Benzenedicarbonyl and benzenetricarbonyl linker pyrazolyl complexes of palladium(II): Synthesis, X-ray structures and evaluation as ethylene polymerisation catalysts

Article abstract of DOI:10.1039/b208376K

A series of novel compounds with pyrazolyl rings (pz) linked by benzenedicarbonyl (L1-L4) and benzenetricarbonyl (L5, L6) have been prepared and structurally characterized. The mutual orientation of their rings was studied by molecular mechanics. These po

Full text of DOI:10.1039/b208376K

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Benzenedicarbonyl and benzenetricarbonyl linker pyrazolyl
complexes of palladium(II): synthesis, X-ray structures and
evaluation as ethylene polymerisation catalysts†
Ilia A. Guzei,*a Kelin Li,b Galina A. Bikzhanova,a James Darkwa*b and Selwyn F. Mapolieb
a Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue,
Madison, WI 53706, USA
b Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville 7535,
South Africa
Received 28th August 2002, Accepted 12th December 2002
First published as an Advance Article on the web 20th January 2003
A series of novel compounds with pyrazolyl rings (pz) linked by benzenedicarbonyl (L1–L4) and benzenetricarbonyl
(L5, L6) have been prepared and structurally characterized. The mutual orientation of their rings was studied by
molecular mechanics. These polydentate species react with PdCl2(NCMe)2 to yield dinuclear complexes in which the
Pd centers coordinate to one or two pz units, a terminal chloride and two bridging chloride ligands. In complex
[{(3,5-tBu2pzCO)3-1,3,5-C6H4}Pd2Cl2(µ-Cl)2]4 the pyrazolyl ligand L5 acts as a bidentate donor despite the presence
of the third pz group. These Pd complexes, when activated with methylaluminoxide (MAO), exhibit activity in
ethylene polymerization.
of poly(1-pyrazolyl) linker compounds is comprised of
Introduction
pyridine, 2,6-bis(1-pyridin-2-ylpyrazol-3-yl)pyridine or ben-
Nitrogen-bound metal complexes containing imidazole and
zene,9 1,3-bis(pyrazol-1-ylmethyl)benzene,10 and tri-substituted
imidazole-like ligands, such as pyrazoles are of interest in pro-
benzene.11 Cyclophosphazenes can also be utilized in this
tein model studies and drug design.1 In particular, pyrazole
role for poly(1-pyrazolyl) compounds as demonstrated by
(pyrazole = pzH) derivatives have been used to mimic isomeric
imidazole coordination in model studies of metalloenzymes.2
Drug related work includes bridging pyrazolato platinum
complexes as anti-cancer agents.3 The widest application of
pyrazoles is observed in geminal poly(1-pyrazolyl) compounds
that form versatile ligands.4 Geminal poly(1-pyrazolyl) com-
pounds are uninegative ligands with bonding modes ranging
from bidentate to tetradentate.4 Poly(1-pyrazolyl) ligands are
known to stabilize metals in both high and low oxidation
states.5 Pyrazolyl compounds are dominated by BR and BR2
linkers as in RB(3,5-RЈ2pz)3 and R2B(3,5-RЈ2pz)2 (R = H,
alkyl, aryl; pz = C3H3N2), with a few that do not have borate
linkers. The preparative chemistry of poly(1-pyrazolyl) ligands
includes modification of the substituents at the carbon atoms
of the pz rings as well as the linkers that hold the pyrazolyl
moieties together. The choice of substituents affects the nucleo-
philicity of the nitrogen atoms and hence the strength of bond-
ing to the ligated metal. Thus, the overall electrophilic nature
of the metal complex can be fine tuned by the choice of pz
substituents, linkers, or both.
While a variety of substituted pyrazolyl rings in poly-
(1-pyrazolyl) compounds has been extensively studied,4 the
modification of linking units has received little attention. In
1980 Mani and Scapacci reported the first example of a non-
boron linker poly(1-pyrazolyl) compound by preparing tris(3,5-
dimethylpyrazolyl-1-methyl)amine.6 This was soon followed by
the work of Driessen et al. on N,NЈ-(bis(3,5-dimethylpyrazolyl-
1-methyl)aminoethane,7a which demonstrated that the amino-
ethane linker allowed the ligand to discriminate between
metal ions in complex formation due to the modified nucleo-
philicity of the pz rings. This shows that sterically compact non-
borate pyrazolyl ligands discriminate between different metal
ions better than their borate congeners.7 In a related work,
Sorrel et al.8 reported the use of 2,6-bis[bis(1-pyrazolyl)ethyl-
amino]-p-cresol derivatives as ligands for copper. Another class
Chandrasekar et al.12 and others.13 However, none of the latter
affects the donor ability of the nitrogen atoms in the pyrazolyl
units considerably.
An interesting property of pz ligand metal complexes is their
catalytic activity in oligomerisation and polymerisation of
olefins14 in addition to the ability to activate C–H bonds.15 For
example, in oligomerisation and polymerisation catalysis of
olefins, the electrophilicity of [R2C(pz)2PdMe]ϩ 14b (R = Me, Ph)
is considered crucial since the first step in the oligomerisation or
polymerisation reaction involves the formation of a palladium–
olefin complex. In order to increase the catalytic activity of the
pz complexes the presence of a strong electrophilic metal is
essential.
Recently, we have set out to explore the influence of electron-
withdrawing carbonyl groups located between substituted pz
ligands and benzene linkers on nucleophilicity of the pyrazolyl
nitrogen atoms and their bonding with the central metal in a
number of palladium complexes. Here we report the syntheses
and structures of the new type of ligands with several pz
moieties as well as syntheses, structures, and catalytic activity
of Pd complexes bearing these ligands.
Ϫ
Ϫ
Preliminary investigations of these palladium pyrazolyl
complexes as ethylene polymerisation catalysts, show the
pyrazolyl palladium compounds are able to catalyse this
reaction though the catalysts decompose over time.
Experimental
All reactions were performed under a dry, deoxygenated nitro-
gen atmosphere using standard Schlenk techniques. Et3N was
dried over KOH. Toluene and hexane were dried with sodium/
benzophenone and dichloromethane with P2O5. 3,5-ditert-
butylpyrazole16 was prepared according to
a
literature
procedure.
3,5-Dimethylpyrazole,
1,2-benzenedicarbonyl
dichloride, 1,3-benzenedicarbonyldichlorideand1,3,5-benzene-
tricarbonyl trichloride were obtained from Aldrich and used
as received. Ethylene (99.9%) was purchased from AFROX
(South Africa) and used as received. Methylaluminoxane
† Electronic supplementary information (ESI) available: molecular
structures and bond lengths and angles for L2, L3, L6 and 2. See http://
www.rsc.org/suppdata/dt/b2/b208376k/
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 7 1 5 – 7 2 2
715

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(10% wt.) in toluene was purchased from Aldrich and trans-
ferred in a glove box. The NMR spectra were recorded on a
Gemini 2000 instrument (1H at 200 MHz, 13C at 50.3 MHz) at
room temperature. The chemical shifts are reported in δ(ppm)
and referenced to residual proton and 13C signals of deuterated
chloroform as internal standard. 13C NMR spectra of poly-
ethylene were recorded in 1,2,4-trichlorobenzene at 115 ЊC. The
number- and weight-average molecular weights (Mn and Mw)
and polydispersity (Mw/Mn) of polymers were determined by
high temperature gel permeation chromatography (trichloro-
benzene, 145 ЊC, rate = 1.000 mL minϪ1) on a Waters 2000
instrument. These measurements were performed at the Group
Technologies Research and Development laboratory of SASOL
Polymers. Thermal analyses were performed on a Universal
V2.3H TA instrument. Elemental analysis was performed on
a Carlo Erba NA analyzer in the Department of Chemistry,
University of the Western Cape.
5-tBu); 1.07 (s, 18H, 3-tBu). 13C{1H} NMR (CDCl3): δ 167.9;
162.9; 157.7; 137.5; 130.0; 129.1; 106.1; 33.2; 32.2; 29.6; 29.1.
1,3,5-Tris(3,5-di-tert-butylpyrazolyl-1-carbonyl)benzene (L5)
To a solution of 1,3,5-benzenetricarbonyl trichloride (0.50 g,
1.88 mmol) in toluene (60 mL) was added a solution of 3,5-di-
tert-butylpyrazole (1.02 g, 3.76 mmol) in toulene (20 mL)
and Et3N (2 mL). The mixture was heated at 60 ЊC for 18 h,
filtered solvent removed in vacuo give a solid residue which
was chromatographed on a silica gel column using CH2Cl2
as eluent. Evaporation of the eluate gave analytically pure
L5. Yield = 0.60 g, 46%. Anal. Calc. for C42H60N6O3: C,
72.38; H, 8.68; N, 12.06. Found: C, 71.95; H, 9.32; N, 11.41%.
1H NMR (CDCl3): δ 8.80 (s, 3H, Ph); 6.17 (s, 2H, pyrazole);
1.46 (s, 18H, 5-tBu); 1.18 (s, 18H, 3-tBu). 13C{1H} NMR
(CDCl3): δ 166.2; 152.3; 144.6; 137.0; 132.7; 111.0; 33.2; 32.1;
29.5; 29.3.
Compound L6 was synthesized in a similar fashion.
1,3-Bis(3,5-di-tert-butylpyrazolyl-1-carbonyl)benzene (L1)
1,3-Benzenedicarbonyl dichloride (0.60 g, 2.07 mmol) was
added to a solution of 3,5-di-tert-butylpyrazole (1.00 g, 5.56
mmol) in dry toluene (40 mL), followed by the addition of Et3N
(2 mL). A white precipitate formed immediately and the mix-
ture was stirred at 80 ЊC overnight. Upon cooling and filtration,
the filtrate was evaporated to yield an oil, which was chromato-
graphed (silica gel) using CH2Cl2–hexane (4:1) as eluent. The
eluate was evaporated to produce a white solid. Yield = 1.00 g,
73%. Anal. Calc. for C30H42N4O2: C, 73.43; H, 8.63; N, 11.42.
Found: C, 73.75; H, 9.19; N, 11.36%. 1H NMR (CDCl3): δ 8.52
1,3,5-Tris(3,5-dimethylpyrazolyl-1-carbonyl)benzene (L6)
This compound was prepared from the reaction of 1,3,5-
benzenetricarbonyl trichloride (1.00 g, 3.77 mmol) and 3,5-di-
methylpyrazole (1.09 g, 11.30 mmol). Yield = 0.77 g, 46%. Anal.
Calc. for C24H24N6O3: C, 64.85; H, 5.44; N, 18.91. Found: C,
64.82; H, 5.33; N, 18.43%. 1H NMR (CDCl3): δ 8.77 (s, 3H, Ph);
6.55 (s, 2H, pyrazole); 2.64 (s, 6H, 5-CH3); 2.24 (s, 6H, 3-CH3).
13C{1H} NMR (CDCl3): δ 166.7; 152.6; 145.1; 137.4; 133.1;
111.5; 14.3; 13.9.
3
2
(t, 1H, Ph, JHH = 1.8 Hz); 8.15 (dd, 2H, Ph, JHH = 12.2 Hz,
2
3JHH = 1.8 Hz); 7.48Ϫ7.55 (t, 1H, Ph, JHH = 12.2 Hz); 6.17
Di-ꢀ-chloro-dichloro[1,3-bis(3,5-di-tert-butylpyrazolyl-1-
carbonyl)benzene]dipalladium(II) (1)
(s, 2H, 4-pyrazole); 1.46 (s, 18H, 5-tBu); 1.21 (s, 18H, 3-tBu).
13C{1H} NMR (CDCl3): δ 168.1; 162.8; 157.7; 135.8; 135.1;
134.1; 127.0; 105.6; 33.1; 32.2; 29.8; 29.7.
Ligand L1 (0.42 g, 0.77 mmol) was added to a solution of
[PdCl2(NCMe)2] (0.40 g, 1.54 mmol) in CH2Cl2 (40 mL). A red,
homogeneous solution formed immediately. After stirring for a
further 8 h at room temperature, the solvent was evaporated to
give a red residue. Recrystallization from CH2Cl2–diethyl ether
at Ϫ15 ЊC yielded analytically pure product (0.62 g, 95%) as red
crystals suitable for X-ray analysis. Anal. Calc. for C30H42-
Cl4N4O2Pd2: C, 42.63; H, 5.01; N, 6.63. Found: C, 42.69;
H, 4.79; N, 6.60%. 1H NMR (CDCl3): δ 9.05 (dd, 2H, Ph,
Compounds L2 and L3 were prepared in a similar fashion.
1,3-Bis(3,5-dimethylpyrazolyl-1-carbonyl)benzene (L2)
This compound was prepared from the reaction of 1,3-benzene-
dicarbonyl dichloride (2.16 g, 10.40 mmol) and 3,5-di-
methylpyrazole (2.00 g, 20.81 mmol). Yield = 2.15 g, 64%. Anal.
Calc. for C18H18N4O2: C, 67.07; H, 5.63; N, 17.38. Found: C,
67.47; H, 5.57; N, 17.10%. 1H NMR (CDCl3): δ 8.57Ϫ8.59
3
3
2JHH = 7.8 Hz, JHH = 1.8 Hz); 8.42 (t, 1H, Ph, JHH = 1.8 Hz);
2
3
2
8.28 (t, 1H, Ph, JHH = 7.8 Hz); 6.36 (s, 2H, 4-pyrazole); 1.83
(t, 1H, Ph, JHH = 1.8 Hz); 8.18 (dd, 2H, Ph, JHH = 7.8 Hz,
(s, 18H, 5-tBu); 1.47 (s, 18H, 3-tBu). 13C NMR{1H} (CDCl3):
δ 168.8, 168.7, 163.7, 140.5, 136.8, 133.8, 131.7, 109.7, 33.6,
33.4, 31.4, 30.3.
3JHH = 1.8 Hz); 7.56 (t, 1H, Ph, JHH = 7.8 Hz); 6.06 (s, 2H,
2
4-pyrazole); 2.63 (s, 6H, 5-CH3); 2.23 (s, 6H, 3-CH3). 13C{1H}
NMR (CDCl3): δ 167.3; 152.2; 145.0; 134.8; 134.1; 133.2; 127.2;
111.1; 14.2; 13.7.
Di-ꢀ-chloro-dichloro[1,3-bis(3,5-dimethylpyrazolyl-1-carbonyl)-
benzene]dipalladium(II)–dichloromethane (2)
1,3-Bis(3-methylpyrazolyl-1-carbonyl)benzene (L3)
Complex 2 was prepared following the procedure for 1 above
but using L2 (0.25 g, 0.77 mmol) and [PdCl2(NCMe)2] (0.40 g,
1.54 mmol). Recrystallization from CH2Cl2–diethyl ether at
Ϫ15 ЊC yielded red crystals suitable for X-ray analysis. Yield =
0.53 g, 96%. Anal. Calc. for C19H20Cl6N4O2Pd2: C, 29.95; H,
This compound was prepared from the reaction of 1,3-benzene-
dicarbonyl dichloride (2.16 g, 10.40 mmol) and 3-methyl-
pyrazole (1.73 mL, 20.81 mmol). Yield = 2.02 g, 66%. Anal.
Calc. for C16H14N4O2: C, 65.30; H, 4.79; N, 19.04. Found: C,
66.88; H, 4.59; N, 19.22%. 1H NMR (CDCl3): δ 8.88 (t, 1H, Ph,
3JHH = 1.9 Hz); 8.36 (dd, 2H, Ph, 2JHH = 8.0 Hz, 3JHH = 1.8 Hz);
1
2.65; N, 7.35. Found: C, 29.31; H, 2.17; N, 7.36%. H NMR
(CDCl3): δ 8.78 (dd, 2H, Ph, 2JHH = 7.9 Hz, 3JHH = 1.7 Hz); 8.31
(t, 1H, Ph, 2JHH = 7.9 Hz); 7.94 (t, 1H, Ph, 3JHH = 1.7 Hz); 6.27
(s, 2H, 4-pyrazole); 2.76 (s, 6H, 5-CH3); 2.64 (s, 6H, 3-CH3).
13C{1H} NMR (CDCl3): δ 166.0, 157.5, 150.3, 138.3, 135.2,
133.4, 131.3, 112.7, 16.1, 14.1.
8.33 (d, 2H, 5-pyrazole, 2JHH = 2.6 Hz); 7.64 (t, 1H, Ph, 2JHH
=
2
8.0 Hz); 6.35 (d, 2H, 4-pyrazole, JHH = 2.6 Hz); 2.35 (s, 6H,
3-CH3). 13C{1H} NMR (CDCl3): δ 165.0; 154.7; 135.4; 134.6;
131.9; 131.6; 127.8; 110.51; 14.0.
1,2-Bis(3,5-di-tert-butylpyrazolyl-1-carbonyl)benzene (L4)
Di-ꢀ-chloro-dichlorobis[1,3-bis(3,5-di-tert-butylpyrazolyl-1-
carbonyl)benzene]dipalladium(II) (3)
The procedure is similar to that for compound L1 but using 3,5-
di-tert-butylpyrazole (2.00 g, 11.09 mmol) and 1,2-benzene-
dicarbonyl dichloride (0.80 mL, 5.55 mmol). Yield = 1.27 g, 42%
Anal. Calc. for C30H42N4O2: C, 73.43; H, 8.63; N, 11.42. Found:
C, 73.30; H, 9.76; N, 11.38%. 1H NMR (CDCl3): δ 7.80 (dd, 2H,
Ligand L2 (0.50 g, 1.54 mmol) was added to a solution of
[PdCl2(NCMe)2] (0.40 g, 1.54 mmol) in CH2Cl2 (40 mL). A red
precipitate formed immediately. After stirring overnight, the
precipitate was filtered off and washed with CH2Cl2 to give pure
product. Yield = 0.40 g, 52%. Anal. Calc. for C37H38Cl6N8O4-
2
3
2
Ph, JHH = 5.4 Hz, JHH = 3.2 Hz); 7.50 (dd, 2H, Ph, JHH
=
3
5.9 Hz, JHH = 3.3 Hz); 6.06 (s, 2H, 4-pyrazole); 1.36 (s, 18H,
D a l t o n T r a n s . , 2 0 0 3 , 7 1 5 – 7 2 2
716

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Pd2: C, 40.98; H, 3.53; N, 10.33. Found: C, 41.05; H, 3.20; N,
10.68%.
Di-ꢀ-chloro-dichloro[1,3,5-bis(3,5-di-tert-butylpyrazolyl-1-
carbonyl)benzene]dipalladium(II) (4)
To a solution of [PdCl2(NCMe)2] (0.25 g, 0.96 mmol) in CH2Cl2
(40 mL), was added 0.34 g (0.48 mmol) of L5. A red, homo-
geneous solution formed immediately. After stirring overnight,
the solvent was evaporated to give a red residue, which was
recrystallized from CH2Cl2–hexane to give a red powder. Yield
= 0.48 g, 94%. Anal. Calc. for C42H60Cl4N6O3Pd2: C, 47.97; H,
1
5.75; N, 7.99. Found: C, 47.56; H, 6.10; N, 7.09%. H NMR
3
(CDCl3): δ 9.50 (d, 2H, Ph, JHH = 1.8 Hz); 8.49 (t, 1H, Ph,
3JHH = 1.6 Hz); 6.35 (s, 2H, 4-pyrazole); 6.22 (s, 1H, 4-pyrazole);
1.81 (s, 18H, 5-tBu); 1.57 (s, 9H, 5-tBu) 1.48 (s, 18H, 3-tBu); 1.24
(s, 9H, 3-tBu). 13C{1H} NMR (CDCl3): δ 168.6, 168.3, 164.8,
163.8, 158.8, 142.4, 138.5, 138.4, 133.3, 109.8, 106.7, 33.7, 33.4,
31.4, 30.4, 29.9.
General procedure for polymerisation of ethylene
Polymerisation was carried out in a 300 mL stainless steel auto-
clave, which was loaded with the catalyst and co-catalyst,
methylaluminoxane (MAO), in a nitrogen purged glove box.
This was done as follows: the autoclave was charged with a
palladium complex in dry toluene (150 mL), and appropriate
amount of MAO (10% in toluene) (Al:Pd = 1000:1) was added
in a glove box. The reactor was sealed and removed from the
glove box. The autoclave was flushed three times with ethylene
and heated to the polymerization temperature. Ethylene was
continuously supplied to maintain constant pressure during the
polymerization. After the set experiment time, excess ethyl-
ene was vented and the polymerization quenched by adding
ethanol. The polymer was filtered off, washed with 2 M HCl
followed by ethanol. It was dried in an oven overnight at 50 ЊC
under vacuum.
X-Ray structural determination
Crystal evaluation and data collection were performed on a
Bruker CCD-1000 diffractometer with Mo-Kα (λ = 0.71073 Å)
radiation and the diffractometer to crystal distance of 4.9 cm.
Crystal data, data collection, and refinement parameters are
listed in Tables 1 and 2. The initial cell constants were obtained
from three series of ω-scans at different starting angles. The
reflections were successfully indexed by an automated indexing
routine built in the SMART program. These highly redundant
datasets were corrected for Lorentz and polarization effects.
The absorption correction was based on fitting a function to the
empirical transmission surface as sampled by multiple equiv-
alent measurements.17 The structures were solved by direct
methods and refined by least-squares techniques using the
SHELXTL program.18 All non-hydrogen atoms were refined
with anisotropic displacement coefficients. All hydrogen atoms
were included in the structure factor calculation at idealized
positions and were allowed to ride on the neighbouring atoms
with relative isotropic displacement coefficients.
CCDC reference numbers 178094, 178095, 178097 and
185333–185338.
See http://www.rsc.org/suppdata/dt/b2/b208376k/ for crystal-
lographic data in CIF or other electronic format.
Results and discussion
Synthesis of ligands
Compounds L1–L6 were synthesized according to Scheme 1
from the reaction of 1,3-benzenedicarbonyl dichloride (L1–
L3), 1,2-benzenedicarbonyl dichloride (L4), or 1,3,5-benzene-
tricarbonyl trichloride (L5 and L6) and two (three in case of
L5 and L6) equivalents of the appropriate pyrazole.
D a l t o n T r a n s . , 2 0 0 3 , 7 1 5 – 7 2 2
717

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Table 2 Crystal data and structure refinement for complexes 1, 2 and 4
1
2
4
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
C30H42Cl4N4O2Pd2
845.28
173(2)
C19H20Cl6N4O2Pd2
761.89
296(2)
C42H60Cl4N6O3Pd2ؒ4/3CH2Cl2
1136.49
173(2)
Triclinic
Triclinic
Triclinic
¯
¯
¯
P1
P1
P1
11.8754(10)
12.1953(10)
14.4906(13)
86.828(2)
72.340(2)
63.363(2)
1779.4(3)
2
1.578
1.343
0.40 × 0.30 × 0.20
CCD-1000
Empirical
0.7750/0.6157
3.41
11.4285(11)
11.5080(11)
11.9381(12)
100.520(2)
118.329(2)
98.458(2)
1308.3(2)
2
1.934
2.012
0.25 × 0.20 × 0.06
P4/CCD 1K
Empirical
0.8888/0.6332
4.07
10.6994(6)
14.6275(7)
17.7885(10)
72.212(1)
86.365(1)
81.477(1)
2621.1(2)
2
1.440
1.033
0.40 × 0.40 × 0.20
P4/CCD 1K
Empirical
0.8201/0.6828
4.83
γ/Њ
V/Å3
Z
Dc/Mg mϪ3
µ(Mo-Kα)/mmϪ1
Crystal size/mm
Diffractometer
Absorption correction
T max/T min
R(F)a (%) [I > 2σ(I )]
R(w F 2)a (%) (all data)
11.04
10.90
13.06
2
a Quantity minimized = R(w F 2) = Σ[w(Fo2 Ϫ Fc2)]/Σ[(wFo )2]1/2; R = Σ∆/Σ(Fo), ∆ = |(Fo Ϫ Fc)|.
Scheme 1
1
Examination of the H NMR spectra of compounds L1–L3
reveals the effect of the carbonyl groups on the benzene pro-
tons. The signals of the protons on carbon 2 of the benzene
linkers show the largest downfield shifts, while the protons of
carbon 5 are least affected. Compound L4 has a typical
AAЈBBЈ spin system for the 1,2-benzene linker. These data
confirm C2 symmetry of compounds L1–L4 in solution.
ESI.† All bond distances and angles in the six structures fall
within the expected ranges while some torsion angles deserve
special discussion, vide infra. The structures of the 1,3-(3,5-
R2pzC(O))2C6H4 and 1,2-(3,5-R2pzC(O))2C6H4 compounds in
the solid state can possess either C2 or Cs symmetry. Hypo-
thetically, a C2v arrangement is conceivable for a highly strained
molecule but since this is not realistic and it will not be con-
sidered here. In solution, the pyrazolyl-1-ylcarbonyl benzene
rings substituents are enantiotopic. The C2 symmetry is
attained when the pz substituents on the benzene ring reside on
the opposite sides of its plane. The Cs symmetry is observed
when both substituents are on the same side of the ring with the
Solid-state structures of L1–L6 were determined by single
crystal X-ray crystallography. Crystallographic parameters for
L1–L6 are presented in Table 1. The molecular structural
diagrams of L1, L4 and L5 are shown in Figs. 1–3, respectively,
while the structural diagrams of L2, L3 and L6 are deposited as
D a l t o n T r a n s . , 2 0 0 3 , 7 1 5 – 7 2 2
718

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Fig.
1
Molecular drawing of L1 shown with 30% probability
ellipsoids. The hydrogen atoms are omitted for clarity. Selected bond
lengths [Å] and angles [Њ]: N(1)–N(2), 1.3889(14); N(3)–N(4),
1.3837(15); N(2)–C(12), 1.4057(16); N(3)–C(19) 1.4186(17); O(1)–
C(12), 1.2098(16); O(2)–C(19), 1.2060(17); C(12)–C(13), 1.4952(18);
C(17)–C(19), 1.4966(19); N(1)–N(2)–C(12), 118.16(10); N(4)–N(3)–
C(19) 116.67(10); O(1)–C(12)–N(2), 120.30(12); N(2)–C(12)–C(13),
Fig. 3 Molecular drawing of L5 with the preferred orientations of the
disordered groups shown with 30% probability ellipsoids. The hydrogen
atoms are omitted for clarity. Selected bond lengths [Å] and angles [Њ]:
N(1)–N(2), 1.387(3); N(3)–N(4), 1.385(3); N(5)–N(6), 1.382(3); N(1)–
C(7), 1.423(3); N(4)–C(19) 1.404(3); N(5)–C(31), 1.409(3); O(1)–C(7),
1.205(3); O(2)–C(19), 1.209(3); O(3)–C(31), 1.210(3); C(1)–C(7),
1.494(4); C(3)–C(19), 1.497(4); C(5)–C(31), 1.493(3); N(2)–N(1)–C(7),
117.5(2); N(3)–N(4)–C(19) 116.77(19); N(6)–N(5)–C(31), 116.63; O(1)–
C(7)–N(1), 120.1(2); O(1)–C(7)–C(1), 121.4(2); N(1)–C(7)–C(1),
118.4(2); O(2)–C(19)–N(4), 120.8(2); O(2)–C(19)–C(3), 120.3(2); N(4)–
C(19)–C(3), 118.9(2). O(3)–C(31)–N(5), 120.6(2); O(3)–C(31)–C(5),
121.6(2); N(5)–C(31)–C(5), 117.8(2).
119.80(11);
121.95(12);
117.66(11).
O(1)–C(12)–C(13),
O(2)–C(19)–N(3),
119.90(12);
120.39(12);
O(2)–C(19)–C(17),
N(3)–C(19)–C(17),
tautomers. Therefore, during the synthesis of L3 the least
sterically hindered product was formed.
The structures of L5 and L6 can exists in a variety of ener-
getically similar conformations as revealed by the results of
molecular modeling calculations carried out on a simplified
analogue molecule 1,3,5-(3,5-H2pzC(O))3C6H3. Its highest
symmetry attainable without inducing considerable steric
repulsion between the bulky substituent is C3 with the three pz
substituents tilted in the same fashion relative to the benzene
ring. It is also possible to envision a Cs arrangement when
the mirror plane contains one pz substituent and dissects the
phenyl ring through the carbons bearing this substituent and
the carbon in the para position while the other substituents
arranged as mirror images across this mirror. Neither however
is observed in the solid-state structures of L5 and L6 as both
molecules are asymmetrical. It is worth mentioning that in
compound L5 all three pz substituents are on the same side of
the benzene ring (pseudo-C3 symmetry) while in L6 two sub-
stituents are on one side of the ring and the third one is on the
other.
Fig.
2
Molecular drawing of L4 shown with 30% probability
ellipsoids. The hydrogen atoms are omitted for clarity. Selected bond
lengths [Å] and angles [Њ]: N(1)–N(2), 1.3894(18); N(3)–N(4),
1.3779(19); N(1)–C(5), 1.407(2); N(3)–C(24) 1.393(2); O(1)–C(12),
1.212(2); O(2)–C(19), 1.205(2); C(18)–C(19), 1.503(2); C(12)–C(13),
1.490(2); N(2)–N(1)–C(7), 117.59(13); N(4)–N(3)–C(19) 116.18(13);
O(1)–C(12)–C(13), 120.07(15); O(2)–C(19)–C(18), 120.82(16); O(1)–
C(12)–N(1), 121.06(15); O(2)–C(19)–N(3), 122.71(16); N(1)–C(12)–
C(13), 118.86(14); N(3)–C(19)–C(18), 116.36(14).
There are several common features shared by L1–L6. In all
these molecules the configuration about the single bond C–N in
mirror plane perpendicular to the plane of the ring. Molecular
modeling calculations with the MMFFs force field performed
on the simplified model of these compounds, 1,3-(3,5-H2-
pzC(O))2C6H4, indicated that these two symmetrical conform-
ations are energetically equivalent and are close in energy
to a number of calculated energetic minima corresponding
to various Ci arrangements. Thus, the spatial arrangement
observed in the solid state depends strongly upon the inter-
molecular interactions in the lattice as well as on packing forces.
The X-ray single crystal structural analysis concurs with this
assessment.
the O᎐C–N–N linkage is inevitably E. This spatial arrangement
᎐
maximizes delocalization of the electron density between the
carbonyl and the pz ring. It is important to notice that while
benzyldialdehyde is planar, compounds L1–L6 cannot achieve
planarity due to either close proximity of the pyrazolyl sub-
stituent in the 2-position to the ortho hydrogen of the phenyl
ring, or due to unfavorable interactions between the nitrogen
lone pair and the ortho hydrogen. Thus, a conjugated system
delocalized over the two rings and the carbonyl cannot be
attained. The C᎐O group can, however, be coplanar with
᎐
The structure of L3 possesses crystallographic two-fold
symmetry (molecular symmetry C2) while the structures of L1,
L2 and L4 are not symmetrical in the solid state (molecular
symmetry Ci). Interestingly, the pz substituents in L1, L2 and
L4 are on the same side of the benzene ring in an arrangement
that is closer to the Cs symmetry than to C2. One additional
structural feature of L3 to be noted is the asymmetrical
substitution of the pz ligands with the Me group being in the
3 position. In solution, 3-MepzH and 5-MepzH are indis-
tinguishable due to a dynamic equilibrium between these
either ring since both pyrazolyl and phenyl groups possess a
delocalized π-system. The preferred ring is the pyrazole.
The C–N bond in the O᎐C–N–N linkage is expected to be
᎐
shorter than the generic Csp2–Nsp2 single bond due to electronic
resonance. The C–N bond is the shortest when the torsion angle
O–C–N–N is 180Њ and longest when the angle is 90Њ. The length
of the C–N bond can ideally be described as a cosine function
of the O᎐C–N–N torsion angle. Fig. 4 shows the dependence of
᎐
the C–N bond distance in the free ligand O᎐C–N–N linkage on
᎐
the O᎐C–N–N torsion angle. It represents 14 values observed in
᎐
D a l t o n T r a n s . , 2 0 0 3 , 7 1 5 – 7 2 2
719

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Fig. 4 Dependence of the C–N bond distance in the free ligand O᎐C–
᎐
N–N linkage on the O᎐C–N–N torsion angle. The abscissa shows the
᎐
value of the O=C–N–N torsion angle while the ordinate is the
corresponding C–N bond length. The squares show the theoretical and
triangles the experimentally observed values.
Fig. 5 A molecular drawing of 1 shown with 50% probability
ellipsoids. The H atoms are omitted for clarity. Selected bond lengths
[Å] and angles [Њ]: Pd(1)–N(1), 2.029(3); Pd(2)–N(3), 2.040(3); Pd(1)–
Cl(1), 2.2683(11); Pd(2)–Cl(2), 2.2647(11); Pd(1)–Cl(4), 2.3094(11);
Pd(2)–Cl(4), 2.3031(11); Pd(1)–Cl(3), 2.3640(10); Pd(2)–Cl(3),
2.3844(11); Pd(1)–Pd(2), 3.2117(5); N(1)–Pd(1)–Cl(1), 89.08(10); N(3)–
Pd(2)–Cl(4), 178.22(10); N(1)–Pd(1)–Cl(4), 179.17(10); Cl(2)–Pd(2)–
Cl(4), 91.36(4); Cl(1)–Pd(1)–Cl(4), 91.49(4); N(3)–Pd(2)–Cl(3),
93.19(10); N(1)–Pd(1)–Cl(3), 93.69(10); Cl(2)–Pd(2)–Cl(3), 176.78(4);
Cl(1)–Pd(1)–Cl(3), 176.99(4); Cl(4)–Pd(2)–Cl(3), 85.43(4); Cl(4)–
Pd(1)–Cl(3), 85.76(4).
L1–L6 and several theoretical values obtained by performing
MMFFs calculations on 3,5-H2pz–C(O)–Ph.
An attempt to parameterize the conformations of the mole-
cules by considering torsion angles O᎐C–C–C and O᎐C–N–N
᎐
᎐
as well as the dihedral angle between the pz and Ph planes, did
not reveal any systematic trend. MMFFs calculations con-
firmed that the most energetically favorable conformations are
those in which the carbonyl is coplanar with the pz ring. The
experimentally observed values in Fig. 4 lie above the theoreti-
cally calculated values, but the differences are not statistically
significant and are accounted for by the standard uncertainties
intrinsic to the X-ray single crystal analysis and the actual sub-
stitution pattern. The dihedral angles between the pz and Ph
planes in L1–L6 were about 30Њ regardless of the substituents
on the pyrazole.
Synthesis of metal complexes
Compounds L1 and L2 react with [PdCl2(NCMe)2] in a 1:2
ratio to form red Pd complexes 1 and 2 (Scheme 1) in high
yields, whereas a similar reaction with L3 gave intractable
materials. These complexes were characterized by multinuclear
NMR spectroscopy, elemental analysis and single crystal X-ray
analyses. The reaction between L2 and [PdCl2(NCMe)2] in a 1:1
ratio yielded complex 3, which, once isolated, became insoluble
in common organic solvents such as CH2Cl2, toluene, DMSO
and THF. Thus, it was characterized by elemental analysis.
Even though complex 3 is formulated as a dimeric structure
(Scheme 1) the possibility of it being an oligomer, which could
explain its insoluble nature, cannot be discounted. Interestingly,
the reaction of L1 with [PdCl2(NCMe)2] in either 1:2 or 1:1
ratios produced exclusively complex 1. The 1H NMR spectrum
of 1 has its most downfield chemical shift associated with pro-
tons in positions 4 and 6 of the benzene linker and illustrates
that on complexation, L1 is locked into a rigid framework that
does not allow free rotation of the carbonyl functional groups.
This is confirmed by the solid state structure of 1 (Fig. 5). The
X-ray structures of 1 and 2 show how each pyrazolyl unit in
both ligands is bonded to different Pd atoms with the nitrogen
atom lone pair. Complexes 1 and 2 are thus stabilized via
bridging chlorides (Fig. 5).
Fig. 6 A molecular drawing of 4 shown with 50% probability
ellipsoids. The H atoms are omitted for clarity. Selected bond lengths
[Å] and angles [Њ]: Pd(1)–N(1), 2.030(4); Pd(2)–N(3), 2.033(4); Pd(1)–
Cl(1), 2.2564(13); Pd(2)–Cl(2), 2.2789(17); Pd(1)–Cl(4), 2.3669(13);
Pd(2)–Cl(4), 2.3418(15); Pd(1)–Cl(3), 2.3023(13); Pd(2)–Cl(3),
2.3074(13); Pd(1)–Pd(2), 3.2569(6); N(1)–Pd(1)–Cl(1), 89.89(12); N(3)–
Pd(2)–Cl(3), 178.36(15); N(1)–Pd(1)–Cl(3), 174.96(10); Cl(2)–Pd(2)–
Cl(3), 91.22(6); Cl(1)–Pd(1)–Cl(3), 91.17(5); N(3)–Pd(2)–Cl(4),
93.08(15); N(1)–Pd(1)–Cl(4), 94.69(10); Cl(2)–Pd(2)–Cl(4), 175.30(4);
Cl(1)–Pd(1)–Cl(4), 175.30(5); Cl(3)–Pd(2)–Cl(4), 85.28(4); Cl(4)–
Pd(1)–Cl(3), 84.82(5).
Complex 4 was synthesized by reacting ligand L5 with
1
[PdCl2(NCMe)2] in a 1:2 ratio (Scheme 1). The H NMR of
complex 4 showed two types of protons associated with the
pyrazolyl groups in a 2:1 intensity ratio. The first type of
pyrazolyl group consists of two pyrazolyl units bonded to Pd
atoms (6.35 ppm); whereas the second type of pyrazolyl group
is not bound (6.22 ppm). The NMR data for 4 and elemental
analysis support the proposed formula, which was confirmed by
X-ray crystallography (Fig. 6). The reaction of L6 with [PdCl2-
(NCMe)2], in either a 1:2 or a 1:1 ratio, led to sparingly soluble
products which were not further characterised.
In forming the Pd complexes (1–4) it is clear from the types
of products that the bonding modes of ligands L1, L2 and
L5 are different compared other pyrazolyl ligands.19 Literature
reports show that pyrazolyl units in 1,3,5-tris(pyrazolyl-1-
ylmethyl)benzene19a and 1,3,5-tris(pyrazolyl-1-ylmethyl)ben-
zene19b form complexes that have only one metal bonded to two
pyrazolyl units, contrary to what we observed in complexes 1, 2
and 4. The bonding mode in L1, L2 and L5 to palladium is
likely to be determined by two main factors, namely electro-
withdrawing groups on the linkers and steric hindrance by the
substituents on the pyrazolyl units. In experiments performed
with [PdClMe(cod)] as a source of palladium, ligands L1, L2
and L5 were unable to displace cod in [PdClMe(cod)] to form
the corresponding pyrazolyl palladium complex. The above
results also indicate that the pyrazolyl compounds L1, L2
and L5 are weaker donors than 3,5-Me2pz and 3,5-tBu2pz
which readily react with [PdCl2(cod)] to form [Pd(3,5-R2pz)2Cl2]
D a l t o n T r a n s . , 2 0 0 3 , 7 1 5 – 7 2 2
720

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Table 3 Ethylene polymerisation data and conditionsa
Expt.
Cat.
Pressure/atm
TON/kg molϪ1 hϪ1
Mp/ЊC (DSC)
Mn (×105)
Mw (×105)
Mw/Mn
1
2
3
4
5
6
1
1
2
2
4
4
5
1
5
1
5
1
2591.4
1843.0
503.0
392.9
1099.2
215.2
136.04
136.80
136.31
136.58
136.53
136.08
4.420
4.504
4.569
4.631
4.369
4.514
9.130
9.377
9.384
9.727
9.018
9.550
2.04
2.08
2.05
2.10
2.06
2.12
a [Pd] = 12.5 × 10Ϫ6 M; Al:Pd = 1000:1; polymerization temperature = 30 ЊC; polymerisation time = 30 min.
(R = Me, tBu) and [Pd(3,5-tBu2pz)2Cl(Me)], respectively.20
Further evidence that L1, L2 and L5 are weakly bonded to Pd
in 1–4 complexes is provided by the reaction of these complexes
with known weak ligands like thiophene and tetrahydro-
thiophene. We were able to isolate free pyrazolyl ligands in such
reactions. For example the reaction of complex 1 with pyridine
produced [Pd2(py)2Cl4] within 5 min, a product characterised by
1H NMR and elemental analysis;21 which demonstrates how
weakly bonded L1 is in complex 1. We believe the relatively
weak donor ability of the ligands L1, L2 and L5, compared to
other pyrazolyl or pyridine derivatives as ligands, makes the Pd
centres in the complexes formed by L1, L2 and L5 more
electrophilic; a hypothesis we are using to investigate the ability
of cations of 1 to form phenylacetylene complexes.
The presence of conformational tension in the bridging
ligands also manifests itself in the values of the O᎐C–N–N
᎐
torsion angles. The carbonyl groups link two aromatic systems,
the pyrazole ring and benzene moiety. It has been demon-
strated, from the ligand structures discussed earlier, that the free
ligands L1 and L2 cannot be planar due to steric consider-
ations, but the carbonyl group is usually coplanar with the
pyrazolato ring with the E configuration about the O᎐C–N–N
᎐
bond. The expected torsion angle O᎐C–N–N is 180Њ. However,
᎐
all experimentally observed values are considerably different
in 1 (O(2)–C(6)–N(2)–N(1) 147.0(5)Њ; O(1)–C(13)–N(4)–N(3)
134.1(5)Њ), 2 (O(1)–C(12)–N(2)–N(1) 115.1(4)Њ; O(2)–C(19)–
N(4)–N(3) 122.5(4)Њ) and 4 (O(1)–C(12)–N(2)–N(1) 119.1(5)Њ;
O(2)–C(19)–N(4)–N(3) 119.6(6)Њ). The torsion angle closest to
linearity is found for the one uncoordinated pyrazole in 4
(O(3)–C(31)–N(5)–N(6) (158.3(5)Њ)). The carbonyl vectors are
not coplanar with the benzene rings either, which is in accord
with the conformation of the free ligands in the solid state.
Consequently, the coordination of the pyrazolato nitrogen
atoms to palladium metal centres is strong enough to cause
significant puckering of the ligand and yet accommodate it as a
bridging moiety. In addition, molecules 1, 2 and 4 deviate
significantly from the possible Cs symmetry.
Whereas compounds L1, L2 and L5 formed soluble products,
L3 and L6 formed insoluble or sparingly soluble products,
respectively, whilst L4 did not react at all. It is likely that the
inability of L4 to form a complex is due the steric bulk of
the tert-butyl substituents on the pyrazolyl units, thus leaving
no room for the two PdCl2 units required to form a complex.
The molecular structures of 1 and 4 are presented in
Figs. 5 and 6, and crystallographic information for 1, 2 and 4 is
tabulated in Table 2. The Pd atoms in the dinuclear complexes
1, 2 and 4 are in slightly distorted square planar configurations
with the bond angles about the Pd atoms ranging between
84.35(5) and 94.68(12)Њ. Each Pd metal and the four atoms
comprising its coordination sphere, three chlorines and one
nitrogen, are planar within 0.07 Å in the three complexes. The
Pd–Cl(terminal), Pd–Cl(bridging trans to N) and Pd–Cl-
(bridging trans to Cl), bond lengths in 1, 2 and 4 average to
2.266(8), 2.305(4) and 2.360(15) Å, respectively, and fall within
the usual ranges for these interactions. The disparity between
the metal–chlorine distances to the bridging atoms warrants
special mentioning. The trans influence of the pyrazolato lig-
ands as a good π-donor is not reflected in these structures. The
metal–chloride distance trans to the pz ligand is shorter as the
latter is a weaker σ-donor than the chloride. The average Pd–N
bond distance in 1, 2 and 4 (2.032(5) Å) is somewhat shorter
than the average value of 2.1(1) Å calculated for 59 Pd–N(pz)
bond lengths reported to the Cambridge Structural Database
(CSD),22 however the difference is not statistically significant.
The unique feature of 1, 2 and 4 that sets them apart from all
but one other dinuclear Pd complexes with the L2Pd(µ2-Cl)2-
PdL2 core is the smaller dihedral angle between the planes
defined by the Pd centres and two bridging Cl atoms. Thus, the
angle between planes Pd(1)–Cl(3)–Cl(4) and Pd(2)–Cl(3)–Cl(4)
spans 136.31(5), 138.61(5) and 143.11(7)Њ in 1, 2 and 4, respect-
ively. This folding shortens the Pd–Pd separation to 3.2004(6),
3.2117(5) and 3.2569(6) Å, correspondingly. Undoubtedly, such
strained ligand arrangement stems from the incorporation of
a bidentate bridging ligand into the system. The only other
Pd complex with similar geometry [Pd2Cl4((R,R)-1,5-bis-
{o-(p-toluenesulfinyl)phenoxy}-3-oxapentane)].(CH2Cl2)2 was
reported by Hambley et al. in 1985.5d There the corresponding
parameters measured 139.0Њ and 3.280(1) Å. In 21 other
relevant complexes reported to the CSD the Pd–µ2-Cl2–Pd
rhombuses were planar with the Pd–Pd distances averaging
3.45(5) Å.
Ethylene polymerisation
Ethylene polymerisation reactions were performed with com-
plexes 1, 2 and 4 using MAO as co-catalyst. The results of the
polymerisation are in Table 3. Polymerization was performed at
5 atm and 1 atm, with catalytic activity at 5 atm substantially
higher. The catalytic activity was found to decrease in the order
1 > 4 > 2. Whilst 1 and 4 have good solubility in toluene, 2 has a
low solubility in toluene. This low solubility of 2 is likely to be
the cause of its low activity.
The polymers were characterised by a combination of
high temperature 13C NMR, high temperature gel permeation
chromatograph (GPC) and by thermal analysis (TGA DSC).
Polyethylene isolated in these experiments had melting points
of about 136 ЊC and a single 13C NMR peak characteristic of
high density polyethyelene (HDPE). The catalytic activity of 1
was about twice that of 4. It was also about the same magnitude
more active than [Pd(3,5-tBu2pz)2Cl2]20 (TON = 1005.7 kg
molϪ1 hϪ1). Quite clearly the presence of carbonyl groups in the
pyrazolyl ligands in 1 improves its electrophilic behaviour and
hence its catalytic activity compared to [Pd(3,5-tBu2pz)2Cl2]. We
expected 4 to have a similar catalytic activity to 1 since the
coordination environment of the active metal species for
polymerization in both 1 and 4 are the same. The lower activity
of 4 could be due to the presence of the non-coordinating
pyrazolyl unit, which could be complexing with the co-catalyst
MAO, thus reducing the amount of active palladium catalyst
available for the polymerization. Formation of an Al–pyrazolyl
adduct when MAO is used to activate 4 is feasible as Al–NR3
adducts are well known.23 Examples of pyrazolyl–Al com-
pounds have also been reported in the literature [Al(1,3,5-
Me3pz]24 and [Tp*2Al][AlCl4].4d Though all three catalysts
have a reasonable catalytic activity, they appear to deactivate
over time. The deactivation is probably the result of ligand dis-
D a l t o n T r a n s . , 2 0 0 3 , 7 1 5 – 7 2 2
721

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J Chem. Soc., Chem. Commun., 1987, 1, 93; (c) P. K. Byers, J. Canty,
sociation from the metal centre. The possibility of the active
catalyst being a ligand–Al compound, formed from a dissoci-
ated ligand and MAO, can be discounted; since a blank poly-
merisation reaction performed with L1 and MAO (1:1000) at
ethylene pressure of 5 atm and 30 ЊC gave only a small amount
of polymer.
The results of the polymerization studies demonstrate that
fine-tuning the electrophilicity of the palladium centre in
pyrazolyl complexes catalysts should lead to highly active
olefin polymerization catalysts. However a balance between the
stability of the catalyst and its electrophilic behaviour has to be
found. We are currently investigating this.
B. W. Skelton and A. H. White, Organometallics, 1990, 9, 826;
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Conclusions
A series of six compounds with pz rings connected with benzene-
dicarbonyl and benzenetricarbonyl have been prepared and
fully analytically characterized. The presence of the carbonyl
functional groups reduce the σ-donor ability of the nitrogen
atoms of the pz ligands. When activated with MAO, Pd com-
plexes with these ligands show activity in ethylene polymeriz-
ation. The reduced σ-donor ability of ligands L1–L6 may play
a role in the catalytic process as it facilitates the break of the
Pd–N bonds to assist coordination of the substrate to the metal
center. Further studies of the polymerization process will be
presented in a future report.
9 G. Dong, J. P. Matthews, D. C. Craig and A. T. Baker, Inorg. Chim.
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10 C. M. Hartshorn and P. J. Steel, Organometallics, 1998, 17, 3487.
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Acknowledgements
This work was supported by the National Research Foundation
(South Africa). We thank SASOL polymers for the high
temperature GPC data.
15 (a) C. K. Gosh, D. P. S. Rodgers and W. A. G. Graham, J. Chem.
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17 R. H. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33.
18 G. Sheldrick, Bruker SHELXTL (Version 5.1), Analytical X-ray
Systems, Madison, WI, 1997.
19 (a) C. M. Hartshorn and P. J. Steel, Chem. Commun., 1997, 541;
(b) W-K. Chang, S-C. Sheu, G-H. Lee, Y. Wang, T-I. Ho and Y-C.
Lin, J. Chem. Soc., Dalton Trans., 1993, 687.
References and notes
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2 (a) W. H. Armstrong, A. Spool, G. C. Papaefthymion, R. B. Franked
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3 S. Komeda, M. Lutz, A. L. Spek, M. Chikuma and J. Reedijk,
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20 K. Li, I. A. Guzei, J. Darkwa and S. F. Mapolie, J. Organomet.
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21 (py)2Pd2Cl4: Anal. Calc. for C10H10Cl4N2Pd2: C, 23.42; H, 1.97;
N, 5.46. Found: C, 22.06; H, 1.41; N, 5.43%. 1H NMR (CDCl3):
2
3
δ 8.58 (dd, 2H, py, JHH = 6.6 Hz, JHH = 1.4 Hz); 7.84 (tt, 1H, py,
2JHH = 7.6 Hz, JHH = 1.5 Hz); 7.37 (td, 2H, py, JHH = 7.6 Hz,
3
2
3JHH = 1.6 Hz).
22 F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 31.
23 (a) J. J. Eisch, in Comprehensive Organometallic Chemistry II,
ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, 1995,
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M. Bochmann, Advanced Inorganic Chemistry, John Wiley & Sons,
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24 I. P. Romm, T. A. Zayakina, V. N. Sheinker, E. N. Guryanova,
A. D. Garnovskii and O. Osipov, Zh. Obshch. Khim., 1976, 46, 2279.
D a l t o n T r a n s . , 2 0 0 3 , 7 1 5 – 7 2 2
722