Synthesis and reactions of Cp*2Hf(η2- PhC2SiMe3) with water and carbon dioxide

Article abstract of DOI:10.1021/om8003064

The complexation of phenyl(trimethylsilyl)acetylene by decamethylhafnocene gave the complex Cp*₂Hf(η²-PhC ₂SiMe₃) (1-Hf). By comparison of detailed spectroscopic and structural data as well as of some regioselective reactions of 1-Hf to the titanium analogue Cp*2Ti(η²-PhC₂SiMe ₃) (1-Ti) and the zirconium complex Cp*₂Zr(η²-PhC₂SiMe₃) (1-Zr) one can try to understand how the metals interact in these complexes with differently substituted acetylenic carbon atoms. AU data for 1-Hf show an extremely strong interaction of the alkyne with hafnium compared to the analogous compounds of titanium and zirconium. Complex 1-Hf reacted with water at the Hf-C(Ph) bond to form the complex Cp*₂Hf(OH)-C(SiMe ₃)=CHPh (2-Hf). With carbon dioxide, a mixture of regioisomeric hafnafuranones 4a/b-Hf was formed.

Full text of DOI:10.1021/om8003064

3954
Organometallics 2008, 27, 3954–3959
Synthesis and Reactions of Cp*2Hf(η2-PhC2SiMe3) with Water and
Carbon Dioxide†
Torsten Beweries, Vladimir V. Burlakov,‡ Stephan Peitz, Perdita Arndt,
Wolfgang Baumann, Anke Spannenberg, and Uwe Rosenthal*
Leibniz-Institut fu¨r Katalyse e. V. an der UniVersita¨t Rostock, Albert-Einstein-Str. 29a, D-18059 Rostock, Germany.
ReceiVed April 4, 2008
The complexation of phenyl(trimethylsilyl)acetylene by decamethylhafnocene gave the complex
Cp*2Hf(η2-PhC2SiMe3) (1-Hf). By comparison of detailed spectroscopic and structural data as well as of
some regioselective reactions of 1-Hf to the titanium analogue Cp*2Ti(η2-PhC2SiMe3) (1-Ti) and the
zirconium complex Cp*2Zr(η2-PhC2SiMe3) (1-Zr) one can try to understand how the metals interact in
these complexes with differently substituted acetylenic carbon atoms. All data for 1-Hf show an extremely
strong interaction of the alkyne with hafnium compared to the analogous compounds of titanium and
zirconium. Complex 1-Hf reacted with water at the Hf-C(Ph) bond to form the complex
Cp*2Hf(OH)-C(SiMe3)dCHPh (2-Hf). With carbon dioxide, a mixture of regioisomeric hafnafuranones
4a/b-Hf was formed.
scopic and structural methods. In general, one can tune the
metal-alkyne interaction by changing the metals, the cyclo-
pentadienyl ligands, or any additional ligands L. The observed
trends, i.e., larger coordination shifts in the IR and 13C NMR
spectra as well as longer C-C bond distances and bending back
angles of the substituents, indicate a stronger complexation of
the alkyne in complexes with hafnium and/or pentamethylcy-
clopentadienyl ligands (compared to titanium and zirconium and/
or cyclopentadienyl). If an additional ligand L is present, the
interaction of the alkyne with the metal generally becomes
weaker.
Introduction
In group 4 chemistry, the complexation of bis(trimethyl-
silyl)acetylene by metallocenes leads to three-membered met-
allacyclopropenes Cp′2M(η2-Me3SiC2SiMe3) (Cp′ ) substituted
or unsubstituted η5-cyclopentadienyl). Such titanium and zir-
conium compounds show a very broad chemistry.1 All attempts
to obtain the analogous well-defined hafnium complexes failed
for many years. The reason for this was assumed to be the
enhanced reducing ability of hafnium compounds compared to
those of zirconium. For the case of (s-cis-η4-diene) metallocene
complexes, Erker and co-workers described the σ to π ratio of
the diene bonding to be shifted to a larger σ character for
hafnium compared to zirconium, giving shorter Hf-C than
Zr-C bonds.2 Some consequences of the significantly different
reactivity of hafnium compared to zirconium were shown by
the Chirik group in the functionalization of molecular nitrogen
with carbon dioxide in a hafnocene complex.3
Results and Discussion
The reaction of decamethylhafnocene dichloride Cp*2HfCl2
with PhC2SiMe3 and lithium in toluene resulted in formation
of the dark blue crystalline complex Cp*2Hf(η2-PhC2SiMe3) (1-
Hf) in 49% yield (Scheme 1).
Recently, we found during the synthesis of Cp*2Hf(η2-
Me3SiC2SiMe3) several examples of the consequences of such
higher reducing ability of hafnocene compounds; e.g., ring
opening of THF4a,b and a tandem Si-C/C-H bond cleavage4c
can occur.
Scheme 1. Formation of Complex 1-Hf
In this work, we investigated the complexation of phenyl-
(trimethylsilyl)acetylene by decamethylhafnocene by spectro-
Complex 1-Hf is sensitive toward moisture and can be
exposed to air for several minutes without decomposition. Its
IR spectrum shows ν(Ct C) at 1528 cm-1. As expected, there
are two signals in the 13C NMR spectrum at 246.8 (CSiMe3)
and 259.2 ppm (CPh). Discrimination of the alkyne carbon
atoms in phenyl(trimethylsilyl)acetylene was achieved by
observation of the 13C-1H coupling patterns.5,8d These data
indicate the strong complexation of the alkyne, leading to the
hafnacyclopropene structure. The structure of complex 1-Hf was
confirmed by X-ray analysis (Figure 1). The C1-C2 bond
distance of 1.334(3) Å is in the range of a CdC double bond.
Moreover, the coordination mode of the alkyne is proved by
the different Hf-C bond lengths of Hf1-C1 2.155(2) and
Hf1-C2 2.197(2) Å. The reason for this difference can be found
† This work is dedicated to Professor Günther Oehme on the occasion
of his 70th birthday.
* To whom correspondence should be addressed. Tel: ++49-381-1281-
176. Fax: ++49-381-1281-51176. E-mail: uwe.rosenthal@catalysis.de.
‡ On leave from the A. N. Nesmeyanov Institute of Organoelement
Compounds, Russian Academy of Sciences, Vavilov St. 28, 117813,
Moscow, Russia.
(1) Rosenthal, U.; Burlakov, V. V. In Titanium and Zirconium in Organic
Synthesis; Marek, I., Ed.; Wiley-VCH: New York, 2002; p 355.
(2) (a) Kru¨ger, C.; Mu¨ller, G.; Erker, G.; Dorf, U.; Engel, K. Organo-
metallics 1985, 4, 215. (b) Erker, G.; Kru¨ger, C.; Mu¨ller, G. AdV.
Organomet. Chem. 1985, 24, 1.
(3) (a) Bernskoetter, W. H.; Olmos, A. V.; Pool, J. A.; Lobkovsky, E.;
Chirik, P. J. J. Am. Chem. Soc. 2006, 128, 10696. (b) Bernskoetter, W. H.;
Lobkovsky, E.; Chirik, P. J. Angew. Chem. 2007, 119, 2916; Angew. Chem.,
Int. Ed. 2007, 46, 2858. (c) ChirikP. J. Dalton Trans. 2007, 16, and
references cited therein.
10.1021/om8003064 CCC: $40.75
2008 American Chemical Society
Publication on Web 06/24/2008

Synthesis and Reactions of Cp*2Hf(η2-PhC2SiMe3)
Organometallics, Vol. 27, No. 15, 2008 3955
Table 1. Comparison of Spectroscopic Data of L2M(η2-PhC2SiMe3)a
M ) Hf
(1-Hf)
M ) Ti
(1-Ti)
M ) Zr
(1-Zr)
M ) Ni
(1a-Ni)
ν(Ct C)/cm-1
∆ν(Ct C)/cm-1
δ(CPh)/ppm
δ(CSiMe3)/ppm
∆δ/ppm
1528
632
259.2
246.8
12.4
153.2
152.8
0.4
1625
535
224.9
213.2
11.7
118.9
119.2
-0.3
1.308(3)
1618
542
235.1
222.5
12.6
129.1
128.5
0.6
1768
392
157.1
128.2
28.9
51.1
34.8
16.3
∆δ(CPh)/ppm
∆δ(CSiMe3)/ppm
∆(∆δ)
d(Ct C)/Å
1.334(3)
1.340(9)
a L ) Cp*, M ) Hf (1-Hf), Ti (1-Ti), Zr (1-Zr); L ) Ph3P, M ) Ni
Figure 1. Molecular structure of complex 1-Hf. Hydrogen atoms
are omitted for clarity. The thermal ellipsoids correspond to 30%
probability. Selected bond lengths (Å) and angles (deg): C1-C2
1.334(3), Hf1-C1 2.155(2), Hf1-C2 2.197(2), C2-Si1 1.849(2),
C1-C3 1.472(3); C1-Hf1-C2 35.69(8), C1-C2-Si1 140.1(2),
C2-C1-C3 134.8(2).
(1a-Ni).8d For free alkyne: IR ν(Ct C) 2160 cm-1 13C ΝΜR
;
δ(CSiMe3) 94.0 ppm, δ(CPh) 106.0 ppm; ∆δ ) δ(CPh) 106.0 ppm -
δ(CSiMe3) 94.0 ppm ) 12.0 ppm; ∆∆δ ) ∆δ(CPh) - ∆δ(CSiMe3).
established.8b Thus, in the 13C NMR spectra of these complexes
with R ) SiMe3 larger shifts were observed compared to R )
Ph. Unsymmetrically substituted complexes (Ph and SiMe3) give
upon coordination a smaller polarization of the carbon atoms
for titanium and zirconium (compared to the free alkyne). This
is not the case for Ni(0) complexes and was assumed to be a
result of electron delocalization in the metallacyclopropenes of
the early transition metals.8c
in the electronic polarization in the alkyne, leading to a partial
positive charge at C(Ph) and to a partial negative charge at the
Si (ꢀ-effect of Me3Si groups).6 For this reason, the Hf-C(Ph)
bond is stronger and shorter than the Hf-C(SiMe3) bond. Such
effects have been observed before; especially for electron-rich
late transition metals, this becomes even more relevant due to
the high s-electron density, which is attracted by the partial
positive charge of the C(Ph) of the alkyne (Scheme 2).7
All spectroscopic data for 1-Hf show a significantly stronger
interaction of the alkyne with hafnium compared to the
analogous compounds of titanium 1-Ti9 and zirconium 1-Zr10
as indicated by the higher shifts ∆ν(Ct C), δ(CPh), and
δ(CSiMe3) in comparison to the starting alkyne (Table 1). With
regard to different changes at the different substituted C-atoms,
surprisingly there is no trend connected with the stronger
complexation. In this respect, hafnium behaves similar to
titanium and zirconium. One explanation could be the above-
discussed delocalization in the three-membered ring.
Scheme 2. Coordination of PhC2SiMe3 at the Hafnocene
Fragment
In contrast to what was found in the case of the bis(tri-
methylsilyl)acetylene complex Cp*2Hf(η2-Me3SiC2SiMe3), the
synthesis of compound 1-Hf is not accompanied by the
formation of side products, i.e., vinylidene complexes or
hafnacyclopentenes formed by Si-C and C-H bond activation.4a,c
With respect to reductive coupling, no reactions with an excess
of alkyne to give hafnacyclopentadienes were observed.
The comparison of the structural data of complexes 1-Hf,
1-Ti, and 1-Zr gives the same tendency for the complexation
of phenyl(trimethylsilyl)acetylene as described before:8c–e
shorter M-C(Ph) than M-C(SiMe3) bonds and larger
C-C-Si than C-C-Cipso(Ph) bending back angles. With
regard to the difference in the M-C distances in the
metallacyclopropene unit (∆d), unexpectedly, there is no
trend which indicates a stronger complexation in the case of
Hf. The stronger interaction with the alkyne in 1-Hf compared
to the Ti compound 1-Ti can be derived from the C1-C2
bond length. The distance C1-C2 in 1-Zr is essentially the
same as the bond length in 1-Hf, even though the spectro-
scopic data for 1-Hf indicate a considerably stronger bonding
of the alkyne than in 1-Zr. This inconsistency might be
clarified by DFT calculations. Compared to the alkyne
complex Cp*2Hf(η2-Me3SiC2SiMe3) (C1-C2 1.337(4),
Hf1-C1 2.188(3), Hf1-C2 2.184(3) Å), there is a clear
Another way of explaining the coordination of phenyl(tri-
methylsilyl)acetylene at the metal center is a combination of
inductive parameters with spectroscopic data as reported previ-
ously for complexes with late transition metals such as Ni(0).8a
A correlation of the these parameters of the substituents R with
the coordination shifts in the IR and 13C NMR spectra was
described, e.g., for Ph larger coordination shifts of the alkyne
were found (compared to SiMe3).8a A similar result was found
in the IR data for the early transition metals titanium and
zirconium, but in the 13C NMR spectra the reverse case was
(4) (a) Beweries, T.; Burlakov, V. V.; Bach, M. A.; Arndt, P.; Baumann,
W.; Spannenberg, A.; Rosenthal, U. Organometallics 2007, 26, 247. (b)
Beweries, T.; Ja¨ger-Fiedler, U.; Burlakov, V. V.; Bach, M. A.; Arndt, P.;
Baumann, W.; Spannenberg, A.; Rosenthal, U. Organometallics 2007, 26,
3000. (c) Beweries, T.; Burlakov, V. V.; Bach, M. A.; Peitz, S.; Arndt, P.;
Baumann, W.; Spannenberg, A.; Rosenthal, U.; Pathak, B.; Jemmis, E. D.
Angew. Chem. 2007, 119, 7031; Angew. Chem., Int. Ed. 2007, 46, 6907.
(5) Baumann, W.; Pellny, P.-M.; Rosenthal, U. Magn. Reson. Chem.
2000, 38, 515.
(6) (a) Wierschke, S. G.; Chandrasekhar, J.; Jorgensen, W. L. J. Am.
Chem. Soc. 1985, 107, 1496. (b) Lambert, L. B.; Wang, G.; Finzel, R. B.;
Teramura, D. H. J. Am. Chem. Soc. 1987, 109, 7838.
(7) Boag, N. M.; Green, M.; Grove, D. M.; Howard, J. A. K.; Spencer,
J. L.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1980, 2170.
(8) (a) Rosenthal, U.; Schulz, W. J. Organomet. Chem. 1987, 321, 103.
(b) Rosenthal, U.; Go¨rls, H. J. Organomet. Chem. 1988, 348, 135. (c)
Rosenthal, U.; Oehme, G.; Burlakov, V. V.; Petrovskii, P. V.; Shur, V. B.;
Vol’pin, M. E. J. Organomet. Chem. 1990, 391, 119. (d) Rosenthal, U.;
Nauck, C.; Arndt, P.; Pulst, S.; Baumann, W.; Burlakov, V. V.; Go¨rls, H.
J. Organomet. Chem. 1994, 484, 81, and references cited therein. (e) Boag,
N. M.; Green, M.; Howard, J. A. K.; Stone, F. G. A.; Wadepohl, H. J. Chem.
Soc., Dalton Trans. 1981, 862.
(9) (a) Rosenthal, U.; Go¨rls, H.; Burlakov, V. V.; Shur, V. B.; Vol’pin,
M. E. J. Organomet. Chem. 1992, 426, C53. (b) Burlakov, V. V.; Polyakov,
A. V.; Yanovsky, A. I.; Struchkov, Yu. T.; Shur, V. B.; Vol’pin, M. E.;
Rosenthal, U.; Go¨rls, H. J. Organomet. Chem. 1994, 476, 197.
(10) List, A. K.; Koo, K.; Rheingold, A. L.; Hillhouse, G. L. Inorg.
Chim. Acta 1998, 270, 399.

3956 Organometallics, Vol. 27, No. 15, 2008
Scheme 3. Formation of Complexes 2-M by Reaction of the Metallacyclopropenes 1-M with Water
Beweries et al.
Table 2. Some NMR Parameters That Are Useful To Determine the Regiochemistry of Protonation of Coordinated PhC2SiMe3 to an Alkenyl
Ligand
compound
dCH δ(1H)
dCH 1J(C,H)
OH δ(1H)
SiMe3 δ(13C)
J(Si,Hvinyl)
2-Hf
2-Zr
2-Ti
8.40
8.40
4.72
5.51
155
153
131
134
4.25
4.58
7.98
7.7
7.3
1.1
0.7
22 (3J)
22 (3J)
6.0 (2J)
6.4 (2J)
Cp2Ti(OMe)-C(Ph)dCH(SiMe3) (ref 9a)
difference in the structural parameters, showing the effect
groups of the permethyltitanocene fragment. The X-ray structure
of the replacement of one Me3Si group by
group.
a
Ph
of 2-Ti is shown in Figure 3.
Reaction of 1-Hf with water to 2-Hf. 1-Hf reacted with
water at the Hf-C(Ph) bond to form the complex
Cp*2Hf(OH)-C(SiMe3)dCHPh (2-Hf) (Scheme 3), which was
isolated as colorless needles in 71% yield.
The molecular structure of complex 2-Hf (Figure 2)
displays a hafnocene fragment coordinated with an alkenyl
unit and a hydroxyl group. Unlike in similar alkenyl
complexes of Ti and Zr,11,13b there is no agostic interaction
between the hafnium center and the hydrogen atom at C2.
The C1-C2 distance of 1.355(4) Å is in the range of a CdC
double bond; this feature can also be derived from the IR
data (ν(Ct C) 1593 cm-1).
Figure 3. Molecular structure of complex 2-Ti. Hydrogen atoms
(except H1 and H2) are omitted for clarity. The thermal ellipsoids
correspond to 30% probability. Selected bond lengths (Å) and angles
(deg): C1-C2 1.347(2), C1-Ti1 2.211(2), Ti1-O1 1.877(1);
Ti1-C1-C2 124.0(1), C3-C1-C2 116.7(1), C1-C2-Si1
131.3(1).
The bond length of C1-C2 (1.347(2) Å) is indicative of the
CdC double bond character; compared to the starting complex
1-Ti, this bond is longer (C1-C2 1.308(3) Å). As in 2-Hf, no
agostic interaction between the metal center and H2 was found.
The 1H NMR spectrum shows characteristic signals due to the
OH group at 7.98 ppm and the hydrogen atom in ꢀ position at
4.72 ppm.
Figure 2. Molecular structure of complex 2-Hf. Hydrogen atoms
(except H1 and H2) are omitted for clarity. The thermal ellipsoids
correspond to 30% probability. Selected bond lengths (Å) and angles
(deg): C1-C2 1.355(4), C1-Hf1 2.319(3), Hf1-O1 1.984(2);
Hf1-C1-C2 110.5(2), C1-C2-C3 130.6(3), C2-C1-Si1
115.0(2).
In contrast to 2-Ti, the regioselectivity of the hydrolysis of
2-Zr is the same as that of 2-Hf (Scheme 3). Colorless needles
of 2-Zr were obtained from n-hexane. The spectroscopic data
indicate the existence of a σ-alkenyl-complex: 1H NMR signals
at 4.58 and 8.40 ppm can be assigned to the OH group and the
ꢀ-CH, respectively. The IR spectrum shows a characteristic OH
1
In the H NMR spectrum, the signal for the OH group is a
singlet at 4.25 ppm. The peak for the ꢀ-H is located at 8.40
ppm, compared to the similar complex Cp2Hf[-C(SiMe3)d
CH(SiMe3)]2O (3-Hf) (δ ) 7.96 ppm).12 This is in the same
range; however, there is a slight shift downfield due to the
different electronic properties of the alkyne substituents.
absorption band at 3676 cm-1
.
Compared to 2-Hf, 2-Zr shows no significant differences
in spectroscopic data. However, both complexes clearly differ
from the titanium complex 2-Ti and the related protolysis
products Cp2Ti(OAlkyl)-C(Ph)dCH(SiMe3).13a In the latter
case, hydrolytic attack occurred at the M-C(SiMe3) bond.
The regiochemistry of the hydrolysis of the M-C bonds in
alkyne complexes can be determined safely by several NMR
parameters (Table 2), but the best are the scalar coupling
Reaction of 1-Ti and 1-Zr with Water and Comparison
of the Products with 2-Hf. The reaction of 1-Ti with water
was investigated to compare the products with those obtained
with 1-Hf. 1-Ti reacted with water at the Ti-C(SiMe3) bond
to form the yellow complex Cp*2Ti(OH)-C(Ph)dCH(SiMe3)
(2-Ti) (Scheme 3) in 53% yield. This is exactly the opposite of
what was found for 1-Hf and may be due to the high steric
demand of the SiMe3 group which is located in the ꢀ position
to the metal center to minimize steric hindrance with the methyl
constants between vinylic H and 29Si which is large (3Jtrans
)
for the R-silyl-substituted alkenyl ligands at Hf and Zr but
small (2J) for the ꢀ-silyl-substituted alkenyls at Ti (last
column of Table 2).

Synthesis and Reactions of Cp*2Hf(η2-PhC2SiMe3)
Organometallics, Vol. 27, No. 15, 2008 3957
Scheme 4. Reaction of Complex 1-Hf with CO2 To Give
4a-Hf and 4b-Hf
)CHSiMe3 (5b-Hf). These were not isolated but characterized
in the reaction mixture (see the Experimental Section). Once
again, this behavior is completely analogous to that of the
zirconafuranones 4a/b-Zr.13d
Conclusion
All spectroscopic and structural data for Cp*2Hf(η2-
PhC2SiMe3) (1-Hf) show an extremely strong interaction of the
alkyne with hafnium compared to the analogous compounds of
titanium 1-Ti and zirconium 1-Zr. There is no directed influence
of this stronger coordination on the different substituted C-atoms
C(Ph) and C(SiMe3). Reactions of the alkyne complexes 1-M
with water gave σ-alkenyl complexes. Depending on the metal,
the hydrolysis proceeds at the M-C(SiMe3) bond (M ) Ti) or
at the M-C(Ph) bond (M ) Zr, Hf). Moreover, the hafnocene
alkyne complex 1-Hf was reacted with CO2 to give by insertion
into both Hf-C bonds unselectively a mixture of hafnafuranones
4a-Hf and 4b-Hf. This reaction behavior is in principle the same
as found for 1-Zr but in contrast to the titanium complex 1-Ti,
which gives an insertion of CO2 at the C(SiMe3). We found
that in both cases the titanium complex is reacting clearly
different from its zirconium and hafnium analogues, which
sometimes react in the same manner (this work) or differently,
as shown before.14
Reaction of 1-Hf with Carbon Dioxide to 4-Hf. Reactions
of metallocene alkyne complexes with carbon dioxide have been
studied extensively.13 These simple reactions can provide useful
information with respect to the influence of the Cp ligand and
the alkyne substituents on the regioselectivity of the insertion
of other substrates in stoichiometric and catalytic reactions.
The alkyne complex 1-Hf reacted with CO2 to give a mixture
of the regioisomeric hafnafuranones 4a-Hf and 4b-Hf (Scheme
4). From an n-hexane solution of this mixture, 4a-Hf and 4b-
Hf crystallized as yellow prisms and yellow needles, respec-
tively. Due to their similar solubility in suitable organic solvents,
these complexes could not be separated. For this reason, for
NMR investigations a mixture of 4a-Hf and 4b-Hf was used.
However, only a small amount of the crystals of 4a-Hf obtained
from n-hexane were suitable for X-ray analysis.
This complex is a hafnafuranone (Figure 4) that contains a
bent hafnocene fragment, which is similar to the zirconafuranone
Experimental Section
General Methods. All operations were carried out under argon
with standard Schlenk techniques. Prior to use, nonhalogenated
solvents were freshly distilled from sodium tetraethylaluminate and
stored under argon. Deuterated solvents (C6D6, THF-d8) were treated
with sodium tetraethylaluminate, distilled, and stored under argon.
Cp*2HfCl2 was purchased from MCAT (Metallocene Catalysts &
Life Science Technologies, Konstanz, Germany) and used without
further purification. The following spectrometers were used. Mass
spectra: AMD 402. NMR spectra: Bruker AV 300/AV 400.
Chemical shifts (1H, 13C, 29Si) are given relative to SiMe4 and are
referenced to signals of the used solvent: C6D6 (δH 7.16, δC 128.0),
THF-d8 (δH 1.73, δC 25.2). The spectra were assigned with the
help of DEPT and shift correlation experiments. Melting points:
sealed capillaries, Bu¨chi 535 apparatus. Elemental analyses: Leco
CHNS-932 elemental analyzer.
Preparation of 1-Hf. Cp*2HfCl2 (2.06 g, 4.0 mmol) and finely
cut lithium (0.110 g, 15.8 mmol) were suspended in 20 mL of
toluene, and 1-phenyl-2-trimethylsilylacetylene (0.787 mL, 4.0
mmol) was added. The mixture was stirred for 10 days at 60 °C,
followed by subsequent removal of all volatiles in vacuum. The
blue-green residue was extracted with n-hexane at 55 °C (3 × 10
mL), and the blue filtrate was concentrated to half-its volume,
filtered, and stored at -78 °C. After 24 h, dark blue crystals had
formed, which were isolated by decanting of the mother liquor,
Figure 4. Molecular structure of complex 4a-Hf. Hydrogen atoms
are omitted for clarity. The thermal ellipsoids correspond to 30%
probability. Selected bond lengths (Å) and angles (deg): Hf1-C1
2.292(2), C1-C2 1.363(3), C2-C3 1.504(3), C3-O1 1.332(2),
Hf1-O1 2.030(1), C3-O2 1.220(2), C1-Hf1-O1 76.16(6),
C2-C1-C4 119.0(2), C1-C2-Si1 127.6(2).
4a-Zr described earlier.13d The double-bond character of C1-C2
is indicated by the bond length of 1.363(3) Å.
NMR spectra and behavior of 4a/b-Hf closely resemble those
of the analogous Zr complexes13d that result from CO2 addition
to 1-Zr. One remarkable feature is the hindered rotation of the
trimethylsilyl group in 4b-Hf, which is indicated by its
temperature-dependent 1H and 13C NMR signals. Line broaden-
ing is perceptible even at ambient temperature. Below 240 K,
two signals of intensity ratio 1:2 are registered for the three
methyl groups (see the Experimental Section). The bulky
trimethylsilyl group in R position of the hafnacycle is con-
strained between the bulky Cp* ligands; therefore, it cannot
rotate freely and “locks in” in with one methyl group in the
mirror plane of the molecule which is represented by the
metallacycle.
(11) Rosenthal, U.; Ohff, A.; Michalik, M.; Go¨rls, H.; Burlakov, V. V.;
Shur, V. B. Organometallics 1993, 12, 5016.
(12) Spannenberg, A.; Beweries, T.; Bach, M. A.; Rosenthal, U. Z.
Kristallogr. NCS 2007, 222, 187.
(13) Examples: (a) Lefeber, C.; Ohff, A.; Tillack, A.; Baumann, W.;
Kempe, R.; Burlakov, V. V.; Rosenthal, U.; Go¨rls, H. J. Organomet. Chem.
1995, 501, 179. (b) Lefeber, C.; Ohff, A.; Tillack, A.; Baumann, W.; Kempe,
R.; Burlakov, V. V.; Rosenthal, U. J. Organomet. Chem. 1995, 501, 189.
(c) Thomas, D.; Peulecke, N.; Burlakov, V. V.; Baumann, W.; Spannenberg,
A.; Kempe, R.; Rosenthal, U. Eur. J. Inorg. Chem. 1998, 1495. (d) Pellny,
P.-M.; Burlakov, V. V.; Baumann, W.; Spannenberg, A.; Rosenthal, U. Z.
Anorg. Allg. Chem. 1999, 625, 910. (e) Burlakov, V. V.; Pellny, P.-M.;
Arndt, P.; Baumann, W.; Spannenberg, A.; Shur, V. B.; Rosenthal, U. Chem.
Commun. 2000, 241. (f) Arndt, P.; Spannenberg, A.; Baumann, W.; Becke,
S.; Rosenthal, U. Eur. J. Inorg. Chem. 2001, 2885.
Both complexes 4a/b-Hf suffer easy hydrolysis to yield the
respective hafnocene carboxylates Cp*2Hf(OH)OC(dO)-
CSiMe3dCHPh (5a-Hf) and Cp*2Hf(OH)OC(dO)-CPhd
(14) Ritter, S. K. Chem. Eng. News 2007, 85 (41), 42, and references
cited therein.

3958 Organometallics, Vol. 27, No. 15, 2008
Beweries et al.
washed with cold n-hexane, and dried in vacuum to give 1.22 g
(2.0 mmol, 49%) of complex 1-Hf: mp 187-189 °C under Ar; IR
(nujol mull, cm-1) 1528 (Ct C); NMR (C6D6, 296 K) 1H (400
MHz) δ 0.40 (s, 9H, SiMe3), 1.82 (s, 30H, Cp*), 6.99 (m, 2H,
o-Ph), 7.01 (m, 1H, p-Ph), 7.27 (m, 2H, m-Ph); 13C (100 MHz) δ
4.2 (SiMe3), 11.6 (C5Me5), 118.2 (C5Me5), 125.8 (p-Ph), 128.2 (m-
Ph), 131.3 (o-Ph), 132.2 (i-Ph), 246.8 (CSiMe3), 259.2 (CPh); 29Si
(79 MHz) δ -8.0. MS (70 eV, m/z) 624 [M]+. Anal. Calcd for
C31H44HfSi: C, 59.74; H, 7.12. Found: C, 59.33; H, 6.82.
eV, m/z) 535 [M - OH]+, 377 [Cp*2ZrOH]+. Anal. Calcd. for
C31H46ZrOSi: C, 67.21; H, 8.37. Found: C, 66.92; H, 7.82.
Preparation of 3-Hf. See ref 12: NMR (297 K, C6D6) 1H (300
MHz) δ 0.34 (s, 18 H, R-SiMe3), 0.40 (s, 18 H, ꢀ-SiMe3), 6.00 (s,
20 H, Cp), 7.96 (br s, 2 H, )CH); 13C (75 MHz) δ 2.3 (ꢀ-SiMe3),
4.2 (R-SiMe3), 110.6 (Cp), 158.6 (dCH), 235.0 (HfC).
Preparation of 4a-Hf and 4b-Hf. Cp*2Hf(η2-PhC2SiMe3) (1-
Hf) (0.749 g, 1.20 mmol) was dissolved in 10 mL of n-hexane.
The blue-green solution was filtered, the Ar atmosphere was
removed in vacuum, and the Schlenk tube was flushed with dry
CO2. The color of the reaction mixture changed to yellow, and after
2 h, yellow crystals formed, which were separated by decanting of
the mother liquor, washed with cold n-hexane, and dried in vacuum
to give 0.214 g (0.32 mmol, 51%) of a mixture of complexes 4a-
Hf and 4b-Hf. From this precipitate single yellow prisms of 4a-
Hf were selected and used for an X-ray analysis. Both species were
characterized by NMR spectroscopy in THF-d8 solution at 307 K
as a mixture which contained also varying amounts of their
hydrolysis products 5a-Hf, Cp*2Hf(OH)OC(dO)-C(SiMe3)d
CHPh, and 5b-Hf, Cp*2Hf(OH)OC(dO)-CPh)CH(SiMe3). Not all
signals were identified. 4a-Hf: 1H (400 MHz) δ 0.02 (s, 9H, SiMe3),
1.92 (s. 30H, Cp*), 6.78 (m, 2H, o-Ph), 7.22 (m, 2H, m-Ph); 13C
(100 MHz) δ 2.1 (SiMe3), 11.3 (C5Me5), 122.0 (C5Me5), 126.5 (p-
Ph), 128.1 (m-Ph), 129.4 (o-Ph), 158.6 (C-SiMe3), 240.7 (C-Ph);
29Si (79 MHz) δ -10.4. 4b-Hf: 1H (400 MHz) δ -0.12 (br s, 9H,
SiMe3), 2.06 (s, 30H, Cp*), 7.11 (m, 2H, o-Ph), 7.12 (m, 1H, p-Ph),
7.19 (m, 2H, m-Ph); 13C (100 MHz) δ 5.6 (SiMe3), 11.8 (C5Me5),
122.2 (C5Me5), 126.6 (p-Ph), 127.3 (m-Ph), 130.5 (o-Ph), 146.1
(i-Ph), 163.2 (CO), 165.6 (C-Ph), 228.6 (C-SiMe3); 29Si (79 MHz)
Preparation of 2-Hf. Cp*2Hf(η2-PhC2SiMe3) (1-Hf) (0.749 g,
1.20 mmol) was dissolved in 10 mL of benzene, and water (0.022
mL, 1.22 mmol) was added to the blue solution. The mixture was
agitated and kept at room temperature. After 2 weeks, the solvent
was removed in vacuum from the colorless solution. The white
residue was dissolved in 5 mL of benzene, and the resulting solution
was filtered and slowly concentrated in an argon flush to half-its
volume. After 24 h at room temperature, colorless needles had
formed, which were isolated, washed with cold n-hexane, and dried
in vacuum to give 0.548 g (0.85 mmol, 71%) of complex 2-Hf:
mp 184-186 °C under Ar; IR (KBr, cm-1) 1239 (SiMe3), 1593
(CdC), 3681 (OH); NMR (C6D6, 296 K) 1H (300 MHz) δ 0.24 (s,
9H, SiMe3), 1.91 (s, 30H, Cp*), 4.25 (s, 1H, OH), 7.10 (m, 1H,
p-Ph), 7.23 (m, 2H, m-Ph), 7.34 (m, 2H, o-Ph), 8.40 (s, 1H, CH);
13C (75 MHz) δ 7.7 (SiMe3), 12.0 (C5Me5), 118.3 (C5Me5), 125.9
(p-Ph), 127.8 (m-Ph), 128.4 (o-Ph), 147.6 (i-Ph), 158.7 (CH-Ph),
207.4 (C-SiMe3); MS (70 eV, m/z) 642 [M]+, 625 [M - OH]+.
Anal. Calcd for C31H46HfOSi: C, 58.06; H, 7.23. Found: C, 57.83;
H, 7.17.
Preparation of 2-Ti. Cp*2Ti(η2-PhC2SiMe3) (1-Ti) (0.463 g,
0.94 mmol) was dissolved in 15 mL of benzene, and water (0.017
mL, 0.94 mmol) was added. The dark red solution was stirred and
kept at room temperature. After 10 days, the solvent was removed
in vacuum from the yellow solution. The yellow residue was
dissolved in 10 mL of n-hexane, and the solution was filtered and
kept at room temperature. After 2 h, yellow crystals had formed,
which were isolated, washed with cold n-hexane, and dried in
vacuum to give 0.253 g (0.49 mmol, 53%) of complex 2-Ti: mp
124-126 °C under Ar; IR (KBr, cm-1) 1236 (SiMe3), 1588 (CdC),
3628 (OH); NMR (THF-d8, 296 K) 1H (300 MHz) δ -0.19 (s,
9H, SiMe3), 1.86 (s, 30H, Cp*), 4.72 (s, 1H, CH), 6.85 (m, 1H,
p-Ph) 6.95 (m, 4H, o/m-Ph), 7.98 (s, 1H, OH); 13C (75 MHz) δ
1.1 (SiMe3), 12.5 (C5Me5), 121.8 (C5Me5), 124.5 (p-Ph), 126.5 (m-
Ph), 127.9 (o-Ph), 132.7 (CH-SiMe3), 158.1 (i-Ph), 224.8 (C-Ph);
MS (70 eV, m/z) 493 [M - OH]+, 335 [Cp*2TiOH]+. Anal. Calcd
for C31H46TiOSi: C, 72.91; H, 9.08. Found: C, 72.20; H, 9.19.
Preparation of 2-Zr. Cp*2Zr(η2-PhC2SiMe3) (1-Zr) (0.365 g,
0.68 mmol) was dissolved in 8 mL of benzene, and water (0.012
mL, 0.68 mmol) was added. The blue-green solution was agitated
and kept at room temperature. After 1 week, the solvent was
removed in vacuum from the colorless solution. The residue was
dissolved in 5 mL of warm n-hexane, and the resulting solution
was filtered and allowed to cool to room temperature. After 24 h,
colorless needles were formed, which were isolated, washed with
cold n-hexane and dried in vacuum to give 0.253 g (0.46 mmol,
67%) of complex 2-Zr: mp 173 °C under Ar; IR (KBr, cm-1) 1238
1
δ -14.6. 4b-Hf at 207 K: H δ -0.05 (br s, 3H, SiMe3), -0.22
(br s, 6H, SiMe3), 2.05 (s, 30H, Cp*); 13C δ 5.4 (1C SiMe3), 5.5
1
(2C SiMe3), 11.9 (C5Me5), 121.8 (C5Me5). 5a-Hf: H (400 MHz)
δ 0.07 (s, 9H, SiMe3), 1.91 (s. 30H, Cp*), 3.76 (br s, OH), 7.24
(m, 2H, o-Ph), 8.50 (s, 1H, CH); 13C (100 MHz) δ 1.4 (SiMe3),
11.2 (C5Me5), 118.8 (C5Me5), 128.5 (m-Ph), 128.7 (p-Ph), 129.1
(o-Ph), 139.5 (i-Ph), 140.2 (C-SiMe3), 155.6 (C-Ph), 177.8 (CO);
29Si (79 MHz) δ -7.2 (3JSi,H ) 11.6 Hz). 5b-Hf: 1H (400 MHz) δ
-0.12 (s, 9H, SiMe3), 1.84 (s. 30H, Cp*), 3.66 (br s, OH), 7.15 (s,
1H, CH), 7.24 (m, 2H, o-Ph), 7.29 (m, 2H, m-Ph); 13C (100 MHz)
δ -0.6 (SiMe3), 11.0 (C5Me5), 118.7 (C5Me5), 127.9 (p-Ph), 128.0
(m-Ph), 130.5 (o-Ph), 140.2 (i-Ph), 143.0 (C-SiMe3), 152.9 (C-Ph),
174.0 (CO); 29Si (79 MHz) δ -8.1 (2JSi,H ) 2.7 Hz); MS for 4-Hf
(70 eV, m/z) 668 [M]+.
Diffraction data were collected on a STOE IPDS diffractometer
using graphite-monochromated Mo KR radiation. The structures
were solved by direct methods (SHELXS-9715 and SIR 2004,16
respectively) and refined by full-matrix least-squares techniques on
F2 (SHELXL-9717). XP (Bruker AXS) was used for graphical
representations. X-ray data are shown in Table 3.
Table 3. Crystallographic Data
1-Hf
2-Hf
2-Ti
4a-Hf
cryst syst
space group
a (Å)
b (Å)
c (Å)
triclinic
P1
9.703(2)
monoclinic triclinic
Monoclinic
P21/c
10.2069(5)
j
j
P21/c
P1
9.1336(4)
15.937(1)
10.366(2) 11.7378(5) 10.3287(4) 17.1456(4)
15.583(3) 16.5513(9) 16.5723(7) 17.6053(6)
1
(SiMe3), 1593 (CdC), 3676 (OH); NMR (C6D6, 296 K) H (400
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
83.09(3)
72.17(3)
72.66(3)
1423.5(5) 2828.2(3)
2
1.454
3.722
200(2)
90.00
114.011(5) 104.347(3) 105.079(3)
90.00 107.040(3) 90.00
93.569(3)
90.00
MHz) δ 0.25 (s, 9H, SiMe3), 1.88 (s, 30H, Cp*), 4.58 (s, 1H, OH),
7.10 (m, 1H, p-Ph), 7.22 (m, 2H, m-Ph), 7.34 (m, 2H, o-Ph), 8.40
(s, 1H, CH). 13C (100 MHz) δ 7.3 (SiMe3), 12.0 (C5Me5), 119.3
(C5Me5), 125.9 (p-Ph), 127.8 (m-Ph), 128.4 (o-Ph), 146.2 (i-Ph),
155.2 (CH-Ph), 207.0 (C-SiMe3); 29Si (79 MHz) δ -16.0; MS (70
1432.7(1)
2
2974.9(2)
4
Z
4
density (g · cm-3
)
1.506
3.752
200(2)
42379
5982
4974
321
1.184
0.361
200(2)
21698
5936
4713
328
1.490
3.573
200(2)
56772
8008
6637
338
µ(Mo KR) (mm-1
T (K)
)
(15) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure
Solution, University Go¨ttingen, Germany, 1997.
(16) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano,
G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl.
Crystrallogr. 2005, 38, 381.
(17) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement, University Go¨ttingen, Germany, 1997.
no. of rflns (measd) 20436
no. of rflns (indep) 5597
no. of rflns (obsd)
no. of params
5270
298
R1 (I > 2σ(I))
wR2 (all data)
0.014
0.037
0.022
0.050
0.031
0.086
0.018
0.039

Synthesis and Reactions of Cp*2Hf(η2-PhC2SiMe3)
Organometallics, Vol. 27, No. 15, 2008 3959
Supporting Information Available: Crystallographic data in
CIF file format, including bond lengths and angles of compound
1-Hf, 2-Hf, 2-Ti, and 4a-Hf (data). This material is available free
of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We thank our technical staff in par-
ticular Regina Jesse and Petra Bartels for assistance. Support
by the Deutsche Forschungsgemeinschaft (SPP 1118, Project
No. Ro 1269/6 and GRK 1213) and the Russian Foundation
forBasicResearch(projectcode05-03-32515)isacknowledged.
OM8003064