β-Diketiminato 3d-metal compounds: Synthesis, characterization and catalytic behavior towards ethylene

Article abstract of DOI:10.1016/j.ica.2011.01.063

The lithium β-diketiminate (1c, [Li{N(2,6-ⁱPr ₂C₆H₃)C(Ph)CHC(^tBu)NH}]₂ represented as (LiL)₂) reacted with 3d-metal (II) chlorides to afford the corresponding compounds (2-7). All metal compounds were fully characterized by elemental, spectroscopic analyses and the single-crystal X-ray diffraction. The coordination geometries around the metals are shown to be tetrahedral within the trinuclear Co₂Li compound (2), planar in ML₂ (M = Co, 3), pseudo-tetrahedral conformation in the ML₂ with M as Mn (4), Fe (5) or Zn (6), and square planar in the dinickel compound (7). Indicated by the trimetallic Co₂Li compound 2, a six-membered ring is constructed of three metal atoms and three bridged chlorides as a twisted conformation. An inversion center is present in the centroid of the Ni₂Cl₂ four-membered ring within compound 7. The plausible mechanism of forming ML ₂ was proposed through the chloro-bridged multinuclear compounds on the basis of isolated intermediates of trinuclear (2) and dinuclearic (7) compounds. Upon treatment with methylaluminoxane (MAO), the nickel compound 7 possessed good activity towards ethylene oligomerization, whereas the other metal compounds showed moderate activities towards ethylene polymerization.

Full text of DOI:10.1016/j.ica.2011.01.063

Inorganica Chimica Acta 370 (2011) 215–223
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
b-Diketiminato 3d-metal compounds: Synthesis, characterization and catalytic
behavior towards ethylene
b,
Shifang Yuan a,b, Shengdi Bai a, Hongbo Tong a, Xuehong Wei a, Diansheng Liu a, , Wen-Hua Sun
⇑
⇑
a Institute of Applied Chemistry, Shanxi University, Taiyuan 030006, China
b Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
a r t i c l e i n f o
a b s t r a c t
The lithium b-diketiminate (1c, [Li{N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH}]2 represented as (LiL)2) reacted
with 3d-metal (II) chlorides to afford the corresponding compounds (2–7). All metal compounds were
fully characterized by elemental, spectroscopic analyses and the single-crystal X-ray diffraction. The
coordination geometries around the metals are shown to be tetrahedral within the trinuclear Co2Li com-
pound (2), planar in ML2 (M = Co, 3), pseudo-tetrahedral conformation in the ML2 with M as Mn (4), Fe (5)
or Zn (6), and square planar in the dinickel compound (7). Indicated by the trimetallic Co2Li compound 2,
a six-membered ring is constructed of three metal atoms and three bridged chlorides as a twisted con-
formation. An inversion center is present in the centroid of the Ni2Cl2 four-membered ring within com-
pound 7. The plausible mechanism of forming ML2 was proposed through the chloro-bridged
multinuclear compounds on the basis of isolated intermediates of trinuclear (2) and dinuclearic (7) com-
pounds. Upon treatment with methylaluminoxane (MAO), the nickel compound 7 possessed good activ-
ity towards ethylene oligomerization, whereas the other metal compounds showed moderate activities
towards ethylene polymerization.
Article history:
Received 14 November 2010
Received in revised form 10 January 2011
Accepted 19 January 2011
Available online 31 January 2011
Keywords:
b-Diketiminate
Late transition metal
Molecular structure
Ethylene oligomerization
MAO
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
dinickel compounds have shown catalytic behavior in ethylene
polymerization and oligomerization [35]. Recently b-diketiminato
The 1,5-diazapentadienyls (known as b-diketiminates) have at-
tracted attention due to their physical properties [1–6], and their
exploitations as ancillary ligands in transition metal chemistry
[7,8] since 1960s. Lappert et al. have reported a number of sym-
metric b-diketiminato ligands and metal compounds thereof [9–
15], and a number of review articles have also recently appeared
[16,17]. b-Diketiminate metal compounds can in general be re-
ported by a number of structural types, for example, ML2 (L =
zirconium compounds have intensively been investigated in
ethylene polymerization [43–47], and extensive research has been
conducted with the nonsymmetrical N^N b-diketiminato ligands,
(2-C5H5N)C(H)C(Ph)N(SiMe3) [48] and N(SiMe3)2C(C5H5N)CHC(tBu)
[49,50]. However, there are no reports containing mononuclear,
dinuclear and trinuclear complexes and understanding the forma-
tion mechanism.
The nonsymmetrical b-diketiminato ligand (1c, [Li{N(2,6-
iPr2C6H3)C(Ph)CHC(tBu)NH}]2 (LiL)2) has been reacted with various
metal chlorides. The trinuclear chloro-bridged compound
{N(R)C(Ph)}2CH, M = Co [9,10], M = Mn, Fe, Ni or Cu [18]), ML(g3
-
C3H5) (L = {N(SiMe3)C(Ph)}2CH, M = Ni, Pd) [18], [KL(THF)3]2
(L = Si(Me)2{NC(Ar)}2CH, Ar = 4-tBuC6H4) [19] and their derivatives
[20–28]. In the case of the dinuclear compounds, the species are
dominated by halo-bridged structures. Various metals have been
[(CoL)2(l-Cl)3Li(THF)2] (2) was isolated, and transformed into the
ML2 compound (M = Co, 3). Typical ML2 derivatives were isolated
when the metal is Mn (4), Fe (5) or Zn (6), as well as a chloro-
employed such as palladium [PdL(
[18] or {C(Me)N(Ph)}2CH [29–31], zinc [ZnL(
[CrLCl(
-Cl)]2 (L = {C(Me)N(2,6-iPr2C6H3)}2HC) [33,34], nickel
-Cl)]2 (L = {C(Me)N(Ar)}2CH) [35–38], or @CH(dmpz)2 [39],
-Cl)]2ꢀ2CH3OH [40], [NiLCl( -Cl)]2 [41,42] and cobalt
-Cl)]2 (L = {C(Me)N(Ar)}2CH) [38]. We note that some
l
-Cl)]2 (L = {N(SiMe3)C(Ph)}2CH)
bridged dinickel compound [(NiL)2(l-Cl)2, 7]. Interest in nickel
l
-F)]2 [32], chromium
compounds chelating P^P, N^O, P^N and N^N ligands is the catalysis
center around their use as for ethylene oligomerization and poly-
merization [51–54]. The catalytic activity was explored for the
l
[NiL(
[NiL(
[CoL(
l
l
l
l
dinickel compound [(NiL)2(l-Cl)2, 7] with high activity observed
in ethylene oligomerization, whereas the other metal complexes
showed only moderate activities towards ethylene oligomeriza-
tion. Herein the synthesis and characterization of the title com-
pounds are reported in detail as well as the catalytic behavior in
ethylene oligomerization.
⇑
Corresponding authors. Tel.: +86 10 62557955; fax: +86 10 62618239.
E-mail addresses: dsliu@sxu.edu.cn (D. Liu), whsun@iccas.ac.cn (W.-H. Sun).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.063

216
S. Yuan et al. / Inorganica Chimica Acta 370 (2011) 215–223
resultant solution was stirred overnight. The yellow solution was
2. Experimental
concentrated under vacuum and purified on a silica gel column
using petroleum ether/ether (3:1) as the eluent to get the product
1d (0.64 g, 1.8 mmol) in 90% isolated yield as colorless crystals,
mp: 81–83 °C. Anal. Calc. for C25H34N2: C, 82.69; H, 9.28; N, 3.85.
Found: C, 82.71; H, 9.26; N, 3.86%. 1H NMR (C6D6): d 0.77–0.79
(d, 6H, CH(CH3)2), 0.97–0.99 (d, 6H, CH(CH3)2), 1.17 (s, 9H,
C(CH3)3), 2.87–2.89 (m, 2H, CH(CH3)2), 3.69 (NH2), 4.95 (s, 1H,
CH), 6.82 (m, 3H, aryl), 7.04 (m, 5H, Ph). 13C NMR (C6D6): d 21.30
(CH, Pr), 23.90 (CH3, Pr), 27.38, 28.57 (CH3, Bu), 35.30 (C, Bu),
89.58 (CH), 121.75 (aryl), 126.77–127.10 (Ph), 137.05 (ipso-CPh),
139.66 (ipso-CiPr), 145.54 (ipso-CAr), 165.68 (N@C), 166.24 (ipso-
CtBu).
All manipulations were carried out under a nitrogen atmo-
sphere using standard Schlenk techniques. Hexane, tetrahydrofu-
ran, toluene and diethyl ether are dried using sodium potassium
alloy and distilled under nitrogen prior to use. Dichloromethane
is distilled over CaH2. The PhMeC@N(2,6-iPr2C6H3) (1a) was pre-
pared according to the literature [55,56]. The NMR spectra were re-
corded on a Bruker DKX-300 spectrometer with TMS as an internal
standard. Elemental analyses were performed with a Flash EA 1112
microanalyzer. The polymerization grade ethylene was supplied by
Beijing Yansan Petrochemical Co. The Et2AlCl (1.90 M in toluene)
and methylaluminoxane (MAO, 1.46 M in toluene) solution were
purchased from Ablemarle Corporation. Deuterated solvents C6D6
and CDCl3 were dried over activated molecular sieves (4 Å) and
freshly distilled before use. GC was performed with a VARIAN
CP-3800 gas chromatograph equipped with a flame ionization
i
i
t
t
2.2. Synthesis of late-transition compounds 2–7
2.2.1. [N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH]2Co2(
l
-Cl)3Liꢀ2THF (2)
detector and a 30-m (0.2 mm i.d., 0.25 lm film thickness) CP-Sil
To the solution of 1c (0.74 g, 1 mmol) in 25 ml THF at ꢁ78 °C,
the CoCl2 (0.26 g, 2 mmol) was added. The resulting mixture was
stirred for 10 min, then warmed up to room temperature and stir-
red for 24 h. Volatile compounds were removed, and the resulting
residues were solvated in 50 ml CH2Cl2. The filtrate was concen-
5 CB column. Melting points of polyolefins were measured on a
Perkin–Elmer DSC-7 differential scanning calorimetry (DSC) ana-
lyzer. Under a nitrogen atmosphere, a sample of about 2–6 mg
was heated from 20 to 160 °C at a rate of 10 °C/min and kept for
5 min at 160 °C to remove the thermal history, then cooled at a rate
of 10 °C/min to 20 °C. The DSC trace and the melting points of the
samples were obtained from the second scanning run.
trated and crystallized as black-green crystals
2
(0.46 g,
0.42 mmol) in 42% yield, mp: 167–170 °C (with dec). Anal. Calc.
for C58H80Cl3Co2LiN4O2: C, 63.50; H, 7.30; N, 5.11. Found: C,
63.55; H, 7.29; N, 5.13%.
2.1. Preparations of ligands 1a–1d
2.2.2. [N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH]2Co (3)
2.1.1. [LiCH2PhC@N(2,6-iPr2C6H3)] (1b)
Method one: To the solution of 1c (0.74 g, 1 mmol) in 25 ml THF
at ꢁ78 °C, the CoCl2 (0.13 g, 1 mmol) was added. The resulting mix-
ture was stirred for 10 min, then refluxed for 3 h. Volatile com-
pounds were removed, and the resulting residues were extracted
in 50 ml toluene. The filtrate was concentrated and crystallized
as red crystals 3 (0.62 g, 0.73 mmol) in 73% yield.
Method two: The compound 2 (0.55 g, 0.5 mmol) was refluxed in
toluene for 12 h. The filtrate was concentrated and crystallized as
red crystals 3 (0.32 g, 0.41 mmol) in 82% yield. Mp: 252–254 °C
(with dec). Anal. Calc. for C50H66N4Co: C, 76.79; H, 8.51; N, 7.16.
Found: C, 76.80; H, 8.50; N, 7.15%.
To the solution of 1a (0.56 g, 2 mmol) in 25 ml THF at ꢁ78 °C,
LDA (0.21 g, 2 mmol) was added. The mixture was stirred for 2 h
at ꢁ78 °C, then warmed to room temperature for 5 h. The resultant
solution was concentrated under vacuum and layered with hexane
to give the light yellow solid. Recrystallization from its THF solu-
tion gave colorless crystals 1b (0.56 g, 1.96 mmol) in 98% yield.
1H NMR (300 MHz C6D6): d 0.81–0.88 (d, 2H, CH2), 0.93–0.94 (d,
4H, THF), 1.04–1.06, 1.34–1.36 (2d, 12H, CH(CH3)2), 2.99–3.11 (d,
4H, THF), 3.58–3.62 (m, 2H, CH(CH3)2), 3.72 (s, H, NH), 6.79–6.81
(m, 1H, Ph), 6.85–6.97 (m, 3H, Aryl), 7.09–7.12 (d, 2H, Ph), 7.78–
7.81 (d, 2H, Ph). 13C NMR (75 MHz C6D6): d 16.60 (CH2), 16.72
(THF), 19.43, 19.44 (CH(CH3)2), 59.30 (THF), 63.06 (CH(CH3)2),
112.50 (p-Ar), 114.64 (m-Ar), 117.58 (o-Ph), 118.08 (p-Ph),
135.85 (m-Ph), 141.40 (ipso-CPh), 145.17 (ipso-CAr), 152.34
(ipso-CAr-N), 172.98 (N@C).
2.2.3. [N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH]2Mn (4)
Using the same procedure as compound 2, the compound 4 was
isolated as brown crystals (0.60 g, 0.76 mmol) in 76% yield, mp:
182–184 °C (with dec). Anal. Calc. for C50H66N4Mn: C, 77.18; H,
8.48; N, 7.21. Found: C, 77.22; H, 8.45; N, 7.20%.
2.1.2. [N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NHLi]2 (1c)
To the solution of 1b (0.57 g, 2 mmol) in 25 ml THF at 0 °C, tBuCN
(0.22 ml, 2 mmol) was added dropwise to form a rose red solution,
which gradually disappeared and changed to a brown solution. The
mixture was then warmed up to room temperature and kept stir-
ring for 12 h. Then 25 ml hexane was layered on the red solution,
and the precipitate was observed and collected as light yellowish
solid of 1c (0.72 g, 0.97 mmol) in 97% yield. Anal. Calc. for
2.2.4. [N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH]2Fe (5)
Using the same procedure as compound 2, the compound 5 was
obtained as red crystals (0.47 g, 0.6 mmol) in 60% yield, mp: 188–
189 °C (with dec). Anal. Calc. for C50H66N4Fe: C, 77.21; H, 8.24; N,
7.21. Found: C, 77.15; H, 8.26; N, 7.19%.
2.2.5. [N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH]2Zn (6)
C
50H64N4Li2: C, 81.62; H, 8.74; N, 7.59. Found: C, 81.64; H, 8.71;
N, 7.62%. 1H NMR (C6D6): d 0.79–0.79 (d, 6H, CH(CH3)2), 1.02–1.04
(d, 6H, CH(CH3)2), 1.10 (s, 9H, C(CH3)3), 2.74–2.75 (m, 2H,
CH(CH3)2), 5.04 (s, 1H, CH), 7.06–7.08 (m, 3H, aryl), 7.13–7.57 (m,
Using the same procedure as compound 2, the compound 6 was
obtained as light-yellow crystals (0.67 g, 0.85 mmol) in 85% yield,
mp: 226–229 °C (with dec). 1H NMR (300 MHz CDCl3) d 0.838
(s, 18H, C(CH3)3), 1.11–1.24 (m, 6H, CH(CH3)2), 3.43 (m, 2H,
CH(CH3)2), 4.80 (s, 1H, CH), 5.83 (s, 1H, NH), 6.88 (m, 6H, aryl),
7.09 (d, 8H, Ph), 7.26 (d, 2H, Ph). 13C NMR (75 MHz CDCl3) d
5H, Ph). 13C NMR (C6D6): d 21.43 (CH, Pr), 23.75 (CH3, Pr), 27.77
(CH3, Bu), 28.83 (C, Bu), 89.73 (CH), 123.51 (aryl), 124.00–126.59
(Ph), 130.64 (ipso-CPh), 135.69 (ipso-CiPr), 145.73 (ipso-CAr),
165.62 (N@C), 166.08 (ipso-CtBu). 7Li NMR (C6D6): d 1.52.
i
i
t
t
i
i
t
24.13, 25.26 (CH3, Pr), 27.84 (CH, Pr), 28.98 (CH3, Bu), 39.39 (C,
tBu), 91.88 (CH), 122.51, 123.38 (aryl), 126.96, 127.63, 129.20
(Ph), 141.93 (ipso-CiPr), 142.98 (ipso-CPh), 147.59 (ipso-CAr),
169.24 (ipso-CPh), 181.40 (ipso-CtBu). Anal. Calc. for C50H66N4Zn:
C, 77.20; H, 8.24; N, 7.21. Found: C, 77.13; H, 8.27; N, 7.17%.
2.1.3. [N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH2] (1d)
To the solution of 1c (0.74 g, 1 mmol) in 25 ml diethyl ether at
0 °C, distilled water (0.08 ml, 4 mmol) was slowly added. The

S. Yuan et al. / Inorganica Chimica Acta 370 (2011) 215–223
217
2.2.6. [(N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH)Ni(
l
-Cl)]2 (7)
2.4. Procedure for ethylene oligomerization and polymerization
2.4.1. At 1 atm ethylene
Using the same procedure compound 2, the compound 7 was
obtained as black-red crystals (0.28 g, 0.31 mmol) in 31% yield,
mp: 240–242 °C (with dec). 1H NMR (300 MHz CDCl3) d 0.92 (s,
9H, C(CH3)3), 0.97–0.99 (d, 6H, CH(CH3)2), 2.25–2.27 (d, 6H,
CH(CH3)2), 3.89 (s, 2H, CH(CH3)2), 4.71 (s, 1H, CH), 6.78–6.88 (m,
3H, C6H3), 6.88–6.98 (m, 5H, C6H5). 13C NMR (75 MHz CDCl3) d
A flame-dried, three-necked flask was loaded with the catalyst
precursor and purged three times with nitrogen. Ethylene was then
charged in the flask along with freshly distilled toluene and the
mixture stirred for 10 min under 1 atm of ethylene pressure. The
reaction temperature was controlled with a water bath and the re-
quired amount of co-catalyst was then injected with a syringe. The
reaction mixture was stirred for the required time and then the
reaction was quenched by addition of 5% aqueous hydrogen chlo-
ride. The contents and distribution of oligomers were determined
by GC. The polymerization reaction was quenched by addition of
acidic ethanol. The precipitated polymer was washed with ethanol
several times and dried in vacuum at 60 °C to a constant weight.
i
i
t
24.32, 27.32 (CH3, Pr), 29.38 (CH, Pr), 29.94 (CH3, Bu), 37.75 (C,
tBu), 95.46 (CH), 124.02, 126.03 (aryl), 127.78, 129.00 (Ph),
141.50 (ipso-CPh), 144.10 (ipso-CAr), 144.69 (ipso-CiPr), 161.97
(ipso-CPh), 171.21 (ipso-CtBu). Anal. Calc. for C50H66N4Ni2Cl2: C,
65.81; H, 7.24; N, 6.14. Found: C, 65.79; H, 7.27; N, 6.11%.
2.3. X-ray crystallographic studies
The data for 1b, 1d and 2–7 compounds were collected with
Mo Ka
radiation (k = 0.71073 Å) on a Bruker Smart Apex CCD dif-
2.4.2. At 10 atm ethylene
fractometer at 298(2)–173(2) K. Crystals were coated in oil and
then directly mounted on the diffractometer under a stream of cold
A 250-ml stainless steel reactor equipped with a mechanical
stirrer and a temperature controller was heated under vacuum at
least 2 h at above 80 °C, then cooled to the required reaction tem-
perature under ethylene atmosphere and charged with toluene, the
desired amount of cocatalyst, and a toluene solution of catalytic
precursor; the total volume was 100 ml. The reactor was sealed
and pressurized to the desired ethylene pressure, and the ethylene
pressure was maintained with feeding of ethylene. After the reac-
tion was carried out for the required period, the pressure was re-
leased. A small amount of the reaction solution was collected,
the reaction in this small sample was terminated by the addition
nitrogen gas. A total of N reflections were collected by using
x scan
mode. Intensities were corrected for Lorentz and polarization
effects and empirical absorption. The structures were solved by
direct methods and refined by full-matrix least squares on F2. All
non-hydrogen atoms were refined anisotropically. The hydrogen
atoms were placed in calculated positions. Structure solution and
refinement were performed by using the SHELXL-97 package [57].
Crystal data and details of data collection and refinements for 1b,
1d and 2–7 are summarized in Table 1.
Table 1
Crystal data and structure refinement for compounds 1b, 1d and 2–7.
Compound
1b
1d
2
3
4
5
6
7
Formula
Formula weight
T (K)
Crystal system
Space group
a (Å)
C
32H48LiNO3
C25H34N2
362.54
223(2)
C58H82Cl3Co2LiN4O2 C50H66CoN4
C50H66N4Mn
778.01
223(2)
monoclinic
C2/c
17.198(6)
12.821(7)
20.655(11)
90
93.07(8)
90
4547(4)
0.327
C50H66N4Fe
778.92
223(2)
orthorhombic
Pccn
14.064(5)
16.974(6)
18.841(6)
90
90
90
4498(4)
0.372
C50H66N4Zn
788.44
293(2)
orthorhombic
Pccn
13.964(14)
16.985(15)
18.834(15)
90
90
90
4467(7)
0.587
C25H33ClN2Ni
455.69
293(2)
501.65
173(2)
triclinic
1098.43
293(2)
782.00
173(2)
triclinic
monoclinic
C2/c
monoclinic
C2/c
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
9.5595(19)
11.331(2)
14.764(3)
86.47(3)
81.59(3)
73.86(3)
1519.2(5)
0.068
11.025(4)
11.156(3)
11.566(4)
66.354(6)
64.955(4)
62.488(4)
1105.11(6)
0.063
29.686(7)
10.206(2)
20.220(5)
90
13.182(3)
21.701(4)
15.162(3)
90
9.647(3)
10.275(5)
13.052(6)
88.28(4)
68.91(3)
88.78(4)
1206.5(9)
0.927
b (Å)
c (Å)
a
(°)
b (°)
(°)
V (Å3)
104.547(4)
90
96.22(3)
90
c
5930(2)
0.736
4311.9(15)
0.436
l
(mmꢁ1
)
Z
2
2
4
4
4
4
4
2
qcalc (g/cm3)
h (°)
1.097
1.090
1.230
1.205
1.136
1.150
1.172
1.254
1.39–27.49
ꢁ12 6 h 6 12
ꢁ14 6 k 6 14
ꢁ17 6 l 6 19
18 468
2.18–25.01
ꢁ12 6 h 6 13
ꢁ13 6 k 6 12
ꢁ11 6 l 6 13
4289
1.42–25.01
ꢁ34 6 h 6 35
ꢁ12 6 k 6 10
ꢁ23 6 l 6 23
11 217
1.82–27.48
ꢁ17 6 h 6 17
ꢁ21 6 k 6 28
ꢁ19 6 l 6 19
17 453
1.98–25.00
ꢁ20 6 h 6 20
ꢁ10 6 k 6 15
ꢁ22 6 l 6 24
8864
1.88–25.01
ꢁ16 6 h 6 16
ꢁ17 6 k 6 20
ꢁ13 6 l 6 22
16 531
2.16–25.01
ꢁ16 6 h 6 16
ꢁ20 6 k 6 14
ꢁ22 6 l 6 21
17 082
1.67–25.01
ꢁ11 6 h 6 11
ꢁ12 6 k 6 11
ꢁ10 6 l 6 15
4940
Index ranges
Number of reflections
collected
Number of
6937 (0.0251) 3675 (0.0345) 5096 (0.0767)
4822 (0.0457) 3916 (0.0564) 3878 (0.0657) 3909 (0.0593) 4129 (0.0287)
independent
reflections (Rint
Number of
parameters
)
363
251
370
277
256
256
256
269
Goodness-of-fit (GOF)
1.112
1.300
1.282
1.190
1.202
0.919
1.007
1.145
on F2
F(0 0 0)
548
396
2328
1684
1676
1680
1696
484
Completeness to h (%)
Final R indices
[I > 2r(I)]
99.3
94.2
97.5
97.4
97.5
97.7
99.1
96.9
R1 = 0.0652,
wR2 = 0.1795
R1 = 0.0689,
wR2 = 0.1830
0.430 and
R1 = 0.1477,
wR2 = 0.3757
R1 = 0.1650,
wR2 = 0.4033
0.669 and
ꢁ0.672
R1 = 0.1266,
wR2 = 0.3301
R1 = 0.1788,
wR2 = 0.3610
0.793 and ꢁ1.043
R1 = 0.0713,
wR2 = 0.1946
R1 = 0.0756,
wR2 = 0.1979
0.818 and
ꢁ0.618
R1 = 0.0781,
wR2 = 0.1980
R1 = 0.1018,
wR2 = 0.2259
0.619 and
ꢁ0.594
R1 = 0.0661,
wR2 = 0.1960
R1 = 0.1003,
wR2 = 0.2440
0.729 and
ꢁ0.489
R1 = 0.0576,
wR2 = 0.1677
R1 = 0.0825,
wR2 = 0.1903
0.771 and
ꢁ0.412
R1 = 0.0784,
wR2 = 0.2232
R1 = 0.0870,
wR2 = 0.2411
0.562 and
ꢁ1.445
R indices (all data)
Largest difference in
peak and hole (e Å3) ꢁ0.342

218
S. Yuan et al. / Inorganica Chimica Acta 370 (2011) 215–223
of 5% aqueous hydrogen chloride, and the organic layer was
analyzed by gas chromatography (GC) for determining the compo-
sition and mass distribution of oligomers obtained. The polymeri-
zation reaction was quenched by addition of acidic ethanol. The
precipitated polymer was washed with ethanol several times and
dried in vacuum.
X-ray diffraction analysis. Except for nickel, the commonly re-
ported ML2 compounds (D) [58] were observed for all metals.
The trimetallic compound (2, B type) proved to be an intermediate
in forming CoL2 (3, D type). Elimination of LiCl and THF within
compound B happened, the chloro-bridged dinickel compound
[NiL(l-Cl)]2 (7) was formed (represented as C). Therefore, the ini-
tial step in the reaction of the metal (II) chlorides with 1c would
form the chloro-metal bonding in intermediate A, which further
rearrange to form the trimetallic compound B. It would be better
to isolate all types of the compounds with the same metal, but
their analogs provided enough information for a plausible reaction
mechanism as shown in Scheme 2.
3. Results and discussion
3.1. Synthesis and characterization
The stoichiometric reaction of 2,6-diisopropyl-N-(1-phenyleth-
ylidene)benzenamine (CH3(Ph)C@N(2,6-iPr2C6H3), 1a) [55] with
lithium diisopropylamide (LDA) in THF quantitatively formed the
lithium compound CH2(Ph)C(2,6-iPr2C6H3)NLiꢀ3THF (1b). Further
reaction of 1b with an equivalent of tBuCN in THF gave the
nonsymmetrical b-diketiminato lithium complex (1c) via a C–C
coupling reaction. Quenching the ether solution of 1c with water,
N-(3-amino-4,4-dimethyl-1-phenylpent-2-enylidene)-2,6-diisopro-
pylbenzenamine (HL, 1d) was obtained, which proved the formula
LiL and was consistent with the elemental and NMR analysis.
Referring to the b-diketiminato lithium analogs [9–12,48–50], the
b-diketiminato lithium (1c) is reasonably assumed as dimer (LiL)2
(Scheme 1).
3.2. Crystal structures
The molecular structure of 1b is illustrated in Fig. 1, and its
selected bond lengths and angles are tabulated in Table 2. The
tBu
Ph
tBu
NH
Ph
Ar
Cl *
N
NH
M
Li
Ar
M
N
Cl
Ar
MCl2
Cl
Li
Li
Ar
Li
HN
N
*
Cl
HN
But
N
But
Ph
The b-diketiminato lithium (1c) was reacted with various
transition metal (II) chlorides to form the corresponding metal
compounds (2–7) (Scheme 1). The trinuclear compound [CoL]2(l-
Ph
A
1c
transformation
tBu
Cl)3Li(THF)2 (2) was recrystallized from its THF solution at room
temperature; and was shown a twisted conformation with three
bridging chlorides, two cobalt atoms and one lithium. The com-
pound 2 was refluxed in toluene and produced a trinuclear CoL2
compound (3), which was also isolated by refluxing the mixture
of 1c with CoCl2 in THF. The typical pseudo-tetrahedral ML2 com-
pounds for Mn (4), Fe (5) and Zn (6) were easily isolated from the
correspondent reactions of 1c with the respective metal (II) chlo-
ride. In the reaction of nickel dichloride, however, a chloro-bridged
Ph
tBu
Ph
Ar
N
Ph
Ar
HN
NH
M
Cl
N
Cl
Cl
Li
M
M
M
Cl
N
Ar
Cl
C
N
H
tBu
Ph
N
H
N
LiCl
tBu
Ar
O O
MCl2
Ph
B
dinickel compound [NiL(
l
-Cl)]2 (7) with a planar square geometry
tBu
Ar
N
H
N
was isolated.
M
D
All b-diketiminato metal compounds were slightly sensitive in
solution, but stable in the solid state. The microanalysis data of
all compounds 1b, 1d and 2–7 were in agreement with the pro-
posed structures, and the compounds 1a–1d, 6 and 7 were charac-
terized by NMR spectroscopy; moreover, the molecular structures
of compounds 1b, 1d and 2–7 were confirmed by single-crystal
N
Ar
N
H
Ph
tBu
Scheme 2. Plausible mechanism for forming multinuclear metal compounds.
tBu
NH
Ph
Ar
Ar
Ph
N
tBu
N
Cl
Ph
Ar
Ar
Ph
iPr
iPr
1eq tBuCN
THF
Co
Cl
1eq LDA
THF
NH Li
tBu
CoCl2
THF
Co
Cl
N
H
N
Ph
N
N
NH
Li
Li(THF)3
Ar
N
tBu
Li
1a
O
Ph
1c
1b
Ar
O
2
MCl2
H2O
Ar =
THF
Ar
NiCl2
Toluene
THF
Et2O
tBu
tBu
Ph
Ar
N
tBu
Ph
H
N
Ph
Ar
N
NH
Ni
N
NH2
Cl
M
Ni
N
N
H
N
Cl
HN
tBu
Ph
Ar
1d
tBu
Ph
Ar
M = Co (3), Mn (4),
Fe (5), Zn (6)
7
Scheme 1. Synthesis of compounds 1–7.

S. Yuan et al. / Inorganica Chimica Acta 370 (2011) 215–223
219
Fig. 2. ORTEP drawing of 1d with thermal ellipsoids drawn at the 30% probability
level. Hydrogen atoms are omitted for clarity.
Fig. 1. ORTEP drawing of 1b with thermal ellipsoids drawn at the 30% probability
level. Hydrogen atoms are omitted for clarity.
Table 2
Selected bond lengths (Å) and angles (°) for 1b and 1d.
1b
Bond lengths
N(1)–C(1)
N(1)–C(9)
N(1)–Li(1)
Li(1)–O(2)
1.3572(18)
1.4209(17)
1.994(3)
C(1)–C(2)
C(1)–C(3)
Li(1)–O(1)
Li(1)–O(3)
1.359(2)
1.495(2)
1.967(3)
2.028(3)
2.064(3)
Bond angles
C(1)–N(1)–C(9)
C(9)–N(1)–Li(1)
N(1)–C(1)–C(3)
113.89(11)
110.98(11)
115.32(12)
C(1)–N(1)–Li(1)
N(1)–C(1)–C(2)
C(2)–C(1)–C(3)
134.85(12)
127.29(14)
117.36(14)
1d
Bond lengths
N(1)–C(13)
C(13)–C(14)
N(2)–C(21)
Fig. 3. ORTEP drawing of 2 with thermal ellipsoids drawn at the 30% probability
level. Hydrogen atoms are omitted for clarity. Symmetry operation: ꢁx, y, ꢁz + 1/2.
1.284(6)
1.439(7)
1.330(6)
N(1)–C(1)
C(14)–C(21)
C(21)–C(22)
1.429(6)
1.355(7)
1.545(7)
lengths and angles are tabulated in Table 3. The cluster M2Li(
core is a six-membered chelate ring with a twisted conformation.
Each Co atom is coordinated to two chloride ions and a -NCCCN
ring of the b-diketiminato ligand, whereas the cationic four coordi-
nate lithium is bound by two chlorides and two THF molecules. The
Co–Cl [C1(2)] bond distances are 2.340(3) Å, which are slightly
l-Cl)3
Bond angles
C(13)–N(1)–C(1)
C(21)–C(14)–C(13)
N(2)–C(21)–C(22)
122.0(4)
126.1(4)
115.8(4)
N(1)–C(13)–C(14)
N(2)–C(21)–C(14)
C(14)–C(21)–C(22)
121.2(4)
121.3(4)
122.8(4)
l,g
lithium atom is coordinated with an j
1-enamido ligand and three
longer than data observed in the compounds [CoL(l-Cl)]2 [38]
and CoLCl2Li(THF)2(L@(N(Dipp)C(Me))2CH) (2.293–2.295 Å) [59],
THF molecules, consistent with the use of a bulky enamido ligand
along with coordinated THF molecules [13]. The bond distance of
Li–N is 1.994(3) Å and the length of C(1)–C(2) is 1.359(2) Å. The
dihedral angle of the aryl ring and phenyl ring to the plane C(2)–
C(1)–C(3)–N–Li are 87.18° and 47.20°, respectively.
Table 3
Selected bond lengths (Å) and angles (°) for 2.
Bond lengths
In the NCCCN moiety of compound 1d (Fig. 2 and Table 1), the
bond distances N(1)–C(13), C(13)–C(14), C(14)–C(21) and N(2)–
C(21) are 1.284(6), 1.439(7), 1.355(7) and 1.330(6) Å, respectively,
and their bond features alternately appear as double and single
ones. The bond angles of N(1)–C(13)–C(14), C(13)–C(14)–C(21)
and C(14)–C(21)–N(2) are 121.2(4)°, 126.1(4)° and 121.3(4)°,
respectively, indicate that the NCCCN moiety is a near coplanar
system. Due to the steric strain of the bulky 2,6-diisopropylphenyl,
the dihedral angles of the aryl or phenyl to the NCCCN plane are
81.62° and 62.95°, respectively.
Co–N(2)
Co–N(1)
N(1)–C(13)
N(1)–C(1)
C(21)–C(22)
Co–Cl(1)
1.929(8)
1.954(7)
1.342(12)
1.457(11)
1.552(13)
2.287(3)
C(13)–C(20)
C(20)–C(21)
N(2)–C(21)
C(13)–C(14)
Cl(1)–Li
1.377(13)
1.395(14)
1.304(13)
1.521(13)
2.361(15)
2.340(3)
Co–Cl(2)
Bond angles
N(2)–Co–N(1)
C(13)–N(1)–Co
N(1)–Co–Cl(1)
N(1)–Co–Cl(2)
Cl(1)–Co–Cl(2)
Co–Cl(1)–Li
96.0(3)
C(1)–N(1)–Co
C(21)–N(2)–Co
C(1)–N(1)–Co
N(2)–Co–Cl(2)
N(2)–Co–Cl(1)
Co–Cl(2)–Co0
122.1(6)
125.5(7)
122.0(5)
101.9(3)
120.3(3)
102.42(16)
118.8(6)
114.8(2)
118.8(2)
105.29(10)
99.4(4)
The molecular structure of the trinuclear cobalt compound
(CoL)2(l-Cl)3Liꢀ2THF (2) is shown in Fig. 3, while the selected bond

220
S. Yuan et al. / Inorganica Chimica Acta 370 (2011) 215–223
and Co(OMes2)2Li(THF)2(l-Cl)2 Li(THF)2 (2.297(1) Å) [60]; whilst
the bond lengths of Co–Cl [Cl(1) and
l
-Cl(1)0] 2.287(3) Å are in
agreement with the observations (2.293–2.297 Å) related the
Co–Cl–Li fragments [58]. The Cl(2) atom lies in the plane of the
Co–Co–Li, however, the Cl(1) and Cl(1)0 atoms are out of
Co–Cl(2)–Co–Li plane with one above and another below. The dis-
tances of Cl(1) and Cl(1)0 to the Co–Cl(2)–Co–Li plane are equal at
4.56 Å, and the dihedral angle between Co–Cl(1)0–Li and Co–Cl(2)–
Co–Cl(1)–Li is 75.71°. The Li–Cl and Li–O distances [2.361(15) and
1.938(17) Å] are also similar to previously reported compounds
[59–64]. Regarding the b-diketiminato moiety, the bond distances
Co–N [1.956(7) and 1.920(7) Å] and the bond angle N–Co–N (96.0°)
are typical for b-diketiminato compounds [9–18,59–73]. The dihe-
dral angles between C(13)–C(20)–C(21) or N(1)–Co–N(2) and
N(1)–C(13)–C(21)–N(2) are 16.33° and 36.88°, whilst the dihedral
angle between C(13)–C(20)–C(21) and N(1)–Co–N(2) is 20.56°.
The MNCCCN backbone features a full-boat conformation which
is wider than that of compounds 3–7. The dihedral angles of the
aryl and phenyl to the six-membered metallic ring are 75.81°
and 55.88°, respectively.
Fig. 5. ORTEP drawing of 4 with thermal ellipsoids drawn at the 30% probability
level. Hydrogen atoms and solvent are omitted for clarity. Symmetry operation: ꢁx,
ꢁy, ꢁz + 1/2.
The molecular structures of cobalt 3, manganese 4, iron 5 and
zinc 6 complexes possessed a similar distorted tetrahedral geome-
try (Figs. 4–7), and their selected bond lengths and angles are illus-
trated in Tables 4 and 5, respectively.
The metal cores of compounds 3–6 are coordinated by four
nitrogen atoms of two b-diketiminato ligands, and the six-
memberedmetalocyclicringsadaptshallowboat-shaped conforma-
tions. The two six-membered rings are either orthogonality (4, 5, 6)
(cf. the dihedral angle at the metal M, which increases in the se-
quence Mn (48°) < Fe (63.02°) < Zn (64.46°), as shown in Table 5)
or co-planarity (3, Co (5.35°)). The difference is attributed to steric
effects. The bond distances of Mn–N in compound 4 are in the range
[2.071(3)–2.114(3) Å], which are a little longer than the M–N bond
in its analogs, for example Co–N [1.880(3)–1.962(2) Å] in 3, Fe–N
[1.978(3)–2.044(3) Å] in 5, Zn–N [1.955(3)–2.038(3) Å] in 6. These
are caused by the differences of their ionic radii and electrophilic
behaviors. The bond angle [N(1)–Co–N(2)0 88.84(11)°] in 3 and
[N(1)–Mn–N(2) 87.85(13)°] in 4 are smaller than [N(1)–Fe–N(2)
91.24(13)°] in 5 and [N(1)–Zn–N(2) 93.12(11)°] in 6. The dihedral
angles of the aryl and phenyl to the six-membered metal rings de-
crease in the sequence 3 (84.80° and 77.83°) > 4 (83.52° and
60.21°) > 5 (82.24° and 50.17°) > 6 (82.43° and 49.23°).
Fig. 6. ORTEP drawing of 5 with thermal ellipsoids drawn at the 30% probability
level. Hydrogen atoms and solvent are omitted for clarity. Symmetry operation:
ꢁx + 1/2, ꢁy + 1/2, ꢁz.
Fig. 7. ORTEP drawing of 6 with thermal ellipsoids drawn at the 30% probability
level. Hydrogen atoms and solvent are omitted for clarity. Symmetry operation:
ꢁx + 1/2, ꢁy + 1/2, z.
Fig. 4. ORTEP drawing of 3 with thermal ellipsoids drawn at the 30% probability
level. Hydrogen atoms are omitted for clarity. Symmetry operation: ꢁx, y, ꢁz + 1/2.

S. Yuan et al. / Inorganica Chimica Acta 370 (2011) 215–223
221
Table 4
Endocyclic bond distances (a–f) (Å) and angles (
a
–h) (°) in the M{N(Ar)C(Ph)CHC
(tBu)NH} moieties of 3–6.
Compound
3
4
5
6
Ph
tBu
e
f
γ
β
δ
ε
c
d
α
N
N
θ
a
b
Ar
M
a (Å)
b (Å)
c (Å)
d (Å)
e (Å)
f (Å)
1.962(2)
1.880(3)
1.351(4)
1.322(4)
1.384(4)
1.398(4)
126.6(2)
125.1(3)
124.5(3)
120.2(3)
134.6(2)
88.84(11)
2.114(3)
2.071(3)
1.353(5)
1.305(5)
1.395(6)
1.420(6)
125.0(3)
124.7(3)
129.0(3)
121.5(3)
129.7(3)
87.85(13)
2.046(3)
1.972(3)
1.343(4)
1.319(4)
1.402(5)
1.393(5)
123.7(2)
124.1(3)
128.6(3)
121.7(3)
128.5(2)
90.91(10)
2.038(3)
1.955(3)
1.331(4)
1.309(4)
1.407(5)
1.389(5)
121.5(2)
125.3(3)
128.4(3)
122.4(2)
127.0(2)
93.12(11)
a
(°)
b (°)
(°)
d (°)
(°)
c
e
Fig. 8. ORTEP drawing of 7 with thermal ellipsoids drawn at the 30% probability
level. Hydrogen atoms and solvent are omitted for clarity. Symmetry operation: ꢁx,
ꢁy, ꢁz.
h (°)
Table 5
Table 6
Selected bond distances (a–f) (Å), angles (
atoms of 4–6.
a–h) (°) and dihedral angles (°) around metal
Selected bond lengths (Å) and angles (°) for 7.
Bond lengths
Compound
3
4
5
6
Ni(1)–N(1)
N(1)–C(9)
Ni(1)–N(2)
N(2)–C(14)
Ni(1)–Cl
1.818(4)
1.305(6)
1.878(4)
1.436(6)
1.882(4)
2.8821(17)
C(8)–C(9)
N(2)–C(1)
C(1)–C(8)
C(1)–C(2)
Ni(1)–Cl0
Cl–Cl0
1.397(7)
1.328(6)
1.392(8)
1.496(7)
1.869(4)
2.400(9)
Ph
Ar
tBu
Ph
Ar
b
ε
a
δ
e
d
N
C
γ
θ
C
β
tBu
M
c
N
N
N
C
f
α
M
Ni(1)–Ni(10)
a (Å)
b (Å)
c (Å)
d (Å)
e (Å)
f (Å)
1.447(4)
1.508(4)
1.542(4)
0.108
0
1.441(5)
1.503(5)
1.543(5)
ꢁ0.292
ꢁ0.210
0.143
113.7(2)
120.1(3)
120.3(3)
115.0(3)
118.2(3)
120.3(3)
48
1.447(4)
1.495(5)
1.531(4)
0.414
1.432(4)
1.491(5)
1.540(4)
0.432
Bond angles
N(1)–Ni(1)–N(2)
N(2)–C(1)–C(8)
C(1)–C(8)–C(9)
Cl–Ni(1)–Cl0
93.81(18)
124.3(5)
124.9(5)
79.6(2)
C(1)–N(2)–Ni(1)
C(9)–N(1)–Ni(1)
N(1)–C(9)–C(8)
Ni(1)–Cl–Ni(10)
124.6(4)
131.0(4)
120.4(5)
100.4(2)
0.168
0.179
0
ꢁ0.013
115.3(2)
119.4(3)
121.0(3)
114.9(3)
120.1(3)
118.2(3)
63.02
ꢁ0.029
116.0(2)
120.5(3)
120.8(3)
113.9(3)
118.8(3)
118.3(3)
64.46
a
(°)
b (°)
(°)
d (°)
(°)
h (°)
Dihedral angle at M (°)
120.08(18)
113.3(2)
121.4(3)
113.5(3)
119.4(3)
120.5(3)
5.35°
c
and 0.039 Å) and lie on opposite sides, which may partly be
caused by the steric repulsion between the aryl and phenyl
groups out-of-the-plane of the NCCCN plane (the dihedral angles
81.52° and 56.43°).
e
To summarize, the important geometrical parameters associ-
ated with compounds 2–7 indicate the bond lengths M–N(Ar)
and M–N decrease in the sequence 4 > 5 > 6 > 3 > 2 > 7 with the
characteristic M–N(Ar) > M–N. The mean C–N lengths are similar
The molecular structure of the nickel compound (NiL)2(l-Cl)2
(7) is illustrated in Fig. 8, and the selected bond lengths and an-
gles are shown in Table 6. The Ni centers adopts a typical square
planar coordination geometry, with two N and two bridging Cl
atoms occupying the four coordination sites and displaying typi-
cal bond lengths and angles. The Ni–N distances [1.818(4) and
1.878(4) Å] are unexpectedly different. The nonbonded Niꢀ ꢀ ꢀNi
distance [2.8821(17) Å] is shorter than those (Niꢀ ꢀ ꢀNi separation
3.2966(8)–3.458(1) Å) reported in the chloro-bridged dinickel
compound bearing bulky b-diketiminato ligands [35–37], and
longer than the interacting Ni–Ni bond (2.38–2.81 Å) [67–74],
suggesting a weak Ni–Ni interaction in compound 7. The bridging
Ni–Cl distances [1.869(4) and 1.882(4) Å] are also shorter than
previously reported Ni–Cl [2.2997(9)–2.4840(6) Å] [35–37,39,
41,42], perhaps due to the sterically imposing b-diketiminate
and the high-spin Ni(II). The bond angle N(1)–Ni–N(2)
(93.81(18)°) is typical for b-diketiminato compounds [9–18,35–
37]. The dihedral angles between C(9)–C(8)–C(1) or N(1)–Ni–
N(2) and N(1)–C(9)–C(1)–N(2) are 2.18° and 7.02°, whilst the
dihedral angle between N(1)–Ni–N(2) and Cl(1)–Ni–Cl(1)0 is
2.84°; C(8) and Ni lie on same side. The MNCCCN moiety is a boat
conformation as seen in compounds 3–6. The Cl(1) and Cl(1)0
atoms are out the N(1)–Ni–N(2) planes (mean deviation 0.076
as C(sp2)@N(sp2) bond. The bond angle of N–M–N in
3
[88.84(11)°] and 4 [87.85(13)°] are relatively smaller than those
of its analog compounds 90.91(10)° (5), 93.12(11)° (6),
93.81(18)° (7), and 96.0(3)° (2), respectively. The compound 2
has a twisted conformation formed by three bridging-chlorides
and three metal centers, whereas the compound 3 gives a planar
structure. In compounds 4–6, with a distorted tetrahedral coordi-
nation, the dihedral angles between two NMN planes are 48° in
4, 63.02° in 5 and 64.46° in 6. Compound 7 adopts a dinuclear
square planar geometry.
3.3. Ethylene reactivity
The compounds 2, 5 and 7 are investigated for their catalytic
behavior towards ethylene in the presence of cocatalysts. In gen-
eral, nickel compounds are the most considered among these com-
pounds, and compound 7 is used in selecting suitable cocatalysts.
Using methylaluminoxane (MAO) as cocatalyst showed better
activity than that of diethylaluminum chloride (Et2AlCl) (entries
1–2 in Table 7). The dimerization mostly occurred when using
Et2AlCl. In the presence of MAO, the ratio of Al/Ni and pressure

222
S. Yuan et al. / Inorganica Chimica Acta 370 (2011) 215–223
Table 7
Ethylene oligomerization and polymerization of 2 and 7 system.a
b
e
Entry
Cat.
Cocat.
Al/M
P (atm)
Oligomers (%)
Act.c
Act.d (PE)
Tm (°C)
P
P
C4/
C
C6/
C
1-C4
1
2
3
4
5
6
7
8
9
7
7
7
7
7
2
2
2
2
Et2AlCl
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
200
1
1
1
1
10
1
1
1
10
14.6
107
79.8
98.1
775
2.21
7.38
4.54
31.1
96.91
81.3
80.3
80.6
73.9
77.4
70.2
72.6
72.8
3.09
61.52
50.5
41.0
46.1
89.0
69.2
71.2
58.2
86.3
–
trace
–
–
1.20
–
–
–
–
1500
1000
2000
1500
1000
1500
2000
1500
18.70
19.7
19.4
26.1
22.6
29.8
27.4
27.2
89.6
a
b
c
Conditions: 5 lmol; 30 min; 30 °C. The total volume: 30 ml toluene for 1 atm or 100 mL toluene for 10 atm.
Determined by GC.
103 g molꢁ1(M) hꢁ1
104 g molꢁ1(M) hꢁ1
.
.
d
e
Determined by DSC.
of ethylene were verified (entries 3–5 in Table 7), and the optimum
condition with molar ratio of Al/Ni at 1500 was observed to pro-
duce butenes and hexenes along with a trace amount of polyethyl-
ene (entry 4 in Table 7), but without higher order olefins. When the
ethylene pressure was increased from 1 to 10 atm, the catalytic
activity increased to 7.75 ꢂ 105 g mol(Ni)ꢁ1 hꢁ1 (entry 5 in Table
7). Moreover, the fractions of hexenes were significantly improved
grateful to Prof. Carl Redshaw and Dr. Lucy Clowes of University
of East Anglia for the English proofreading.
Appendix A. Supplementary material
CCDC 759159–759166 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.01.063.
along with a better selectivity for a-olefins (89.0% for 1-butene of
butenes). Such phenomena are explained by the ethylene insertion
and chain propagation being enhanced by the increase of ethylene
pressure [74]. An activity value for the ethylene polymerization as
high as 1.20 ꢂ 104 g mol(Ni)ꢁ1 hꢁ1 was obtained (entry 5 in Table
7).
The cobalt compound 2 was also investigated in the presence of
MAO (entries 6–9 in Table 7), and showed relative lower activities
in oligomerization than observed for the nickel compound 7. Again,
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