligated Methylpalladium Complexes
Organometallics, Vol. 25, No. 19, 2006 4591
Table 3. Polymerization of Norbornene by 1a, 1b, 2a, and
2ba
Scheme 3. Reaction of 1a with NaBAr4 or AgBAr4
Pd
time yield
(%) TOFc
entry complex Pd (mol %) additiveb T (°C) (h)
Scheme 4. Possible Equilibrium Containing Cationic
Complex 3a
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1b
1b
1b
2a
2a
2a
2b
1.7 × 10-1 NaBAr4
1.7 × 10-2 NaBAr4
1.7 × 10-3 NaBAr4
1.7 × 10-3 NaBAr4
1.7 × 10-1 NaBAr4
1.7 × 10-2 NaBAr4
1.7 × 10-3 NaBAr4
1.7 × 10-1 none
rt
rt
rt
0
rt
rt
rt
rt
rt
40
rt
2
2
2
6
2
2
2
2
6
2
2
95
94
88
95
90
52
0
16
21
43
0
280
2800
26000
9300
270
1500
47
21
130
9
10
11
1.7 × 10-1 none
Table 4. Polymerization of the Methyl Ester of Norbornene
1.7 × 10-1 none
a
Carboxylic Acid by 1a-NaBAr4
1.7 × 10-1 none
a Norbornene (5.8 mmol) was used. Molecular weight was not determined
due to the low solubility of most of the products in organic solvents. b Pd/
NaBAr4 ) 1. c Calculated as (molNB in polymer) molPd h-1
.
-1
entry solvent Pd (mol %) yield (%) TOFc
Mn
Mw/Mn
spectrum, it was clear that the tert-butyl groups of 2a were all
equivalent, like 1a, and the chemical shifts of both complexes
were similar. Despite the very weak coordinating ability of the
triflate anion, triflate anions existed as bridging ligands in 2b,
which is the first example of a triflate-bridged Pd dinuclear
structure. The dinuclear structure is in contrast to the mono-
nuclear structure of the only example of a (o-tol)3P-ligated
palladium triflate complex, [(o-tol)3P]Pd(η3-allyl)OTf.9 Methyl
groups on the phosphine in the 1H NMR spectrum of 2b showed
a broad peak similar to the case of 1b. One can also expect that
there is an equilibrium between 2b and its corresponding
mononuclear structure; however, there was no proof from NMR.
Polymerization of Norbornene (NB). Complexes 1a, 1b,
2a, and 2b were examined as catalytst precursors for the
homopolymerization of NB.1 The results are summarized in
Table 3. The polymerization did not take place using 1a or 1b
in the absence of any additives. In the presence of NaB(3,5-
(CF3)2C6H3)4 (NaBAr4),64 both 1a and 1b showed catalytic
activity. Catalyst loading could be lowered to 1.7 × 10-3 mol
% of 1a to afford polyNB in excellent yields (entries 1-3).
Longer reaction time and lower temperature improved the yield
(entry 4). The complex 1b displayed moderate catalytic activity
when the catalyst loading was decreased (entries 5-7). In the
case of triflate complexes 2a and 2b, only 2a showed catalytic
activity without NaBAr4 (entry 8). Extension of the reaction
time or elevation of the temperature slightly improved the yield
(entries 9, 10). The result that catalytic activity of 2a was lower
than the 1a-NaBAr4 system indicated that one of the most
1
2
3
4
CHCl3
CHCl3
1.7 × 10-1
CH2Cl2 1.7 × 10-1
13
77
20
54
38
45
59
54
9300
14 000
14 000
19 000
1.3
1.5
2.1
1.3
8.5 × 10-1
CH2Cl2 8.5 × 10-1
a NBE (5.8 mmol) was treated with 1a. b Pd/NaBAr4 ) 1. c Calculated
-1
as (molNBE in polymer) molPd h-1
.
Figure 5. Plot of conversion vs Mn and Mw/Mn in the polymeri-
zation of NBE using 1a-NaBAr4 in CDCl3 at room temperature
(solid circle: Mn; solid square: Mw/Mn).
of NaBAr4 at room temperature, and the resulting mixture was
1
analyzed by H, 31P, 13C, 19F, and 11B NMR spectra.68 All
multinuclear NMR spectra of these two reaction mixtures were
identical. The integration in the 1H NMR spectra indicated the
ratio of the methyl on the palladium to BAr4 to be 1:2. These
results are consistent with the formation of the Cl-bridged
dinuclear complex 3 shown in Scheme 3. A similar Cl-bridged
dinuclear structure of a palladium complex was reported in the
literature.69 An isolated green powder from the reaction of 1a
with AgBAr4 afforded the same results, indicating the formation
-
weakly coordinating counteranions such as B(3,5-(CF3)2C6H3)4
was necessary to afford active species. The obtained polymers
were insoluble in common organic solvents except entries 1, 5,
8, 9, and 10. The 1H NMR spectra of all soluble polymers were
proven to have no olefinic protons, suggesting that the polym-
erization proceeded via addition-type chain propagation, not via
ring-opening metathesis polymerization (ROMP).65 Broadening
1
(66) Zhu, Y. Z.; Liu, J. Y.; Li, Y. S.; Tong, Y. J. J. Organomet. Chem.
2004, 689, 1295-1303.
of all aliphatic regions in the H NMR spectra indicates that
the obtained polymer is atactic.66 The highest activity of 26 000
(67) The best TOF of palladium catalyst ever reported for norbornene
-1
molNB molPd h-1 was achieved in entry 3.1,67
-1
polymerization is 10 000 000 molNB molPd h-1; see ref 6.
(68) The related multinuclear NMR studies were reported for the
activation process of precatalyst, L2PdCl2, or polychlorinated anionic
palladium complexes, using B(C6F5)3 in the polymerization of norbornene.
(a) Lassahn, P. G.; Lozan, V.; Wu, B.; Weller, A. S.; Janiak, C. Dalton
Trans. 2003, 4437-4450. (b) Lassahn, P. G.; Lozan, V.; Janiak, C. Dalton
Trans. 2003, 927-935.
Reaction of 1a with NaBAr4. To identify the active species
in the polymerization of NB, 1a was treated with 1 or 0.5 equiv
(64) Bahr, S. R.; Boudjouk, P. J. Org. Chem. 1992, 57, 5545-5547.
(65) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18-29.

4592 Organometallics, Vol. 25, No. 19, 2006
Yamashita et al.
Table 5. Copolymerization of Norbornene (NB) with the Methyl Ester of Norbornene Carboxylic Acid (NBE) by 1a-NaBAr4
NBEa content
yieldb (NB)
yieldc (NBE)
yieldd (total)
TOFe
Mn
Mw/Mn
f
f
entry
Pd (mol %)
NB/NBE
1
2
3
4
1.7 × 10-1
1.7 × 10-1
1.7 × 10-2
1.7 × 10-2
50/50
80/20
50/50
80/20
0.29
0.13
0.11
0.09
96
92
78
95
39
55
10
38
68
84
44
84
200
250
1600
2300
53 000
56 000
1.3
1.3
1.2
1.1
140 000
120 000g
a NBE content in the copolymer ) b/(a + b), determined by 1H NMR. b Mol of NB in the copolymer/mol of starting NB. c Mol of NBE in the copolymer/
-1
mol of starting NBE. d Mol of NB + NBE in copolymer/mol of starting NB + NBE. e Calculated as (molNB+NBE in copolymer) molPd h-1 f Polystyrene
.
standard in THF. g Polystyrene standard in CHCl3.
Figure 7. Estimated structure of the obtained NB/NBE copolymer.
slightly deviates from the line at high conversion of >70%
probably due to the high viscosity of the reaction solution. The
higher molecular weight distribution in Table 4 than those in
Figure 4 may be attributed to the decomposition of the catalyst
at higher temperature under the conditions of Table 4.
Copolymerization of NB and NBE. The copolymeriza-
tion4,5,7,71 of NB with NBE was examined with the catalyst 1a-
NaBAr4. Copolymerization reactions were carried out with a
50/50 or 80/20 molar ratio (NB/NBE) in CHCl3 at room
temperature for 2 h (Table 5). The NBE content was determined
from the integral ratio of the methoxy group of the ester unit to
1
all the aliphatic protons in H NMR spectra. For quantitative
discussion, we calculate a series of yields based on (1) mol of
NB in copolymer/mol of starting NB, (2) mol of NBE in
copolymer/mol of starting NBE, and (3) mol of NB + NBE in
copolymer/mol of starting NB + NBE (Table 5).
Figure 6. Change of vinylic protons in the 1H NMR spectra during
the copolymerization of NB and NBE with conditions for entry 1
in Table 5. Values of the integral were calculated from the ratio of
each peak to an added ferrocene as internal standard.
The NBE content was 0.29, and 96% of starting NB and 39%
of starting NBE were incorporated into the obtained copolymer
when the reaction was started from NB/NBE ) 50/50 (entry
1). Reducing NBE to a molar ratio of NB/NBE ) 80/20 led to
a decrease of the NBE content to 0.13 (entry 2). It should be
noted that, although the NBE content was lowered, the
incorporated starting NBE monomer was increased (55%, entry
2). Decreasing the amount of catalyst to 1.7 × 10-2 mol %
with NB/NBE ) 50/50 (entry 3) led to a higher TOF (1600)
and Mw (140 000). These higher TOF and Mw come from the
increased monomer/catalyst ratio and the fast polymerization
of NB. The same catalyst loading with NB/NBE ) 80/20
afforded the highest TOF and the lowest NBE content (entry
4). The highest TOF may come from the larger NB/catalyst
ratio, and the lowest NBE content may come from decreasing
the polymerization rate of NBE due to lower concentration of
NBE, as was observed in the yield (NBE).
The copolymerization rate was comparable to those in the
previous examples using palladium or nickel complexes without
phosphine ligands.4,5,7,71 In other words, the vacant site(s) of
the metal center remained reactive, if only one phosphine ligand
exists per metal center. As a result, the highest NBE content
ever reported4,72 was achieved in entry 1. It seems that the Pd
complex was barely poisoned when one of the vacant coordina-
tion sites was occupied by the ester group. In addition, the
narrowest molecular weight distributions of 1.1 could be
achieved.4,5,7,71
of 3 even in the reaction with excess amounts of the silver salt.
One can expect the dissociation equilibrium of 3 to produce
cationic species 4 or olefin-coordinated cationic species 4′ as
an active catalyst (Scheme 4). In the presence of an excess of
NaBAr4 and olefinic monomers, 1a may be completely con-
verted to 4 or 4′.
Polymerization of the Methyl Ester of Norbornene Car-
boxylic Acid (NBE). The most active catalyst 1a-NaBAr4 for
polymerization of NB also catalyzed the polymerization of NBE
(endo/exo ) 1.1/1.0). The results were summarized in Table 4.
When CH2Cl2 was used as a solvent, the activity was slightly
increased from that with CHCl3. Higher catalyst loadings were
required to obtain higher yields than that in the polymerization
of norbornene (entries 2 and 4). All the obtained polymeric
materials were analyzed by NMR spectroscopy. Most probably,
the polymer is soluble in CHCl3 and was atactic because the
polymer has broadened peaks, as was observed in the previous
examples.4,5,7 The highest activity of 59 molNBE molPd h-1
-1
was achieved in entry 3.6,70 even in the presence of the formal
vacant site on the central palladium. A plot of conversion versus
molecular weight was confirmed to be linear when the polym-
erization was carried out at room temperature in CDCl3, which
is characteristic for living polymerization (Figure 5). The plot
(69) Foley, S. R.; Shen, H.; Qadeer, U. A.; Jordan, R. F. Organometallics
2004, 23, 600-609.
(70) The best TOF of a palladium catalyst ever reported for polymeri-
(71) Suzuki, H.; Matsumura, S.-i.; Satoh, Y.; Sogoh, K.; Yasuda, H.
React. Funct. Polym. 2004, 58, 77-91.
zation of NBE is 310 molNBE molPd h-1; see ref 4.
-1

Bulky Monophosphine-Ligated Methylpalladium Complexes
Organometallics, Vol. 25, No. 19, 2006 4593
were carried out using a GL Sciences instrument (HPLC pump
PU610, LC columns oven Model556) equipped with a Shodex SE-
61 RI detector, SIV GPC board, and two columns (Shodex KF-
804L). The GPC columns were eluted with tetrahydrofuran at 40
°C at 1 mL/min. Chloroform, dichloromethane, hexane, and
tetrahydrofuran were purchased as dehydrated solvents from Kanto
Chemical. The other chemicals were used as received from the
chemical company. Pd(cod)MeCl,6 NaB(3,5-(CF3)2C6H3)4,64 and
The NBE content of 0.29 in entry 1 was higher than 0.11 in
entry 3. This corresponds to the higher reactivity of NB than
that of NBE. If the copolymer had a random character to afford
a similar consumption rate of each comonomer, the obtained
copolymer would have similar composition and lead to similar
NBE content.
1
Monitoring the Copolymerization by H NMR Spectros-
copy. To check the relative consumption rate of comonomers
qualitatively, the copolymerization reaction was monitored by
1H NMR spectroscopy. Under the conditions in entry 1 of Table
5, a faster consumption of the NB peak at δ 5.96 than that of
the NBE peaks was observed in the 1H NMR monitoring of the
copolymerization (Figure 6). The consumption of NB was much
faster than that of NBE. Additionally, the obtained copolymer
showed a monomodal peak in each GPC analysis. These results
suggest that poly(NB) grew up first with some incorporation
of NBE until most of the NB monomer was consumed, and
then the poly(NBE) chain propagated slowly. This means the
obtained copolymer may have a diblock-type character, which
consists of a polyNB part containing a little NBE and a polyNBE
part (Figure 7).
73
AgB(3,5-(CF3)2C6H3)4 were prepared as previously reported.
Syntheses of Three-Coordinated Methylpalladium Chloride
t
Complexes. Synthesis of Bu3PPd(Me)Cl (1a). In a globebox, to
a mixture of tBu3P (0.411 g, 2.03 mmol) and (cod)Pd(Me)Cl (0.539
g, 2.03 mmol) was added CH2Cl2 (1 mL) at room temperature.
The reaction mixture was stirred at room temperature for 5 min
and was poured into vigorously stirred hexane to precipitate a
yellow solid. The resulting solid was isolated by filtration to give
the desired product (0.560 g, 84%): 1H NMR (CDCl3, 500 MHz)
δ 1.49 (d, J ) 13 Hz, 27H), 1.75 (d, J ) 0.8 Hz, 3H); 13C{1H}
NMR (CDCl3, 125 MHz) δ -1.90 (CH3), 31.8 (d, J ) 3.8 Hz,
CH3), 39.8 (d, J ) 11 Hz, 4°); 31P{1H} NMR (CDCl3, 202 MHz)
δ 70.1 (s); mp 163.2-164.8 °C (dec). Anal. Calcd for C13H30-
ClPPd: C, 43.47; H, 8.42. Found: C, 43.47; H, 8.29.
Conclusion. Four new monophosphine-ligated methylpalla-
dium complexes, 1a,b [LPd(Me)Cl]n (n ) 1 or 2), and 2a,b
[LPd(Me)OTf]n (n ) 1 or 2) were synthesized and structurally
characterized. X-ray crystallography revealed that 1a and 2a
are the first examples of three-coordinate alkylpalladium
complexes. 1b was proven to have a chloride-bridged dinuclear
structure. It was first shown that triflate anions were able to
exist as bridging ligands to the palladium atom in 2b. The
combination of 1a and NaBAr4 is highly active for the
homopolymerization of norbornene (NB). The system 1a-
NaBAr4 also catalyzed the polymerization of methoxycarbon-
ylnorbornene (NBE). The obtained copolymer was endowed
with the highest ester content ever reported, possibly because
the palladium center with a monodentate ligand was barely
poisoned by the ester coordination. At the same time, the
narrowest molecular weight distribution was achieved for the
copolymer, possibly due to the long lifetime of the ligated metal
complex.
Synthesis of {[(o-tol)3P]Pd(Me)Cl}2 (1b). To a mixture of (o-
tol)3P (0.660 g, 2.16 mmol) and (cod)Pd(Me)Cl (0.574 g, 2.17
mmol) was added CH2Cl2 (4 mL) at room temperature. The reaction
mixture was stirred at room temperature for 4 h and was poured
into vigorously stirred hexane to precipitate an off-white solid. The
resulting solid was isolated by filtration through a filtering paper
to give the desired product (0.907 g, 91%): 1H NMR (CDCl3, 500
MHz) δ 0.35-0.65 (br s, 3H), 1.45-3.55 (br, 9H), 6.95-7.65 (br,
12H); 13C{1H} NMR (CDCl3, 125 MHz) δ 4.8-6.7 (br, CH3),
22.8-25.3 (br, CH3), 124.4-126.6 (CH), 128.1-129.7 (br, 4°),
131.0-133.0 (br, CH), 142.0-144.4 (br, 4°); 31P{1H} NMR
(CDCl3, 202 MHz) δ 36.2 (s); mp 207.7-209.3 °C (dec). Anal.
Calcd for C22H24ClPPd: C, 57.28; H, 5.24. Found: C, 57.00; H,
5.33.
Syntheses of Methylpalladium Triflate Complexes. Synthesis
of tBu3PPd(Me)OTf [OTf ) OSO2CF3] (2a). In a glovebox, to a
mixture of AgOTf (0.411 g, 2.03 mmol) and 1a (0.539 g, 0.138
mmol) was added CH2Cl2 (1 mL) at room temperature. The reaction
mixture was stirred at room temperature for 1 h and was filtered
through a Celite pad. Volatiles were removed from the filtrate under
reduced pressure to obtain a dark green solid (0.560 g, 77%): 1H
Experimental Section
3
NMR (CDCl3, 500 MHz) δ 1.51 (d, JPH ) 13 Hz, 27H), 1.67 (s,
General Methods. Unless otherwise noted, all reactions and
manipulations were conducted by using standard Schlenk or vacuum
line techniques under argon except for the filtration procedures
through filtering papers. 1H (500 MHz), 11B{1H} (160 MHz), 13C-
{1H} (125 MHz), 19F{1H} (470 MHz), and 31P{1H} (202 MHz)
NMR spectra were recorded on a JNM-ECP500 spectrometer with
shifts relative to the residual protiated solvent, an external BF3-
OEt2 standard, the deuterated solvent, CFCl3, and an external 85%
H3PO4 standard. High-resolution mass spectrometry was performed
on a JEOL JMS-AX505H spectrometer. Matrix-assisted laser
desorption/ionization time-of-flight mass spectrometry (MALDI-
TOF-MS) was performed on an Applied Biosystems BioSpectrom-
etry workstation model Voyager-DE STR spectrometer using
dithranol as a matrix. Elemental analyses were performed by the
Microanalytical Laboratory of the Department of Chemistry,
Graduate School of Science, The University of Tokyo. Melting
points were determined by using a Yanaco MP-500D. X-ray
crystallographic analyses were recorded on a Rigaku Mercury CCD
diffractometer. Gel permeation chromatography (GPC) analyses
3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 0.71 (s, CH3), 31.7 (s,
1
CH3), 40.4 (d, J ) 8.5 Hz, 4°), 120.1 (q, JFC ) 318 Hz, CF3);
31P{1H} NMR (CDCl3, 202 MHz) δ 76.9 (s); 19F{1H} NMR
(CDCl3, 470 MHz) δ -77.4 (s); mp 60.9-62.3 °C (dec); HRMS-
FAB (m/z) [M - CF3SO3]+ calcd for C13H30PPd, 321.1126,
322.1136, 323.1120, 325.1124, 327.1137; found, 321.1109, 322.1139,
323.1132, 325.1132, 327.1137.
Synthesis of {[(o-tol)3P]Pd(Me)OTf}2 (2b). To a mixture of
AgOTf (0.232 g, 0.907 mmol) and 1b (0.233 g, 0.507 mmol) was
added CH2Cl2 (5 mL) at room temperature. The reaction mixture
was stirred at room temperature for 1 h, filtered with Celite, and
poured into vigorously stirred hexane to precipitate an off-white
solid. The resulting solid was washed with hexane three times to
give the desired product (0.0715 g, 25%): 1H NMR (CDCl3, 500
MHz) δ 0.75 (s, 3H), 2.10-2.50 (br s, 9H), 7.17-7.25 (br, 6H),
7.40 (t, J ) 7.5 Hz, 3H), 7.48-7.64 (br, 3H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 6.07 (CH3), 23.1 (d, J ) 8.2 Hz, CH3), 118.9
1
(q, JFC ) 317 Hz, CF3), 125.4. (4°), 125.8 (d, J ) 13 Hz, CH),
131.3 (CH), 132.2 (d, J ) 8.2 Hz, CH), 135.2 (br, CH), 142.9 (d,
J ) 9.1 Hz, 4°); 31P{1H} NMR (CDCl3, 202 MHz) δ 34.7 (s);
19F{1H} NMR (CDCl3, 470 MHz) δ -77.7 (s); mp 173.2-174.1
(72) In the abstract No. PB124 of the 52nd Symposium on Organome-
tallic Chemistry, Japan 2005, Wakatsuki reported that a combination of
CpNi(Me)(PPh3) and B(C6F5)3 could catalyze the copolymerization of NB
and NBE with high NBE content and high molecular weight: b/(a + b) )
up to 0.57, Mn ) up to 407 000, Mw/Mn ) down to 1.57.
(73) Miller, K. J.; Kitagawa, T. T.; Abu-Omar, M. M. Organometallics
2001, 20, 4403-4412.

4594 Organometallics, Vol. 25, No. 19, 2006
Table 6. Crystallographic Data and Structure Refinement Details for 1a, 1b, 2a, and 2b
Yamashita et al.
1a
1b
2a
2b
formula
fw
C13H30ClPPd
359.19
C23H25Cl4PPd
580.60
C14H30F3O3PPdS
472.81
C23H24F3O3PPdS
574.85
T (K)
120(2)
120(2)
120(2)
120(2)
λ (Å)
0.71070
triclinic
P1h
0.71070
triclinic
P1h
0.71070
monoclinic
P21/n
8.0898(10)
16.7280(13)
14.8439(18)
90
104.9956(15)
90
1940.4(4)
4
1.619
1.182
968
0.71070
triclinic
P1h
cryst syst
space group
a (Å)
8.551(9) Å
9.521(9) Å
9.873(11)
91.59(2)
91.034(20)
94.29(2)
801.0(14)
2
9.385(18)
10.88(2)
11.97(2)
81.62(9)
80.91(9)
83.78(9)
1190(4)
2
9.727(2)
10.568(2)
13.079(3)
67.835(11)
74.702(12)
72.953(11)
1172.4(5)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D
calc (g/cm3)
1.489
1.402
372
1.620
1.305
584
1.628
0.995
580
µ (mm-1
F(000)
)
cryst size (mm)
2θ range (deg)
0.60 × 0.60 × 0.40
3.02-25.00
4948
2707/0.0183
155
0.50 × 0.20 × 0.10
3.00-25.00
7490
4068/0.0452
266
0.40 × 0.30 × 0.15
3.09-24.99
18 062
3408/0.0215
329
0.50 × 0.40 × 0.30
3.03-25.00
7303
3986/0.0117
293
no. of reflns collected
no. of indep reflns/Rint
no. of params
GOF on F2
1.212
0.961
1.078
1.055
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
0.0315, 0.0916
0.0322, 0.0918
0.0357, 0.0809
0.0398, 0.0823
0.0219, 0.0522
0.0230, 0.0528
0.0202, 0.0519
0.0211, 0.0524
°C (dec); HRMS-FAB (m/z) [M - CF3SO3]+ calcd for C22H24-
PPd, 423.0656, 424.0667, 425.0651, 427.0655, 429.0667; found,
423.0624, 424.0646, 425.0662, 427.0662, 429.0664.
into acidified ethanol. The resulting solid was separated by filtration,
washed with methanol several times, and dried under vacuum at
60 °C.
X-ray Crystallography. Details of the crystal data and a
summary of the intensity data collection parameters for 1a, 1b,
2a, and 2b are listed in Table 6. In each case a suitable crystal was
mounted with mineral oil to the glass fiber and transferred to the
goniometer of a Rigaku Mercury CCD diffractmeter with graphite-
Reaction of 1a with NaBAr4. A screw-capped NMR tube was
charged with 1a (10.0 mg, 0.0278 mmol) and NaB(3,5-(CF3)2C6H3)4
(24.7 mg, 0.0278 mmol or 12.3 mg, 0.0139 mmol), and CDCl3
was vacuum-transferred. After shaking the NMR tube, the NMR
spectra were collected. Except for the integral ratio of the BAr4
part to others, all the NMR spectra were identical to the product
from the following reaction of 1a with NaBAr4.
monochromated Mo KR radiation (λ ) 0.710 69 Å) to 2θmax
)
55°. The structures were solved by direct methods with SIR-9774
or SHELXS75 and refined by full-matrix least-squares techniques
against F2 (SHELXL-9775). The intensities were corrected for
Lorentz and polarization effects. The non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were refined isotropically
in the difference Fourier maps or placed using AFIX instructions.
General Procedure for Norbornene Polymerization. A 20 mL
Schlenk flask was charged with 1a (3.6 mg, 0.010 mmol) and NaB-
(3,5-(CF3)2C6H3)4 (8.9 mg, 0.010 mmol), and this mixture was
dissolved in CHCl3 (1.0 mL). The solution was degassed by three
freeze-pump-thaw cycles. Another 20 mL Schlenk flask was
charged with norbornene (546 mg, 5.80 mmol) and CHCl3 (4.0
mL), and the solution was degassed by three freeze-pump-thaw
cycles. To this flask was added the solution of palladium complex
at room temperature. After being stirred for the indicated time, the
reaction mixture was poured into acidified ethanol. The resulting
solid was separated by filtration, washed with methanol several
times, and dried under vacuum at 60 °C.
Reaction of 1a with AgBAr4. In a glovebox, to a mixture of
AgBAr4 (135 mg, 0.139 mmol) and 1a (50.0 mg, 0.139 mmol)
was added CH2Cl2 (4 mL) at room temperature. The reaction
mixture was stirred at room temperature for 3 h and was filtered
through a Celite pad. The filtrate was poured into vigorously stirred
hexane to precipitate a green solid. The resulting solid was isolated
by filtration to give the desired product (79.5 mg, 74%). A mass
pattern in the MALDI-TOF-MS analysis of the product was
identical to a calculated pattern for the cationic part of 3 (see
Supporting Information): 1H NMR (CDCl3, 500 MHz) δ 1.49 (d,
3JPH ) 13 Hz, 27H), 1.74 (s, 3H), 7.53 (s, 2H), 7.71 (s, 4H); 13C-
{1H} NMR (CDCl3, 125 MHz) δ 0.69 (s, CH3), 31.9 (s, CH3), 40.9
(d, J ) 12.5 Hz, 4°), 117.7 (sp, 3JFC ) 3.8 Hz, CH), 124.8 (q, 1JFC
2
3
) 273 Hz, CF3), 129.1 (qq, JFC ) 16 Hz, JBC ) 2.9 Hz, 4°),
135.0 (s, CH), 162.0 (q, 1JBC ) 49.9 Hz, 4°); 31P{1H} NMR (CDCl3,
202 MHz) δ 74.6 (s); 19F{1H} NMR (CDCl3, 470 MHz) δ -62.2
(s); 11B{1H} NMR (CDCl3, 160 MHz) δ 6.95 (s); mp 111.4-113.3
°C (dec).
General Procedure for Norbornene Polymerization at Low
Catalyst Loading. In a glovebox, 1a (9.0 mg, 0.025 mmol) and
NaB(3,5-(CF3)2C6H3)4 (22.5 mg, 0.025 mmol) were placed into a
screw-capped, 5 mL volumetric flask. After dissolution of the
mixture in CHCl3, the resulting solution was diluted to 5 mL to
make a stock solution. A 20 mL Schlenk flask was charged with
norbornene (546 mg, 5.80 mmol) and CHCl3 (4.8 mL), and the
solution was degassed by three freeze-pump-thaw cycles. A 200
µL portion of the stock solution was syringed into the flask. After
being stirred for the indicated time, the reaction mixture was poured
General Procedure for the Methyl Ester of Norbornene
Carboxylic Acid Polymerization. A 20 mL Schlenk flask was
charged with 1a (3.6 mg, 0.010 mmol) and NaB(3,5-(CF3)2C6H3)4
(8.9 mg, 0.010 mmol), and this mixture was dissolved in CHCl3
(1.0 mL). The solution was degassed by three freeze-pump-thaw
cycles. Another 20 mL Schlenk flask was charged with the methyl
ester of norbornene carboxylic acid (0.89 mL, 5.8 mmol) and CHCl3
(4.0 mL), and the solution was degassed by three freeze-pump-
thaw cycles. To this flask was added the solution of palladium
complex at room temperature. After being stirred for the indicated
time, the reaction mixture was poured into acidified ethanol. The
resulting polymer was separated by filtration, washed with methanol
several times, and dried under vacuum at 60 °C: 1H NMR (CDCl3,
500 MHz) δ 0.82-3.07 (br, CH, CH2), 3.38-4.00 (br, COOCH3).
(74) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115-119.
(75) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.

Bulky Monophosphine-Ligated Methylpalladium Complexes
Organometallics, Vol. 25, No. 19, 2006 4595
Procedure for Plot of Conversion versus Molecular Weight
(Figure 5). A 20 mL Schlenk flask was charged with 1a (18.0 mg,
0.050 mmol) and NaB(3,5-(CF3)2C6H3)4 (44.5 mg, 0.050 mmol),
and the mixture was dissolved in CDCl3 (4.0 mL). The solution
was degassed by three freeze-pump-thaw cycles. Another 20 mL
Schlenk flask was charged with the methyl ester of norbornene
carboxylic acid (0.89 mL, 5.8 mmol) and CDCl3 (1.0 mL), and the
solution was degassed by three freeze-pump-thaw cycles. To this
flask was added the solution of palladium complex and phenan-
threne (103.4 mg, 0.58 mmol) as internal standard at room
temperature. After being stirred, a 0.1 mL aliquot of the reaction
mixture was transferred to an NMR sample tube by use of syringe,
and the solution was diluted by CDCl3 up to 0.6 mL. After
collection of the NMR spectrum, the solution in the NMR sample
tube was immediately poured into methanol to stop polymerization,
and volatiles were removed under reduced pressure to conduct GPC
analysis.
charged with norbornene (273 mg, 2.90 mmol), the methyl ester
of norbornene carboxylic acid (0.45 mL, 2.9 mmol), and CHCl3
(4.0 mL), and the solution was degassed by three freeze-pump-
thaw cycles. To this flask was added the solution of palladium
complex at room temperature. After being stirred for the indicated
time, the reaction mixture was poured into acidified ethanol. The
resulting solid was separated by filtration, washed with methanol
several times, and dried under vacuum at 60 °C: 1H NMR (CDCl3,
500 MHz) δ 0.13-3.09 (br, CH, CH2), 3.29-3.96 (br, COOCH3).
Acknowledgment. We are grateful to Prof. Takayuki
Kawashima and Prof. Kei Goto at the University of Tokyo for
use of the X-ray diffractometer. This work was supported by a
Grant-in-Aid for Scientific Research on Priority Areas “Ad-
vanced Molecular Transformations of Carbon Resources” from
the Ministry of Education, Culture, Sports, Science and Tech-
nology, Japan.
General Procedure for Copolymerizaton of Norbornene with
the Methyl Ester of Norbornene Carboxylic Acid. A 20 mL
Schlenk flask was charged with 1a (3.6 mg, 0.010 mmol) and NaB-
(3,5-(CF3)2C6H3)4 (8.9 mg, 0.010 mmol), and this mixture was
dissolved in CHCl3 (1.0 mL). The solution was degassed by three
freeze-pump-thaw cycles. Another 20 mL Schlenk flask was
Supporting Information Available: Crystallographic data of
1a, 1b, 2a, and 2b are available free of charge via the Internet at
http://pubs.acs.org.
OM060347W