Oligomerization and regioselective hydrosilylation of styrenes catalyzed by cationic allyl nickel complexes bearing allylphosphine ligands

Article abstract of DOI:10.1039/b705579j

The complexes [Ni(η³-CH₂CHCH₂) Br(κ¹P-PR₂CH₂CHCH₂)] (R = Ph 1, ⁱPr 2) and [Ni(η³-CH₂C(R′)CH ₂)(κ¹P-PR₂CH₂CHCH ₂)₂][BAr′₄] (R′ = H, R = Ph 4a, R = ⁱPr 4b; R′ = CH₃, R = Ph 5a, R = ⁱPr 5b; Ar′ = 3,5-C₆H₃(CF₃)₂) have been prepared and characterized. The X-ray crystal structures of 1, 2 and 5b have been determined. 4a-b and 5a-b are catalyst precursors for the oligomerization of RC₆H₄CHCH₂ to oligostyrene (R = H) or oligo(4-methylstyrene) (R = CH₃) respectively, without the need of a co-catalyst such as methylalumoxane. The catalytic activities range from moderate to high. The oligomerization reactions are carried out in the temperature interval 25-40 °C in 1,2-dichloroethane, using an olefin/catalyst ratio equal to 200, yielding oligostyrenes with a high isotactic fraction content P_m, with M_n in the range 700-1900 Dalton, and polydispersities between 1.22 and 1.64. The cationic complexes 4a-b and 5a-b are also effective catalyst precursors for the hydrosilylation reactions of styrene or 4-methylstyrene with PhSiH₃ in 1,2-dichloroethane at 40 °C using an olefin/catalyst ratio equal to 100, leading selectively to RC₆H₄CH(SiH₂Ph)CH ₃ (R = H, CH₃) in 50-79% yield. The Royal Society of Chemistry.

Full text of DOI:10.1039/b705579j

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www.rsc.org/dalton | Dalton Transactions
Oligomerization and regioselective hydrosilylation of styrenes catalyzed by
cationic allyl nickel complexes bearing allylphosphine ligands†‡
Iqbal Hyder, Manuel Jime´nez-Tenorio, M. Carmen Puerta and Pedro Valerga*
Received 13th April 2007, Accepted 24th May 2007
First published as an Advance Article on the web 18th June 2007
DOI: 10.1039/b705579j
3
1
i
=
The complexes [Ni(g -CH2CHCH2)Br(j P-PR2CH2CH CH2)] (R = Ph 1, Pr 2) and
3
ꢀ
1
ꢀ
ꢀ
i
ꢀ
=
[Ni(g -CH2C(R )CH2)(j P-PR2CH2CH CH2)2][BAr 4] (R = H, R = Ph 4a, R = Pr 4b; R = CH3,
R = Ph 5a, R = Pr 5b; Arꢀ = 3,5-C6H3(CF3)2) have been prepared and characterized. The X-ray crystal
i
structures of 1, 2 and 5b have been determined. 4a–b and 5a–b are catalyst precursors for the
=
oligomerization of RC6H4CH CH2 to oligostyrene (R = H) or oligo(4-methylstyrene) (R = CH3)
respectively, without the need of a co-catalyst such as methylalumoxane. The catalytic activities range
from moderate to high. The oligomerization reactions are carried out in the temperature interval
25–40 ◦C in 1,2-dichloroethane, using an olefin/catalyst ratio equal to 200, yielding oligostyrenes with
a high isotactic fraction content Pm, with Mn in the range 700–1900 Dalton, and polydispersities
between 1.22 and 1.64. The cationic complexes 4a–b and 5a–b are also effective catalyst precursors for
the hydrosilylation reactions of styrene or 4-methylstyrene with PhSiH3 in 1,2-dichloroethane at 40 ◦C
using an olefin/catalyst ratio equal to 100, leading selectively to RC6H4CH(SiH2Ph)CH3 (R = H, CH3)
in 50–79% yield.
leads to the cationic bis(phosphine) species [Ni(Indenyl)(PPh3)2]+
Introduction
which are much less active.14,15 In order to circumvent this
deactivation pathway, a number of indenyl ligands functionalized
with different tethered, hemilabile moieties such as amines16–18 or
pendant olefins14 that can occupy the open site around the Ni
center. We have recently shown the ability of cationic allyl and
The role played by NiII complexes in the fields of catalytic
olefin oligomerization and polymerization is now very well
established.1–3 The catalytic properties of NiII complexes can
be modified and tuned by the use of suitable ligands.1 The a-
diimine systems developed by Brookhart and co-workers, used
in combination with methylalumoxane (MAO) are among the
most prominent examples of these catalyst.3 On the other hand,
SHOP (Shell higher olefin process)-type systems use hemilabile
ligands containing P and O donor atoms, being capable of
olefin oligomerization and polymerization without the need of an
aluminium-containing chemical as co-catalyst.4–7 Brookhart and
3
indenyl nickel complexes of the type [Ni(g -CH2C(R)CH2)(P)2]+
and [Ni(2-methylindenyl)(P)2]+ ((P)2 = (PMeiPr2)2, (PPhiPr2)2,
1,2-bis(diisopropylphosphino)ethane (dippe)) to serve as catalyst
precursors for the polymerization of styrene, leading to essentially
atactic polystyrenes of rather high molecular weights.19 It had been
3
previously shown that the addition of phosphine ligands to [Ni(g -
CH2C(R)CH2)(COD)]+ causes a dramatic increase in the catalytic
activity towards styrene polymerization, which leads to low
molecular weight polystyrenes with increased stereoregularities,
as inferred from the change in the isotactic content Pm from
0.65 up to 0.90 in some cases.20,21 This was attributed to the
generation of active cationic monophosphine and diphosphine
3
co-workers have reported that the cationic allyl complex [Ni(g -
CH2CHCH2)(PtBu2CH2COPh)]+ is active for the aluminium-free
polymerization of ethylene and copolymerization of ethylene and
methyl 10-undecenoate.8 This system takes advantage of the hemi-
labile character of the P,O-donor phenacyldi-tert-butylphosphine
for the stabilization of reactive 14-electron species. Coordina-
tively unsaturated cationic indenyl nickel complexes of the type
[Ni(Indenyl)(PPh3)]+ generated in situ have been shown to catalyze
the dimerization of ethylene,9 oligo- and polymerization of styrene
and norbornene10,11 as well as the hydrosilylation of several olefins
and ketones.12,13 Phosphine scavenging by [Ni(Indenyl)(PPh3)]+
3
species [Ni(g -CH2C(R)CH2)(P)n]+ (n = 1, 2) in situ. The addi-
3
tion of either SbPh3 or AsPh3 to [Ni(g -CH2C(R)CH2)(COD)]+
produces a similar effect, leading mainly to styrene oligomers.22 It
appears then that coordinatively unsaturated fragments of the type
3
[Ni(g -CH2C(R)CH2)(P)]+ or [Ni(indenyl)(P)]+ exhibit catalytic
properties superior to those of their bis(phosphine) analogues.
3
In an attempt to produce monophosphine complexes [Ni(g -
CH2C(R)CH2)(P)]+ amenable to isolation, yet maintaining most of
its catalytic abilities for olefin oligo/polymerization and hydrosily-
Departamento de Ciencia de Materiales e Ingenier´ıa Metalu´rgica y Qu´ımica
Inorga´nica, Facultad de Ciencias, Universidad de Ca´diz, 11510, Puerto Real,
Ca´diz, Spain. E-mail: pedro.valerga@uca.es; Fax: +34 956016288; Tel: +34
956016340
† CCDC reference numbers 638224–638227. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b705579j
‡ Electronic supplementary information (ESI) available: X-Ray crys-
tal structure of 3b; relevant GPC/SEC chromatograms. See DOI:
10.1039/b705579j
=
lation, we envisaged the use of allylphosphines PR2CH2CH CH2
(R = Ph, Pr) as co-ligands. Similarly to the approach used
i
by Zargarian and co-workers when they introduced a pendant
hemilabile olefin ligand in their [Ni(Indenyl)(PPh3)]+ system,14 the
=
use of PR2CH2CH CH2 might also provide useful insights into
the possible mechanisms of interaction between the olefin and the
3000 | Dalton Trans., 2007, 3000–3009
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3
[Ni(g -CH2C(R)CH2)(P)]+ fragment. Allyldiphenylphosphine is
known to act as a potentially P,C,C-hemilabile ligand in com-
plexes, by p-coordination of the double bond of the allyl group
to the metal. For instance, treatment of [CpRuCl(PPh3)(j1P-
=
PPh2CH2CH CH2)] with NaPF6 in EtOH leads to [CpRu(PPh3)-
3
23
=
(j P, C, C -PPh2CH2CH CH2)][PF6].
The homologous Cp*
3
=
derivative [Cp*Ru(PPh3)(j P, C, C -PPh2CH2CH CH2)][PF6] has
been prepared by Zn reduction of [{Cp*RuCl2}n] in acetonitrile in
=
the presence of PPh2CH2CH CH2 and subsequent treatment with
NaPF6.24 Some complexes containing j P, C, C -PR2CH2CH CH2
3
=
(R = Ph, iPr) ligands have been structurally characterized by single
crystal X-ray diffraction.24,25
In this work we describe the preparation of neutral and cationic
allyl and 2-methylallyl nickel complexes bearing the potentially
i
=
hemilabile phosphine ligands PR2CH2CH CH2 (R = Pr, Ph).
Although the attempts to isolate [Ni(g -CH2C(R)CH2)(j3P, C, C -
PR2CH2CH CH2)] met little success, we have prepared
and characterized cationic bis(phosphine) derivatives [Ni(g -
CH2C(R)CH2)(j P-PR2CH2CH CH2)2] which have been shown
to be active catalyst precursors for the oligomerization of styrene
and 4-methylstyrene with a significant degree of stereoregularity,
as well as for the regioselective hydrosilylation reactions of these
olefins with PhSiH3.
3
+
=
3
Fig.
1
ORTEP drawing (50% thermal ellipsoids) of the com-
3
1
1
+
=
=
plex [Ni(g -CH2CHCH2)Br(j P-PPh2CH2CH CH2)] (1). Selected bond
lengths (A) and angles (◦) with estimated standard deviations in
˚
parentheses: Ni(1)–C(1) 1.999(3); Ni(1)–C(2) 1.999(3); Ni(1)–C(3)
2.066(3); Ni(1)–P(1) 2.1941(10); Ni(1)–Br(1) 2.3224(7); C(1)–C(2)
1.415(5); C(2)–C(3) 1.366(5); C(4)–C(5) 1.489(4); C(5)–C(6) 1.313(5);
Br(1)–Ni(1)–P(1) 97.77(2); C(1)–C(2)–C(3) 120.4(3).
Results and discussion
Preparation of the complexes
3
The neutral allyl derivatives [Ni(g -CH2CHCH2)Br(j1P-
PR2CH2CH CH2)] (R = Ph 1, iPr 2) were prepared by
=
reaction of [Ni(COD)2] with either allyl bromide or 3-bromo-
2-methylpropene and the corresponding phosphine in diethyl
ether, followed by recrystallisation from toluene–petroleum ether
(Chart 1).
Chart 1
Fig.
2 ORTEP drawing (50% thermal ellipsoids) of the com-
3
1
i
=
plex [Ni(g -CH2CHCH2)Br(j P-P Pr2CH2CH CH2)] (2). Selected bond
These complexes were isolated in the form of red crystalline
solids, very air-sensitive in solution, where they decompose readily.
Both 1 and 2 exhibit four very broad resonances in their 1H NMR
spectra attributable to the inequivalent syn- and anti- protons of
lengths (A) and angles (◦) with estimated standard deviations in
˚
parentheses: Ni(1)–C(1) 2.057(4); Ni(1)–C(2) 1.998(4); Ni(1)–C(3)
1.998(4); Ni(1)–P(1) 2.1924(11); Ni(1)–Br(1) 2.3324(8); C(1)–C(2)
1.386(5); C(2)–C(3) 1.389(6); C(4)–C(5) 1.496(5); C(5)–C(6) 1.321(5);
Br(1)–Ni(1)–P(1) 99.11(3); C(1)–C(2)–C(3) 118.8(4).
the g -allyl ligand, whereas the 13C{ H} NMR spectra show three
3
1
3
separate resonances for the carbon atoms of the g -allyl ligand.
The chemical shift and splitting pattern of the H and 13C{ H}
square-planar as expected for monomeric 16-electron g -allyl
1
1
3
NMR signals of the phosphine allyl substituent in 1 and 2 do not
complexes. The double bond of the allylphosphine ligands points
away from the metal, clearly indicating that there is no p-
interaction at all with the nickel atom, as was already inferred
from NMR spectroscopic data.
=
differ much from those corresponding to free PR2CH2CH CH2
(R = Ph, iPr). This suggests that there is no significant interaction
between the allylic double bond and the nickel atom. This has been
confirmed by the determination of their respective X-ray crystal
structures. ORTEP views of complexes 1 and 2 are respectively
shown in Fig. 1 and 2, together with the most relevant bond
distances and angles.
The sets of Ni–C, Ni–P and Ni–Br bond lengths for 1 and 2
are fully consistent with the data reported in the literature for re-
lated compounds, such as [Ni(g -CH2CHCH2)Br(PPh3)],26 [Ni(g -
3
3
CH2CHCHCH2Ph)Br(PMe3)],27 and the dimer [{NiBr(PiPr3)}2(l-
3
3
The crystal structures of complexes 1 and 2 consist of discrete
molecules. The co-ordination geometry around nickel is pseudo-
g ,g -(CH2CHCH2CH2)2].28 The bond lengths C(1)–C(2) and
C(2)–C(3) are not equal in the case of 1, but they are almost
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identical in the case of 2. The values are intermediate between
single and double bonds, and compare well with data in the
literature.26–28 The angles formed by the least squares planes
defined by the allyl ligands and the plane defined by the NiBrP
moieties are 66.4(3)◦ for 1 and 65.9(3)◦ for 2.
Attempts to isolate the homologous complexes of 1 and 2 bear-
3
3
ing a g -methylallyl ligand instead of g -allyl were unsuccessful.
Although the course of the reactions of [Ni(COD)2] with 2-methyl-
1-bromopropene and the allylphosphines seems to be the same as
3
for the preparation of 1 or 2, upon work-up no g -methylallyl
derivatives were isolated. Instead, dark red or purple crystalline
1
=
materials, identified as [NiBr2(j P-PR2CH2CH CH2)2] (R = Ph
i
3a, Pr 3b) were obtained. The X-ray crystal structure of 3b
as well as comments on the NMR spectral properties of these
complexes are supplied as part of the electronic supplementary
information (ESI‡). We had previously reported the preparation
of the related dibromo complexes [NiBr2(PRiPr2)2] (R = Me,
Ph). These compounds were recovered from the reaction mixtures
with Li(2-methylindenyl) during attempts made to prepare the
derivatives [Ni(2-methylindenyl)Br(PRiPr2)].19 We suggested that
presumably [Ni(2-methylindenyl)Br(PRiPr2)] are unstable and
undergo redistribution reactions, leading to the starting dibromo
complexes plus [Ni(2-methylindenyl)2]. It is likely that in the course
Chart 2
iPr 5b) were synthesized by following an analogous procedure,
replacing allyl bromide by 2-methyl-1-bromopropene. The X-ray
crystal structure of 5b was determined. An ORTEP view of the
complex cation in 5b is shown in Fig. 3.
3
of the preparation of the neutral g -methylallyl derivatives with
=
PR2CH2CH CH2 reductive coupling of the allyl moieties occurs
in the presence of the phosphine ligands, although this issue was
not investigated any further.
We carried out bromide abstraction reactions from 1 and 2 in
an attempt to prepare cationic derivatives in which the double
bond of the phosphine allyl substituent might fill the vacant
3
=
position left by bromide (i. e., j P, C, C -PR2CH2CH CH2). Upon
addition of NaBArꢀ4 to a fluorobenzene solution of either 1 or
2, a yellow solution and a finely divided black precipitate was
formed almost immediately. The black precipitate suggests the
reduction of NiII to Ni0. The work-up of the solutions led to
3
the isolation of the cationic allylbis(phosphine) complexes [Ni(g -
1
ꢀ
i
=
CH2CHCH2)(j P-PR2CH2CH CH2)2][BAr 4] (R = Ph 4a, Pr 5a).
Hence, the halide abstraction reaction takes place with partial
decomposition. Apparently, the monophosphine species generated
in situ upon bromide removal, either [Ni(g -CH2CHCH2)(j3P, C,
3
ꢀ
3
=
C-PR2CH2CH CH2)][BAr 4] or the even more reactive [Ni(g -
1
ꢀ
Fig.
3 ORTEP drawing (50% thermal ellipsoids) of the com-
=
CH2CHCH2)(j P-PR2CH2CH CH2)][BAr 4] have a very strong
tendency for adding an extra phosphine ligand. Rather than filling
the gap generated by bromide abstraction with the coordination
of the double bond of the phosphine allyl substituent as intended,
3
1
i
+
=
plex cation [Ni(g -CH2C(CH3)CH2)(j P-P Pr2CH2CH CH2)2] in 5b.
Hydrogen atoms have been omitted. Selected bond lengths (A)
˚
and angles (◦) with estimated standard deviations in parentheses:
Ni(1)–C(1) 2.049(4); Ni(1)–C(2) 2.040(4); Ni(1)–C(3) 2.047(4); Ni(1)–P(1)
2.2215(13); Ni(1)–P(2) 2.2386(13); C(1)–C(2) 1.399(6); C(2)–C(3)
1.396(7); C(2)–C(4) 1.499(7); C(11)–C(12) 1.489(6); C(12)–C(13) 1.310(7);
C(20)–C(21) 1.475(7); C(21)–C(22) 1.311(8); P(1)–Ni(1)–P(2) 110.61(5);
C(1)–C(2)–C(3) 116.2(5); torsion angle C(11)– P(1)– P(2)–C(20) 21.4(2).
=
these species readily scavenge PR2CH2CH CH2 from another
complex present in the mixture (most likely 1 or 2) furnishing
the corresponding bis(phosphine) derivatives accompanied by
decomposition products (Chart 2). The fate of the allyl ligands
during the decomposition process was not investigated in detail.
The yield of 4a and 5a from these reactions was below 50%
as expected, since the starting neutral monophosphine complexes
The complex cation in 5b has a pseudo-square-planar struc-
3
ture, very similar to those of the related complexes [Ni(g -
3
=
1 or 2 were the only source for PR2CH2CH CH2. These com-
CH2C(CH3)CH2)(PiPr2Ph)2]+,19 [Ni(g -CH2CHCH2)(PPh3)2]+,14
3
pounds were more conveniently prepared in higher yields by
and [Ni(g -C(CH3)2C(CH3)CH2)(PPh3)2]+.29 The Ni–C and Ni–
3
reaction of [{Ni(g -CH2CHCH2)(l-Br)}2] (generated in situ by
P separations suggest a fairly symmetrical arrangement of the
phosphines and the allyl ligand, consistent with the essentially
identical C(1)–C(2) and C(2)–C(3) bond lengths in the allyl
ligand. The Ni–P bond distances are slightly longer than those
observed for the neutral complexes 1 and 2, but shorter than in
reaction of [Ni(COD)2] with allyl bromide) with two equivalents
=
of PR2CH2CH CH2 in diethyl ether, followed by subsequent
treatment with NaBArꢀ4. The methylallyl derivatives [Ni(g -
CH2C(CH3)CH2)(j P-PR2CH2CH CH2)2][BAr 4] (R = Ph 4b,
3
1
ꢀ
=
3002 | Dalton Trans., 2007, 3000–3009
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3
[Ni(g -CH2C(CH3)CH2)(PiPr2Ph)2]+.19 The double bonds of the
best results were obtained using as solvent 1,2-dichloroethane
at a temperature of 40 ◦C, with a monomer/catalyst molar
ratio equal to 200 under a dinitrogen atmosphere. The amounts
of oligostyrene or oligo(4-methylstyrene) increase steadily with
reaction time. After 1 h at 40 ◦C the conversion of the olefin into
oligomers is almost complete in most cases. When 4b is used as
catalyst, the oligomerization reaction is very fast and exothermic,
causing the mixture to boil even though no external source of
heat is applied. In this case, the conversion is complete in far
less than 5 min. The oligomerization reactions of 4-methylstyrene
are in general slower, although when 4b is used as catalyst the
oligomerization is as fast and exothermic as in the case of the
reaction with styrene. With the sole exception of the reactions
catalyzed by 4b, the oligostyrene or oligo(4-methylstyrene) yields
drop rapidly when the temperature is lowered. Periods of time
of 5 h or longer are necessary to achieve significant conversions
when the reactions are performed at 25 ◦C. The individual yields
of oligostyrene or oligo(4-methylstyrene) obtained using each of
the catalysts after the appropriate reaction times and the resulting
turnover frequency (Nt)30 are listed in Table 1.
phosphine allyl substituents point away from the nickel atom, and
no close contact between nickel and any of these carbon atoms
has been detected. The dihedral angle between planes C(11)–
P(1)–P(2) and P(1)–P(2)–C(20) is 21.4(3)◦, which indicates an
i
=
almost eclipsed conformation of the P Pr2CH2CH CH2 ligands
with respect to each other, whereas the angle formed by the least
squares planes defined by the allyl ligand and the plane defined by
the NiP2 moiety is 67.6(3)◦.
Although we did not succeed in the isolation of
cationic complexes of the type [Ni(g -CH2C(R)CH2)(j3P, C, C -
PR 2CH2CH CH2)] containing one allylphosphine ligand acting
in a hemilabile fashion, the 16-electron cationic bis(phosphine)
complexes 4a–b and 5a–b have been shown to be active catalyst
precursors for the oligomerization of styrene and 4-methylstyrene,
as well as for the hydrosilylation reactions of these olefins with
PhSiH3.
3
ꢀ
+
=
Oligomerization reactions
Examination of the values of Nt indicate that the methylal-
lyl complexes are significantly more active that their counter-
parts bearing allyl. On the other hand, the systems containing
The cationic allyl and methylallyl derivatives 4a–b and 5a–b
are catalytic precursors for the oligomerization of styrene or 4-
methylstyrene in the absence of a co-catalyst such as MAO. The
Table 1 Oligomerization of styrene catalyzed by complexes 4a–b and 5a–b
Oligomerc
Distribution
Entrya
1
Catalyst
Olefin
T/◦C
t/h
0.5
Yield (%)
26
Nt /h−1
Pm
Mw
1008
342
218
985
345
223
17653
1059
305
191
937
343
217
1678
340
212
1472
331
223
27028
1660
1453
403
256
1263
410
Mn
808
336
215
799
340
220
9841
813
301
188
765
337
214
1128
336
208
1030
326
Mw/Mn
weightd (%)
b
4a
Styrene
40
103
nde
1.25
1.02
1.01
1.23
1.01
1.01
1.79
1.30
1.01
1.02
1.22
1.02
1.01
1.49
1.01
1.02
1.43
1.01
1.01
1.51
1.55
1.33
1.01
1.02
1.26
1.02
1.02
1.53
1.54
1.02
1.64
1.03
86
11
3
84
12
4
41
47
10
2
81
15
4
95
4
1
91
7
2
2
3
4a
4a
Styrene
Styrene
40
15
1
94
80
187
7
0.79
0.66
24
4
5
6
4b
5b
5b
Styrene
Styrene
Styrene
25
40
40
<0.08
100
70
>2486
139
0.78
0.85
0.84
1
1
95
189
221
7
8
4a
4b
Styrene
25
40
15
20
70
9
0.84
0.83
17903
1073
1089
398
250
999
403
247
1844
1344
293
1501
262
6
93
90
7
4-Methyl- styrene
100
10
3
9
5a
4-Methyl- styrene
25
<0.08
100
>2486
0.76
86
10
4
100
97
3
253
10
11
5b
5b
4-Methyl- styrene
4-Methyl- styrene
40
40
5
1
40
100
16
0.85
0.83
2814
2057
300
2456
270
199
12
4b
4-Methyl- styrene
25
22
100
9
0.85
98
2
a Experimental conditions: substrate (1 g), solvent:1,2-dichloroethane (1 mL), [olefin]/[Ni]= 200. b Nt = (moles of converted styrene or 4-
methylstyrene)/[(moles of catalyst) × time]. c Determined by GPC/SEC. d Estimated by area integration of the distribution peaks in the GPC/SEC
chromatogram. e nd = not determined.
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=
PPh2CH2CH CH2 are in general more active that those with
resonances corresponding to the ipso-carbon atoms of the phenyl
groups of polystyrene gives information relevant to the tacticity
of polystyrenes.19,20,21 The isotactic contents, Pm, calculated from
i
=
P Pr2CH2CH CH2, but the differences are not as remarkable as
those attributable to the presence of one methyl substituent on the
allyl ligand.
1
the analysis of the intensity distribution of the 13C{ H} NMR
The oligostyrenes obtained in these catalytic reactions were
characterized by GPC/SEC and their mass features, at the end of
the oligomerization reaction, are listed in Table 1. For the reactions
performed at 40 ◦C, and also for the reactions catalyzed by 4b, the
GPC traces indicate rather narrow molecular weight distributions,
which can be treated as multimodal: one main peak (80–100%)
corresponding to oligostyrene or oligo(4-methylstyrene), and two
small peaks (summing to less than 20%) attributable respectively
to the trimers and dimers of styrene or 4-methylstyrene. In a
few cases the amounts of trimer and dimer were negligible and
the molecular weight distributions were treated as unimodal.
The values of Mn range from 700 to 1900 Dalton for the main
peak of the distributions, with polydispersity indexes (Mw/Mn)
in the range 1.22–1.64. In the cases in which the reactions were
resonances corresponding to the ipso-carbon atoms of the phenyl
groups for the oligomers obtained in this work fall in the range
0.76 to 0.85 (with the exception of entry 3 in Table 1). It can
be concluded that the oligostyrenes resulting from the catalytic
reactions under study have high isotactic content, and hence any
possible mechanism for the oligomerization reaction must account
for the observed stereoregularity. In our case, both the Mn and
the Pm values are similar to those observed for the oligostyrenes
3
resulting from the reactions catalyzed by the system [Ni(g -
CH2C(CH3)CH2)(COD)]+/PR3 (PR3 = PPh3, P(OPh3), P(o-Tol)3,
PMe3, PnBu3, PCy3).20,21 For this system, an insertion mechanism
was proposed involving addition of styrene to a Ni–H bond to
3
yield a styryl complex, bound to the nickel center in an g -benzylic
fashion, which by multiple insertion and subsequent b-hydride
elimination gives rise to regioregular head-to-tail polystyrene
chains containing methyl and unsaturated end-groups (Scheme 1).
◦
performed at temperatures of 25 C or below (with exception of
those in which catalyst 4b was used), a higher molecular weight
distribution peak was observed in addition to those present in the
GPC traces of the oligomerization runs performed at 40 ◦C. This
peak accounts for the 41% of the distribution weight in the case of
the oligostyrene obtained in the reaction catalyzed by 4a at 15 ◦C,
and has a Mn value of 9841 Dalton and a polydispersity index of
1.79 (entry 3). A similar peak having a Mn value of 17903 Dalton
and a polydispersity index of 1.51 is present in the oligostyrene
◦
resulting from the reaction catalyzed by 5b at 25 C, but in this
case this peak represents only 6% of the total distribution weight
(entry 7). The observed values of Mn for the main peak in the
GPC traces depend essentially on the substituents present on
the phosphine ligand. Thus, the reactions catalyzed by complexes
=
containing PPh2CH2CH CH2 led always to oligomers with Mn
values lower than in the case of oligomers resulting from reactions
i
=
catalyzed by complexes bearing P Pr2CH2CH CH2. The values
of Mn of 799–765 are consistent with chains of 7–8 styrene units
(i.e. C14–C16) in the case of catalysis with 4a–b (entries 1–4),
whereas for the reactions catalyzed by complexes 5a–b (entries 5–
7) the values of Mn between 1073 and 1128 suggest longer chains,
of 9–10 styrene units (C18–C20). The oligomers derived from 4-
methylstyrene have slightly longer carbon chains than in the case
of oligostyrenes: between 8 and 10 monomer units for the reactions
catalyzed by 4a–b (entries 8,9), and between 11 and 16 for the
reactions catalyzed by 5a–b (entries 10–12). The values of Mn are
rather indifferent to the presence of either allyl or methylallyl in
the catalyst precursors.
The variation of Mn with the conversion into oligostyrene
suggests that the oligomerization processes hereby considered are
clearly not living. We have monitored the variation of Mn as a
function of the oligostyrene yield for the reaction catalyzed by 4a.
Mn increases initially with conversion to a value which, after that,
remains stable when the conversion increases. The values of Mn
measured for the oligomers obtained in the reactions catalyzed
by 5a–b at low conversion figures are essentially identical to those
measured at the end of the processes.
Scheme 1
Alternatively, Zargarian and co-workers have suggested a
Ni-initiated electrophilic route for the styrene polymerization
mediated by [Ni(1-L-Indenyl)(PPh3)]+ (L = CH2CH2CH CH2,
=
=
SiPh2CH2CH CH2, Scheme 2), involving the formation of a
polymer chain-centered carbocation.14
The polymer chain grows via nucleophilic attack of styrene,
until it undergoes b-elimination to give a Ni–H species and
a carbocation-terminated polymer chain. The latter continues
growing via an electrophilic mechanism (cationic polymerization)
leading to polystyrene with high molecular weight. The nickel
hydride could then initiate a different polymerization process via
an insertion mechanism similar to that outlined above, leading to
low molecular weight oligo- or polystyrenes.14
Given the similarities between the molecular weight distribu-
tions and the isotactic contents of the oligomers obtained in our
3
systems and those of the [Ni(g -CH2C(CH3)CH2)(COD)]+/PR3
The oligostyrenes obtained in the catalytic runs were also
system,20,21 it seems logical to assume that the mechanism in our
case is analogous to that shown in Scheme 1. However, at low
temperatures a second mechanism, competing with the insertion
mechanism could be at work, as inferred from the bimodal, higher
1
1
characterized by means of H and 13C{ H} NMR spectroscopy
(1,1,2,2-tetrachloroethane-d2, 120 ◦C). According to the literature,
1
the analysis of the intensity distribution of the 13C{ H} NMR
3004 | Dalton Trans., 2007, 3000–3009
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Table 2 Hydrosilylation reactions of styrene or 4-methylstyrene with
PhSiH3 catalyzed by complexes 4a–b and 5a–ba
Entry
Catalyst
Olefin
Yieldb (%)
1
2
3
4
5
6
7
8
4a
4b
5a
5b
4a
4b
5a
5b
Styrene
Styrene
Styrene
Styrene
4-Methylstyrene
4-Methylstyrene
4-Methylstyrene
4-Methylstyrene
74
47
79
68
50
40
60
70
a Experimental conditions: olefin (1 mmol), PhSiH3 (2 mmol), solvent:
1,2-dichloroethane (0.25 mL), temperature: 40 ◦C, [olefin]/[Ni] = 100.
b Calculated as: [mmol of RC6H4CH(SiH2Ph)CH3 obtained/mmol of
=
RC6H4CH CH2] × 100 (R = H, CH3).
Scheme 2
molecular weight distributions and the lower isotactic content
of the polymers obtained under these conditions (i.e. entry 3,
Table 1). This could be a cationic mechanism similar to that shown
in Scheme 2. In our previous report on styrene polymerization
by cationic allyl and 2-methylindenyl nickel phosphine complexes
we also pointed out that two mechanisms were operative, one of
them being presumably of the insertion type, but the mechanism
responsible for the bulk of the polystyrenes obtained during the
reactions was either cationic or even free-radical, accounting
for the observed high molecular weights and their low isotactic
contents (essentially atactic polystyrenes).19
been reported for the cationic bis(phosphine) complex [Ni(1-
Methylindenyl)(PPh3)2][BPh4],14 a result which is in sharp contrast
with the reactivity of our systems. Studies on the dehydrooligomer-
ization of PhSiH3 catalyzed by [Ni(1-Methylindenyl)(CH3)(PR3)]
(R = Ph, Cy, Me) have led to the proposal of a catalytic cycle
which involves the formation of nickel silyl and hydrido species
as intermediates.31 For the hydrosilylation of styrene a nickel
hydride species has also been invoked as the active intermediate
in these reactions. In the case of cationic species, the Ni–H
should be generated via the transfer of hydride from PhSiH3
to the highly electrophilic [Ni(1-Methylindenyl)(PR3)]+ fragment,
leaving a [PhSiH2]+ which might be trapped by free PR3 furnishing
[R3P-SiH2Ph]+. However, it was not possible to obtain direct
NMR spectroscopic evidence for the formation of a Ni–H bond,
although free phosphine was detected in the early stages of the
catalytic cyle.12,14
In order to gather some additional information on the possible
oligomerization mechanism, we performed an NMR experiment
in which we monitored the reaction of 4a with ca. 10 equivalents of
styrene in CD2Cl2 at 35 ◦C. Consumption of styrene and formation
1
of oligostyrene was observed in the H NMR, but there was no
decrease in the intensity of the Ni–allyl or phosphine resonances.
We have monitored by NMR spectroscopy the reaction of 4b
1
Consistent with this, the 31P{ H} NMR showed one singlet at the
◦
with ca. 10 equivalents of PhSiH3 in CD2Cl2 at 35 C first, and
position expected for 4a. These observations suggest that only
a small fraction of the catalyst precursor is initiated, followed
by rapid propagation and chain growth. This sort of behavior
has been also observed in ethylene polymerization catalyzed by
1
then with styrene (ca. 10 equivalents). Fig. 4 shows the 31P{ H}
NMR spectra at different stages of this process.
Shortly after the addition of PhSiH3, two sets of resonances
corresponding to AB spin systems (two doublets each set, JPP
=
3
[Ni(g -CH2CHCH2)(tBu2PCH2COPh)][BArꢀ4].8
19 Hz) begin to appear in the 31P{ H} NMR spectrum. After
10 min, the intensity of the doublets has increased at the expense of
the intensity of the singlet of 4b, and a new singlet begins to arise at
20.4 ppm. After 15 min, the intensities of the doublets decrease as
the intensity of the new singlet at 20.4 ppm increases. At this point,
the 1H NMR reveals the formation of the dimer (PhSiH2)2 (singlet
at 4.60 ppm) and the disappearance of the resonances attributable
to 4b, being replaced by rather uninformative complex multiplet
signals. No hydride resonances were present. When styrene was
added, the formation of PhCH(CH3)SiH2Ph was detected shortly
afterwards by 1H NMR spectroscopy, but no further changes
1
Hydrosilylation reactions
The cationic complexes 4a–b and 5a–b act as catalyst precursors
for the regioselective hydrosilylation reactions of styrene or 4-
methylstyrene with PhSiH3. These reactions have been carried
out using a 1% mol catalyst load in 1,2-dichloroethane at
40 ◦C. Under these conditions, the hydrosilylation products
isolated upon purification were either C6H5CH(CH3)SiH2C6H5
or CH3C6H4CH(CH3)SiH2C6H5, resulting from the reaction of
PhSiH3 with styrene or with 4-methylstyrene respectively. The
amounts of the b-isomers RC6H5CH2CH2SiH2C6H5 if present,
were absolutely negligible. The yields of isolated hydrosilylation
products after 5 h were in the range 50–79%. The corresponding
figures for each catalyst and olefin are listed in Table 2.
These results compare well in terms of activity and regios-
electivity with those reported by Zargarian and co-workers
using substituted indenyl nickel complexes as catalyst precursors,
although no activator (i.e. MAO, or NaBPh4) is needed in our
case.12,14 Furthermore, very low activity for hydrosilylation has
1
occur in the 31P{ H} NMR. These data clearly indicate that there
is no phosphine dissociation in our system under study, since
=
no signals attributable to free PPh2CH2CH CH2 were detected.
Furthermore, the observation of resonances corresponding to
AB spin systems upon addition of PhSiH3 indicate that the two
phosphorus atoms remain bonded to the metal, and that they
become inequivalent. The values of 19 Hz for the JPP coupling
constants are consistent with a cis-arrangement of the phosphorus
atoms, hence their inequivalence must arise from changes in the
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Toluene and fluorobenzene were of anhydrous quality and used as
received. All solvents were deoxygenated immediately before use.
The ligand diphenylallylphosphine was purchased from Aldrich,
whereas diisopropylallylphosphine was obtained by reaction of
PCliPr2 with one equivalent of allylmagnesium chloride in diethyl
ether. The complex [Ni(COD)2] was obtained according to the
literature.32 Styrene was purified by treatment with CaH2 fol-
lowed by trap-to-trap distillation. NMR spectra were taken on
Varian Inova 400 MHz or Varian Gemini 300 MHz equipment.
1
Chemical shifts are given in ppm from SiMe4 (1H and 13C{ H}),
1
or 85% H3PO4 (31P{ H}). Microanalysis was performed on an
elemental analyzer model LECO CHNS-932 at the Servicio
Central de Ciencia y Tecnolog´ıa, Universidad de Ca´diz. Molecular
weight distributions of oligomers were determined at 25 ◦C
by GPC/SEC using Merck-Lacrom equipment fitted with one
column Polystyragel PS40 (10 mm, 7.8 × 300 mm). The oligomer
samples were eluted with THF at a flow rate of 1 cm3 min−1. The
system was calibrated using a Merck polystyrene standard kit.
3
1
=
[Ni(g -CH2CHCH2)Br(j P-PPh2CH2CH CH2)] (1)
To a slurry of [Ni(COD)2] (0.54 g, 2 mmol) in diethyl ether (20 mL)
cooled in a liquid N2–ethanol bath, allyl bromide (173 lL, 2 mmol)
was added. The mixture was warmed to room temperature and
stirred for 1 h. During this time, the color of the mixture changed
from yellow to red. At this stage diphenylallylphosphine (0.44 mL,
2 mmol) was added. The mixture was stirred for 15 min. The color
of the solution became dark red. The solvent was removed in vacuo,
and the resulting solids were dissolved in toluene. The solution was
filtered, layered with petroleum ether and cooled to −20 ◦C. Red
crystals were obtained, which were separated from the mother
liquor by decantation and dried under an argon stream. Yield:
0.59 g, 74%. Anal. Calcd for C18H20BrNiP: C, 53.3; H, 4.97. Found:
C, 53.4; H, 4.99%. 1H NMR (400 MHz, CD2Cl2, 298 K): d 1.90,
2.85 (s br, 1 H each, CHsynHantiCHCHsynHanti), 2.95, 4.10 (s br, 1 H
Fig. 4 31P{ H} NMR spectra (CD2Cl2, 35 ◦C) of: (a) 4b; (b) 4b plus
1
PhSiH3 after 5 min, (c) 4b plus PhSiH3 after 10 min, (d) 4b plus PhSiH3
after 15 min, (e) 10 min after addition of styrene to (d).
each, CHsynHantiCHCHsynHanti), 3.24 (m, 2 H, Ph2PCH2CH CH2),
ligands in a trans-position with respect to these phosphorus atoms,
although the hydrosilylation of the double bond of the phosphine
allyl substituent can not be disregarded. After a brief period of
time, the phosphorus atoms become equivalent again, and the
new singlet resonance at 20.4 ppm in the 31P{ H} NMR might be
=
=
4.91, 5.01 (d br, 1 H each, Ph2PCH2CH CH2), 5.34 (m, 1 H,
CH2CHCH2), 5.87 (m, 1 H, Ph2PCH2CH = CH2), 7.43, 7.57 (m,
10 H, PC6H5); 31P{ H} NMR (161.89 MHz, CD2Cl2, 298 K):
1
1
d 20.26 (s); 13C{ H} NMR (100.57 MHz, CD2Cl2, 298 K): d
1
attributed to the catalytically active species for the hydrosilylation
process. Although these data are insufficient to support a detailed
mechanistic proposal, they point to an initial activation process of
the pre-catalyst by reaction with PhSiH3 which does not involve
phosphine dissociation, to yield the catalytically active species.
Since Si–H bond activation takes place during the process, the
participation of nickel silyl and hydrido species is assumed, as
suggested by Zargarian and co-workers,12,14,31 but little can be said
about the nature of such species. Further work might shed new
information on the catalytically active species, as well as expand
the scope of applicability of these hydrosilylation reactions.
=
33.5 (d, JCP = 23.5 Hz, Ph2PCH2CH CH2), 54.1, 72.8 (br,
CH2CHCH2), 110.2 (s, CH2CHCH2), 119.38 (d, JCP = 9.75 Hz,
=
Ph2PCH2CH = CH2), 130.9 (s, Ph2PCH2CH CH2), 128.6, 130.4,
133.1 (s, PC6H5).
3
1
i
=
[Ni(g -CH2CHCH2)Br(j P-P Pr2CH2CH CH2)] (2)
This compound was obtained by a procedure analogous for
i
=
that used for 1, using P Pr2CH2CH CH2 (0.3 mL, 2 mmol)
=
instead of PPh2CH2CH CH2. Yield: 0.61 g, 65%. Anal. Calcd
for C12H24BrNiP: C, 42.7; H, 7.16. Found: C, 42.4; H, 7.09%.
1H NMR (400 MHz, C6D6, 298 K) d 0.92, 1.06 (br, 12 H,
PCH(CH3)2), 1.32, 2.42 (br, 1 H each, CHsynHantiCHCHsynHanti),
Experimental
i
=
1.78 (m br, 2 H, PCH(CH3)2), 2.42 (br, 2 H, Pr2PCH2CH CH2),
All synthetic operations were performed under a dry dinitrogen
or argon atmosphere following conventional Schlenk techniques.
Tetrahydrofuran, diethyl ether and petroleum ether (boiling point
range 40–60 ◦C) were obtained oxygen- and water-free from
an Innovative Technology, Inc. solvent purification apparatus.
2.92, 4.19 (br, 1 H each, CHsynHantiCHCHsynHanti), 4.91, 4.95 (br,
i
=
2 H, Pr2PCH2CH CH2), 4.74 (br, 1 H, CH2CHCH2), 5.87 (br,
1 H, Pr2PCH2CH = CH2). 31P{ H} NMR (161.89 MHz, C6D6,
i
1
298 K) d 32.7 (s); 13C{ H} NMR (100.57 MHz, C6D6, 298 K): d
1
18.3, 19.34 (br, PCH(CH3)2), 24.4 (d, JCP = 21.2 Hz, PCH(CH3)2),
3006 | Dalton Trans., 2007, 3000–3009
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i
1
=
=
(d, JCP = 23.5 Hz, Ph2PCH2CH CH2), 71.7 (br, CH2CHCH2),
27.9 (d, JCP = 19.51 Hz, Pr2PCH2CH CH2), 47.2, 74.5 (br,
=
CH2CHCH2), 108.4 (s, CH2CHCH2), 117.5 (d, JCP = 9.8 Hz,
116.3 (s, CH2CHCH2), 121.7 (br, Ph2PCH2CH CH2), 128.7 (s,
Ph2PCH2CH CH2), 129.3, 131.8, 132.1 (C6H5).
i
i
=
=
Pr2PCH2CH = CH2), 133.5 (s, Pr2PCH2CH CH2).
Data for 4b. Yield: 2.16 g, 77%. Anal. Calcd for
C66H49BF24NiP2: C, 55.5; H, 3.45. Found: C, 55.6; H, 3.62%.
1H NMR (400 MHz, CD3COCD3, 298 K): d 1.94 (s, 3 H,
CH2C(CH3)CH2), 3.03 (br, 2 H, CHsynHantiC(CH3)CHsynHanti),
1
i
=
trans-[NiBr2(j P-PR2CH2CH CH2)2] (R = Ph 3a, Pr 3b)
To a slurry of anhydrous NiBr2 (0.22 g, 1 mmol) in ethanol
(20 mL), either PPh2CH2CH CH2 (0.44 mL, 2 mmol) or
=
=
3.11 (br, 4 H, Ph2PCH2CH CH2), 3.83 (br, 2 H, CHsynHanti
-
i
=
P Pr2CH2CH CH2 (0.30 mL, 2 mmol) was added. The color
C(CH3)CHsynHanti), 4.99, 5.07 (d, 2 H each, Ph2PCH2CH CH2),
=
immediately changed to dark red (3a) or dark purple (3b) with
precipitation of a crystalline material. The reaction mixture was
stirred at room temperature for 30 min. The resulting crystalline
precipitate was filtered off, washed with ethanol and petroleum
ether, and dried under vacuum.
=
5.72 (br, 1 H, Ph2PCH2CH CH2), 7.44, 7.51 (m, 20 H, C6H5);
31P{ H} NMR (161.89 MHz, CD3COCD3, 298 K): d 19.10 (s);
1
13C{ H} NMR (75.4 MHz, CD3COCD3, 298 K): d 22.9 (s,
1
=
CH2C(CH3)CH2), 34.0 (d, JCP = 25.6 Hz, Ph2PCH2CH CH2),
71.6 (br, CH2C(CH3)CH2), 119.8 (s, CH2C(CH3)CH2), 120.9 (d,
Data for 3a. Yield: 0.57 g, 85%. Anal. Calcd for
C30H30Br2NiP2: C, 53.7; H, 4.51. Found: C, 53.9; H, 4.69%.
1H NMR (400 MHz, CD2Cl2, 193 K) d 3.12 (br, 4 H,
=
=
JCP = 8.5 Hz, Ph2PCH2CH CH2), 130.1 (s, Ph2PCH2CH CH2),
129.6, 131.7, 133.5 (m, C6H5).
=
=
Ph2PCH2CH CH2), 4.95 (br, 4 H, Ph2PCH2CH CH2), 5.90 (br,
3
1
i
ꢀ
=
[Ni(g -CH2C(R)CH2)(j P-P Pr2CH2CH CH2)2][BAr 4] (R = H
1
2 H, Ph2PCH2CH = CH2), 7.60 (br, 20 H, C6H5); 31P{ H} NMR
5a, R = Me 5b)
(161.89 MHz, CD2Cl2, 193 K): d 6.48 (s); 13C{ H} NMR not
1
recorded.
These compounds were prepared by a identical procedure to that
for 4a–b, using P Pr2CH2CH CH2 (0.30 mL, 2 mmol) instead of
PPh2CH2CH CH2.
i
=
Data for 3b. Yield: 0.49 g, 92%. Anal. Calcd for
C18H38Br2NiP2: C, 40.4; H, 7.17. Found: C, 40.6; H, 7.34%. H
=
1
NMR (400 MHz, C6D6, 298 K): d 1.19 (d, JHH = 6.8 Hz, 6 H,
Data for 5a. Yield: 1.83 g, 73%. Anal. Calcd for
C53H55BF24NiP2: C, 49.8; H, 4.33. Found: C, 49.9; H, 4.51%. H
NMR (400 MHz, CD2Cl2, 298 K): d 1.22 (m, 24 H, PCH(CH3)2),
1
PCH(CH3)2), 1.56 (d, JHH = 7.2 Hz, 6 H, PCH(CH3)2), 2.72 (m,
=
4 H, PCH(CH3)2), 2.64 (d, 4 H, Ph2PCH2CH CH2), 4.99, 5.03
i
i
=
(d, 2 H each, Pr2PCH2CH CH2), 6.42 (m, 2 H, Pr2PCH2CH =
2.25 (m, 4 H, PCH(CH3)2), 2.45 (d, JHH = 13.2 Hz, 2 H,
CH2); 31P{ H} NMR (161.89 MHz, CD3COCD3, 213 K): d
CHsynHantiCHCHsynHanti), 2.76 (m, 4 H, Pr2PCH2CH CH2), 4.27
1
i
=
16.97 (s); 13C{ H} NMR (75.4 MHz, CD3COCD3, 213 K): d
(br, 2 H, CHsynHantiCHCHsynHanti), 5.26, 5.28 (d, 2 H each,
1
i
i
=
=
18.9, 20.3 (s, PCH(CH3)2), 26.8 (s, Pr2PCH2CH CH2), 117.2 (s,
Pr2PCH2CH CH2), 5.58 (br, 1 H, CH2CHCH2), 5.79 (br, 2 H,
i
i
1
Pr2PCH2CH CH2), 134.6 (s, Pr2PCH2CH CH2).
iPr2PCH2CH = CH2). 31P{ H} NMR (161.89 MHz, CD3COCD3,
=
=
298 K): d 32.2 (s); 13C{ H} NMR (75.4 MHz, CD2Cl2, 298 K):
1
3
1
ꢀ
=
d 18.8, 18.9, 19.9 (s, PCH(CH3)2), 26.8 (m, PCH(CH3)2),
[Ni(g -CH2C(R)CH2)(j P-PPh2CH2CH CH2)][BAr 4] (R = H
i
=
28.2 (m, Pr2PCH2CH CH2), 66.0 (br, CH2CHCH2), 114.6 (s,
4a, Me 4b)
i
=
CH2CHCH2), 121.2 (t, JCP = 4.6 Hz, Pr2PCH2CH CH2), 128.7
To a slurry of [Ni(COD)2] (0.54 g, 2 mmol) in diethyl ether
(20 mL) cooled in a liquid N2–ethanol bath, allyl bromide (for
4a, 173 lL) or 2-methyl-1-bromopropene (for 4b, 205 lL) was
added. The mixture was warmed to room temperature and stirred
for 1 h. During this time it changed from yellow to red. At this
stage NaBArꢀ4 (1.76 g, 2 mmol) was added, and the mixture was
stirred for 1 h. During this time the color changed from red to
orange. Diphenylallylphosphine (0.44 mL, 2 mmol) was added.
The mixture was stirred for 15 min, and then filtered through
Celite. The solvent was removed in vacuo, and the resulting sticky
solid was repeatedly triturated and washed with petroleum ether
until a yellow-orange powder was obtained. Recrystallisation from
dichloromethane–petroleum ether afforded in both cases yellow-
orange crystals, which were filtered off, washed with petroleum
ether and dried in vacuo.
i
=
(s, Pr2PCH2CH CH2).
Data for 5b. Yield: 1.95 g, 78%. Anal. Calcd for
C54H57BF24NiP2: C, 50.1; H, 4.44. Found: C, 50.4; H, 4.61%.
1H NMR (400 MHz, CD3COCD3, 298 K): d 1.06–1.41 (m,
24 H, PCH(CH3)2), 2.01 (s, 3 H, CH2C(CH3)CH2), 2.47 (m,
4 H, PCH(CH3)2), 2.78 (br, 2 H, CHsynHantiC(CH3)CHsynHanti),
i
=
2.99 (m, 4 H, Pr2PCH2CH CH2), 4.25 (d, JHH = 4.4 Hz,
2 H, CHsynHantiC(CH3)CHsynHanti), 5.23, 5.32 (d, 2 H each,
Pr2PCH2CH CH2), 6.01 (m, 2 H, Pr2PCH2CH CH2); 31P{ H}
i
i
1
=
=
NMR (161.89 MHz, CD3COCD3, 298 K): d 33.3 (s); 13C{ H}
1
NMR (75.4 MHz, CD2Cl2, 298 K): d 19.0, 19.2 (s, PCH(CH3)2),
20.2 (d, JCP = 6.1 Hz, PCH(CH3)2), 22.7 (s, CH2C(CH3)CH2),
i
=
26.7 (m, PCH(CH3)2), 28.6 (m, Pr2PCH2CH CH2), 66.2 (m,
CH2C(CH3)CH2), 118.0 (s, overlapping with one BArꢀ4 resonance,
i
=
CH2C(CH3)CH2), 121.1 (t, JCP = 4.6 Hz, Pr2PCH2CH CH2),
Data for 4a. Yield: 2 g, 72%. Anal. Calcd for C65H47BF24NiP2:
i
=
130.3 (t, JCP = 3.3 Hz, Pr2PCH2CH CH2).
C, 55.2; H, 3.35. Found: C, 55.0; H, 3.28%. 1H NMR
=
(400 MHz, CDCl3, 298 K) d 2.61 (m, 6 H, Ph2PCH2CH CH2 +
X-Ray structure determinations
CHsynHantiCHCHsynHanti), 3.89 (br, 2 H, CHsynHantiCHCHsynHanti),
=
4.83, 5.03 (d, 2 H each, Ph2PCH2CH CH2), 5.32 (m, 1 H,
Crystal data and experimental details are given in Table 3. X-Ray
diffraction data were collected on a Bruker SMART APEX 3-
circle diffractometer (graphite-monochromated MoKa radiation,
=
CH2CHCH2), 5.45 (m, 2 H, Ph2PCH2CH CH2), 7.10, 7.25, 7.37
(m, 20 H, C6H5); 31P{ H} NMR (161.89 MHz, CDCl3, 298 K):
1
d 16.48 (s); 13C{ H} NMR (100.57 MHz, CDCl3, 298 K): d 34.0
k = 0.71073 A) with CCD area detector at the Servicio Central
1
˚
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Table 3 Summary of crystallographic data for 1, 2, 3b and 5b
Compound
Formula
FW
1
2
3b
5b
C18H20BrNiP
405.93
C12H24BrNiP
337.90
C18H38Br2NiP2
534.95
C54H57P2NiBF24
1293.46
T/K
100
100
100
100
Crystal size/mm
Crystal system
Space group
0.07 × 0.16 × 0.29
Orthorrhombic
Pbca (no. 61)
11.461(2)
16.298(3)
18.029(4)
0.17 × 0.35 × 0.49
Monoclinic
P21/c (no. 14)
12.436(3)
7.4524(16)
15.775(4)
96.071(4)
1453.8(6)
4
0.30 × 0.36 × 0.40
Monoclinic
P21/n (no. 14)
8.2979(17)
15.238(3)
9.3390(19)
104.40(3)
1143.8(4)
2
0.18 × 0.24 × 0.37
Monoclinic
P21/c (no. 14)
12.799(3)
11.980(2)
37.938(8)
99.13(3)
5743(2)
4
1.496
5.08
˚
a/A
˚
b/A
˚
c/A
b/◦
3
˚
Volume/A
3367.7(11)
8
1.601
Z
qcalc/g cm−3
1.544
41.6
1.553
44.8
l(MoKa)/cm−1
36.1
F(000)
1648
696
548
2640
Max. and min. transmission factors
Theta range for data collection
Reflections collected
1.000 – 0.754
2.3 < h < 25.2
21191
1.000 – 0.667
2.6 < h < 25.0
5722
1.000 – 0.696
2.6 < h < 25.0
7892
1.000 – 0.851
1.6 < h < 25.0
35584
Unique reflections
No. of observed reflections (I > 2rI)
No. of parameters
2992 (Rint = 0.055)
2508 (Rint = 0.059)
2015 (Rint = 0.028)
10098 (Rint = 0.048)
2580
2143
1979
9238
250
140
110
768
Final R1, wR2 values (I > 2rI)
Final R1, wR2 values (all data)
Residual electron density peaks/e A
0.0341, 0.0772
0.0468, 0.0773
+0.90, −0.35
0.0345, 0.0783
0.0403, 0.0804
+0.86, −0.54
0.0265, 0.0588
0.0272, 0.0592
+0.44, −0.37
0.0770, 0.1540
0.0860, 0.1594
+0.81, −0.46
−3
˚
de Ciencia y Tecnolog´ıa de la Universidad de Ca´diz. Hemispheres
of the reciprocal space were measured by omega scan frames with
d(x) 0.30◦. Corrections for absorption and crystal decay (insignif-
icant) were applied by semi-empirical methods from equivalents
using the program SADABS.33 The structures were solved by direct
methods, completed by subsequent difference Fourier synthesis
and refined on F2 by full matrix least-squares procedures using
the program SHELXTL.34 The program ORTEP-335 was used for
plotting.
Hydrosilylation reactions
General procedure. A Schlenk tube was loaded with 2 mmol
PhSiH3, 1,2-dichloroethane (0.25 mL) and the corresponding
freshly-prepared catalyst (0.01 mol) under dinitrogen. Then,
1 mmol of either styrene or 4-methylstyrene was added. The system
was warmed up to 40 ◦C using a thermostatic bath. The mixture
was stirred for 5 h at this temperature. After this period of time,
a dark red solution was obtained. The volatiles were pumped
off. The resulting oily residue was dissolved in dichloromethane,
and passed through a silica column. Removal of the solvent
afforded the corresponding hydrosilylation products in the form
of yellowish oils. Their NMR properties were compared with data
in the literature.12,36
Oligomerization reactions
General procedure. A Schlenk tube was loaded with 10 mmol
of either styrene or 4-methylstyrene, 1,2-dichloroethane (1 mL)
and the corresponding freshly-prepared catalyst (0.05 mol) under
dinitrogen. In most cases, the system was warmed to 40 ◦C using a
thermostatic bath. In other instances the reactions were performed
at 25 ◦C. After the corresponding period of time, the deep red
reaction mixture was quenched by addition of methanol. The
volatiles were pumped off, and the residue treated with methanol
to yield a white precipitate, which was filtered off and dried in
vacuum. The oligostyrenes were dissolved in dichloromethane
(10 mL), and filtered through a silica gel plug. The silica gel
was washed with several small portions of dichloromethane
in order to remove all traces of oligomer. The solvent was
removed from the combined filtrate. The residue was treated
with methanol until a powder was obtained. The resulting pre-
cipitate of oligostyrene or oligo(4-methylstyrene) was filtered off,
washed with petroleum ether and dried in vacuum until constant
weight.
NMR data for C6H5CH(SiH2Ph)CH3:1H (400 MHz, CDCl3,
298 K): d 1.36 (d, 3JHH = 7.6 Hz, 3 H, CH(SiH2Ph)CH3), 2.53 (m,
1 H, CH(SiH2Ph)CH3), 4.24 (s br, 2 H, CH(SiH2Ph)CH3), 7.00–
4.50 (m, 10 H, C6H5). 13C{ H} (100.57 MHz, CDCl3, 298 K): d
1
16.6 (s, CH(SiH2Ph)CH3), 25.6 (s, CH(SiH2Ph)CH3), 122.3, 127.4,
128.1, 128.6, 130.0, 133.4, 135.9, 144.3 (s, C6H5).
NMR data for CH3C6H4CH(SiH2Ph)CH3: 1H (400 MHz,
CDCl3, 298 K): d 1.47 (d, 3JHH = 6.8 Hz, 3 H, CH(SiH2Ph)CH3),
2.33 (s, 3 H, CH3C6H4), 2.62 (m, 1 H, CH(SiH2Ph)CH3), 4.35
3
(d, JHH = 2.8 Hz, 2 H, CH(SiH2Ph)CH3), 7.00–7.50 (m, 9 H,
1
C6H4, C6H5). 13C{ H} (100.57 MHz, CDCl3, 298 K): d 16.6 (s,
CH(SiH2Ph)CH3), 20.9 (s, CH3C6H4), 24.8 (s, CH(SiH2Ph)CH3),
127.0, 127.8, 129.1, 129.7, 133.2, 135.6, 141.5 (s, C6H4, C6H5).
Acknowledgements
In all cases, the oligomerization reactions were contrasted
against a blank consisting of a reaction mixture identical to the
system under study, but with no catalyst added. The amounts of
oligomer obtained in the blank reaction were negligible in all cases.
We thank the Ministerio de Ciencia y Tecnolog´ıa (DGICYT,
Project CTQ2004–00776/BQU, Iqbal Hyder sabbatical leave
SB2004–0068) and Junta de Andaluc´ıa (PAI FQM188 and Project
of Excellence PAI05_FQM_00094) for financial support.
3008 | Dalton Trans., 2007, 3000–3009
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The Royal Society of Chemistry 2007
©

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18 L. F. Groux and D. Zargarian, Organometallics, 2003, 22, 3124–
3133.
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This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 3000–3009 | 3009
©