New ansa-niobocene complexes. X-ray crystal structure of [Me2Si(η5-C5H4) 2]Nb(=NtBu)Cl. Stereoselective synthesis of meso-[Me2Si(η5-C5H3SiMe 3)2]Nb(=NtBu)Cl

Article abstract of DOI:10.1021/om980561n

The ansa-niobocene complex [Me₂Si(η⁵-C₅-H₄) ₂]Nb(=N^tBu)Cl (1) has been prepared and its structure determined by single-crystal X-ray diffraction. The alkyl complexes [Me₂Si(η⁵-C₅-H₄) ₂]Nb(=N^tBu)(R) (R = Me (2), Et (3), CH₂Ph (4), CH₂CH=CH₂ (5)) were prepared by the reaction of 1 and the corresponding Grignard reagent. Using the trimethylsilyl-substituted ansa ligand Me₂Si(C₅H₃SiMe₃)₂, [Me₂Si(η⁵-C₅-H₄) ₂]Nb(=N^tBu)Cl (6) was prepared and isolated uniquely as the meso-isomer. Nevertheless the synthesis of Me₂Si(η⁵-C₅H₃SiMe ₃)₂]NbCl₂ (7) yielded a mixture of meso- and rac-isomers. Reduction of 7 in the presence of ligand (RC=CR) (R = Me, Ph) gave [Me₂Si(η⁵-C₅H₃SiMe ₃)₂]NbCl(RC=CR) (R = Me (8), Ph (9)). Both complexes were initially isolated as mixtures of meso- and racisomers and in the case of 9 could be separated due to their differing solubilities in hexane.

Full text of DOI:10.1021/om980561n

5454
Organometallics 1998, 17, 5454-5459
New a n sa -Niobocen e Com p lexes. X-r a y Cr ysta l
Str u ctu r e of [Me2Si(η5-C5H4)2]Nb(dNtBu )Cl.
Ster eoselective Syn th esis of
m eso-[Me2Si(η5-C5H3SiMe3)2]Nb(dNtBu )Cl
Antonio Antin˜olo, Antonio Otero,* Sanjiv Prashar, and Ana M. Rodriguez
Departamento de Quı´mica Inorga´nica, Orga´nica y Bioquı´mica, Facultad de Quı´micas,
Campus Universitario, Universidad de Castilla-La Mancha, 13071-Ciudad Real, Spain
Received J uly 6, 1998
The ansa-niobocene complex [Me2Si(η5-C5H4)2]Nb(dNtBu)Cl (1) has been prepared and
its structure determined by single-crystal X-ray diffraction. The alkyl complexes [Me2Si-
(η5-C5H4)2]Nb(dNtBu)(R) (R ) Me (2), Et (3), CH2Ph (4), CH2CHdCH2 (5)) were prepared
by the reaction of 1 and the corresponding Grignard reagent. Using the trimethylsilyl-
substituted ansa ligand Me2Si(C5H3SiMe3)2, [Me2Si(η5-C5H3SiMe3)2]Nb(dNtBu)Cl (6) was
prepared and isolated uniquely as the meso-isomer. Nevertheless the synthesis of [Me2Si-
(η5-C5H3SiMe3)2]NbCl2 (7) yielded a mixture of meso- and rac-isomers. Reduction of 7 in
the presence of ligand (RCtCR) (R ) Me, Ph) gave [Me2Si(η5-C5H3SiMe3)2]NbCl(RCtCR)
(R ) Me (8), Ph (9)). Both complexes were initially isolated as mixtures of meso- and rac-
isomers and in the case of 9 could be separated due to their differing solubilities in hexane.
In tr od u ction
Furthermore the use of substituted ansa ligands in
the stereoselective synthesis of group 4 metal complexes
and their importance in catalysis is receiving special
attention,8 although only one example for group 5, an
ansa-vanadocene complex, has been reported.8 It has
been shown that steric effects in the transition metal
catalyst greatly affect the polymerization of olefins, and
bulky ligands, such as substituted ansa ligands, would
therefore aid stereospecific olefin coordination and po-
lymerization.9 In addition the chiral nature of these
ligands would also strongly influence stereoselectivity.9
The importance of catalysts based on group 5 precur-
sors is now growing due in part to the less air-sensitive
nature of their complexes in comparison with their
group 4 analogues.10
Our recent results in the chemistry of ansa-niobocene
complexes encouraged us to explore the preparation of
this class of complexes for group 5 elements using the
trimethylsilyl-substituted ansa ligand Me2Si(C5H3-
SiMe3)2. We report here our results on the synthesis
and structural details of new ansa-niobocene complexes
[Me2Si(η5-C5H4)2]Nb(dNtBu)X, as an extension of the
work previously communicated,4 as well as the isolation
and characterization of the first substituted ansa-
niobocene complexes, [Me2Si(η5-C5H3SiMe3)2]Nb(X)(Y).
The use of ansa-cyclopentadienyl ligands has received
wide attention in the chemistry of group 4 metals,1 due
mainly to its ability to impart on its complexes a high
and selective degree of catalytic activity.2
For group 5 metals few such compounds are known
and normally exhibit a σ-bond between the ansa ligand
and the metal.3 We recently reported the first ansa-
niobocene complexes in which the cyclopentadienyl rings
are bound only in an η5 mode to niobium.4 Since this
first account, some ansa-niobocene complexes of this
type have been described, [Me2C(η5-C5H4)2]Nb(dNR)-
Cl (R ) Bu, SiMe3),5 [Me2C(η5-C5H4)2]Nb(µ-H2)BH2,6
t
[Me2C(η5-C5H4)2]NbH(PMe3),6 and [Me2C(η5-C5H4)2]Nb-
(dNC6H4Me2-2,5)Cl.7
* Corresponding author. E-mail: aotero@qino-cr.uclm.es.
(1) Comprehensive Organometallic Chemistry II; Abel, E. W., Stone,
F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, U.K., 1995;
Vol. 4.
(2) See: Rieger, B.; J any, G.; Fawzi, R.; Steimann, M. Organome-
tallics 1994, 13, 647.
(3) (a) Lemenovskii, D. A.; Aleksandrov, A. V.; Fedin, V. P. Koord.
Khim. 1980, 6, 877 (Chem. Abstr. 1980, 93, 186 497). (b) Lemenovskii,
D. A.; Fedin, V. P.; Aleksandrov, A. V.; Slovohotov, Yu. L.; Struchkov,
Yu. T. J . Organomet. Chem. 1980, 201, 257. (c) Dorer, B.; Diebold, J .;
Weyand, O.; Britzinger, H.-H. J . Organomet. Chem. 1992, 427, 245.
(d) Chernega, A. N.; Green, M. L. H.; Suarez, A. G. Can. J . Chem.
1995, 73, 1157. (e) Herrmann, W. A.; Baratta, W. J . Organomet. Chem.
1996, 506, 357. (f) Djakovitch, L.; Herrmann, W. A. J . Organomet.
Chem. 1997, 545, 399. (g) Herrmann, W. A.; Baratta, W.; Herdtweck,
E. Angew. Chem., Int. Ed. Engl. 1996, 35, 1951. (h) Antonelli, D. M.;
Gomes, P. T.; Green, M. L. H.; Martins, A. M.; Mountford, P. J . Chem.
Soc., Dalton Trans. 1997, 2435. (i) Gomes, P. T.; Green, M. L. H.;
Martins, A. M.; Mountford, P. J . Organomet. Chem. 1997, 541,
121.
Resu lts a n d Discu ssion
We have previously described4 the synthesis of the
ansa-niobocene dichloride complexes [Me2Si(η5-C5H4)2]-
(7) Herrmann, W. A.; Baratta, W.; Herdtweck, E. J . Organomet.
Chem. 1997, 541, 445.
(4) Antin˜olo, A.; Martinez-Ripoll, M.; Mugnier, Y.; Otero, A.; Prashar,
S.; Rodriguez, A. M. Organometallics 1996, 15, 3241.
(5) Bailey, N. J .; Cooper, J . A.; Gailus, H.; Green, M. L. H.; J ames,
J . T.; Leech, M. A. J . Chem. Soc., Dalton Trans. 1997, 3579.
(6) Bailey, N. J .; Green, M. L. H.; Leech, M. A.; Saunders, J . F.;
Tidswell, H. M. J . Organomet. Chem. 1997, 538, 111.
(8) Huttenloch, M. E.; Dorer, B.; Rief, U.; Prosenc, M.-H.; Schmidt,
K.; Brintzinger, H. H. J . Organomet. Chem. 1997, 541, 219.
(9) Mo¨hring, P. C.; Coville, N. J . J . Organomet. Chem. 1994, 479, 1,
and references therein.
(10) J affart, J .; Nayral, C.; Mathieu, R.; Etienne, M. Eur. J . Inorg.
Chem. 1998, 425, and references therein.
10.1021/om980561n CCC: $15.00 © 1998 American Chemical Society
Publication on Web 11/13/1998

New ansa-Niobocene Complexes
Organometallics, Vol. 17, No. 25, 1998 5455
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1 w ith ESDs in P a r en th esesa
Nb-Cp(1)
Nb-Cl
2.110(2)
2.448(1)
1.756(3)
1.449(4)
Nb-N
Nb-C(8)
Cp(1)-Nb-Cp(1A)
Nb-N-C(8)
Si-C(1)-Cp(1)
C(1)-Nb-C(1A)
Cl-Nb-Cp(1)
N-Nb-Cp(1)
Cl-Nb-N
121.21
178.8(2)
160.2(2)
94.17(6)
104.27
113.61
95.15(9)
F igu r e 1. Proposed structure for [Me2Si(η5-C5H4)2]Nb-
(dNtBu)Cl (1).
a
Symmetry element A is x, -y + 1/2, z. Cp(1) is the centroid of
the cyclopentadienyl ring C(1)-C(5).
the cent(1)-Nb-cent(2) angle is 6-7° smaller ([Me2C(η5-
C5H4)2]Nb(dNtBu)Cl 113.3°)5 and thus clearly illus-
trates the fundamental difference between the two types
of ansa ligands (see Table 2). The cent(1)-Nb-cent(2)
angles of the non-ansa-niobocene complexes (η5-C5H5)2-
Nb(dNtBu)Cl (124.0°)11 and (η5-C5H4SiMe3)2Nb(dNC6-
H5)Cl (124.9°)14 are of values similar to that of 1.
The imide ligand is able to act as either a two- or four-
electron donor. In the first case the nitrogen atom
would be sp2 hybridized and therefore result in the
bending back of the imide substituent. In the second
case the nitrogen would be sp hybridized and the
metal-nitrogen-substituent angle linear. In 1 this
angle Nb-N-C(8) of 178.8(2)° reveals the latter case
to prevail. This phenomenon is also seen in the other
ansa-imido and non-ansa-niobocene complexes reported,
although steric effects cause some degree of bending
back (see Table 2). The formal electron count is 20
electrons. The Nb-N bond distance of 1.756(3) Å is in
agreement with a triple bond between the niobium and
nitrogen atoms and is similar to those observed for other
complexes of this type (see Table 2).
F igu r e 2. Molecular structure and atom-labeling scheme
for [Me2Si(η5-C5H4)2]Nb(dNtBu)Cl (1).
NbCl2 by the reaction of NbCl4(THF)2 and [Me2Si(η5-
C5H4)2]Tl2, and from this some alkyne-containing ansa-
niobocene compounds [Me2Si(η5-C5H4)2]NbCl(RCtCR)
were also isolated. Now, we have considered an alter-
native method to prepare ansa-niobocene complexes
11
using Nb(dNtBu)Cl3(py)2 as starting material. The
preparation of [Me2Si(η5-C5H4)2]Nb(dNtBu)Cl (1) was
achieved by the reaction of Nb(dNtBu)Cl3(py)2 and [Me2-
12
Si(η5-C5H4)2]Li2 in THF. Complex 1 was isolated as
a yellow solid after appropriate workup, and X-ray
quality crystals were obtained by the slow recrystalli-
zation of 1 in toluene. It was spectroscopically charac-
terized. The 1H NMR spectrum reveals the presence
of a system similar to that obtained for the previously
reported [Me2Si(η5-C5H4)2]NbCl(MeCtCMe),4 where the
symmetry of the molecule (Cs) in solution is such that
there is only one plane of symmetry and the two methyl
groups of SiMe2 become inequivalent, as do the cyclo-
pentadienyl protons (Ha, Hb, Ha′, and Hb′), thus giving
two singlets for the former and four multiplets for the
latter (Figure 1) (see Experimental Section).
The molecular structure of 1 was established by X-ray
crystal studies. The molecular structure and atomic
numbering scheme are shown in Figure 2. Selected
bond lengths and angles are given in Table 1.
The structure shows the Me2Si(C5H4)2 ansa ligand
chelating the niobium center, where both cyclopenta-
dienyl rings are bound to the metal in an η5 mode. The
cent(1)-Nb-cent(2) angle of 121.21° is somewhat smaller
than that observed for the only other identical ansa
system group 5 compound reported, namely, [Me2Si-
(η5-C5H3SiMe3)2]NbCl(MeCtCMe),4 which exhibits a
cent(1)-Nb-cent(2) angle of 130.0°. For similar niobi-
um complexes containing the CMe2-bridged ansa ligand
Alkylation reactions on complex 1 were also consid-
ered. The alkylation of 1 by the appropriate alkylmag-
nesium chloride gave the corresponding alkyl products
[Me2Si(η5-C5H4)2]Nb(dNtBu)(R), R ) Me (2); Et (3);
CH2Ph (4); CH2CHdCH2 (5), which were isolated after
appropriate workup, as air-sensitive yellow crystalline
solids in modest yields (see Experimental Section). The
different complexes were characterized spectroscopi-
1
cally. In the H NMR spectrum of 3, as illustrated in
Figure 3, the ethyl group displays an A3BC pattern,
indicating the presence of an unusually weak agostic
interaction between an R-hydrogen atom of the ethyl
group and the metal center (J AB ) 8.0 Hz, J AC ) 7.5
Hz, J BC ) 14.0 Hz). This proposal should be considered
cautiously, because in the 13C NMR spectrum we have
1
not been able to distinguish the two J (13C-1H) con-
stants corresponding to the CH2 group. Two ethyl
complexes of niobium have been reported in which a
similar agostic interaction between the methlyene group
of ethyl and the metal has been observed.15
(13) Chernega, A. N.; Green, M. L. H.; Suarez, A. G. J . Chem. Soc.,
Dalton Trans. 1993, 3031.
(14) Antin˜olo, A.; Espinosa, P.; Fajardo, M.; Go´mez-Sal, P.; Lo´pez-
Mardomingo, C.; Martin-Alonso, A.; Otero, A. J . Chem. Soc., Dalton
Trans. 1995, 1007.
(15) (a) Antin˜olo, A.; Carrillo-Hermosilla, F.; del Hierro, I.; Otero,
A.; Fajardo, M.; Mugnier, Y. Organometallics 1997, 16, 4161. (b)
Yasuda, H.; Yamamoto, H.; Arai, T.; Nakamura, A.; Chen, J .; Kai, Y.;
Kasai, N. Organometallics 1991, 10, 4058.
(11) Sundermeyer, J .; Putterlik, J .; Foth, M.; Field, J . S.; Ramesar,
N. Chem. Ber. 1994, 127, 1201.
(12) (a) Reddy, K. P.; Petersen, J . L. Organometallics 1989, 8, 2107.
(b) Bajgur, C. S.; Tikkanen, W. R.; Petersen, J . L. Inorg. Chem. 1985,
24, 2539.

5456 Organometallics, Vol. 17, No. 25, 1998
Antin˜olo et al.
Ta ble 2. Selected Str u ctu r a l Da ta on a n sa - a n d Non -a n sa -n iobocen e Im id o Com p lexes
Cp-Nb-Cp (deg)
Nb-N-C (deg)
Nb-N (Å)
ref
[Me2Si(η5-C5H4)2]Nb(dNtBu)Cl
[Me2Si(η5-C5H4)2]NbCl(MeCtCMe)
[Me2C(η5-C5H4)2]Nb(dNSiMe3)Cl
[Me2C(η5-C5H4)2]Nb(dNtBu)Cl
[Me2C(η5-C5H4)2]Nb(dNtBu)Br
[Me2C(η5-C5H4)2]Nb(dNtBut)I
[Me2C(η5-C5H4)2]Nb(µ-H2)BH2
[Me2C(η5-C5H4)2]NbH(PMe3)
121.21
130.0
114.2
113.3
113.4
114.2
125.0
126.1
not reported
not reported
122.7
124.0
124.9
178.8(2)
1.756(3)
this work
4
5
5
5
5
6
6
167.71(7)
178.4(3)
178.3(2)
171.8(2)
1.777(1)
1.762(3)
1.765(2)
1.770(2)
[Me2C(η5-C5H4)2]Nb(dNAr)Cla
[Me2C(η5-C5H4)2]Nb(dNAr)N(Me)2[B(C6H5)4]a
(η5-C5H5)2Nb(dNtBu)Clb
167.5(1)
166.8(1)
173.6(4)
179.4(5)
165.1(2)
1.798(2)
1.803(2)
1.789(4)
1.737(6)
1.792(2)
7
7
13
(η5-C5H4SiMe3)2Nb(dNC6H5)Cl
14
a
b
Ar ) C6H4Me2-2,5. Two independent molecules exist in the unit cell.
F igu r e 4. Different isomers for complexes [Me2Si(η5-
C5H4)2]Nb(X)(Y).
C5 ring. This effect gives rise to the stereoisomer meso-
(R,S) (I) and the enantiomers rac-(R,R) (III) and (S,S)
(IV) (Figure 4). In addition, if groups X and Y are
different, there exists another meso form (II) in which
the SiMe3 substituents are pointing either toward or
away from X. By varying X or Y and therefore their
steric or electronic properties, the stereoselective syn-
thesis of only one of these isomers should be possible.
1H NMR spectroscopy will show clearly the existence
of the meso- and rac-isomers. The meso-complex con-
tains a plane of symmetry (Cs), and thus the two
cyclopentadienyl rings of the ansa ligand will be equiva-
lent. They are however inequivalent in the rac-complex
due to the lack of symmetry (C1).
Figu r e 3. 1H NMR spectra of [Me2Si(η5-C5H4)2]Nb(dNtBu)-
(Et) in the ethyl region: (a) experimental; (b) simulated.
In the 1H NMR spectrum of compound 4 the CH2
protons of the benzyl group are equivalent, indicating
free rotation of the niobium-carbon bond in solution.
This is also observed in 5, which furthermore shows an
AB system for the terminal olefinic protons of the η1-
allyl group (see Experimental Section).
The complete absence of niobium complexes contain-
ing substituted ansa ligands and the stereoselective
catalytic properties of their group 4 analogues has led
us to investigate these compounds. To prepare substi-
tuted ansa-niobocenes, we have considered the use of
the trimethylsilyl-substituted ansa ligand Me2Si(C5H3-
SiMe3)2, and different families of substituted ansa-nio-
bocene complexes of the stoichiometry [Me2Si(η5-C5H3-
SiMe3)2]Nb(X)(Y) have been prepared. The preparation
of substituted ansa ligand complexes of niobium can
lead to a variety of isomers depending on the configu-
ration of the cyclopentadienyl rings. The carbon atoms
linked to the SiMe3 substituent become chiral in the
niobocene complexes due to the fact that they are also
linked to niobium and two distinct carbon atoms in the
First, using the identical synthetic method employed
in the preparation of 1, complex [Me2Si(η5-C5H3SiMe3)2]-
Nb(dNtBu)Cl (6) was prepared by the reaction of Nb-
(dNtBu)Cl3(py)2 and [Me2Si(η5-C5H3SiMe3)2]Li2 in a 1:1
molar ratio. It was prepared in a stereoselective
synthesis uniquely as the meso-isomer as was revealed
1
by H NMR spectroscopy. The meso-isomer contains a
plane of symmetry, which makes the cyclopentadienyl
rings of the ansa ligand equivalent, and hence only three
1
signals for the ring protons are observed in its H NMR
spectrum, which in addition gave the expected signals
for the tBu and the SiMe3 groups and two for SiMe2 (see
Experimental Section). In the case of 6, the rac-isomer
is probably disfavored due to steric effects, and for this

New ansa-Niobocene Complexes
Organometallics, Vol. 17, No. 25, 1998 5457
Con clu d in g Rem a r k s
In conclusion we report the synthesis and character-
ization of new halo and alkyl ansa-niobocene complexes,
as well as the preparation of the first substituted ansa-
niobocene complexes, with the substituted ansa ligand
Me2Si(C5H3SiMe3)2, [Me2Si(η5-C5H3SiMe3)2]Nb(X)(Y).
Exp er im en ta l Section
F igu r e 5. Proposed structure for meso-[Me2Si(η5-C5H3-
SiMe3)2]Nb(dNtBu)Cl (6).
Gen er a l P r oced u r es. All reactions were performed using
standard Schlenk-tube techniques in an atmosphere of dry
nitrogen. Solvents were distilled from appropriate drying
agents and degassed before use.
same reason the SiMe3 groups should be pointing away
from the bulky imido group (Figure 5), although the
influence of electronic effects cannot be ruled out.
Complex [Me2Si(η5-C5H3SiMe3)2]NbCl2 (7) was pre-
pared by a similar method employed in the synthesis
of [Me2Si(η5-C5H4)2]NbCl2,4 using the lithium reagent
[Me2Si(η5-C5H3SiMe3)2]Li2 instead of the corresponding
thallium derivative. The compound isolated should be
a mixture of rac- and meso-isomers, although only one
set of 10 signals was observed in its ESR spectrum. This
is most certainly due to the small difference between
the rac- and meso-isomers, which the resolution of the
spectrometer was unable to differentiate. The values
of giso (1.9847) and a93Nb (104.36 G) are analogous to
other niobocene(IV) complexes, with the unpaired elec-
tron mainly located at the metal center.16
The complexes [Me2Si(η5-C5H4)2]Li2,12 NbCl4(THF)2,17 and
Nb(dNtBu)Cl3(py)211 were prepared as described earlier. THF
or Et2O solutions of ClMgR (R ) Me, Et, CH2Ph, and CH2-
CHdCH2) were purchased from Aldrich and used directly.
18
Me2Si(C5H4SiMe3)2 was prepared by the published method
and converted into its lithium salt by reaction with a slight
excess of n-butyllithium in hexane. ESR spectra were taken
at the X-band with a Bruker ESP 300 spectrometer. IR
spectra were recorded on a Perkin-Elmer PE 883 IR spectro-
photometer. 1H and 13C spectra were recorded on Varian FT-
300 and Varian Gemini FT-200 spectrometers and referenced
to the residual deuterated solvent. Microanalyses were carried
out with a Perkin-Elmer 2400 microanalyzer.
[Me2Si(η5-C5H4)2]Nb(dNtBu )Cl (1). THF (50 mL) was
added to a solid mixture of Nb(dNtBu)Cl3(py)2 (1.56 g, 3.64
mmol) and [Me2Si(η5-C5H4)2]Li2 (0.73 g, 3.65 mmol). The
resulting yellow solution was stirred under reflux for 8 h.
Solvent was removed in vacuo and hexane added (75 mL) to
the resulting solid. The mixture was filtered and the filtrate
concentrated (ca. 10 mL) and cooled to -30 °C. The resulting
yellow solid that precipitated from the solution was isolated
We have considered the reduction processes of 7 in
the presence of the appropriate alkyne ligands. The
reduction of 7 with Na/Hg in a 1:1 molar ratio in the
presence of the alkyne RCtCR, R ) Me, Ph, yields the
alkyne-containing complexes [Me2Si(η5-C5H3SiMe3)2]-
NbCl(RCtCR), R ) Me (8); Ph (9), in a behavior similar
to that previously described for complex [Me2Si(η5-C5-
H4)2]NbCl2.4 9 was initially isolated from toluene
extraction of the reaction as an approximately 1:1
mixture of its rac- and meso-isomers, which supports
the proposal that 7 is also a mixture of its rac- and meso-
isomers. These isomers were separated on cooling a
hexane solution. The green meso-isomer was highly
soluble and the yellow rac-isomer only partially soluble
in this medium. However, for 8 no notable difference
in solubility of the rac- and meso-isomers was observed,
and thus separation was not possible. 8 was isolated
as a green solid corresponding to an approximately 1:1
by filtration (1.02 g, 72%). IR (Nujol): νNbdC 1245 cm-1 1H
.
NMR (200 MHz, C6D6): δ 0.03 (3H), 0.23 (3H) (s, SiMe2), 0.97
(s, 9H, CMe3), 5.94 (2H), 6.05 (2H), 6.31 (2H), 6.51 (2H) (m,
C5H4). 13C{1H} NMR (300 MHz, C6D6): δ -6.78, -5.09
(SiMe2), 30.22 (CMe3), 72.34 (CMe3), 100.49, 117.07, 117.99,
119.73, 130.37 (C1) (C5H4)2. Anal. Calcd for C16H23ClNNbSi:
C, 49.81; H, 6.01; N, 3.63. Found: C, 49.58; H, 5.91; N, 3.60.
[Me2Si(η5-C5H4)2]Nb(dNtBu )(Me) (2). A 3 M solution of
ClMgMe in THF (0.32 mL, 0.94 mmol) was added to a stirring
solution of 1 (0.30 g, 0.78 mmol) in THF (25 cm3) at -78 °C.
The yellow solution was allowed to warm to room temperature
and stirred for 15 h. Solvent was removed in vacuo and the
remaining green oil extracted in hexane. A yellow crystalline
solid was obtained by concentrating (5 mL) and cooling (-30
°C) the solution (0.12 g, 42%). IR (Nujol): νNbdC 1260 cm-1
.
1H NMR (200 MHz, C6D6): δ 0.10 (3H), 0.32 (3H) (s, SiMe2),
0.96 (s, 9H, CMe3), 1.08 (s, 3H, Me), 5.55 (2H), 5.86 (2H), 5.94
(2H), 6.40 (2H) (m, C5H4). 13C{1H} NMR (300 MHz, C6D6): δ
-6.25, -5.15, (SiMe2), 4.41 (Me), 30.91 (CMe3), 66.55 (CMe3),
100.11, 113.39, 113.97, 114.35, 123.77 (C1) (C5H4). Anal. Calcd
for C17H26NNbSi: C, 55.88; H, 7.17; N, 3.83. Found: C, 56.12;
H, 7.24; N, 3.81.
1
mixture of its rac- and meso-isomers. The H spectra
of the rac-isomer of 8 and 9 show the expected signals
for a complex that does not contain a plane of symmetry;
that is, the cyclopentadienyl rings of the ansa ligand
are inequivalent and give rise to six signals. In the
meso-isomer there is a plane of symmetry, which makes
the cyclopentadienyl rings of the ansa ligand equivalent,
and hence three signals are observed in its 1H NMR
spectrum (see Experimental Section).
According to Figure 4, when X * Y, two isomers are
possible for the meso-confirmation. However, in both 8
and 9 only one meso-complex is observed. It is reason-
able to assume that due to steric effects, this isomer
would have the SiMe3 substituents of the cyclopenta-
dienyl ring pointing away from the voluminous acetyl-
ene group.
Me2Si(η5-C5H4)2]Nb (dNtBu )(E t ) (3). A 2 M solution of
ClMgEt in Et2O (0.50 mL, 1.00 mmol) was added to a stirring
solution of 1 (0.32 g, 0.83 mmol) in THF (25 mL) at -78 °C.
The yellow solution was allowed to warm to room temperature
and stirred for 15 h. Solvent was removed in vacuo and the
remaining green oil extracted in hexane. A yellow crystalline
solid was obtained by concentrating (5 mL) and cooling (-30
°C) the solution (0.16 g, 52%). IR (Nujol): νNbdC 1245 cm-1
.
1H NMR (200 MHz, C6D6): δ 0.13 (3H), 0.34 (3H) (s, SiMe2),
(17) Pedersen, S. F.; Hartung, J . B.; Roskamp, E. J .; Dragovich, P.
S. Inorg. Synth. 1992, 29, 119.
(16) Antin˜olo, A.; Fajardo, M.; de J esu´s, E.; Mugnier, Y.; Otero, A.
J . Organomet. Chem. 1994, 470, 127.
(18) Wiesenfeldt, H.; Reinmuth, A.; Barsties, E.; Evertz, K.; Brintz-
inger, H. H. J . Organomet. Chem. 1989, 369, 359.

5458 Organometallics, Vol. 17, No. 25, 1998
Antin˜olo et al.
0.97 (s, 9H, CMe3), 1.91 (m, 3H CH2CH3), 2.02 (m, 2H, CH2-
CH3), 5.36 (2H), 5.80 (2H), 6.06 (2H), 6.34 (2H) (m, C5H4).
13C{1H} NMR (300 MHz, C6D6): δ -5.71, -5.51 (SiMe2), 20.20
(CH2CH3), 22.39 (CH2CH3), 31.33 (CMe3), 70.80 (CMe3), 101.44,
111.68, 111.89, 116.89, 120.98 (C1) (C5H4). Anal. Calcd for
of Na). To the mixture was added THF (100 mL). To this
stirred solution was added via microsyringe MeCtCMe (0.151
mL, 1.92 mmol), and the reaction mixture was allowed to stir
at room temperature for 3 h. The solvent was removed under
reduced pressure and toluene (50 mL) was added. The
suspension was filtered and solvent removed in vacuo from
the filtrate, yielding a green solid (0.68 g, 69%). A displace-
ment reagent ((S)-(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol) was
added to a sample of 8 in the NMR tube, and the 1H NMR
resonances of the rac-isomer were doubled. A 1H 13C correla-
tion experiment (HETCOR) carried out on these isomers has
allowed us to assign the resonances corresponding to the
C
18H28NNbSi: C, 56.98; H, 7.44; N, 3.69. Found: C, 56.74;
H, 7.31; N, 3.63.
Me2Si(η5-C5H4)2]Nb(dNtBu )(CH2P h ) (4). A 1 M solution
of ClMgCH2Ph in Et2O (0.96 mL, 0.96 mmol) was added to a
stirring solution of 1 (0.30 g, 0.78 mmol) in THF (25 mL) at
-78 °C. The yellow solution was allowed to warm to room
temperature and stirred for 15 h. Solvent was removed in
vacuo and the remaining green oil extracted in hexane. A dark
yellow crystalline solid was obtained by concentrating (5 mL)
and cooling (-30 °C) the solution (0.15 g, 44%). IR (Nujol):
different types of carbon atoms. IR (Nujol): νCtC 1700 cm-1
.
rac-[Me2Si(η5-C5H3SiMe3)2]NbCl(MeCtCMe), 8a , 1H NMR
(200 MHz, C6D6): δ 0.05 (3H), 0.22 (3H) (s, SiMe2), 0.18 (9H),
0.40 (9H) (s, SiMe3), 2.27 (3H), 2.39 (3H) (s, MeCtCMe), 4.63
(1H), 5.10 (1H), 5.14 (1H), 5.35 (1H), 5.50 (1H), 6.53 (1H) (m,
C5H3SiMe3). meso-[Me2Si(η5-C5H3SiMe3)2]NbCl(MeCtCMe),
8b, 1H NMR (200 MHz, C6D6): δ 0.15 (3H), 0.17 (3H) (s, SiMe2),
0.31 (s, 18H, SiMe3), 2.27 (3H), 2.39 (3H) (s, MeCtCMe), 4.98
(2H), 5.27 (2H), 5.64 (2H) (m, C5H3SiMe3). 8a 13C{1H} NMR
(300 MHz, C6D6): δ -8.34, -7.52 (SiMe2), 4.05, 10.56 (SiMe3),
11.83, 18.86 (tCMe), 96.36, 96.54, 97.51, 97.74, 98.40, 99.32,
116.88, 118.00, 125.80, 126.12 (C5H3SiMe3), 126.71, 149.98
(tCMe). 8b 13C{1H} NMR (300 MHz, C6D6): δ -4.34, -3.52
(SiMe2), 7.85, (SiMe3), 11.83, 18.86 (tCMe), 96.48, 97.67, 98.96,
117.45, 125.72 (C5H3SiMe3), 126.71, 149.98 (tCMe). Anal.
Calcd for C22H36ClNbSi3: C, 51.49; H, 7.07. Found: C, 51.30;
H, 6.97.
νNbdC 1241 cm-1
.
1H NMR (200 MHz, C6D6): δ -0.05 (3H),
0.26 (3H) (s, SiMe2), 0.96 (s, 9H, CMe3), 3.34 (s, 2H, CH2Ph),
5.49 (2H), 5.66 (2H), 5.98 (2H), 6.32 (2H) (m, C5H4), 6.80-
7.45 (m, 5H, CH2Ph). 13C{1H} NMR (300 MHz, C6D6): δ -6.64,
-4.76 (SiMe2), 32.43 (CH2Ph), 31.87 (CMe3), 71.39 (CMe3),
101.55, 101.67, 108.55, 116.57 (C1), 117.64 (C5H4), 125.06,
130.45, 147.12 (C1) (CH2Ph). Anal. Calcd for C23H30NNbSi:
C, 62.57; H, 6.85; N, 3.17. Found: C, 62.80; H, 6.94; N, 3.15.
[Me2Si(η5-C5H4)2]Nb(dNtBu )(CH2CHdCH2) (5). A 2 M
solution of ClMgCH2CHdCH2 in THF (0.56 mL, 1.12 mmol)
was added to a stirring solution of 1 (0.36 g, 0.93 mmol) in
THF (25 mL) at -78 °C. The yellow solution was allowed to
warm to room temperature and stirred for 15 h. Solvent was
removed in vacuo and the remaining green oil extracted in
hexane. A yellow crystalline solid was obtained by concentrat-
ing (5 mL) and cooling (-30 °C) the solution (0.16 g, 43%). IR
[Me2Si(η5-C5H3SiMe3)2]NbCl(P h CtCP h ) (9). 7 (1.05 g,
2.12 mmol) was added to sodium amalgam (0.049 g, 2.12 mmol
of Na). To the mixture was added THF (100 mL). To this
stirred solution was added PhCtCPh (0.38 g, 2.12 mmol) and
the reaction mixture was allowed to stir at room temperature
for 3 h. The solvent was removed under reduced pressure,
and toluene (50 mL) was added. The suspension was filtered
and solvent removed in vacuo from the filtrate, yielding a green
solid (0.98 g, 72.6%). The mixture of isomers was separated
by adding hexane to the green solid. The resultant yellow
precipitate of rac-[Me2Si(η5-C5H3SiMe3)2]NbCl(PhCtCPh), 9a ,
was isolated by filtration and dried under vacuum (0.45 g).
Solvent was removed from the green filtrate under reduced
pressure to give a green solid of meso-[Me2Si(η5-C5H3SiMe3)2]-
NbCl(PhCtCPh), 9b (0.53 g). IR (Nujol): νCtC 1750 cm-1. rac-
[Me2Si(η5-C5H3SiMe3)2]NbCl(PhCtCPh), 9a , 1H NMR (200
MHz, C6D6): δ 0.19 (3H), 0.22 (3H) (s, SiMe2), -0.17 (9H), 0.19
(9H) (s, SiMe3), 5.15 (1H), 5.37 (1H), 5.48 (1H), 5.93 (1H), 6.21
(1H), 6.67 (1H) (m, C5H3SiMe3), 7.08-7.32, 7.66, 7.83 (m, 10H,
PhCtCPh). meso-[Me2Si(η5-C5H3SiMe3)2]NbCl(PhCtCPh), 9b,
1H NMR (200 MHz, C6D6): δ 0.22 (3H), 0.24 (3H) (s, SiMe2),
0.14 (s, 18H, SiMe3) 5.60 (2H), 5.74 (2H), 6.18 (2H) (m, C5H3-
SiMe3). 9a 13C{1H} NMR (300 MHz, acetone-d6): δ -6.34,
-4.52 (SiMe2), 3.34, 10.88 (SiMe3), 96.36, 96.54, 97.51, 97.74,
98.40, 99.32, 116.88, 118.00, 125.80, 126.12 (C5H3SiMe3),
141.59, 159.68 (tCPh), 126.24, 127.56, 127.74, 128.06, 128.20,
128.35, 128.94, 131.82, 139.20, 140.08 (tCPh). 9b 13C{1H}
NMR (300 MHz, acetone-d6): δ -4.34, -3.52 (SiMe2), 7.85,
(SiMe3), 96.48, 97.67, 98.96, 117.45, 125.72 (C5H3SiMe3),
141.59, 159.68 (tCPh), 126.24, 127.56, 127.74, 128.06, 128.20,
128.35, 128.94, 131.82, 139.20, 140.08 (tCPh). Anal. Calcd
for C32H40ClNbSi3: C, 60.31; H, 6.33. Found: C, 60.68; H, 6.45.
(Nujol): νNbdC 1258 cm-1 1H NMR (200 MHz, C6D6): δ 0.09
.
(3H), 0.30 (3H) (s, SiMe2), 0.93 (s, 9H, CMe3), 2.82 (d, 2H, CH2-
2
CHdCH2) J (1H-1H) 8.5 Hz, 4.85 (cis), 5.04 (trans) (dd, 2H,
2
2
CH2-CHdCH2) J gem(1H-1H) 2.6 Hz, J cis(1H-1H) 9.9 Hz,
2J trans(1H-1H) 16.8 Hz, 5.41 (2H), 5.86 (2H), 5.91 (2H), 6.33
(2H) (m, C5H4), 6.61 (m, 1H, CH2-CHdCH2). 13C{1H} NMR
(300 MHz, C6D6): δ -6.12, -5.40 (SiMe2), 31.02 (CMe3), 37.30
(CH2-CHdCH2), 68.40 (CMe3), 101.24, 113.21, 113.57, 117.30,
123.13 (C1) (C5H4), 103.78 (CH2-CHdCH2), 150.40 (CH2-CHd
CH2). Anal. Calcd for C19H28NNbSi: C, 58.30; H, 7.21; N, 3.58.
Found: C, 58.01; H, 7.09; N, 3.49.
m eso-[Me2Si(η5-C5H3SiMe3)2]Nb(dNtBu )Cl (6). THF (50
mL) was added to a solid mixture of Nb(dNtBu)Cl3(py)2 (0.55
g, 1.28 mmol) and [Me2Si(η5-C5H3SiMe3)2]Li2 (0.44 g, 1.28
mmol). The resulting yellow solution was stirred under reflux
for 8 h. Solvent was removed in vacuo and hexane added (75
mL) to the resulting solid. The mixture was filtered and the
filtrate concentrated (10 mL) and cooled to -30 °C. The
resulting orange solid that precipitated from the solution was
isolated by filtration (0.47 g, 69%). IR (Nujol): νNbdC 1234
cm-1
SiMe2), 0.45 (s, 18H, SiMe3), 0.99 (s, 9H, CMe3), 6.23 (4H), 6.58
(2H), (m, C5H3SiMe3). 13C{1H} NMR (300 MHz, C6D6):
.
1H NMR (200 MHz, C6D6): δ 0.08 (3H), 0.35 (3H) (s,
δ
-7.12, -4.05 (SiMe2), 0.48 (SiMe3), 30.81 (CMe3), 69.76 (CMe3),
102.15, 122.56, 125.52, 125.66 (Cipso), 134.55 (Cipso) (C5H3-
SiMe3). Anal. Calcd for C22H39ClNNbSi3: C, 49.84; H, 7.41;
N, 2.64. Found: C, 49.68; H, 7.37; N, 2.64.
[Me2Si(η5-C5H3SiMe3)2]NbCl2 (7). THF (200 mL) was
added to a mixture of NbCl4(THF)2 (8.65 g, 22.83 mmol) and
[Me2Si(η5-C5H3SiMe3)2]Li2 (7.87 g, 22.83 mmol). The reaction
mixture was stirred at room temperature for 16 h, after which
solvent was removed in vacuo. The resulting solid was
extracted several times in toluene (4 × 150 mL), solvent was
removed under reduced pressure, and the resulting brown solid
was dried under vacuum (9.55 g, 84%). IR (Nujol): νSi-Me 1302
X-r a y Str u ctu r e Deter m in a tion for [Me2Si(η5-C5H4)2]-
Nb(dNBu t)Cl (1). A crystal of 1 was sealed in a Lindemann
capillary under dry nitrogen and used for data collection.
Intensity data were collected on a NONIUS-MACH3 diffrac-
tometer equipped with graphite-monochromated Mo KR radia-
tion (λ ) 0.710 73 Å) using an ω/2θ scan technique to a
maximum value of 56°. The final unit cell was determined
from 25 well-centered high-angle reflections that were widely
scattered in reciprocal space. Data were corrected for Lorentz
and polarization effects, and absorption correction was carried
cm-1, νC-C(Cp) 1200, 1043, 834 cm-1, νNb-Cl 270 cm-1
. Anal.
Calcd for C18H30Cl2NbSi3: C, 43.72; H, 6.11. Found C, 43.56;
H, 6.02.
[Me2Si(η5-C5H3SiMe3)2]NbCl(MeCtCMe) (8). 7 (0.95 g,
1.92 mmol) was added to sodium amalgam (0.044 g, 1.92 mmol

New ansa-Niobocene Complexes
Organometallics, Vol. 17, No. 25, 1998 5459
methods,20 and refinement was carried out by full-matrix least-
squares (SHELXL-97).21 All non-hydrogen atoms were refined
with anisotropic thermal parameters. The hydrogen atoms
were included in calculation positions but nonrefined. Weights
were optimized in the final cycles. Atomic scattering factors
were taken from ref 22. Crystallographic data are given in
Table 3. Other detailed data are supplied in the Supporting
Information.
Ta ble 3. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 1
empirical formula
fw
C16H23ClNNbSi
385.80
temp
293(2) K
wavelength
cryst syst, space group
unit cell dimens
0.710 70 Å
monoclinic, P21/m
a ) 6.942(2) Å, R ) 90°
b ) 10.5000(10) Å,
â ) 98.33(2)°
Ack n ow led gm en t. The authors gratefully acknowl-
edge financial support from the Direccio´n General de
Ensen˜aza Superior e Investigacio´n, Spain (Grant No.
PB 95-0023-C02-01), Union Fenosa, and the Euro-
pean Union for a postdoctoral grant to S.P. under the
Human Capital and Mobility Program (Contract No.
ERBCHRXCT930281). We would also like to thank
Prof. Mugnier, for providing ESR data.
c ) 12.370(2) Å, γ ) 90°
volume
Z, calcd density
abs coeff
892.1(3) Å3
4, 1.436 g/cm3
8.82 cm-1
transmission range
F(000)
0.721-1.000
396
cryst size
θ range for data collection
index ranges
0.5 × 0.4 × 0.4 mm
2.56-27.98°
0 e h e 9, 0 e k e 13,
-16 e l e 16
Su p p or tin g In for m a tion Ava ila ble: Tables of complete
crystal data (Table SI), non-hydrogen atom coordinates (Table
SII), complete bond distances and angles (Table SIII), aniso-
tropic displacement parameters (Table SIV), hydrogen atom
coordinates (Table SV), weighted least-squares planes (Table
SVI), intermolecular contacts less than 3.50 Å (Table SVII),
possible hydrogen bonds (Table SVIII), and ORTEP and crystal
packing drawings (29 pages). Ordering information is given
on any current masthead page. A list of structure factors is
available on request from the authors.
no. of reflns collected/unique
completeness to 2θ
refinement method
2265/2265 [R(int) ) 0.0000]
27.98, 99.8%
full-matrix least-squares on F2
no. of data/restraints/parameters 2265/0/103
goodness-of-fit on F2
0.708
final R indices [I > 2σ(I)]a
R indices (all data)
R1 ) 0.0252, wR2 ) 0.0712
R1 ) 0.0309, wR2 ) 0.0844
0.526 and -0.459 e Å-3
largest diff peak and hole
R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]]0.5
.
a
out on the basis of a ψ scan.19 Analysis of systematic absences
in the data was consistent with monoclinic space group P21
and P21/m, and the choice of the latter alternative was
vindicated by the success of the subsequent solution and
refinement. The asymmetric unit comprises one independent
half-molecule of 1. The structure was solved by the direct
OM980561N
(20) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 435-
436.
(21) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
Crystal Structures from Diffraction Data; University of Go¨ttingen,
Go¨ttingen, Germany, 1993.
(19) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(22) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1974.