[Ni(η3-CH2C(CH3) CH2)(SbPh3)3][BAr′4]: An extremely active cationic allyl nickel-stibine catalyst for the oligomerization of styrene

Article abstract of DOI:10.1039/b302553e

The pseudotetrahedral, formally 5-coordinate complex [Ni(η³-CH₂C(CH₃)CH₂) (SbPh₃)₃][BAr′₄] (Ar′ = 3,5-C₆H₃(CF₃)₂) as well as the 4-coo

Full text of DOI:10.1039/b302553e

[Ni(h3-CH2C(CH3)CH2)(SbPh3)3][BArA4]: an extremely active cationic
allyl nickel–stibine catalyst for the oligomerization of styrene
Manuel Jiménez-Tenorio,a M. Carmen Puerta,a Isabel Salcedo,a Pedro Valerga,*a Sandra I. Costa,b
Pedro T. Gomesb and Kurt Mereiterc
a Departamento de Ciencia de Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de
Ciencias, Universidad de Cádiz, Apartado 40, 11510 Puerto Real, Cádiz, Spain.
E-mail: pedro.valerga@uca.es; Fax: 34 956 016288; Tel: 34 956 016340
b Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa,
Portugal; Fax: 351 218464457; Tel: 351 218419232
c
Institute of Chemical Technologies and Analytics (E171), Vienna University of Technology, Getreidemarkt
9, A-1060 Vienna, Austria; Fax: 43 1 58801 17199; Tel: 43 1 58801 17111
Received (in Cambridge, UK) 6th March 2003, Accepted 1st April 2003
First published as an Advance Article on the web 15th April 2003
The pseudotetrahedral, formally 5-coordinate complex
[Ni(h3-CH2C(CH3)CH2)(SbPh3)3][BArA4]
(ArA
extremely active catalytic precursors for the oligomerization of
styrene (eqn. 1).§
=
3,5-C6H3(CF3)2) as well as the 4-coordinate derivative
[Ni(h3-CH2C(CH3)CH2)(AsPh3)2][BArA4] act as extremely
efficient catalysts for the oligomerization of styrene.
(1)
3
Cationic allyl complexes of nickel of the type [(h -allyl)-
Ni(L)2]+ (L = N-, O- or P-donor group) have found consider-
able utility in recent years for olefin polymerisation reactions.1,2
3
4
The complex [(h -2-methylallyl)Ni(h -COD)]+ (COD
=
The highly exothermic reactions take place quantitatively in
less than one minute, reaching a turnover frequency larger than
2000 min21 (Table 1). If a co-ordinating solvent such as THF is
used, the turnover frequency decreases dramatically, although
the product distribution does not seems to be much affected. As
occurred with PPh3, addition of one equivalent of SbPh3 or
AsPh3 to 1 also causes an increase in the turnover frequency, but
never reaches the activity of neat 2 or 3 as catalysts. The
analysis of the product distribution indicates that ca. 80%
corresponds to the head-to-tail dimer when 2 is used as catalyst.
In the case of 3, the dimer accounts for ca. 50% of the total and
1,5-cyclooctadiene)3 is a very active homogeneous catalyst
precursor for the low molecular weight polymerisation of
styrene which does not require the use of either organoalumin-
ium or organoboron compounds as activators. Addition of
phosphine or phosphite ligands to this precursor causes in
general an increase in the catalytic activity giving rise to
regioregular head-to-tail low molecular weight polymers.2 The
most notorious case is met when one equivalent of PPh3 is
added, since the turnover frequency increases to a value above
1013 min21 for a highly exothermic reaction which leads to a
100% conversion of oligo(styrene) in less than one minute (Mn
= 740). This has been interpreted in terms of the in situ
3
higher oligomers are also present. When [(h -2-methylallyl)-
Ni(PPh3)2]+ is used as catalyst the mixture consists mainly of
heptamer and higher oligomers. Thus, a trend is observed in the
degree of oligomerization of styrene as a function of the co-
ligand used: passing from PPh3 to SbPh3 through AsPh3 causes
3
formation of the highly reactive 14-electron species [(h -
3
2-methylallyl)Ni(PPh3)]+, since the complex [(h -2-methy-
lallyl)Ni(PPh3)2]+ has been shown to be much less active
(turnover frequency 6.8 min21).2 Whereas many types of N-
3
and P-donor ligands in conjunction with [{(h -allyl)Ni(m-
Br)}2]/NaBArA4 have been screened for olefin polymerisation,1
Sb- or even As-donor ligands have never been evaluated for this
purpose, as far as we are aware. Compared to their phosphine
and arsine homologues, stibines in general are poorer donors,
that tend to promote higher coordination numbers in their
complexes and to reduce the tendency to dissociation,4 leading
to significant differences in reactivity.5
3
4
We have found that the reaction of [(h -2-methylallyl)Ni(h -
COD)][BArA4] (1) with an excess of SbPh3 in CH2Cl2 leads to
3
the novel 5-coordinate complex [(h -2-methylallyl)Ni(Sb-
Ph3)3][BArA4] (2).† At variance with this, the reaction of 1 with
3
AsPh3 yielded under the same conditions the 4-coordinate [(h -
3
2-methylallyl)Ni(AsPh3)2][BArA4] (3)† homologue of [(h -
2-methylallyl)Ni(PPh3)2]+, with no evidence for the formation
of a 5-coordinate species. The crystal structure of 2 (Fig. 1)‡
revealed a rare distorted tetrahedral geometry around the Ni
atom in the complex cation comprising the three Sb atoms and
the central carbon atom of the 2-methylallyl unit C(2). The other
only known case of a similar tetrahedral arrangement in an allyl-
nickel derivative has been found very recently for the phosphine
3
complex
[(h -allyl)Ni(triphos)][BPh4]
(triphos
=
Fig. 1 Selected bond lengths (Å) and angles (°) for 2: Ni–C(2) 2.013(5), Ni–
C(3) 2.076(5), Ni–C(1) 2.228(9), Ni–Sb(1) 2.5175(7), Ni–Sb(2) 2.5222(7),
Ni–Sb(3) 2.5650(7), C(1)–C(2) 1.355(9), C(2)–C(3) 1.403(7), C(2)–C(4)
1.466(10), Sb(1)–Ni–Sb(2) 100.35(3), Sb(1)–Ni–Sb(3) 110.24(2), Sb(2)–
Ni–Sb(3) 99.76(2), C(1)–C(2)–C(3) 116.1(6).
PPh(CH2CH2PPh2)2).6 The most remarkable feature is the
unsymmetrically bonded 2-methylallyl (Ni–C(1) 2.228(9) Å,
Ni–C(3) 2.076(5) Å), whereas Ni–Sb separations are consistent
with the scarce available data in the literature.7 Both 2 and 3 are
1168
CHEM. COMMUN., 2003, 1168–1169
This journal is © The Royal Society of Chemistry 2003

Table 1 Catalytic oligomerization of styrene
Product distribution (%)
Total
yield (%)
Entry
Catalyst
Conditionsa
Ntb/min21
Dimer
Trimer
Tetramer
Pentamer
Hexamer
1
2
3
4
5
6
7
2
2
3
3
CH2Cl2, 1 min
THF, 2 h
CH2Cl2, 1 min
THF, 2 h
CH2Cl2, 45 min
CH2Cl2, 2 h
CH2Cl2, 30 min
1965
10.7
2052
8.1
43.8
13.8
65.8
100
66
100
48
100
86
100
78.7
83.0
52.6
59.3
86.5
88.3
57.5
17.1
14.4
26.6
27.0
12.1
10.5
25.4
4.2
2.0
11.8
9.0
1.4
1.2
—
—
—
3.7
—
—
—
—
0.5
5.2
4.6
—
—
6.6
1 + SbPh3
1 + 2 SbPh3
1 + AsPh3
10.5
a Room temperature. Catalyst+styrene ratio 1+2000. b Turnover frequency.
anion showed orientation disorder and were refined as pairs of CF3 with
complementary orientations (dominant orientation with anisotropic dis-
placement parameters, subordinate orientation with isotropic displacement
parameters). CCDC 205627. See http://www.rsc.org/suppdata/cc/b3/
b302553e/ for crystallographic data in CIF or other electronic format.
§ General procedure: A Schlenk tube was loaded with 0.0005 equivalents of
the catalyst (2, 3, or 1 + SbPh3/1 + AsPh3 in the appropriate ratios) and
dichloromethane (2 mL). Then, 1 equivalent of neat styrene was added.
When 2 or 3 are used, a violent, exothermic reaction takes place in a few
seconds, causing the mixture to boil. After stirring for the corresponding
period of time (Table 1) at room temperature, MeOH (5 ml) was added and
the mixture exposed to air. The volatiles were removed in vacuo. Then, the
residue was extracted with dichloromethane and filtered through a plug of
silica gel. The silica gel was washed with several portions of dichloro-
methane, and the washings combined with the filtrate. Removal of the
solvent using a rotary evaporator first, and a vacuum pump afterwards
afforded an oily mixture of styrene oligomers in quantitative yield. The
ratios of the different oligomers present in the mixture were established by
gel permeation chromatography (GPC) and by integration of the relevant
signals in the 1H NMR spectrum.
an increase in the amount of dimer and a reduction in the
amount of higher oligomers. A similar product distribution, but
much lower activities, have been observed when the palladium
compound [(h -2-methylallyl)Pd(h -COD)][BF4] is used as
catalyst precursor.8 Complexes 2 and 3 are also active towards
the oligomerization of dienes and other olefins, and the system
is currently under study. From this work it becomes clear that
stibine ligands may play an important role in the future
development of highly active nickel catalysts for olefin
oligomerization.
We thank the M. C. Y. T. of Spain (DGICYT, Project
BQU2001-4046, Acciones Integradas HU2001-0020 and
HP2001-0064/CRUP E-30/02), Junta de Andalucía (FQM-
0188), and FCT, Portugal (Project POCTI/42015/QUI/2001 and
PRAXIS XXI/BD/19638/99) for financial support.
3
4
Notes and references
†
Selected spectroscopic data: All new compounds gave satisfactory
analytical data.
2: [NMR, CD2Cl2, d] 1H, 2.04 (s, 3H, CH2C(CH3)CH2), 2.94 (s, 2H,
CHsynHantiC(CH3)CHsynHanti), 4.31 (s, 2H, CHsynHantiC(CH3)CHsynHanti),
7.27, 7.28, 7.33, 7.44 (m, 45H, Sb(C6H5)3). 13C{1H} 23.94 (s,
CH2C(CH3)CH2), 65.21 (s, CH2C(CH3)CH2), 126.79 (s, CH2C(CH3)CH2),
129.84, 130.32, 136.09 (Sb(C6H5)3). 3: [NMR, CDCl3, d] 1H, 2.01 (s, 3H,
CH2C(CH3)CH2), 2.80 (s, 2H, CHsynHantiC(CH3)CHsynHanti), 3.69 (s, 2H,
CHsynHantiC(CH3)CHsynHanti), 7.20, 7.28, 7.40 (m, 30H, As(C6H5)3).
13C{1H} 23.13 (s, CH2C(CH3)CH2), 70.07 (s, CH2C(CH3)CH2), 125.92 (s,
CH2C(CH3)CH2), 129.64, 131.14, 132.66 (As(C6H5)3).
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‡ Crystal data for 2: C90H64BF24NiSb3, FW = 2036.18, triclinic, space
5 C. Grünwald, M. Laubender, J. Wolf and H. Werner, J. Chem. Soc.,
Dalton Trans., 1998, 833.
group P1 (no. 2), Dc = 1.553 g cm23, Z = 2, a = 14.075(3), b = 17.525(3),
¯
c = 18.742(3) Å, a = 93.20(1), b = 106.50(1), g = 98.89(1)°, V =
4355.1(14) Å3, T = 297(2) K, Bruker AXS SMART platform 3-circle
diffractometer with CCD area detector, l(MoKa) = 0.71073 Å, m = 1.228
mm21. Of 50300 reflections measured, 18811 were unique. Refinement on
F2 concluded with the values R1 = 0.0480 and wR2 = 0.0894 for 1144
parameters and 14082 data with I > 2sI. 7 of the 8 CF3 groups of the BArA4
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Organometallics, 2001, 20, 2579.
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