Palladium(II) complexes containing P～N～O donors. Ligand effect of tridentate versus bidentate coordination on the oligomerization of ethylene

Article abstract of DOI:10.1021/om0201462

Palladium complexes containing the [(RO)_nC₆H_5-nC=]N(C₆H₄PPh ₂-o) (P～N～O) ligand were synthesized, and the hemilability of the coordinating oxygen donors toward the metal center was studied. In the case of oxygen being a ether functionality (R = Me), acetonitrile readily replaces the tridentate ether donor in [Pd(P～N～O)Me]BF₄ (1) to yield [Pd(P～N～O)(MeCN)-Me]BF₄ (2). The labile nature of the ether donor assists the complex 1 in catalyzing the oligomerization of ethylene. Presumably, the temporary coordination of the ether donor to the vacant site during migratory insertion suppresses the β-elimination, which allows the elongation of the alkyl chain.

Full text of DOI:10.1021/om0201462

Organometallics 2002, 21, 3203-3207
3203
P a lla d iu m (II) Com p lexes Con ta in in g P ∼N∼O Don or s.
Liga n d Effect of Tr id en ta te ver su s Bid en ta te
Coor d in a tion on th e Oligom er iza tion of Eth ylen e
Ping-Yung Shi, Yi-Hung Liu, Shie-Ming Peng, and Shiuh-Tzung Liu*
Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
Received February 20, 2002
Palladium complexes containing the [(RO)nC6H5-nCd]N(C6H4PPh2-o) (P ∼N∼O) ligand were
synthesized, and the hemilability of the coordinating oxygen donors toward the metal center
was studied. In the case of oxygen being a ether functionality (R ) Me), acetonitrile readily
replaces the tridentate ether donor in [Pd(P ∼N∼O)Me]BF4 (1) to yield [Pd(P ∼N∼O)(MeCN)-
Me]BF4 (2). The labile nature of the ether donor assists the complex 1 in catalyzing the
oligomerization of ethylene. Presumably, the temporary coordination of the ether donor to
the vacant site during migratory insertion suppresses the â-elimination, which allows the
elongation of the alkyl chain.
In tr od u ction
oligomerization, presumably due to less steric bulkiness
around the metal center and the trans influence of the
hetero-donor bidentate ligand.10 In this work, an in-
tramolecular hemilabile ether donor is introduced into
the P ∼N system (Chart 1), which hopefully would
suppress the â-elimination by temporary coordination
of the vacant site during migratory insertion of olefins
for the chain growth.7,8,11
Recently, searching of all kinds of catalysts for the
polymerization of olefins has received much attention.1-4
It appears that bulky substituents near the active metal
center hinder the chain transfer process or associative
displacement, which allows the polymerization to pro-
ceed smoothly and afford a high-molecular-weight
material.1-4 On the other hand, a less sterically bulky
environment or a combination of hetero-donor bidentate
coordination generally activates the oligomerization of
olefins.5-7 We have studied the insertion activity of
[(P ∼N)PdRL]+ toward various unsaturated substrates,
and such a mixed-donor system allows us to isolate the
metal-capped polymerization intermediates of various
monomers.9 However, it only catalyzes the di- and
trimerization of ethylene without any polymerization or
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10.1021/om0201462 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 06/22/2002

3204 Organometallics, Vol. 21, No. 15, 2002
Shi et al.
Ta ble 1. Selected Sp ectr a l Da ta of Com p lexes a n d Liga n d s
1H NMRa
-OCH3
compd
-CHdN-
Pd-CH3
31P NMR
IR νCdNc (cm-1
)
L1
L2
8.69
8.68
9.26
9.46
8.85
9.17
3.81, 3.68
-12.8
-14.9
38.6
41.7
43.8
1621
1621
1617
1615
1608
1609
[(P ∼N)PdMe(NCMe)]+
0.58 (J P-H ) 1.60)
0.63 (J P-H ) 1.96)
0.65 (J P-H ) 1.84)
1
4.24, 3.91
2
3b
51.1
a
b
In CDCl3, in units of ppm, with J in Hz. In acetone-d6. c In KBr.
F igu r e 1. ORTEP plot of the cationic portion of complex
1.
Ch a r t 1
F igu r e 2. 1H NMR spectra of 1 with various amounts of
acetonitrile in CDCl3.
Resu lts a n d Discu ssion
Com p lexes. Both P ∼N∼O ligands (L1 and L2) were
prepared by condensation of o-(diphenylphosphino)-
aniline with 2,4-dimethoxybenzaldehyde and 2-hydroxy-
benzaldehyde, respectively. Cationic 1 was prepared by
the reaction of L1 with (COD)PdMeCl, followed by the
addition of AgBF4 in a dichloromethane solution, and
complex 1 was obtained as yellow crystals by recrys-
tallization from a dichloromethane/ether solution, for
which a single-crystal X-ray structure has been deter-
mined (Figure 1). Spectral data of ligands and complexes
are summarized in Table 1 for comparison. The 1H NMR
spectrum of 1 shows two different methoxy signals
(Figure 2a, 4.24 and 3.91 ppm), where the 2-methoxy
group is the one bound to the metal center, as evidenced
by both the coordination chemical shift (δcomplex - δfree
ligand) and X-ray structural analysis. However, the
coordinating ether donor readily undergoes a displace-
ment reaction by acetonitrile (Scheme 1). Figure 2 shows
the 1H NMR spectra of complex 1 with various amounts
of acetonitrile in CDCl3 at room temperature. As the
concentration of acetonitrile increases, the signal of the
Sch em e 1
bound methoxy group shifts to upper field and eventu-
ally the ether donor goes to the free state. This observa-
tion indicates that the intramolecular coordination of
ether to the palladium center is substituted by aceto-
nitrile, which is generally considered as a weak coor-
dinating ligand. The acetonitrile-substituted complex 2

Pd(II) Complexes Containing P∼N∼O Donors
Organometallics, Vol. 21, No. 15, 2002 3205
Ta ble 2. Selected Bon d Dista n ces (Å), Bon d An gles
(d eg), a n d Tor sion An gles (d eg) of P a lla d iu m (II)
Com p lexes
1
3
[L2Pd(H2O)]BF4
Pd-P
2.177(1)
2.117(3)
2.178(3)
2.047(4)
2.183(1)
2.071(3)
2.039(2)
2.156(3)
2.2018(8)
1.990(2)
2.047(2)
Pd-N
Pd-O1
Pd-C1
Pd-O2
N-C10
2.062(2)
1.296(4)
1.289(5)
1.304(4)
N-Pd-P
85.56(9)
169.74(9)
84.9(1)
86.21(8)
175.67(8)
93.1(1)
85.65(7)
178.16(7)
93.70(9)
P-Pd-O1
N-Pd-O1
N-Pd-C1
N-Pd-O2
C1-Pd-O1
O1-Pd-O2
C9-C10-N
C10-N-Pd
179.4(2)
177.7(1)
176.4(1)
F igu r e 3. Molecular structure of 3.
95.6(2)
87.5(1)
89.00(9)
128.9(3)
120.9(2)
126.9(4)
124.2(3)
129.0(3)
121.5(2)
O1-Pd-N-C10
P-Pd-N-C11
O1-Pd-N-C11
P-Pd-N-C10
28.9
21.4
166.6
155.0
2.7
2.8
178.5
178.4
19.4
11.6
154.8
162.3
Cr ysta llogr a p h y. For complexes 1, 3, and [(L2)Pd-
(H2O)]BF4‚1/2CH2Cl2, single crystals were grown by slow
solvent evaporation from a mixed solvent of dichloro-
methane and ether. In case of 4, it is obtained as the
aqua-coordinated form, presumably due to the exchange
of water molecules with acetonitrile upon crystallization.
Figures 1, 3, and 4 display the ORTEP diagrams of 1,
3, and [(L2)Pd(H2O)]BF4, respectively. Selected bond
distances and bond angles are collected in Table 2. All
three complexes show square-planar coordination ge-
ometry around palladium, with bond angles slightly
deviating from 90° by virtue of the constraints imposed
by the fused chelating rings. Thus, the angles of
P-Pd-N in these three complexes are slightly larger
than those of the type [(P ∼N)PdRL] reported earier.5
As for the chelating rings, not all of them are in a planar
conformation, as evidenced by the dihedral angles. The
P, Pd, N, C10, C11, and O1 atoms lie almost in the same
plane, as the dihedral angles of O1-Pd-N-C10, P-Pd-
N-C11 and P-Pd-N-C10 are 2.7, 2.8 and 178.4°,
respectively, indicating that the two chelating rings in
3 are fused in a planar geometry; those rings in
complexes 1 and [L2Pd(H2O)]BF4 do not have such a
relationship.
There are no significant differences observed in the
Pd-P bond lengths among all complexes. However, the
distance of Pd-O1 in 1 appears to be longer by ca. 0.14
Å than those in 3 and [L2Pd(H2O)]BF4, indicating that
the coordinating ability of ether is weaker than that of
phenolate. This is also consistent with the ligand
substitution results described above, showing that the
coordinating methoxy group is readily replaced by
acetonitrile. However, comparable distances are found
in [L2Pd(H2O)]BF4, where the difference between
Pd-O1(phenolate) (2.047(2) Å) and Pd-O2(water)
(2.062(2) Å) is only about 0.02 Å.
F igu r e 4. ORTEP plot of [(P ∼N∼O)Pd(H2O)]+.
is stable as long as it is in the presence of acetonitrile
under a nitrogen atmosphere, but the ether donor
readily coordinates back to the metal center once the
acetonitrile is removed. This observation clearly dem-
onstrates the hemilability of the ether donor in hybrid
multidentate species.12
The phenol type ligand L2 could provide two kinds of
palladium complexes upon substitution with (COD)-
PdMeCl. In the presence of triethylamine, the phenoxide
readily forms from L2, which then replaces the chloride
ligand to provide the neutral palladium-methyl com-
plex 3, whereas a cationic complex of the type [(L2)Pd-
(MeCN)]+ (4) is obtained by mixing L2, (COD)PdMeCl,
and AgBF4 in the presence of acetonitrile. Here the
methyl group on the palladium is presumably removed
via an elimination of methane. Both complexes 3 and 4
are characterized by spectroscopic and elemental analy-
ses. However, the coordination of the phenolate is
confirmed by crystal structure analysis. X-ray-quality
crystals of 3 and [L2Pd(H2O)]BF4 were obtained for their
structural determination. Figures 3 and 4 display their
ORTEP plots, which are clearly in agreement with the
structure expected. As for complex 4, the coordinating
acetonitrile, which is different from the coordinating
water molecule, appeared in the crystal structure, as
1
confirmed by its H NMR shift at 2.60 ppm in acetone-
d6 and infrared absorptions at 2327 and 2301 cm-1
(νNtCMe).
Complex 3 exhibits an unusual stability in solution,
even in air. Unlike complex 1, the acetonitrile molecule
does not undergo a substitution reaction to replace the
oxygen donor in both 3 and 4, indicating that the
phenolate donor is strongly bonded to the palladium
center. However, the acetonitrile in 4 is readily replaced
by other ligands such as water. Thus, the aqua-
palladium complex [L2Pd(H2O)]BF4 was obtained upon
crystallization in the presence of moisture.
Oligom er iza tion of Eth ylen e. As mentioned ear-
lier, the complex [(P ∼N)PdMeL]+ catalyzes the di- and
trimerization of ethylene and the introduction of a labile
ether donor in the palladium complexes was expected
to hinder the â-elimination by temporarily coordinating
to the vacant site, which would propagate the chain
growth as the olefin inserts. Indeed, we have observed
(12) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680.

3206 Organometallics, Vol. 21, No. 15, 2002
Shi et al.
Ta ble 3. Oligom er iza tion of Eth ylen e Ca ta lyzed by
P a lla d iu m Com p lexesa
from the copolymerization of CO and olefin or the
oligomerization of alkynes catalyzed by [(P ∼N)PdR-
(CH3CN)]+.9c However, attempts to isolate the single
ethylene insertion intermediate failed. As for compounds
3 and 4, no catalytic activity toward ethylene is ob-
served. It is believed that the nonlabile phenolate donor
occupies the coordination sphere, which causes in-
sufficient sites for the catalytic cycle.
yield
major
entry cat. P (psi) T (°C) t (h) (mg) activityd productse
1
2
3
4
5
6
7
8
9
1
1
1
150
150
300
300
300
300
500
500
500
500
500
30
70
30
30
30
0
30
70
110
30
30
24
24
12
24
24
24
24
24
24
24
24
33
36
31
40.2
32
2.6
5.3
0.8
9.0
0.8
C6-C8
C10-C14
C10-C14
C12-C16
C8-C14
C6-C10
C10-C14
C12-C16
C12-C16
1
1b
1
31
0.8
In summary, the designed P ∼N∼O ligand, possessing
a labile ether donor, coordinates to the palladium center
and forms the stable complex 1. From crystal structure
analyses, this P ∼N∼O ligand linked through an o-
phenylene and aryl imine backbone readily forms a
tridentate chelate with palladium metal ion. The hemi-
labile ether donor is easily replaced by a weakly
coordinating ligand such as acetonitrile, and this pen-
dant ether donor plays an important role in the stabi-
lization of the coordinated unsaturated resting species,
which hinders the â-elimination and allows further
insertion to take place during the ethylene oligomer-
ization process.
1
46.3
84.7
86.3
14.3
48.1
49.5
1c
1c
3
10
11
4
a
Catalyst (30 mg) in CH2Cl2 (30 mL) was loaded in an 100 mL
autoclave. Mixed solvent CH2Cl2:CH3CN ) 4:1. c Chlorobenzene
b
as solvent, In units of 10-3 g mmol-1 h-1
.
e Based on 1H NMR
d
and GC analysis.
Sch em e 2
Exp er im en ta l Section
Gen er a l In for m a tion . All reactions, manipulations, and
purification steps were performed under
a dry nitrogen
atmosphere. Tetrahydrofuran was distilled under nitrogen
from sodium benzophenone ketyl. Dichloromethane and ac-
etonitrile were dried over CaH2 and distilled under nitrogen.
Other chemicals and solvents were of analytical grade and
were used as received, unless otherwise stated. Pd(COD)MeCl
and o-diphenylphosphinoaniline were prepared by procedures
reported earlier.13
the activity of 1 in the oligomerization of ethylene, and
the results are summarized in Table 3. Entries 1-9
summarize the activity of compound 1 toward ethylene,
whereas entries 10 and 11 show the negative results in
the catalytic polymerization of ethylene via compounds
3 and 4, respectively. The oligomers obtained in this
work were characterized by 1H NMR spectroscopy, and
the degree of oligomerization is estimated by the
integration ratio of the terminal methyl group (δ 0.85)
versus the methylene units (δ 1.23). From NMR spectra,
we did not observe any branching on these oligomeric
products.
Nuclear magnetic resonance spectra were recorded in CDCl3
or acetone-d6 on either a Bruker Avance 400 or AM-300
spectrometer. Chemical shifts are given in parts per million
relative to Me4Si for 1H and 13C NMR and relative to 85% H3-
PO4 for 31P NMR. Infrared spectra were measured on a Nicolet
Magna-IR 550 spectrometer (Series II) as KBr pellets, unless
otherwise noted.
Complex 1 does catalyze the conversion of ethylene
into oligomers, but the degree of oligomerization is poor
as compared to that for the palladium(II) unsymmetrical
diimine systems reported by Kress and co-workers.8 The
lower activity of 1 relative to that of the palladium-
diimine system is presumably due to the nonsymmetric
P ∼N bidentates conferring a reactivity difference at the
trans sites. Thus, the insertion may have higher activa-
tion energy than the homo-bidentate system does. In
addition, the coordination of ether during the chain
growth might affect the coordination of ethylene to the
metal center, which slows down the reaction. Indeed,
increasing the pressure of ethylene or the reaction
temperature appears to provide a better activity of the
catalyst (entries 1, 4, and 7), but not the degree of
oligomerization. Compared to the di- or trimerization
of ethylene catalyzed by the cationic complex [(P ∼N)-
PdRL]+, the extra coordination of ether in 1 does
prevent the â-elimination or chain transfer from occur-
ring at the resting state of chain propagation. In fact,
the FAB mass spectrum of the reaction product does
show an m/z value corresponding to the metal-capped
oligomers X (Scheme 2), indicating that such a coordi-
nation of ether readily stabilizes the insertion interme-
diate. Such kinds of intermediates have been isolated
Liga n d L1. In a 10 mL round-bottom flask was placed a
mixture of o-(diphenylphosphino)aniline (0.5 g, 1.8 mmol) and
2,5-dimethoxybenzaldehyde (0.5 g, 3 mmol) under nitrogen.
The mixture was heated to 55 °C for 20 h. After it was cooled
to room temperature, the reaction mixture was dissolved in a
mixture of dichloromethane and ethanol. Upon crystallization,
the desired compound was obtained as yellow solids (yield 0.49
g, 63%). IR (KBr): 1621 cm-1 (νNdC). 1H NMR (acetone-d6, 400
MHz): δ 8.69 (s, 1 H, -NdCH), 7.39-7.15 (m, 15 H, Ar), 6.97
(d, J ) 1.84 Hz, 2 H, Ar H), 6.70 (m, 1 H, Ar H), 3.81 (s, 3 H,
O-CH3), 3.68 (s, 3 H, O-CH3). 13C NMR: δ 154.5-153.6 (Ar
and -NdCH), 137.6-110.3 (m, Ar), 55.8 (s, O-CH3), 55.0 (s,
O-CH3). 31P NMR: δ - 12.79. Anal. Calcd for C27H24NO2P:
C, 76.22; H, 5.69; N, 3.29. Found: C, 75.89; H, 5.55; N, 3.17.
Liga n d L2. The preparation of L2 is similar to that for L1,
except 2-hydroxybenzaldehyde was used. L2 is a yellow solid
(yield 78%). IR (KBr): 1621 cm-1 (νNdC). 1H NMR (acetone-d6,
400 MHz): δ 12.50 (d, J P-H ) 0.92 Hz, 1 H, -OH), 8.67 (s, 1
H, -NdC-H), 7.51-6.86 (m, 18 H, Ar). 13C NMR: δ 163.5
(-NdCH), 160.9, 151.9, 136.4-116.7 (Ar). 31P NMR: δ -14.95.
Anal. Calcd for C25H20NOP: C, 78.73; H, 5.29; N, 3.67.
Found: C, 78.70; H, 5.14; N, 3.65.
(13) (a) Cooper, M. K.; Downes, J . M.; Duckworth, P. A. Inorg. Synth.
1989, 25, 129. (b) Rulke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier,
C. J .; van Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32,
5769.

Pd(II) Complexes Containing P∼N∼O Donors
Organometallics, Vol. 21, No. 15, 2002 3207
[(L2)Pd(H2O)]BF4
Ta ble 4. Selected Cr ysta llogr a p h ic Da ta for Com p lexes 1, 2, a n d [(L2)P d (H2O)]BF 4
1
2
formula
fw
temp, K
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C28H27BF4NO2PPd
633.69
295(2)
triclinic
P1h
8.4375(1)
10.7895(1)
15.5608(1)
89.930(1)
87.958(1)
74.651(1)
1365.15(2)
2
C26H22NOPPd
501.82
295(2)
monoclinic
P21/c
9.8631(2)
13.1038(2)
17.4209(1)
C51H44B2Cl2F8N2O4P2Pd2
1268.14
150(2)
monoclinic
P21/c
11.4929(4)
19.4797(7)
22.8521(8)
90
93.112(1)
90
5108.5(3)
4
90
97.482(1)
90
2232.38(6)
4
Z
D
calcd, Mg/m3
1.542
1.493
1.649
F(000)
640
1016
2536
cryst size, mm
θ range, deg
no. of rflns collected
no. of indep rflns
refined method
R (I > 2σ(I))
0.20 × 0.20 × 0.15
1.31-25.00
14 611
0.25 × 0.20 × 0.15
0.20 × 0.25 × 0.35
2.06-25.00
38 433
1.95-25.00
23 850
4792 (Rint ) 0.0368)
3945 (Rint ) 0.0335)
full-matrix least squares on F2
R1 ) 0.0326
wR2 ) 0.0944
1.051
8999 (Rint ) 0.0202)
R1 ) 0.0426
wR2 ) 0.1071
1.037
R1 ) 0.0296
wR2 ) 0.0789
1.058
goodness of fit on F2
Com p lex 1. To a solution of [(COD)PdMeCl] (0.6 g, 2.26
mmol) in dichloromethane (5 mL) was added a solution of L1
in dichloromethane (5 mL) under a nitrogen atmosphere. To
this resulting light yellow solution was added AgBF4 (0.42 g,
2.27 mmol) and acetonitrile (5 mL). After it was stirred for 1
h, the reaction mixture was filtered through Celite to remove
AgCl. The filtrate was concentrated, and the residue was
dissolved in a mixture of dichloromethane and ether for
crystallization. Complex 1 crystallized as yellow crystalline
solids (yield 1.12 g, 79%). IR (KBr): 1615 cm-1 (νNdC). 1H NMR
(acetone-d6, 400 MHz): δ 9.46 (s, 1 H, -NdCH), 8.11(m, 1 H,
Ar H), 7.90 (m, 1 H, Ar H), 7.75-7.25 (m, 15 H, Ar H), 4.24 (s,
3 H, -OCH3), 3.90 (s, 3 H, -OCH3), 0.62 (s, 3 H, Pd-CH3).
13C NMR: δ 165.4 (-NdCH), 155.6-153.0 (m, Ar), 135.1-
128.3 (s, Ar), 123.9-116.8 (s, Ar), 62.0 (O-CH3), 56.4 (O-CH3),
0.5 (d, J P-C ) 12.4 Hz, Pd-CH3). 31P NMR: δ 44.7. Anal. Calcd
for C28H27BF4NO2PPd: C, 53.07; H, 4.29; N, 2.21. Found: C,
52.74; H, 4.09; N, 2.13.
Com p lex 3. In a flask loaded with [(COD)PdMeCl] (0.34 g,
1.3 mmol) was added a solution of L2 (0.5 g, 1.3 mmol) and
triethylamine (0.26 g, 2.6 mmol) in THF (5 mL). The resulting
yellow solution was stirred at room temperature for 1 h. The
reaction mixture was concentrated, and the residue was
extracted with dichloromethane/water. The organic portion
was dried with Na2SO4 and concentrated to give 3 as a yellow
solid (yield 0.5 g, 77%) which is essentially identical with that
reported by Parr and Slawin.7d IR (KBr): 1608 cm-1 (νNdC).
1H NMR (CDCl3, 400 MHz): δ 8.85 (s, 1 H, NdCH), 7.66-
7.02 (m, 17 H, Ar H), 6.55 (m, 1 H, Ar H), 0.65 (d, J ) 1.84
Hz, 3 H, Pd-CH3). 13C NMR: δ 169.6 (-NdCH), 158.2, 154.7,
136.8-114.5 (Ar), - 1.4 (d, J P-C ) 32.4 Hz, Pd-CH3). 31P
NMR: δ 43.8. Anal. Calcd for C26H22NOPPd: C, 62.23; H, 4.42;
N, 2.79. Found: C, 62.16; H, 3.80; N, 2.71.
MHz): δ 9.17 (s, 1 H, NdCH), 8.38-6.71 (m, 17 H, Ar H), 2.60
(s, 3 H, CH3CN). 13C NMR: δ 166.7 (-NdCH), 160.1, 157.6,
138.8-116.4 (Ar), 2.3 (CH3CN). 31P NMR: δ 51.1. Anal. Calcd
for C27H22BF4N2OPPd: C, 52.76; H, 3.61; N, 4.56. Found: C,
52.55; H, 3.42; N, 4.22.
Oligom er iza tion of Eth ylen e. In an autoclave (100 mL)
were placed the complex (30 mg) and predried dichloromethane
(30 mL). Upon flushing with ethylene gas several times, a
constant pressure of ethylene gas was achieved. During the
reaction, ethylene was refilled when the pressure was found
to drop. The reaction mixture was stirred for a period of time,
and the reaction products were analyzed by GC and spectros-
1
copy. H NMR: δ 1.23 (br), 0.85 (br).
Cr ysta llogr a p h y. Crystals suitable for X-ray determina-
tion were obtained for 1, 3, and [L2Pd(H2O)]BF4 by slow
evaporation of dichloromethane/ether solutions at room tem-
perature. Cell parameters were determined by either
a
Siemens SMART CCD or a CAD-4 diffractometer. Crystal data
for complexes 1, 3, and [L2Pd(H2O)]BF4 are listed in Table 4,
and their ORTEP plots are shown in Figures 1-3, respectively
(labels of phenyl groups are omitted for clarity). Other crystal-
lographic data are deposited as Supporting Information.
Ack n ow led gm en t. We thank the National Science
Council for financial support (Grant No. NSC90-2113-
M-002-038).
Su p p or tin g In for m a tion Ava ila ble: Complete descrip-
tions of the X-ray crystallographic structure determinations
of 1, 3, and [L2Pd(H2O)]BF4, including tables of atomic
coordinates, isotropic and anisotropic thermal parameters, and
bond distances and angles, and an FAB mass spectrum of
metal-capped oligomers X. This material is available free of
charge via the Internet at http://pubs.acs.org.
Com p lex 4. The preparation of this complex is similar to
that for 1, except ligand L2 was used (yield 74%). IR (KBr):
1608 cm-1 (νNdC); 2327, 2301 (νNtCMe). 1H NMR (CDCl3, 400
OM0201462