Amido-imido niobium complexes with chloro-silyl-and amino-silyl-functionalized cyclopentadienyl ligands

Article abstract of DOI:10.1021/om9806491

The chloro-imido complex [Nb(η⁵-C₅H₄-SiMe₂Cl)(CH ₂Ph)Cl(N^tBu)] undergoes selective substitution of the Nb-Cl bond when it is reacted with LiNH^tBu, giving [Nb(η⁵-C₅H₄-SiMe₂-Cl)(CH ₂Ph)(NH^tBu)(N^tBu)], whereas preferential reaction at the Si-Cl bond occurs with NH₂^tBu, giving [Nb(η⁵-C₅H₄-SiMe₂(NH ^tBu)}(CH₂Ph)Cl(N^tBu)], which is then transformed into [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}(CH₂Ph)(NH^tBu)(N^tBu)] on further reaction with NH₂^tBu. Chemical reactivity studies demonstrate that a spontaneous transformation of [Nb(η⁵-C₅H₄-SiMe₂Cl)(CH ₂Ph)(NH^tBu)(N^tBu)] into [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}(CH₂Ph)Cl(N^tBu)] takes place, via an intermolecular reaction, by attack of the silicon-bonded chlorine at the unsaturated niobium center. Benzylation of [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}(CH₂Ph)Cl(N^tBu)] with Mg(CH₂Ph)₂·2THF gives [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}(CH₂Ph)₂(N^tBu)], which also results from reaction of the chloro-silyl derivative [Nb(η⁵-C₅H₄-SiMe₂Cl)(CH ₂Ph)₂(N^tBu)] with NH₂^tBu. The dichloro-imido complex [Nb(η⁵-C₅H₄-SiMe₂Cl)Cl ₂(N^tBu)], readily obtained from [Nb(η⁵-C₅H₄-SiMe₂Cl)Cl ₄], also reacts preferentially at the Si-Cl bond when treated with NH₂^tBu to give [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}Cl₂(N^tBu)], which is further transformed into [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}Cl(NH^tBu)(N^tBu)]; the latter is alternatively prepared by reaction of [Nb(η⁵-C₅H₄-SiMe₂Cl)Cl ₄] with a large excess of NH₂^tBu. The tetrachloro compound reacts with excess LiNH^tBu to give the constrained-geometry complex [Nb{η⁵-C₅H₄-SiMe₂(η ¹-N^tBu)}(NH^tBu)(N^tBu)], which is converted into the chloro-niobium derivative by reaction with SiMe₃Cl. These constrained-geometry complexes may also be obtained from the dichloro derivative [Nb(η⁵-C₅H₄-SiMe₂Cl)Cl ₂(N^tBu)], by reaction with 3 or 2 equiv of LiNH^tBu, respectively. Thermal treatment of the benzyl compounds [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}(CH₂-Ph)X(N^tBu)] (X = Cl, CH₂Ph) at 160°C results in formation of the silyl-amido complexes [Nb{η⁵-C₅H₄-SiMe₂(η ¹-N^tBu)}X(N^tBu)] (X = Cl, CH₂Ph) with elimination of toluene, whereas a similar transformation of the related iminoacyl complex [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}{η²-[C(CH₂Ph){N(2,6-Me ₂C₆H₃)}](CH₂Ph)(N^tBu)] produces a simultaneous isomerization to give the vinylamido compound [Nb{η⁵-C₅H₄-SiMe₂(η ¹-N^tBu)}{N(CH=CHPh)(2,6-Me₂C₆H ₃)}(N^t-Bu)]. Insertion of CN(2,6-Me₂C₆H₃) into the niobium-benzyl bonds of complexes [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}(CH₂Ph)X(N^tBu)] (X = Cl, CH₂Ph) and [Nb{η⁵-C₅H₄-SiMe₂(η ¹-N^tBu)}-(CH₂Ph)(N^tBu)] leads to the iminoacyl compounds [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}{η²-[C(CH₂Ph)-{N(2,6-Me ₂C₆H₃)}]}X(N^tBu)] (X = Cl, CH₂Ph) and [Nb{η⁵-C₅H₄-SiMe₂(η ¹-N^tBu)}{η²-[C(CH ₂-Ph){N(2,6-Me₂C₆H₃)}]}(N ^tBu)], respectively. All of the reported new compounds were characterized by elemental analyses and ¹H and ¹³C NMR spectroscopy, and the X-ray molecular structure of [Nb{η⁵-C₅H₄-SiMe₂(NH ^tBu)}Cl₂(N^tBu)] was studied by diffraction methods.

Full text of DOI:10.1021/om9806491

546
Organometallics 1999, 18, 546-554
Am id o-Im id o Niobiu m Com p lexes w ith Ch lor o-Silyl-
a n d Am in o-Silyl-F u n ction a lized Cyclop en ta d ien yl
Liga n d s
M. Isabel Alcalde, M. Pilar Go´mez-Sal, and Pascual Royo*
Departamento de Quı´mica Inorga´nica, Universidad de Alcala´, Campus Universitario,
E-28871 Alcala´ de Henares, Spain
Received J uly 29, 1998
The chloro-imido complex [Nb(η5-C5H4-SiMe2Cl)(CH2Ph)Cl(NtBu)] undergoes selective
substitution of the Nb-Cl bond when it is reacted with LiNHtBu, giving [Nb(η5-C5H4-SiMe2-
Cl)(CH2Ph)(NHtBu)(NtBu)], whereas preferential reaction at the Si-Cl bond occurs with
t
NH2 Bu, giving [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2Ph)Cl(NtBu)], which is then transformed
t
into [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2Ph)(NHtBu)(NtBu)] on further reaction with NH2 Bu.
Chemical reactivity studies demonstrate that a spontaneous transformation of [Nb(η5-C5H4-
SiMe2Cl)(CH2Ph)(NHtBu)(NtBu)] into [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2Ph)Cl(NtBu)] takes
place, via an intermolecular reaction, by attack of the silicon-bonded chlorine at the
unsaturated niobium center. Benzylation of [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2Ph)Cl(NtBu)]
with Mg(CH2Ph)2‚2THF gives [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2Ph)2(NtBu)], which also
results from reaction of the chloro-silyl derivative [Nb(η5-C5H4-SiMe2Cl)(CH2Ph)2(NtBu)]
t
with NH2 Bu. The dichloro-imido complex [Nb(η5-C5H4-SiMe2Cl)Cl2(NtBu)], readily obtained
from [Nb(η5-C5H4-SiMe2Cl)Cl4], also reacts preferentially at the Si-Cl bond when treated
t
with NH2 Bu to give [Nb{η5-C5H4-SiMe2(NHtBu)}Cl2(NtBu)], which is further transformed
into [Nb{η5-C5H4-SiMe2(NHtBu)}Cl(NHtBu)(NtBu)]; the latter is alternatively prepared by
reaction of [Nb(η5-C5H4-SiMe2Cl)Cl4] with a large excess of NH2 Bu. The tetrachloro compound
t
reacts with excess LiNHtBu to give the constrained-geometry complex [Nb{η5-C5H4-SiMe2(η1-
NtBu)}(NHtBu)(NtBu)], which is converted into the chloro-niobium derivative by reaction
with SiMe3Cl. These constrained-geometry complexes may also be obtained from the dichloro
derivative [Nb(η5-C5H4-SiMe2Cl)Cl2(NtBu)], by reaction with 3 or 2 equiv of LiNHtBu,
respectively. Thermal treatment of the benzyl compounds [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2-
Ph)X(NtBu)] (X ) Cl, CH2Ph) at 160 °C results in formation of the silyl-amido complexes
[Nb{η5-C5H4-SiMe2(η1-NtBu)}X(NtBu)] (X ) Cl, CH2Ph) with elimination of toluene, whereas
a similar transformation of the related iminoacyl complex [Nb{η5-C5H4-SiMe2(NHtBu)}{η2-
[C(CH2Ph){N(2,6-Me2C6H3)}](CH2Ph)(NtBu)] produces a simultaneous isomerization to give
the vinylamido compound [Nb{η5-C5H4-SiMe2(η1-NtBu)}{N(CHdCHPh)(2,6-Me2C6H3)}(Nt-
Bu)]. Insertion of CN(2,6-Me2C6H3) into the niobium-benzyl bonds of complexes [Nb{η5-
C5H4-SiMe2(NHtBu)}(CH2Ph)X(NtBu)] (X ) Cl, CH2Ph) and [Nb{η5-C5H4-SiMe2(η1-NtBu)}-
(CH2Ph)(NtBu)] leads to the iminoacyl compounds [Nb{η5-C5H4-SiMe2(NHtBu)}{η2-[C(CH2Ph)-
{N(2,6-Me2C6H3)}]}X(NtBu)] (X ) Cl, CH2Ph) and [Nb{η5-C5H4-SiMe2(η1-NtBu)}{η2-[C(CH2-
Ph){N(2,6-Me2C6H3)}]}(NtBu)], respectively. All of the reported new compounds were
characterized by elemental analyses and 1H and 13C NMR spectroscopy, and the X-ray
molecular structure of [Nb{η5-C5H4-SiMe2(NHtBu)}Cl2(NtBu)] was studied by diffraction
methods.
In tr od u ction
only allows their fixation on solid supports2 but also
offers new, direct synthetic strategies for constrained-
geometry catalysts with bidentate η5-cyclopentadienyl-
silyl-η1-amido ligands, in good yields.3 These con-
strained-geometry catalysts can also be fixed on silica
supports if they contain one additional Si-Cl bond, such
Silyl-substituted cyclopentadienyl rings have been
extensively used to prepare Ziegler-Natta type olefin
polymerization catalysts because the presence of the
electron-withdrawing silyl substituent improves their
catalytic activity.1 The presence of additional function-
alities, particularly chlorine, on these silyl groups not
(2) (a) J ackson, R.; Ruddlesden, J .; Thompson, D. J .; Whelan, R. J .
Organomet. Chem. 1977, 125, 57. (b) Booth, B. L.; Ofunne, G. C.;
Stacey, C.; Tait, P. J . T. J . Organomet. Chem. 1986, 315, 143. (c)
Ofunne, G. C.; Booth, B. L.; Tait, P. J . T. Indian J . Chem., Sect. A
1988, 27A, 1040; Chem. Abstr. 1989, 111, 154424. (d) Antberg, M.;
Lueker, H.; Boehm, L. Eur. Pat. Appl. EP 293,815 (Hoechst), 1988;
Chem. Abstr. 1989, 111, 195585.
* To whom correspondence should be addressed. Tel.: 34-1-8854765.
Fax: 34-1-8854683. E-mail: proyo@inorg.alcala.es.
(1) (a) Mo¨hring, P. C.; Coville, N. J . J . Organomet. Chem. 1994, 479,
1. (b) Brintzinger, H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,
R. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
10.1021/om9806491 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 01/23/1999

Nb Complexes with Functionalized Cp Ligands
Organometallics, Vol. 18, No. 4, 1999 547
Sch em e 1
as those obtained from initial silylcyclopentadienyl
ligands which contain two Si-Cl bonds.4 The extended
use of this type of ligand to prepare group 5 metal
complexes has been scarcely studied, and only isolated
examples of related constrained-geometry group 5 metal
compounds have been reported.5
In contrast, high-valent group 5 metal imido cyclo-
pentadienyl complexes isolobal6 with the very well-
known group 4 dicyclopentadienyl derivatives have been
extensively studied in the last few years.7
their use as starting materials to obtain new ((aminosi-
lyl)cyclopentadienyl)niobium chloro- and benzyl-imido
([Nb{η5-C5H4-SiMe2(NHtBu)}XY(NtBu)] (X, Y ) Cl, Bz)),
((chlorosilyl)cyclopentadienyl)niobium amido-imido ([Nb-
(η5-C5H4-SiMe2Cl)Bz(NHtBu)(NtBu)]), and ((aminosilyl)-
cyclopentadienyl)niobium amido-imido ([Nb{η5-C5H4-
SiMe2(NHtBu)}X(NHtBu)(NtBu)] (X ) Cl, Bz)) com-
pounds, used as precursors to prepare the new con-
strained-geometry niobium derivatives [Nb{η5-C5H4-
SiMe2-η1-NtBu)}X(NtBu)] (X ) Cl, Bz, NHtBu, N(CHd
CHPh)(2,6-Me2C6H3)) and to study the insertion reactions
of 2,6-dimethylphenyl isocyanide into their niobium-
benzyl bonds.
We have recently reported8 the synthesis and char-
acterization of new chlorosilyl-substituted cyclopenta-
dienyl imido-dichloro ([Nb(η5-C5H4-SiMe2Cl)Cl2(NtBu)],
1), imido-chloro-benzyl ([Nb(η5-C5H4-SiMe2Cl)(CH2-
Ph)Cl(NtBu)], 2), imido-dibenzyl ([Nb(η5-C5H4-SiMe2-
Cl)(CH2Ph)2(NtBu)], 3), and tetrachloro ([Nb(η5-C5H4-
SiMe2Cl)Cl4], 4) niobium derivatives. We herein report
Resu lts a n d Discu ssion
Rea ction s w ith NH2tBu . We reported9 that prefer-
ential reaction at the Si-Cl bonds takes place when
cyclopentadienylzirconium halides containing both Si-
Cl and M-Cl bonds are reacted with an excess of less
polar amines. As shown in Scheme 1, reaction of [Nb-
(η5-C5H4-SiMe2Cl)(CH2Ph)Cl(NtBu)] (2) with 2 equiv of
(3) (a) Herrmann, W. A.; Marcus, J . A.; Morawietz, M. J . A.;
Priermeier, T. Angew. Chem., Int. Ed. Engl. 1994, 33, 1946. (b)
Herrmann, W. A.; Baratta, W.; Morawietz, M. J . A. J . Organomet.
Chem. 1995, 497, C4. (c) Carpenetti, D. W.; Klopennburg, L.; Kupec,
J . T.; Petersen, J . L. Organometallics 1996, 15, 1572. (d) Amor, F.;
Okuda, J . J . Organomet. Chem. 1996, 520, 245. (e) Chen, Y.-X.; Marks,
T. J . Organometallics 1997, 16, 3649. (f) Schwink, L.; Knochel, P.;
Eberle, T.; Okuda, J . Organometallics 1998, 17, 7.
(4) Royo, B.; Royo, P.; Cadenas, L. M. J . Organomet. Chem. 1998,
551, 293.
(5) Herrmann, W. A.; Baratta, W. J . Organomet. Chem. 1996, 506,
357.
(6) (a) Williams, D. N.; Mitchell, J . P.; Poole, A. D.; Siemeling, V.;
Clegg, W.; Hockless, D. C. R.; O’Neil, P. A.; Gibson, V. C. J . Chem.
Soc., Dalton Trans. 1992, 739. (b) Chan, M. C. W.; Cole, J . M.; Gibson,
V. C.; Howard, J . A. K.; Lehmann, C.; Poole, A. D.; Siemeling, V. J .
Chem. Soc., Dalton Trans. 1998, 103.
(7) (a) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239. (b) Gibson,
V. C.; Poole, A. D. J . Chem. Soc., Chem. Commun. 1995, 2261. (c)
Green, M. L. H.; J ames, J . T.; Saunders, J . F. J . Chem. Soc., Chem.
Commun. 1996, 1343. (d) Green, M. L. H.; J ames, J . T.; Chernega, A.
N. J . Chem. Soc., Dalton Trans. 1997, 1719. (e) Green, M. L. H.; J ames,
J . T.; Saunders, J . F.; Souter, J . J . Chem. Soc., Dalton Trans. 1997,
1281. (f) Gountcher, T. I.; Tilley, T. D. J . Am. Chem. Soc. 1997, 119,
12831. (g) Antonelli, D. M.; Gomes, P. T.; Green, M. L. H.; Martins, A.
M.; Mountford, P. J . Chem. Soc., Dalton Trans. 1997, 2435.
(8) Alcalde, M. I.; Go´mez-Sal, P.; Mart´ın, A.; Royo, P. Organome-
tallics 1998, 17, 1144.
t
NH2 Bu in hexane at room temperature gave, after
separation of the ammonium salt formed, the amino-
silyl complex [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2Ph)Cl(Nt-
Bu)] (5), which was isolated as a brown oil and charac-
terized by NMR spectroscopy (see Experimental Section).
t
The same reaction carried out using 1 equiv of NH2 Bu
and 2 equiv of NEt3 also resulted in the formation of
complex 5 instead of the constrained-geometry deriva-
tives observed9b in the reaction with the related group
4 metal complexes. Compound 5 was obtained when the
hexane solution that gave 6, discussed below, was
stirred for 24 h at room temperature (see Scheme 1).
(9) (a) Ciruelos, S.; Cuenca, T.; Go´mez-Sal, P.; Manzanero, A.; Royo,
P. Organometallics 1995, 14, 177. (b) Ciruelos, S.; Cuenca, T.; Go´mez,
R.; Go´mez-Sal, P.; Manzanero, A.; Royo, P. Organometallics 1996, 15,
5577.

548 Organometallics, Vol. 18, No. 4, 1999
Alcalde et al.
Sch em e 2
As shown in Scheme 1, reaction of 5 with 2 equiv of
NH2 Bu in hexane at room temperature afforded the
yellow crystalline solid identified by elemental analysis,
NMR spectroscopy, and X-ray diffraction methods.
The H and 13C NMR spectra for complexes 8 and 10
t
corresponding amino-silyl complex [Nb{η5-C5H4-SiMe2-
(NHtBu)}(CH2Ph)(NHtBu)(NtBu)] (7) in 83% yield. Com-
plex 7 was isolated as a dark brown oil and character-
ized by NMR spectroscopy. Likewise, complex 7 can also
be directly obtained by reaction of 2 with 4 equiv or
1
show the expected singlet due to the equivalent methyl-
silyl groups and two singlets between δ 1.04 and 1.15
corresponding to the two types of Si-amine and Nb-
imido tert-butyl groups. Complex 8 shows two doublets
due to the diastereotopic protons of the two niobium-
bonded methylene benzyl moieties. The remaining
amino-silyl compounds 5, 7, and 9 have a chiral metal
center which causes the two silicon-bonded methyl
groups to be inequivalent, appearing as two singlets in
the high-field region between δ 0.31 and 0.43. Complex
5 and complexes 7-10 show either two or three types
of tert-butyl groups, which can be easily identified by
the Cipso resonances in their 13C NMR spectra, shifted
from δ 49-50 (Si-NHtBu) to δ 56-57 (Nb-NHtBu) and
δ 65-70 (NbdNtBu).
t
excess NH2 Bu.
A selective reaction was also observed when the
dibenzyl derivative [Nb(η5-C5H4-SiMe2Cl)(CH2Ph)2(Nt-
Bu)] (3), prepared as reported previously,8 was reacted
with 2 equiv of the amine at room temperature in
hexane to give the amino-silyl complex [Nb{η5-C5H4-
SiMe2(NHtBu)}(CH2Ph)2(NtBu)] (8) in 90% yield, after
separation of the ammonium salt formed. The same
compound was also isolated in high yield by benzylation
of 5 using Mg(CH2Ph)2‚2THF as alkylating agent.
Complex 8 was isolated as a greenish solid and was
characterized by elemental analysis, NMR spectroscopy,
and mass spectrometry.
The molecular structure of compound 10, obtained by
X-ray diffraction studies, is shown in Figure 1 with the
atomic labeling scheme, and selected bond lengths and
angles are presented in Table 1.
A similar reaction was carried out by adding a great
excess of amine (15/1 molar ratio) to the tetrachloro
complex [Nb(η5-C5H4-SiMe2Cl)Cl4] (4) in toluene (Scheme
2). After the mixture was stirred for 48 h at room
temperature, the amino-silyl derivative [Nb{η5-C5H4-
SiMe2(NHtBu)}Cl(NHtBu)(NtBu)] (9) was isolated in
70% yield, after removal of the ammonium salt, as a
pale yellow solid which was identified by elemental
The structure is typical of half-sandwich imido com-
plexes, and the structural parameters are comparable
to those of related compounds, such as [Nb(η5-C5H5)-
t
i
Cl2(NR)] (R ) Me, Bu, C6H5 Pr2-2,6).6a The Nb1-N1
distance of 1.748(8) Å is in the range expected for a
triple bond and is very similar to those in other imido-
dichloro niobium compounds, for which the distances
range from 1.744(3) to 1.761(6) Å; the imido group is
also almost linear (169.1(8)°). The Nb-C(ring) distances
vary slightly, ranging from 2.532(8) to 2.363(10) Å with
a maximum deviation of 0.169 Å, where the longest
distance corresponds to the substituted carbon atom.
The centroid of the cyclopentadienyl ring is displaced
0.144 Å with respect to a point located in the direction
perpendicular to the niobium center, one of the larger
shifts described for this type of compound. The most
interesting feature of this structure is the trans orienta-
tion of the silyl substituent with respect to the imido
t
analysis and NMR spectroscopy. When the amine NH2 -
Bu was added in a controlled manner, initially imido
substitution occurred at two of the Nb-Cl bonds to give
[Nb(η5-C5H4-SiMe2Cl)Cl2(NtBu)] (1). The Si-Cl bond of
1 reacts further with the amine to give complex 10,
followed by reaction of the amine with another Nb-Cl
bond to give 9 as the final product.
Transformation of the niobium chloro-amido complex
9 into the dichloro derivative [Nb{η5-C5H4-SiMe2(NHt-
Bu)}Cl2(NtBu)] (10) was easily achieved in quantitative
yield by reaction of 9 with 1 equiv of SiMe3Cl in toluene
at room temperature. Complex 10 was isolated as a dark

Nb Complexes with Functionalized Cp Ligands
Organometallics, Vol. 18, No. 4, 1999 549
showed the expected two singlets for the inequivalent
Me-Si groups and two doublets for the methylenic
benzyl protons, due to the asymmetry imposed by the
chiral metal center. The presence of the metal-bonded
tert-butylamido group was confirmed by its Cipso reso-
nance observed at δ 56.5.
Some of the compounds obtained by reactions with
t
the amine NH2 Bu could also be isolated using the
amide LiNHtBu. Thus, reaction of complex 2 with 2
equiv of LiNHtBu in hexane gave complex 7 in high
yield, although in diethyl ether a mixture of 7, 15, and
other unidentified products was obtained. Similarly,
reaction of 3 with 1 equiv of LiNHtBu gave lower yields
of the dibenzyl derivative 8 (see Scheme 1). However,
different reaction products were obtained in some cases;
thus, reaction of the tetrachloro complex 4 with a 5
equiv excess of LiNHtBu (see Scheme 2) resulted in
complete substitution of the chlorine moieties to give
the constrained-geometry complex [Nb{η5-C5H4-SiMe2(η1-
NtBu)}(NHtBu)(NtBu)] (11), which was easily, quanti-
tatively transformed into the chloro derivative [Nb{η5-
C5H4-SiMe2(η1-NtBu)}Cl(NtBu)] (14; see below) by
reaction with SiMe3Cl in hexane at room temperature.
Complex 14 was also obtained from the reaction of
complex 1 with 2 or 3 equiv of LiNHtBu, together with
very small amounts of 9 and 11, respectively, through
deprotonation of the intermediate amido derivative10 by
F igu r e 1. View of the molecular structure of complex 10.
Ta ble 1. Bon d Len gth s (Å) a n d An gles (d eg) for 10
Nb(1)-N(1)
Nb(1)-Cl(1)
Nb(1)-Cl(2)
Nb(1)-C(4)
Nb(1)-C(3)
Nb(1)-C(2)
Nb(1)-C(5)
Nb(1)-C(1)
Si(1)-N(2)
Si(1)-C(10)
Si(1)-C(11)
Si(1)-C(1)
N(1)-C(12)
1.748(8)
2.352(3)
2.358(3)
2.363(10)
2.398(10)
2.442(10)
2.459(10)
2.532(8)
1.719(9)
1.849(13)
1.848(12)
1.862(9)
1.478(14)
N(2)-C(6)
C(1)-C(5)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(6)-C(8)
C(6)-C(7)
C(6)-C(9)
C(12)-C(13)
C(12)-C(14)
C(12)-C(15)
Nb(1)-Cp(1)
1.455(14)
1.413(14)
1.438(13)
1.445(17)
1.417(17)
1.361(16)
1.47(2)
1.525(18)
1.533(19)
1.43(2)
LiNHtBu with elimination of NH2 Bu and LiCl. Both
t
11 and 14 are brown oils characterized by NMR
spectroscopy.
Stu d ies Rela ted to th e Tr a n sfor m a tion of Com -
p lex 6 in t o 5. We have discussed above that a slow
exchange between the Si-Cl and Nb-NHtBu takes
place at room temperature in the complex [Nb(η5-C5H4-
SiMe2Cl)(CH2Ph)(NHtBu)(NtBu)] (6), which is quanti-
tatively transformed in 24 h into [Nb{η5-C5H4-SiMe2(NHt-
Bu)}(CH2Ph)Cl(NtBu)] (5). This exchange between Si-
Cl and Nb-NHtBu bonds is comparable to the well-
known11 use of Me3Si-Cl to halogenate metal-amido
compounds. The transformation of 6 into 5 may be
proposed to occur through intra- or intermolecular
attack of the silicon-bonded chlorine on the unsaturated
niobium center, as represented in Scheme 3 A.
We carried out several studies to distinguish between
both intra- and intermolecular transformations. Initially
we observed that this transformation was more rapid
in THF than in toluene, C6D6, or hexane and when it
1.46(2)
1.49(2)
2.122
N(1)-Nb(1)-Cl(1) 101.5(3)
N(1)-Nb(1)-Cl(2) 102.7(3)
C(11)-Si(1)-C(1)
111.8(5)
C(12)-N(1)-Nb(1) 169.1(8)
Cl(1)-Nb(1)-Cl(2) 105.39(13) C(6)-N(2)-Si(1)
132.6(8)
129.2(7)
126.2(7)
N(2)-Si(1)-C(10)
N(2)-Si(1)-C(11)
114.8(6)
105.1(5)
C(10)-Si(1)-C(11) 109.1(7)
C(5)-C(1)-Si(1)
C(2)-C(1)-Si(1)
N(1)-Nb(1)-Cp(1) 119.62
Cl(2)-Nb(1)-Cp(1) 113.59
Cl(1)-Nb(1)-Cp(1) 112.40
N(2)-Si(1)-C(1)
C(10)-Si(1)-C(1)
110.3(4)
105.8(5)
ligand, which is located in a staggered disposition
instead of the usually eclipsed orientation found for most
compounds of this type. The very short Si1-N2 bond
distance of 1.719(9) Å and the Si1-N2-C6 angle of
132.6(8)° indicate an important contribution of N sp2
and double-bond character of the Si-N bond.
1
was monitored by H NMR spectroscopy formation of a
mixture of complexes [Nb{η5-C5H4-SiMe2(NHtBu)} (CH2-
Ph)(NHtBu)(NtBu)] (7) and [Nb(η5-C5H4-SiMe2Cl)(CH2-
Ph)Cl(NtBu)] (2) was observed. Formation of 7 contain-
ing two NHtBu groups provides evidence of the intermol-
ecular mechanism proposed in Scheme 3A. This mixture
was further transformed into [Nb{η5-C5H4-SiMe2(NHt-
Bu)}(CH2Ph)Cl(NtBu)] (5) in the same way. In a similar,
but slower, reaction in C6D6 7 was also observed,
although as a lower proportion of the reaction mixture.
Further evidence was obtained when a 1/1 molar ratio
of 6 and the dichloro derivative [Nb(η5-C5H4-SiMe2Cl)-
Cl2(NtBu)] (1) were stirred in C6D6 (see Scheme 3B). In
Rea ction s w ith LiNHtBu . We also reported9 that
preferential reaction of the M-Cl bonds takes place
when cyclopentadienylmetal halides containing both
Si-Cl and M-Cl bonds are reacted with polar alkali-
metal amides. As shown in Scheme 1, when [Nb(η5-
C5H4-SiMe2Cl)(CH2Ph)Cl(NtBu)] (2) was reacted with
1 equiv of LiNHtBu in hexane at room temperature for
a limited period of time, the amido niobium complex
[Nb(η5-C5H4-SiMe2Cl)(CH2Ph)(NHtBu)(NtBu)] (6) was
isolated as a brown oil which was characterized by NMR
spectroscopy (see Experimental Section). The reaction
time could not be extended for more than 1 h, because
complex 6 underwent a further reaction, discussed
above, and was finally transformed into the amino-silyl
derivative [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2Ph)Cl(Nt-
Bu)] (5). The 1H and 13C NMR spectra of complex 6
(10) Baldwin, T. C.; Huber, S. R.; Bruck, M. A.; Wigley, D. E. Inorg.
Chem. 1993, 32, 5682.
(11) (a) Herrmann, W. A.; Baratta, W.; Herdtweck, E. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 1951. (b) Duchateau, R.; Lancaster, S. J .;
Thornton-Pett, M.; Bochmann, M. Organometallics 1997, 16, 4995.

550 Organometallics, Vol. 18, No. 4, 1999
Alcalde et al.
Sch em e 3
Sch em e 4
this reaction only a small amount of 6 was transformed
into 5, leaving an appropriate molar ratio of unreacted
1; the major reaction products were 2 and 10. This result
is consistent with the same intermolecular attack by the
silicon-bonded chlorine of [Nb(η5-C5H4-SiMe2Cl)Cl2(Nt-
Bu)] on the niobium center of 6. In a final experiment,
a 1/1 molar ratio of complexes 7 and 2 were reacted in
C6D6 (Scheme 3C). This reaction was faster than the
transformation of 6 into 5, probably because formation
of 7 is unfavorable in this solvent, and rendered complex
5 in high yield.
The NMR characterization of all the complexes in-
volved in these studies was made on the basis of the
spectral behavior known for isolated samples of each
component.
Rea ction s of Ben zyl Com p lexes w ith CN(2,6-
Me2C6H3). Insertion of CN(2,6-Me2C6H3)8,12 into the
niobium-benzyl bonds of the 16-electron mono- and
dibenzyl complexes [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2-
Ph)X(NtBu)] (X ) Cl (5), CH2Ph (8)) readily took place
when 5 and 8 were stirred for several hours in hexane
at room temperature to give the iminoacyl derivatives
[Nb{η5-C5H 4-SiMe2(NH t Bu )}{η2-[C(CH 2P h ){N(2,6-
Me2C6H3)]}X(NtBu)] (X ) Cl (12), CH2Ph (13)) in high
yield (Scheme 4).
The iminoacyl derivatives 12 and 13 were isolated as
a brown oil and a pale yellow solid, respectively, and
were characterized by elemental analysis (13) and NMR
spectroscopy. Both complexes are asymmetric molecules
showing the expected inequivalency of all of their
substituents, consistent with the proposed formulation
(see Experimental Section for detailed assignments).
The presence of the iminoacyl group was confirmed by
the resonances observed in the 13C NMR spectra at δ
227.7 and 231.5 due to the iminoacyl carbon atom.
(12) (a) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059. (b)
Go´mez, M.; Go´mez-Sal, P.; J ime´nez, G.; Mart´ın, A.; Royo, P.; Sa´nchez-
Nieves, J . Organometallics 1996, 15, 3579.

Nb Complexes with Functionalized Cp Ligands
Organometallics, Vol. 18, No. 4, 1999 551
Complex 6 is a formally 18-electron species that does
not react with isocyanide; instead, it is slowly trans-
formed into 5 (see above), which then undergoes the
insertion leading to complex 12.
carbon and at δ 150.9 (J C-H ) 165 Hz) for the terminal
carbon, indicating the trans disposition of the two vinylic
hydrogens.
As shown in Scheme 4, complex 15 reacted with CN-
(2,6-Me2C6H3) at 50 °C in hexane to give the related
iminoacyl derivative [Nb{η5-C5H4-SiMe2(η1-NtBu)}{η2-
[C(CH2Ph){N(2,6-Me2C6H3)]}(NtBu)] (17), isolated after
removal of the solvent as a brown oil, which was
identified by NMR spectroscopy. The 1H NMR spectrum
of 17 showed two doublets due to the diastereotopic
benzyl methylenic protons shifted to low field (δ 3.42,
3.58) and all the remaining signals expected for an
asymmetric molecule with a chiral metal center (see
Experimental Section). The 13C NMR spectrum shows
the iminoacyl carbon resonance at δ 236.3. Thermal
treatment of 17 for 3 days at 160 °C causes its isomer-
ization to 16, as shown in Scheme 4.
Th er m a l Con ver sion of Am in o-Silyl Com p lexes
[Nb{η5-C5H4-SiMe2(NHtBu )}(CH2P h )X(NtBu )] in to
Con str ain ed Silyl-Am ido Der ivatives [Nb{η5-C5H4-
SiMe2-η1-Nt Bu )}X((Nt Bu )]. [Ti(η5-C5H4-SiMe2Cl)Cl3]
readily reacts with LiNHtBu at room temperature to
give the constrained-geometry complex [Ti{η5-C5H4-
SiMe2(η1-NtBu)Cl2].9 In a similar reaction using the
related zirconium complex, only very low yields were
obtained and the reaction has never been observed for
other transition-metal compounds.
We have described above the synthesis of constrained
amido-silyl complexes and were interested in studying
the accessibility of similar niobium complexes via the
thermal transformation of appropriate benzyl com-
plexes13 containing the (aminosilyl)cyclopentadienyl
ligand. As shown in Scheme 2, when hexane solutions
of [Nb{η5-C5H4-SiMe2(NHtBu)}(CH2Ph)X(NtBu)] (X ) Cl
(5), CH2Ph (8)) were heated for 3 days at 160 °C in
sealed tubes, elimination of toluene was observed and
the constrained η1-amidosilyl-η5-cyclopentadienyl com-
plexes [Nb{η5-C5H4-SiMe2(η1-NtBu)}X(NtBu)] (X ) Cl
(14), CH2Ph (15)) were isolated as brown oils in high
yields. Complex 15 can also be obtained in high yield
via benzylation of 14 with Mg(CH2Ph)2‚2THF. Not only
does similar thermal treatment of the iminoacyl complex
[Nb{η5-C5H4-SiMe2(NHtBu)}{η2-[C(CH2Ph){N(2,6-Me2-
C6H3)]}(CH2Ph)(NtBu)] (13) eliminate toluene but also
a further isomerization of the η2-iminoacyl group takes
place to finally give the vinylamido derivative [Nb{η5-
C5H4-SiMe2(η1-NtBu)}{N(CHdCHPh)(2,6-Me2C6H3)}(Nt-
Bu)] (16). This isomerization, which consists of a 1,2-
hydrogen shift,12a,14 was not perturbed by addition of
pyridine as expected for a formally 18-electron η2-
iminoacyl-imido-Cp-silyl-amido intermediate com-
pound isolated as 17 (see below), for which a â-hydrogen
abstraction process is highly unlikely. No coordination
of the eneamide moiety was observed. Although we have
not carried out mechanistic studies for this process, the
behavior observed could be better explained by invoking
the amidocarbene resonance structure of the η2-iminoa-
cyl group. Complexes 14 and 15 were characterized by
NMR spectroscopy (see Experimental Section). These
complexes showed two singlets for the inequivalent
methyl groups bonded to silicon and four multiplets for
the inequivalent ring protons (two overlapped for 14),
due to the presence of the chiral niobium center. The
diastereotopic benzyl methylenic protons of 15 were
observed as two doublets with J H-H ) 11.5 Hz. The
assignment of signals due to other groups and their 13C
NMR spectra were consistent with the proposed formu-
lation. The most relevant resonances observed for
complex 16 were the two doublets at δ 4.90 and 8.82
(J H-H ) 14 Hz) due to the olefinic protons of the vinyl
moiety, which appear in the 13C NMR spectrum as two
singlets at δ 101.6 (J C-H ) 152 Hz) for the N-bound
Con clu sion s
Formation of the imido derivative is the first step in
the reaction of [Nb(η5-C5H4-SiMe2Cl)Cl4] with LiNHt-
t
Bu or NH2 Bu, whereas selective reactions of imido
complexes [Nb(η5-C5H4-SiMe2Cl)XCl(NtBu)] (X ) Cl,
CH2Ph) take place at the Nb-Cl bond, leading to
amido-niobium compounds when LiNHtBu is used, and
at the Si-Cl bond, leading to amino-silyl derivatives
t
when NH2 Bu is employed. In the latter case, further
reactions take place in the presence of excess amine to
give amino-silyl-amido-niobium complexes. Intermo-
lecular rearrangements between Si-Cl and Nb-NHt-
Bu bonds are always observed, whatever the remaining
substituents bonded to the metal center are, and lead
to the thermodynamically more stable amino-silyl
chloro-niobium derivatives. Deprotonation of proto-
nated amido-niobium complexes with strongly basic
solutions of LiNHtBu in diethyl ether gives cyclopenta-
dienylsilylamido-niobium complexes. These barely ac-
cessible constrained-geometry niobium compounds [Nb-
{η5-C5H4-SiMe2(η1-NtBu)}X(NtBu)] can also be obtained
by heating the amino-silyl compounds at 160 °C.
Insertion of CN(2,6-Me2C6H3) into niobium-benzyl
bonds is easily achieved for both open and cyclic
compounds to give the corresponding iminoacyl deriva-
tives. The η2-iminoacyl substituent in the constrained
compounds is readily isomerized to the vinylamido
derivatives through a 1,2-hydrogen shift by thermal
treatment at 160 °C.
Exp er im en ta l Section
Gen er a l Com m en ts. All manipulations were performed
under an inert atmosphere of argon using standard Schlenk
techniques or a drybox. Solvents used were previously dried
and freshly distilled under argon: tetrahydrofuran from
sodium benzophenone ketyl, toluene from sodium, hexane from
sodium-potassium amalgam. Unless otherwise stated, re-
agents were obtained from commercial sources and used as
t
received. NH2 Bu (Aldrich) was distilled before use and stored
under argon. LiNHtBu was prepared in hexane in almost
quantitative yield from NH2 Bu and nBuLi (Aldrich, 1.6 M in
t
hexane). [Nb(η5-C5H4-SiMe2Cl)Cl2(NtBu)] (1), [Nb(η5-C5H4-
SiMe2Cl)(CH2Ph)Cl(NtBu)] (2), [Nb(η5-C5H4-SiMe2Cl)(CH2Ph)2-
(NtBu)] (3), and [Nb(η5-C5H4-SiMe2Cl)Cl4] (4) were prepared
by reported methods.8 IR spectra were recorded in Nujol mulls
between CsI pellets, over the range 4000-200 cm-1 on a
Perkin-Elmer 583 spectrophotometer. 1H and 13C NMR spectra
(13) (a) Mu, Y.; Piers, W. E.; MacQuarrie, D. C.; Zaworotko, M. J .;
Young, V. G. Organometallics 1996, 15, 2720. (b) Chen, Y.-X.; Fu, P.-
F.; Stern, C.-L.; Marks, T. J . Organometallics 1997, 16, 5958.
(14) (a) Beshouri, S. M.; Fanwick, P. E.; Rothwell, I. P.; Huffman,
J . C. Organometallics 1987, 6, 891. (b) Beshouri, S. M.; Chebi, D. E.;
Fanwick, P. E.; Rothwell, I. P.; Huffman, J . C. Organometallics 1990,
9, 2375.

552 Organometallics, Vol. 18, No. 4, 1999
Alcalde et al.
were recorded on a Varian Unity VXR-300. Chemical shifts,
in ppm, were measured relative to the residual 1H and 13C
resonances of benzene-d6 used as solvent, δ 7.15 (1H) and 128.0
(13C), and coupling constants are in Hz. C, H, and N analyses
were carried out with a Perkin-Elmer 240 C analyzer for all
the solid compounds. Compounds reported as oily products (5-
7, 11, 12, 14-17) could not be purified by sublimation due to
their limited thermal stability. Purification was carried out
by extraction into pentane, filtration, and removal of solvent
under vacuum, and the purity was confirmed by NMR spec-
troscopy. All attempts made to obtain acceptable analytical
data for these oily products failed due to their air sensitivity,
thermal transformation, and difficulties in the manipulation
and weighting of samples. Therefore, the analytical values
found for all these compounds which were ca. 1% (C) deviated
are not included in the Experimental Section.
C5H4), 5.95 (m, 1H, C5H4), 6.01 (m, 1H, C5H4), 6.80-7.25 (m,
Ph). 13C NMR (75 MHz, C6D6, δ): 2.7, 3.3 (SiMe2), 32.5 (CMe3),
33.8 (CMe3), 34.2 (CMe3), 40.5 (CH2Ph), 49.8 (CMe3), 56.1
(CMe3), 65.7 (CMe3), 107.1, 108.9, 112.4, 119.7 (C2-C5, C5H4)
(Cipso not observed), 121.3, 128.2, 129.9, 130.4, 131.7, 153.8
(Ph). IR (ν, cm-1): 3378, 3253.
P r ep a r a tion of [Nb(η5-C5H4SiMe2NHtBu )(CH2P h )2(Nt-
Bu )] (8). A solution of [Nb(η5-C5H4SiMe2Cl)(CH2Ph)2(NtBu)]
t
(3; 1.0 g, 1.99 mmol) in hexane (60 mL) was treated with NH2 -
Bu (0.29 g, 0.42 mL, 3.98 mmol) at -78 °C. The mixture was
then warmed to room temperature and stirred overnight. The
resulting suspension was filtered and the solution concentrated
(10 mL) and cooled to -40 °C to give a greenish solid which
was characterized as 8 (0.97 g, 1.79 mmol, 90% yield).
Data for 8 are as follows. Anal. Calcd for C29H43N2SiNb: C,
1
64.41; H, 8.03; N, 5.18. Found: C, 64.28; H, 8.01; N, 5.04. H
P r ep a r a tion of [Nb(η5-C5H4SiMe2NHtBu )(CH2P h )Cl-
(NtBu )] (5). The brown complex 5 was obtained by the
procedure (2, 0.30 g, 0.67 mmol; LiNHtBu; 0.053 g, 0.67 mmol;
reaction time 24 h) described below for 6.
NMR (300 MHz, C6D6, δ): 0.38 (s, 6H, SiMe2), 0.72 (br s, 1H,
NH), 1.11 (s, 9H, CMe3), 1.15 (s, 9H, CMe3), 1.70 (d, 2H, J HH
) 8 Hz, CH2Ph), 1.96 (d, 1H, J HH ) 8 Hz, CH2Ph), 5.52 (m,
2H, C5H4), 5.93 (m, 2H, C5H4), 6.90-7.06 (m, Ph). 13C NMR
(75 MHz, C6D6, δ): 3.0 (SiMe2), 31.9 (CMe3), 33.8 (CMe3), 41.5
(CH2Ph), 49.7 (CMe3), 66.4 (CMe3), 106.7, 113.7 (C2-C5, C5H4),
115.8 (Cipso C5H4), 124.9-140.1 (Ph). IR (ν, cm-1): 3390. MS:
m/z [assignment, relative intensity (%)] 449 [(M+- CH2Ph),
5 was also obtained when a hexane solution of [Nb(η5-C5H4-
SiMe2Cl)(CH2Ph)Cl(NtBu)] (2; 0.30 g, 0.67 mmol) was treated
t
with NH2 Bu (0.098 g, 0.14 mL, 1.34 mmol). This mixture was
stirred at room temperature for 12 h and was then filtered.
The volatiles were removed under reduced pressure to give a
brown oil which after purification by extraction into pentane,
filtration, and removal of solvent under vacuum was charac-
terized as 5 (0.26 g, 0.53 mmol, 80% yield).
t
15]; 393 [(M+- Bu), 5].
P r ep a r a tion of [Nb(η5-C5H4SiMe2NHtBu )Cl(NHtBu )-
(NtBu )] (9). A solution of [Nb(η5-C5H4SiMe2Cl)Cl4] (4; 1.50 g,
3.82 mmol) in toluene (100 mL) was treated with an excess of
Data for 5 are as follows. 1H NMR (300 MHz, C6D6, δ): 0.41
(s, 3H, SiMe2), 0.42 (s, 3H, SiMe2), 1.11 (s, 9H, CMe3), 1.15 (s,
9H, CMe3), 2.89 (d, 1H, J HH ) 8 Hz, CH2Ph), 3.25 (d, 1H, J HH
) 8 Hz, CH2Ph), 5.67 (m, 1H, C5H4), 5.88 (m, 1H, C5H4), 6.05
(m, 1H, C5H4), 6.19 (m, 1H, C5H4), 6.80-7.25 m, Ph). 13C NMR
(75 MHz, C6D6, δ): 2.9, 3.0 (SiMe2), 31.2 (CMe3), 33.9 (CMe3),
49.7 (CMe3), 51.5 (CH2Ph), 68.0 (CMe3), 106.0, 111,1, 111.2,
120.6 (C2-C5, C5H4) (Cipso not observed), 128.2, 128.4, 129.9,
131.7 (Ph). IR (υ, cm-1): 3339. MS: m/z [assignment, relative
NH2 Bu (4.19 g, 6.02 mL, 57.32 mmol), and the mixture was
t
stirred at room temperature for 48 h. After complete removal
of solvent, the residue was extracted into hexane (2 × 20 mL).
The resulting extract was concentrated (10 mL) and cooled to
-30 °C to give a pale yellow solid characterized as 9 (1.25 g,
2.67 mmol, 70% yield).
Data for 9 are as follows. Anal. Calcd for C19H39N3SiNb: C,
1
48.96; H, 8.45; N, 9.02. Found: C, 48.49; H, 8.20; N, 8.62. H
NMR (300 MHz, C6D6, δ): 0.42 (s, 3H, SiMe2), 0.43 (s, 3H,
SiMe2), 1.13 (s, 9H, CMe3), 1.22 (s, 9H, CMe3), 1.33 (s, 9H,
CMe3), 6.06 (m, 1H, C5H4), 6.15 (m, 1H, C5H4), 6.19 (m, 1H,
C5H4), 6.54 (m, 1H, C5H4), 8.08 (br s, 1H, NH). 13C NMR (75
MHz, C6D6, δ): 2.7, 3.4 (SiMe2), 31.9 (CMe3), 33.6 (CMe3), 33.8
(CMe3), 49.9 (CMe3), 57.2 (CMe3), 67.2 (CMe3), 105.9, 107.0,
116.6, 123.2 (C2-C5, C5H4), 118.9 (Cipso C5H4). IR (ν, cm-1):
3347, 3267.
P r epar ation of [Nb(η5-C5H4SiMe2NHtBu )Cl2(NtBu )] (10).
SiMe3Cl (0.30 g, 0.35 mL, 2.79 mmol) was added to a solution
of 9 (1.30 g, 2.79 mmol) in toluene (50 mL). The reaction
mixture was stirred for 2 h, and solvent was completely
removed under vacuum. The resulting oily product was dis-
solved in a minimum amount of hexane (5 mL) and cooled to
-30 °C to give a dark yellow crystalline product characterized
as 10 (1.08 g, 2.51 mmol, 90%).
Data for 10 are as follows. Anal. Calcd for C15H29N2SiNb:
C, 41.96; H, 6.82; N, 6.52. Found: C, 42.57; H, 6.98; N, 6.52.
1H NMR (300 MHz, C6D6, δ): 0.45 (s, 6H, SiMe2), 1.04 (s, 9H,
CMe3), 1.08(s, 9H, CMe3), 6.10 (m, 2H, C5H4), 6.49 (m, 2H,
C5H4). 13C NMR (75 MHz, C6D6, δ): 2.2 (SiMe2), 30.4 (CMe3),
33.7 (CMe3), 49.7 (CMe3), 70.0 (CMe3), 110.0, 123.1 (C2-C5,
C5H4) (Cipso not observed). IR (ν, cm-1): 3374.
t
intensity (%)] 429 [(M+- Bu), 0.7]; 413 [(M+- NHtBu), 2.7];
393 [(M+- CH2Ph), 5.9].
P r ep a r a tion of [Nb(η5-C5H4SiMe2Cl)(CH2P h )(NHtBu )-
(NtBu )] (6). A mixture of [Nb(η5-C5H4SiMe2Cl)(CH2Ph)Cl(Nt-
Bu)] (2; 0.30 g, 0.67 mmol) and LiNHtBu (0.053 g, 0.67 mmol)
in 50 mL of hexane was stirred at room temperature for 1 h
and then filtered. Solvent was removed from the resulting
brown solution under vacuum, giving a brown oil which was
purified by extraction into pentane, filtration, and removal of
solvent under vacuum to be characterized as 6 (0.27 g, 0.56
mmol, 85% yield).
Data for 6 are as follows. 1H NMR (300 MHz, C6D6, δ): 0.37
(s, 3H, SiMe2), 0.40 (s, 3H, SiMe2Cl), 1.22 (s, 9H, CMe3), 1.29
(s, 9H, CMe3), 2.64 (d, 1H, J HH ) 10 Hz, CH2Ph), 2.92 (d, 1H,
J HH ) 10 Hz, CH2Ph), 5.70 (m, 1H, C5H4), 5.78 (m, 1H, C5H4),
5.88 (m, 1H, C5H4), 6.03 (m, 1H, C5H4), 6.90-7.30 (m, Ph), 7.41
(br s, 1H, NH). 13C NMR (75 MHz, C6D6, δ): 3.2, 3.6 (SiMe2-
Cl), 32.5 (CMe3), 33.9 (CMe3), 41.0 (CH2Ph), 56.5 (CMe3), 66.0
(CMe3), 107.3, 109.5, 112.3, 119.4 (C2-C5, C5H4) (Cipso not
observed), 121.4, 128.2, 128.4, 129.9, 131.8, 153.3 (Ph). IR (ν,
cm-1): 3286.
P r ep a r a tion of [Nb(η5-C5H4SiMe2NHtBu )(CH2P h )(NHt-
Bu )(NtBu )] (7). A solution of [Nb(η5-C5H4SiMe2Cl)(CH2Ph)-
Cl(NtBu)] (2; 0.60 g, 1.34 mmol) in hexane (60 mL) was treated
P r ep a r a t ion of [Nb (η5-C5H 4SiMe2-η1-Nt Bu )(NH t Bu )-
(NtBu )] (11). A diethyl ether (30 mL) solution of LiNHtBu (0.5
g, 6.27 mmol) was slowly added to a suspension of [Nb(η5-C5H4-
SiMe2Cl)Cl4] (2; 0.49 g, 1.25 mmol) in diethyl ether (50 mL),
and the reaction mixture was stirred overnight. The solvent
was removed from the resulting suspension under vacuum,
and the residue was extracted into hexane (50 mL). Removal
of the solvent under vacuum gave an oily brown product which
was characterized as 11 (0.43 g, 1.00 mmol, 80%). Data for 11
are as follows. 1H NMR (300 MHz, C6D6, δ): 0.48 (s, 3H,
SiMe2), 0.52 (s, 3H, SiMe2), 1.24 (s, 9H, CMe3), 1.25 (s, 9H,
CMe3), 1.36 (s, 9H, CMe3), 5.63 (br s, 1H, NH), 5.93 (m, 1H,
t
with NH2 Bu (0.39 g, 0.56 mL, 5.36 mmol). The mixture was
stirred at room temperature for 18 h and was then filtered.
Solvent was completely removed from the resulting solution,
giving a dark brown oil which was purified by extraction into
pentane, filtration, and removal of solvent under vacuum to
be characterized as 7 (0.58 g, 1.11 mmol, 83% yield).
Data for 7 are as follows. 1H NMR (300 MHz, C6D6, δ): 0.31
(s, 6H, SiMe2), 0.62 (br s, 1H, NH), 1.07 (s, 9H, CMe3), 1.26 (s,
9H, CMe3), 1.33 (s, 9H, CMe3), 2.60 (d, 1H, J HH ) 10.6 Hz,
CH2Ph), 3.02 (d, 1H, J HH ) 10.6 Hz, CH2Ph), 5.71 (m, 2H,

Nb Complexes with Functionalized Cp Ligands
Organometallics, Vol. 18, No. 4, 1999 553
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 10
C5H4), 6.06 (m, 1H, C5H4), 6.22 (m, 1H, C5H4), 6.37 (m, 1H,
C5H4). 13C NMR (75 MHz, C6D6, δ): 2.7, 3.2 (SiMe2), 32.8
(CMe3), 34.1 (CMe3), 34.7 (CMe3), 53.8 (CMe3), 54.8 (CMe3),
65.1 (CMe3), 107.5, (Cipso C5H4), 108.0, 109.0, 115.6, 116.2 (C2-
C5, C5H4). IR (ν, cm-1): 3291.
empirical formula
fw
C15H29C12N2NbSi
429.30
temp
293(2) K
P r epar ation of [Nb(η5-C5H4SiMe2NHtBu ){η2-[C(CH2P h )-
{N(2,6-Me2C6H3)}]}Cl(NtBu )] (12). A mixture of [Nb(η5-C5H4-
SiMe2NHtBu)(CH2Ph)Cl(NtBu)] (5; 0.6 g, 1.24 mmol) and
CN(2,6-Me2C6H3) (0.16 g, 1.24 mmol) in hexane (50 mL) was
stirred for several hours. Solvent was completely removed in
vacuo to give an oily brown product in quantitative yield which
was purified by extraction into pentane, filtration, and removal
of solvent under vacuum to be characterized as 12.
Data for 12 are as follows. 1H NMR (300 MHz, C6D6, δ):
0.53 (s, 3H, SiMe2), 0.59 (s, 3H, SiMe2), 1.05 (s, 9H, CMe3),
1.20 (s, 9H, CMe3), 1.86 (s, 3H, Me2C6H3NdC), 2.16 (s, 3H,
Me2C6H3NdC), 3.58 (br s, 2H, PhCH2CdN), 5.47 (m, 1H,
C5H4), 6.05 (m, 2H, C5H4), 6.60 (m, 1H, C5H4), 6.80-7.25 (m,
Ph). 13C NMR (75 MHz, C6D6, δ): 3.3, 3.6 (SiMe2), 18.6
(Me2C6H3NdC), 18.9 (Me2C6H3NdC), 31.6 (CMe3), 33.9 (CMe3),
43.3 (PhCH2CdN), 49.7 (CMe3), 67.1 (CMe3), 103.9, 108.0,
113.4, 119.1 (C2-C5, C5H4) (Cipso not observed), 126.4-140.6,
(Ph), 227.7 (PhCH2CdN). IR (ν, cm-1): 3329, 1640.
wavelength
cryst syst
space group
unit cell dimens
a
b
c
0.710 73 Å
monoclinic
P212121
11.795(2) Å
12.828(3) Å
14.227(3) Å
V
Z
2152.6(8) Å3
4
density (calcd)
abs coeff
F(000)
cryst size
θ range for data collection
index ranges
1.325 g/cm3
0.860 mm-1
888
0.30 × 0.25 × 0.20 mm
2.14-25.04°
-13 < h < 0, -15 < k < 0,
-16 < l < 16
no. of rflns collected
no. of obsd rflns (I > 2σ(I))
abs cor
4134
3389
N/A
refinement method
full-matrix least squares on F2
P r epar ation of [Nb(η5-C5H4SiMe2NHtBu ){η2-[C(CH2P h )-
{NC (2,6-Me2C6H3)}](CH2P h )(NtBu )] (13). 13 was synthe-
sized from 8 (0.6 g, 1.11 mmol) and isocyanide (0.14 g, 1.11
mmol) in a manner analogous to that described for 12 and
isolated as a white solid after recrystallization from pentane
(0.67 g, 1.00 mmol, 90%).
Data for 13 are as follows. Anal. Calcd for C38H52N3SiNb:
C, 67.92; H, 7.82; N, 6.25. Found: C, 67.76; H, 7.78; N, 5.77.
1H NMR (300 MHz, C6D6, δ): 0.49 (s, 3H, SiMe2), 0.52 (s, 3H,
SiMe2), 0.98 (br s, 1H, NH), 1.14 (s, 9H, CMe3), 1.15 (s, 9H,
CMe3), 1.62 (s, 3H, Me2C6H3NdC), 1.69 (s, 3H, Me2C6H3Nd
no. of data/restraints/params 3773/0/190
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
1.113
R1 ) 0.0897, wR2 ) 0.2358
R1 ) 0.1029, wR2 ) 0.2449
calc w ) 1/[σ2(Fo2) + (0.2000P)2]a
1.052 and -1.141 e/Å3
weighting scheme
largest diff peak and hole
P ) (Fo + Fc2)/3.
a
2
1H, J HH ) 11.5 Hz, CH2Ph), 5.57 (m, 1H, C5H4), 5.76 (m, 1H,
C5H4), 5.88 (m, 1H, C5H4), 6.05 (m, 1H, C5H4), 6.82-7.25 (m,
Ph). 13C NMR (75 MHz, C6D6, δ): 1.0, 1.5 (SiMe2), 32.8 (CMe3),
34.7 (CMe3), 46.8 (NbCH2Ph), 56.8 (CMe3), 65.0 (CMe3), 104.1
(Cipso C5H4), 107.6, 107.9, 117.2, 121.6 (C2-C5, C5H4), 123.0,
127.4, 128.5, 153.0 (Ph).
P r ep a r a tion of [Nb(η5-C5H4SiMe2-η1-NtBu ){N(CHdCH-
P h ) (2,6-Me2C6H3)}(NtBu )] (16). 16 was synthesized from 13
(2.0 g, 2.98 mmol) in a manner analogous to that described
for the preparation of 14 (method B) and isolated as a brown
oil in quantitative yield.
C), 2.90 (d, 1H, J HH ) 9.1 Hz, NbCH2Ph), 3.19 (d, 1H, J HH
)
9.1 Hz, NbCH2Ph), 3.64 (m, 2H, PhCH2CdN), 5.37 (m, 1H,
C5H4), 5.71 (m, 1H, C5H4), 6.00 (m, 1H, C5H4), 6.09 (m, 1H,
C5H4), 6.80-7.20 (m, 13H, Ph). 13C NMR (75 MHz, C6D6, δ):
3.3, 3.6 (SiMe2), 18.3 (Me2C6H3NdC), 18.7 (Me2C6H3NdC), 32.8
(CMe3), 33.8 (CMe3), 37.1 (NbCH2Ph), 43.5 (PhCH2CdN), 49.8
(CMe3), 65.6 (CMe3), 106.7, 109.1, 110.7, 116.8 (C2-C5, C5H4)
(Cipso not observed), 126.4-140.6 (Ph), 231.5 (PhCH2CdN). IR
(ν, cm-1): 3344, 1620.
Data for 16 are as follows. 1H NMR (300 MHz, C6D6, δ):
0.35 (s, 3H, SiMe2), 0.42 (s, 3H, SiMe2), 1.31 (s, 9H, CMe3),
1.42 (s, 9H, CMe3), 2.28 (s, 3H, Me2C6H3NCHdCHPh), 2.30
(s, 3H, Me2C6H3NCHdCHPh), 4.90 (d, 1H), 8.82 (d, 1H, J HH
) 14 Hz, Me2C6H3NCHdCHPh), 5.43 (m, 1H, C5H4), 5.65 (m,
1H, C5H4), 5.79 (m, 1H, C5H4), 6.32 (m, 1H, C5H4), 6.80-7.30
(m, Ph). 13C NMR (75 MHz, C6D6, δ): 2.0, 2.2 (SiMe2), 18.7
(Me2C6H3NCHdCHPh), 19.5 (Me2C6H3NCHdCHPh), 32.9
P r ep a r a tion of [Nb(η5-C5H4SiMe2-η1-NtBu )Cl(NtBu )]
(14). Meth od A. SiMe3Cl (0.60 mL, 4.75 mmol) was added to
a solution of [Nb(η5-C5H4SiMe2-η1-NtBu)(NHtBu)(NtBu)] (11;
1.0 g, 2.33 mmol) in hexane (50 mL). The reaction mixture
was stirred for 24 h, and the solvent was removed under
vacuum to give 14 as an oily brown product in quantitative
yield.
Meth od B. A hexane (50 mL) solution of [Nb(η5-C5H4SiMe2-
NHtBu)(CH2Ph)Cl(NtBu)] (5; 0.70 g, 1.44 mmol), in a sealed
tube, was heated to 160 °C for 3 days. The volatiles were
removed under reduced pressure to give an oily brown product
which after purification by extraction into pentane, filtration,
and removal of solvent under vacuum was characterized as
14 (0.40 g, 1.01 mmol, 70% yield).
(CMe3), 34.2 (CMe3), 56.9 (CMe3), 66.3 (CMe3), 101.6 (d, J CH
152 Hz, Me2C6H3NCH)CHPh), 107.3 (Cipso C5H4), 108.2, 108.6,
)
119.4, 120.8 (C2-C5, C5H4), 123.0-151.3 (Ph), 150.9 (d, J CH
165 Hz, Me2C6H3NCHdCHPh).
)
P r epar ation of[Nb(η5-C5H4SiMe2-η1-NtBu ){η2-[C(CH2P h )-
{N(2,6-Me2C6H3)}](NtBu )] (17). A mixture of 15 (0.90 g, 2.01
mmol) and isocyanide (0.26 g, 2.01 mmol) in hexane (50 mL)
was heated to 50 °C and stirred for 4 h. The solvent was
evaporated in vacuo, and the resulting brown oil was purified
by extraction into pentane, filtration, and removal of solvent
under vacuum to be characterized as 17 in quantitative yield.
Data for 17 are as follows. 1H NMR (300 MHz, C6D6, δ):
0.50 (s, 3H, SiMe2), 0.67 (s, 3H, SiMe2), 1.16 (s, 9H, CMe3),
1.30 (s, 9H, CMe3), 1.93 (s, 3H, Me2C6H3NdC), 1.97 (s, 3H,
Me2C6H3NdC), 3.42 (d, 1H, J HH ) 16.1 Hz, PhCH2CdN), 3.58
(d, 1H, J HH ) 16.1 Hz, PhCH2CdN), 5.31 (m, 1H, C5H4), 5.98
(m, 1H, C5H4), 6.08 (m, 1H, C5H4), 6.39 (m, 1H, C5H4), 6.90-
7.20 (m, Ph). 13C NMR (75 MHz, C6D6, δ): 3.9, 4.3 (SiMe2),
18.0 (Me2C6H3NdC), 18.9 (Me2C6H3NdC), 32.7 (CMe3), 35.1
(CMe3), 43.9 (PhCH2CdN), 54.4 (CMe3), 65.5 (CMe3), 105.1,
Data for 14 are as follows. 1H NMR (300 MHz, C6D6, δ):
0.27 (s, 3H, SiMe2), 0.37 (s, 3H, SiMe2), 1.20 (s, 9H, CMe3),
1.37 (s, 9H, CMe3), 5.70 (m, 1H, C5H4), 6.35 (m, 1H, C5H4),
6.43 (m, 2H, C5H4). 13C NMR (75 MHz, C6D6, δ): 1.2, 1.5
(SiMe2), 32.1 (CMe3), 33.9 (CMe3), 57.8 (CMe3), 66.0 (CMe3),
107.7, 109.7, 120.1, 121.8 (C2-C5, C5H4) (Cipso not observed).
P r ep a r a t ion of [Nb (η5-C5H 4SiMe2-η1-Nt Bu )(CH 2P h )-
(NtBu )] (15). 15 was synthesized from 8 (0.80 g, 1.48 mmol)
in a manner analogous to that described for the preparation
of 14 (method B) and isolated as a brown oil (0.48 g, 1.08 mmol,
73% yield).
Data for 15 are as follows. 1H NMR (300 MHz, C6D6, δ):
0.29 (s, 3H, SiMe2), 0.31(s, 3H, SiMe2), 1.26 (s, 9H, CMe3), 1.38
(s, 9H, CMe3), 2.67 (d, 1H, J HH ) 11.5 Hz, CH2Ph), 2.98 (d,

554 Organometallics, Vol. 18, No. 4, 1999
Alcalde et al.
107.9 (C2-C5, C5H4), 109.7 (Cipso, C5H4), 113.3, 114.7 (C2-C5,
C5H4), 125.7-144.9 (Ph), 236.3 (PhCH2CdN). IR (ν, cm-1):
1632.
refined by least squares against F2 (SHELXL 97).16 All non-
hydrogen atoms were refined anisotropically, and the hydrogen
atoms were introduced from geometrical calculations and
refined using a riding model with fixed thermal parameters.
5
Cr ysta l Str u ctu r e Deter m in a tion of [Nb(η -C5H4SiMe2
NHtBu )Cl2 (NtBu )] (10). Yellow crystals of compound 10 were
obtained by crystallization from dry hexane at -30 °C, and a
suitable sized crystal was introduced, under argon, in a
Lindemann tube and mounted in an Enraf-Nonius CAD 4
automatic four-circle diffractometer with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å). Crystallographic and
experimental details are summarized in Table 2. Data were
collected at room temperature (25 °C). Intensities were cor-
rected for Lorentz and polarization effects in the usual manner.
No absorption or extinction corrections were made. The
structure was solved by direct methods (SHELXL 90)15 and
Ack n ow led gm en t. We acknowledge the DGICYT
(project PB97-0776) for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables giving posi-
tional and thermal parameters and bond distances and angles
1
for 10 and figures giving H NMR spectra for complexes 5-7,
11, 12, and 14-17 (35 pages). Ordering information is given
on any current masthead page.
OM9806491
(16) Sheldrick, G. M. SHELXL 97; University of Go¨ttingen: Go¨t-
tingen, Germany, 1997.
(15) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.