The synthesis and application of novel Ni(ii) N-alkyl dipyridylaldiminato complexes as selective ethylene oligomerisation catalysts

Article abstract of DOI:10.1039/c4dt00537f

A series of N-alkyl 2,2′-dipyridylamine ligands of general formula (2-C₅H₃NR)₂NR′, (a): R = H, R′ = Me; (b): R = H, R′ = benzyl; (c): R = H, R′ = methylcyclohexyl; (d): R = H, R′ = neopentyl; (e): R = Me, R′ = Me) were prepared by a modified method involving base-mediated N-alkylation with the respective alkyl halide. Reaction of the ligands, a-e, with NiCl₂(DME) allowed for the isolation of μ-Cl Ni(ii) complexes: [Ni(μ-Cl){a}Cl]₂ (1a); [Ni(μ-Cl){b}Cl]₂ (1b); [Ni(μ-Cl){c}Cl]₂ (1c); [Ni(μ-Cl){d}Cl]₂ (1d) and [Ni(μ-Cl){e}Cl]₂ (1e). The complexes were characterised by FT-IR spectroscopy, magnetic susceptibility measurements, mass spectrometry, elemental analyses and in the case of 1a, SCD analysis. In the case of complex 1e, an acid-mediated hydrolysis process was identified. The product of hydrolysis, the protonated ligand and a tetrachloronickelate salt (1e-A), was characterised by SCD analysis. Activation of 1a-1e with alkyl aluminium reagents generated highly active catalysts for the oligomerisation of ethylene, with activities of up to 864 kg _oligomers mol_Ni^-1 h^-1 and high selectivity toward the formation of butenes. In general, trans 2-butene was observed as the major isomer, with the exception of 1e. In the case of 1e, the selectivity for 1-butene was 98%, thereby demonstrating the significant effect that the introduction of a low degree of steric pressure in the coordination sphere of the catalyst has on selectivity.

Full text of DOI:10.1039/c4dt00537f

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
The synthesis and application of novel Ni(II) N-alkyl
dipyridylaldiminato complexes as selective
ethylene oligomerisation catalysts†
Cite this: Dalton Trans., 2014, 43,
9892
Andrew J. Swarts and Selwyn F. Mapolie*
A series of N-alkyl 2,2’-dipyridylamine ligands of general formula (2-C5H3NR)2NR’, (a): R = H, R’ = Me; (b):
R = H, R’ = benzyl; (c): R = H, R’ = methylcyclohexyl; (d): R = H, R’ = neopentyl; (e): R = Me, R’ = Me) were
prepared by a modified method involving base-mediated N-alkylation with the respective alkyl halide.
Reaction of the ligands, a–e, with NiCl2(DME) allowed for the isolation of µ-Cl Ni(II) complexes: [Ni(µ-Cl)-
{a}Cl]2 (1a); [Ni(µ-Cl){b}Cl]2 (1b); [Ni(µ-Cl){c}Cl]2 (1c); [Ni(µ-Cl){d}Cl]2 (1d) and [Ni(µ-Cl){e}Cl]2 (1e). The
complexes were characterised by FT-IR spectroscopy, magnetic susceptibility measurements, mass spec-
trometry, elemental analyses and in the case of 1a, SCD analysis. In the case of complex 1e, an acid-
mediated hydrolysis process was identified. The product of hydrolysis, the protonated ligand and a tetra-
chloronickelate salt (1e-A), was characterised by SCD analysis. Activation of 1a–1e with alkyl aluminium
reagents generated highly active catalysts for the oligomerisation of ethylene, with activities of up to
864 kgoligomers molNi h−1 and high selectivity toward the formation of butenes. In general, trans
−1
Received 20th February 2014,
Accepted 12th May 2014
2-butene was observed as the major isomer, with the exception of 1e. In the case of 1e, the selectivity for
1-butene was 98%, thereby demonstrating the significant effect that the introduction of a low degree of
steric pressure in the coordination sphere of the catalyst has on selectivity.
DOI: 10.1039/c4dt00537f
www.rsc.org/dalton
development of late transition metal catalysts of Ni and Pd
which were capable of ethylene polymerisation/co-polymeris-
Introduction
The field of transition metal-mediated olefin oligomerisation ation with non-polar and polar α-olefins.3 Of particular signifi-
and polymerisation has seen phenomenal growth over the past cance was the work done on Ni and Pd systems ligated by
three decades. Initial reports detailed the application of early diimine ligands, which displayed both remarkable activity and
transition metal catalyst systems of Ti, Zr and Hf constrained selectivity when applied to olefin homo- and co-polymerisation
geometry catalysts (CGC’s) which displayed exceptional activity or oligomerisation reactions, thereby circumventing the
in ethylene polymerisation.1 Despite their high activity, these inherent limitations of early transition metal catalyst systems.4
catalyst systems generally showed low levels of chain entrap- Seminal experimental and computational contributions by
ment in ethylene homopolymerisation as well as low levels of Brookhart and others elucidated the key features in homo- and
co-monomer enchainment in ethylene/α-olefin co-polymeris- co-polymerisation reactions of this class of catalysts. In the
ation.2 In addition, the inherent oxophilicity of these catalysts case of palladium, low temperature spectroscopic and compu-
necessitate the rigorous exclusion of oxygen and water and pre- tational investigations identified the catalyst resting states to
cluded the use of polar α-olefins in co-polymerisation reac- be Pd–alkyl π-olefin species, establishing zero-order kinetics in
tions. Brookhart, Grubbs and Gibson paved the way for the olefin; barriers to insertion were determined to be in the range
17–18 kcal mol−1; branching in homopolymerisation was
established to proceed via the isomerisation of π-agostic Pd–
Stellenbosch University, Department of Chemistry and Polymer Science, Private Bag X1,
alkyl species with isomerisation barriers of 8–9 kcal mol−1
;
Matieland, 7602 Stellenbosch, South Africa. E-mail: 15428958@sun.ac.za,
smapolie@sun.ac.za; Fax: +27 (0)21 808 3849; Tel: +27 (0)21 808 2722
†Electronic supplementary information (ESI) available: Contains additional
experimental data, Fig S1–S7: includes ESI-MS spectra, the solid state and solu-
tion appearance of complex 1e, 1H NMR and FT-IR spectra of 1e and the
additional species formed in solution as well as GC-FID spectra showing the for-
mation of 1- and 2-butenes during catalysis. CCDC 981834 and 981835 for 1a
and 1e-A. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c4dt00537f
chain transfer proceeded via associative exchange of free olefin
and that the degree of branching in the obtained polymer was
independent of ethylene pressure while the morphology of the
polymer was pressure dependent.5 For Ni(II) analogues, the
degree of branching within the polymer formed during Ni(II)–
diimine catalysed polymerisation was found to differ signifi-
cantly with varying reaction conditions and the structure of
9892 | Dalton Trans., 2014, 43, 9892–9900
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Scheme 1 Switchable catalytic selectivity as a function of steric bulk in
Cr(III)-catalysed ethylene tetramerisation.
the catalytically active species. The degree of branching was
shown to be negligible at low reaction temperatures and high
ethylene pressures when employing pre-catalysts with
decreased steric bulk. In contrast, employing sterically encum-
bered pre-catalysts at high temperatures and low ethylene
pressure led to the formation of highly branched polyethy-
lene.6 Ethylene insertion barriers were found to be 4–5 kcal
mol−1 lower in energy in comparison to their Pd congeners,7
while the energy barriers for insertion from sterically encum-
bered analogues were slightly lower than the less sterically con-
gested Ni–alkyl species. With key mechanistic insights
established, numerous reports have since been published
detailing the catalytic application of complexes bearing nitro-
gen donor ligands in olefin transformations.8
Gambarotta and co-workers recently reported the synthesis
and application of Cr(III) complexes bearing N-alkyl dipyridyl-
aldimine ligands in selective ethylene tetramerisation.9 They
found that these complexes, after activation with an alu-
minium alkyl co-catalyst, catalysed the formation 1-octene
selectively as well as a significant amount of wax. During the
course of their catalytic investigations they found that the
introduction of steric bulk in the form of Me-groups ortho to
the pyridine nitrogen atoms switched the product selectivity
from 1-octene to 1-hexene (Scheme 1).
Scheme 2 Synthesis of dinuclear Ni(II) N-alkyl 2,2’-dipyridylaldiminato
complexes.
solvents and were characterised by FT-IR and 1H NMR spec-
troscopy (a, b, d) as well as 13C{1H} NMR spectroscopy, ESI-MS
and elemental analysis (c, e).
The N-alkyl-2,2′-dipyridylamine ligands (a–e) were reacted
with NiCl2(DME) to afford dimeric Ni(II) N-alkyl-2,2′-dipyridyl-
aldiminato complexes, 1a–1e in high yields (Scheme 1). The
complexes were isolated as blue-green (1a), green (1b and 1c)
or yellow-green (1d) paramagnetic and hygroscopic solids
which displayed solubility in polar coordinating solvents and
alcohols. In the case of complex 1e, a pale purple-pink solid
was isolated. The complexes were found to be insoluble in
ethers, alkanes and chlorinated solvents. Complexes 1a–1e
were characterised by a range of spectroscopic and analytical
techniques.
Characterisation of the complexes by FT-IR spectroscopy
showed a shift to higher wavenumbers of the pyridyl ring
imine absorption bands, observed in the range 1597–1600 and
1565–1581 cm−1 for the complexes. Analogous shifts have
been observed previously for related Ni(II) complexes, which is
indicative of ligand coordination to nickel.12 Characterisation
by ESI-MS spectrometry of complexes 1a–1e revealed interest-
ing solvent-dependent fragmentation behaviour. When aceto-
nitrile–0.1% formic acid solution was employed as the solvent
during the ESI-MS experiment, mass fragments corresponding
to mononuclear, dinuclear and trinuclear species were
observed (Fig. S1†). Species aggregation is a common pheno-
menon during the ESI-MS experiment and has been reported
previously for palladium complexes.13 In contrast to what was
observed when employing acetonitrile–formic acid as solvent,
the ESI-MS spectra obtained when employing 100% MeOH as
dissolution and introduction solvent show the absence of
dinuclear and trinucleas species. Instead, in all cases isotope
clusters were observed which correspond to a doubly-charged
species with the formulation [M + Na + MeOH]2+ where M =
[Ni(µ-Cl){L}Cl]2 (Fig. S2†). The experimental solid state mag-
Intrigued by these results, we set out to evaluate the effect
that increasing the electron-donating ability of the N-alkyl sub-
stituent and the introduction of steric bulk in the ortho posi-
tion of the pyridyl ring would have on activity and selectivity in
Ni(II)-catalysed ethylene oligo-/polymerisation. Herein we
report our synthetic and catalytic application of a series of
novel dinuclear Ni(II) N-alkyl dipyridylaldiminato complexes.
Results and discussion
Synthesis and characterisation
A series of known as well as novel N-alkyl-2,2′-dipyridylamine
ligands of general formula (2-C5H3NR)2NR′, a: R = H, R′ = Me;
b: R = H, R′ = benzyl; c: R = H, R′ = methylcyclohexyl; d: R = H,
R′ = neopentyl; e: R = Me, R′ = Me) were prepared by a modified
method involving base-mediated N-alkylation (Scheme 2).
Ligands a,10 b11 and d9 have been reported previously whereas
c and e are novel. The ligands were isolated, after column
chromatography, as yellow oils (a, c, d, e) or as a solid (b) in
60–90% yield. The ligands displayed solubility in most organic
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 9892–9900 | 9893

View Article Online
Paper
Dalton Transactions
netic susceptibility values for complexes 1a–1e are in the range
µeff 3.89–4.47µB, higher than the spin-only value of 2.83µB
expected for two unpaired electrons.14 Despite this, experi-
mentally determined values are within the range observed
reported for high-spin dimeric Ni(II) complexes with S = 1.15
The structure of complex 1a was unambiguously deter-
mined by SCD analysis on single crystals grown by vapor
diffusion of diethyl ether into a methanol solution of the
complex. The molecular structure consists of a MeOH-solvated
µ-Cl Ni(II)2 dimer, 1a·2MeOH (Fig. 1), residing on a crystallo-
graphic inversion center.
Metric parameters and crystallographic data are tabulated
in Tables 1 and 2 respectively. The coordination sphere of the
Ni(II) centre is distorted octahedral with the equatorial plane
occupied by two bridging Cl atoms and the N atoms of the
chelate ligand while the axial positions are occupied by a term-
inal Cl atom and a bound MeOH molecule.
The Ni1–Cl1 and Ni1–Cl2 bond lengths of 2.394(6) and
2.415(5) Å respectively fall within the expected range reported
for other µ-Cl Ni(II) dimeric structures.8i,16 In addition the N1–
O1 bond length of 2.165(1) Å falls within the range observed
for MeOH solvated-Ni(II) complexes.17 The deviation from pla-
narity in the octahedral geometry is as a result of chelation of
the ligand to the metal centre, with a N1–Ni1–N2 angle of
85.77°. The bound MeOH molecule is also slightly tilted
Table 2 Crystallographic data pertaining to complex 1a·2MeOH
1a·2MeOH
24H30Cl4N6Ni2O2
Empirical formula
C
Temperature
Crystal system
Space group
a/Å
b/Å
100(2)
Monoclinic
P2/n
8.4860(14)
14.430(2)
11.5135(19)
90.00
95.387(2)
90.00
1403.64
1
c/Å
α (°)
β (°)
γ (°)
V/Å3
Z
F(000)
712
1.6411
1.757
Dc (g cm−3
)
μ/mm−1
Reflections [Fo > 4(Fo)]
Parameters
GOF
R1 (I > 2δ)
wR2
3237
178
1.045
0.0208
0.0263
within the crystal structure as observed by the O1–Ni1–Cl2
angle of 81.37°. All other bond lengths and angles fall within
the expected range for this class of complexes.
Complex 1e displayed interesting solution behaviour during
attempts at recrystallisation. The complex was isolated as a
pale purple-pink solid, the colour of which suggested a square
planar geometry around the metal centre, alluding to the
metal centre being diamagnetic (Fig. S3†).
When 1e was dissolved in dichloromethane it formed a
pink-red coloured solution. Previous literature reports have
described square planar Ni(II) complexes as red or pink
coloured solids.18 However, analytical data, specifically mag-
netic susceptibility data determined in the solid state, was con-
sistent with a paramagnetic dinuclear chloro-bridged Ni(II)
complex (µeff: 4.47µB). Analysis of the complex by 1H NMR
spectroscopy in CD2Cl2 also showed broad, poorly resolved
resonances, consistent with a paramagnetic transition metal
complex (Fig. S4†). Prolonged storage of a solution of 1e in
dichloromethane resulted in the formation of a pale-yellow
precipitate, together with blue crystals (Fig. S3†). Removal of
the supernatant and analysis of the pale-yellow precipitate by
FT-IR spectroscopy showed absorption bands identical to com-
mercially available NiCl2 (Fig. S5†). This initial result
suggested that the complex dissociates in solution to generate
the uncoordinated dipyridylamine ligand and nickel chloride.
Layering of the pink-red solution with pentane and storage at
5 °C generated blue crystals which were analysed crystallo-
graphically (1e-A). The asymmetric unit consists of a tetrachlor-
onickelate anion which is charge-balanced by two
N-protonated 6,6′-dimethyl-2,2′-dipyridylamine ligands, which
is effectively a tetrachloronickelate salt (Fig. 2). Selected bond
lengths and angles (Table 3) as well as crystallographic para-
meters (Table 4), are tabulated. The cationic and anionic por-
tions are effectively dissociated, as evidenced by Ni–N1 and
Ni–N1′ bond distances of 5.540 and 5.768 Å. The Ni- and
Fig. 1 Molecular structure of 1a·2MeOH drawn at 50% probability ellip-
soids. Hydrogen atoms omitted for clarity.
Table 1 Selected bond lengths (Å) and angles (°) for complex
1a·2MeOH
Bond lengths (Å)
Bond angles (°)
Ni1–N1
Ni1–N2
Ni1–O1
Ni1–Cl1
Ni1–Cl2
2.036(2)
2.044(1)
2.165(1)
2.394(6)
2.415(5)
N1–Ni1–N2
N1–Ni1–Cl1
N1–Ni1–Cl2
N1–Ni1–O1
N2–Ni1–Cl1
N2–Ni1–Cl2
85.76(6)
92.51(4)
175.19(4)
93.90(5)
94.00(4)
173.61(4)
9894 | Dalton Trans., 2014, 43, 9892–9900
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Fig. 3 Crystal packing for 1e-A along the b-axis, showing the rhombus-
shaped packing around the Ni-centre, with interleaving layers annotated
as a and b.
Fig. 2 Molecular structure of the crystals isolated as 1e-A, drawn at
50% probability. Ni and O atoms located on a centre of inversion.
Selected hydrogen atoms omitted for clarity.
Interleaving layers of metal anion, water and ligand pack
infinitely along the b axis, in an a/b motif. A number of reports
in literature detail the crystallographic characterisation of tran-
sition metal-/pyridinium ion-pairs,19 with only five reports
corresponding to the preparation of tetrachloronickelate
species.20
In all cases, the synthetic procedure for the isolation of the
ion-pairs requires the presence of hydrochloric acid to proto-
nate the pyridine ligand and generate the tetrachloronickelate
anion. We thus propose that the formation of species 1e-A is
mediated by hydrochloric acid, known to be present in
dichloromethane in trace quantities.
Table 3 Selected bond lengths (Å) and angles (°) for complex 1e-A
Bond lengths (Å)
Bond angles (°)
Ni1–Cl1
Ni1–Cl2
Cl1⋯H1
Cl2⋯H7A
2.275(6)
2.258(7)
2.321
Cl1–Ni1–Cl2
Cl1–Ni1–Cl1
116.44(2)
100.12(2)
3.620
Table 4 Crystallographic data pertaining to complex 1e-A
1e-A
26H32Cl4N6NiO
Empirical formula
C
Temperature
Crystal system
Space group
a/Å
b/Å
100(2)
Monoclinic
C2/c
21.751(4)
11.949(2)
13.415(2)
90.00
123.276(2)
90.00
2915.0(8)
4
1336
1.6411
1.064
3380
180
Reactivity of complexes 1a–1e toward ethylene
We evaluated the reactivity of complexes 1a–1e, in the presence
of alkylaluminium reagents as co-catalysts, in ethylene oligo-/
polymerisation. Our initial catalysis optimisation runs were
conducted with complex 1a as pre-catalyst (Table 5). We found
that pre-catalyst/co-catalyst interactions had an effect on the
generation of an active catalyst system. Initial catalyst screen-
ing with complex 1a/MAO at Al : Ni ratio of 500 : 1 did not gene-
rate an active catalyst system (Table 5, entry 1), as evidenced by
the absence of both oligomers and polymers in the reaction
mixture. Previous reports of Ni(II)-catalysed ethylene oligomeri-
sation demonstrated an increase in catalytic activity when
employing chlorobenzene as solvent.21
c/Å
α (°)
β (°)
γ (°)
V/Å3
Z
F(000)
Dc (g cm−3
)
μ/mm−1
Reflections [Fo > 4(Fo)]
Parameters
GOF
R1 (I > 2δ)
wR2
1.058
0.0326
0.0749
When conducting our reactions in chlorobenzene as
solvent, no ethylene oligomerisation or polymerisation was
observed (Table 5, entry 2). We found that activation of
complex 1a with MAO at Al : Ni ratios of ≥1000 : 1 in toluene
generated a catalyst system capable of oligomerising ethylene
O-atoms are located on an inversion centre and display H⋯Cl
interactions related by symmetry of 2.198 Å. In addition, H⋯Cl
interactions are observed between the N-Me and the Cl atoms
bound to nickel with a distance of 3.619 Å (Fig. 3). The mole-
cules are packed in rows parallel to the c axis, with the rows
stabilised by π–π stacking interactions of 3.645 Å and 3.490 Å.
Consecutive rows along the a axis are linked via H-bonding to
each other.
−1
with activities of 123 kgoligomers molNi h−1 and turn-over fre-
quencies of 4 × 103 h−1 (Table 5, entry 3). The formation of
long-chain oligomers or polymer was not observed. The cata-
lyst system displayed high selectivity toward the formation of
1- and 2-butenes (98%), with up to 47% 1-butene formed. The
formation of small amounts of internal C6-isomers and
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 9892–9900 | 9895

View Article Online
Paper
Dalton Transactions
Table 5 Optimisation of co-catalyst and Al : Ni ratios employing complex 1a, comparative evaluation of complexes 1b–1e and evaluation of reaction
parameters on activitya
Activity (kgoligomers
molNi−1 h−1
)
TOF (×103 h−1
)
% C4
% C6
% C8
1-C4 : trans 2-C4 : cis 2-C4
e
e
Entry
Complex
Co-catalyst
Al : Ni
1
1a
1a
1a
1a
1a
1a
1a
1b
1c
1d
1e
1a
1a
MAO
MAO
MAO
500 : 1
500 : 1
1000 : 1
500 : 1
1000 : 1
125 : 1
250 : 1
250 : 1
250 : 1
250 : 1
250 : 1
250 : 1
250 : 1
—
—
123
—
—
—
—
—
2b
3
4
—
—
10
21
24
19
21
18
31
9
98
—
—
97
99
>99
>99
>99
>99
>99
98
2
0
47 : 42 : 21
—
—
4
5
6
7
8
9
10
11
12c
13d
MMAO
MMAO
DEAC
DEAC
DEAC
DEAC
DEAC
DEAC
DEAC
DEAC
—
—
2.5
1
0
0
0
0
1
2
—
—
0.5
0
0
0
0
0
0
0
421
589
662
527
600
499
864
249
33 : 39 : 28
26 : 46 : 28
36 : 38 : 26
22 : 48 : 30
34 : 40 : 26
98 : 1.2 : 0.8
27 : 44 : 29
20 : 50 : 30
a n(pre-catalyst): 10 µmol. Solvent (V): PhMe, 50 ml. Ethylene P: 5 bar. Reaction T: 30 °C. Reaction time: 30 min. TOF: n(ethylene consumed)/n
(nickel)·h. MAO: methylaluminoxane. MMAO: modified methylaluminoxane. DEAC: diethyl aluminium chloride. b Chlorobenzene as solvent.
c Ethylene P: 10 bar. d Reaction time: 90 min. e In all cases, the percentage of 1-hexene and 1-octene within the C6- and C8-fraction is less than 1%.
C8-isomers was also observed. However, less than 1% of the tion, employing DEAC as co-catalyst, with an Al : Ni ratio of
higher olefin fraction corresponds to 1-hexene and 1-octene. 250 : 1. Under the evaluated reaction conditions, complexes
Contrary to what has been reported previously for Ni(II) phos- 1a–1e were highly active catalysts for the oligomerisation of
phinito-imine complexes,18 activation of complex 1a with ethylene, forming butenes as major products (Table 5, entries
MMAO with Al : Ni ratios of 500 : 1 and 1000 : 1 did not gene- 7–11). The observed activity varied between 499–662 kgoligomers
h
−1, while the observed turn-over frequencies varied
−1
rate an active catalyst system (Table 5, entries 4 and 5).
molNi
Activation of complex 1a with DEAC at an Al : Ni ratio 125 : between 18–24 × 103 h−1, in the range observed for previously
1 generated highly active species, capable of oligomerising reported Ni(II) phenyl-ether pyrazole complexes.8j
ethylene with high activities and at low co-catalyst loading
The observed activity of complexes 1a–1e is slightly lower
(Table 5, entry 6). Increasing the amount of DEAC to an Al : Ni than that reported previously for Ni(II) complexes in ethylene
ratio of 250 : 1 resulted in the formation of an active species oligomerisation, while the selectivity for 1-butene displayed by
capable of dimerising ethylene to butenes with an activity of 1e is higher than most reported in literature. Cámpora and co-
589 kgoligomers molNi h−1 and a turn-over frequency of 21 × workers reported the application of Ni(II) phosphinito-imine
−1
103 h−1 (Table 5, entry 7). A selectivity of 99% to butenes was complexes as catalysts in ethylene oligomerisation.18 When
observed, with the selectivity toward 1-butene found to be activated with MMAO as co-catalyst, activities of up to 20.1 ×
26%. No significant differences were observed in the selectivity 10−3 h−1 and selectivities of up to 100% for the formation of
towards butenes and specifically 1-butene, when employing 1-butene was observed. Employing DEAC as co-catalyst gener-
activated complex 4a with either MAO or DEAC as co-catalyst. ated even more active catalysts, consistent with our obser-
The significant difference in catalytic activity as a function of vation, with activities of up to 1685.3 × 10−3
h
−1, while the
the co-catalyst employed may be as a result of the different maximum selectivity for 1-butene was found to be 50%. Braun-
active species which is formed during activation employing stein, Giambastiani and co-workers reported the catalytic
MAO or DEAC. Brookhart and co-workers demonstrated experi- application of Ni(II) phosphinito-oxazoline complexes in ethyl-
mentally that ethylene insertion to produce oligomers and ene oligomerisation.23 Activation with ethyl aluminium
polymers proceed from the catalyst resting state, the Ni–ethyl dichloride (EADC) generated catalysts with activities of up to
π-ethylene species.22 Assuming that an analogous Ni–ethyl 79 × 103 h−1 and selectivities for 1-butene of up to 22%. In con-
π-ethylene species is the catalyst resting state for our catalyst trast, activation with MAO produced catalysts with significantly
system, alkylation and alkyl-abstraction by DEAC, in the pres- higher activities of up to 230 × 103 h−1, while the selectivity for
ence of ethylene would generate the catalyst resting state 1-butene was observed to decrease to 16%. Recently, Piers and
directly. In contrast, alkylation and alkyl-abstraction by MAO co-workers demonstrated the ethylene oligomerisation behav-
under identical conditions would generate the Ni-methyl iour of Ni(II) phosphine-borate complexes in the absence of a
π-ethylene species, which would need to undergo a number of co-catalyst. These catalysts displayed TON’s of up to 2000 in
chain propagation and termination steps to generate the cata- one hour. Selectivities for 1-butene was reported up to 70%
lyst resting state. It is this reason which we believe account for with the remainder of the olefin products corresponding to
the increased catalytic activity for ethylene oligomerisation hexenes.
observed when employing DEAC as co-catalyst. Next, we evalu-
When considering the activation of complexes 1a–1d with
ated complexes 1a–1e comparatively in ethylene oligomerisa- DEAC as co-catalyst, no clear correlation between the observed
9896 | Dalton Trans., 2014, 43, 9892–9900
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
reactivity and the bridgehead N-alkyl substituents could be with decomposition of the catalytically active species and is
established. Thus the effect of the N-alkyl substituents on the generally observed for nickel- and palladium-catalysed olefin
observed catalytic activity is negligible. On the contrary, com- oligo- or polymerisation reactions.3a Our results have demon-
paring the activity of 1a and 1e, the introduction of steric bulk strated the significant impact that tuning the coordination
in the ortho positions of the pyridylamine ligand result in sphere of the catalyst can have on the observed product selecti-
−1
a decrease in activity, from 589 kgoligomers molNi
h−1 to vity. In this example, the introduction of methyl groups in the
−1
499 kgoligomers molNi h−1. The observed decrease is as a result ortho position of the dipyridylamine ligands increases olefin
of increased barriers to associative exchange and β-hydrogen isomerisation barriers, thereby leading to the preferential for-
transfer with increased steric bulk, leading to lower observed mation of 1-butene.
catalytic activity, as well as a less electrophilic metal centre
which decreases the rate of ethylene insertion.22,24 When con-
sidering the selectivity toward 1-butene for complexes 1a–1d, no
clear trend emerges (Table 5, entries 7–10). This again high-
Conclusions
lights the negligible effect the bridgehead N-alkyl substituents A series of chloro-bridged dinuclear Ni(II) complexes, 1a–1e,
has on the observed selectivity. In general, for complexes 1a– ligated by N-alkyl dipyridylaldimine ligands were prepared.
1d, the major isomer formed during catalysis is the thermody- Characterisation by various spectroscopic and analytical tech-
namically favoured trans 2-butene, in the range 38–46% niques identified the complexes as paramagnetic Ni(II) com-
(Table 5, entries 7–10, Fig. S6†). The percentages of 1-butene plexes. During ESI-MS analysis of the complexes, interesting
and cis 2-butene formed was found to vary as well, in the range solvent-dependent fragmentation and aggregation processes
22–36% and 26–30% respectively. The varying selectivity for 1- were identified. In the case of complex 1e a unique acid-
and 2-butenes may be attributed to secondary isomerisation mediated hydrolysis process was identified, the product of
reactions which are difficult to control. These processes have which was characterised crystallographically. Following acti-
been identified employing low temperature spectroscopic tech- vation with alkylaluminium reagents, complexes 1a–1e gene-
niques,22 and have been observed previously in Ni(II)-catalysed rated species capable of oligomerising ethylene with high
−1
ethylene oligomerisation.18 In contrast, when employing activity, up to 864 kgoligomers molNi h−1 and high selectivity
complex 1e as catalyst, the observed selectivity for 1-butene is toward 1-butene, 98% in the case of 1e. Consistent with pre-
98% (Table 5, entry 11, Fig. S7†). This marked increase in vious literature reports on Ni(II)-catalysed ethylene oligomeri-
1-butene selectivity is attributed to the presence of the o-Me sation, an increase in ethylene pressure was found to increase
substituents which retards the isomerisation of 1-butene, by the observed catalytic activity, while an increase in reaction
increasing steric pressure within the nickel coordination time resulted in a decrease in the observed catalytic activity.
sphere. This is as a result of the re-inserted olefin being
oriented within the plane of the metal centre prior to elimin-
ation, which destabilises the active species and decreases the
propensity toward isomerisation. In addition, it has been
established by both experiment and theory, that the olefin iso-
Experimental section
General considerations
merisation barriers are much higher for sterically bulky Ni– All transformations were performed using standard Schlenk
alkyl olefin species, in comparison to their less sterically bulky techniques under a nitrogen atmosphere. Solvents were dried
analogues.6,7,24c It is these factors, a combination of steric and by refluxing over the appropriate drying agents followed by dis-
electronic effects, which we believe account for the observed tillation prior to use and all other reagents were employed as
difference in butene selectivity for complexes 1a and 1e.
obtained. ESI-MS (positive ion mode) analyses were performed
Finally, we evaluated the effect of varying reaction para- on Waters API Quattro Micro and Waters API Q-TOF Ultima
meters on activity employing complex 1a and DEAC as co-cata- instruments by direct injection of sample. FT-IR analysis was
lyst. It should be noted that we did not evaluate the effect of performed on a Thermo Nicolet AVATAR 330 instrument, and
temperature due to the highly exothermic nature of the oligo- was recorded as neat spectra (ATR) unless otherwise specified.
merisation reaction. We found that increasing ethylene Melting point determinations were performed on a Stuart
pressure from 5 bar to 10 bar, resulted in a significant increase Scientific SMP3 melting point apparatus and are reported as
in catalytic activity, which was found to be 864 kgoligomers uncorrected. Magnetic susceptibility measurements were
−1
molNi h−1, corresponding to a TOF of 31 × 103 h−1 (Table 5, recorded on a Sherwood Scientific MK1 magnetic suscepti-
entry 12). This increase is attributable to an increased equili- bility balance. Samples were weighed and sealed in a glovebox
brium concentration of monomer present in solution at higher prior to analysis. Measurements were conducted in duplicate.
ethylene pressures and has been observed previously for Ni(II) MAO (1.0 M in toluene, Sigma-Aldrich), MMAO (7 wt% in hep-
catalyst systems capable of oligomerising and polymerising tanes, Azko-Nobel) and DEAC (1.8 M in toluene, Sigma-
ethylene.17c,18,25 Increasing the reaction time, from 30 minutes Aldrich) was purchased from commercial sources and used as
to 90 minutes resulted in a dramatic decrease in catalytic received. NiCl2(DME) was prepared according to a modified
activity, from 589 kgoligomers molNi h−1 to 249 kgoligomers literature procedure, where the NiCl2·2H2O in the literature
−1
molNi h−1 (Table 5, entry 13). This decrease is consistent procedure was replaced with NiCl2·6H2O.26 Satisfactory micro-
−1
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 9892–9900 | 9897

View Article Online
Paper
Dalton Transactions
analysis could not be obtained for all the prepared complexes δ 6.82–6.87 (dt, 2H, 3JH–H 7.19 Hz, H2); δ 4.20 (s, 2H, H6); δ 0.88
and in some cases (1a, 1b, 1c and 1d) the data was fitted to (s, 9H, H7).
species which showed trace solvent inclusion.
Synthesis of (6,6′-dimethyl-2,2′-dipyridyl)-N-methylamine
(e). To stirred solution of 2-bromo-6-methylpyridine
(499 mg, 2.9 mmol) and 2-amino-6-methylpyridine (345 mg,
a
Synthesis of N-alkyl-2,2′-dipyridylamine ligands, 1a–1e
Synthesis of 2,2′-dipyridyl-N-methylamine (a). To a stirred 3.19 mmol) in anhydrous PhMe (45 ml) was added Pd2(dba)3
slurry of KOH (786 mg, 14.018 mmol) in DMSO (10 ml) was (133 mg, 0.145 mmol), rac-BINAP (68 mg, 0.110 mmol) and
added solid 2,2′-dipyridylamine (600 mg, 3.504 mmol). The KOtBu (531 mg, 4.73 mmol) in rapid succession. The reaction
reaction mixture was stirred for 45 min after which neat iodo- mixture was heated for 15 h while stirring at 90 °C. After the
methane (497 mg, 3.504 mmol) was added neat. The reaction allotted time the reaction mixture was quenched with EtOH
mixture was stirred at room temperature for 20 h. After the (15 ml), filtered through celite and the solvent removed
allotted time the reaction mixture was quenched with water in vacuo. The crude product amine was isolated as a brown oil
(50 ml) and the aqueous layer extracted with EtOAc (3 × 100 ml and was sufficiently pure (determined by 1H NMR spec-
portions). The organic layer was separated, dried over MgSO4 troscopy) and employed directly in the methylation step. The
and the solvent removed in vacuo. The orange-brown crude oil same synthetic procedure as outlined above (a) was employed
was purified by flash chromatography employing EtOAc– for the synthesis of e using 6-methyl-N-(6-methylpyridin-2-yl)-
hexane (9 : 1) as eluent. The pure product was obtained as a pyridin-2-amine as starting amine and iodomethane as
yellow oil. Yield: 582 mg, 89%. FT-IR (ATR, neat, ν): 1580 and reagent. The product was isolated as a yellow oil after purifi-
1557 cm−1 (CvN). 1H NMR (CDCl3, 300 MHz): δ 8.33–8.36 (dd, cation by flash chromatography employing pentane as eluent.
2H, 3JH–H 7.92 Hz, H1); δ 7.51–7.57 (m, 2H, H3); δ 7.15–7.19 (dt, Yield: 289 mg, 46% overall. FT-IR (ATR, neat, ν): 1591 and
3
2H, JH–H 8.51 Hz, H4); δ 6.84–6.88 (m, 2H, H2); δ 3.63 (s, 3H, 1568 cm−1. 1H NMR (CDCl3, 300 MHz): δ 7.40 (t, 2H, 3JH–H 7.48
3
3
H6).
Hz, H3); δ 6.95 (d, 2H, JH–H 8.36 Hz, H4); δ 6.70 (d, 2H, JH–H
Synthesis of 2,2′-dipyridyl-N-benzylamine (b). The same syn- 7.19 Hz, H2); δ 3.63 (s, 3H, H6); δ 2.48 (s, 6H, H7). 13C{1H} NMR
thetic procedure as outlined above for ligand a was employed (CDCl3, 75.38 MHz): δ 157.45 (C5); δ 157.00 (C1); δ 137.13 (C3);
for the synthesis of b, using benzyl chloride as reagent. The δ 115.83 (C2); δ 111.10 (C4); δ 35.84 (C6); δ 24.43 (C7). ESI-MS:
product was isolated as a bright-yellow solid after recrystallisa- m/z 214 [M + H]+. % Found (% calc.) for C12H15N3: C: 73.13
tion from hexane. Yield: 755 mg, 82%. FT-IR (ATR, neat, ν): (73.21); H: 6.84 (7.09); N: 19.58 (19.70).
1581 and 1561 cm−1 (CvN). 1H NMR (CDCl3, 300 MHz):
3
Synthesis of µ-Cl Ni(II) N-alkyl dipyridylaldiminato complexes,
1a–1e
δ 8.31–8.33 (dd, 2H, JH–H 7.63 Hz, H1); δ 7.48–7.54 (m, 2H,
H3); δ 7.33–7.36 (br. d, 2H, JH–H 7.34 Hz, H4); δ 7.25–7.28 (m,
3
2H, H9,10); δ 7.15–7.20 (m, 3H, H8,8′,9); δ 6.82–6.87 (dt, 2H,
3JH–H 7.19 Hz, H2); δ 5.51 (s, 2H, H6).
Synthesis of [Ni(µ-Cl){2,2′-dipyridyl-N-methylamine}Cl]2,
1a. To a stirred slurry of NiCl2(DME) (237 mg, 1.079 mmol) in
Synthesis of 2,2′-dipyridyl-N-methylcyclohexylamine (c). The DCM (20 ml) was added a solution of 2,2′-dipyridyl-N-methyl-
same synthetic procedure as outlined above for ligand a was amine (200 mg, 1.079 mmol) in DCM (5 ml). The reaction
employed for the synthesis of c, using (bromomethyl)cyclo- mixture was stirred for 23 h at room temperature. After the
hexane as reagent. The product was isolated as an orange oil allotted time the solvent was removed in vacuo and the blue-
after purification by flash chromatography (EtOAc–hexane green solid residue obtained dissolved in MeCN and cannula-
1 : 4). Yield: 823 mg, 88%. FT-IR (ATR, neat, ν): 1580 and filtered into another dry Schlenk tube. The blue-green filtrate
1558 cm−1 (CvN). 1H NMR (CDCl3, 300 MHz): δ 8.32–8.34 (dd, was reduced in volume and layered with Et2O to form a blue-
2H, 3JH–H 7.78 Hz, H1); δ 7.48–7.54 (m, 2H, H3); δ 7.06–7.10 (dt, green solid which was filtered, washed with ether and dried
3
3
2H, JH–H 8.51 Hz, H4); δ 6.82–6.86 (dt, 2H, JH–H 7.19 Hz, H2); in vacuo. Yield: 282 mg, 83%. FT-IR (ATR, neat, ν): 1598,
δ 4.06 (d, 2H, JH–H 7.34 Hz, H6); δ 1.79–1.87 (m, 1H, H7); 1577 cm−1 (CvN). ESI-MS m/z 342 [M + Na + MeOH]2+. µeff
:
3
δ 1.59–1.74 (m, 5H, H8,9,10); δ 1.13–1.22 (m, 3H, H9′,10′); 4.15µB. % Found (Calc.) for [C22H22Cl4N6Ni2·0.5 CH2Cl2]:
δ 0.92–1.03 (m, 2H, H8′). 13C{1H} (CDCl3, 75.38 MHz,): δ 158.05 C: 40.23 (40.21); H: 3.41 (3.45); N: 12.42 (12.50).
(C5); δ 148.17 (C1); 136.95 (C3); δ 116.73 (C2); δ 114.86 (C4);
Synthesis of [Ni(µ-Cl){2,2′-dipyridyl-N-benzylamine}Cl]2, 1b.
δ 54.18 (C6); δ 37.24 (C7); δ 30.98 (C8,8′); δ 26.54 (C10); δ 26.00 Complex 1b prepared according to the same synthetic pro-
(C9,9′). ESI-MS: m/z 268.2 [M + H]+. % Found (% calc.) for cedure as outlined for complex 1a, with 2,2′-dipyridyl-N-ben-
C17H21N3: C: 76.01 (76.37); H: 7.80 (7.92); N: 15.38 (15.72).
zylamine employed as ligand. Yield: 272 mg, 90%. FT-IR (ATR,
Synthesis of 2,2′-dipyridyl-N-neopentylamine (d). The same neat, ν): 1597, 1578 cm−1 (CvN). ESI-MS m/z 418 [M + Na +
synthetic procedure as outlined above ligand a was employed MeOH]2+. µeff: 3.89µB. % Found (Calc.) for [C34H30Cl4N6Ni2·0.2
for the synthesis of d, using neopentyl iodide as reagent. The CH2Cl2]: C: 51.82 (51.85); H: 4.33 (4.39); N: 10.75 (10.78).
product was isolated as a colourless oil after purification by
Synthesis of [Ni(µ-Cl){2,2′-dipyridyl-N-methylcyclohexyl-
flash chromatography (EtOAc–hexane 1 : 4). Yield: 823 mg, amine}Cl]2, 1c. Complex 1c prepared according to the same
88%. FT-IR (ATR, neat, ν): 1581 and 1559 cm−1
.
1H NMR synthetic procedure as outlined for complex 1a, with 2,2′-
3
(CDCl3, 300 MHz): δ 8.31–8.34 (dd, 2H, JH–H 7.78 Hz, H1); dipyridyl-N-methylcyclohexylamine employed as ligand. Yield:
δ 7.47–7.53 (m, 2H, H3); δ 7.03–7.06 (dt, 2H, 3JH–H 8.36 Hz, H4); 241 mg, 81%. FT-IR (ATR, neat, ν): 1600, 1577 cm−1 (CvN).
9898 | Dalton Trans., 2014, 43, 9892–9900
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
ESI-MS m/z 424 [M + Na + MeOH]2+. µeff: 4.01µB. % Found A liquid sample was filtered through a syringe filter and ana-
(Calc.) for [C34H42Cl4N6Ni2·0.6 CH2Cl2]: C: 48.45 (48.95); H: lyzed by GC-FID employing p-xylene as internal standard,
4.83 (5.14); N: 10.11 (9.88).
taking care to maintain the temperature below −20 °C to mini-
Synthesis of [Ni(µ-Cl){2,2′-dipyridyl-N-neopentylamine}Cl]2, mize the loss of volatile reaction products. The observed oligo-
1d. Complex 1d prepared according to the same synthetic pro- mers were quantified against calibrated standards. Quenching
cedure as outlined for complex 1a, with 2,2′-dipyridyl-N-neo- the reaction mixture did not precipitate any polymers and no
pentylamine employed as ligand. Yield: 258 mg, 74%. FT-IR long-chain oligomers were observed after work-up.
(ATR, neat, ν): 1600, 1581 cm−1 (CvN). ESI-MS m/z 398
[M + Na + MeOH]2+. µeff: 4.32µB. % Found (Calc.) for
[C34H42Cl4N6Ni2·0.3 CH2Cl2]: C: 45.71 (45.86); H: 4.71 (4.71);
N: 11.24 (11.32).
Synthesis of [Ni(µ-Cl){6,6′-dimethyl-2,2′-dipyridyl-N-methyl-
References
amine}Cl]2, 1e. Complex 1e prepared according to the same
synthetic procedure as outlined for complex 1a, with 6,6′-
dimethyl-2,2′-dipyridyl-N-methylamine employed as ligand.
Yield: 196 mg, 53%. FT-IR (ATR, neat, ν): 1600, 15 651 cm−1
(CvN). ESI-MS m/z 370 [M + Na + MeOH]2+. µeff: 4.47µB. %
Found (Calc.) for C26H30Cl4Ni6Ni2: C: 45.49 (45.54); H: 3.98
(4.41); N: 12.06 (12.06).
1 (a) D. D. Devore, F. J. Timmers, D. L. Hasha, R. K. Rosen,
T. J. Marks, P. A. Deck and C. L. Stern, Organometallics,
1995, 14, 3132–3134; (b) H. G. Alt, K. Föttinger and
W. Milius, J. Organomet. Chem., 1999, 572, 21–30;
(c) H. Sinn and W. Kaminsky, in Advances in Organometallic
Chemistry, ed. F. G. A. Stone and R. West, Academic Press,
1980, vol. 18, pp. 99–149.
2 (a) K. A. Frazier, R. D. Froese, Y. He, J. Klosin,
C. N. Theriault, P. C. Vosejpka, Z. Zhou and K. A. Abboud,
Organometallics, 2011, 30, 3318–3329; (b) L. Li, M. V. Metz,
H. Li, M.-C. Chen, T. J. Marks, L. Liable-Sands and
A. L. Rheingold, J. Am. Chem. Soc., 2002, 124, 12725–12741;
(c) M. Delferro and T. J. Marks, Chem. Rev., 2011, 111,
2450–2485.
3 (a) S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev.,
2000, 100, 1169–1204; (b) C. Wang, S. Friedrich,
T. R. Younkin, R. T. Li, R. H. Grubbs, D. A. Bansleben and
M. W. Day, Organometallics, 1998, 17, 3149–3151;
(c) T. R. Younkin, E. F. Connor, I. H. Jason, S. K. Friedrich,
R. H. Grubbs and D. A. Bansleben, Science, 2000, 287, 460–
462; (d) V. C. Gibson and S. K. Spitzmesser, Chem. Rev.,
2002, 103, 283–316.
Isolation of [6-methylpyridinium-6′-methyl-N-methylpyridin-
2-amine]2 [Ni(Cl)4]2−
+
A solution of complex 1e (30 mg, 0.043 mmol) was dissolved in
dichloromethane (0.5 ml). The pink-red solution was layered
with pentane and stored at 5 °C. The formation of a yellow pre-
cipitate was observed, with concomitant formation of blue
crystals. The yellow precipitate was analysed by FT-IR, spectral
features was consistent with NiCl2. The blue crystals were iso-
lated and characterised by X-ray crystallography.
X-Ray crystal structure determination
Single crystals of complexes 1a·2MeOH and 1e-A were
mounted on a nylon loop and centred in a stream of cold
nitrogen at 100(2) K. Crystal evaluation and data collection
were performed on a Bruker-Nonius SMART Apex II CCD diffr-
actometer with Mo Kα radiation (λ = 0.71073 Å). Data collec-
tion, reduction and refinement were performed using SAINT27
and SADABS,28 which forms part of the APEX II software
package. The structures were solved by direct methods and
refined by full-matrix least-squares on F2 using SHELX-9729
within the X-Seed graphic user interface.30 All non-hydrogen
atoms were refined anisotropically and all hydrogen atoms
were placed using calculated positions and riding models.
4 (a) S. O. Ojwach, I. A. Guzei, L. L. Benade, S. F. Mapolie and
J. Darkwa, Organometallics, 2009, 28, 2127; (b) W. Keim,
Angew. Chem., Int. Ed. Engl., 1990, 29, 235–244.
5 (a) L. K. Johnson, C. M. Killian and M. Brookhart, J. Am.
Chem. Soc., 1995, 117, 6414–6415; (b) F. C. Rix and
M. Brookhart, J. Am. Chem. Soc., 1995, 117, 1137–1138;
(c) F. C. Rix, M. Brookhart and P. S. White, J. Am. Chem.
Soc., 1996, 118, 4746–4764; (d) D. J. Tempel and
M. Brookhart, Organometallics, 1998, 17, 2290–2296;
(e) S. Mecking, L. K. Johnson, L. Wang and M. Brookhart,
J. Am. Chem. Soc., 1998, 120, 888–899; (f) D. J. Tempel,
L. K. Johnson, R. L. Huff, P. S. White and M. Brookhart,
J. Am. Chem. Soc., 2000, 122, 6686–6700; (g) L. H. Shultz,
D. J. Tempel and M. Brookhart, J. Am. Chem. Soc., 2001,
123, 11539–11555; (h) T. K. Woo, P. M. Margl, P. E. Blöchl
and T. Ziegler, J. Phys. Chem. B, 1997, 101, 7877–7880;
(i) A. Michalak and T. Ziegler, J. Am. Chem. Soc., 2001, 123,
12266–12278; ( j) M. J. Szabo, N. M. Galea, A. Michalak,
S.-Y. Yang, L. F. Groux, W. E. Piers and T. Ziegler, J. Am.
Chem. Soc., 2005, 127, 14692–14703; (k) S.-Y. Yang,
M. J. Szabo, A. Michalak, T. Weiss, W. E. Piers, R. F. Jordan
and T. Ziegler, Organometallics, 2005, 24, 1242–1251;
Procedure for preparative-scale ethylene oligomerisation
In a glovebox under a nitrogen atmosphere, a 250 ml Parr
high-pressure autoclave was charged with the required amount
of solvent and co-catalyst, and was sealed prior to being
attached to the ethylene feed. The reactor was brought to
temperature at which point a dispersion of the pre-catalyst in
toluene (total volume: 50 ml) was added via syringe under
positive ethylene pressure. The ethylene feed was maintained
at the required pressure throughout the catalytic run, with the
volume of ethylene consumed monitored throughout the cata-
lytic run. After the allotted time, the reactor was cooled to
−78 °C and the reaction mixture quenched with MeOH (5 ml).
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 9892–9900 | 9899

View Article Online
Paper
Dalton Transactions
(l) A. Haras, A. Michalak, B. Rieger and T. Ziegler, Organo- 16 (a) J. Peng and Y. Kishi, Org. Lett., 2011, 14, 86–89; (b) J. Yu,
metallics, 2006, 25, 946–953.
X. Hu, Y. Zeng, L. Zhang, C. Ni, X. Hao and W.-H. Sun, New
J. Chem., 2011, 35, 178–183; (c) T. V. Laine, M. Klinga and
M. Leskelä, Eur. J. Inorg. Chem., 1999, 1999, 959–964.
6 D. P. Gates, S. A. Svejda, E. Oñate, C. M. Killian,
L. K. Johnson, P. S. White and M. Brookhart, Macro-
molecules, 2000, 33, 2320–2334.
7 (a) S. A. Svejda, L. K. Johnson and M. Brookhart, J. Am.
Chem. Soc., 1999, 121, 10634–10635; (b) J. C. Jenkins and
M. Brookhart, J. Am. Chem. Soc., 2004, 126, 5827–5842;
(c) L. Deng, P. Margl and T. Ziegler, J. Am. Chem. Soc., 1997,
119, 1094–1100; (d) D. G. Musaev, R. D. J. Froese,
M. Svensson and K. Morokuma, J. Am. Chem. Soc., 1997,
119, 367–374.
17 (a) W.-H. Sun, S. Song, B. Li, C. Redshaw, X. Hao, Y.-S. Li
and F. Wang, Dalton Trans., 2012, 41, 11999–12010;
(b) L. Zhao, V. Niel, L. K. Thompson, Z. Xu, V. A. Milway,
R. G. Harvey, D. O. Miller, C. Wilson, M. Leech,
J. A. K. Howard and S. L. Heath, Dalton Trans., 2004, 1446–
1455; (c) R. Gao, M. Zhang, T. Liang, F. Wang and
W.-H. Sun, Organometallics, 2008, 27, 5641–5648.
18 L. Ortiz de la Tabla, I. Matas, P. Palma, E. Álvarez and
J. Cámpora, Organometallics, 2012, 31, 1006–1016.
8 (a) B. M. Boardman and G. C. Bazan, Acc. Chem. Res., 2009,
42, 1597–1606; (b) J. Flapper, H. Kooijman, M. Lutz, 19 (a) C. Tamuly, N. Barooah, A. S. Batsanov, R. Kataky and
A. L. Spek, P. W. N. M. van Leeuwen, C. J. Elsevier and
P. C. J. Kamer, Organometallics, 2009, 28, 3272–3281;
(c) S. Abraham, C.-S. Ha and I. Kim, Macromol. Rapid
Commun., 2006, 27, 1386–1392; (d) B. Blom, M. J. Overett,
R. Meijboom and J. R. Moss, Inorg. Chim. Acta, 2005, 358,
3491–3496; (e) R. D. Broene, M. Broookhart,
W. M. Lamanna and A. F. Volpe Jr., J. Am. Chem. Soc., 2005,
127, 17194–17195; (f) M. P. Conley, C. T. Burns and
R. F. Jordan, Organometallics, 2007, 26, 6750–6759;
J. B. Baruah, Inorg. Chem. Commun., 2005, 8, 689–691;
(b) X.-F. Shi, Z.-Y. Xing, L. Wu and W.-Q. Zhang, Inorg.
Chim. Acta, 2006, 359, 603–608; (c) L. Li, M. M. Turnbull,
C. P. Landee, J. Jornet, M. Deumal, J. J. Novoa and
J. L. Wikaira, Inorg. Chem., 2007, 46, 11254–11265;
(d) J. Kuhnert, I. Cisarova, M. Lamac and P. Stepnicka,
Dalton Trans., 2008, 2454–2464; (e) G. D. Potter, M. C. Baird
and S. P. C. Cole, J. Organomet. Chem., 2007, 692, 3508–
3518.
(g) M. D. Doherty, S. Trudeau, P. S. White, J. P. Morken and 20 (a) M. R. Bond and R. D. Willett, Acta Crystallogr., Sect. C:
M. Brookhart, Organometallics, 2007, 26, 1261–1269;
(h) S. P. Meneghetti, P. J. Lutz and J. Kress, Organometallics,
1999, 18, 2734–2737; (i) F. Speiser, P. Braunstein,
L. Saussine and R. Welter, Inorg. Chem., 2004, 43, 1649–
Cryst. Struct. Commun., 1993, 49, 861–865; (b) L. Cao,
U. Englert and Q. Li, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2008, 64, m377; (c) Z.-X. Du and J.-P. Qu, Acta Crys-
tallogr., Sect. E: Struct. Rep. Online, 2009, 65, m1656.
1658; ( j) A. H. D. P. S. Ulbrich, R. R. Campedelli, 21 C. Obuah, B. Omondi, K. Nozaki and J. Darkwa, J. Mol.
J. L. S. Milani, J. H. Z. d. Santos and O. d. L. Casagrande Catal. A: Chem., 2014, 382, 31–40.
Jr., Appl. Catal., A, 2013, 453, 280–286; (k) Y.-y. Wang, 22 M. D. Leatherman, S. A. Svejda, L. K. Johnson and
S.-a. Lin, F.-m. Zhu, H.-y. Gao and Q. Wu, Inorg. Chim. Acta,
2009, 362, 166–172.
9 S. Licciulli, I. Thapa, K. Albahily, I. Korobkov,
S. Gambarotta, R. Duchateau, R. Chevalier and K. Schuhen,
Angew. Chem., Int. Ed., 2010, 49, 9225–9228.
10 M. J. Rauterkus, S. Fakih, C. Mock, I. Puscasu and
B. Krebs, Inorg. Chim. Acta, 2003, 350, 355–365.
11 S. Fakih, W. C. Tung, D. Eierhoff, C. Mock and B. Krebs,
Z. Anorg. Allg. Chem., 2005, 631, 1397–1402.
M. Brookhart, J. Am. Chem. Soc., 2003, 125, 3068–3081.
23 P. Chavez, I. G. Rios, A. Kermagoret, R. Pattacini, A. Meli,
C. Bianchini, G. Giambastiani and P. Braunstein, Organo-
metallics, 2009, 28, 1776–1784.
24 (a) C. Zhang, W.-H. Sun and Z.-X. Wang, Eur. J. Inorg. Chem.,
2006, 4895; (b) M. Brookhart, F. C. Rix, J. M. DeSimone and
J. C. Barborak, J. Am. Chem. Soc., 1992, 114, 5894–5895;
(c) L. Deng, T. K. Woo, L. Cavallo, P. M. Margl and T. Ziegler,
J. Am. Chem. Soc., 1997, 119, 6177–6186.
12 (a) R. Malgas-Enus, S. F. Mapolie and G. S. Smith, J. Organo- 25 (a) B. A. Rodriguez, M. Delferro and T. J. Marks, Organo-
met. Chem., 2008, 693, 2279–2286; (b) R. Malgas-Enus, PhD
thesis, Stellenbosch University, 2010.
13 (a) R. Ares, M. López-Torres, A. Fernández, D. Vázquez-
García, M. T. Pereira, J. M. Vila, L. Naya and J. J. Fernández,
metallics, 2008, 27, 2166–2168; (b) H.-L. Mu, W.-P. Ye,
D.-P. Song and Y.-S. Li, Organometallics, 2010, 29, 6282–
6290; (c) D.-P. Song, J.-Q. Wu, W.-P. Ye, H.-L. Mu and
Y.-S. Li, Organometallics, 2010, 29, 2306–2314.
J. Organomet. Chem., 2007, 692, 4197–4208; (b) J.-P. Taquet, 26 L. G. L. Ward, Inorg. Synth., 1971, 13, 154–164.
O. Siri, P. Braunstein and R. Welter, Inorg. Chem., 2006, 45, 27 Bruker AXS Inc., Madison, WI, Version 6.45, 2003.
4668–4676.
28 R. H. Blessing, Acta Crystallogr., Sect. A: Fundam. Crystal-
logr., 1995, 51, 33–38.
29 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystal-
logr., 2008, 64, 112–122.
14 G. L. Miessler and D. A. Tarr, Inorganic Chemistry, Pearson
Prentice Hall, London, United Kingdom, 3rd edn, 2004.
15 M. Schär, D. Saurenz, F. Zimmer, I. Schädlich,
G. Wolmershäuser, S. Demeshko, F. Meyer, H. Sitzmann, 30 (a) L. J. Barbour, J. Supramol. Chem., 2001, 1, 189–191;
O. M. Heigl and F. H. Köhler, Organometallics, 2013, 32,
6298–6305.
(b) J. L. Atwood and L. J. Barbour, Cryst. Growth Des., 2003,
3, 3–8.
9900 | Dalton Trans., 2014, 43, 9892–9900
This journal is © The Royal Society of Chemistry 2014