The tetracyclopentadienyls of titanium, zirconium and hafnium: New synthetic procedures and reactivity

Article abstract of DOI:10.1016/S0022-328X(97)00778-X

In toluene as medium, the tetra(cyclopentadienyl) derivatives of Group 4 elements, MCp₄ (M=Ti, Zr, Hf), have been prepared in high yields from MCp₂Cl₂ and NaCp. The reactivity of ZrCp₄ with species containing active protons such as Ph₃SiOH or strong acids has been studied. Substituted bis(cyclopentadienyl) derivatives were produced except in the case of the reaction between ZrCp₄ and CF₃SO₃H. In this case, the tris(cyclopentadienyl) derivative ZrCp₃(CF₃SO₃) was obtained as a pale yellow crystalline material, reactive with water to give the μ-oxo derivative of zirconium(IV), [ZrCp₂(CF₃SO₃)]₂O, which has been characterized by standard methods and by X-ray diffraction. Crystal data: C₂₂H₂₀F₆O₇S₂Zr₂, M=756.96 g mol^-1, monoclinic, space group C2/c (no. 15), a=19.525(4), b=9.028(2), c=16.152(5) A, β=107.31(2)°, V=2718.2(1) A³, Z=4, d_calc=1.850 g cm^-3, λ(Cu-K_α)=1.54184 A, T=291 K, μ=85.66 cm^-1, F(000)=1496, R=0.054, Rw=0.049.

Full text of DOI:10.1016/S0022-328X(97)00778-X

Journal of Organometallic Chemistry 555 (1998) 49–56
The tetracyclopentadienyls of titanium, zirconium and hafnium: new
synthetic procedures and reactivity
a
b
a,
a
Fausto Calderazzo , Ulli Englert , Guido Pampaloni *, Giovanna Tripepi
a
Dipartimento di Chimica e Chimica Industriale, Uni6ersit a` di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy
b
Institut f u¨ r Anorganische Chemie der Rheinisch-Westf a¨ lischen Technischen Hochschule, Professor-Pirlet-Strasse 1, D-52074 Aachen, Germany
Received 8 September 1997; received in revised form 3 December 1997; accepted 3 December 1997
Abstract
In toluene as medium, the tetra(cyclopentadienyl) derivatives of Group 4 elements, MCp (M=Ti, Zr, Hf), have been prepared
4
in high yields from MCp Cl and NaCp. The reactivity of ZrCp with species containing active protons such as Ph SiOH or strong
2
2
4
3
acids has been studied. Substituted bis(cyclopentadienyl) derivatives were produced except in the case of the reaction between
ZrCp and CF SO H. In this case, the tris(cyclopentadienyl) derivative ZrCp (CF SO ) was obtained as a pale yellow crystalline
4
3
3
3
3
3
material, reactive with water to give the v-oxo derivative of zirconium(IV), [ZrCp (CF SO )] O, which has been characterized by
2
3
3 2
−
1
standard methods and by X-ray diffraction. Crystal data: C H F O S Zr , M=756.96 g mol , monoclinic, space group C2/c
2
2
20
6
7
2
2
˚ ˚
3
−3
(
1
no. 15), a=19.525(4), b=9.028(2), c=16.152(5) A, i=107.31(2)°, V=2718.2(1) A , Z=4, dcalc=1.850 g cm , u(Cu–K )=
h
˚
.54184 A, T=291 K, v=85.66 cm , F(000)=1496, R=0.054, Rw=0.049. © 1998 Elsevier Science S.A. All rights reserved.
−1
Keywords: Zirconium; X-ray diffraction; Derivative
in the seventies by a number of generally low-to-
medium-yielding reactions [3], particularly for the zirco-
nium and hafnium derivatives. Their reactivity has been
studied, most of the work being confined to the reac-
1
. Introduction
Hydrocarbyl derivatives of bis(cyclopentadienyl)
compounds of Group 4 elements (titanium, zirconium,
hafnium) are of great interest for their implications in
the activation of small molecules such as olefins, CO,
CO , N , H , etc, [1]. A renewed interest for the funda-
tion of MCp , M=Zr, Hf, with active protons in
4
aqueous medium (water, hydrofluoric acid, nitric acid
[
4]): only one report exists on the reaction of ZrCp4
2
2
2
with alcohols, thiols and chlorinated carboxylic acids
5]. It has also been reported that the thermal decompo-
sition of TiCp or the reduction of ZrCp with KC
mental properties of this class of compounds originated
[
from the discovery that cationic metallocene alkyls of
+
general formula [MCp R] are catalytically active spe-
4
4
8
2
afford TiCp ([3]b) or ZrCp [6], respectively.
cies in the homogeneus polymerization of olefins [2].
At variance with the large number of studies on
MCp R (R=organyl fragment) derivatives, the tetra(-
3
3
In the solid state TiCp and HfCp have a formal
4
4
5
valence electron counting of 16 (two p - and two
p -cyclopentadienyls); ZrCp contains three p - and
one p -cyclopentadienyl groups [7], corresponding to an
2
2
1
5
cyclopentadienyl) derivatives, MCp , M=Ti, Zr, Hf,
4
4
1
represent a largely neglected class of related com-
pounds. These compounds, as well as several of their
cyclopentadienyl-substituted congeners were prepared
electron counting of 20. The three compounds are
fluxional in solution: TiCp
room temperature (r.t.) which become sharp at low
shows two broad singlets at
4
temperature (ca. −27°C) [3], while ZrCp and HfCp
*
Corresponding author. +39 509 18221219; fax: +39 5020237;
4
4
e-mail: pampa@dcci.unipi.it
show one single resonance even at −150°C [8].
0
022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00778-X

5
0
F. Calderazzo et al. / Journal of Organometallic Chemistry 555 (1998) 49–56
Both in the solid state and in solution, the tetra(cy-
or Et O ([3]b); no decomposition is noticed at r.t. and
2
clopentadienyl) derivatives can be regarded to be simi-
lar to the bis(cyclopentadienyl)dialkyls of general
formula MCp R . In the framework of our recent
TiCp was isolated in satisfactory yields. In our hands
4
TiCp4 is a dark brown solid extremely sensitive to
moisture and gives dark coloured solutions (from green
to blue) in toluene or in ethereal solvents.
2
2
studies on organometallics of early transition elements
9], we therefore decided to reinvestigate these systems.
[
As far as zirconium and hafnium are concerned, the
In this paper we report on high-yield syntheses of
lower solubility of MCp (M=Zr, Hf) with respect to
4
MCp (yields ranging from 60%, M=Ti, to 90%, M=
TiCp , requires an extraction (with toluene at ca. 50°C
4
4
Zr, Hf) and on their reactions with substances contain-
ing active protons in non aqueous media.
under reduced pressure) of the solid materials origi-
nated from Eq. (2): we have thus obtained good (80%)
[
12] to excellent (86%) yields of ZrCp4 and HfCp4,
respectively.
MCp Cl is slowly converted to MCp
in the presence of excess NaCp. We have not been able
2. Results and discussion
3
(M=Zr, Hf)
4
to isolate pure ZrCp Cl or to reproduce the synthesis of
2.1. Synthesis
3
ZrCp Cl reported by Etievant and coworkers [13]. By
3
the reaction of ZrCp Cl with NaCp (1:1 molar ratio),
The study of the MCp derivatives, M=Ti, Zr, Hf,
began with a re-examination of their synthetic proce-
dures. A literature survey pointed out several facts: (a)
2
2
4
ZrCp Cl is effectively formed but in a mixture with
3
ZrCp Cl : all attempts to separate the compounds were
2
2
unsuccessful. Moreover, we have not been able to ob-
tain ZrCp Cl in a pure state by alternative routes such
the preparation of TiCp had to be reconsidered in view
4
of the fact that this substance has been reported as
greenish–black’ ([3]a) or ‘violet-black’ ([3]b), probably
as a function of the nature of the solvent and tempera-
ture; (b) no direct ‘cyclopentadienylation’ reaction of
3
as the reactions of ZrCp with stoichiometric amounts
‘
4
of ZrCp Cl . On the other hand, HfCp Cl is the only
2
2
3
cyclopentadienyl derivative in solution (5.71 ppm) when
equimolar amounts of HfCp and HfCp Cl are mixed
TiCl appeared to have been reported as yet; (c) details
4
2
2
4
in C D .
on the large scale preparation of MCp are not readily
6
6
4
Other potential cyclopentadienylating agents, beside
NaCp, have been taken into consideration, in toluene
available (especially in the case of HfCp ); (d) the yields
4
of the ‘cyclopentadienylation reaction’ starting from
MCp Cl are low especially in the case of the zirconium
as medium. No reaction takes place between ZrCp Cl
2
2
2
2
and TlCp. By taking into consideration the M–Cl bond
energies of the dinuclear molecules in the gas phase as
a homogeneus set of comparative data (Tl–Cl, 372.8;
compound.
NMR monitoring of the reaction of TiCl with NaCp
4
in C D showed that TiCp Cl (5.97 ppm) [10] and
6
6
2
2
−
1
Zr–Cl, 489.5 kJ mol ) [14], the possibility existed that
in the case of thallium the thermodynamically favoured
reaction was the reverse, i.e. the formation of TlCp
TiCp Cl (5.59 ppm) ([3]a) are intermediates to TiCp .
3
4
Also, NMR experiments have shown that the reaction
of MCp Cl (M=Zr, Hf) with NaCp in C D proceeds
2
2
6
6
from ZrCp . In fact, ZrCp reacts with TlCl in toluene
with the intermediate rapid formation of MCp Cl,
4
4
3
to give a quantitative conversion to ZrCp Cl and
which slowly reacts to give the final product. From a
qualitative comparison, hafnium appears to react more
slowly than zirconium: this is consistent with the gen-
eral trend for substitution reactions in inorganic sys-
tems of cations in their usual oxidation state [11], i.e.
rates decrease from 4d to 5d.
2
2
TlCp, see Eq. (3).
ZrCp +2TlCl“ZrCp Cl +2TlCp
(3)
4
2
2
Thus, tetra(cyclopentadienyl)zirconium(IV) behaves
as a cyclopentadienylating agent of thallium(I).
The formation of MCp from MCp Cl and NaCp
4
2
2
The effect of the solvent was studied. In the
ZrCp Cl /NaCp system, when THF was used as
can be summarized as described in (Eq. (1)), M=Ti,
and (Eq. (2)), M=Zr, Hf.
2
2
medium, an inseparable mixture of ZrCp and decom-
4
NaCp
NaCp
NaCp
position products was obtained. ZrCp is not stable in
TiCl4 “ TiCp Cl “ TiCp Cl “ TiCp
(1)
4
2
2
3
4
THF and slowly reacts to give a suspension containing
an almost insoluble, yellow material. A GC/MS analy-
sis of the solution showed the presence of dicyclopenta-
diene as major product.
NaCp
NaCp
MCp Cl “ MCp Cl “ MCp4
M=Zr, Hf
2
2
3
(
2)
By operating in toluene in a biphasic system, TiCp4
has been obtained as a dark brown solid from either
TiCl or TiCp Cl and NaCp. In both cases, the reac-
2.2. Reacti6ity
4
2
2
tion is fast and no control of the temperature is re-
quired during the reaction and subsequent work-up as
in the case of the preparations performed in THF ([3]a)
The study of reactivity was mainly confined to
ZrCp4.

F. Calderazzo et al. / Journal of Organometallic Chemistry 555 (1998) 49–56
51
ZrCp promptly reacts with Ph SiOH to give com-
ZrCp +2CF COOH“ZrCp (CF COO) +2CpH
4 3 2 3 2
4
3
pound 4, deriving from protonolysis of two cyclopenta-
dienyl rings, see Eq. (4). Compound 4 is known to be
obtained in high yields from ZrCp Me and Ph SiOH
(7)
On the other hand, the reaction of one equivalent of
CF SO H with ZrCp , (Eq. (8)), produces the tris(cy-
clopentadienyl) derivative 5, which easily forms the
bis(cyclopentadienyl) 6 upon treatment with one equiv-
alent of the acid.
2
2
3
3
3
4
[
15].
ZrCp +2Ph SiOH“ZrCp (Ph SiO) (4)+2CpH
(4)
Attempts to obtain the product of monosubstitution
ZrCp (Ph SiO) failed even when using a Zr/Si molar
4
3
2
3
2
3 3
CF SO H
3
3
ZrCp
“
ZrCp (CF SO )(5)
4
3
3
3
−
CpH
ratio of 1 (in this case half of the starting material was
recovered unchanged).
CF
3
SO
3
H
“
ZrCp (CF SO ) (6)
(8)
2
3
3 2
−CpH
n
On the other hand, [N Bu H][CF SO ] reacts
3
3
3
Compound 5 is so prone to give 6 that the preparation
of 5 must be performed under high dilution of the
reactants and by slow addition of a heptane solution of
the acid (see Section 3) to a toluene suspension of
ZrCp . By operating in this way, 5 has been isolated in
good yields as a pale yellow crystalline material ex-
tremely sensitive to moisture. As a matter of fact, while
recording the H-NMR spectrum of 5 we observed the
quick reduction of the intensity of the resonance of the
Cp protons at 6.03 ppm (only one peak is observed due
to the rapid exchange of the Cp ligands), probably due
to adventitious water; at the same time, the resonances
typical of CpH grow together with a signal at 5.82 ppm.
promptly with tetra(cyclopentadienyl)zirconium(IV) to
give ZrCp (CF SO ), Eq. (5), and only the use of a
3
3
3
n
[
N Bu H][CF SO ]/Zr molar ration of 2 allows the
3 3 3
preparation of the bis(cyclopentadienyl) derivative
ZrCp (CF SO ) , vide infra.
4
2
3
3 2
n
ZrCp +[N Bu H][CF SO ]
4
3
3
3
1
n
“
ZrCp (CF SO )+N Bu +CpH
(5)
3
3
3
3
The experimentally verified reactions between ZrCp4
n
and Ph SiOH or [N Bu H][CF SO ] suggest that the
3
3
3
3
driving force of the proton transfer reactions to Cp is
the formation of the zirconium–oxygen bond.
19
In the F-NMR spectrum, the intensity of the −77.8
ppm resonance decreases while the resonance at −78.3
ppm, due to [ZrCp (CF SO )] O, vide infra, increases.
The availability of ZrCp and the fact that the reac-
4
tions reported in Eqs. (4) and (5) are reminescent of the
protonolysis of ZrCp Me by alcohols or carboxylic
2
3
3 2
2
2
This observation prompted us to investigate the reac-
tion of 6 with moisture (NMR) and with water on a
preparative scale. The NMR experiment confirmed the
observations reported above and we isolated the v-oxo
derivative of zirconocene 7 containing triflate as addi-
tional ligand (Eq. (9))
acids [15–18], prompted us to investigate the reactions
of ZrCp4 with fluorinated, strong acids such as
CF COOH and CF SO H.
The choice of the fluorinated acids stems from the
fact that the conjugate base of these acids should be a
relatively weak ligand and, in principle, species such as
3
3
3
ZrCp L should become stable enough, with respect to
3
2
ZrCp (CF SO )+H O
3
3
3
2
the product of disubstitution ZrCp L , to be isolatable
2
2
(
see Eq. (6)).
HX
“[ZrCp
2
(CF
3
SO )]
3
O+2CpH(7)
2
(9)
HX
ZrCp “ ZrCp X “ ZrCp X
Compound 7 has been characterized by conventional
analytical and spectroscopic methods; moreover, a X-
ray crystallographic study has shown the compound to
be a centrosymmetric v-oxo derivative of zirconiu-
m(IV), see Fig. 1.
4
3
2
2
X=CF COO, CF SO
3
(6)
3
3
In this connection, it is worth mentioning that com-
pounds of general formula MCp X are known in the
3
literature and examples are: ZrCp Cl [13], ZrCp H [19],
Some selected distances and angles are reported in
Table 1. The Zr–C mean distances and the Zr–O(1)
separation of 2.509 and 1.946(1) A, respectively, are
3
3
5
ZrCp · · ·H· · ·AlEt [20], or M[E(p -C H ) ]CpCl,
3
3
5
4 2
˚
M=Zr, Hf, E=CMe2 [21], M=Zr E=SiMe2,
CMe CMe [22], Cp Zr(P H) [23]. Polystyrene-linked
similar to those observed in the other structurally char-
2
2
3
4
zirconium and hafnium tris(cyclopentadienyl) deriva-
acterized v-oxo zirconocene derivatives: [ZrCp Cl] O
2
2
˚
[2.50 and 1.94 A (mean value)] [27], [ZrCp Me] O
2 2
tives of general formula (polystyrene-Cp)MCp Cl have
2
˚
[2.474 (mean value) and 1.948(1) A] [28],
been prepared [24]. Noteworthy is a recent paper by
Erker and coworkers with a crystallographic and syn-
thetic study on donor-ligand-stabilized tris(cyclopenta-
˚
[ZrCp (SPh)] O [2.547 (mean value) and 1.968(3) A ]
2
2
˚
[29], [ZrCp (NCO)] O [Zr–O=1.946(3) A] [30]. The
2
2
dienyl) cations of zirconium(IV) of general formula
Cp ligands are substantially planar with a maximum
+
˚
[
ZrCp L] [25].
deviation from planarity of 0.007 A. The Zr-ring cen-
3
˚
The reaction of ZrCp with CF COOH in toluene is
troid distances are 2.211(2) and 2.218(3) A.
4
3
fast and produces the known ZrCp (CF COO) [16]
independent of the acid/Zr molar ratio (see Eq. (7)).
The Zr–O–Zr fragment is almost linear [175.6(5)°] as
observed in [ZrCp Cl] O [168.9(8)°] [27], [ZrCp Me] O
2
3
2
2
2
2
2

5
2
F. Calderazzo et al. / Journal of Organometallic Chemistry 555 (1998) 49–56
1
19
H-(200 MHz, TMS as reference) and F-NMR (188
MHz, CFCl as reference) spectra were measured on a
3
Varian Gemini 200BB instrument.
TiCp Cl (Fluka) and ZrCp Cl (Fluka) were com-
2
2
2
2
mercial products used without purification. Ph SiOH
3
and AgCF SO3 were commercial products (Aldrich)
3
dried on P O in vacuo for 24 h prior to use.
4
10
HfCp Cl [10] and the cyclopentadienyl derivatives of
2
2
sodium and thallium were prepared according to litera-
ture [36]. NaCp·xTHF was prepared from finely di-
vided sodium and freshly prepared cyclopentadiene in
THF. The colorless solution was evaporated to dryness
and the resulting solid was transferred into vials sealed
under an argon atmosphere. The compound contains
variable amounts of THF depending on the drying
conditions. TlCp was obtained from a vigorously
stirred aqueous solution of TlOH (from Tl SO and
Fig. 1. PLATON [26] plot of the molecular structure of
ZrCp (CF SO )] O. Displacement ellipsoids are drawn at the 30%
probability level.
2
4
[
NaOH) and cyclopentadiene. The pale yellow solid was
dried on P O in vacuo for 24 h, transferred into vials
2
3
3 2
4
10
and sealed under an argon atmosphere.
Trifluoromethanesulfonic acid, CF SO H, was used
Table 1
˚
3
3
Selected bond distance (A) and angles (°) of [ZrCp (CF SO )] O
2
3
3 2
in a mixture with the corresponding anhydride as a
solution in heptane (0.026 M). The total amount of
trifluorosulfonate groups was determined by acid/base
titration in aqueous solution, while the CF SO H/
Zr
Zr
S
Zr
O1
O2
O1
O2
C1
O2
Zr
S
1.946(1)
2.129(6)
1.80(1)
94.9(2)
175.6(5)
153.2(4)
S
S
S
S
S
O4
O2
O3
O3
O4
1.403(6)
1.472(5)
1.414(7)
111.5(4)
112.7(4)
3
3
19
O1
Zr
Zr
O2
O2
(
CF SO ) molar ratio was obtained from the F-
3 3 2
NMR spectrum.
n
[
N Bu H][CF SO ] was prepared by slow addition of
3 3 3
n
Estimated standard deviations in parentheses refer to the least signifi-
cant digit.
N Bu to a heptane solution of CF SO H/(CF SO ) O,
3 3 3 3 3 2
vide supra. The colorless solid was filtered and dried in
1
vacuo (92% yield). H-NMR (CDCl , 25°C): l=8.8
3
[
[
174.1(3)°] [28], [ZrCp (SPh)] O [165.8(2)°] [29] and
2 2
(br, 1 H), 3.06 (m, 6 H), 1.71 (m, 6 H), 1.46 (m, 6 H),
ZrCp (NCO)] O [165.7(2)°] [30]. The linearity of the
19
2
2
0.98 (t, 9 H). F-NMR (CDCl , 25°C): l= −78.46 (s).
3
M–O–M bridge, as observed in other structurally char-
acterized v-oxo derivatives of Group 4 [31], suggests
that maximum overlap of the empty orbitals of the
3
.1. Preparation of MCp , M=Ti, Zr, Hf
4
MCp X fragments with lone pairs on oxygen [32] is
2
3.1.1. NMR study of the reaction of MCp Cl2
2
operative in compound 7. The resulting increase of
bond order results in the Zr–O(1) distance [1.946(1)]
which is shorter than the Zr–O(2) separation [2.129(6)
(M=Zr, Hf) with NaCp
M=Zr. A NMR tube was charged with ZrCp Cl
2
2
(
0.014 g, 0.048 mmol), C D (1 ml) and NaCp·0.5THF
6 6
˚
A]; the latter is comparable to those observed in
(
0.033 g, 0.27 mmol) for a NaCp/Zr molar ratio of 5.6.
˚
˚
ZrCp (CF SO ) ·THF
[2.219(6)
A]
[33],
2
3
3 2
A spectrum recorded after 5 min showed the presence
[
ZrCp (bipy)(CF SO )]CF SO [2.228(7) A] [34] and
2
3
3
3
3
of ZrCp Cl (l=5.69 ppm) [13] as the only product in
3
˚
[ZrCp (CF SO )] (v-H) ·0.5THF [2.205(2) A] [35].
2 3 3 2 2
{
solution. After ca. 15 h shaking at r.t., the spectrum
showed one signal only at 5.57 ppm typical of ZrCp4
(
[3]h)([8]b).
3. Experimental
By using NaCp/Zr molar ratios B4, a mixture of
ZrCp Cl , ZrCp Cl and ZrCp was found after com-
2
2
3
4
Unless otherwise stated, all of the operations were
parable reaction times.
M=Hf. A NMR tube was charged with HfCp Cl
carried out under an atmosphere of prepurified argon.
Solvents were dried by conventional methods prior to
use.
IR spectra were recorded on a FT-1725X instrument
on solutions or nujol or polychlorotrifluoroethylene
2
2
(
0.016 g, 0.042 mmol), C D (1 ml) and NaCp·0.5THF
6 6
(
0.032 g, 0.26 mmol), for a NaCp/Hf molar ratio of 6.5.
A spectrum recorded after 5 min showed a signal due to
unreacted starting material (l=5.82 ppm) [10] and a
(
PCTFE) mulls prepared under rigorous exclusion of
moisture and air.
new resonance at l=5.71 ppm (HfCp Cl). After 30
3
min shaking at r.t., the spectrum showed signals at 5.71

F. Calderazzo et al. / Journal of Organometallic Chemistry 555 (1998) 49–56
53
and 5.63 ppm, the latter typical of HfCp [8]. After ca.
from the solution by distillation under reduced pres-
sure. A GC/MS analysis of the solution showed the
presence of dicyclopentadiene [(m/z; assignment, rela-
4
4
0 h shaking at r.t., HfCp was the only cyclopentadi-
4
enyl compound present in solution.
+
+
By using NaCp/Hf molar ratios B4, a mixture of
HfCp Cl , HfCp Cl and HfCp was found after a reac-
tive abundance, %): 132, M , 35; 117, M −CH , 5;
3
+
+
6
+
3
91, C H , 5; 66, C H , 100; 51,C H −CH , 5; 39,
2
2
3
4
7
7
5
5
6
+
tion time of ca. 50 h.
C H , 8.
3 3
1
HfCp ([8]b), yellow, 86% yield. H-NMR (200 MHz,
4
3.1.2. Preparation
C D , 25°C): l=5.63 (s). The spectrum remains un-
6
6
M=Ti, 1. (a) from TiCl . A solution of TiCl (0.125
changed at −90°C.
4
4
g, 1.32 mmol) in toluene (50 ml) was treated at r.t. with
solid NaCp·0.08THF (0.74 g, 7.9 mol). The colour of
the suspension quickly changed from yellow to red to
brown and, after ca. 10 min, to blue–green. After 4 h
stirring at r.t., the suspension was filtered, the solid was
washed with toluene (10 ml) and the solution was dried
in vacuo at r.t. The brown residue was suspended in
heptane (10 ml) and filtered. The solid was dried in
3
.2. Reaction of 2 with TlCl
Solid TlCl (0.155 g, 0.65 mmol) and ZrCp (0.111 g,
.32 mmol) were stirred in toluene for ca. 72 h at r.t.
4
0
During this period, the starting yellow suspension be-
came almost colorless. After filtration, the solution was
dried in vacuo at r.t. and the residue was dissolved in
C D and identified by H-NMR as a ca. 2:1 mixture of
TlCp (6.05 ppm) and ZrCp Cl (5.91 ppm).
2 2
vacuo at r.t. (0.13 g, 33% yield) and identified as TiCp4
1
6
6
1
(
[3]a) by H-NMR (200 MHz, C D , 25°C): l=5.30
6
6
(
s), 6.00 (s) ppm.
b) from TiCp Cl . A suspension of TiCp Cl (1.35 g,
(
2
2
2
2
3
.3. Reaction of 2 with compounds containing acti6e
5.4 mmol) in toluene (150 ml) was treated with
protons
NaCp·0.2THF (2.74 g, 26.7 mmol) obtaining a brown
suspension, that quickly turned blue–green. After 2 h
stirring at r.t., the suspension was filtered. The filtrate
was evaporated to dryness under reduced pressure at
r.t. and heptane (25 ml) was added; the resulting sus-
pension was filtered, the brown solid was dried in vacuo
3
.3.1. Ph SiOH
3
Ph SiOH (0.58 g, 2.1 mmol) was added to a yellow
3
suspension of 2 (0.37 g, 1.05 mmol) in toluene (100 ml).
After 5 h stirring at r.t., a colourless solution was
obtained. After ca. 15 h, the solution was evaporated to
dryness under reduced pressure at r.t. and heptane was
added (10 ml). The suspension was filtered, the colorless
solid was washed with heptane (3×5 ml) and dried in
vacuo affording ZrCp (Ph SiO) , 4 [15], (0.706 g, 98%),
identified from analytical and spectral (IR, NMR) data.
The same compound (IR, NMR) was obtained in a
lower yield (41%) by using a Ph SiOH/Zr molar ratio of
and identified as TiCp ([3]a) (1.00 g, 60% yield) by
4
1
H-NMR (200 MHz, C D , 25°C): l=5.30 (s), 6.00 (s)
6
6
ppm. The solid material is stable at r.t. and can be
stored in sealed vials under an argon atmosphere at
−
30°C for several months.
2
3
2
M=Zr, 2, Hf, 3. The compounds were prepared by
a modification of the published procedure consisting of
extracting the crude reaction mixture with toluene un-
der reduced pressure. Only the preparation of the com-
pound with M=Zr is described in detail, the other
being performed in a similar way, the only difference
being the reaction time: 12 h for zirconium, 48 h for
hafnium. A suspension of ZrCp Cl (2.13 g, 7.3 mmol)
3
1
.
3.3.2. CF COOH
3
A suspension of 2 (0.18 g, 0.52 mmol) in toluene (15
ml) was cooled at ca. −40°C and treated with 0.09 ml
of a CF COOH/(CF CO) O mixture (5% w/w, 1.04
2
2
in toluene (250 ml) was treated with NaCp·0.2THF
3.45 g, 33.7 mmol). After 12 h stirring at r.t., the
3
3
2
(
mmol of CF COOH). A colourless solution was ob-
3
resulting yellow suspension was filtered and the solid
was extracted for about 6 h with refluxing toluene
under reduced pressure (bath temperature, ca. 50°C).
The extract was evaporated to dryness under reduced
pressure at r.t. and heptane (25 ml) was added; the
resulting suspension was filtered, and the yellow solid
tained. The solvent was partially removed in vacuo at
r.t., heptane (10 ml) was added and the resulting solid
was filtered and dried in vacuo at r.t. The colorless
solid (0.16 g, 82% yield) was identified as
ZrCp (CF COO) [16]. Anal. Found: C, 37.4; H, 1.8.
2
3
2
C H F O Zr Calc.: C, 37.6; H, 2.2. IR (nujol and
14
10
6
4
was dried in vacuo and identified as ZrCp ([3]h)([8]b)
PCTFE): v˜ =3092(mw), 1718(vs), 1405(ms), 1185(s),
4
1
−
(
2.21 g, 80% yield) by H-NMR (200 MHz, C D ,
1140(s), 1016(m), 808(s), 743(s), 718(m), 605(mw) cm
6
6
1
19
25°C): l=5.57 (s).
1. H-NMR (200 MHz, C D , 25°C): l=5.69. F-
6 6
Solid 2 (0.04 g, 0.11 mmol) was dissolved in THF (5
NMR (C D , 25°C): l= −75.9.
6
6
ml) giving a yellow solution. After 48 h stirring at r.t.,
a suspension of a yellow–orange solid in a light-yellow
solution was obtained. The volatiles were removed
The same compound (IR, NMR) was obtained in a
lower yield (36%) by using a CF COOH/Zr molar ratio
3
of 1.

5
4
F. Calderazzo et al. / Journal of Organometallic Chemistry 555 (1998) 49–56
3
.3.3. CF SO H (CF SO H/Zr molar ratio=1)
3.4.2. Preparation
3
3
3
3
A 0.026 M solution of CF SO H (75 ml, 1.95 mmol)
Water (2.6 ml, 0.14 mmol) was added to a suspension
3
3
in heptane-containing (CF SO ) O was added dropwise
of ZrCp (CF SO ) (0.12 g, 0.27 mmol) in toluene (10
3
3 2
3
3
3
(
(
2 h) to a suspension of 2 (0.73 g, 2.08 mmol) in toluene
100 ml). After 24 h stirring at r.t., the resulting pale-
ml). After 4 h stirring at r.t., a colorless suspension was
obtained which turned pale-yellow after 24 h stirring at
r.t. The suspension was evaporated to dryness under
reduced pressure at r.t. and the colourless solid dried in
vacuo was identified as 7 (0.05 g, 49% yield). Anal.
Found: C, 34.9; H, 2.6. C H F O S Zr Calc.: C, 34.9;
yellow suspension was filtered and the pale-yellow solid
was dried in vacuo and identified as ZrCp (CF SO ), 5,
(
3
3
3
0.54 g, 60% yield). Anal. Found: C, 44.2; H, 3.3.
C H F SO Zr Calc.: C, 44.1; H, 3.5. IR (nujol and
1
6
15
3
3
22 20
6
7
2
2
PCTFE): v˜ =3112(w), 3047(w), 1444(m), 1339(ms),
H, 2.7. IR (nujol and PCTFE): v˜ =3112(w), 1435(w),
1365(m), 1339(s), 1293(m), 1263(m), 1239(s), 1212(s),
1187(s), 1172(s), 1125(m), 1070(m), 1020(s), 917(w),
838(m), 815(s), 741(s), 633(s), 608(m), 593(m), 569(w),
1
1
5
6
327(m), 1262(m), 1238(m), 1212(s), 1183(m), 1097(m),
021(s), 815(s), 742(m), 687(m), 633(ms), 605(w),
−
1 1
92(w), 506(w) cm . H-NMR [37] (C D , 25°C): l=
6
6
1
9
−1 1
.03 (s). F-NMR (C D , 25°C): l= −77.8 (s).
525(w), 505(m) cm . H-NMR (C D , 25°C): l=5.82
6
6
6 6
19
The same compound contaminated by small amounts
of ZrCp (CF SO ) , 6, see below, was obtained by
(s). F-NMR (C D , 25°C): l= −78.3 (s).
6 6
2
3
3 2
reaction of ZrCp with [NBu H][CF SO ] in C D in a
4
3
3
3
6
6
1:1 molar ratio.
3.5. Crystal structure solution and refinement of 7
3
.3.4. CF SO H (CF SO H/Zr molar ratio=2)
A complete list of all atomic coordinates, anisotropic
displacement parameters, and interatomic distances are
available as Supplementary Material and have been
deposited with the Fachinformationszentrum Karl-
sruhe, D-76344, Eggenstein-Leopoldshafen (FRG), de-
pository number CSD-407980.
3
3
3
3
Triflic acid (containing ca. 15% of (CF SO ) O; 0.1
3
2 2
ml, 1.0 mmol of CF SO H) was added at −60°C to a
3
3
suspension of 2 (0.18 g, 0.51 mmol) in toluene (20 ml).
A pale-brown solid immediately formed. After 0.5 h
stirring at r.t., the suspension was cooled at −30°C
overnight; after filtration, the resulting pale-brown solid
was filtered and dried in vacuo (0.11 g) and identified as
ZrCp (CF SO ) , 6, [17]. The solution was evaporated
3.5.1. Crystal data
C H F O S Zr , M=756.96 g mol , monoclinic,
22 20 6 7 2 2
2
3
3 2
−
1
to dryness under reduced pressure at r.t. and heptane
10 ml) was added. The suspension was filtered and an
additional crop (0.09 g) of ZrCp (CF SO ) was iso-
(
space group C2/c (no. 15), a=19.525(4), b=9.028(2),
˚
˚
3
c=16.152(5) A, i=107.31(2)°, V=2718.2(1) A , Z=
2
3
3 2
−
3
˚
lated (75% total yield). IR (nujol and PCTFE): v˜ =
4, dcalc=1.850 g cm , u(Cu–K )=1.54184 A, T=
h
−
1
3
1
1
122(w), 1439(w), 1337(s), 1321(s), 1292(m), 1267(s),
238(vs), 1228(s), 1212(vs), 1176(s), 1129(w), 1098(m),
071(m), 1028(vs), 859(m), 832(s), 767(w), 723(m),
291 K, v=85.66 cm , F(000)=1496.
Single crystals of [ZrCp (CF SO )] O were obtained
2
3
3 2
by slow cooling of a toluene solution at −30°C. Dif-
fraction data were collected at 291 K on a colorless rod
of approximate dimensions 0.7×0.3×0.25 mm with
an ENRAF NONIUS CAD4 diffractometer using
graphite-monochromated Cu–Kh radiation (u=
−
1
6
69(w), 633(s), 620(m s), 589(m), 518(m), 508(w) cm
.
1
19
H-NMR (CDCl3, 25°C): l=6.6 (s).
CDCl , 25°C): l= −77.5 (s).
F-NMR
(
3
The same compound was obtained (60% yield) by
˚
reaction of ZrCp Cl with two equivalents of
1.54184 A). A total of 5031 reflections were recorded
2
2
AgCF SO in toluene.
with the ꢀ−2q scan mode in the range 4.0BUB
3
3
6
8.0°. An empirical absorption correction based on
3
.4. Reaction of ZrCp (CF SO ) with H O: synthesis
azimuthal c scans [39] was applied before averaging
over symmetry equivalent data. 2637 independent in-
tensities were used to solve the structure by direct
methods [40]. A full-matrix least-squares refinement [41]
based on 1484 unique observations with I\1.0 |(I)
was carried out with anisotropic displacement parame-
ters for all non-hydrogen atoms. Hydrogen atoms were
located in idealized positions with isotropic thermal
parameters U(H)=1.3 U(C) and allowed to ride on
3
3
3
2
of [ZrCp (CF SO )] O, 7
2
3
3 2
3
.4.1. NMR monitoring
A NMR tube was charged with ZrCp (CF SO )
3
3
3
(
0.016 g, 0.037 mmol) and C D (1 ml) and the suspen-
6 6
sion was treated with H O (1 ml, 0.055 mmol). A
2
1
H-NMR spectrum recorded after 5 min showed a
signal due to unreacted starting material (l=6.03
ppm), and new resonances at l=5.82 ppm, assigned to
their C-atoms. Refinement converged with 178 parame-
2
[
ZrCp (CF SO )] O (vide infra), and at 6.42, 6.50 and
ters using a statistical weighting scheme w=1/[S (F )]
2
3
3
2
o
2
.93 ppm assigned to CpH [38]. The conversion of
at values of R=0.054 and R =0.049, GOF=1.206.
w
ZrCp (CF SO ) into [ZrCp (CF SO )] O was almost
complete in about 10 min.
Atomic coordinates are given in Table 2. Calculations
were performed using the SDP system of programs [41].
3
3
3
2
3
3 2

F. Calderazzo et al. / Journal of Organometallic Chemistry 555 (1998) 49–56
55
Table 2
monosubstitution can be isolated, presumably due to
the weak coordinating power of the conjugated base.
Atomic coordinates and equivalent isotropic displacement parameters
for [ZrCp (CF SO )] O
2
3
3 2
˚
2
Atom
x
y
z
Beq(A )
Acknowledgements
Zr
S
F1
F2
F3
O1
O2
O3
0.10254(4)
0.1068(1)
0.1552(3)
0.0423(3)
0.1134(4)
0.000
0.0931(3)
0.0487(4)
0.1768(4)
0.1028(5)
0.0770(6)
0.1076(5)
0.1782(5)
0.1913(5)
0.1257(6)
0.2097(5)
0.1678(5)
0.1034(5)
0.1065(5)
0.1726(5)
0.0394(1)
0.2321(3)
0.4762(7)
0.4739(8)
0.4943(8)
0.0311(9)
0.1868(7)
0.1954(9)
0.1991(9)
0.430(1)
-0.219(1)
-0.151(1)
-0.118(1)
-0.169(1)
-0.229(1)
0.140(1)
0.064(1)
0.148(1)
0.267(1)
0.263(1)
0.30898(4)
0.4990(1)
0.4547(5)
0.4339(4)
0.5630(5)
0.250
0.4079(3)
0.5304(4)
0.5502(4)
0.4861(7)
0.3461(6)
0.4237(6)
0.4316(6)
0.3541(6)
0.3036(6)
0.2720(6)
0.1981(5)
0.1666(5)
0.2190(6)
0.2847(6)
3.54(1)
4.82(6)
10.1(2)
9.3(2)
11.3(2)
3.6(2)
4.7(2)
8.5(2)
7.7(2)
6.9(3)
6.6(3)
6.0(3)
6.2(3)
7.0(3)
7.6(3)
6.7(3)
6.6(3)
6.7(3)
7.6(3)
7.3(3)
We thank the Consiglio Nazionale delle Ricerche
(
CNR, Roma), Progetto Strategico Metodologie Inno-
vative for financial support and Dr Luciano Pandolfo,
Universit a` di Padova, for the collection of the GC–MS
data.
O4
C1
C10
C11
C12
C13
C14
C20
C21
C22
C23
C24
References
[
1] (a) G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.), Comprehen-
sive Organometallic Chemistry, vol. 3, Pergamon Press, Oxford,
1
982. (b) E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.), Com-
prehensive Organometallic Chemistry II, a Review of the Litera-
ture 1982–1994, vol. 4, Pergamon Press, Oxford, 1995. (c) D.J.
Cardin, M.F. Lappert, C.L. Raston, Chemistry of Organo–Zir-
conium and –Hafnium Compounds, Ellis Horwood, Chichester,
1
986.
2] (a) W. Kaminsky, M. Arndt, Adv. Polymer Sci. 127 (1997) 144.
b) M. Bochmann, J. Chem. Soc. Dalton Trans. (1996) 255. (c)
[
[
Anisotropically refined atoms are given in the form of the isotropic
(
2
equivalent displacement parameter defined as: (4/3)ꢀ[a ꢀbeta(1,1)+
H.H. Brintzinger, D. Fischer, R. M u¨ lhaupt, B. Rieger, R.M.
Waymouth, Angew. Chem. Int. Ed. Engl. 34 (1995) 1143. (d)
P.C. M o¨ hring, N.J. Coville, J. Organomet. Chem. 479 (1994) 1,
and references therein.
2
2
b ꢀbeta(2,2)+c ꢀbeta(3,3)+ab(cosk)beta(1,2)+ac(cosi)beta(1,3)+
bc(cosh)beta(2,3)]. Estimated standard deviations in parentheses refer
to the least significant digit.
3] TiCp : (a) J.L. Calderon, F.A. Cotton, J. Takats, J. Am. Chem.
4
Soc. 93 (1971) 3587. (b) F.W. Siegert, H.J. De Liefde Meijer, J.
Organomet. Chem. 20 (1969) 141. (c) O. Khan, A. Dormond,
J.P. Letourneux, J. Organomet. Chem. 132 (1977) 149. (d) A.
Dormond, O. Khan, J. Tirouflet, J. Organomet. Chem. 110
4
. Conclusions
A close re-examination of the synthetic procedures to
the tetra(cyclopentadienyl) derivatives of titanium(IV),
zirconium(IV) and hafnium(IV) has shown that: (a) the
compounds are not stable in ethereal solvents; (b) the
best preparative results have been obtained in aromatic
hydrocarbons (toluene); (c) the nature of the cyclopen-
tadienylating agent is critical: as a matter of fact, TlCp
does not react with ZrCp Cl (ZrCp is really a cy-
clopentadienylating agent for TlCl), although its reac-
tion with NaCp (a biphasic solid–liquid system) is
complete and fast.
(
1976) 321. MCp , M=Zr, Hf: (e) A.V. Medvedeva, D.M.
4
Ryabenko, Zh. Prikl. Khim. (Leningrad) 45 (1972) 1296; Chem.
Abstr. 77 (1972) 75301x. (f) M.Kh. Minacheva, E.M. Brainina,
R.Kh. Freidlina, Dokl. Akad. Nauk SSSR 173 (1967) 581.
Chem. Abstr. 67 (1967) 32760x. (g) E.M. Brainina, M.Kh.
Minacheva, R.Kh. Freidlina, Izv. Akad. Nauk SSSR Ser. Khim.
(1965) 1877; Chem. Abstr. 64 (1966) 3594b. (h) E.M. Brainina,
G.G. Dvoryantseva, Izv. Akad. Nauk. SSSR Ser. Khim. (1967)
2
2
4
4
42; Chem. Abstr. 67 (1967) 21990w.
[
4] (a) M.Kh. Minacheva, O.A. Mikhailova, Z.S. Klemenkova, B.V.
Lokshin, G.I. Timofeeva, Metalloorg. Khim. 4 (1991) 1282;
Chem. Abstr. 116 (1992) 83829q. (b) M.Kh. Minacheva, V.I.
Dostovalova, Z.S. Klemenkova, O.A. Mikhailova, E.M. Brain-
ina, B.V. Lokshin, Metalloorg. Khim. 2 (1989) 647; Chem.
Abstr. 112 (1990) 139275t. (c) E.M. Brainina, M.Kh. Minacheva,
Z.S. Klemenkova, B.V. Lokshin, O.A. Mikhailova, Izv. Akad.
Nauk. SSSR Ser. Khim. (1987) 1848; Chem. Abstr. 109 (1988)
93213d.
The use of THF may be harmful in some cases. As a
matter of fact, ZrCp is not stable in THF; the high
affinity for oxygen of Group 4 elements in high oxyda-
tion state may trigger the deoxygenation of the ether.
4
The reactivity, which has been studied for ZrCp , is
4
similar to that of ZrCp R (R=hydrocarbyl group)
derivatives, i.e. two cyclopentadienyl ligands are lost as
[5] (a) E.M. Brainina, E.V. Bryukhova, B.V. Lokshin, N.S. Alimov,
Izv. Akad. Nauk. SSSR Ser. Khim. (1973) 891; Chem. Abstr. 79
2
2
(
1973) 42642x. (b) M.Kh. Minacheva, E.M. Brainina, Izv. Akad.
Nauk. SSSR Ser. Khim. (1972) 139; Chem. Abstr. 77 (1972)
9770n.
CpH by reaction of ZrCp with weak protic substances
4
such as diols or tertiary ammonium salts: as a general
rule, the product is the dicyclopentadienyl derivative
ZrCp L (L =two singly negatively charged oxygen
1
[6] W.W. Lukens Jr., R.A. Andersen, Organometallics 14 (1995)
3435.
2
2
2
[
7] TiCp : (a) J.L. Calderon, F.A. Cotton, B.G. DeBoer, J.J.
4
ligand). On the other hand, once a very strong Brønsted
acid is used, high yields of the monosubstituted deriva-
Takats, J Am. Chem. Soc. 93 (1971) 3592. ZrCp : (b) R.D.
4
Rogers, R.V. Bynum, J.L. Atwood, J. Am. Chem. Soc. 100
(1978) 5238. (c) V.I. Kulishov, E.M. Brainina, N.G. Bokiy,
Yu.T. Struchkov, J. Chem. Soc. Chem. Commun. (1970) 475. (d)
tive ZrCp (CF SO ) are obtained. It is worth noting
3
3
3
that only with the strong acid CF SO H, the product of
3
3

5
6
F. Calderazzo et al. / Journal of Organometallic Chemistry 555 (1998) 49–56
V.S. Sudarikov, V.I. Kulishov, N.G. Bokiy, Yu.T. Struchkov,
Zh. Strukt. Khim. 10 (1969) 558; Chem. Abstr. 71 (1969)
5262m. HfCp : (e) R.D. Rogers, R.V. Bynum, J.L. Atwood,
J. Am. Chem. Soc. 103 (1981) 692. (f) V.I. Kulishov, E.M.
Brainina, N.G. Bokiy, Yu.T. Struchkov, J. Organomet. Chem.
[20] H. Sinn, W. Kaminsky, H.-J. Vollmer, R. Woldt, Angew. Chem.
Int. Ed. Engl. 19 (1980) 390.
7
[21] (a) G.M. Diamond, M.L.H. Green, N.A. Popham, A.N.
Chernega, J. Chem. Soc. Dalton Trans. (1993) 2535. (b) G.M.
Diamond, A.N. Chernega, P. Mountford, M.L.H. Green, J.
Chem. Soc. Dalton Trans. (1996) 921.
[22] T. Ushioda, M.L.H. Green, J. Haggitt, X. Yan, J. Organomet.
Chem. 518 (1996) 155.
4
3
6 (1972) 333. (g) V.I. Kulishov, N.G. Bokiy, Yu.T. Struchkov,
Zh. Strukt. Khim. 13 (1972) 1110; Chem. Abstr. 78 (1973)
6894a.
7
[
[
8] (a) E.M. Brainina, N.P. Gambaryan, B.V. Lokshin, P.V. Petro-
vskii, Yu.T. Struchkov, Izv. Akad. Nauk. SSSR Ser. Khim.
[23] M. Baudler, B. Wingert, Z. Anorg. Allg. Chem. 619 (1993) 1977.
[24] B.-H. Chang, R.H. Grubbs, C.H. Brubaker Jr., J. Organomet.
Chem. 280 (1985) 365.
[25] (a) T. Brackemeyer, G. Erker, R. Fr o¨ hlich, Organometallics 16
(1997) 531. (b) T. Brackemeyer, G. Erker, R. Fr o¨ hlich, J. Prigge,
U. Peuchert, Chem. Ber. 130 (1997) 899.
(1972) 187; Chem. Abstr. 77 (1972) 19755m. (b) E.M. Brainina,
M.Kh. Minacheva, B.V. Lokshin, E.I. Fedin, P.V. Petrovskii,
Izv. Akad. Nauk. SSSR Ser. Khim. (1969) 2492; Chem. Abstr.
7
2 (1970) 67067g.
9] (a) F. Calderazzo, G. Pampaloni, J. Organomet, Chem. 500
1995) 47. (b) F. Calderazzo, I. Ferri, G. Pampaloni, S. Troy-
[26] A.L. Spek, PLATON94, University of Utrecht, The Nether-
lands, 1994.
(
anov, J. Organomet. Chem. 518 (1996) 189. (c) F. Calderazzo,
U. Englert, I. Ferri, M.L.H. Green, G. Pampaloni,
Organometallics 16 (1997) 3100.
[27] J.F. Clarke, M.G.B. Drew, Acta Crystallogr. 30B (1974) 2267.
[28] W.E. Hunter, D.C. Hrncir, R.V. Bynum, R.A. Penttila, J.L.
Atwood, Organometallics 2 (1983) 750.
[
[
[
[
[
[
[
10] P.M. Druce, B.M. Kingston, M.F. Lappert, T.R. Spalding, R.C.
[29] J.L. Petersen, J. Organomet. Chem. 166 (1979) 179.
[30] N. Klouras, N. Tzavellas, C.P. Raptopoulou, Z. Anorg. Allg.
Chem. 623 (1997) 1027.
[31] F. Bottomley, L. Sutin, Adv. Organomet. Chem. 28 (1988) 339.
[32] J.W. Lauher, R. Hoffmann, J. Am. Chem. Soc. 98 (1976) 1729.
[33] U. Thewalt, W. Lasser, Z. Naturforschg. 38B (1983) 1501.
[34] U. Thewalt, W. Lasser, J. Organomet. Chem. 363 (1989) C12.
[35] G.A. Luinstra, U. Rief, M.H. Prosenc, Organometallics 14
(1995) 1551.
[36] G. Thieme, Synthetic Methods of Organometallic and Inorganic
Chemistry (Herrmann/Brauer), vol. 1, in: W.A. Herrmann, A.
Salzer (Eds.), Verlag, Stuttgart, 1996, p. 52.
[37] The NMR data refer to freshly prepared solutions examined
within 10 min from preparation. On standing additional peaks
are formed.
[38] E. Pretsch, T. Clerc, J. Seibl, W. Simon, Tabellen zur Struk-
turaufkl a¨ rung Organischer Verbindungen, 2nd ed., Springer-Ver-
lag, Berlin, 1981, p. H230.
[39] A.C.T. North, D.C. Phillips, F.S. Mathews, Acta Crystallogr.
24A (1968) 351.
[40] G.M. Sheldrick, SHELXS-86, Program for Crystal Structure
Solution, University of G o¨ ttingen, Germany, 1986.
[41] ENRAF-NONIUS SDP, Version 5.0, Delft, The Netherlands,
1989.
Srivastava, J. Chem. Soc. A (1969) 2106.
11] F. Calderazzo, Insertion Reactions: Principles and Applications,
Wiley, New York, in preparation.
12] Yields as high as 40% of ZrCp have been obtained starting from
4
ZrCl4 [3e].
13] P. Etievant, B. Gautheron, G. Tainturier, Bull. Soc. Chim.
France (1978) 292.
14] CRC Handbook of Chemistry and Physics, 77th ed., CRC Press,
Boca Raton, FL, 1996, pp. 9–51.
15] E.A. Babaian, D.C. Hrncir, S.G. Bott, J.L. Atwood, Inorg.
Chem. 25 (1986) 4818.
16] (a) E.M. Brainina, R. Kh, Freidlina, Izv. Akad. Nauk. SSSR
Otd. Khim. Nauk. (1963) 835; Chem. Abstr. 59 (1963) 7548b. (b)
P.C. Wailes, H.J. Weigold, J. Organomet. Chem. 24 (1970) 413.
17] G.A. Luinstra, J. Organomet. Chem. 517 (1996) 209.
18] (a) G. Erker, S. Dehnicke, M. Rump, C. Kr u¨ ger, S. Werner, M.
Nolte, Angew. Chem. Int. Ed. Engl. 30 (1991) 1349. (b) D.W.
Stephan, Organometallics 9 (1990) 2718. (c) G. Erker, R. Noe, J.
Chem. Soc. Dalton Trans. (1991) 685. (d) T.T. Nadasdi, D.W.
Stephan, Can. J. Chem. 69 (1991) 167.
[
[
[
19] E.M. Brainina, L.I. Strunkina, B.V. Lokshin, M.G. Ezernit-
skaya, Izv. Akad. Nauk. SSSR Ser. Khim. (1981) 447; Chem.
Abstr. 95 (1981) 62334g.
.