2-(N-Alkylcarboxamide)-6-iminopyridyl palladium and nickel complexes: Coordination chemistry and catalysis

Article abstract of DOI:10.1039/c1dt11079a

The 2-(N-alkylcarboxamide)-6-iminopyridine ligands (L1-L7) can bind as either mono-anionic tridentate NNN ligands on reaction with PdCl ₂(CH₃CN)₂, to form complexes LPdCl (C1-C7), or as neutral tridentate NNO ligands with NiCl₂·6H₂O, to produce complexes LNiCl₂ (C8-C14). All metal complexes were characterized by IR spectroscopy and elemental analysis, and in the case of the palladium complexes, by ¹H and ¹³C NMR spectroscopy. The crystal structures of C3, C4, C6, C10, and C12 were determined by X-ray crystallography, and revealed a distorted square geometry around the palladium centre, whereas for nickel, a distorted square-pyramidal geometry was adopted. The representative palladium complex (C3) was further reacted with AgBF ₄ in acetonitrile affording the salt [L3Pd(CH₃CN)][BF ₄] (C15) and the structure of this was confirmed by single-crystal X-ray diffraction. By contrast, carrying out the reaction in dichloromethane rather than acetonitrile, in the presence of malononitrile (CNCH₂CN), resulted in the formation of the bimetallic palladium complex [L3Pd(CNCH ₂CN)PdL3]·2[BF₄] (C16). Upon activation with diethylaluminium chloride, all the nickel complexes showed high activity for ethylene dimerization. Furthermore, the palladium complexes exhibited good activities in the vinyl-polymerization of norbornene upon activation with MAO.

Full text of DOI:10.1039/c1dt11079a

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PAPER
2-(N-Alkylcarboxamide)-6-iminopyridyl palladium and nickel complexes:
coordination chemistry and catalysis†
Wenjuan Zhang,*a Youhong Wang,a Jiangang Yu,a Carl Redshaw,*b Xiang Haoa and Wen-Hua Sun*a
Received 9th June 2011, Accepted 12th September 2011
DOI: 10.1039/c1dt11079a
The 2-(N-alkylcarboxamide)-6-iminopyridine ligands (L1–L7) can bind as either mono-anionic
tridentate NŸNŸN ligands on reaction with PdCl2(CH3CN)2, to form complexes LPdCl (C1–C7), or as
neutral tridentate NŸNŸO ligands with NiCl2·6H2O, to produce complexes LNiCl2 (C8–C14). All metal
complexes were characterized by IR spectroscopy and elemental analysis, and in the case of the
palladium complexes, by 1H and 13C NMR spectroscopy. The crystal structures of C3, C4, C6, C10, and
C12 were determined by X-ray crystallography, and revealed a distorted square geometry around the
palladium centre, whereas for nickel, a distorted square-pyramidal geometry was adopted. The
representative palladium complex (C3) was further reacted with AgBF4 in acetonitrile affording the salt
[L3Pd(CH3CN)][BF4] (C15) and the structure of this was confirmed by single-crystal X-ray diffraction.
By contrast, carrying out the reaction in dichloromethane rather than acetonitrile, in the presence of
malononitrile (CNCH2CN), resulted in the formation of the bimetallic palladium complex
[L3Pd(CNCH2CN)PdL3]·2[BF4] (C16). Upon activation with diethylaluminium chloride, all the nickel
complexes showed high activity for ethylene dimerization. Furthermore, the palladium complexes
exhibited good activities in the vinyl-polymerization of norbornene upon activation with MAO.
palladium complexes always possess a square planar geometry
due to the electronic configuration of [Kr]4d10, while nickel
Introduction
[electronic configuration of [Ar]3d84s2] can adopt different types of
geometries such as trigonal bipyramid,4f,5 tetrahedral6 and square
planar,7 depending on the geometrical constraints imposed by the
ligands present. These differences can greatly affect their catalytic
properties toward olefin polymerization. For example, nickel com-
plexes bearing 2-(ethylcarboxylato)-6-imino pyridines can pro-
duce long-branched polymers,4f whereas the palladium analogues
showed very poor results for ethylene polymerization, but high
activity for norbornene polymerization.4g In the development of
nickel and palladium complexes for ethylene reactivity, bidentate
ligands were generally employed,8a–c whilst a limited number of
tridentate complexes have also been utilised.8d In recent years,
our group has developed a series of tridentate transition metal
complexes that exhibited high activity for ethylene reactivity.4f,5 As
a consequence, N-alkyl-6-(1-(arylimino)ethyl)picolinamides (L)
were prepared and used to form their neutral nickel complexes,
which showed catalytic activities in ethylene oligomerization,
the Kumada–Corriu reaction and in the polymerization of
methyl acrylate.9 Encouraged by observations that palladium
complexes bearing ligands derived from long-chain alkylimines
could produce polyethylenes with high molecular weights,2i–l it
was envisaged that N-alkyl-6-(1-(arylimino)ethyl)picolinamides
(L) were worthy of further investigation. In particular, palladium
complexes and their catalytic behaviour with such a ligand set
are worthy targets. In this paper, the different coordination
characteristics of nickel and palladium complexes containing
Since the discovery that palladium(II) and nickel(II) complexes
containing a-diimine ligands exhibited notable catalytic activities
for the polymerization of ethylene and a-olefins,1 research focusing
on the coordination chemistry of Ni(II) and Pd(II), together
with their catalytic application in olefin polymerization,2 as
well as other organic transformations,3 has greatly increased.
In the development of late transition metal complexes, a va-
riety of different coordination modes for particular ligands
can be observed, which can be dependent upon the particular
combination of metal and ligand.4 For example, the ligand 2-
Ph2PC6H4NHC(O)CH2NHCO2Bz (Bz = PhCH2) displays various
coordination modes when coordinated with a range of late
transition-metal precursors.4b Complex anions of zinc, palladium
and nickel that contain partially deprotonated forms of the
N,N,O-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide ligand
also display a range of coordination modes, which are dependant
on the electronic requirements of the metal centres.4i However,
aKey Laboratory of Engineering Plastics and Beijing National Laboratory for
Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, China. E-mail: whsun@iccas.ac.cn; Fax: +86 10 62618239;
Tel: +86 10 62557955
bSchool of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK.
E-mail: carl.redshaw@uea.ac.uk; Fax: +44 (0)1603 592003; Tel: +44
(0)1603 593137
† CCDC reference numbers 828935–828940 for crystallographic data of
complexes C3, C4, C6, C10, C12, and C15. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt11079a
12856 | Dalton Trans., 2011, 40, 12856–12865
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Table 1 Selected bond lengths and bond angles for the palladium
complexes C3, C4 and C6
N-alkyl-6-(1-(arylimino)ethyl)picolinamides will be addressed,
and their catalytic properties will be presented.
C3 (iPr, Bu)
C4 (2,6-Me-4-Br, Bu) C6 (Et, Oct)
Results and discussion
˚
Bond lengths/A
Pd1–N2
Pd1–N3
Pd1–N1
Pd1–Cl1
C2–N1
N2–C3
N3–C8
N2–C7
1.932(4) Pd–N(2)
2.018(4) Pd–N(3)
1.930(3) Pd–N2
2.004(3) Pd–N3
2.058(3) Pd–N1
2.2898(11) Pd–Cl
1.914(5)
2.010(6)
2.082(6)
2.2746(18)
1.321(8)
1.346(7)
1.295(8)
1.447(8)
1.326(9)
1. Synthesis and characterization of palladium complexes
(C1–C7) and nickel complexes (C8–C14)
2.088(4) Pd–N(1)
2.2951(13) Pd–Cl
1.301(6) N(1)–C(2) 1.290(5) N2–C7
1.346(7) N(1)–C (13) 1.442(4) N2–C3
1.336(7) N(3)–C(8) 1.344(5) N1–C2
1.334(6) N(3)–C(9) 1.457(5) N1–C17
1.472(7) N(2)–C(7) 1.332(4) N3–C8
The ligands were prepared according to our previous work9 and
treatment of PdCl2(CH3CN)2 with one equiv. of the corresponding
ligand in CH2Cl2 afforded the palladium complexes C1–C7 in
1
good yields (Scheme 1). Their structures were confirmed by H
N3–C9
and 13C NMR spectroscopy as well as by elemental analysis.
Compared with the 1H NMR spectra of the free ligands, the
signals of the N–H grouping (broad peak around 8.05 ppm) had
disappeared, whilst other protons on the pyridine and benzene
rings had shifted to higher field, suggesting the formation of the
Pd–Namide linkage. For example, in the 1H NMR spectra of C3 and
L3, the signals for Py–H of L3 (8.51, 8.31 and 7.97 ppm) changed to
d = 8.20, 7.99 and 7.73 ppm. During these reactions, it is assumed
that the coordination of Npy and Nimine to palladium initially
occurs followed by intramolecular deprotonation (releasing HCl),
and finally the tridentate palladium complexes are formed, as
reported by Gregorio Sanchez.10 The results of the treatment
of PdCl2(CH3CN)2 with two equiv. of L3, affording C3, also
supported this pathway.
Bond angles/◦
N2–Pd1–N3 81.19(18) N2–Pd–N3 80.86(13) N2–Pd–N3 81.4(2)
N2–Pd1–N1 79.02(16) N2–Pd–N1 79.40(12) N2–Pd–N1 79.2(2)
N3–Pd1–N1 160.20(16) N3–Pd–N1 160.23(13) N3–Pd–N1 160.59(19)
N2–Pd1–Cl1 179.93(15) N2–Pd–Cl 179.02(9) N2–Pd–Cl 179.10(19)
N3–Pd1–Cl1 98.87(13) N3–Pd–Cl 100.11(10) N3–Pd–Cl 98.21(18)
N1–Pd1–Cl1 100.93(12) N1–Pd–Cl 99.62(9) N1–Pd–Cl 101.20(16)
C7–N2–Pd1 117.1(3) C2–N1–Pd 113.9(2) C7–N2–Pd 117.0(4)
C3–N2–Pd1 119.2(3) C13–N1–Pd 125.4(2) C3–N2–Pd 119.4(4)
C8–N3–Pd1 114.2(4) C8–N3–Pd 115.1(3) C2–N1–Pd 114.2(4)
C9–N3–Pd1 128.2(3) C9–N3–Pd 126.1(3) C17–N1–Pd 127.1(4)
C9–N3–Pd 126.9(5)
suggested the presence of N–H. Fortunately, single crystals of the
palladium complex C3, C4 and C6 could be grown from their
CH2Cl2 solution when covered with diethyl ether and their struc-
tures were determined by single-crystal X-ray diffraction (Fig. 1–
3). Selected bond length and bond angles are collected in Table 1.
Fig. 1 An ORTEP drawing of C3 with thermal ellipsoids drawn at the
30% probability level. Hydrogen atoms are omitted for clarity.
Fig. 1–3 show that these complexes possess similar structures
with distorted square planar geometry around the palladium
centre; the palladium centre is coordinated by three N atoms and
one chloride, suggesting the formation of a s-bond for the Pd–
Namide. On comparison of analogous bond lengths and angles,
there is evidence of some substituent effects, for example, the
Scheme 1 The synthesis of palladium complexes C1–C7 and nickel
complexes C8–C14.
In contrast, the stoichiometric reaction of the ligand with one
equiv. of NiCl2·6H2O in ethanol gave the nickel complexes C8–
C14 in high yield (as shown in Scheme 1), in which the N–H of the
imide remained ‘free’ and coordination with nickel was via the O
centre. These nickel complexes were also characterized by IR spec-
troscopy and elemental analysis. Comparing their IR spectra with
˚
shorter bond lengths of Pd–Npy and Pd–Cl in C6 [1.914(5) A
˚
˚
and 2.2746(18) A] compared with those of C3 [1.932(4) A and
˚
˚
˚
2.2951(14) A] and C4 [1.930(3) A and 2.2898(11) A], and the
˚
shorter bond length of Pd–Nimide in C4 [2.004(3) A] compared
with that of C3 [2.018(4) A] and C6 [2.010(6) A]. However, the
substituents have little effect on a number of the bond angles
present.
those of the corresponding ligands, the absorption of the C
N
in the ligand shifts to 1640–1642 cm-1, which is indicative of the
coordination of the Nimine to the nickel. The appearance of an N–H
signal at around 3225 cm-1 in the IR spectra of the nickel complex
˚
˚
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Table 2 Selected bond lengths and angles of nickel complexes C10 and
C12
C10 (iPr, Bu)
C12 (iPr, Oct)
˚
Bond lengths/A
Ni–N2
Ni–O1
Ni–N1
Ni–Cl1
Ni–Cl2
1.975(4)
2.127(3)
2.139(4)
2.1907(16)
2.2927(16)
1.983(4)
2.162(4)
2.166(5)
2.2156(17)
2.288(2)
Bond angles/◦
N2–Ni–O1
N2–Ni–N1
O1–Ni–N1
N2–Ni–Cl1
O1–Ni–Cl1
N1–Ni–Cl1
N2–Ni–Cl2
O1–Ni–Cl2
N1–Ni–Cl2
Cl1–Ni–Cl2
76.95(14)
77.12(14)
151.39(14)
150.82(12)
96.13(10)
100.62(11)
95.91(11)
93.70(11)
100.79(11)
112.94(6)
76.41(15)
77.47(16)
151.56(16)
151.68(15)
95.14(12)
102.60(12)
95.55(14)
95.69(13)
97.84(14)
112.31(7)
Fig. 2 An ORTEP drawing of C4 with thermal ellipsoids drawn at the
30% probability level. Hydrogen atoms are omitted for clarity.
Fig. 5 An ORTEP drawing of C12 with thermal ellipsoids drawn at the
30% probability level. Hydrogen atoms and solvent (Et2O) are omitted for
clarity.
Fig. 3 An ORTEP drawing of C6 with thermal ellipsoids drawn at the
2. Synthesis and characterization of cationic palladium
complexes and their reactions with organic compounds
30% probability level. Hydrogen atoms are omitted for clarity.
Single crystals of nickel complexes C10 and C12 were obtained
by diffusion of Et2O to their ethanol solution and their structures
were determined by single-crystal X-ray crystallography (Fig. 4
and 5). Selected bond lengths and angles are collected in Table
2. Fig. 4 and 5 reveal that both C10 and C12 possess similar
structures with the nickel coordinated by Npyridine, Nimine and Oimide
together with two chlorides to form a distorted square-pyramidal
geometry, with the apical atom being Cl2; this is very different
to the geometry observed for the palladium complexes. There is
little effect exerted by the alkyl substituent on the Nimide, and, as
a consequence, the corresponding bond lengths and bond angles
have almost the same values.
The cationic mononuclear palladium complex C15 was prepared
by treatment of C3 with one equiv. of AgBF4 in acetonitrile
and was isolated as an orange powder in moderate yield (shown
in Scheme 2). It was characterized by NMR spectroscopy and
the molecular structure was determined by single-crystal X-ray
1
crystallography. Looking at the H NMR spectrum, the signals
ascribed to the H-Py of C3 (8.20, 7.99, 7.73 ppm) shifted to lower
Fig. 4 An ORTEP drawing of C10 with thermal ellipsoids drawn at the
30% probability level. Hydrogen atoms are omitted for clarity.
Scheme 2 The synthesis of cationic palladium complexes C15 and C16.
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Table 3 The 1H NMR data for palladium complexes C3, C15 and C16
d/ppm
C3
C15
C16
H-Py
8.20
7.99
7.73
7.35–7.23
3.02
3.36
2.23
1.43
1.16
8.45
8.39
7.92
7.43–7.32
3.09
3.18
1.99
1.38
1.24
8.37
8.17
7.95
7.52–7.22
2.96
3.12
2.37
1.34
1.19
H-Py
H-Py
H-Ph
CH(CH3)2
N-CH2-
N
CCH3
CH(CH3)2
CH(CH3)2
–(CH2)3–CH3
0.90
0.90
0.89
field in C15 (8.45, 8.37, 7.92 ppm), whilst signals ascribed to Ph-H
in C3 (7.43, 7.23 ppm) shifted to higher field in C15 (7.34, 7.41
ppm), and signals of N-CH2 and CH3C N (3.34, 2.22 ppm in
C3) also shifted to higher field (3.18, 2.00 in C15). The resonance
for CH3CN can also be observed clearly at d = 2.49 in the H
NMR spectrum of C15, suggesting that it is coordinated with the
Fig. 7 An ORTEP drawing of C15 with thermal ellipsoids drawn at the
30% probability level. Hydrogen atoms are omitted for clarity. Selected
1
◦
˚
bond lengths (A) and bond angles ( ): Pd1–N2 1.915(3); Pd1–N3 1.992(3);
Pd1–N4 2.007(3); Pd1–N1 2.049(3); N2–Pd1–N3 81.35(13); N2–Pd1–N4
177.00(13); N3–Pd1–N4 99.03(13); N2–Pd1–N1 79.80(12); N3–Pd1–N1
161.10(12); N4–Pd1–N1 99.87(12); C26–N4–Pd1 174.8(4).
palladium centre.
Treatment of C3 with one equiv. of AgBF4 and 0.5 equiv.
of CNCH2CN in dichloromethane afforded the cationic dimeric
palladium complex C16, which was characterized by 1H and
1
13C NMR spectroscopy and elemental analysis. The H NMR
are a little shorter than those of C3 [Pd–N1 2.087(4), Pd–N2 1.938,
Pd–N3 2.021(4)]; the reason is probably the counter anion.
Attempts to prepare the homoleptic palladium [PdL2][BF4]2
complex by treatment of [PdCl2(CH3CN)2] with two equiv. of the
ligand (molar ratio 1 : 2) and a stoichiometric amount of AgBF4
failed (Scheme 3), although during the reaction process, a white
precipitate was observed. The resultant yellow powder is difficult
to dissolve in common organic solvents and the 1H NMR spectrum
(d6-DMSO) showed that there is no significant difference from that
of C3, thus it is proposed that this compound is a cationic complex,
formatted as C17. After crystallization in CH3CN, the compound
C15 was obtained, which also supported this proposal.
spectrum clearly showed the signals of CNCH2CN (d = 3.60) and
also the integration ratio of hydrogens in CNCH2CN to that in
Py–H was consistent with the dimeric species (shown in Fig. 6).
Comparing the 1H NMR spectrum of C3 with those of C15 and
C16, the signals of Py–H (d = 8.20, 7.99, 7.73 ppm) and Ar–
H (7.35–7.23 ppm) shifted to lower field (7.92–8.45 ppm in C15,
7.95–8.37 ppm in C16) and (7.43–7.32 ppm in C15, 7.52–7.22 ppm
in C16), respectively, and N–CH2 (3.36 ppm) shifted to higher field
(3.18 ppm in C15, 3.12 ppm in C16) (Table 3). However, attempts
to obtain the crystal structure of C16 were unsuccessful due to the
nature of the very thin crystals obtained.
Fig. 6 The 1H NMR spectrum of dimeric cationic palladium complex
C16.
Scheme 3 Attempted synthesis of the homoleptic palladium complex
[PdL2][BF4]2.
The crystal structure of the mono cationic palladium complex
C15, however, was confirmed by single-crystal X-ray crystallogra-
phy and the structure is shown in Fig. 7. The palladium is coordi-
nated by N,N,N atoms and the geometry around Pd can best be de-
scribed as square planar, similar to that of C3. The bond lengths of
Pd–N of C15 [Pd–N1 2.049(3), Pd–N2 1.915(4), Pd–N3 1.992(3)]
1H NMR monitoring of the monocationic complex C15 with
one equiv. of norbornene derivatives or diphenylacetylene showed
no difference with that of C15, indicating no reaction between the
palladium complexes with these organic substrates.
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Table 4 Ethylene dimerization by nickel complexes C8–C14/Et2AlCla
C13 (Et, Do) > C11 (Et, Oct) > C9 (Et, Bu) (runs 14, 12, 10).
However, the a-olefin selectivity increased when a shorter chain
was present. These results are possibly due to the ability of the
longer alkyl group to protect the active species and thereby lead
to the higher observed activity. In contrast, bulkier substituents
on the benzene ring resulted in lower activity, which led to the
reactivity order of C8 (Me, Bu) > C9 (Et, Bu) > C10 (iPr, Bu) (run
9–11), C11 (Et, Oct) > C12 (iPr, Oct) (runs 12–13) and C13 (Et,
Do) > C14 (iPr, Do) (runs 14–15). This observation is probably due
to the substituents on the benzene ring being closer to the metal
centre than the Nimide–alkyl, and thus hindering the coordination of
ethylene to the active species and thereby decreasing the reactivity.
In contrast, the selectivity for 1-butene increased with bulkier
substituents on the ortho-position of the aryl ring, as shown by
the order C8 (Me, Bu) < C9 (Et, Bu) < C10 (iPr, Bu) (runs 9–
11) and C11 < C12, C13 < C14. The reason is probably that the
b-elimination barrier in the bulkier substituent catalyst systems
is higher than that of smaller substituents, which will favour the
generation of linear olefins.12
Run
Pro-catalyst
T/◦C
Time
Activityb
a-olefin/%
1c
C10 (iPr, Bu)
C10 (iPr, Bu)
C10 (iPr, Bu)
C10 (iPr, Bu)
C10 (iPr, Bu)
C10 (iPr, Bu)
C10 (iPr, Bu)
C10 (iPr, Bu)
C8 (Me, Bu)
C9 (Et, Bu)
0
30
30
30
30
10
20
40
50
20
20
20
20
20
20
20
0.81
0.92
0.76
0.71
0.83
0.95
0.73
0.62
83.4
12.2
9.2
62.1
62.9
66.7
63.2
68.3
69.1
71.2
70.1
92.1
94.0
99.1
72.9
76.3
70.2
72.3
2c
20
40
60
20
20
20
20
20
20
20
20
20
20
20
3c
4c
5c
6c
7c
8c
9d
10d
11d
12d
13d
14d
15d
C10(iPr, Bu)
C11((Et, Oct)
C12(iPr, Oct)
C13(Et, Do)
C14(iPr, Do)
15.9
15.6
28.6
20.5
-1
a Condition: 5 mmol Ni, Al/Ni = 500. b 105 g molNi h-1. c 1 atm ethylene,
30 mL toluene. d 10 atm ethylene, volume 100 mL toluene.
3. Ethylene dimerization by nickel complexes
4. Vinyl-polymerization of norbornene by palladium complexes
C1–C7, C15, C16
As mentioned previously, the purpose of our research is to access
promising catalysts for olefin polymerization. With this in mind,
the catalytic behaviour toward ethylene polymerization of the
complexes was evaluated. The palladium complexes showed very
poor results in the presence of co-catalysts such as MAO, AlEtCl2,
MMAO or AlEt2Cl for ethylene polymerization. By contrast, the
nickel complexes showed high activity (up to 106 g molNi h-1) in
the presence of AlEt2Cl for ethylene dimerization and the results
are collected in Table 4.
Initially, complex C10 was employed to select the preferred co-
catalyst. In the presence of MAO or MMAO, the pro-catalyst C10
showed only moderate activity for ethylene dimerization, which
was much lower than that observed with Et2AlCl. The following
investigations were thus conducted with Et2AlCl employed as
co-catalyst. The optimized experiments showed that the highest
activity was achieved at the 500 : 1 molar ratio of Al/Ni and
the investigations for the nickel complexes C8–C14 were thus
conducted in the presence of Et2AlCl with an Al/Ni ratio of
500 : 1 (see Table 4). Varying the temperature from 20 ◦C to
60 ◦C resulted in a rapid decrease of reactivity, but with little
change of the selectivity for the a-olefin (runs 2–4, Table 4).
This phenomenon may be due to the deactivation of the active
species at higher temperature, as observed for most reported nickel
complexes.11 The data also showed that on prolonging the time,
the activity increased and then decreased gradually, suggesting
that the activation of the catalyst requires time and then a slow
decay occurs over time (runs 2, 5–8, Table 4). The highest activity
was achieved after 20 min, and so the subsequent dimerization of
ethylene by C8–C14 at 10 atm ethylene pressure was conducted
over 20 min.
Palladium complexes were widely reported as efficient catalysts
for norborene polymerization.13 As the palladium complexes C1–
C7 showed very poor results for ethylene polymerization, their
catalytic potential for norbornene polymerization was investigated
and the results are collected in Table 5. The blank experiments
indicated that only one component alone of either the palladium
complexes or the MAO could not initiate the polymerization
of norbornene. Only in the presence of MAO was high activ-
ity observed for norbornene polymerization for the palladium
complexes. The ligand environment has a big effect on the
catalytic activity of these systems for norbornene polymerization.
Increasing the chain length of the Nimide-alkyl led to lower activity,
as shown by the order: C6 (Et, Oct) < C2 (Et, Bu); C7 (iPr,
Do) < C3 (iPr, Bu); C5 (Me, Oct) < C1(Me, Bu). The reason
is probably due to the longer chain of the N-alkyl hindering
the insertion of the norbornene. Another interesting result is
the higher activity observed on introducing a bromine atom, as
illustrated by the order of polymerization of norborene C4 (Me,
Br, Bu) > C1 (Me, Bu). The cationic palladium complexes C15
and C16 performed with better activity than did the monochloride
palladium complexes C1–C7, except for C4.
-1
Table 5 Norbornene polymerization by palladium complexes C1–C7,
C15, C16/MAOa
Run
Complexes
Polymer/g
Activityb
Yield/%
1
2
3
4
5
6
7
8
9
C1 (Me, Bu)
C2 (Et, Bu)
C3 (iPr, Bu)
C4 (Me, Br, Bu)
C5 (Me, Oct)
C6 (Et, Oct)
C7 (iPr, Do)
C15
0.561
0.584
0.552
0.654
0.542
0.523
0.361
0.670
0.615
4.49
4.67
4.42
5.23
4.34
4.19
2.89
5.36
4.92
47.7
49.7
47.0
55.7
46.1
44.5
30.7
57.0
52.2
The results showed that increasing the ethylene pressure not
only led to higher activity, as shown by C10 (runs 6 and 11), but
also increased the selectivity for 1-butene from 69.1% at 1 atm
to 99.1% at 10 atm. The ligand environment had an influence
on the observed catalytic behaviour, and the reactivity decreased
with a shorter chain at the N-alkyl in these complexes under the
same conditions, which was illustrated by the activity order of C14
(iPr, Do) > C12 (iPr, Oct) > C10 (iPr, Bu) (runs 15, 13, 11) and
C16
a Conditions: 2.5 mmol Pd, MAO, Al:Pd:NB = 1000 : 1 : 5000, total volume
30 mL, 20 ◦C, 30 min. b activity:105 g mol-1 h-1.
12860 | Dalton Trans., 2011, 40, 12856–12865
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All the resultant norbornene polymers possessed very high
molecular weight, which was beyond the measurement scale of
GPC, because of solubility problems in dichlorobenzene. The IR
spectra indicated that vinyl-type polymerization occurred rather
than ring-opening metathesis polymerization (ROMP), due to the
absence of peaks corresponding to C C double bond.
(1H, s, N-H), 7.96 (1H, t, J = 7.79, Py-H), 7.23 (2H, s, Ph-H),
3.52 (2H, m, NH-CH2-), 2.21 (3H, s, CH3C N), 2.00 (6H, s, Ph-
CH3), 1.67 (2H, m, –CH2–), 1.45 (2H, m, –CH2–CH3), 0.98 (3H, t,
J = 7.24, –CH2–CH3). 13C NMR (CDCl3, 100 MHz, ppm): 166.6,
163.7, 154.2, 148.9, 147.3, 137.8, 130.4, 127.4, 123.4, 115.5, 39.0,
31.7, 20.0, 17.6, 16.4, 13.6.
Synthesis of N-octyl-6-(1-(2,6-diethylphenylimino)ethyl)pico-
Conclusion
linamide
(L6). The
mixture
of
ethyl
6-(1-(2,6-
diethylphenylimino)ethyl)picolinate (0.3761 g, 1.16 mmol)
and 1-octylamine (0.1930 g, 1.50 mmol) was refluxed in methanol
for 3h, and the pure product was isolated as a yellow solid (0.215
g, 0.52 mmol) in 44.8% yield. 1H NMR (CDCl3, 400 MHz, ppm):
8.51 (1H, d, J = 7.88, Py-H), 8.32 (1H, d, J = 7.60, Py-H), 8.05
(1H, s, N-H), 7.97 (1H, t, J = 7.76, Py-H), 7.12 (2H, d, J = 7.48,
Ph-H), 7.04 (1H, t, J = 7.12, Ph-H), 3.52 (2H, m, NH–CH2–),
2.44–2.33 (4H, m, Et-CH2), 2.21 (3H, s, CH3C N), 1.67 (2H, m,
–CH2–), 1.45–1.26 (10H, m, octyl-CH2-), 1.13 (6H, d, J = 7.52,
CH3), 0.87 (3H, t, J = 6.6, octyl–CH3). 13C NMR (CDCl3, 100
MHz, ppm): 165.3, 163.5, 154.3, 148.6, 147.0, 137.4, 130.6, 125.5,
123.1, 123.0, 122.9, 39.0, 31.3, 29.2, 28.8, 28.7, 26.5, 24.1, 22.1,
16.2, 13.6, 13.2.
Monochloropalladium complexes C1–C7, formulated as LPdCl
(L
= L1–L7), were prepared by treatment of 2-(N-alkyl
carboxamide)-6-iminopyridyl with one equiv. of PdCl2(CH3CN)2
in dichloromethane. In contrast, the reaction of the ligands with
one equiv. of NiCl2·6H2O in ethanol afforded the dichloride nickel
complexes C8–C14, formulated as LNiCl2. Further reaction of
C3 with AgBF4 in CH3CN or malononitrile (CNCH2CN) gave
the monocationic palladium complex C15, [L3Pd(CH3CN)][BF4]
and the dimeric cationic palladium complex, formatted as
[L3Pd(CNCH2CN)PdL3]·2[BF4] (C16). All the palladium com-
plexes were characterized by 1H and 13C NMR spectroscopy and
elemental analysis. Molecular structure determinations of C3,
C4, C6 and C15 showed that the coordination geometry around
palladium is best described as distorted square planar, while
molecular structures of C10 and C12 demonstrated the distorted
square-pyramidal geometry at nickel. In the presence of MAO, all
the palladium complexes showed moderate activity for norbornene
polymerization, whilst the nickel complexes exhibited high activity
for ethylene dimerization with the activation of AlEt2Cl, up to 83.4
Synthesis of N-dodecyl-6-(1-(2,6-diisopropylphenylimino)-
ethyl)picolinamide (L7). The mixture of ethyl 6-(1-(2,6-
diisopropylphenylimino)ethyl)picolinate (0.1980 g, 0.56 mmol)
and 1-dodecamine (0.185 g, 1 mmol) in methanol gave a yellow oil
(0.216 g, 0.44 mmol) in 78.4% yield. IR (KBr, cm-1): 3333 (N–H),
2953, 2920, 2851, 1649 (C O), 1637 (C N), 1568, 1489, 1321.
1H NMR (CDCl3, 300 MHz, ppm): 8.51 (1H, d, J = 7.90, Py-H),
8.32 (1H, d, J = 7.61, Py-H), 8.06 (1H, s, N-H), 7.97 (1H, t, J =
7.83, Py-H), 7.19–7.11(3H, m, Ph-H), 3.50 (2H, m, NH–CH2–),
2.71 (2H, m, CH(CH3)2), 2.23 (3H, s, CH3C N), 1.65 (2H, m,
–CH2–), 1.28 (18H, m, –CH2–), 1.15 (12H, d, J = 6.79, CH3), 0.86
(3H, t, J = 7.23, CH3). 13C NMR (CDCl3, 100 MHz, ppm): 165.6,
163.8, 154.5, 148.9, 146.0, 137.7, 135.5, 123.6, 123.4, 123.2, 122.9,
39.3, 31.7, 29.6, 29.5, 29.4, 29.2, 28.2, 26.9, 23.0, 22.7, 22.5, 16.9,
13.9.
¥ 105 g molNi h-1.
-1
Experimental
All manipulations of air- or/and moisture-sensitive compounds
were carried out under a nitrogen atmosphere using standard
Schlenk techniques. Melting points (Mp) were determined with
a digital electrothermal apparatus without calibration. The IR
spectra were recorded on a Perkin–Elmer FT-IR 2000 spectropho-
1
tometer using KBr discs in the range of 4000–400 cm-1. The H
and 13C NMR spectra were recorded on a Bruker DMX-400 MHz
or 300 MHz instrument at ambient temperature using TMS as an
internal standard. Splitting patterns are designated as follows: s,
singlet; bs, broad singlet; d, doublet; dd, double doublet; t, triplet;
m, multiplet. The elemental analyses were performed on a Flash
EA 1112 microanalyser. Distribution of oligomers obtained was
measured on a Varian VISTA 6000 GC spectrometer and a HP
5971A GC–MS detector. L1–L3, L5, L7 were prepared according
to the literature.9
Synthesis of palladium complexes C1–C7
General route. To the CH2Cl2 solution (40 mL) containing
PdCl2(CH3CN)2 (0.2594 g, 1 mmol), one equiv. of ligand was
added at room temperature, and the mixture was stirred overnight.
The solution was then concentrated and petrol ether was added
into the solution to precipitate the complex, and the precipitate
was collected as an orange powder.
C1. Yield: 55.5%. IR (KBr, cm-1): 3420, 3072, 2956, 2928,
2869, 1671, 1617, 1588, 1769. 1H NMR (CDCl3, 400 MHz, ppm):
8.19 (1H, t, J = 7.88, Py-H), 7.98 (1H, d, J = 8.00, Py-H), 7.72
(1H, d, J = 7.84, Py-H), 7.15 (3H, s, Ph-H), 3.35 (2H, t, J = 7.28,
N–CH2–), 2.28 (6H, s, PhCH3), 2.21 (3H, s, CH3C N), 1.64–
1.57 (2H, m, –CH2–), 1.41–1.34 (2H, m, –CH2–), 0.90 (3H, t, J
= 7.32, –CH2CH3). 13C NMR (CDCl3, 100 MHz, ppm): 175.5,
170.8, 155.4, 153.1, 143.2, 140.6, 128.7, 128.5, 127.8, 127.0, 125.3,
47.1, 32.7, 20.6, 18.6, 16.7, 14.3. Anal. calcd for C20H24ClN3OPd:
C 51.74, H 5.21, N 9.05. Found: C 51.60, H 5.34, N 8.96.
Synthesis of palladium complexes and nickel complexes
Synthesis of N-butyl-6-(1-(2,6-dimethyl-4-bromophenylimino)
ethyl)picolinamide (L4). The mixture of ethyl 6-(1-(2,6-dimethyl-
4-bromophenylimino)ethyl)picolinate (0.2735 g, 0.73 mmol) and
1-butylamine (0.108 g, 1.48 mmol) in methanol gave N-butyl-6-(1-
(2,6-dimethyl-4-bromophenylimino)ethyl)picolin-amide (0.0942
◦
g, 0.23 mmol) as a yellow solid in 32.1% yield. mp: 117–118 C.
IR (KBr, cm-1): 3344 (N–H), 2967, 2955, 2929, 1655 (C O), 1643
1
(C N), 1569, 1534, 1206. H NMR (300 MHz, CDCl3, ppm):
C2. Yield: 73.8%. IR (KBr, cm-1): 3415, 3069, 2962, 2931,
2871, 1672, 1617, 1587, 1458, 1374, 758. H NMR (CDCl3, 400
1
8.49 (1H, d, J = 7.89, Py-H), 8.33 (1H, d, J = 7.54, Py-H), 8.00
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MHz, ppm): 8.23 (1H, t, J = 7.90, Py-H), 8.02 (1H, d, J = 7.80,
Py-H), 7.78 (1H, d, J = 7.80, Py-H), 7.34–7.23 (3H, m, Ph-H),
3.39 (2H, t, J = 7.18, N–CH2–), 2.80–2.76 (2H, m, CH2CH3), 2.58–
2.54 (2H, m, CH2CH3), 2.25 (3H, s, CH3C N), 1.67–1.63 (2H,
m, –CH2–), 1.41–1.33 (8H, m, –CH2– and CH2CH3), 0.94 (3H, t,
J = 7.30, CH3). 13C NMR (CDCl3, 100 MHz, ppm): 175.4, 170.6,
155.4, 153.0, 142.0, 140.5, 134.1, 128.1, 126.8, 126.1, 125.0, 47.1,
32.5, 24.5, 20.4, 17.1, 14.1, 13.7. Anal. calcd for C22H28ClN3OPd:
C 53.67, H 5.73, N 8.53. Found: C 53.64, H 5.95, N 8.04.
Py-H), 7.77 (1H, d, J = 7.77, Py-H), 7.32 (1H, t, J = 7.60, Ph-H),
7.24 (2H, d, J = 7.57, Ph-H), 3.33 (2H, t, J = 6.96, N–CH2–),
3.05–2.98 (2H, m, CH(CH3)2), 2.22 (3H, s, CH3C N), 1.60 (2H,
m, –CH2–), 1.42 (6H, d, J = 6.50, CH(CH3)2), 1.21 (br, s, 18H,
–CH2–), 1.16 (6H, d, J = 6.70, CH(CH3)2), 0.85 (3H, t, J = 5.67,
–CH3). 13C NMR (CDCl3, 100 MHz, ppm): 175.6, 170.8, 155.4,
153.0, 140.6, 140.5, 139.3, 128.6, 126.9, 125.2, 123.9, 47.4, 32.0,
30.5, 29.8, 29.7, 29.4, 28.9, 27.4, 23.8, 23.7, 22.7, 17.6, 14.2, 11.5.
Anal. calcd for C32H48ClN3OPd·0.2CH2Cl2: C 59.54, H 7.51, N
6.47. Found: C 59.66, H 7.57, N 6.37.
C3. Yield: 87.3%. IR (KBr, cm-1): 3425, 3069, 2961, 2929,
1
2869, 1671, 1618, 1587, 1460, 1366, 756. H NMR (CDCl3, 400
Synthesis of nickel complexes (C8–C14)
MHz, ppm): 8.20 (1H, t, J = 7.83, Py-H), 7.99 (1H, d, J = 7.93,
Py-H), 7.73 (1H, d, J = 7.86, Py-H), 7.33 (1H, t, J = 7.68, Ph-H),
7.23 (2H, s, Ph-H), 3.36 (2H, t, J = 7.17, N–CH2–), 3.05–2.98 (2H,
m, CH(CH3)2), 2.23 (3H, s, CH3C N), 1.64 (2H, m, –CH2–), 1.43
(6H, d, J = 6.57, CH(CH3)2), 1.38 (2H, m, –CH2–), 1.16 (6H, d, J =
6.76, CH(CH3)2), 0.90 (3H, t, J = 7.22, CH3). 13C NMR (CDCl3,
100 MHz, ppm): 175.4, 170.8, 155.5, 153.1, 140.5, 140.4, 139.3,
128.7, 127.0, 125.0, 123.9, 47.2, 32.6, 28.9, 23.8, 23.7, 20.5, 17.6,
14.3. Anal. calcd for C24H32ClN3OPd: C 55.39, H 6.20, N 8.07.
Found: C 55.18, H 6.47, N 7.65.
A solution of the ligand in 30 mL ethanol was added dropwise to
an equimolar amount of NiCl2·6H2O (0.2377 g, 1 mmol) in ethanol
solution and the reaction mixture was stirred at room temperature
for 6 h. The solution was then concentrated and diluted with
diethyl ether. The resulting precipitate was collected, washed with
diethyl ether, and dried in vacuum. All of the complexes were
prepared in high yield in this manner.
C8. Yield: 82.0%. IR (KBr, cm-1): 3225, 3071, 2928, 2862,
1641, 1590, 1464, 1439, 1370, 1276, 759. Anal. calcd for
C20H25Cl2N3NiO: C 53.02, H 5.56, N 9.28. Found: C 53.55, H
5.95, N 9.45.
C4. Yield: 90.0%. IR (KBr, cm-1): 3276, 3070, 2958, 2925,
1
2854, 1671, 1616, 1587, 1465, 757. H NMR (CDCl3, 400 MHz,
ppm): 8.39 (1H, br, Py-H), 8.16 (1H, br, Py-H), 7.86 (1H, br, Py-
H), 7.30 (3H, s, Ph-H), 3.36 (2H, br, N-CH2-), 2.26 (9H, s, Ph-CH3
and CH3C N). 13C NMR (CDCl3, 100 MHz, ppm): 177.0, 153.1,
151.9, 142.1, 138.6, 131.2, 131.1, 127.2, 125.6, 123.9, 120.9, 47.1,
31.8, 20.4, 18.4, 17.1, 14.2. Anal. calcd for C20H23BrClN3OPd: C
44.22, H 4.27, N 7.74. Found: C 44.56, H 4.04, N 7.66.
C9. Yield: 92.0%. IR (KBr, cm-1): 3239, 3070, 2963, 2873,
1640, 1591, 1465, 1440, 1373, 1276, 1190, 1034, 760. Anal. calcd
for C22H29Cl2N3NiO: C 52.66, H 5.87, N 8.25. Found: C: 52.68, H
5.96, N 8.18.
C10. Yield: 88.8%. IR (KBr, cm-1): 3213, 3071, 2964, 2871,
2340, 1644, 1589, 1553, 1464, 1442, 1369, 1273, 834, 807, 755, 593.
Anal. calcd for C24H33Cl2N3NiO: C 56.62, H 6.53, N 8.25. Found:
C 56.77, H 6.67, N 8.14.
C5. Yield: 55.1%. IR (KBr, cm-1): 3654, 3069, 2950, 2864,
1727, 1617, 1587, 1560, 1467, 1426, 1367, 1279, 1199, 1092, 817,
791, 756. 1H NMR (CDCl3, 400 MHz, ppm): 8.19 (1H, t, J = 7.72,
Py-H), 7.98 (1H, d, J = 7.85, Py-H), 7.73 (1H, d, J = 7.84, Py-H),
7.15 (3H, s, Ph-H), 3.34 (2H, t, J = 7.10, N–CH2–), 2.28 (6H, s,
Me), 2.21 (3H, s, CH3C N), 1.62 (6H, s, –CH2–), 1.29–1.24 (6H,
m, –CH2–), 0.87–0.82 (3H, m, –CH2CH3). 13C NMR (CDCl3, 100
MHz, ppm): 175.4, 170.7, 155.5, 153.1, 143.2, 140.6, 128.7, 128.3,
127.8, 127.0, 125.1, 47.5, 32.0, 30.5, 29.7, 29.5, 27.4, 22.7, 18.6,
17.7, 16.6, 14.2. Anal. calcd for C24H32ClN3OPd: C 55.39, H 6.20,
N 8.07. Found: C 54.99, H 6.04, N 7.66.
C11. Yield: 66.1%. IR (KBr, cm-1): 3237, 3073, 2928, 2856,
1642, 1591, 1552, 1463, 1439, 1373, 1276, 1190, 761.5. Anal. calcd
for C26H37Cl2N3NiO: C 58.13, H 6.94, N 7.82. Found: C 57.92, H
6.88, N 8.10.
C12. Yield: 82.8%. IR (KBr, cm-1): 3225, 3071, 2928, 2862,
1641, 1590, 1464, 1439, 1370, 1276, 1187, 759. Anal. calcd for
C28H41Cl2N3NiO: C 59.50, H 7.31, N 7.43. Found: C 58.94, H
7.32, N 7.19.
C6. Yield: 45.4%. IR (KBr, cm-1): 3076, 2920, 2846, 2163,
1614, 1590, 1558, 1429, 1371, 1342, 1093, 1007, 823, 763, 717. 1H
NMR (CDCl3, 400 MHz, ppm): 8.18 (1H, t, J = 7.90, Py-H), 7.95
(1H, d, J = 7.86, Py-H), 7.76 (1H, d, J = 7.83, Py-H), 7.27 (1H,
t, J = 7.68, Ph-H), 7.18 (2H, d, J = 7.57, Ph-H), 3.32 (2H, t, J =
7.39, N–CH2–), 2.77–2.71 (2H, m, Ph-CH2CH3), 2.53–2.48 (2H,
m, Ph-CH2CH3), 2.20 (3H, s, CH3C N), 1.60 (2H, m, –CH2–),
1.32-1.22 (16H, m, Ph-CH2CH3 and –CH2–CH2–), 0.83 (3H, t,
J = 5.67, octyl-CH3). 13C NMR (CDCl3, 100 MHz, ppm): 175.6,
170.7, 155.4, 153.1, 142.1, 140.6, 134.2, 128.1, 126.9, 126.2, 125.2,
47.4, 32.0, 30.5, 29.7, 29.5, 27.4, 24.6, 22.7, 17.2, 14.2, 13.8. Anal.
calcd for C26H36ClN3OPd·0.2CH2Cl2: C 55.65, H 6.49, N 7.43.
Found: C 55.62, H 6.53, N 7.04.
C13. Yield: 78.0%. IR (KBr, cm-1): 3248, 3068, 2925, 2854,
1642, 1591, 1466, 1374, 1277, 1035, 760. Anal. calcd for
C30H45Cl2N3NiO: C 60.73, H 7.64, N 7.08. Found: C 60.90, H
7.88, N 7.10.
C14. Yield: 43.0%. IR (KBr, cm-1): 3221, 3070, 2926, 2855,
2367, 1640, 1589, 1464, 1369, 1275, 761. Anal. calcd for
C32H49Cl2N3NiO·CH2Cl2: C 56.12, H 7.28, N 5.95. Found: C
56.13, H 6.88, N 6.10.
Synthesis of mono-cationic palladium complex C15
A slight excess amount of AgBF4 (0.1 g, 0.51 mmol) was added
into 40 mL CH3CN solution containing one equiv. of complex
C3 (0.2330 g, 0.45 mmol), immediately a white precipitate was
observed and the mixture was stirred for >12 h. Then the
precipitate was filtered and the solution was collected and all the
C7. Yield: 45.9%. IR (KBr, cm-1): 3246, 3067, 2960, 2925,
1
2853, 1674, 1617, 1585, 1464, 1366, 755. H NMR (CDCl3, 400
MHz, ppm): 8.18 (1H, t, J = 7.80, Py-H), 7.96 (1H, d, J = 7.79,
12862 | Dalton Trans., 2011, 40, 12856–12865
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Table 6 Crystal data and refinement details for C3, C4, C6, C10, C12 and C15
C3(iPr, Bu)
C4(Me,Br, Bu)
C6(Et, Oct)
C10(iPr, Bu)
C12(iPr, Oct)
C15a
Empirical formula
C24H32ClN3OPd
C20H23BrClN3OPd C26H36ClN3OPd
C24H33Cl2N3NiO C28H41Cl2N3NiO2·
(C4H10O)n (n = 0.94)
C26 H32 BF4N4OPd
Formula weight
Crystal color
T/K
520.38
yellow
173(2)
543.18
orange
293(2) K
0.71073 A
Triclinic,
¯
P1
548.43
yellow
293 (2) K
0.71073 A
Rhombohedral
R3c
509.14
red
634.48
red
609.79
red
293(2) K
293(2) K
293(2)K
0.71073 A
˚
˚
˚
˚
˚
˚
˚
Wavelength (A)
0.71073 A
0.71073 A
Monoclinic
P21/n
0.71073 A
Monoclinic
P21/n
Crystal system
Monoclinic
Cc
Monoclinic
P21/c
Space group
˚
a/A
13.403(3)
14.090(3)
12.618(3)
90.00
98.67(3)
90.00
2355.7(8)
4
1.467
9.833(2)
10.801(2)
11.479(2)
117.58(3)
94.67(3)
90.15(3)
1075.9(4)
2
31.280(4)
31.280(4)
14.424(3)
90
90
120
12222(3)
18
1.341
10.797(2)
16.923(3)
13.860(3)
90
92.19(3)
90
13.574(6)
17.728(7)
15.650(7)
90
109.81(2)
90
14.325(3)
11.604(2)
20.709(7)
90.00
125.93(2)
90.00
2787.4(12)
4
1.453
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
Volume/A
Z
2530.5(9)
4
1.336
3543(3)
4
1.189
Dcalc/Mg m-3
1.677
m/mm-1
0.921
1072
2.858
540
0.803
5112
0.998
1072
0.727
1357
0.718
1244
F(000)
Crystal size/mm
0.46 ¥ 0.33 ¥ 0.32 0.37 ¥ 0.20 ¥ 0.15
2.1099 to 27.4853 2.01 to 27.33
-17<=h<=15,
-18<=k<=18,
-16<=l<=14
9432
4332
0.0386
0.00(4)
0.37 ¥ 0.20 ¥ 0.15 0.46 ¥ 0.26 ¥ 0.21 0.33 ¥ 0.30 ¥ 0.22
0.35 ¥ 0.33 ¥ 0.25
1.76 to 30.01
-20<=h<=20,
-16<=k<=12,
-28<=l<=29
28 773
8118
-0.0539
0.45(7)
q range/◦
1.30 to 27.48
-40<=h<=0,
0<=k<=35,
-18<=l<=15
34 533
1.90 to 27.48
0<=h<=13,
0<=k<=21,
-17<=l<=17
18 044
1.72 to 25.01
-16<=h<=15,
-21<=k<=18,
-18<=l<=18
27 403
Limiting indices
0<=h<=12,
13<=k<=13,
-14<=l<=14
9726
No. of rflns collected
No. of unique rflns
Rint
4746
3132
5697
6229
0.0318
—
0.0633
—
0.0916
—
0.1385
—
Flack parameter
Completeness to q (%) 99.3
97.7
1.083
0.0364,
0.0987
0.0480,
0.1089
100.0
0.894
0.0334,
0.0912
0.0462,
0.0941
0.490 and -0.444
98.3
0.913
0.0679,
0.0912
0.1328,
0.1743
99.7
0.923
0.0740,
0.1865
0.1328,
0.2193
99.8
1.121
0.0639,
0.1323
0.0729,
0.1377
1.024 and -0.878
Goodness-of-fit on F2
R1 [I > 2s(I)]
1.076
0.0365,
0.0941
0.0389,
0.1087
wR2 [I > 2s(I)]
R1 (all data)
wR2 (all data)
Largest diff peak and
0.917 and -0.718
1.225 and -1.058
0.601 and -0.544 0.705 and -0.416
-3
˚
hole/e A
solvent removed. The residue was extracted with CH2Cl2 and from
the combined solution was removed all the solvent. The cationic
complex C15 (0.1673 g, 0.27 mmol) was obtained in yield (60.6%)
as a yellow powder. IR (KBr, cm-1): 3334, 3090, 2958, 2928, 2865,
2361, 2332, 2168, 1980, 1623, 1560, 1436, 1367, 1281, 1026, 802,
overnight, the precipitate was filtered, and then all solvent was
removed to afford a brown residue, complex C16 (0.1768 g, 0.146
mmol). Yield: 73.9%. IR (KBr, cm-1): 3446, 3088, 2958, 2927,
2865, 2362, 2133, 1622, 1593, 1561, 1436, 1365, 1280, 1053, 824,
1
800, 757. H NMR (CDCl3, 400 MHz, ppm): 8.37 (2H, t, J =
1
756. H NMR (CDCl3, 400 MHz, ppm): 8.45 (1H, t, J = 8.08,
7.52, Py-H), 8.17 (2H, d, J = 7.56, Py-H), 7.94 (2H, d, J = 7.92,
Py-H), 7.38–7.18 (3H, m, Ph-H), 3.60 (2H, s, CNCH2CN), 3.11
(4H, t, J = 6.56, NH–CH2–), 2.98 (4H, m, CH(CH3)2), 2.37 (6H,
s, CH3C N), 1.50–1.45 (4H, m, –CH2–), 1.30 (12H, d, J = 6.72,
CH(CH3)2), 1.26–1.24 (4H, m, –CH2–), 1.19 (12H, d, J = 6.83,
CH(CH3)), 0.85 (3H, t, J = 6.72, CH3). 13C NMR (CDCl3, 100
MHz, ppm): 178.7, 170.6, 154.9, 153.7, 143.1, 139.8, 139.1, 133.0,
129.0, 128.1, 127.5, 125.0, 124.4, 47.5, 33.0, 29.8, 29.0, 23.8, 23.6,
20.5, 17.7, 14.3, 8.6, 5.0, 1.1. Anal. calcd for C51H66B2F8N8O2Pd2:
C 50.64, H 5.50, N 9.26. Found: C 50.61, H 5.50, N 9.30.
Py-H), 8.39 (1H, d, J = 7.92, Py-H), 7.92 (1H, d, J = 7.72, Py-
H), 7.42 (1H, t, J = 7.88, Ph-H), 7.33 (2H, d, J = 7.64, Ph-H),
3.18 (2H, t, J = 6.96, NH–CH2–), 3.07 (2H, m, CH(CH3)2), 2.50
(3H, s, CH3C N), 1.99 (3H, s, CH3C N), 1.57–1.46 (2H, m,
–CH2–), 1.39 (8H, m, CH(CH3) and –CH2–), 1.23 (6H, d, J =
6.60, CH(CH3), 0.90 (3H, t, J = 7.22, CH3). 13C NMR (CDCl3,
100 MHz, ppm): 180.5, 154.4, 154.1, 144.2, 139.5, 129.6, 129.3,
127.9, 124.7, 122.5, 47.9, 33.0, 28.8, 23.8, 23.7, 20.4, 18.0, 14.2.
Anal. calcd for C26H35BF4N4OPd·CH2Cl2: C 46.48, H 5.34, N
8.03. Found: C 46.31, H 5.40, N 7.79.
Synthesis of dimeric cationic palladium complex C16
General procedure for ethylene dimerization
To a CH2Cl2 solution (30 mL) containing complex C3 (0.2050 g,
0.394 mmol), one equiv. of AgBF4 (0.077 g, 0.395 mmol) was added
and then stirred for 30 min. The white precipitate was observed
immediately. After 10 min, the toluene solution (1 mL) containing
0.5 equiv. of CNCH2CN was added to the mixture and the solution
color changed from yellow to orange. The mixture was stirred
Ethylene dimerization under 1 atm ethylene. The pro-catalyst
was dissolved in toluene using standard Schlenk techniques, and
the reaction solution was stirred with a magnetic stir bar under
ambient ethylene atmosphere. The required amount of co-catalyst
(MAO, MMAO) was added by a syringe. After the reaction was
carried out for the required period, the reaction solution was
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quenched with 10% hydrochloric acid/ethanol. An aliquot of the
reaction mixture was analyzed by GC.
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X-Ray crystallography measurement
Single-crystal X-ray diffraction studies for C4, C6, C10 and C12
were carried out on a Rigaku Rapid IP diffractometer with
˚
graphite-monochromated Mo-Ka radiation (l = 0.71073 A).
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diffractometer with graphite-monochromated Mo-Ka radiation
˚
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˚
ror monochromated Mo-Ka radiation (l = 0.71073 A). Cell
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Acknowledgements
This work is supported by MOST 863 program no. 2009AA034601
and National Natural Science Foundation of China (no.
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Dalton Trans., 2011, 40, 12856–12865 | 12865
©