Synthesis and structural characterization of [H(OEt2)2]+[(C3H3N2){B(C6F5)3}2]- - a Br?nsted acid with an imidazole-derived 'non-coordinating' anion

Article abstract of DOI:10.1016/S0022-328X(01)01292-X

Lithium imidazolide, generated by NH deprotonation of imidazole with n-butyllithium, reacts with two molar equivalents of tris(pentafluorophenyl)borane with NB bond formation to yield the product Li⁺[(C₃H₃N₂){B(C₆F₅)₃}₂]^- (6a, isolated in >70% yield). The analogous reaction sequence starting from 4,5-dimethylimidazole gives the corresponding salt 6b. Its THF coordination product [Li(THF)₄]⁺[(C₃HMe₂N₂){B(C₆F₅)₃}₂]^- (6b·THF) was characterized by X-ray diffraction. Deprotonation of benzimidazole followed by the addition of two B(C₆F₅)₃ equivalents gave the corresponding benzimidazolide-based anion, isolated as the lithium compound 6c. The lithium salts 6 of the large 'non-nucleophilic' anion system [(C₃HR₂N₂){B(C₆F₅)₃}₂]^- were employed in the generation of Group 4 metallocene cations by salt metathesis. Treatment of 6a with HCl in diethyl ether afforded the product [H(OEt₂)₂]⁺[(C₃H₃N₂){B(C₆F₅)₃}₂]^- (9), that was also characterized by X-ray crystal structure analysis. The Br?nsted acid 9 was used to generate the Group 4 metallocene cation system [Cp₂Zr(CH₃)(OEt₂)]⁺ (11) (with [(C₃H₃N₂){B(C₆F₅)₃}₂]^- anion) starting from dimethylzirconocene.

Full text of DOI:10.1016/S0022-328X(01)01292-X

Journal of Organometallic Chemistry 641 (2002) 148–155
www.elsevier.com/locate/jorganchem
Synthesis and structural characterization of
[H(OEt2)2]+[(C3H3N2){B(C6F5)3}2]− — a Brønsted acid with an
imidazole-derived ‘non-coordinating’ anion
Dominik Vagedes, Gerhard Erker *, Roland Fro¨hlich 1
Organisch-Chemisches Institut der Uni6ersita¨t Mu¨nster, Corrensstrasse 40, D-49149 Mu¨nster, Germany
Received 6 July 2001; accepted 16 August 2001
Dedicated to Professor Rolf Gleiter on the occasion of his 65th birthday
Abstract
Lithium imidazolide, generated by NꢀH deprotonation of imidazole with n-butyllithium, reacts with two molar equivalents of
tris(pentafluorophenyl)borane with NꢀB bond formation to yield the product Li+[(C3H3N2){B(C6F5)3}2]− (6a, isolated in \70%
yield). The analogous reaction sequence starting from 4,5-dimethylimidazole gives the corresponding salt 6b. Its THF coordina-
tion product [Li(THF)4]+[(C3HMe2N2){B(C6F5)3}2]− (6b·THF) was characterized by X-ray diffraction. Deprotonation of
benzimidazole followed by the addition of two B(C6F5)3 equivalents gave the corresponding benzimidazolide-based anion, isolated
as the lithium compound 6c. The lithium salts 6 of the large ‘non-nucleophilic’ anion system [(C3HR2N2){B(C6F5)3}2]− were
employed in the generation of Group 4 metallocene cations by salt metathesis. Treatment of 6a with HCl in diethyl ether afforded
the product [H(OEt2)2]+[(C3H3N2){B(C6F5)3}2]− (9), that was also characterized by X-ray crystal structure analysis. The Brønsted
acid 9 was used to generate the Group 4 metallocene cation system [Cp2Zr(CH3)(OEt2)]+ (11) (with [(C3H3N2){B(C6F5)3}2]−
anion) starting from dimethylzirconocene. © 2002 Published by Elsevier Science B.V.
Keywords: Non-coordinating anion; Catalyst activation; Zirconocene complexes; Protonation; Metallocene cation formation
1. Introduction
anions such as [B(C6H5)4]−, [B(C6F5)4]− or
[B{C6H3(CF3)2}4]− (see Scheme 1) were successfully
The development of methods and reagents for the
selective generation of alkyl Group 4 metallocene
cations [1,2] and related systems is of great importance
since such species can serve as very active homogeneous
Ziegler–Natta catalysts under specific reaction condi-
tions [3]. Among the various other methods, pro-
tonolytic removal of an alkyl group from, e.g.
dimethylzirconocene provides an entry into stable
[Cp2ZrR]+ systems [4], provided a suitable Brønsted
acid that carries a low-nucleophilicity anion [5] with it
is employed. Not only the trialkylammonium salts
[R3NH]+ (or their dialkylanilinium analogs) with
* Corresponding author. Fax: +49-251-83-365-03.
E-mail address: erker@uni-muenster.de (G. Erker).
1 X-ray crystal structure analyses.
Scheme 1.
0022-328X/02/$ - see front matter © 2002 Published by Elsevier Science B.V.
PII: S0022-328X(01)01292-X

D. Vagedes et al. / Journal of Organometallic Chemistry 641 (2002) 148–155
149
Scheme 2.
employed [2,4], but also the [H(OEt2)2]+ salts with
these anions [6]. The structural features of the
[H(OEt2)2]+ ion were characterized in the past in the
case of salts with rather nucleophilic anions such as
[Zn2Cl6]2− [7], but only recently was the X-ray crystal
structure analysis of [H(OEt2)2]+[B(C6F5)4]− reported
in the literature [8,9].
The large imidazole-based anion [(C3H3N2)-
{B(C6F5)3}2]− was introduced very recently into the
homogeneous Ziegler–Natta catalyst activation chem-
istry. The corresponding triethylammonium salt, char-
acterized by X-ray diffraction, was employed by
LaPointe et al. [10] for activating a titanium-based
‘constrained geometry’ catalyst [11,12] used for the
effective ethene–1-octene copolymerization. This has
prompted us to report here the results of our related
study, namely the preparation of the [H(OEt2)2]+ salt
of this imidazole–B(C6F5)3-derived anion and its X-ray
crystal structure analysis.
the corresponding Li+[(C3HMe2N2){B(C6F5)3}2]− salt
6b (93% isolated), and B(C6F5)3 also added cleanly to
both nitrogen atoms of the lithium benzimidazolide
reagent 5c to yield the corresponding salt 6c, containing
the benzannelated complex anion system (see Scheme
2).
The B(C6F5)3-modified lithium imidazolide (6a) was
employed as a chloride anion abstracting reagent [14]
for the synthesis of an internally donor ligand-stabilized
zirconocene cation. As a substrate we chose the zir-
conocene dichloride complex 7 described earlier bearing
a 1-methyl-1-di(p-tolyl)phosphinoethyl substituent at
each Cp-ligand [15]. Treatment of
[(C3H2N2){B(C6F5)3}2]− (6a) in dichloromethane solu-
tion at room temperature resulted in rapid
precipitation of lithium chloride and formation of the
[(C3H2N2){B(C6F5)3}2]− [(kP:h5-
salt of the
7
with Li+
a
CpꢀCMe2PAr2)2ZrCl]+ cation reported earlier [15]. The
product 8 was isolated in ca. 80% yield (see Scheme 3).
We have used the anion [(C3H3N2){B(C6F5)3}2]− for
preparing a H+-etherate salt. For that purpose, a sus-
pension of the lithium salt 6a was treated with one
molar equivalent of HCl in ether at −30 °C. The
resulting lithium chloride coproduct was removed from
the reaction mixture by treatment with dichloro-
methane and the [H(OEt2)2]+[(C3H3N2){B(C6F5)3}2]−
product (9, see Scheme 4) crystallized from CH2Cl2 at
−30 °C (85% isolated). Product 9 was characterized by
X-ray crystal structure analysis (see below). It shows
2. Results and discussion
2.1. Syntheses and reaction of the
[(C3HR2N2){B(C6F5)3}2]− salts
We took a synthetic approach that was slightly dif-
ferent from that reported by LaPointe et al. [10]. In our
case, imidazole (4a) was N-deprotonated by the treat-
ment with n-butyllithium in toluene. The resulting
lithium imidazolide (5a) was then treated with two
molar equivalents of B(C6F5)3 [13] to yield the corre-
sponding salt Li+[(C3H3N2){B(C6F5)3}2]− (6a). Com-
1
typical H-NMR singlets of the anion at l 7.47 (1H,
2-H) and l 6.80 (2H, 4-/5-H) and a broad H+-reso-
nance at l 16.3 (in addition to the ether resonances).
The [H(OEt2)2]+ reagent 9 was used as a Brønsted
acid of a low-nucleophilicity anion for the generation of
an alkyl-zirconocene cation. In dichloromethane-d2 so-
lution Cp2Zr(CH3)2 (10) was treated with one molar
equivalent of the reagent 9 at room temperature. In-
stantaneous methane evolution was observed by the
formation of the cation [Cp2Zr(CH3)(OEt2)]+ (11 with
[(C3H3N2){B(C6F5)3}2]− anion). The mono-etherate
1
pound 6a shows a simple two line H-NMR spectrum
in benzene-d6–THF-d8 (10:1) solution [l 7.95 (1H, 2-
H), 6.84 (2H, 4-/5-H), with the corresponding 13C-
NMR signals at l 141.4 (C-2) and 124.3 (C-4/-5)].
Analogous treatment of lithium 4,5-dimethylimida-
zolide (5b) with tris(pentafluorophenyl)borane afforded

150
D. Vagedes et al. / Journal of Organometallic Chemistry 641 (2002) 148–155
Scheme 3.
complex of the Cp2ZrMe+ cation was identified spec-
troscopically (for details see Section 3). One equivalent
of diethyl ether was set free in the course of this
protonation reaction (identified by 1H-/13C-NMR
spectroscopy).
two ether molecules (of which one OEt2 entity is disor-
dered). Although the H+ was found at a position
between the two ether oxygen atoms, its large thermal
parameters do not allow for a meaningful description
of the hydrogen bond in compound 9 in detail [7,9].
The [(C3H3N2){B(C6F5)3}2]− anion of 9 also contains
a planar imidazolide-derived core of atoms. The
C3H3N2 hetarene unit is delocalized with N1ꢀC2 and
2.2. X-ray crystal structure analyses
,
N3ꢀC2 bonds both amounting to 1.327(6) A. The
The new compounds 6b and 9 were characterized by
X-ray diffraction. The salt 6b contains separated cation
and anion moieties in the crystal. In the crystal of 6b
the lithium cation is tetrahedrally coordinated by four
(disordered) THF molecules. The anion contains a cen-
tral planar delocalized 4,5-dimethylimidazolide core.
,
,
N1ꢀC5 (1.389(6) A) and N3ꢀC4 (1.378(6) A) bonds are
,
again slightly longer (C4ꢀC5: 1.340(7) A). The confor-
mational arrangement of the bulky ꢀB(C6F5)3 groups,
that are bonded to the pair of nitrogen atoms, is
slightly different in 9 than in 6c. In the latter (see
above) the two tris(pentafluoroaryl)borane groups are
oriented relative to each other at the central
C3HMe2N2ꢀ group in such a way that the resulting
complex anion is almost Cs-symmetric (see Fig. 1). In 9
the conformational positions of the three aryl and the
hetaryl group at each boron center is different, so that
even in an idealized description the resulting overall
rotameric structure of this anion in the crystal must be
regarded of a chiral type.
,
,
The N1ꢀC2 (1.320(4) A) and N3ꢀC2 (1.331(4) A)
bonds (see Fig. 1) are both slightly shorter than the
,
,
adjacent N1ꢀC5 (1.393(4) A) and N3ꢀC4 (1.392(4) A)
bonds. The C4ꢀC5 bond length in 6b amounts to
,
1.350(4) A. Both imidazolide nitrogen atoms are planar
tricoordinate (for bond angles see Fig. 1). Each of the
nitrogen centers contains a B(C6F5)3 unit bonded to it
,
,
(N1ꢀB1: 1.589(4) A; N3ꢀB2: 1.582(4) A). The boron
centers B1 and B2 both show pseudotetrahedral coordi-
nation environments. The conformational arrangement
of the three ꢀC6F5 aryl groups and the planar hetaryl
substituent at each boron atom is characterized by an
approximate orientation of two C6F5 groups and the
hetarene moiety at each boron center as a three-bladed
propeller (of opposite chirality sense at B1 and B2) [16].
In each case, it is the ꢀC6F5 substituent that occupies
the ‘pivot’ position at each Ar4B− subgroup (i.e. the
C11ꢀC16 substituent at B1 and the C51ꢀC56 group at
B2, see Fig. 2). In each case, this specific ꢀC6F5 ring is
oriented coplanar with the adjacent BꢀN vector (copla-
nar orientation of the C11ꢀC16, B1, N1 and C51ꢀC51,
B2, N3 centers, respectively).
We conclude that the salts Li+[(C3HR2N2)-
{B(C6F5)3}2]− (6) (with a range of imidazolide sub-
stituent
variations)
and
[H(OEt2)2]+[(C3H3N2)-
Single crystals of the compound 9 were obtained
from dichloromethane at −30 °C. The X-ray crystal
structure analysis shows the presence of non-interacting
[H(OEt2)2]+ cations and [(C3H3N2){B(C6F5)3}2]−
anions.
The cation contains two diethyl ether molecules that
are bridged by a proton (observed) located between the
Scheme 4.

D. Vagedes et al. / Journal of Organometallic Chemistry 641 (2002) 148–155
151
,
Fig. 1. Molecular structure of 6b. Selected bond lengths (A) and bond angles (°): N1ꢀB1 1.589(4), N1ꢀC2 1.320(4), N1ꢀC5 1.393(4), C2ꢀN3
1.331(4), N3ꢀB2 1.582(4), N3ꢀC4 1.392(4), C4ꢀC5 1.350(4), C4ꢀC7 1.492(4), C5ꢀC6 1.491(4), B1ꢀC11 1.653(5), B1ꢀC21 1.650(4), B1ꢀC31 1.644(5),
B2ꢀC41 1.656(5), B2ꢀC51 1.645(5), B2ꢀC61 1.657(5), LiꢀO71 1.918(8), LiꢀO76 1.912(9), LiꢀO81 1.870(9), LiꢀO86 1.917(9); B1ꢀN1ꢀC2 126.3(2),
B1ꢀN1ꢀC5 127.3(2), C2ꢀN1ꢀC5 106.3(2), N1ꢀC2ꢀN3 112.2(2), B2ꢀN3ꢀC2 126.1(2), B2ꢀN3ꢀC4 127.9(2), C2ꢀN3ꢀC4 105.8(2), N3ꢀC4ꢀC5 108.0(3),
N3ꢀC4ꢀC7 123.1(3), C5ꢀC4ꢀC7 128.9(3), N1ꢀC5ꢀC4 107.6(3), N1ꢀC5ꢀC6 123.3(3), C4ꢀC5ꢀC6 129.1(3), N1ꢀB1ꢀC11 111.8(3), N1ꢀB1ꢀC21
108.9(2), N1ꢀB1ꢀC31 105.1(2), C11ꢀB1ꢀC21 103.1(2), C11ꢀB1ꢀC31 114.7(3), C21ꢀB1ꢀC31 113.2(3), N3ꢀB2ꢀC41 109.0(2), N3ꢀB2ꢀC51 112.8(3),
N3ꢀB2ꢀC61 104.3(2), C41ꢀB2ꢀC51 102.7(2), C41ꢀB2ꢀC61 113.0(3), C51ꢀB2ꢀC61 115.2(3), O71ꢀLiꢀO76 105.9(4), O71ꢀLiꢀO81 106.4(4),
O71ꢀLiꢀO86 113.8(4), O76ꢀLiꢀO81 113.7(5), O76ꢀLiꢀO86 113.0(4), O81ꢀLiꢀO86 104.0(4).
{B(C6F5)3}2]− are easily synthesized starting from the
respective lithium imidazolides and the bulky Lewis
acid B(C6F5)3. Both reagent types exhibit large, bulky
anions that are probably of a low nucleophilicity. Thus,
both reagent types have successfully been employed in
the generation of Group 4 metallocene cation sys-
tems — the systems 6 by means of a salt metathesis,
whereas the reagent 9 seems to be a useful Brønsted
acid for the preparation of reactive alkyl Group 4
metallocene cations [17]. The potential of these and
related compounds as activator reagents in homoge-
neous Ziegler–Natta catalysis is under investigation in
our laboratory.
K and Varian Unity plus (1H: 600 MHz; 13C: 150 MHz;
19F: 564 MHz; 31P: 81 MHz) NMR spectrometer at 298
K (most NMR assignments were secured by 2D NMR
experiments) [18]; a Nicolet 5 DXC FT-IR spectrome-
ter; a Micromass Quattro LC-Z mass spectrometer was
used for the HRMS determination; elemental analysis
were carried out with a Foss–Heraeus CHN-rapid ele-
mental analyzer or a Vario El III micro elemental
analyzer; melting points were determined by differential
scanning calorimetry (2010 DSC, Du Pont/STA Instru-
ments). 4,5-Dimethyl-1H-imidazole (4b) [19], bis(h5-cy-
clopentadienyl)dimethylzirconium (10) [20], and
bis[h5 - {1 - methyl - 1 - di(p - tolyl)phosphinoethyl}cyclo-
pentadienyl]dichlorozirconium (7) [15] were prepared
according to the literature procedures.
3. Experimental
3.1. Preparation of the 1-lithium imidazolide deri6ati6es
5a–c, general procedure
Reactions with organometallic compounds were car-
ried out in an inert atmosphere (Ar) using Schlenk-type
glassware or in a glovebox. Solvents, including deuter-
ated solvents used for NMR spectroscopy, were dried
and distilled under Ar prior to use. The following
instruments were used for the physical characterization
of the compounds: Bruker AC 200 P NMR spectrome-
ter (1H: 200 MHz; 13C: 50 MHz; 11B: 64 MHz) at 300
A suspension of the respective 1-H-imidazole in 20
ml of toluene was cooled to 0 °C and reacted with one
molar equivalent amount of n-butyllithium. After stir-
ring for 2 days at room temperature (r.t.) the solvent
was removed in vacuo. Pentane was added, the solid
was collected by filtration and the product was dried in
vacuo.

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D. Vagedes et al. / Journal of Organometallic Chemistry 641 (2002) 148–155
3.1.1. Preparation of 1-lithium imidazolide (5a)
200 MHz): l=8.12 (s, 1H, 2-H), 7.78, 7.12 (each m,
each 2H, PhꢀH). 13C-NMR (benzene-d6–THF-d8 10:1,
50 MHz): l=153.7 (CH, C-2), 146.4 (C, C-3a, C-7a),
118.3, 116.6 (each CH, each CꢀPh).
Reaction of 1.56 g (22.9 mmol) of imidazole (4a) with
14.3 ml (22.9 mmol) of n-butyllithium in toluene car-
ried out as described above yielded 1.62 g (95%) of the
1
lithium salt 5a as a white solid. H-NMR (benzene-d6–
THF-d8 10:1, 200 MHz): l=7.62 (s, 1H, 2-H), 7.08 (s,
2H, 4-H and 5-H). 13C-NMR (benzene-d6–THF-d8
10:1, 300 K, 50 MHz): l=142.7 (CH, C-2), 124.3 (CH,
C-4).
3.2. Preparation of the lithium imidazolide–
bis[tris(pentafluorophenyl)borane] adduct (6a)
To a suspension of the lithium imidazolide (5a) (74.0
mg, 1.00 mmol) in 10 ml of toluene 1.02 g tris(pen-
tafluorophenyl)borane (2.00 mmol) was added at 0 °C.
The reaction mixture was allowed to warm up to r.t.
and then stirred for another 12 h. The addition of 10 ml
of pentane precipitated the product 6a. Filtration
yielded a white solid (811 mg, 74%). M.p. (dec.)
256 °C. Anal. Calc. for C39H3N2B2F30Li (MW 1098):
C, 42.66; H, 0.28; N, 2.55. Found: C, 42.53; H, 0.88; N,
1.27%. IR (KBr, cm−1): w 3464, 1650, 1522, 1474, 1467,
3.1.2. Preparation of 1-lithium 4,5-dimethylimidazolide
(5b)
A sample of 1.00 g (10.4 mmol) of 4,5-dimethyl-1H-
imidazole (4b) was reacted with 6.50 ml (10.4 mmol) of
n-butyllithium in toluene as described above to yield
1
933 mg (88%) of the white product 5b. H-NMR (ben-
zene-d6–THF-d8 10:1, 200 MHz): l=7.35 (s, 1H, 2-H),
2.22 (s, 6H, 4-CH3 and 5-CH3). 13C-NMR (benzene-d6–
THF-d8 10:1, 300 K, 50 MHz): l=138.6 (CH, C-2),
12.0 (CH3, 4-CH3 and 5-CH3). The signals of the
carbon atoms C-4 and C-5 were not detected.
1
1379, 1286, 1104, 979, 944, 793, 764 and 750. H-NMR
(benzene-d6–THF-d8 10:1, 600 MHz): l=7.95 (s, 1H,
2-H), 6.84 (s, 2H, 4-H and 5-H). 13C-NMR (benzene-
d6–THF-d8 10:1, 150 MHz): l=148.6 (dm, 1J=242
3.1.3. Preparation of 1-lithium benzimidazolide (5c)
Deprotonation of 1.01 g (8.55 mmol) of 1H-benzimi-
dazole (4c) with 5.30 ml (8.55 mmol) of n-butyllithium
in toluene carried out according to the general proce-
dure yielded 1.04 g (94%) of the lithium salt 5c as a
white solid. 1H-NMR (benzene-d6–THF-d8 10:1, 300 K,
1
Hz, o-Ph), 141.4 (CH, C-2), 140.0 (dm, J=249 Hz,
1
p-Ph), 137.5 (dm, J=248 Hz, m-Ph), 124.3 (CH, C-4
and C-5), 121.3 (C, ipso-C). 19F-NMR (benzene-d6–
THF-d8 10:1, 564 MHz): l= −132.4 (m, 12F, o-Ph),
−159.5 (m, 6F, p-Ph), −165.3 (m, 12F, m-Ph). 11B-
NMR (benzene-d6–THF-d8 10:1, 64 MHz): l= −8.5
(w1/2=390 Hz).
3.3. Preparation of the lithium 4,5-dimethylimida-
zolide–bis[tris(pentafluorophenyl)borane] adduct (6b)
Analogously as described above, lithium 4,5-
dimethylimidazolide (5b) (117.0 mg, 1.00 mmol) in 20
ml of toluene was reacted with 1.02 g of tris(pen-
tafluorophenyl)borane (2.00 mmol) to yield 965 mg
(93%) of a white solid. M.p. 105 °C. Anal. Calc. for
C41H7N2B2F30Li (MW 1126): C, 43.73; H, 0.63; N,
2.49. Found: C, 43.77; H, 0.70; N, 1.47%. IR (KBr,
cm−1): w 2984, 1646, 1518, 1472, 1462, 1375, 1284,
1
1089, 1047, 982, 800, 765 and 752. H-NMR (benzene-
d6–THF-d8 10:1, 600 MHz): l=7.92 (s, 1H, 2-H), 1.82
(s, 6H, 4-CH3 and 5-CH3). 13C-NMR (benzene-d6–
1
,
Fig. 2. Molecular structure of 9. Selected bond lengths (A) and bond
THF-d8 10:1, 150 MHz): l=148.7 (dm, J=247 Hz,
1
angles (°) N1ꢀB1 1.587(7), N1ꢀC2 1.327(6), N1ꢀC5 1.389(6), C2ꢀN3
1.327(6), N3ꢀB2 1.577(8), N3ꢀC4 1.378(6), C4ꢀC5 1.340(7), B1ꢀC11
1.630(8), B1ꢀC21 1.652(9), B1ꢀC31 1.649(9), B2ꢀC41 1.649(9),
B2ꢀC51 1.633(10), B2ꢀC61 1.649(8), O71ꢀH1 1.39, O81ꢀH1 1.11;
B1ꢀN1ꢀC2 125.0(4), B1ꢀN1ꢀC5 127.7(4), C2ꢀN1ꢀC5 105.8(4),
N1ꢀC2ꢀN3 112.0(4), B2ꢀN3ꢀC2 127.9(4), B2ꢀN3ꢀC4 124.9(5),
C2ꢀN3ꢀC4 106.0(4), N3ꢀC4ꢀC5 108.4(5), N1ꢀC5ꢀC4 107.8(5),
N1ꢀB1ꢀC11 110.2(4), N1ꢀB1ꢀC21 111.9(4), N1ꢀB1ꢀC31 101.7(5),
C11ꢀB1ꢀC21 103.1(5), C11ꢀB1ꢀC31 115.6(5), C21ꢀB1ꢀC31 114.5(5),
N3ꢀB2ꢀC41 112.6(5), N3ꢀB2ꢀC51 102.3(4), N3ꢀB2ꢀC61 109.6(5),
C41ꢀB2ꢀC51 113.8(5), C41ꢀB2ꢀC61 104.1(4), C51ꢀB2ꢀC61 114.8(5),
O71ꢀH1ꢀO81 157.3.
o-Ph), 140.7 (CH, C-2), 139.9 (dm, J=249 Hz, p-Ph),
1
137.2 (dm, J=248 Hz, m-Ph), 130.1 (CH, C-4 and
C-5), 121.4 (C, ipso-C), 12.1 (CH3, 4-CH3 and 5-CH3).
19F-NMR (benzene-d6–THF-d8 10:1, 564 MHz): l=
−125.3, −130.1, −131.5, −132.0, −134.6, −136.5
(each m, each 2F, o-Ph), −158.8, −159.8, −160.1
(each m, each 2F, p-Ph), −163.4, −164.9, −165.1
(each m, each 2F, m-Ph), −166.0 (br, 6F, m-Ph).
11B-NMR (benzene-d6–THF-d8 10:1, 64 MHz): l=
−9.0 (w1/2=230 Hz).

D. Vagedes et al. / Journal of Organometallic Chemistry 641 (2002) 148–155
153
3.3.1. X-ray crystal structure analysis of 6b
Formula C41H7N2B2F30·Li(C4H8O)4, M=1414.46,
colorless crystal 0.25×0.20×0.05 mm, a=13.254(3),
363 mg (81%) of 8. M.p. 65 °C. IR (KBr, cm−1): w
2964, 2927, 1645, 1600, 1518, 1469, 1283, 1263, 1156,
1
1096, 1018, 864, 805, 794 and 763. H-NMR (CH2Cl2-
d2, 600 MHz): l=8.70 (m, 8H, o-Ph), 7.47 (s, 1H,
2-H), 7.33 (m, 8H, m-Ph), 6.80 (s, 2H, 4-H and 5-H),
6.44 (m, 4H, CpꢀH), 6.23, 6.13 (each m, each 2H,
CpꢀH), 2.41, 2.40 (each s, each 3H, tol-CH3), 1.76 (t,
,
b=13.573(3), c=17.512(1) A, h=92.57(2), i=
3
,
104.50(1), k=98.60(2)°, V=3004.5(11) A , zcalc
=
1.563 g cm−3, v=14.47 cm−1, empirical absorption
correction via „ scan data (0.7145T50.931), Z=2,
J
PH=5.8 Hz, 3H, CH3), 1.55 (t, JPH=5.2 Hz, 3H,
(
,
triclinic, space group P1 (No. 2), u=1.54178 A, T=
223 K, ꢀ/2q scans, 12 704 reflections collected (9h,
CH3). 13C-NMR (CH2Cl2-d2, 150 MHz): l=148.3 (dm,
1J=241 Hz, o-Ph), 142.5 (C, ipso-CH3ꢀC), 142.2 (C,
9k, +l), [(sin q)/u]=0.62 A−1, 12 286 independent
,
1
ipso-[P]ꢀC), 141.3 (CH, C-2), 139.8 (dm, J=248 Hz,
(Rint=0.046) and 6674 observed reflections [I]2|(I)],
1
867 refined parameters, R=0.064, wR2=0.189, maxi-
p-Ph), 139.3 (C, ipso-CpꢀC), 137.3 (dm, J=245 Hz,
mum residual electron density 0.67 (−0.47) e A−3, the
m-Ph), 136.6 (CH, o-PhꢀC), 131.7, 130.7 (each CH,
m-PhꢀC), 124.0 (CH, C-4 and C-5), 120.7 (C, ipso-C),
113.7, 107.1, 100.2 (each CH, each CpꢀC), 35.5 (C,
ꢀC(CH3)2), 30.0, 26.8 (each CH3, each ꢀC(CH3)2), 21.9,
21.7 (each CH3, tol-CH3). 31P-NMR (CH2Cl2-d2, 81
MHz): l= −35.5. 19F-NMR (CH2Cl2-d2, 564 MHz):
l= −133.0 (m, 12F, o-Ph), −160.1 (m, 6F, m-Ph),
−165.6 (m, 12F, m-Ph). 11B-NMR (CH2Cl2-d2, 64
MHz): l= −8.9 (w1/2=140 Hz).
,
THF molecules are heavily disordered, refinement with
split positions is not working, the ‘best’ was taken as a
model for the others (SAME restraint), hydrogens cal-
culated and refined as riding atoms.
3.4. Preparation of the lithium benzimidazolide–
bis[tris(pentafluorophenyl)borane] adduct (6c)
To a suspension of the lithium benzimidazolide (5c)
(62.0 mg, 500 mmol) in 20 ml of CH2Cl2 was added at
0 °C 512 mg of tris(pentafluorophenyl)borane (1.00
mmol). The reaction mixture was allowed to warm up
to r.t. and stirred for another 24 h. The precipitate was
separated by filtration to yield a white solid 450 mg
(78%). M.p. 145 °C. HRMS: calculated for
[C43H5N2B2F30]− 1141.0160. Found 1141.0096. IR
(KBr, cm−1): w 3475, 2987, 2888, 1646, 1518, 1469,
1378, 1284, 1261, 1095, 983, 888, 797 and 753. 1H-
NMR (benzene-d6–THF-d8 10:1, 600 MHz): l=8.49
(s, 1H, 2-H), 7.61 (m, 2H, 4-H and 7-H), 6.90 (m, 2H,
5-H and 6-H). 13C-NMR (benzene-d6–THF-d8 10:1,
3.6. Treatment of the lithium
imidazolide–bis[tris(pentafluorophenyl)borane] adduct
(6a) with hydrogen chloride, formation of complex 9
To a suspension of the lithium salt 6a (1.10 g, 1.00
mmol) in 20 ml of Et2O was added at −30 °C 1.20 ml
of a 1 M HCl solution in ether (1.20 mmol). The
reaction mixture was allowed to warm up to r.t. and the
solvent was removed in vacuo. Dichloromethane (20
ml) was added and the LiCl precipitate was removed by
filtration. The solution was concentrated and the
product was crystallized at −30 °C. The white crystals
obtained (1.05 g (85%)) were suitable for an X-ray
crystal structure analysis of 9, m.p. 155 °C. Anal. Calc.
for C47H24N2B2F30O2 (MW 1240): C, 45.51; H, 1.95; N,
2.26. Found: C, 45.16; H, 2.65; N, 1.35%. IR (KBr,
cm−1): w 3175, 3003, 1647, 1517, 1470, 1387, 1283,
1
150 MHz): l=148.7 (dm, J=246 Hz, o-Ph), 146.6
1
(CH, C-2), 140.0 (dm, J=251 Hz, p-Ph), 137.7 (C,
1
C-3a and C-7a), 137.3 (dm, J=253 Hz, m-Ph), 124.0
(CH, C-5 and C-6), 120.5 (C, ipso-C), 115.3 (CH, C-4
and C-7). 19F-NMR (benzene-d6–THF-d8 10:1, 564
MHz): l= −127.4, −130.2, −131.5, −132.6 (each
m, each 2F, o-Ph), −134.6 (4F, o-Ph), −158.0 (m, 2F,
p-Ph), −159.8 (br, 4F, p-Ph), −163.0, −164.8 (each
m, each 2F, m-Ph), −165.6 (br, 8F, m-Ph). 11B-NMR
1
1096, 978, 876, 752, 698 and 679. H-NMR (CH2Cl2-d2,
600 MHz): l=16.3 (br, 1H, H+), 7.47 (s, 1H, 2-H),
3
6.80 (s, 2H, 4-H and 5-H), 4.08 (q, JHH=7.0 Hz, 8H,
3
OꢀCH2), 1.44 (t, JHH=7.0 Hz, 12H, CH3). 13C-NMR
(CH2Cl2-d2, 150 MHz): l=148.3 (dm, 1J=241 Hz,
1
(benzene-d6–THF-d8 10:1, 64 MHz): l= −8.1 (w1/2
=
o-Ph), 141.3 (C, C-2), 139.8 (dm, J=247 Hz, p-Ph),
1
320 Hz).
137.3 (dm, J=248 Hz, m-Ph), 124.0 (CH, C-4 and
3.5. Treatment of compound 7 with the lithium
imidazolide–bis[tris(pentafluorophenyl)borane] adduct
(6a), formation of the metallocene cation complex 8
3.3.1. X-ray crystal structure analysis of 6b
Formula C41H7N2B2F30·Li(C4H8O)4, M=1414.46,
colorless crystal 0.25×0.20×0.05 mm, a=13.254(3),
,
b=13.573(3), c=17.512(1) A, h=92.57(2), i=
3
To a mixture of 200 mg (250 mmol) of 7 with 272 mg
(250 mmol) of the lithium compound 6a 15 ml of
CH2Cl2 was added. The resulting reaction mixture was
allowed to stir for 1 h and then filtered to remove LiCl.
The solvent was removed in vacuo, pentane was added
and the yellow solid was isolated by filtration to yield
,
104.50(1), k=98.60(2)°, V=3004.5(11) A , zcalc
=
1.563 g cm−3, v=14.47 cm−1, empirical absorption
correction via „ scan data (0.7145T50.931), Z=2,
ether molecules from difference Fourier calculations,
refined isotropically, other hydrogens calculated and
refined as riding atoms.

154
D. Vagedes et al. / Journal of Organometallic Chemistry 641 (2002) 148–155
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(b) M. Aulbach, F. Ku¨ber, Chem. Unserer Zeit 28 (1994) 197;
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Ed. Engl. 34 (1995) 1143;
and Nonius Kappa CCD diffractometer, the later one
equipped with a rotating anode generator Nonius
FR591. Programs used: data collection EXPRESS (Non-
ius B.V., 1994) and COLLECT (Nonius B.V., 1998), data
reduction MOLEN [21] and DENZO-SMN [22], absorption
correction for CCD data SORTAV [23,24], structure
(d) M. Bochmann, J. Chem. Soc. Dalton Trans. (1996) 255;
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(1990) 830; Angew. Chem. Int. Ed. Engl. 29 (1990) 780;
(b) M. Bochmann, S.J. Lancaster, J. Organomet. Chem. 434
(1992) C1.
solution SHELXS-97 [25], structure refinement SHELXL
97 [26], graphics SCHAKAL [27].
-
[5] Review: H.S. Strauss, Chem. Rev. 93 (1993) 927.
[6] (a) M. Brookhart, B. Grant, A.F. Volpe Jr., Organometallics 11
(1992) 3920;
3.7. Treatment of bis(p5-cyclopentadienyl)dime-
thylzirconium (10) with compound 9, formation of
metallocene cation complex 11
(b) R. Taube, S. Wache, J. Organomet. Chem. 428 (1992) 431;
(c) L.K. Johnson, C.M. Killian, M. Brookhart, J. Am. Chem.
Soc. 117 (1995) 6414;
To a solid mixture of 10.0 mg (39.7 mmol) of the
zirconocene complex 10 with 49.2 mg (39.7 mmol) of
compound 9 1.5 ml of CH2Cl2-d2 was added. Methane
evolution occurred immediately and complex 11 was
generated for direct NMR observation. 1H-NMR
(CH2Cl2-d2, 600 MHz): l=7.48 (s, 1H, 2-H), 6.80 (s,
2H, 4-H and 5-H), 6.49 (s, 10H, CpꢀH), 3.46 (q,
(d) J. Ca´mpora, J.A. Lo´pez, P. Palma, P. Valerga, E. Spillner, E.
Carmona, Angew. Chem. 111 (1999) 199; Angew. Chem. Int. Ed.
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Struchkov, O.M. Nefedov, Izv. Akad. Nauk SSSR Ser. Khim. 1
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[9] (a) D. Mootz, M. Steffen, Z. Anorg. Allg. Chem. 482 (1981) 193;
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A.J. Schultz, J.M. Williams, J. Am. Chem. Soc. 106 (1984) 5319.
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Chem. Soc. 122 (2000) 9560.
[11] Review: A.L. McKnight, R.M. Waymouth, Chem. Rev. 98
(1998) 2587.
[12] See also: K. Kunz, G. Erker, S. Do¨ring, R. Fro¨hlich, G. Kehr,
J. Am. Chem. Soc. 123 (2001) 6181 (and references therein).
[13] (a) A.G. Massey, A.J. Park, F.G.A. Stone, Proc. Chem. Soc.
London (1963) 212;
3
3J=7.0 Hz, 2H, OꢀCH2), 1.17 (t, JHH=7.0 Hz, 6H,
CH3), 0.92 (s, 3H, ZrꢀCH3). 13C-NMR (CH2Cl2-d2,
1
150.8 MHz): l=148.3 (dm, J=242 Hz, o-Ph), 141.3
(C, C-2), 139.8 (dm, 1J=248 Hz, p-Ph), 137.3 (dm,
1J=249 Hz, m-Ph), 124.0 (CH, C-4 and C-5), 120.7 (C,
ipso-C), 115.3 (CH, CpꢀC), 66.1 (CH2, OꢀCH2), 44.7
(CH3, ZrꢀCH3), 15.3 (CH3). 19F-NMR (CH2Cl2-d2, 564
MHz): l= −133.0 (m, 12F, o-Ph), −160.0 (m, 6F,
m-Ph), −165.6 (m, 12F, m-Ph). 11B-NMR (CH2Cl2-d2,
64 MHz): l= −8.9 (w1/2=250 Hz).
(b) A.G. Massey, A.J. Park, J. Organomet. Chem. 2 (1964) 245;
(c) A.G. Massey, A.J. Park, in: R.B. King, J.J. Eisch (Eds.),
Organometallic Syntheses, vol. 3, Elsevier, New York, 1986, p.
461.
4. Supplementary material
[14] (a) M. Bochmann, L.M. Wilson, J. Chem. Soc. Chem. Commun.
(1986) 1610;
Crystallographic data for structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 166601–166602, for 6b and 9
respectively. Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
(b) M. Bochmann, L.M. Wilson, M.B. Hursthouse, R.L. Short,
Organometallics 6 (1987) 2556;
(c) L.K. Johnson, S. Mecking, M. Brookhart, J. Am. Chem. Soc.
118 (1996) 267;
(d) S. Mecking, L.K. Johnson, L. Wang, M. Brookhart, J. Am.
Chem. Soc. 120 (1998) 888;
(e) R.A. Widenhoefer, A. Vadehra, P.K. Cheruvu, Organometal-
lics 18 (1999) 4614;
(f) D.J. Tempel, L.K. Johnson, R. Leigh Huff, P.S. White, M.
Brookhart, J. Am. Chem. Soc. 122 (1999) 6686.
[15] B.E. Bosch, G. Erker, R. Fro¨hlich, O. Meyer, Organometallics
16 (1997) 5449.
Acknowledgements
[16] E.L. Eliel, S.H. Wilen, Stereochemistry of Organic Compounds,
Wiley, New York, 1994, pp. 1156–1160 (chap. 14.6).
[17] See also: G. Kehr, R. Roesmann, R. Fro¨hlich, C. Holst, G.
Erker, Eur. J. Inorg. Chem. (2001) 535.
[18] S. Braun, H.-O. Kalinowski, S. Berger, 150 and More Basic
NMR Experiments, VCH, Weinheim, 1998 (and references
therein).
Financial support from the Fonds der Chemischen
Industrie and the Deutsche Forschungsgemeinschaft is
gratefully acknowledged.
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