Reaction of (σ-alkynyl) Group 4 metallocene cation complexes with alkyl- and arylisocyanides

Article abstract of DOI:10.1016/S0022-328X(98)00871-7

The cations [(RCp)₂M(-CC-CH₃)(THF)⁺] (2a-d) [(RCp)₂M=Cp₂Ti, Cp₂Zr, (MeCp)₂Zr, and Cp₂Hf] were generated in situ by treatment of the respective bis(propynyl) Group 4 metallocenes (RCp)₂M(-CC-CH₃)₂ (1a-d) with N,N-dimethylanilinium tetraphenylborate. Addition of excess tert-butylisocyanide gave the isonitrile insertion/addition products [(RCp)₂M(η²-Me₃C-NC-CC-CH ₃)(κ-CN-CMe₃)⁺] (8a-d). Complex 8b was characterized by X-ray diffraction. It contains a η²-iminoacyl ligand with N-inside orientation and there is a κ-tert-butylisocyanide coordinated to the cationic metallocene framework. Complex 8b exhibits the typical structural characteristics of a d^o-configurated isonitrile complex (bond lengths 2.350(4) and 1.148(4) A for the Zr-CN-R unit). Insertion of 2,6-dimethylphenylisocyanide into the Zr-C(sp) σ-bond of in situ generated [Cp₂Hf-CC-CH₃⁺] cation 2d leads to the formation of the analogous cationic hafnocene complex 8e.

Full text of DOI:10.1016/S0022-328X(98)00871-7

Journal of Organometallic Chemistry 571 (1998) 83–89
Reaction of (|-alkynyl) Group 4 metallocene cation complexes with
alkyl- and arylisocyanides
Wolfgang Ahlers, Gerhard Erker *, Roland Fro¨hlich
Organisch-Chemisches Institut der Uni6ersita¨t Mu¨nster, Corrensstraße 40, D-48149 Mu¨nster, Germany
Received 26 May 1998
Abstract
The cations [(RCp)2M(–CꢀC–CH3)(THF)+] (2a–d) [(RCp)2M=Cp2Ti, Cp2Zr, (MeCp)2Zr, and Cp2Hf] were generated in situ
by treatment of the respective bis(propynyl) Group 4 metallocenes (RCp)2M(–CꢀC–CH3)2 (1a–d) with N,N-dimethylanilinium
tetraphenylborate. Addition of excess tert-butylisocyanide gave the isonitrile insertion/addition products [(RCp)2M(p2-Me3C–
NC–CꢀC–CH3)(s-CꢀN–CMe3)+] (8a–d). Complex 8b was characterized by X-ray diffraction. It contains a p2-iminoacyl ligand
with N-inside orientation and there is a s-tert-butylisocyanide coordinated to the cationic metallocene framework. Complex 8b
o
˚
exhibits the typical structural characteristics of a d -configurated isonitrile complex (bond lengths 2.350(4) and 1.148(4) A for the
Zr–CꢀN–R unit). Insertion of 2,6-dimethylphenylisocyanide into the Zr–C(sp) |-bond of in situ generated [Cp2Hf–CꢀC–CH3+
cation 2d leads to the formation of the analogous cationic hafnocene complex 8e. © 1998 Elsevier Science S.A. All rights reserved.
]
Keywords: Group 4 metallocenes; Isocyanide insertion; Alkynyl metallocene cation; do-Metal–isocyanide complex.
1. Introduction
We have tried to find ways to prepare stable deriva-
tives of the [Cp2M–CꢀC–CH3+] cations starting from
the 2·THF systems, generated in THF-solution by the
protonolysis reaction, but failed to do so in many cases.
It appears that any conjugative thermodynamic stabi-
lization of the [Cp2M–CꢀC–CH3+] cations, if y-conju-
gation is at all important in these species, does not lead
to an increased kinetic stabilization of the system. On
the contrary, it appears that the cations 2 and 2·THF
are considerably more reactive and consequently less
stable than their well studied [Cp2M–CH3+] or [Cp2M–
CH3+ ·THF] counterparts [3]. This may actually result
from a much smaller sterical shielding of the very
electrophilic metallocene cation center by the ‘lean’
linear |-alkynyl ligand as compared to the spatially
more demanding |-methyl group. Clean insertion reac-
tions of 2 were eventually observed upon treatment with
an alkyl- and an arylisocyanide. An interesting type of
coordinatively saturated Group 4 metallocene cation
addition products have become readily available by this
route. Such examples are described in this article.
(Alkynyl)metallocene cation complexes (2) of the
Group 4 transition metals are very reactive species. We
have recently shown that the donor–ligand-free systems
[Cp2M–CꢀC–R+] 2 can be generated in situ by treat-
ment of the Cp2M(–CꢀC–R)2 complexes 1 with tritylte-
traphenylborate (4), but instantaneously react with the
starting material 1 to form a dinuclear (v-hydrocar-
byl)bis(zirconocene) cation (5) that contains a planar-te-
tracoordinate carbon atom [1,2] (see Scheme 1). We
have also shown that the THF-stabilized cations
[Cp2M–CꢀC–CH3+ ·THF] (2·THF) are formed by
treatment of 1 with the Brønsted acid N,N-dimethy-
lanilinium tetraphenylborate (3) in THF solution. The
complexes 2·THF were characterized by NMR spec-
troscopy in solution, but rapidly decomposed and could
not be isolated so far [1].
* Corresponding author. Tel.: +49 251 8333221; fax: +49 251
8336503; e-mail: erker@uni-muenster.de
0022-328X/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00871-7

84
W. Ahlers et al. / Journal of Organometallic Chemistry 571 (1998) 83–89
Scheme 1.
and is characteristic for a situation where metal to
2. Results and discussion
carbon y-backbonding is probably completely lacking
and the overall bonding situation may be dominated by
electrostatic bonding contributions [7]. In such a special
situation one would expect that the corresponding IR
w(CꢀN–R) stretching band is not shifted to lower
wavenumbers relative to the free isonitrile but to re-
main unaffected by the do-metal coordination or even
be slightly shifted to higher wavenumbers [8]. Such an
overall situation is actually observed for the electroni-
cally related [Cp3Zr–CꢀNR+] system which may serve
as a reference for this situation [9]. The do-configurated
isonitrile complex [Cp3Zr–CꢀN–CMe3+][BPh4−] ex-
hibits an IR w(CꢀN–) stretching band at 2209 cm−1
which is indeed shifted considerably to higher
wavenumbers as compared to the free tert-butyliso-
cyanide ligand (w˜ =2140 cm−1). Complex 8b shows two
sharp IR bands of about equal intensities at 2203 and
2192 cm−1 arising inter alia from the CꢀC and (M)–
CꢀN(R) moieties. We cannot clearly make an absolute
assignment between these two triple bond vibrations in
this specific case, but it seems that the [Cp2Zr(p2-imi-
noacyl)(CꢀNR)+] cation behaves in the typical way of
an electrostatically dominated do-metal–isonitrile
complex.
The reaction sequence starting from bis(propy-
nyl)zirconocene (1b, readily prepared by treatment of
Cp2ZrCl2 with two molar equivalents of propynyl
lithium in tetrahydrofuran [4]) is a typical example.
Complex 1b was treated with N,N-dimethylanilinium
tetraphenylborate (3) at 0°C in THF. We had previ-
ously shown that under these conditions the THF-stabi-
lized (propynyl)zirconocene cation [(Cp2Zr–CꢀC–
CH3)+ ·THF] (2b) is formed instantaneously. It is gen-
erated almost quantitatively, as was shown by NMR
spectroscopy and it can be very efficiently trapped, as
we have now shown, by a bulky alkyl- or arylisonitrile.
We have, therefore, added tert-butylisocyanide (ca. 5-
fold excess) to the solution at 0°C after a period of a
few minutes. The mixture was kept for ca. 2 h at room
temperature and then worked up to give a single
organometallic product, namely 8b, that was isolated in
\90% yield.
Analysis of the product showed that two molar
equivalents of the isonitrile had reacted with the in situ
generated (alkynyl)zirconocene cation 2b. One of the
isonitriles was inserted in the reactive metal to carbon
|-bond to give a p2-iminoacyl ligand at the bent metal-
locene unit [5,6]. This is supported by the result of an
X-ray crystal structure analysis (see below) and some
very typical spectroscopic data of the product 8b (13C-
NMR in THF-d8: l 215.5 ppm; IR (KBr): w˜ =1624
cm−1). The |-ligand-derived propynyl substituent ex-
hibits 13C-NMR resonances at l 133.7 (C2), 74.8 (C3)
and 6.23 (3-CH3). The second tert-butylisocyanide moi-
ety was added as such to the electrophilic cationic
zirconium center to formally complete the 18-electron
valence shell of the transition metal. The isonitrile
carbon 13C-NMR resonance appears at l 121.6 ppm
This is supported by the results of the X-ray crystal
structure analysis of complex 8b. Suitable single crystals
were obtained by slow diffusion of pentane into a
THF-solution of 8b. A projection of the molecular
structure of the cation of 8b is shown in Fig. 1. In the
crystal the [Cp2Zr(p2-Me3C–NC–CꢀC–CH3)(s-CꢀN–
CMe3)+] cation and the [BPh4−] anion are well sepa-
rated. The cation contains a Group 4 bent metallocene
unit with an averaged C(Cp)–Zr bond length of
˚
2.501(4) A. The Cp(centroid)–Zr–Cp(centroid) angle is
130.4°. Both the p2-iminoacyl ligand and the s-tert-

W. Ahlers et al. / Journal of Organometallic Chemistry 571 (1998) 83–89
85
˚
Fig. 1. A view of the molecular geometry of 8b (cation only) with atom numbering scheme. Selected bond lengths (A) and angles (°): Zr–C1
2.194(3), Zr–N1 2.229(3), Zr–C5 2.350(4), Zr–CCp 2.501(4), C1–N1 1.264(4), C1–C2 1.412(5), C2–C3 1.191(5), C3–C4 1.453(5), N1–C7
1.499(4), C5–N2 1.148(4), N2–C6 1.464(4); C1–Zr–C5 117.36(12), C1–Zr–N1 33.20(11), N1–Zr–C5 84.17(11), Zr–C1–N1 74.9(2), Zr–C1–C2
153.7(3), Zr–N1–C1 71.9(2), Zr–N1–C7 158.8(2), Zr–C5–N2 177.3(3), C1–C2–C3 173.0(4), C2–C3–C4 177.2(4), C2–C1–N1 131.3(3),
C1–N1–C7 129.0(3), C5–N2–C6 176.1(4).
carbon distance observed here seems to be very typical
for a do-configurated Group 4 metal/CꢀNR interaction
that is lacking the typical metal to carbon y-interaction
that characterize the more electron rich metal–CO or
–CꢀNR complexes [13]. The electronically closely re-
lated reference system [Cp3Zr–CꢀN–CMe3+] shows a
butylisocyanide ligand are bonded in the |-ligand plane
at the front side of the bent metallocene wedge [10].
This gives the cation of 8b a formal 18 electron count.
In this arrangement of ligands two regioisomers could
be possible which are distinguished by the relative
positioning of the zirconium bonded iminoacyl nitrogen
atom in the |-ligand plane. The p2-iminoacyl group
could be oriented either in the ‘N-inside’ or the ‘N-out-
side’ fashion [5,6]. Of these only the former orientation
is realized in the complex 8b. The crystal contains a
single regioisomer that is characterized by coordination
of the p2-iminoacyl nitrogen center in the central posi-
tion in the |-ligand plane of the bent metallocene
complex, separating the Zr–C1 and Zr–C5 vectors (see
Fig. 1). The Zr–C1 bond length is rather short at
˚
very similar Zr–C(isonitrile) distance of 2.313(3) A. In
this reference cation the CꢀN– bond length is 1.145(4)
˚
A, which is identical to that of the free uncoordinated
tert-butylisocyanide [9]. Consequently, we have found a
˚
C5–N2 distance of 1.148(4) A in 8b, which again
indicates the lack of any significant population of the
CꢀN-y*-orbital by metal to ligand y-backbonding. It
appears that the do-[Zr+]’CꢀNR interaction in 8b is
dominated by the |-donor properties of the ligand and
the |-acceptor features of the metal center inside the
bent metallocene framework. The resulting bonding
interaction has probably a pronounced electrostatic (i.e.
Coulomb interaction) component [7]. The Zr–CꢀN–
CMe3 unit is close to linear (angles Zr–C5–N2
177.3(3)°, C5–N2–C6 176.1(4)°).
˚
2.194(3) A, it is at the short end of the range of typical
Zr–C(sp2) bonds. The propynyl substituent is attached
˚
at carbon atom C1 (d C2–C3 1.191(5) A). The C1–N1
˚
distance is 1.264(4) A, which is in the imino CꢁN
double bond range, as it is typically observed for p2-
iminoacyl zirconium complexes [11]. The corresponding
˚
Zr–N1 distance is 2.229(3) A; it is only slightly longer
We have employed
a
variety of bis(propy-
than the adjacent Zr–C1 distance (see above).
nyl)metallocenes (1) in the analogous reaction sequence
(see Table 1 and Scheme 1). From each of these starting
materials the corresponding THF-stabilized (propy-
nyl)metallocene cation (2·THF) was generated in situ
by treatment with N,N-dimethylanilinium tetraphenyl-
borate (3) in tetrahydrofuran, and then the respective
isonitrile reagent was added immediately. In each case
effective isonitrile insertion into the metal–C(sp) |-
bond was achieved and the respective (p2-iminoa-
cyl)metallocene cation complexes (8) isolated as their
s-isonitrile adducts (see Scheme 2).
The tert-butylisocyanide ligand is bonded laterally at
the zirconocene unit [6,10] adjacent to the Zr–N1 vec-
tor. The C1–Zr–C5 angle is rather large at 117.36(12)°,
the N1–Zr–C5 angle amounts to 84.17(11)°. The Zr–
˚
C5 bond length is 2.350(5) A. This is a rather long
zirconium to carbon distance; it lies at the high end of
the zirconium to carbon |-bond range, and it is drasti-
cally different from the short bonds encountered in
d2-configurated Group 4 metallocene isonitrile or car-
bon monoxide complexes [12]. The long Zr-isonitrile

86
W. Ahlers et al. / Journal of Organometallic Chemistry 571 (1998) 83–89
Table 1
Selected spectroscopic features of the [R1Cp)2M(p2-R2NꢁC1(–CꢀC–CH3)(s-C5ꢀN–R2)+] complexes 8
M
R1
R2
l C1 a
l C5
w˜CꢀC
CꢀNRb
NꢁC
a
b
c
d
e
Ti
H
H
CH3
H
H
CMe3
CMe3
CMe3
202.5d
215.5
217.1
222.7
230.6e
130.2d
121.6
123.3
2157
2192
2193
2273
2189
2166
2203
2203
2206
1685
1624
1655
1588
1618
Zr
Zr
Hf
Hf
CMe3
121.1
Me2C6Hc3
f
a 13C-NMR spectra in d8-THF unless otherwise noted.
b IR spectra in KBr, tentative relative assignment.
c 2,6-Dimethylphenyl.
d In CDCl3.
e In CD2Cl2.
f Not observed.
and its very limited ability for an electronic stabilization
of the adjacent metallocene cation unit. This unfavor-
able combination of steric and electronic features seems
to make the [Cp2
In this way the bis(methylcyclopentadienyl)zirconium
derived cation 8c was generated from (MeCp)2Zr-
(–CꢀC–CH3)2 (1c) by protonation and treatment with
tert-butylisocyanide. The characteristic spectroscopic
data of 8c are very similar to those of the parent
compound 8b (see Table 1), only that the presence of a
symmetry label at the cyclopentadienyl ligands (Me– at
Cp) leads to a diastereotopic differentiation of the
C5H4Me methine moieties due to the in-plane asymme-
try of the |-ligand framework at this very bent metal-
locene wedge (CH 13C-NMR signals at l 110.1, 109.7,
107.1, and 106.3 ppm for C5H4CH3).
M–CꢀC–R+] cations much more
sensitive then e.g. their [Cp2M–CH3+] relatives. Never-
theless, there is a clean insertion chemistry into the
Zr–C(sp) |-bond observed when sufficiently reactive
reagents are used, such as the isonitriles, that lead to
the formation of stable sterically and electronically
favorable products.
3. Experimental section
The Coulombic interaction between the tert-butyliso-
cyanide ligand and the metal cation seems to be slightly
less pronounced in the corresponding titanium system
8a, that was prepared analogously starting from
Cp2Ti(–CꢀC–CH3)2 (1a). There is only a small shift of
the CꢀN–R IR stretching band to higher wavenumbers
observed for 8a as compared to the related zirconium
complexes (see Table 1). The 13C-NMR resonance of
the s-CꢀNR ligand is observed at l 130.2 ppm (in
CDCl3), and the p2-iminoacyl carbon 13C-NMR signal
is at l 202.5. In contrast, the corresponding hafnocene
complex 8d exhibits the 13C-NMR iminoacyl carbon
resonance at l 222.7 and a much reduced IR w(CN)
band at 1588 cm−1. In the case of the hafnium system
we have also trapped the in situ generated [Cp2Hf(–
CꢀC–CH3)+] cation by an aromatic isocyanide. Addi-
tion of 2,6–dimethylphenylisocyanide resulted in the
clean formation of the respective [Cp2Hf(p2-Ar–NC–
CꢀC–CH3)(s-CꢀNAr)+] cation complex 8e (again with
BPh4− anion).
All reactions were carried out under an argon atmo-
sphere using Schlenk type glassware or in a glove box.
For general information about the experimental condi-
tions, including a list of spectrometers and equipment
used for the physical characterization of the com-
pounds, see Refs. [1,3]. The bis(propynyl)metallocene
starting materials (1) were prepared according to litera-
ture procedures [4]. The (|-propynyl)metallocene
cations (2) had been spectroscopically characterized in
THF-d8 solution previously [1]. For this study they
were in situ generated by treatment with N,N-dimethyl-
anilinium tetraphenylborate (3) in THF solution and
employed in the reactions with the respective isonitrile
reagents without further characterization. For 8b–e
only the NMR data of the cation are listed. The BPh4−
anion signals are as given for the example of 8a.
3.1. Reaction of the propynyltitanocene cation (2a) with
tert-butylisocyanide: formation of 8a
This study shows that |-alkynyl Group 4 metal-
locene cation complexes can be generated by a common
protonation route in tetrahydrofuran and employed in
insertion reactions. It appears that the [Cp2M–CꢀC–
R+] cations are rather sensitive and reactive com-
pounds. This is probably due to the small steric
stabilization provided by the linear |-acetylide ligand
Bis(propynyl)titanocene (1a, 200 mg, 781 mmol) and
N,N-dimethylanilinium tetraphenylborate (3, 345 mg,
781 mmol) were mixed as solids, and 5 ml of tetrahydro-
furan was added at 0°C. The suspension was stirred for
2 min to give a clear solution. One millilitre of tert-

W. Ahlers et al. / Journal of Organometallic Chemistry 571 (1998) 83–89
87
Scheme 2.
butylisocyanide was added and the mixture then
3.2. Reaction of the [Cp2Zr(–CꢀC–CH3)+] cation
with tert-butylisonitrile: formation of 8b
stirred for 3 days at ambient temperature. Solvent and
all volatiles were removed from the dark brown col-
ored solution in vacuo. The residue was treated three
times with each pentane and toluene to give the
product 8a as a reasonably clean solid product. Due
to some remaining unidentified contaminations the
product was only characterized spectroscopically.
Ten millilitres of THF was added at 0°C to a mixture
of 1.00 g (3.34 mmol) of Cp2Zr(–CꢀC–CH3)2 1b and
1.48 g (3.36 mmol) of N,N-dimethylanilinium te-
traphenylborate. After 2 min 2 ml of tert-butyliso-
cyanide was added. The cooling bath was removed and
the mixture stirred for 2 h at ambient temperature.
Solvent was removed in vacuo, and the residue washed
twice with pentane and toluene to give the product 8b
as a solid. Diffusion of pentane into a THF solution of
8b gave single crystals suited for the X-ray crystal
structure analysis. Yield of 8b: 2.30 g (93%), m.p. 151°C
(decomp). 1H-NMR (CDCl3): l=5.61 (s, 10H, Cp),
2.39 (s, 3H, CH3), 1.51 (s, 9H) and 1.23 (s, 9H,
1
Yield: 302 mg (55%). H-NMR (CDCl3, 360.1 MHz):
l=7.50–7.35 (m, 8H, m-BPh4), 7.05–7.00 (m, 8H,
o-BPh4), 6.90–6.85 (m, 4H, p-BPh4), 5.31 (s, 10H,
Cp), 2.35 (s, 3H, CH3), 1.52 (s, 9H) and 1.25 (s, 9H,
C(CH3)3). 13C-NMR (CDCl3, 90.6 MHz): l=202.5
1
(C1), 164.4 (q, ipso-C of BPh4, JCB=50 Hz), 136.4
(o-BPh4), 133.3 (C2), 130.2 (C5), 125.5 (m-BPh4),
121.6 (p-BPh4), 107.0 (Cp), 72.7 (C3), 63.1, 62.3, 29.7
and 28.9 (C(CH3)3), 6.7 (3-CH3). IR (KBr): w˜ =3053,
3035, 2981, 2930, 2166 and 2157 (CꢀC, CꢀN), 1685
(CꢁN), 1580, 1474, 1425, 1370, 1262, 1184, 1016, 819,
732, 704 cm−1. UV/VIS (dichloromethane): umax=253
(m=33500), 274 (m=24700), 314 (m=9000).
1
C(CH3)3). H-NMR (THF-d8, 360.1 MHz): l=5.82 (s,
10H, Cp), 2.38 (s, 3H, CH3), 1.59 (s, 9H) and 1.31 (s,
9H, C(CH3)3). 13C-NMR (THF-d8, 90.6 MHz): l=
215.5 (C1), 133.7 (C2), 121.6 (C5), 108.3 (Cp), 74.8
(C3), 63.6, 61.6, 28.7, 29.5 (C(CH3)3), 6.2 (3-CH3).

88
W. Ahlers et al. / Journal of Organometallic Chemistry 571 (1998) 83–89
GHMBC-NMR [14] (THF-d8, 150.8/599.8 MHz): l=
215.46/2.38 (C1/3-CH3). 11B-NMR (CDCl3): l= −6.7.
IR (KBr): w˜ =3054, 3036, 2980, 2967, 2926, 2853, 2203
and 2192 (CꢀC, CꢀN), 1624 (CꢁN), 1458, 1262, 1094,
1016, 806, 731, 702, 612 cm−1. UV/VIS (dichloro-
methane): umax=239 (m=54400), 265 (m=26900), 273
(m=20700). C47H51N2BZr·C4H8O (817.47): calc. C
74.87, H 7.22, N 3.43; found C 74.39, H 7.07, N 3.63%.
X-ray crystal structure analysis of 8b: formula
C47H51BN2Zr; M=745.93; 0.50×0.40×0.30 mm; a=
2203 and 2193 (CꢀC, CꢀN), 1655 (CꢁN), 1579, 1479,
1427, 1184, 1032, 817, 743, 733, 704, 612 cm−1. UV/
VIS (dichloromethane): umax=239 (m=29000), 267
(m=15100), 285 (m=10100).
3.4. Reaction of the [Cp2Hf–CꢀC–CH+3 ] cation with
tert-butylisocyanide: formation of 8d
Fifteen millilitres of THF was added to a solid
mixture of 1.00 g (2.55 mmol) of bis(propynyl)HfCp2
1d and 1.10 g (2.50 mmol) of N,N-dimethylanilinium
tetraphenylborate at 0°C. After 2 min 1 ml of tert-
butylisocyanide was added to the resulting clear solu-
tion. Workup and treatment with toluene and pentane
analogously as described above gave 1.08 g (51%) of 8d,
˚
13.418(1); b=18.678(1); c=16.831(1) A; i=
3
105.27(1)°; V=4069.3(4) A ; zcalc=1.218 g cm−3
;
˚
v=3.04 cm−1; empirical absorption correction via €
scan data (0.9455C50.999); Z=4; monoclinic; space
group P21/c (No. 14); u=0.71073 A; T=223 K; ꢀ/2q
˚
1
scans; 8621 reflections collected (+h, +k, 9l);
m.p. 141°C (decomp). H-NMR (CDCl3): l=5.55 (s,
[(sin q)/u]=0.62 A−1; 8263 independent and 5308 ob-
10H, Cp), 2.43 (s, 3H, 3-CH3), 1.54 (s, 9H) and 1.23 (s,
9H, C(CH3)3). 1H-NMR (THF-d8, 360.1 MHz): l=
5.78 (s, 10H, Cp), 2.42 (s, 3H, 3-CH3), 1.62 (s, 9H) and
1.31 (s, 9H, C(CH3)3). 13C-NMR (THF-d8, 90.6 MHz):
l=222.7 (C1), 133.1 (C2), 121.1 (C5), 107.0 (Cp), 75.9
(C3), 63.5, 61.3, 29.4 and 28.7 (C(CH3)3), 6.2 (3-CH3).
IR (KBr): w˜ =3054, 2984, 2273 and 2206 (CꢀC, CꢀN),
1588 (CꢁN), 1480, 1432, 1374, 1012, 817, 746, 705
cm−1. UV/VIS (dichloromethane): umax=247 (m=
8000), 264 (sh, m=5800), 272 (sh, m=4200), 288 (sh,
m=1900), 319 (sh, m=1200). Anal. calc. for
C47H51N2BHf (833.24) C, 67.75; H, 6.17; N, 3.36; found
C, 67.23; H, 6.11; N, 2.82%.
˚
served reflections [I]2|(I)]; 467 refined parameters;
R=0.043; wR2=0.105; max residual electron density
0.45 (−0.43) e A−3; hydrogens calculated and refined
˚
as riding atoms. Data set was collected with an Enraf
Nonius MACH3 diffractometer. Programs used: data
reduction, MolEN; structure solution, SHELXS-86;
structure
refinement,
SHELXL-93;
graphics,
SCHAKAL-92. Crystallographic data (excluding struc-
ture factors) for the structures reported in this paper
have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication No.
CCDC-101212. Copies of the data can be obtained free
of charge on application to The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44
1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
3.5. Reaction of the [Cp2Hf–CꢀC–CH+3 ] cation with
2,6-dimethylphenylisocyanide: preparation of 8e
3.3. Reaction of the [(MeCp)2Zr–CꢀC–CH+3 ] cation
with tert-butylisocyanide: formation of 8c
Eight millilitres of THF was added to a solid mixture
of 500 mg (1.28 mmol) of bis(propynyl)hafnocene (1d)
and 505 mg (1.25 mmol) of N,N-dimethylanilinium
tetraphenylborate at 0°C. After formation of a clear
solution 2.0 g of 2,6-dimethylphenylisocyanide was
added. The mixture was stirred for 3 days at ambient
temperature, then the solvent was removed in vacuo
and the residue was stirred with 20 ml of pentane to
give a solid. This was washed twice with 10 ml of
pentane and toluene and dried in vacuo to give 865 mg
(MeCp)2Zr(–CꢀC–CH3)2 (1c, 200 mg, 611 mmol) was
treated with 270 mg (611 mmol) of 3 in 10 ml of THF
at 0°C. After 2 min 0.5 ml of tert-butylisocyanide was
added to the clear solution. Workup carried out
analogously as described above gave a slightly contam-
inated product 8c that still contained some THF. The
product was, therefore, only characterized spectroscopi-
cally. Yield of 8c: 388 mg (75%), m.p. 192°C (decomp).
1H-NMR (CDCl3): l=5.60–5.45 (s, 8H, MeCp), 2.40
(s, 3H, CH3), 1.93 (s, 6H, MeCp), 1.51 (s, 9H) and 1.27
(s, 9H, C(CH3)3); (THF: 3.49 (m, 4H, CH2), 1.77 (m,
1
(73%) of 8e, m.p. 83°C (decomp). H-NMR (CDCl3):
l=7.14 (t, 3H, Ph), 6.98 (t, 3H, Ph), 5.75 (s, 10H, Cp),
2.38 (s, 3H, 3-CH3), 2.08 (s, 6H, PhMe), 1.95 (s, 6H,
1
PhMe), (toluene: 7.46 (m, 5H), 2.32 (s, 3H)). H-NMR
1
4H, CH2)). H-NMR (THF-d8, 360.1 MHz): l=5.80–
(dichloromethane-d2, 360.1 MHz): l=7.30–7.10 (m,
6H, Ph), 6.01 (s, 10H, Cp), 2.39 (s, 3H, 3-CH3), 2.17 (s,
6H, PhMe), 2.04 (s, 6H, PhMe). 13C-NMR
(dichloromethane-d2, 90.6 MHz): l=230.6 (C1), 144.7,
144.4, 134.67 (m-Ph), 132.40 (p-Ph), 130.41 (i-PhMe),
129.96 (i-PhMe), 129.77 (m-Ph), 127.52 (p-Ph), 107.4
(Cp), 76.6 (C3), 19.2 (PhMe), 18.4 (PhMe), 6.79 (3-
CH3), (C5 and C2 not observed). IR (KBr): w˜ =3053,
3034, 2982, 2965, 2919, 2852, 2189 (CꢀC, CꢀN), 1618
5.75 (s, 2H, MeCp), 5.75–5.65 (m, 4H, MeCp), 5.60–
5.55 (m, 2H, MeCp), 2.40 (s, 3H, 3-CH3), 2.00 (s, 6H,
MeCp), 1.60 (s, 9H) and 1.35 (s, 9H, C(CH3)3); (THF:
3.64 (m, 4H, CH2), 1.77 (m, 4H, CH2)). 13C-NMR
(THF-d8, 90.6 MHz): l=217.1 (C1), 133.7 (C2), 123.3
(C5), 110.1, 109.7, 107.1, 106.3 (MeCp), 74.5 (C3), 64.0,
61.3, 29.6 and 29.1 (C(CH3)3), 15.2 (MeCp), 6.2 (3-
CH3). (THF: 68.2, 26.4). IR (KBr): w˜ =3054, 2988,

W. Ahlers et al. / Journal of Organometallic Chemistry 571 (1998) 83–89
89
G. Erker, R. Zwettler, C. Kru¨ger, Chem. Ber. 122 (1989) 1377.
(e) S.M. Beshouri, D.E. Chebi, P.E. Fanwick, I.P. Rothwell, J.C.
Huffman, Organometallics 9 (1990) 2375. (f) F.R. Lemke, D.J.
Szakla, R.M. Bullock, Organometallics 11 (1992) 876. (g) A.S.
Guram, Z. Guo, R.F. Jordan, J. Am. Chem. Soc. 115 (1993)
4902.
(CꢁN), 1601, 1578, 1440, 1427, 1378, 1262, 1202, 1088,
1031, 810, 774, 733, 703, 610 cm−1
UV/VIS
(dichloromethane): umax=231 (m=78000), 259 (sh, m=
42600), 286 (sh, m=16300). Anal. calc. for
C55H51N2BHf (929.33) C, 71.08; H, 5.53; found C,
71.57; H, 6.63%.
.
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Financial support from the Fonds der Chemischen
Industrie, the Bundesministerium fu¨r Bildung, Wis-
senschaft, Forschung und Technologie (BMBF), and
the Deutsche Forschungsgemeinschaft is gratefully
acknowledged.
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