Investigation of 1-hexene isomerization and oligomerization catalyzed with β-diketiminato Ni(II) bromide complexes/methylaluminoxane system

Article abstract of DOI:10.1016/j.molcata.2004.12.024

β-Diketiminato Ni(II) bromide complexes were synthesized and used to catalyze isomerization and oligomerization of 1-hexene in the presence of methylaluminoxane (MAO). GC-MS and GC analysis confirmed that the products are mainly hexene isomers and dimer isomers. 3-Hexene isomers, trimers and higher oligomers were not detected. The results were ascribed to the configuration of the β-diketiminato Ni(II) catalyst. The migration of the Ni atom from a secondary or tertiary carbon to another one along the alkyl chain of the Ni-alkyl intermediates is blocked by the coordination wedge of the β-diketiminato ligands. However, the migration of the Ni atom from a primary carbon to the adjacent secondary or tertiary carbon is thermodynamically favored.

Full text of DOI:10.1016/j.molcata.2004.12.024

Journal of Molecular Catalysis A: Chemical 231 (2005) 27–34
Investigation of 1-hexene isomerization and oligomerization
catalyzed with ␤-diketiminato Ni(II) bromide
complexes/methylaluminoxane system
Junkai Zhang, Haiyang Gao, Zhuofeng Ke, Feng Bao, Fangming Zhu, Qing Wu∗
Institute of Polymer Science, School of Chemistry and Chemical Engineering, Sun Yat-Sen (Zhongshan) University,
Guangzhou 510275, China
Received 11 October 2004; received in revised form 8 December 2004; accepted 20 December 2004
Available online 26 January 2005
Abstract
␤-Diketiminato Ni(II) bromide complexes were synthesized and used to catalyze isomerization and oligomerization of 1-hexene in the
presence of methylaluminoxane (MAO). GC–MS and GC analysis confirmed that the products are mainly hexene isomers and dimer isomers.
3-Hexene isomers, trimers and higher oligomers were not detected. The results were ascribed to the configuration of the ␤-diketiminato Ni(II)
catalyst. The migration of the Ni atom from a secondary or tertiary carbon to another one along the alkyl chain of the Ni-alkyl intermediates
is blocked by the coordination wedge of the ␤-diketiminato ligands. However, the migration of the Ni atom from a primary carbon to the
adjacent secondary or tertiary carbon is thermodynamically favored.
© 2005 Elsevier B.V. All rights reserved.
Keywords: ␤-Diketiminato Ni(II) complexes; 1-Hexene; Isomerization; Oligomerization; Methylaluminoxane
1. Introduction
Researches [5] on ␤-diketiminato metal complexes went
afresh hot in the middle of 1990s. The chemistry of unsat-
urated three-coordinate ␤-diketiminato LTM complexes was
studiedeffectivelybyHolland’sgroup[6]andWarren’sgroup
[7]. The neutral three-coordinate ␤-diketiminato LTM alkyl
complexes (Fe, Co) adopt a tetrahedral structure. Due to the
reduction of Ni(II) atom by alkylation agents, the direct syn-
thesis of the ␤-diketiminato Ni-alkyl complexes by using
methyllithium or Gringnard reagents was reported unpro-
ductive [6f]. Warren and co-workers reported series of four-
coordinate ␤-diketiminato Ni-alkyl lutidine complexes that
adopt square planar structure [7d] (2 in Fig. 1). Recently, the
lutidine-free Ni(II) ␤-agostic alkyl complexes were success-
fully isolated and characterized [7f] (3 in Fig. 1). The alkyl
intermediates of the ␤-diketiminato system favor the pseudo
four-coordinate ␤-agostic alkyl 3 over the four-coordinate
ethylene/M-alkyl complex 1.
In 1995 [1], Brookhart and co-workers first reported the
bulky ␣-diimine Ni(II) and Pd(II) catalysts. These late tran-
sition metal (LTM) catalysts are very active and efficient in
ethylene polymerization [2], and the obtained ethylene poly-
mers are of a novel branching rich microstructure. In the past
decade, the researches on the ␣-olefin polymerization by us-
ing these LTM catalysts were focused on the topics including
temperature, pressure, ligand structure [1,3], and mechanism
[4]. The bulky axial aryl groups of the ␣-diimine catalysts re-
tard the chain transfer, and thus lead to the formation of high
molecular weight polymers. The concept of the axial steric
bulk makes the application of the LTM in ␣-olefin polymer-
ization become promising. The resting state of the cationic ␣-
diimine catalyst species is an olefin/M-alkyl complex, which
adopts a square planar structure [3a] (1 in Fig. 1).
Recently, Gibson gave a review [8] on ␤-diketiminato
transition metal complexes that were used as the ␣-olefin
polymerization catalyst. However, the reports on ␣-olefin
∗
Corresponding author. Tel.: +86 20 84113250; fax: +86 20 84112245.
E-mail address: ceswuq@zsu.edu.cn (Q. Wu).
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2004.12.024

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J. Zhang et al. / Journal of Molecular Catalysis A: Chemical 231 (2005) 27–34
Scheme 1. The preparation of ␤-diketiminato ligand (L) and ␤-diketiminato
Ni(II) complexes (4).
Fig. 1. Structures of the ␣-diimine catalyst species and ␤-diketiminato com-
plexes.
used. The uncertain assignments of the CH(CH3)2 (e) and
the m-Ar (f) in 4a [6c] were clarified by comparing the cor-
responding chemical shift of 4a with 4b. Compared with 4a,
small bulk complex 4b is relative stable and likely to adopt
dimer form in solution. Complexes 4a and 4b are noteworthy
thermal-stable, but sensitive to air and moisture.
polymerization by using the ␤-diketiminato LTM complexes
as catalyst precursor are rare in the past decade [7d,9].
Non-skeleton isomerization of ␣-olefins, which was cat-
alyzed by the transitional metal catalysts, had been reported
everywhere [10]. The isomerization of the substrates was also
reported coming along with the ␣-olefin oligomerization and
polymerization, which were catalyzed by the cationic LTM
active center [11]. To our knowledge, the isomerization and
oligomerization of 1-hexene catalyzed by the neutral LTM
active center were still not reported.
We report here the isomerization and oligomeriza-
tion of 1-hexene catalyzed by using the Ni{(N(C6H3-R2-
2,6)C(Me))2CH}Br/MAO (4 in Fig. 1). One goal is to re-
veal the behaviors of the ␤-diketiminato Ni-R (R = hexyl)
intermediates. That would help understanding the behaviors
of ␤-diketiminato Ni-P (P = polymeric alkyl) intermediates
in the ethylene polymerization process. The other is to make
clear the insertion behaviors of ␣-olefin to the ␤-diketiminato
Ni-P intermediates in the ␣-olefin copolymerization process.
The ␤-diketiminato Ni(II)/MAO system catalyzed ethylene
polymerization and corresponding characterization will be
published elsewhere in the near future.
2.2. The isomerization and dimerization of 1-hexene
Table 1 lists the isomerization and oligomerization data of
1-hexen obtained by using 4a and 4b in the presence of MAO.
GC–MS analysis confirmed the trace of C7 heptene isomers.
This indicates that Ni(II) bromide complex is methylated by
MAO and Ni CH3 intermediate is produced as the initial ac-
tive species. The products are mainly C6 olefin isomers and
C12 olefin dimers. These even number olefins suggest the in-
volvement of the Ni(II)-hydride (Ni H) intermediate in the
isomerization and oligomerization process. The Ni H inter-
mediate might be produced after the insertion of 1-hexene
into the Ni CH3 bond and following the release of C7 hep-
tene via ␤-H elimination.
GC–MS analysis confirmed that the C6 products are
mainly liner inner hexenes (trans- and cis-2-hexene, see
Fig. 3). Scheme 2 shows the proposed mechanism of the 1-
hexeneisomerization. Fig. 4illustratesthenomenclatureused
in this work for the Ni-alkyl intermediates. The 2-Ni-hexyl
intermediates might derive from two procedures. One is 2,1
insertion of 1-hexene to the Ni H active species. The other
is the migration conversion (chain walking) of 1-Ni-hexyl in-
termediate originated from the 1,2 insertion of 1-hexene to
the Ni H intermediate. The wedge shape configuration of the
␤-diketiminato Ni(II) active species might favor the 1,2 mode
insertion of 1-hexene over the 2,1 mode (see Fig. 5). The ␤-
diketiminato Ni(II) catalysts show strong tendency of isomer-
izing the ␣-olefin substrate comparing with the pyridine bis-
imine Fe(II) system, of which only the small bulk catalysts
exhibit this trend [11a,11b]. This isomerization phenomenon
was also observed going along with the 1-hexene polymeriza-
tion process that was catalyzed by the ␣-diimine Pd(II) cata-
lyst. After 3 h reaction at 0 ◦C, 71% of the all hexenes in the
2. Results and discussion
2.1. ␤-Diketiminato nickel complexes (4)
Ni{(N(C6H3-R2-2,6)C(Me))2CH}Br (4a, R = isopropyl;
4b, R = methyl) was prepared according to the literature
method [6c], following a two step procedure as shown in
Scheme 1. Lithium ␤-diketiminato salts were used as pre-
pared in toluene solution and (1,2-dimethoxy-ethane)NiBr2
((DME)NiBr2) was used as the Ni(II) source. 1H NMR chem-
ical shifts of these ␤-diketiminato Ni(II) complexes were
paramagnetically induced by the unpaired spin of the Ni atom
1
[12] (see Fig. 2). H NMR spectrum indicates that there is
an equilibrium that shifts between monomer and dimer [6c],
depending on the concentration, temperature and the solvent

J. Zhang et al. / Journal of Molecular Catalysis A: Chemical 231 (2005) 27–34
29
Fig. 2. 1H NMR spectrum of complex 4a and 4b in C6D6 (∼10 mmol/0.5 mL), at 30 ◦C.
Table 1
The isomerization and dimerization data of 1-hexene catalyzed with 4/MAO system
Catalyst
1-Hexene (mL)
1-Hexene and isomers (%)
Dimers (%)
1-Hexene (%)
Trans-2-hexene (%)
Cis-2-hexene (%)
4aa
4ab
4bb
a
1
0.01
0.01
88.6
81.51
48.46
11.4
18.49
51.54
46.61
7.51
0.65
29.85 (55.91)
66.37 (71.77)
80.75 (81.29)
23.54 (44.09)
26.11 (28.23)
18.59 (18.71)
Measured with GC–MS with DB-5MS column.
Measured by GC with HP-5MS column; temperature 45 ◦C, Cat. 4a and 4b 7 × 10−5 mol, MAO 80 mg, 3 h; the value in parenthesis is the relative abundance
b
of cis- and trans-isomers in 2-hexenes.
Scheme 2. Presumed relationships of the Ni-hexyl intermediates with hexene isomers (ligands were omitted for clarity, R = propyl).

30
J. Zhang et al. / Journal of Molecular Catalysis A: Chemical 231 (2005) 27–34
Fig. 4. Nomenclature for the Ni-alkyl intermediates.
Fig. 3. GC spectrum of the hexene isomers (measured by GC with HP-5MS
GC column, 1-hexene 0.01 mL, Cat. 4a and 4b = 7 × 10−5 mol, MAO 80 mg,
temperature 45 ◦C, 3 h).
Hereby, the preponderance of 2-hexenes in the total hexenes
is regarded as the result of this accumulation circle.
Since the 1,2 insertion of 1-hexene to Ni H is favored
by kinetics, the preponderance of 2-hexenes indicates that
considerable parts of 2-Ni-hexyl intermediates are derived
from 1-Ni-hexyl intermediate. These suggest that the isomer-
ization from 1-Ni-hexyl to 2-Ni-hexyl is thermodynamically
favored.
The distribution of the hexenes was also observed be-
ing greatly affected by the initial concentration of 1-hexene
(see Table 1). Thermodynamic equilibrium cannot be reached
within the experiment time scale (due to the bad stability of
the active species). The trans-/cis-2-hexene ratio should be
relatedtothestabilityoftherespective ␤-agosticalkylspecies
and the freedom of C2 C3 bond rotation (see Scheme 2).
solution remained as 1-hexene, while 29% of them had been
isomerized to internal olefin (2-and 3-hexenes) [11c]. Herein,
The neutral Ni(II) active centers are hedged by the coordina-
tion wedge of the ␤-diketiminato ligands. Due to this configu-
ration feature, the ␤-diketiminato Ni-alkyl species should be
relative idle comparing with the cationic ␣-diimine M-alkyl
species and likely to eliminate. Once the ␤-H elimination
occurred and the hexene/Ni H complexes formed, the rein-
sertion of these binding 2-hexenes into the Ni H bond should
be more difficult than that of 1-hexene (Scheme 2). Moreover,
after being released, the rebinding probability of 2-hexene to
the Ni H intermediate should be lower than that of 1-hexene.
Fig. 5. The sketch map comparison of the literature ␣-diimine Ni(II) complex [14] and ␤-diketiminato Ni(II) complex [6c,6e] (hydrogen and some of methyl
carbon atoms were omitted for clarity. Ni to A1–A2 means the distance of the nickel atom to the line through A1 atom and A2 atom).

J. Zhang et al. / Journal of Molecular Catalysis A: Chemical 231 (2005) 27–34
31
Moreover, decreased steric bulk of the ␤-diketiminato lig-
and leads to increases in the portion of 2-hexenes and the
trans-/cis-2-hexene ratio (see Fig. 3 and Table 1). These sug-
gest that the rotations of Ni C and C2 C3 bonds are relative
free in less bulky 4b/MAO system comparing with 4a/MAO
system.
The active species of the ␤-diketiminato Ni(II)/MAO sys-
tem might adopt square planner structure or tetrahedral struc-
ture. In both cases, the Ni atoms of the ␤-diketiminato Ni(II)
complexes [6] were deeply embodied into the ligands com-
paring with the ␣-diimine Ni(II) complexes [14] (see Fig. 5).
The rotations [4c,15] and the reinsertion of the binding 2-
hexenes to fit the formation of the 3-Ni-hexyl intermediate
were thus not favored by the coordination wedge and became
very difficult (see Scheme 2). The probability of deriving 3-
hexenes was thus greatly lowered. This suggest that the mi-
gration (walking) of the Ni(II) atom from the second carbon
to the third carbon along the hexyl chain is unfavorable in the
␤-diketiminato Ni(II)/MAO system.
GC–MS analysis confirmed that these marked peaks are
the C12 inner olefin isomers (for these peaks: e/m = 168, see
Fig. 6). These dimers should be the elimination products
of the m-Ni-dodecyl intermediates (m = 5), which formed
after the insertion of 1-hexene to the m-Ni-hexyl inter-
mediates (m = 1 or 2) as the literature pathways [11a,b].
The cis- and trans-position isomers of these dimers should
be derived after the ␤-H elimination of Ni with the ␤-
H and ␤ꢀ-H (see Scheme 3). These C12 dimers include
7-methyl-trans-5-undecene (23.36 min), 7-methyl-trans-4-
undecene (25.54 min), trans- or cis-4-dodecene (28.84 min),
and trans-5-dodecene (30.31 min).
GC–MS analysis confirmed that those unmarked peaks
in the spectrum are also C12 inner olefin isomers (their
MS fragment distributions are similar to that of C12 inner
olefins). Some of them, such as 5-methyl-trans-4-undecene
(27.57 min), should be related to the Ni-methyl(undecyl) in-
termediates (see Scheme 3). These multi-substituted olefin
products suggest that the tert-Ni-dodecyl intermediates could
originate from the 1,2 insertion of ␣-olefin, and this is direct
evidence that the metal center can migrate from a primary
carbon to the adjacent tertiary carbon. Hereby, we propose
Scheme 3. The formation pathways of the C12 dimer isomers (I = insertion,
E = elimination, R = propyl).
an alternative pathway that would lead to the formation of
the branch-on-branch structure in the ethylene polymeriza-
tion process [2,13d,17] (see Scheme 4).
In theory, the binding and the direct insertion of the
1-hexene to the m-Ni-dodecyl intermediates (m = 5) are
difficult in both the ␤-diketiminato and ␣-diimine system.
Due to the open configuration of their ligands, ␣-diimine
catalysts are capable of polymerizing ␣-olefins via the
chain-strengthen mechanism [1,2,11c,13] (see Scheme 5).
However, in ␤-diketiminato catalyst systems, after ␤-H elim-
ination and the formation of the dodecene/Ni H complexes,
the rotation and the reinsertion of these binding dodecenes
were blocked by the coordination wedge. The m-Ni-dodecyl
Fig. 6. GC–MS spectrum of the C12 dimers (measured by GC–MS with
DB-5MS column, Cat. 4a 7 × 10−5 mol, MAO 80 mg, temperature 45 ◦C,
3 h).

32
J. Zhang et al. / Journal of Molecular Catalysis A: Chemical 231 (2005) 27–34
Scheme 4. Mechanism for the formation of the branch-on-branch structure in the ethylene polymerization, A mechanism in literature [2], B alternative pathway
proposed here (R = methyl, propyl, amyl, etc.).
tertiary carbon of the alkyl chain is thermodynamically fa-
vored. However, the walking of the Ni atom from the a sec-
ondary carbon to another one along the alkyl chain of the
Ni-alkyl intermediates is unfavorable in the ␤-diketiminato
Ni(II)/MAO systems. Small bulk 4b/MAO is more promis-
ing on the purpose of ␣-olefin isomerization and dimerization
than 4a/MAO.
Scheme 5. “Chain-strengthen” mechanism of the 1-olefin polymerization
catalyzed with ␣-diimine catalysts/MAO system (P = polymeric alkyl chain).
4. Experimental
intermediates (m = 1 or 2), which are fitting for 1-hexene to
insert, cannot be produced as the same mechanism occurred
in the ␣-diimine catalyst systems. Thus, no trimers or higher
4.1. General remarks
oligomers were formed. In less bulky 4b/MAO system, the
portion of dimers is larger than that in 4a/MAO system (see
Table 1). Small bulk 4b/MAO is more promising in ␣-olefin
dimerization than 4a/MAO.
All manipulations were performed by standard Schlenk
techniquesundernitrogenatmosphereorinaM. Braunglove-
box. All the containers were thoroughly dried by heating un-
der vacuum. Hexane and toluene were thoroughly dried over
In general, the obtained dimers are mainly inner olefin
phosphorus pentoxide and sodium respectively. MAO solid
isomers that were derived from the direct ␤(or ␤ꢀ)-H elimi-
was prepared by the controlled hydrolyzation of the trimethy-
nation of the m-Ni-dodecyl intermediates (m = 5). No corre-
sponding olefin products of the m-Ni-dodecyl intermediates
(m < 4) were detected by GC–MS. That is to say, the migra-
laluminum (TMA) at 0–60 ◦C by using Al2(SO4)3·18H2O
(H2O/Al = 1.3) that was dispersed in toluene. (DME)NiBr2
was prepared according to the reported literature [16]. 2,6-
tion (walking) of the Ni(II) atom from a secondary carbon
Diisopropylaniline, 2,6-dimethylaniline, n-butyllithium were
to another one along the alkyl chain of the m-Ni-dodecyl
purchased from Aldrich Chemical Co. Other commercially
available reagents were purchased and used as received.
intermediates is blocked in the ␤-diketiminato Ni(II)/MAO
system.
i
4.2. H{N(C6H3 Pr2-2,6)C(Me)}2CH (L1)
3. Conclusion
The synthetic routes of ␤-diketiminato ligand (L) had
The ␤-diketiminato Ni(II) complex/MAO systems shows
strong tendency of isomerizing the substrate 1-hexene. The
preponderance of 2-hexene in all hexenes is the result of an
accumulation circle. Due to the coordination wedge of the
bulky ␤-diketiminato Ni(II) catalyst, 3-hexenes, trimers and
higher oligomers were not produced. The walking of the Ni
atom from a primary carbon to the adjacent secondary or
been reviewed in literature [5]. In this work, the ␤-
diketiminato ligand was synthesized via the direct con-
densation of 2,6-diisopropylaniline with acetylacetone. 2,6-
Diisopropylaniline (0.05 mol) and acetylacetone (0.02 mol)
in 100 mL toluene were refluxed in a 250 mL flask for 3 h.
After that, the flask was equipped with a Dean–Stark ap-
paratus, and the mixture was further refluxed until no water

J. Zhang et al. / Journal of Molecular Catalysis A: Chemical 231 (2005) 27–34
33
found. The solution was distilled under vacuum to remove the
by-products (amines and ␤-keto-amines). The remains were
recrystallized in methanol. Colorless crystal was obtained,
1.356 g (yield 16.2%). 1H NMR (CDCl3) (ppm): 12.11 (1H,
H N), 7.12 (6H, o- and p-Ar), 4.86 (1H, H-backbone), 3.11
(4H, CH(CH3)2), 1.70(6H, CH3), 1.21(2H, CH(CH3)2), 1.17
(2H, CH(CH3)2). Anal. Calcd. for C29H42N2: C 83.20, H
10.11, N 6.69. Found: C 83.08,H 9.93, N 6.64.
∼10 mM): dimer 48.47 (12H, o-CH3Ar), 45.73 (4H, m-Ar),
−24.97 (2H, p-Ar), −67.98 (6H, CH3); monomer 45.60 (4H,
m-Ar), 41.50 (12H, o-CH3Ar), −24.29 (2H, p-Ar), −79.09
(6H, CH3); monomer/dimer ≈ 1/2.5.
4.6. Isomerization and dimerization of 1-hexene
Under nitrogen atmosphere, MAO (∼80 mg) was dis-
solved in toluene (2 mL) in a 20 mL glass tube, which was
sealed with rubber cap and equipped with magnetic bar. 1-
Hexene (toluene solution, 0.01 mL/mL) and ␤-diketiminato
Ni(II) complexes 4 (7 × 10−5 mol dissolved in 1 mL toluene)
were injected into the tube in sequence. After stirring at 45 ◦C
for 3 h, the mixture was cooled to −20 ◦C in cooling bath,
and terminated with 3 mL ethanol (NaOH solution in 95%
ethanol). Additional water was added and the tube was sealed
after CH4 bubbling out. The upper colorless and transparent
toluene part was collected for GC or GC–MS analysis.
4.3. H{N(C6H3Me2-2,6)C(Me)}2CH (L2)
The synthesis of L2 was preformed as in the case of L1,
using 0.05 mol 2,6-dimethylaniline, 0.02 mol acetylacetone
and 100 mL toluene, and a refluxing time of 3 h. The prod-
uct was obtained as colorless crystal, 1.189 g (yield 19.4%).
1H NMR (CDCl3) (ppm): 12.19 (1H, H N), 7.03 (2H, p-
Ar), 6.94 (4H, m-Ar), 4.87 (1H, H-backbone), 2.16 (12H,
o-CH3Ar), 1.69 (6H, CH3). Anal. Calcd. for C21H26N2: C
82.31, H 8.55, N 9.14. Found: C 82.30, H 8.55, N 9.14.
i
4.7. Measurement
4.4. Ni{(N(C6H3 Pr2-2,6)C(Me))2 CH}Br (4a)
1H NMR spectra were recorded on a Varian INOVA
500NB NMR spectrometer. Elemental analysis was deter-
mined with a Vario EL Series Elemental Analyzer from Ele-
mentar. The GC–MS data were recorded by a Finnigan Voy-
ager GC-8000Top Series GC–MS System with DB-5MS GC
column. The GC spectrum were recorded by a Varian CP3800
Series GC System with a HP-5MS GC column.
The complex (4a) was prepared as the literature method
[6c]. Ligandlithiumsaltwasusedaspreparedintoluenewith-
out further isolation. (DME)NiBr2 was used as Ni(II) source.
The L1 1.20 g (0.003 mol) was dissolved in 50 mL toluene,
and cooled to −78 ◦C. n-Butyllithium 1.1 mL (hexane so-
lution 2.6 M) was injected. The solution was allowed warm
up to room temperature overnight. After that, (DME)NiBr2
1.08 g (0.0035 mol) were added, and the slurry were stirred at
80 ◦C for 12 h. After hot filtration, the filtrate was condensed
by vacuum to 5–8 mL and the complexes were precipitated
and washed twice with hexane. Grey blue solid was obtained,
0.86 g (yield 54.1%). 1H NMR (C6D6) (ppm, ∼5 mM): dimer
55.59 (4H, m-Ar), 36.67 (4H, CH(CH3)2), −26.27 (2H, p-
Ar), −88.08 (6H, CH3); monomer 41.10 (4H, m-Ar), 21.57
(4H, CH(CH3)2), 8.29 (24H, CH(CH3)2), −21.51 (2H, p-
Acknowledgments
The supports by the National Natural Science Foundation
of China (NSFC) and SINOPEC (joint-Project 20334030),
the Science Foundation of Guangdong Province (Projects
039184, 013173) and the Ministry of Education of China (the
Foundation for PHD Training) are gratefully acknowledged.
1
Ar), −60.54 (6H, CH3); monomer/dimer ≈5/1. H NMR
(CD2Cl2) (ppm, ∼10 mM): dimer 56.12 (4H, m-Ar), 36.87
(4H, CH(CH3)2), −26.64 (2H, p-Ar), −88.03 (6H, CH3);
monomer 40.31 (4H, m-Ar), 22.17 (4H, CH(CH3)2), 8.95
(24H, CH(CH3)2), −22.77 (2H, p-Ar), −59.09 (6H, CH3);
monomer/dimer ≈ 2/1.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at 10.1016/j.molcata.2004.
12.024.
4.5. Ni{(N(C6H3Me2-2,6)C(Me))2 CH}Br (4b)
The synthesis of complex 4b was preformed as in
the case of complex 4a, using L2 0.92 g (0.003 mol), n-
butyllithium 1.1 mL (hexane solution 2.6 M) and 50 mL
toluene, (DME)NiBr2 1.08 g (0.0035 mol) and a stirring time
of 12 h at 80 ◦C. Product was obtained as dark blue solid,
0.85 g (yield 67.3%). 1H NMR (C6D6) (ppm, ∼10 mM):
dimer 50.49 (12H, o-CH3Ar), 47.74 (4H, m-Ar), −22.96
(2H, p-Ar), −65.97 (6H, CH3); monomer 47.62 (4H, m-Ar),
43.52 (12H, o-CH3Ar), −22.28 (2H, p-Ar), −77.08 (6H,
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