Synthesis and reactions of heterodinuclear organopalladium-cobalt complexes acting as copolymerization catalyst for aziridine and carbon monoxide

Article abstract of DOI:10.1016/j.jorganchem.2006.04.044

A series of heterodinuclear acylpalladium-cobalt complexes having a bidentate nitrogen ligand, L₂(RCO)Pd-Co(CO)₄ (L₂ = bpy, R = Me (5), Ph (6); L₂ = tmeda, R = Me (7), Ph (8); L₂ = phen, R = Me (9), Ph (10)) are prepared by metathetical reactions of PdRIL₂ with Na⁺[Co(CO)₄]^- followed by treatment with CO. These complexes are characterized by NMR and IR spectroscopies and elemental analyses, and the molecular structures of 6, 8, and 9 are determined by X-ray structure analysis. Geometry at Pd is essentially square planar and the Co atom is considered to have d¹⁰ tetrahedral structure, where cobalt(-I) anion coordinates to palladium(II) cation. Heterodinuclear organopalladium-cobalt complexes are shown to catalyze copolymerization of aziridines and CO under mild conditions. Reaction of (dppe)MePd-Co(CO)₄ (1) with aziridine gives a cationic (aziridine)palladium(II) complex with [Co(CO)₄]^- anion, [PdMe(aziridine)(dppe)]⁺[Co(CO)₄]^- (13).

Full text of DOI:10.1016/j.jorganchem.2006.04.044

Journal of Organometallic Chemistry 692 (2007) 26–35
www.elsevier.com/locate/jorganchem
Synthesis and reactions of heterodinuclear
organopalladium–cobalt complexes acting as copolymerization
catalyst for aziridine and carbon monoxide
Shin-ichi Tanaka, Hideko Hoh, Yoshifumi Akahane, Susumu Tsutsuminai,
*
Nobuyuki Komine, Masafumi Hirano, Sanshiro Komiya
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology,
2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan
Received 1 March 2006; received in revised form 3 April 2006; accepted 7 April 2006
Available online 30 August 2006
Abstract
A series of heterodinuclear acylpalladium–cobalt complexes having a bidentate nitrogen ligand, L2(RCO)Pd–Co(CO)4 (L2 = bpy,
R = Me (5), Ph (6); L2 = tmeda, R = Me (7), Ph (8); L2 = phen, R = Me (9), Ph (10)) are prepared by metathetical reactions of PdRIL2
with Na+[Co(CO)4]ꢀ followed by treatment with CO. These complexes are characterized by NMR and IR spectroscopies and elemental
analyses, and the molecular structures of 6, 8, and 9 are determined by X-ray structure analysis. Geometry at Pd is essentially square
planar and the Co atom is considered to have d10 tetrahedral structure, where cobalt(-I) anion coordinates to palladium(II) cation. Hete-
rodinuclear organopalladium–cobalt complexes are shown to catalyze copolymerization of aziridines and CO under mild conditions.
Reaction of (dppe)MePd–Co(CO)4 (1) with aziridine gives a cationic (aziridine)palladium(II) complex with [Co(CO)4]ꢀ anion,
[PdMe(aziridine)(dppe)]+[Co(CO)4]ꢀ (13).
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Heterodinuclear organopalladium–cobalt complex; Copolymerization; Aziridine; Carbon monoxide
1. Introduction
[2h]. Catalytic carbonylation of thietanes giving thiobuty-
rolactones [3a] and copolymerization of aziridines and
CO promoted by heterodinuclear organopalladium–cobalt
complexes [3b] are notable applications to catalysis. We
wish to report details of the synthesis and reactions of hete-
rodinuclear organopalladium–cobalt complexes as well as
copolymerization of aziridines and carbon monoxide cata-
lyzed by these complexes.
Heterodinuclear complexes and heterometallic clusters
have attracted much attention due to cooperative effect
of different metal centers [1]. We have reported the synthe-
sis and reactions of heterodinuclear organometallic com-
plexes having both M–M0 and M–C bonds, L2RM–M0Ln
(M = Pt, Pd; M0Ln = MoCp(CO)3, WCp(CO)3, Mn(CO)5,
Re(CO)5, FeCp(CO)2, Co(CO)4; R = alkyl, aryl, acyl, H;
L2 = cod, dppe, tmeda, bpy, phen) [2], some of which show
remarkable reactions based on cooperative effect of two
metals such as organic group migration along different
metals [2a,2c,2d,2i], enhanced CO insertion into M–C bond
[2f,2j], and selective ring-opening reactions of thiiranes
2. Results and discussion
2.1. Synthesis and structure of hetetrodinuculer
organopalladium–cobalt complexes
Methylpalladium–cobalt complexes with 1,2-bis(diph-
enylphosphino)ethane (dppe) ligand, (dppe)MePd–
Co(CO)4 (1) was prepared by the metathesis reaction
*
Corresponding author.
E-mail address: komiya@cc.tuat.ac.jp (S. Komiya).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.04.044

S.-i. Tanaka et al. / Journal of Organometallic Chemistry 692 (2007) 26–35
27
of PdMe(NO3)(dppe) with corresponding metalate anions
Na+[Co(CO)4]ꢀ as reported previously [2f,2j]. Acetyl
complex (dppe)(MeCO)Pd–Co(CO)4 (4) was prepared
by the reaction of 1 with CO. However, analogous prep-
arations of organopalladium–cobalt derivatives with
nitrogen ligands such as 2,20-bipyridine (bpy),
N,N,N0,N0-tetramethylethylenediamine (tmeda) and 1,10-
phenanthroline (phen) ligand always gave mixtures of
alkyl (or aryl) and acyl complexes or acyl complexes con-
taminated with unseparable materials, resigning isolation
of the pure compounds. Probably CO, which was pro-
duced by partial decomposition of tetracarbonylcobalt
anion, is considered to insert into the Pd–C bond. In
fact, under carbon monoxide atmosphere, pure acylpalla-
dium–cobalt complex, L2(RCO)Pd–Co(CO)4 (L2 = bpy,
R = Me (5), Ph (6); L2 = tmeda, R = Me (7), Ph (8);
L2 = phen, R = Me (9), Ph (10)) was obtained by the
reactions of PdRIL2 with anionic cobalt complex
Na+[Co(CO)4]ꢀ in THF (Eq. (1)). These acetyl derivative
can also be prepared by oxidative addition of Co(CO-
Me)(CO)4 to Pd(dba)2 in the presence of the correspond-
ing ligands [2i].
These dinuclear acylpalladium–cobalt complexes (5–10)
were characterized by 1H NMR and IR spectroscopies and
elemental analysis as well as by X-ray structure analysis.
1
Selected IR and H NMR data of newly prepared com-
pounds 6, 8, and 10 are summarized in Table 1. IR spectra
of these acyl complexes display strong m(C@O) bands due
to the PdCOR group at 1650 cmꢀ1 and a few strong
m(C„O) bands at 1880–2000 cmꢀ1 whose frequencies are
close to the broad peak due to anionic metal carbonyls
Na+[Co(CO)4]ꢀ, suggesting valency of the Co center close
to Co(-I).
Molecular structures of the acylpalladium–cobalt
complexes having bidentate nitrogen ligand, L2(RCO)Pd–
Co(CO)4 (L2 = bpy, R = Ph (6); L2 = tmeda, R = Ph (8);
L2 = phen, R = Me (9)) were determined by X-ray struc-
ture analysis. The crystallographic data and selected bond
distances and angles are summarized in Tables 2 and 3,
respectively, and ORTEP drawings are depicted in Fig. 1.
˚
All Pd–Co bond distances (ca. 2.6 A) are in a typical range
of the Pd–Co single bond and similar to that for
(py)(PhHNHN = CMeC6H4)Pd–Co(CO)4 (py = pyridine,
˚
2.604(1) A) [4a], but shorter than that for (Me3P)2(PhCO)
˚
Pd–Co(CO)4 (2.7856(7) A) [4b] and (dppe)MePd–Co(CO)4
˚
+
–
(2.682(7) A) [2f,2j]. The geometry at Pd is essentially square
Co(CO)4
R
Co(CO)4
COR
X
R
Na [Co(CO)4]
THF, 0 °C
-NaX
CO
THF, 0 °C
L2Pd
L2Pd
L2Pd
planar, where Co and the acyl groups are bonded to Pd in a
cis fashion. The Co atom is considered to have d10 tetrahe-
dral structure, where cobalt(-I) anion coordinates to palla-
dium(II) cation. Though two carbonyl ligands in these
complexes lie close to Pd atom, they are not considered
to be bridging carbonyls, since the Co–C–O angles are
more than 170ꢁ. However one of the C–Co–C angles (ca.
130ꢁ) is significantly larger than the ideal tetrahedral angle
of 109ꢁ (Table 3), suggesting strong steric repulsion
between ligands at Pd and Co moieties. On the other hand,
L
2 = dppe, R = Me (1)
L2 = bpy, R = Me (2)
2 = tmeda, R = Ph (3)
L2 = dppe, R = Me (4)
L2 = bpy,
R = Me (5)
Ph (6)
L
L
2 = tmeda, R = Me (7)
Ph (8)
L2 = phen, R = Me (9)
Ph (10)
ð1Þ
Table 1
Selected IR and 1H NMR data of heterodinuclear acylpalladium–cobalt complexes
Complex
IR (mCO, cmꢀ1 a
)
1H NMR (ppm)
R
L2
6b
2026 (m)
1961 (s)
1923 (s)
1899 (s)
1645 (m)
8.15 (d, JHH = 7.5 Hz, 2H, o-C6H5)
7.45 (t, JHH = 7.5 Hz, 2H, m-C6H5)
7.40 (t, JHH = 7.5 Hz, 1H, p-C6H5)
8.7 (br, 1H, bpy H6)
8.1–8.3 (br, 2H, bpy H4, H40)
8.1 (br, 2H, bpy H3, H30)
7.6 (br, 1H, bpy H5)
7.4–7.6 (br, 2H, bpy H50, H60)
8c
10d
a
2019 (m)
1948 (s)
1897 (s)
1650 (m)
8.26 (d, JHH = 8.1 Hz, 2H, o-C6H5)
7.0–7.2 (br, 3H, m, p- C6H5)
1.85 (br, 12H, tmeda CH3)
1.4–1.5 (br, 4H, tmeda CH2)
2027 (m)
1952 (s)
1932 (s)
1890 (s)
1645 (m)
8.17 (d, JHH = 7.2 Hz, 2H, o-C6H5)
7.53 (t, JHH = 7.2 Hz, 2H, m-C6H5)
7.44 (t, JHH = 7.2 Hz, 1H, p-C6H5)
9.0 (brs, 1H, H2)
8.9 (br, 2H, H4, H7)
8.4 (br, 1H, H9)
8.0–8.2 (brs, 2H, H3, H8)
IR spectra were measured by KBr pellet method.
b
c
1H NMR spectrum was measured in CDCl3 at room temperature.
1H NMR spectrum was measured in C6D6 at room temperature.
1H NMR spectrum was measured in acetone-d6 at room temperature.
d

28
S.-i. Tanaka et al. / Journal of Organometallic Chemistry 692 (2007) 26–35
Table 2
Crystallographic data for (bpy)(PhCO)Pd–Co(CO)4 (6), (tmeda)(PhCO)Pd–Co(CO)4 (8), and (phen)(MeCO)Pd–Co(CO)4 (9)
6 Æ C6H6
27H19CoN2O5Pd
8
9
Empirical formula
Formula weight
C
C17H19CoN2O5Pd
496.68
C18H11CoN2O5Pd
500.63
616.79
Crystal color, habit
Crystal dimension (mm · mm · mm)
Crystal system
Orange, cubic
0.22 · 0.14 · 0.14
Monoclinic
P21/c
12.41(1)
12.38(1)
Dark red, cubic
0.63 · 0.40 · 0.32
Monoclinic
P21/c
8.69(1)
16.30(1)
Red, prismatic
0.67 · 0.33 · 0.20
Triclinic
ꢀ
Space group
P1
˚
a (A)
9.990(4)
12.460(4)
7.541(4)
105.72(3)
104.01(4)
86.30(3)
876.6(7)
2
˚
b (A)
˚
c (A)
16.328(7)
14.078(7)
a (ꢁ)
b (ꢁ)
c (ꢁ)
95.84(5)
92.97(6)
3
˚
V (A )
2493(2)
4
1.643
1232.00
14.27
1990(2)
4
1.657
992.00
17.65
Z
Dcalc (g cmꢀ3
F0 0 0
)
1.896
492.00
20.06
l (Mo Ka) (cmꢀ1
)
Diffractometer
Radiation (A)
Temperature (ꢁC)
Scan type
Rigaku AFC7R
0.71069
ꢀ160.0
x–2h
Rigaku AFC7R
0.71069
ꢀ160.0
x–2h
Rigaku AFC7R
0.71069
20.0
˚
x–2h
2hmax (ꢁ)
55.0
55.0
55.0
No. of reflection measured
Total
5822
4847
4254
Unique
5563
4537
4021
No. of observation (I > 3.00r(I))
1557
3698
3719
Structure solution
Patterson methods (SAPI)
Patterson methods (SAPI)
Direct methods
0.028
0.041
Ra
RW
0.113
0.171
1.50
0.035
0.056
1.30
b
Goodness of fit indicator
1.20
P
P
a
R = (iFo| ꢀ |Fci)/ |Fo|.
P
P
b
Rw = [ w(|Fo| ꢀ |Fc|)2/ w|Fo|2]0.5
.
the Co atom is deviated from the least square plane con-
sisted of Pd, C1, N1 and N2 atoms by 0.12–0.58 A for
were characterized by comparing the reported NMR and
IR data [5]. The yield was estimated on the basis of
aziridine used and also by assuming that aziridine was con-
sumed as alternative copolymer [6]. Resultant copolymer
from 2-methylaziridine and CO was consisted of regio-
and stereo-isomeric mixtures which were originated from
regioselectivity of the C–N bond cleavage (Table 5, entries
4–10). Ratio of these two units in the copolymer (m/n as
defined in Eq. (2)) were estimated by 1H NMR. In all cases,
less hindered C–N bond of 2-methylaziridine was preferen-
tially cleaved as shown in Table 5. Heterodinuclear com-
plexes having a dppe ligand showed slightly higher
catalytic activity than those having a bpy, phen, or tmeda
ligand. In contrast, heterodinuclear methylpalladium–
molybdenum complex (dppe)MePd–MoCp(CO)3 (11) and
methylplatinum–cobalt complex (dppe)MePt–Co(CO)4 (12)
[2f,2j] showed no or low catalytic activity for copolymeriza-
tion (Table 5, entries 11 and 12). It is interesting to note that
catalytic activity of these Pd–Co complexes were higher than
that of mononuclear Jia’s catalysts Co(COMe)(CO)3(PPh3)
[5a] and Co(COCH2Ph)(CO)4 [5b] (Table 5, entries 13 and
14), and corresponding mononuclear cationic palladium(II)
complexes [PdMe(NCMe)(bpy)]+[BF4]ꢀ and anionic cobalt
complex [PPN]+[Co(CO)4]ꢀ showed no catalytic activity
˚
the acyl and related complexes 1 [2j], 5 [2i], 6, 8 and 9,
and the coordination plane at Pd is slightly twisted, dis-
playing dihedral angles of 3–13ꢁ between N–N–Pd and
Co–C–Pd planes (Table 4). These deviations may also be
due to steric congestion of the Pd metal, causing some
twisting from square planar structure. These structural fea-
tures around both metals are consistent with the electronic
configurations of d8-Pd(II) and d10-Co(-I) electronic config-
urations, which are also supported by the IR data.
2.2. Copolymerization of aziridine and carbon monoxide
catalyzed by hetetrodinuculer organopalladium–cobalt
complexes
When aziridine was heated to 100 ꢁC under 5 MPa of CO
in THF for 6 h in the presence of 1 mol% of dinuclear organ-
opalladium–cobalt complexes having a bidentate nitrogen or
phosphorus ligand, smooth alternative copolymerization of
aziridine and CO proceeded to give water-soluble copolymer
in good yield. Results of copolymerization are summarized
in Table 5. 2-Methylaziridine and N-ethylaziridine were also
copolymerized under similar conditions. These polymers

S.-i. Tanaka et al. / Journal of Organometallic Chemistry 692 (2007) 26–35
29
Table 3
2.3. Reaction of organopalladium–cobalt complex with
aziridines
Selected bond lengths and angles for (bpy)(PhCO)Pd–Co(CO)4 (6),
(tmeda)(PhCO)Pd–Co(CO)4 (8), and (phen)(MeCO)Pd–Co(CO)4 (9)
˚
Bond lengths (A) for (bpy)(PhCO)Pd–Co(CO)4 (6)
In order to obtain further insight concerning the reaction
mechanism, reaction of (dppe)MePd–Co(CO)4 (1) with a
stoichiometric amount of aziridine was followed by
31P{1H} NMR. Upon mixing in THF-d8 at 20 ꢁC, new
two doublets at 60.5 and 40.3 ppm were appeared (Fig. 2).
These signals were assigned to the signal of cationic (aziridine)
palladium complex, [PdMe(aziridine)(dppe)]+[Co(CO)4]ꢀ
(13) by comparing with [PdMe(aziridine)(dppe)]+[SO3-
CF3]ꢀ which was independently prepared by the reaction
of [PdMe(NCMe)(dppe)]+[SO3CF3]ꢀ with aziridine (see
Section 4). The reaction is considered to be in equilibrium
as shown in Eq. (3). Thus, on lowering the temperature,
the equilibrium shifts to the side of aziridine complex 13
as shown in Fig. 2.
Pd(1)–Co(1)
Pd(1)–N(1)
Pd(1)–C(14)
Co(1)–C(18)
Co(1)–C(20)
C(18)–O(2)
C(20)–O(4)
2.569(5)
2.11(3)
2.48(3)
1.79(4)
1.81(3)
1.15(4)
1.18(4)
Pd(1)–C(1)
Pd(1)–N(2)
Pd(1)–C(17)
Co(1)–C(19)
Co(1)–C(21)
C(19)–O(3)
C(21)–O(5)
1.99(3)
2.07(3)
2.53(3)
1.78(4)
1.70(4)
1.13(5)
1.16(4)
Bond angles (ꢁ) for (bpy)(PhCO)Pd–Co(CO)4 (6)
Co(1)–Pd(1)–C(1)
C(1)–Pd(1)–N(1)
Co(1)–C(18)–O(2)
Co(1)–C(20)–O(4)
C(18)–Co(1)–C(19)
C(18)–Co(1)–C(21)
C(19)–Co(1)–C(21)
84.9(10)
104.3(9)
165(3)
173(3)
100(1)
132(1)
101(1)
Co(1)–Pd(1)–N(1)
N(1)–Pd(1)–N(2)
Co(1)–C(19)–O(3)
Co(1)–C(21)–O(5)
C(18)–Co(1)–C(20)
C(19)–Co(1)–C(20)
C(20)–Co(1)–C(21)
104.3(9)
73(1)
172(3)
174(3)
103(1)
110(1)
107(1)
˚
Bond lengths (A) for (tmeda)(PhCO)Pd–Co(CO)4 (8)
+
Pd(1)–Co(1)
Pd(1)–N(1)
Pd(1)–C(14)
Co(1)–C(14)
Co(1)–C(16)
C(14)–O(2)
C(16)–O(4)
2.594(2)
2.283(3)
2.452(4)
1.758(5)
1.770(5)
1.153(5)
1.150(6)
Pd(1)–C(1)
Pd(1)–N(2)
Pd(1)–C(17)
Co(1)–C(15)
Co(1)–C(17)
C(15)–O(3)
C(17)–O(5)
1.967(4)
2.190(3)
2.521(5)
1.781(6)
1.754(4)
1.147(6)
1.162(5)
H
H
N
K
N
[Co(CO)4]−
+
1
(dppe)Pd
ð3Þ
ð4Þ
THF
Me
13
[13]
K =
Bond angles (ꢁ) for (tmeda)(PhCO)Pd–Co(CO)4 (8)
[1][aziridine]
Co(1)–Pd(1)–C(1)
C(1)–Pd(1)–N(1)
Co(1)–C(15)–O(2)
Co(1)–C(17)–O(4)
C(14)–Co(1)–C(16)
C(14)–Co(1)–C(17)
C(15)–Co(1)–C(17)
88.1(1)
90.1(1)
Co(1)–Pd(1)–N(1)
N(1)–Pd(1)–N(2)
Co(1)–C(16)–O(3)
Co(1)–C(18)–O(5)
C(14)–Co(1)–C(15)
C(15)–Co(1)–C(16)
C(16)–Co(1)–C(17)
99.5(1)
82.0(1)
1
In H NMR at ꢀ40 ꢁC, the methylene protons of aziri-
dine coordinated to palladium were observed as two broad
signals at 1.7 and 2.1 ppm, whose coordination shift is ca.
0.5 ppm downfield from free aziridine resonance (Fig. 3).
On raising temperature, the signals due to coordinated azi-
ridine gradually coalesced. On the other hand, addition of
one equivalent of free aziridine at ꢀ40 ꢁC caused extensive
mixing of these signals giving one broad signal at the aver-
aged chemical shift. These facts suggest facile exchange
between the coordinated and free aziridine.
In contrast, the acetyl derivative (dppe)(MeCO)Pd–
Co(CO)4 (4) showed no apparent reaction with aziridine.
However in the presence of large excess aziridine, extensive
line broadening of the 31P{1H} signals of 4 was observed,
suggesting presence of similar coordination equilibrium of
aziridine accompanied by heterolytic cleavage of Pd–Co
bond for 4. Apparent low reactivity may be due to strong
electron withdrawing property by the acyl ligand discourag-
ing ionization of the Pd–Co bond. These facts indicate that
coordination of aziridine is in facile equilibrium in solution.
The equilibrium constants of the reaction of (dppe)-
MePd–Co(CO)4 (1) with various aziridines, such as aziri-
dine, 2-methylaziridine and N-ethylaziridine were
estimated by 31P{1H} NMR in THF (see Section 4). Ther-
modynamic parameters of these processes were obtained
from van’t Hoff analysis (Table 6). Coordination ability
of N-ethylaziridine was significantly small in comparison
with aziridine and 2-methylaziridine. This may be mainly
due to steric congestion by the N-ethyl substituent on coor-
dination. Large negative values of the entropy change
probably suggest strong solvation in the ionic products.
171.7(3)
177.4(4)
101.6(2)
131.7(2)
107.7(2)
177.5(3)
173.3(3)
103.5(2)
111.0(2)
100.5(2)
˚
Bond lengths (A) for (phen)(MeCO)Pd–Co(CO)4 (9)
Pd(1)–Co(1)
Pd(1)–N(1)
Pd(1)–C(15)
Co(1)–C(15)
Co(1)–C(17)
C(15)–O(2)
C(17)–O(4)
2.5729(4)
2.208(2)
2.442(4)
1.776(4)
1.792(3)
1.144(5)
1.128(4)
Pd(1)–C(1)
Pd(1)–N(2)
Pd(1)–C(18)
Co(1)–C(16)
Co(1)–C(18)
C(16)–O(3)
C(18)–O(5)
1.972(3)
2.152(2)
2.555(4)
1.772(3)
1.784(4)
1.138(4)
1.145(4)
Bond angles (ꢁ) for (phen)(MeCO)Pd–Co(CO)4 (9)
Co(1)–Pd(1)–C(1)
C(1)–Pd(1)–N(1)
Co(1)–C(15)–O(2)
Co(1)–C(17)–O(4)
C(15)–Co(1)–C(16)
C(15)–Co(1)–C(18)
C(16)–Co(1)–C(18)
87.17(8)
96.4(1)
Co(1)–Pd(1)–N(1)
N(1)–Pd(1)–N(2)
Co(1)–C(16)–O(3)
Co(1)–C(18)–O(5)
C(15)–Co(1)–C(17)
C(16)–Co(1)–C(17)
C(17)–Co(1)–C(18)
99.24(6)
76.99(8)
177.5(3)
173.3(3)
111.9(2)
103.8(2)
104.1(2)
171.7(3)
177.4(4)
100.6(2)
129.3(2)
104.2(2)
(entries 15,16). Ligands such as bpy and dppe themselves
had also no catalytic activity toward polymerization. These
results suggest that the presence of Pd–Co bond plays an
important synergistic role in this catalytic copolymerization.
R1
R2
N
R2
N
R2
N
cat. (1 mol%)
R
X
+
CO
THF, 100 ˚C, 6 h
R1 O m
O
n
R1
O
(5 MPa)
ð2Þ

30
S.-i. Tanaka et al. / Journal of Organometallic Chemistry 692 (2007) 26–35
C10
C8
C9
O2
O4
C11
C10
N1
O2
C18
Co1
C14
Co1
C8
C12
C13
C14
C16
C9
O3
N1
Pd1
C11
Pd1
C13
N2
C15
C15
C19
O4
N2
O1
O3
C17
O5
C16
O1
C1
C20
C21
C17
C12
C1
O5
C2
C2
C7
C3
C4
C3
C4
C7
C6
C6
C5
C5
6
8
C5
C4
O5
C7
C6
C18
C8
C14
C3
O3
N1
Co1
C9
C16
C13
Pd1
C10
C17
O4
N2
O1
C15
O2
C11
C1
C12
C2
9
Fig. 1. ORTEP drawings of (bpy)(PhCO)Pd–Co(CO)4 (6), (tmeda)(PhCO)Pd–Co(CO)4 (8), and (phen)(MeCO)Pd–Co(CO)4 (9) and all hydrogen atoms
and solvent are omitted for clarity. Ellipsoids represent 50% probability.
Table 4
heterodinuclear organopalladium–cobalt complexes is
shown in Scheme 1. First of all, reversible coordination
Dihedral angles between PdL2 and PdRCo planes and deviations of cobalt
atom from PdRL2 plane of L2RPd-Co(CO)4
of aziridine to palladium takes place to give cationic
˚
Dihedral angles (ꢁ)
between PdL2 and PdRCo
Deviation (A) of cobalt
atom from PdRL2
(aziridine)palladium(II) complex with tetracarbonylcobalt
anion. Then, cobalt anion attacks the methylene carbon
of the coordinated aziridine to open the ring forming a
Pd–NCH2CH2Co unit, where facile CO insertion takes
place to give the acylcobalt moiety [2f,2j]. An analogous
SN2 mechanism has been proposed for ring-opening
reactions of the coordinated thiirane and thietane by
1
5
6
8
9
8.1
3.0
8.2
10.9
12.9
0.38
0.12
0.29
0.49
0.58
Unfortunately no relation between the polymer yield after
3 h catalyzed by complex 1 and the free energy difference
DG for aziridine coordination to 1 was observed. This sug-
gests the importance of the successive following process
such as C–N bond cleavage and CO insertion in the cata-
lytic copolymerization. Analogous coordination equilib-
rium was also observed for (dppe)MePd–MoCp(CO)3
the
heterodinuclear
organoplatinum–cobalt
(or
manganese, rhenium) complexes [2h,3a]. In these cases,
less hindered side of 2-methylaziridine was selectively
cleaved, being consistent with this mechanism. Since
coordination equilibrium is not related to their catalytic
activity, the following C–N bond cleavage or CO
insertion processes may be rate-determining step, in
which the substituent at N atom does not play an impor-
tant role. Reductive elimination of amido moiety associ-
ated with interaction of Pd atom with the acylcobalt
moiety may give a new heterodinuclear acylpalladium–
cobalt complex [7]. Repeated coordination of aziridine
followed by insertion of CO at Co gives copolymer,
though further study is required to clarify the detail
mechanism.
(11) (DH = ꢀ19 kJ molꢀ1
,
DS = ꢀ53 J molꢀ1 Kꢀ1
, DG
(25 ꢁC) = ꢀ3.4 kJ molꢀ1), though it showed no catalytic
activity for polymerization.
2.4. Mechanism of catalytic coplymerization
A possible mechanism for the alternative copolymeri-
zation of aziridine and carbon monoxide catalyzed by

S.-i. Tanaka et al. / Journal of Organometallic Chemistry 692 (2007) 26–35
31
Table 5
Copolymerization of aziridines and COa
3. Conclusions
Entry R1 R2 Catalyst
Yield (%) m/ng
In the present study, synthesis of novel heterodinuclear
acylpalladium–cobalt complexes having a bidentate nitro-
gen ligand, L2(RCO)Pd–Co(CO)4 (L2 = bpy, R = Me (5),
Ph (6); L2 = tmeda, R = Me (7), Ph (8); L2 = phen,
R = Me (9), Ph (10)) is described. Heterodinuclear organo-
palladium–cobalt complexes are shown to catalyze copoly-
merization of aziridines and CO under mild conditions.
The reaction of (dppe)MePd–Co(CO)4 (1) with aziridine
gave a cationic (aziridine)palladium(II) complex with
[Co(CO)4]ꢀ anion, [PdMe(aziridine)(dppe)]+[Co(CO)4]ꢀ
(13). The present results suggest the importance of the ini-
tial cationic aziridine complex formation, to which the
[Co(CO)4]ꢀ anion attacks the less-substituted carbon of
the coordinated aziridine.
1
2b
3
4
5
6
7
8
9
H
H
H
(dppe)MePd–Co(CO)4 (1)
68
51
25
68
69
38
38
–
–
–
(dppe)(MeCO)Pd–Co(CO)4 (4)
(bpy)(MeCO)Pd–Co(CO)4 (5)
(dppe)MePd–Co(CO)4 (1)
(dppe)(MeCO)Pd–Co(CO)4 (4)
(bpy)(MeCO)Pd–Co(CO)4 (5)
(bpy)(PhCO)Pd–Co(CO)4 (6)
Me
3.0
1.5
2.7
1.5
1.9
2.2
3.4
–
(tmeda)(MeCO)Pd–Co(CO)4 (7) 50
(tmeda)(PhCO)Pd–Co(CO)4 (8)
(phen)(MeCO)Pd–Co(CO)4 (9)
(dppe)MePd–MoCp(CO)3 (11)
(dppe)MePt–Co(CO)4 (12)
Co(COMe)(CO)3(PPh3)
Co(COCH2Ph)(CO)4
½PdMeðNCMeÞðbpyÞꢁþBF4ꢀ
[PPN]+[Co(CO)4]ꢀ
32
27
0
10
11
12
13
14
15
16
25
11f
21
0
3.9
–
2.0
–
0
–
17c
18c
19d
20d
21d
22d
23d
24d
25d
26d
27d
28e
a
dppe
bpy
0
0
27
34
69
63
–
–
–
–
–
–
–
–
–
–
–
–
4. Experimental
H
Et (dppe)MePd–Co(CO)4 (1)
(dppe)(MeCO)Pd–Co(CO)4 (4)
(bpy)(MeCO)Pd–Co(CO)4 (5)
(bpy)(PhCO)Pd–Co(CO)4 (6)
4.1. General
(tmeda)(MeCO)Pd–Co(CO)4 (7) 39
All manipulations were carried out under a dry nitrogen
or argon atmosphere using standard Schlenk techniques.
Solvents were dried over and distilled from appropriate
drying agents under N2: hexane, benzene, toluene, diethyl
ether and THF from Na/benzophenone ketyl; CH2Cl2
from P2O5; acetone from Drierite. NMR solvents were
commercially obtained and dried with appropriate drying
agents before use (C6D6 and THF-d8 from Na; CD2Cl2
and CDCl3 from P2O5; acetone-d6 from Drierite).
PdPhI(bpy) [8], PdPhI(tmeda) [9], Na+[Co(CO)4]ꢀ [10],
Co(COMe)(CO)3(PPh3) [11], Co(COCH2Ph)(CO)4 [4b],
[PdMe(NCMe)(bpy)]+[BF4]ꢀ [12], [PPN]+[Co(CO)4]ꢀ [13],
[PdMe(NCMe)(dppe)]+[SO3CF3]ꢀ [14], aziridine [15], and
(tmeda)(PhCO)Pd–Co(CO)4 (8)
Co(COCH2Ph)(CO)4
½PdMeðNCMeÞðbpyÞꢁþBF4ꢀ
[PPN]+[Co(CO)4]ꢀ
bpy
63
62
12e
0
0
Reaction conditions: catalyst (0.01 mmol), aziridine (1 mmol), CO
(5 MPa), THF = 8.0 mL, 100 ꢁC, 6 h.
b
CO (3 MPa).
c
catalyst (0.05 mmol).
CO (3 MPa), 60 ꢁC.
Catalyst (0.05 mmol), CO (3 MPa), 60 ꢁC.
Yield and ratio were not obtained, since the polymer contained a
d
e
f
significant amount of aziridine homopolymer.
g
See Eq. (2).
+
H
–
N
[Co(CO)4]
(dppe)Pd
Me
13
(dppe)MePd-Co(CO)4 (1)
δ 60.5 (d,
δ 40.3 (d,
J
J
PP = 22 Hz)
PP = 22 Hz)
δ 51.9 (d,
δ 38.4 (d,
J
J
PP = 25 Hz)
PP = 25 Hz)
-40 ˚C
-20 ˚C
0 ˚C
20 ˚C
ppm
70
60
50
40
30
Fig. 2. Variable temperature 31P{1H} NMR spectra for the reaction of (dppe)MePd–Co(CO)4 (1) with aziridine in THF–d8.

32
S.-i. Tanaka et al. / Journal of Organometallic Chemistry 692 (2007) 26–35
H
N
Free
+
H
[Co(CO)4]−
N
Solv
(dppe)Pd
Me
−40 °C
−40 °C
13
Solv
dppe
−20 °C
Imp.
0 °C
Imp.
20 °C
2.5
2.0
1.5
1.0
ppm
Fig. 3. Variable temperature 1H NMR spectra for the reaction mixture of (dppe)MePd–Co(CO)4 (1) with aziridine in THF–d8.
Table 6
C, 40.47; H, 4.01; N, 5.43%. Molar electric conductivity
K (THF, r.t.): 0.0189 S cm2 molꢀ1
.
Thermodynamic parameters for the equilibrium of aziridine coordination
to 1
1H NMR and IR data of the new heterodinuclear acyl-
palladium–cobalt complexes 6, 8, and 10 are summarized
in Table 1. Complexes 6 and 10 were synthesized by a sim-
ilar method to that for 8 and the yields, melting point, ele-
mental analytical data and molar electric conductivity in
THF were described below.
R1
R2
DH/kJ molꢀ1
DS/J molꢀ1 Kꢀ1
DG (25 ꢁC)/kJ molꢀ1
H
H
Et
H
Me
H
ꢀ44
ꢀ43
ꢀ38
ꢀ110
ꢀ110
ꢀ120
ꢀ12
ꢀ12
ꢀ0.87
(bpy)(PhCO)Pd–Co(CO)4 (6). PdPhI(bpy) was used
instead of PdPhI(tmeda). Yield: 82%. M.p. 107 ꢁC (dec.).
Anal. Calc. for C25H21CoN2O6Pd: C, 49.16; H, 3.47; N,
4.59. Found: C, 49.42; H, 3.64; N, 4.17%. Molar electric
N-ethylaziridine [15] were prepared by the literature
methods with minor modifications. 2-Methylaziridine was
purchased from Aldrich. NMR spectra were recorded on
conductivity K (THF, r.t.): 0.0199 S cm2 molꢀ1
.
a
JEOL LA-300 spectrometer (300.4 MHz for 1H,
121.6 MHz for 31P). Chemical shifts were reported in
(phen)(PhCO)Pd–Co(CO)4 (10). PdPhI(phen) was
used instead of PdPhI(tmeda). Yield: 8%. M.p. 127 ꢁC
1
ppm downfield from TMS for H and from 85% H3PO4
in D2O for 31P. IR spectra were recorded on a JASCO
FT/IR-410 spectrometer using KBr disks. Elemental anal-
yses were carried out with a Perkin–Elmer 2400 series II
CHN analyzer. Molar electric conductivity was measured
on a TOA Conduct Meter CM 7B.
(dec.). Molar electric conductivity
K
(THF, r.t.):
0.018 S cm2 molꢀ1
.
4.3. Synthesis of [PdMe(aziridine)(dppe)]+[SO3CF3]ꢀ
(13)
To a suspension of [PdMe(NCMe)(dppe)]+[SO3CF3]ꢀ
(181.3 mg, 0.2557 mmol) in THF (12 ml) was added
aziridine (15.0 ll, 0.290 mmol). Stirring at room tempera-
ture for ca. 5 min gave a colorless solution. The reaction
mixture was evaporated to dryness in vacuo giving white
solid. Recrystallization from THF with hexane gave white
powder of 13. Yield: 70% (128.0 mg, 0.1798 mmol). Anal.
Calc. for C30H32F3NO3P2PdS: C, 50.61; H, 4.53; N, 1.97.
4.2. Synthesis of heterodinuclear organopalladium complexes
having a bidentate nitrogen ligand
A typical procedure for (tmeda)(PhCO)Pd–Co(CO)4 (8)
is given. PdPhI(tmeda) (142 mg, 0.333 mmol) and
Na+[Co(CO)4]ꢀ (74.8 mg, 0.386 mmol) were dissolved in
THF, and they were stirred for 2 h at 0 ꢁC under CO atmo-
sphere to give a red solution. The solution was evaporated,
and the resultant solid was extracted with benzene. After
removal of all volatile matters in a vacuum, the residual
solid was recrystallized from CHCl3/ether to give deep
red cubes of (tmeda)(PhCO)Pd–Co(CO)4 (8). Yield: 40%
(66.3 mg, 0.133 mmol). M.p. 100 ꢁC (dec.). Anal. Calc.
for C17H21CoN2O5Pd: C, 40.94; H, 4.24; N, 5.62. Found:
1
Found: C, 50.45; H, 4.70; N, 1.96%. H NMR (CD2Cl2,
r.t.): d 0.53 (dd, JHH = 7.1, 2.3 Hz, 3H, PdCH3), 1.61
(brs, 2H, NH(CH2)2), 2.1–2.6 (m, 6H, dppe CH2), 2.2
(brs, 2H, NH(CH2)2) 2.8 (brs, 1H, NH), 7.3–7.9 (m, 12H,
Ph of dppe). 31P{1H} NMR (CD2Cl2, r.t.): d 38.8 (d,
JPP = 23 Hz), 59.6 (d, JPP = 23 Hz).

S.-i. Tanaka et al. / Journal of Organometallic Chemistry 692 (2007) 26–35
33
1
2
R
R
N
2
+
R
1
L
L
Co(CO)
COR
L
L
N
4
R
−
Pd
[Co(CO) ]
Pd
4
COR
R = Me, Ph
2
2
R
R
N
N
L
L
L
L
Co(CO)
4
CO
Co(CO)
O
Pd
4
Pd
1
R
1
R
O
COR
COR
2
R
N
(OC) Co
4
2
1
L
L
Co(CO)
4
L
R
R
1
Pd
Pd
N
R
N
2
R
COR
L
COR
1
O
R
1
2
R
R
N
CO,
2
+
R
2
1
L
N
2
R
L
Co(CO)
R
4
1
R
-
Pd
Pd
[Co(CO) ]
N
4
N
L
COR
L
COR
n
1
O
R
O
R
Scheme 1. A possible mechanism for copolymerization.
4.4. Copolymerization procedure
1.0 (br, CH3), 2.2 (br, CH2), 4.0 (br, CH). Minor unit:
1H NMR (D2O, r.t.): 1.0 (brs, CH3), 2.3 (CH), 3.1 (br,
CH2).
A typical procedure for the copolymerization reactions
is given. A THF (8.0 ml) solution of catalyst (0.01 mmol)
and aziridine was transferred into a stainless steel auto-
clave under N2 or Ar flow. The autoclave was immedi-
ately closed and pressurized with CO. Then it was
heated to desired temperature using oil bath and the solu-
tion was stirred by magnetic stirrer for an appropriate
time. After the reaction, the autoclave was cooled by ice
water and CO pressure was removed. Water (10 ml) was
added to the reaction mixture and the resulted heteroge-
neous solution was filtered to remove the catalyst. The
aqueous solution was evaporated to dryness to give
copolymer which was purified by reprecipitation from
water/acetone if necessary for aziridine and 2-methylazir-
idine. For N-ethylaziridine, the product was extracted
with CH2Cl2 and reprecipitated by THF/hexane. Copoly-
mer of aziridine and carbon monoxide [5a,5c]. IR (KBr,
cmꢀ1): 1648, 1560 (mCO). 1H NMR (D2O, r.t.): d 2.2
(br, CH2CO), 3.2 (br, NHCH2). Copolymer of N-ethylaz-
iridine and carbon monoxide [5b]: IR (KBr, cmꢀ1): 1636,
4.5. Measurement of equilibrium constants and
thermodynamic parameters
(dppe)MePd–Co(CO)4 (1) (18.5 mg, 0.0268 mmol) was
placed in a NMR tube, and THF (600 ll) was added. Glass
capillary containing settled amount of PPh3 in C6D6 was
added as an external standard. Then a THF solution of azi-
ridine (1.10 M, 17.0 ll, 0.0187 mmol) was added. The
amount of the products and starting compounds in solu-
1
tion was estimated by 31P{1H} and H NMR with calibra-
tion. Equilibrium constants were given by an expression of
[[PdMe(aziridine)(dppe)]+[Co(CO)4]ꢀ (13)]/[1][aziridine].
[13] and [1] were measured by the relative intensities of
the dppe signals to external standard. Concentration of azi-
ridine was calculated by subtracting the concentration of
13 from the initial aziridine concentration, since no side
reaction was observed. Thermodynamic parameters DH
and DS were obtained according to van’t Hoff plot. Esti-
mated equilibrium constants K/Mꢀ1 (temperature/ꢁC) for
1 are shown below. Aziridine: 140(19), 86(30), 47(40),
31(50), 14(60). 2-Methylaziridine: 150(20), 89(30), 50(40),
29(50), 17(60). N-Ethylaziridine: 1.9(19), 1.1(30), 0.71(40),
0.42(50), 0.28(60).
1
1459 (mCO). H NMR (CDCl2CDCl2, 120 ꢁC): d 1.0 (br,
CH3CH2N), 2.4 (br, NHCH2CH2CO), 3.2 (br,
CH3CH2N), 3.5 (br, NHCH2CH2CO). Copolymer of 2-
methylaziridine and carbon monoxide: IR (KBr, cmꢀ1):
1649, 1553 (mCO). Major unit: 1H NMR (D2O, r.t.): d

34
S.-i. Tanaka et al. / Journal of Organometallic Chemistry 692 (2007) 26–35
(d) D.F. Shriver, H. Kaesz, R.D. Adams (Eds.), The Chemistry of
4.6. X-ray structure analyses
Metal Cluster Complexes, VCH, New York, 1990.
[2] (a) S. Komiya, I. Endo, Chem. Lett. (1988) 1709;
(b) K. Miki, N. Kasai, I. Endo, S. Komiya, Bull. Chem. Soc. Jpn. 62
(1989) 4033;
Diffraction experiments were performed on a Rigaku
four-circle diffractometer RASA-7R diffractometer with
graphite-monochromatized Mo Ka radiation (0.71069 A).
˚
(c) A. Fukuoka, T. Sadashima, T. Sugiura, X. Wu, Y. Mizuho, S.
Komiya, Organometallics 13 (1994) 4033;
A single crystal was selected by use of a polarized micro-
scope and mounted in a capillary tube (GLASS, 0.7 mm/),
which was sealed by small flame torch. The unit cells were
determined by the automatic indexing of the 20 centered
reflections. The structures were solved and refined by a full
matrix least-square procedure using the TEXSAN crystal
solution package (Rigaku) operating on a SGI O2 worksta-
tion [16]. An absorption correction was applied with the
program PSI-scan. The structure of 6 and 8 were solved
by Patterson methods (SAPI), and the structure of 9 was
solved by direct methods. For complexes 8 and 9, all
non-hydrogen atoms were found on difference Fourier
maps, and refined anisotropically, and all hydrogen atoms
were located in the calculated positions, which were not
refined. Complex 6 was refined isotropically due to low
quality of the crystal and the hydrogen atoms were not
included for the least-square calculations. The crystallo-
graphic data and details associated with data collection
are given in Table 2. ORTEP drawings of complexes 6, 8
and 9 were illustrated in Fig. 1 and the bond lengths and
angles are listed in Table 3.
(d) A. Fukuoka, T. Sadashima, I. Endo, N. Ohashi, Y. Kambara, T.
Sugiura, K. Miki, N. Kasai, S. Komiya, J. Organomet. Chem. 473
(1994) 139;
(e) A. Fukuoka, T. Sugiura, T. Yasuda, T. Taguchi, M. Hirano, S.
Komiya, Chem. Lett. (1997) 329;
(f) A. Fukuoka, S. Fukagawa, M. Hirano, S. Komiya, Chem. Lett.
(1977) 377;
(g) T. Yasuda, A. Fukuoka, M. Hirano, S. Komiya, Chem. Lett.
(1998) 29;
(h) S. Komiya, S. Muroi, M. Furuya, M. Hirano, J. Am. Chem. Soc.
122 (2000) 170;
(i) N. Komine, H. Hoh, M. Hirano, S. Komiya, Organometallics 19
(2000) 5251;
(j) A. Fukuoka, S. Fukagawa, M. Hirano, N. Koga, S. Komiya,
Organometallics 20 (2001) 2065;
(k) S. Tsutsuminai, N. Komine, M. Hirano, S. Komiya, Organomet-
allics 22 (2003) 4238;
(l) S. Tsutsuminai, N. Komine, M. Hirano, S. Komiya, Organomet-
allics 23 (2004) 44;
(m) A. Kuramoto, K. Nakanishi, T. Kawabata, N. Komine, M.
Hirano, S. Komiya, Organometallics 25 (2006) 311;
(n) N. Komine, S. Tsutsuminai, H. Hoh, T. Yasuda, M. Hirano, S.
Komiya, Inorg. Chem. Acta 359 (2006) 3699.
[3] (a) M. Furuya, S. Tsutsuminai, H. Nagasawa, N. Komine, M.
Hirano, S. Komiya, Chem. Commun. (2003) 2046;
(b) N. Komine, S. Tanaka, S. Tsutsuminai, Y. Akahane, M. Hirano,
S. Komiya, Chem. Lett. 33 (2004) 858.
Acknowledgements
[4] (a) G.L. Borgne, S.E. Bouaoud, D. Grandjean, P. Braunstein, J.
Dchand, M. Pfeffer, J. Organomet. Chem. 136 (1977) 375;
(b) Y. Misumi, Y. Ishii, M. Hidai, J. Chem. Soc., Dalton Trans.
(1995) 3489.
[5] (a) L. Jia, E. Ding, W.R. Anderson, Chem. Commun. (2001) 1436;
(b) L. Jia, H. Sun, J.T. Shay, A.M. Allgeier, S.D. Hanton, J. Am.
Chem. Soc. 124 (2002) 7282;
The work was financially supported by Grant-in-Aid for
Scientific Research from the Ministry of Education, Sci-
ence, Culture, Sports, Science and Technology, Japan
and the 21th Century COE program of ‘‘Future Nano-
materials’’ in Tokyo University of Agriculture and
Technology.
(c) J. Zhao, E. Ding, A.M. Allgeier, L. Jia, J. Polym. Sci., Part A:
Polym. Chem. 41 (2003) 376;
(d) D.J. Darensbourg, A.L. Phelps, N.L. Gall, L. Jia, J. Am. Chem.
Soc. 126 (2004) 13808.
Appendix A. Supplementary data
[6] Degree of polymerization of the copolymers was calculated as 30–70
by comparing 1H NMR signals due to the terminal acetyl group
methylene signal of the copolymer, though accurate values were
difficult to obtain due to signal overlapping. These estimated values
are approximately the same order to the obtained yields, suggesting
that one catalyst molecule produces one alternative copolymer
molecule.
[7] Introduction of carbon monoxide to a THF solution of complex 13,
which was prepared from 1 and aziridine (1:2), at room temperature
gave a complex having high catalytic activity for copolymerization on
interaction with CO (1 atm) at room temperature in low yield (ꢂ20
w%/1). This complex had low solubility in non polar solvents such as
benzene and toluene, and could also be formed from the acyl
complex, but it gradually decomposed to give uncharacterizable
material in solution. IR spectrum of this compound shows strong
m(CO) bands at 1884 cmꢀ1 assignable to [Co(CO)]ꢀ and 1676 cmꢀ1
due to the acyl unit. 31P{1H} NMR in CD2Cl2 shows an AB quartet
at d 49.0 and 30.5 ppm with a coupling constant of 38 Hz, suggesting
square planar cis configuration at Pd. Three resonances at d 2.74 (t,
J = 6.8 Hz), 3.0 (br), and 4.4 (br) in 1:1:1 ratio in CD2Cl2 are
assignable to the two methylene and NH2 protons. The compound is
Crystallographic data for the structural analysis of 6, 8,
and 9 have been deposited with the Cambridge Crystallo-
graphic Data Centre, as CCDC Nos. 299822, 299821 and
299820. A copy of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, faxint. +44 1223 336 033 or
email: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/
j.jorganchem.2006.04.044.
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tentatively characterized as
a cationic acylpalladium complex
(c) M.J. Chetcuti, in: R.D. Adams (Ed.), Comprehensive Organome-
tallic Chemistry II, vol. 10, Pergamon Press, Oxford, UK, 1995;
[(dppe){NH2CH2CH2C(O)-j2C,N}Pd]+[Co(CO)4]ꢀ, which could be

S.-i. Tanaka et al. / Journal of Organometallic Chemistry 692 (2007) 26–35
35
formed by hydrolysis of a putative intermediate [(dppe){NH(CO-
Me)CH2CH2C(O)-j2C,N}Pd]+[Co(CO)4]ꢀ under the reaction condi-
tions, though further detail studies are still required to clarify the
structure and formation mechanism. The copolymer, which was
obtained by this complex, contained a negligible amount of terminal
acyl unit.
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