Indenyl abstraction versus alkyl abstraction of [(Indenyl)ScR 2(thf)] by [Ph3C] [B(C6F5) 4]: Aspecific and syndiospecific styrene polymerization

Article abstract of DOI:10.1002/chem.200802220

A method has been demonstrated to study the indenyl abstraction and alkyl abstraction of [(indenyl)ScR₂(thf)] by [Ph₃C] [B(C ₆F₅)₄] through syndiospecific styerne polymerization. It was observed durin

Full text of DOI:10.1002/chem.200802220

DOI: 10.1002/chem.200802220
Indenyl Abstraction versus Alkyl Abstraction of [(Indenyl)ScR2ACTHNUTRGNEU(GN thf)] by
[Ph3C] [BACHTNUGTRENUNG(C6F5)4]: Aspecific and Syndiospecific Styrene Polymerization
Xin Xu,[a, b] Yaofeng Chen,*[a] and Jie Sun[a]
The metallocene complex [Cp2TiCl2] (Cp=cyclopenta-
dienyl) was investigated for olefin polymerization upon acti-
vation with AlR3 or AlR2Cl half a century ago, and showed
low catalytic activity.[1] Nineteen years later, Sinn, Kaminsky,
and co-workers found that the use of methylaluminoxane
(MAO) as the activator greatly enhanced the activity of
[Cp2MR2] (M=Ti and Zr) to olefin polymerization.[2] Subse-
quent mechanistic studies revealed that the active species in
Group IV metallocene/MAO systems are cationic metallo-
cene alkyls, which are generated through a reaction involv-
ing an alkyl abstraction of the neutral metallocene com-
plexes by MAO.
earth metal alkyl complexes could also be converted into
the cationic species through alkyl abstraction, and the cat-
ionic species generated generally show much higher activity
than the neutral ones.[6–10] For example, the [Cp’ScR2-
AHCTNUGTERN(GNUN thf)]/ACHTUNREGT[GNNUN Ph3C][BACTHNUGTREN(UNGN C6F5)4] (Cp’=substituted cyclopentadienyl)
systems exhibit good catalytic activities for syndiospecific
polymerization of styrene,[11] syndiospecific copolymeriza-
tion of styrene and ethylene (or isoprene),[11a,12] and alter-
nating copolymerization of ethylene and norborn
ducing some materials that have excellent properties. Re-
cently, we prepared a series of mono(indenyl)–Sc–dialkyl
complexes and studied their reactivity towards styrene poly-
merization with [Ph3C][B(C6F5)4] as the activator. The study
revealed an interesting observation that [Ph3C][B(C6F5)4]
abstract not only the alkyl ligand but also the p-bonded ind-
enyl ligand, and the resulting two types of cationic species
ene,[13] pro-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
An alternative route to access the cationic metallocene
alkyl species is by employing a well-defined strong Lewis
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
acid, such as BACHTUNGTRENNUNG(C6F5)3, to abstract the alkyl group of neutral
metallocene alkyl complexes.[3] However, in some cases, the
ACHTUNGTRENNUNG
counterions [R B
(C6F5)3]À form “tight” ion pairs with the
catalyze styrene polymerization to give syndiotactic poly-
styrene (sPS) and atactic PS (aPS), respectively. Herein we
describe these results.
À
highly electrophilic cations through R bridging and compete
with coordination of the monomer, which results in a de-
crease in catalytic activity, especially in a-olefin polymeriza-
The first ligand precursors that were tried for preparing
tion.[3a,4] To overcome this problem, [Ph3C][B
G
mono
(methyl)indene and 1,3-bis(isopropyl)indene.[14] However,
the alkane elimination reactions of these two compounds
with [Sc(CH2SiMe3)3A(thf)2] did not occur at room tempera-
A
complexes
were
1,3-bis-
contains a more weakly coordinating anion [B
U
ACHTUNGTRENNUNG
A
CHTUNGTRENNUNG
À
product Ph3C R, and the resulting “loose” ion pairing com-
ture, and raising the reaction temperature caused the gradu-
al decomposition of the Sc–trialkyl complexes, giving none
of the desired complexes. In comparison with alkyl substitu-
ents, the SiMe3 group is relatively electron withdrawing,[15]
and we hoped that this property of the SiMe3 substituent
would promote the alkane elimination reaction of the relat-
plexes [Cp2MR]+[B
G
for olefin polymerization.[3a,5] It was found that neutral rare-
[a] X. Xu, Prof. Dr. Y. Chen, J. Sun
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
ed ligand precursor with [Sc
the ligand precursor 1,3-bis(trimethylsilyl)indene was pre-
pared, and its reaction with [Sc(CH2SiMe3)3A(thf)2] was inves-
tigated. To our delight, the reaction worked and the desired
mono(indenyl)–Sc–dialkyl complex was produced. Subse-
ACHTUNTGRENGU(N CH2SiMe3)3CAHTUNGTREN(NUNG thf)2]. Therefore,
A
CHTUNGTRENNUNG
354 Fenglin Road, Shanghai 200032 (P.R. China)
Fax : (+86)2164166128
E-mail: yaofchen@mail.sioc.ac.cn
AHCTUNGTRENNUNG
[b] X. Xu
quently, seven other ligand precursors with the SiMe3 sub-
stituent were synthesized, and reactions of these ligand pre-
cursors with [ScACHTNUGTRENNU(G CH2SiMe3)3ACHTUNGTRENN(GUN thf)2] all gave the mono-
Laboratory of Advanced Materials and Institute of Fine Chemicals
East China University of Science and Technology
130 Meilong Road, Shanghai 200237 (P.R. China)
AHCTUNGTREG(NNNU indenyl)–Sc–dialkyl complexes (Scheme 1). These Sc com-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200802220.
plexes were characterized by NMR spectroscopy (1H, 13C)
846
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 846 – 850

COMMUNICATION
Scheme 1. Synthesis of the monoACHTNUTRGNE(UNG indenyl)–Sc–dialkyl complexes.
Figure 1. ORTEP view of 1; thermal ellipsoids set at the 30% probability
level, hydrogen atoms are omitted for clarity. Selected bond distances
À
À
À
À
[ꢂ] and angles [8]: Sc C1 2.608(3), Sc C2 2.549(3), Sc C3 2.493(3), Sc
and elemental analysis. Single crystals of 1, 4, 6, and 7 were
grown from solutions in hexane, and the solid-state struc-
tures were determined by X-ray diffraction.[16] The structure
of 1 is shown in Figure 1, whereas those of 4, 6, and 7 are
given in the Supporting Information. The structural data in-
dicate h5 hapticity of the indenyl ligands in all of the com-
plexes.
À
À
À
À
C4 2.538(3), Sc C5 2.615(3), Sc C21 2.191(3), Sc C25 2.221(3), Sc O
2.1616(19); C21–Sc–C25 106.10(11).
and 9). GPC traces of the sPS produced by 1 and 8 show
monomodal peaks, and the polymers are of high molecular
weight (240 ~450ꢁ103) and narrow polydispersity (PDIs=
1.37). The aPS generated by 2 is also of narrow monomodal
molecular weight distribution (PDI=1.72), but the molecu-
lar weight is only 3.9ꢁ103. On the other hand, GPC traces
display bimodal peaks for the polymers produced by 3–7, in
which the high molecular weight fractions are sPS, whereas
the low molecular weight fractions are the aPS. Further-
more, the molecular weights and polydispersities of the two
fractions are similar to those of the polymers produced by 1
(or 8) and 2, respectively, and the ratios of sPS to aPS are in
agreement with those revealed by the solvent extraction ex-
periments. These observations indicate that there are two
Upon activation with [Ph3C][B
ACHTNUGTRNE(NNUG C6F5)4], most of these
mono(indenyl)–Sc–dialkyl complexes showed good activities
ACHTUNGTRENNUNG
for styrene polymerization (Table 1),[17] and the activities are
in the order of 5 <6 ꢀ 3 ꢀ 7 <4 <2 <8 ꢀ 1. The activity
of 1 is up to 12066 kgPS/molSch (Table 1, entry 2), which is
comparable to those of the most active transition-metal sty-
rene polymerization catalysts.[11a,18] The [(C5Me4SiMe3)Sc-
ACHTUNGTRENNUNG(CH2SiMe3)2ACHTUNGTRENNUNG(thf)]/ACHTUNGTRENNUNG[Ph3C][BACHTNUGRTNE(NUGN C6F5)4] system has been report-
ed for the highly syndiospecific styrene polymerization.[11a]
Surprisingly, solvent extraction experiments and 13C NMR
spectroscopy indicated that mono
[Ph3C][B(C6F5)4] systems pro-
ACHTUNGTRNE(UNGN indenyl)–Sc–dialkyl/ACHTUGN-
T
ACHTUNGTRENNUNG
duced not only highly sPS, but
also aPS, or sPS and aPS mix-
tures. The microstructures of PS
are greatly influenced by inden-
yl ligands. Complexes 1 and 8,
in which both the 1 and 3 posi-
tions of the indenyl ligands are
substituted by bulky SiMe3
groups, produced highly sPS
(Table 1, entries 1, 2, and 10),
whereas 2, with the 1-SiMe3 in-
denyl ligand, gave aPS (Table 1,
entry 4). The other complexes
3–7 provided sPS and aPS mix-
tures, and among them the
complexes with methyl groups
at the 3 position of the indenyl
ligands, 4 and 5, have higher
syndiospecific selectivity than
those with H at the 3 position
of indenyl ligands, 3, 6, and 7
Table 1. Styrene polymerization catalyzed by mono
Entry Complex Yield
Activity[b] sPS[c]
[min] [%]
(C6F5)4] systems.[a]
ACHTUNGTREN(UNNG indenyl)–Sc–dialkyl/ACHTUNTRGEG[NNNU Ph3C][BACHTGUNTRENNUGN
[f]
T
aPS[d]
[%]
High Mn
fraction
Low Mn
Tm
[%]
fraction
[oC]
M
N
M
(103) PDI
nACHTUNGTRENNUNG
1
1
1
1
2
3
4
5
6
7
8
2
4
1
1
3
3
3
3
3
3
3
1
1
1
3
100
100
0
100
81
100
41
81
88
100
89
58
75
6033
12066
–
2011
1634
2011
811
1634
1778
6033
5367
3500
1511
13
>99
>99
–
<1
<1
–
247
448
–
1.37
1.37
–
–
–
–
–
–
–
271
270
–
2[g]
3[h]
4
0
100
83
12
20
63
–
–
3.9
1.72
–
5
6
7
8
17
88
80
37
20
>99
0
86
0
0
581
430
422
301
225
437
–
n.d.
–
–
1.51 4.4
1.46 3.7
1.40 5.6
1.27 4.6
1.29 4.2
1.37
–
n.d. n.d.
1.80 270
1.53 269
1.56 270
1.70 265
1.82 268
–
n.d.
n.d. n.d.
1.67
1.66
9
80
10
11
12
13[i]
14[j]
<1
100
14
100
100
–
n.d.
270
–
ScR3
9
–
–
3.4
6.4
–
–
30
42
[a] Polymerization conditions: catalyst (18 mmol), 268C, Sc complex/ACHTNURTGENNUG[Ph3C][BAHCUTGNTREN(NGUN C6F5)4] (1:1 mol/mol), monomer/
Sc complex (1000:1 mol/mol), toluene/monomer (7:1 v/v). [b] kgPS/molLnh. [c] Percentage of polymers that
are insoluble in 2-butanone at reflux. [d] Percentage of polymers that are soluble in 2-butanone at reflux.
[e] Determined by GPC relative to the polystyrene standards. [f] Differential scanning calorimetry (DSC) anal-
ysis of the polymers that are insoluble in 2-butanone at reflux. [g] Monomer/Sc complex (2000:1 mol/mol).
[h] Without [Ph3C][B
ACHTGNUENRTNU(G C6F5)4]. [i] [ScACHUTNGTNER(NUNG CH2SiMe3)3ACHTNUGTRENNUN(G thf)2]/AHTCGNUTERN[NNUG Ph3C][BACTHUNGTRNUEGN(C6F5)4] (1:2 mol/mol). [j] Monomer/Lu com-
(Table 1, entries 6 and 7 vs. 5, 8, plex (150:1 mol/mol).
Chem. Eur. J. 2009, 15, 846 – 850
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
847

Y. Chen et al.
types of active species involved in the polymerizations: one
for the syndiospecific polymerization and the other for the
aspecific polymerization. The predominant active species is
dependent on the ligands; the complexes with 1,3-substitut-
ed indenyl ligands have more tendency to form the active
species for syndiospecific polymerization than other com-
plexes. The formation of syndiotactic and atactic PS mix-
tures is common in organotitanium-complex-catalyzed sty-
rene polymerization, and one explanation for this is the co-
existence of several active species formed by different Ti ox-
idation states (2+, 3+, and 4+).[19] However, the Sc ion is
generally in the 3+ oxidation state and it is very difficult to
reduce. It is a generally held view that there is only one
type of active species, [Cp’ScR]+, generated from the
Scheme 2. The two types of reactions between mono
complexes and [Ph3C][B(C6F5)4].
ACHTUNGERTN(NUNG indenyl)–Sc–dialkyl
AHCTUNGTRENNUNG
[Cp’ScR2]/ACHTUNGTRENNUNG[Ph3C][BACHTUNGTRENNUNG(C6F5)4] systems through alkyl abstrac-
tion.
We began to investigate the underlying reasons for the
unusual styrene polymerization behavior mentioned above
N
N
ACHTNUGRTNE(NGNU C6F5)4] was tested for styrene polymeri-
by studying the reactions of monoACTHNUGTRNEUNG(indenyl)–Sc–dialkyl com-
1
plexes with [Ph3C][B
(C6F5)4]. The H NMR spectra indicat-
N
ACHTUNGTRENNUNG
ed that the addition of one equivalent of borate to 1 in C6D6
results in the rapid disappearance of 1 and the formation of
(Mn =3.9ꢁ103; PDI=1.72). Increasing the steric bulk
around the 3 position of the indenyl ligand can retard the in-
denyl abstraction process and subsequently benefit the alkyl
abstraction process. Therefore, reaction of 6 with [Ph3C][B-
the cationic mono
(SiMe3)2A(C9H5)Sc(CH2SiMe3)
SiMe3; a similar observation has been noted for the reaction
of [(C5Me4SiMe3)Sc(CH2SiMe3)2A(thf)] with [Ph3C][B-
(C6F5)4].[11a] On the other hand, the reaction of 2 with
[Ph3C][B(C6F5)4] in C6D6 is completely different, giving not
ACHTUNGTRENNUG
C
E
E
N
ACHTUNGTRENNUNG
R
ACHTUNGTRENNUNG
A
U
A
ACHTUNGTRENNUNG
R
catalyzes styrene polymerization to give a syndiotactic and
atactic PS mixture. The most efficient way to repress the in-
denyl abstraction process is by introducing a non-hydrogen
substitutent at the 3 position of the indenyl ligand, as can be
seen from compounds 4 and 5, in which the Me substituents
at the 3 positions of the indenyl ligands give predominantly
sPS mixtures, 1 and 8 that have greater steric bulk due to
the SiMe3 substituents, and hence, produce pure sPS.
ACHTUNGTRENNUNG
Ph3CCH2SiMe3 but 1-Ph3C-3-SiMe3-indene. To further iden-
tify this product, 1-Ph3C-3-SiMe3-indene was prepared by
treating 2 with [Ph3C][BACHTNUGTRNE(UGN C6F5)4] in toluene, and character-
ized by NMR (1H, 13C) spectroscopy and mass spectrometry.
Moreover, 1H NMR spectroscopic monitoring of the reac-
tion of 6 with [Ph3C][BACHTUNRGTENUNG(C6F5)4] in C6D6 showed the forma-
tion of Ph3CCH2SiMe3 (minor product) and 1-Ph3C-3-SiMe3-
4,7-(Me)2-indene (major product); the latter was also ob-
tained from the reaction in toluene and characterized by
NMR (1H, 13C) spectroscopy and mass spectrometry.
In summary, [Ph3C][B
lent hydride and alkyl abstraction properties, however, the
present study on mono(indenyl)–Sc–dialkyl/[Ph3C][B(C6F5)4]
systems has found that [Ph3C][B(C6F5)4] can abstract a p-
ACHTNUGRTEN(NGNU C6F5)4] is best known for its excel-
N
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
The above investigations clearly show two types of reac-
bonded indenyl ligand rather than a s-alkyl ligand. The ab-
straction pathway is influenced by the substituents on the in-
denyl ligands, and can be controlled by employing different
indenyl ligands. For the styrene polymerization, two abstrac-
tion pathways, alkyl abstraction and indenyl abstraction,
result in syndiospecific and aspecific styrene polymerization,
respectively, and different types of polystyrene were pro-
duced by using Sc–dialkyl complexes with different indenyl
ligands.
tions occurring between mono
ACHTUNGTNER(NUNG indenyl)–Sc–dialkyl com-
plexes and [Ph3C][B(C6F5)4]: alkyl and indenyl abstraction
AHCTUNGTRENNUNG
(Scheme 2), and the reaction type is dependent on the
nature of indenyl ligand. The [Ph3C]+ moiety is best known
for its excellent ability to abstract hydride and alkyl ligands,
and so abstraction of the more strongly held h5-indenyl ob-
served here is really unexpected. We believe that this repre-
sents the first example of [Ph3C]+ abstracting a Cp-type p
ligand rather than a s-alkyl ligand.[20] A mono
dialkyl complex [(1-SiMe3C9H6)Lu(CH2SiMe3)
also prepared. It reacted with [Ph3C][B(C6F5)4] to give only
the indenyl abstraction products. The 9/[Ph3C][B(C6F5)4]-cat-
ACHTUNGTRENNUNG
A
CHTUNGTRENNUNG
AHCTUNGTRENNUNG
Experimental Section
A
ACHTUNGTRENNUNG
alyzed styrene polymerization produced low molecular
weight aPS with a low activity of 13 kgPS/molLuh (Table 1,
entry 14).
Complex 1: 1,3-(SiMe3)2C9H6 (520 mg, 2.0 mmol) and [Sc
AHCTUNGTRENNUNG
ACHTNUGERTN(NUGN CH2SiMe3)3-
mixture was stirred at room temperature for one day, and then at 508C
for a further 8 h. The reaction mixture was filtered, and evaporation of
the resulting solution in vacuo gave a pale-yellow oil. Recrystallization of
the oily residue from hexane at À358C afforded 1 as pale-yellow crystals
(610 mg, 56%). M. p. 82–848C; 1H NMR (300 MHz, C6D6, 258C): d=
Indenyl abstraction results in the formation of [Sc-
A
2ACHTUNGTRENNUNG
(thf)n]+ species, which could be responsible for
AHCTNUGTERN(GNNU CH2SiMe3)3-
848
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Chem. Eur. J. 2009, 15, 846 – 850

Syndiospecific and Aspecific Styrene Polymerization
COMMUNICATION
7.73 (q, 2H; Ind4, Ind7), 7.63 (s, 1H; Ind2), 6.96 (q, 2H; Ind5, Ind6), 3.34
Angew. Chem. 2007, 119, 1941–1945; Angew. Chem. Int. Ed. 2007,
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(brs, 4H; THF), 1.08 (brs, 4H; THF), 0.48 (s, 18H; SiMe3), 0.27 (s, 18H;
SiMe3), 0.01 (d, 2J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
(H,H)=11.1 Hz, 2H; CH2SiMe3); 13C NMR (75 MHz, C6D6, 258C): d=
137.0, 136.6, 125.2, 122.0, 114.8 (s, 9C; Ind), 71.8 (s, 2C; THF), 45.5 (brs,
2C; CH2SiMe3), 24.6 (s, 2C; THF), 4.1(s, 6C; CH2SiMe3), 1.0 ppm (s, 6C;
SiMe3); elemental analysis calcd (%) for C27H53Si4OSc: C 58.85, H 9.70;
found: C 58.04, H 9.39.
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A typical procedure for styrene polymerization: The mono
ACHTUNGTREN(NUNG indenyl)–di-
A
R
ACHTUNGTRENNUNG
were mixed in toluene (14 mL). The above reaction mixture was stirred
at room temperature for 2 min, and then styrene (1.81 g, 18 mmol) was
added under vigorous stirring. The reaction solution became very viscous
after several seconds, and the polymerization was quenched with acidic
methanol (2 mL). The reaction mixture was poured into methanol
(50 mL) to precipitate the polymer. The resulting polymer was isolated,
washed with methanol, and dried under vacuum for one day to give a
constant weight.
For full experimental details see the Supporting Information.
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Acknowledgements
This work was supported by the National Natural Science Foundation of
China, Chinese Academy of Sciences and Shanghai Municipal Commit-
tee of Science and Technology (No. 07JC14063). We thank Prof. Yunjie
Luo (Ningbo Institute of Technology, Zhejiang University) for the gener-
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Keywords: borates · cations · polymerization · rare-earth
metals · substituent effects
[14] There is only one report on monoACTHNUTRGENUGN(indenyl)rare-earth metal dialkyl
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[16] Crystal data for 1: C27H53OScSi4; Mr =551.01; monoclinic; space
group P21/n; a=10.1647(9), b=15.8130(15), c=22.023(2) ꢂ; b=
96.452(2)8; V=3517.5(6) ꢂ3; Z=4; MoKa
, l=0.71073 ꢂ; T=
293(2) K; R=0.0562; wR=0.1245 for 3894 unique reflections with
I>2s(I). Crystal data for 4: C25H47OScSi3; Mr =492.86; monoclinic;
space group P21/c; a=10.5487(12), b=15.8307(19), c=19.058(2) ꢂ;
b=92.224(2)8; V=3180.2(7) ꢂ3; Z=4; MoKa
, l=0.71073 ꢂ; T=
293(2) K; R=0.0762; wR=0.1941 for 2076 unique reflections with
I>2s(I). Crystal data for 6: C26H49OScSi3; Mr =506.88; monoclinic;
space
group
P21/c;
a=14.6377(8),
b=21.5594(12),
c=
20.7491(11) ꢂ; b=98.8010(10)8; V=6470.9(6) ꢂ3; Z=8; MoKa, l=
0.71073 ꢂ; T=293(2) K; R=0.0698; wR=0.1711 for 5840 unique re-
flections with I>2s(I). Crystal data for 7: C23H43OScSi3; Mr =
464.80; monoclinic; space group P21/c; a=10.7689(17), b=
18.381(3), c=15.372(3) ꢂ; b=104.151(3)8; V=2950.3(8) ꢂ3; Z=4;
MoKa, l=0.71073 ꢂ; T=293(2) K; R=0.0629; wR=0.1391 for 3012
unique reflections with I>2s(I). CCDC-701470, 701471, 701472,
and 701473 contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
[17] BACTHUNRGTNE(UGN C6F5)3 was tested as the activator for 1 and 2 and only very small
amount of polymer was produced in both cases.
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Chem. Eur. J. 2009, 15, 846 – 850
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
849

Y. Chen et al.
[20] a) To the best of our knowledge, only two examples of Cp-type
ligand abstraction by [Ph3C]+ have been reported; for the reaction
et al. reported examples of Cp-type ligand abstraction by AlR3 in
the bis(fluorenyl) and bisACHTNUTRGNE(NUG indenyl) divalent rare-earth metal com-
of [Ph3C][B
erates [Al
(C5Me4)2]+[B
Twamley, Organometallics 2006, 25, 5582–5586 and for the reaction
of [Ph3C][B(C6F5)4] with bis(indenyl) rare-earth metal amide [RE(2-
R-idenyl)2N(SiMe3)2] to provide [RE(2-R-indenyl)N(SiMe3)2][B-
G
E
plexes: H. Nakamura, Y. Nakayama, H. Yasuda, T. Maruo, N. Kane-
hisa, Y. Kai, Organometallics 2000, 19, 5392–5399; d) recently, Chen
et al. described an interesting observation of an electrophilic addi-
tion of [Ph3C]+, through the para-carbon of Ph, to silyl ketene
acetal rather than the hydride abstraction: Y. Zhang, E. Y.-X. Chen,
Macromolecules 2008, 41, 36–42.
R
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG(C6F5)4], see: O. Tardif, S. Kaita, Dalton Trans. 2008, 2531–2533;
b) Hou et al. reported examples of allyl abstraction by [Ph3C]+ in
mono(cyclopentadienyl)diallyl complexes: N. Yu, M. Nishiura, X.
Li, Z. Xi, Z. Hou, Chem. Asian J. 2008, 3, 1406–1414; c) Yasuda
Received: October 27, 2008
Published online: December 15, 2008
850
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 846 – 850