Studies on the reactivity of Nb(η5-C5H4SiMe3) 2(X)(L), X = H,Cl; L = CNXylyl, CNCy, CO and Nb(η5-C5H4SiMe3) 2(H)3 complexes toward the Lewis acids B(C6F5)3 and BF3

Article abstract of DOI:10.1016/S0022-328X(00)00107-8

The reaction of the electron-rich, coordinatively saturated, niobocene-hydride or -halide complexes Nb(η⁵-C₅H₄SiMe₃) ₂(X)(L), X = H or Cl, L = 2,6-dimethylphenylisocyanide (CNXylyl), cyclohexylisocyanide (CNCy) and carbonyl (CO), with the strong Lewis acid (B(C₆F₅)₃) gives the zwitterionic compounds [(η⁵-C₅H₄SiMe₃) ₂(CNXylyl)Nb(μ-X)(B(C₆F₅)₃)] (1), [(η⁵-C₅H₄SiMe₃) ₂(CNCy)Nb(μ-X)(B(C₆F₅)₃)] (2), [(η⁵-C₅H₄SiMe₃) ₂(CO)Nb(μ-X) (B(C₆F₅)₃)] (3), respectively, where the complexes possess a bridging hydride or halide group. Similarly, the starting niobocene-hydride species react with BF₃ to afford the corresponding zwitterionic complexes containing a bridging hydride ligand, namely [(η⁵-C₅H₄SiMe₃) ₂(CNXylyl)Nb(μ-H)(BF₃)] (4), [(η⁵-C₅H₄SiMe₃) ₂(CNCy)Nb(μ-H)(BF₃)] (5), [(η⁵-C₅H₄SiMe₃) ₂(CO)Nb(μ-H)(BF₃)] (6). The reaction of the hydride containing compounds 1-3 with the appropriate ligand L (1:1 molar ratio for 1 and 2) in toluene at room temperature leads to the ionic compounds [(η⁵-C₅H₄SiMe₃) ₂Nb(CNXylyl)₂][(HB(C₆F₅) ₃)] (7), [(η⁵-C₅H₄SiMe₃) ₂Nb(CNCy)₂][(HB(C₆F₅)₃)] (8), and [(η⁵-C₅H₄SiMe₃) ₂Nb(CO)₂][(HB(C₆F₅)₃)] (9), which contain two coordinated L ligands and a noncoordinated [(HB(C₆F₅)₃)]^- counteranion. Analogous complexes were not observed in the same reaction for 4-6. Finally, the compound [Nb(η⁵-C₅H₄SiMe₃) ₂(H)₃] reacts in acetone with (B(C₆F₅)₃) in a clean reaction to give the ionic compound [(η⁵-C₅H₄SiMe₃) ₂Nb][((CH₃)₂CHO)B(C₆F ₅)₃)] (10), which contains the isopropoxide borate ion [((CH₃)₂CHO)B(C₆F₅) ₃)]^- as the counteranion.

Full text of DOI:10.1016/S0022-328X(00)00107-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 609 (2000) 123–129
Studies on the reactivity of Nb(h5-C5H4SiMe3)2(X)(L), X=H,Cl;
L=CNXylyl, CNCy, CO and Nb(h5-C5H4SiMe3)2(H)3 complexes
toward the Lewis acids B(C6F5)3 and BF3
Antonio Antin˜olo, Fernando Carrillo-Hermosilla, Juan Ferna´ndez-Baeza,
Santiago Garc´ıa-Yuste, Antonio Otero *, Javier Sa´nchez-Prada, Elena Villasen˜or
Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica, Facultad de Qu´ımicas, Uni6ersidad de Castilla-La Mancha, Campus Uni6ersitario,
13071 Ciudad Real, Spain
Received 9 December 1999; received in revised form 31 January 2000
Abstract
The reaction of the electron-rich, coordinatively saturated, niobocene–hydride or –halide complexes Nb(h5-
C5H4SiMe3)2(X)(L), X=H or Cl, L=2,6-dimethylphenylisocyanide (CNXylyl), cyclohexylisocyanide (CNCy) and carbonyl (CO),
with the strong Lewis acid (B(C6F5)3) gives the zwitterionic compounds [(h5-C5H4SiMe3)2(CNXylyl)Nb(m-X)(B(C6F5)3)] (1),
[(h5-C5H4SiMe3)2(CNCy)Nb(m-X)(B(C6F5)3)] (2), [(h5-C5H4SiMe3)2(CO)Nb(m-X) (B(C6F5)3)] (3), respectively, where the com-
plexes possess a bridging hydride or halide group. Similarly, the starting niobocene-hydride species react with BF3 to afford the
corresponding zwitterionic complexes containing a bridging hydride ligand, namely [(h5-C5H4SiMe3)2(CNXylyl)Nb(m-H)(BF3)]
(4), [(h5-C5H4SiMe3)2(CNCy)Nb(m-H)(BF3)] (5), [(h5-C5H4SiMe3)2(CO)Nb(m-H)(BF3)] (6). The reaction of the hydride containing
compounds 1–3 with the appropriate ligand L (1:1 molar ratio for 1 and 2) in toluene at room temperature leads to the ionic
compounds [(h5-C5H4SiMe3)2Nb(CNXylyl)2][(HB(C6F5)3)] (7), [(h5-C5H4SiMe3)2Nb(CNCy)2][(HB(C6F5)3)] (8), and [(h5-
C5H4SiMe3)2Nb(CO)2][(HB(C6F5)3)] (9), which contain two coordinated L ligands and a noncoordinated [(HB(C6F5)3)]− coun-
teranion. Analogous complexes were not observed in the same reaction for 4–6. Finally, the compound [Nb(h5-C5H4SiMe3)2(H)3]
reacts in acetone with (B(C6F5)3) in a clean reaction to give the ionic compound [(h5-C5H4SiMe3)2Nb][((CH3)2CHO)B(C6F5)3)]
(10), which contains the isopropoxide borate ion [((CH3)2CHO)B(C6F5)3)]− as the counteranion. © 2000 Elsevier Science S.A. All
rights reserved.
Keywords: Metallocenes; Niobocene; Boranes; Halides; Hydrides
known of their electrophilic cationic metallocene com-
plexes [3]. Furthermore, hydride complexes of transi-
1. Introduction
tion metals represent one of the most important classes
The chemistry of electrophilic cationic complexes
such as [Cp2MR]+ (M=Ti, Zr, Hf) and other related
compounds has received much attention in recent years.
This is due to the fact that the title complexes have
been implicated in a number of important processes,
such as alkene polymerization [1] and insertion reac-
tions of unsaturated molecules [2]. In contrast, these
aspects of Group 4 metallocenes have no parallels in
the analogous Group 5 metal species because little is
of compounds because of their chemical reactivity and
importance in catalysis [4]. In this field, the study of the
reactivity of several families of transition metal hy-
drides toward Lewis acid reagents, such as ZnR2, AlR3
and BR3, has been thoroughly considered [5]. Particu-
larly, the behavior of metallocene–hydride complexes
of group 5 metals with different classes of Lewis acid
metals fragments was studied in the last 25 years, giving
rise to the isolation of several di- and polynuclear
complexes [6]. Recently, as part of our strategy to study
the reactivity of hydride-niobocene complexes, namely
Nb(h5-C5H4SiMe3)2(H)(L), L=CO, P(OR)3, we have
* Corresponding author. Tel.: +34-926-295326; fax: +34-926-
295318.
E-mail address: aotero@qino-cr.uclm.es (A. Otero).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00107-8

124
A. Antin˜olo et al. / Journal of Organometallic Chemistry 609 (2000) 123–129
studied their behavior with different Lewis acidic
coinage cations, and different families of polynuclear
systems associating transition-metal polyhydrides and a
coinage cation, such as [(Nb(h5-C5H4SiMe3)2-
(P(OR)3)(m-H)(AuPPh3))PF6] (R=Me, Et, Ph) [7],
These compounds show similar solubilities to the
previously described complexes 1–3. Attempts to pre-
pare suitable crystals of 1–6 for X-ray crystal structure
determinations were unsuccessful.
We have also studied the behavior of the zwitterionic
species 1–6 toward the addition of p-acid ligands. In
fact, the reaction of 1a–3a and 3b with L (in a 1:1
molar ratio for isocyanides and an excess for CO) in
toluene at room temperature (r.t.) for 48 h resulted in
the slow precipitation of the ion pairs, [(h5-
C5H4SiMe3)2Nb(L)2][XB(C6F5)3] (7–9) (Eq. (3)), which
were isolated as red–orange solids.
[(Nb(h5-C5H4SiMe3)2(CO)(m-H)(AuPPh3))PF6]
[8],
[(Nb(h5-C5H4SiMe3)2(CO)(m-H))2M)PF6] (M=Cu, Ag,
Au) [8], [(Nb(h5-C5H4RR%)2(H)3)2M)A] (R=R%=H,
R=H, R%=SiMe3, R=R%=SiMe3; M=Cu, Ag, Au,
A=PF−6 , BF−4 ) [9], were isolated. In order to follow
exploring this chemistry, we have decided to study the
reactivity of hydride– and halide–niobocene com-
plexes, Nb(h5-C5H4SiMe3)2(X)(L) (X=H, Cl; L=CO,
isocyanide) and [Nb(h5-C5H4SiMe3)2(H)3], toward the
Lewis acid B(C6F5)3 and BF3 and this paper will focus
on the synthesis and structural details of new zwitteri-
onic complexes containing a bridging hydride or halide
[(h5-C5H4SiMe3)2(L)Nb(m-X)(BY3)] and new cationic d2
complexes, [(h5-C5H4SiMe3)2Nb(L)2][XB(C6F5)3)] and
[(h5-C5H4SiMe3)2Nb][(CH3)2CHO)B(C6F5)3)].
[(h5-C5H4SiMe3)2(L)Nb(m-X)B(C6F5)3]+L
“[(h5-C5H4SiMe3)2Nb(L)2][XB(C6F5)3]
(3)
7a: X=H, L=CNXylyl; 8a: X=H, L=CNCy; 9a:
X=H, L=CO; 9b: X=Cl, L=CO.
Complexes 7–9 are considerably more stable than
1–3 in donor solvents such as acetone or THF, but
even in these cases it was not possible to isolate suitable
crystals for X-ray crystal structure determinations. The
same process for 1b, 2b and 4–6 gave rise to decompo-
sition products. It is probable that in these reactions it
is not possible to stabilize the expected ion pairs [(h5-
C5H4SiMe3)2Nb(L)2][HBF3] for 4–6, because the corre-
sponding counter-anion [HBF3]− is unstable [10].
Finally, we considered here the reaction of 1a–3a and
3b with p-acid ligands, L%, different to that present in
the appropriate starting complex, giving rise to the
formation of the corresponding ion pair [(h5-
C5H4SiMe3)2Nb(L)(L%)][XB(C6F5)3], although these
compounds were not isolated as pure samples due to
the fact that they tend to disproportionate easily to give
the symmetrical species [(h5-C5H4SiMe3)2Nb(L)2]-
[XB(C6F5)3] and [(h5-C5H4SiMe3)2Nb(L%)2][XB(C6F5)3].
The reactivity of [Nb(h5-C5H4SiMe3)2(H)3] towards
B(C6F5)3 has also been considered. The trihydride spe-
cies reacts with B(C6F5)3 in acetone at −78°C, in a 1:1
molar ratio, to give the ion pair [(h5-C5H4SiMe3)2Nb]-
[((CH3)2CHO)B(C6F5)3] 10 (Eq. (4)), which was isolated
as a yellowish–white solid after the appropriate work
up.
2. Results and discussion
The reaction of one equivalent of the niobocene
complexes Nb(h5-C5H4SiMe3)2(X)(L), (L=2,6-dime-
thylphenylisocyanide (CNXylyl), cyclohexylisocyanide
(CNCy) and carbonyl (CO)), with one equivalent of
(B(C6F5)3) in toluene at low temperature (−78°C) re-
sulted in the formation of a deep red or green solution
from which air-sensitive solids, corresponding to the
zwitterionic compounds [(h5-C5H4SiMe3)2(L)Nb(m-
X)(B(C6F5)3)] (1–3), which were isolated after the ap-
propriate work up (Eq. (1)).
Nb(h5-C5H4SiMe3)2(X)(L)+B(C6F5)3
“[(h5-C5H4SiMe3)2(L)Nb(m-X)B(C6F5)3]
(1)
1a: X=H, L=CNXylyl; 1b: X=Cl, L=CNXylyl; 2a:
X=H, L=CNCy; 2b: X=Cl, L=CNCy; 3a: X=H,
L=CO; 3b:X=Cl, L=CO.
The complexes are partially soluble in toluene and
alkenes and soluble in donor solvents, such as acetone
or THF, in which they decompose slowly. Similarly, the
reaction of the same starting hydride–niobocene com-
plexes with one equivalent of BF3·Et2O in toluene at
low temperature (−78°C) gave the appropriate zwitte-
rionic complexes [(h5-C5H4SiMe3)2(L)Nb(m-H)(BF3)]
(4a–6a) (Eq. (2)), which were isolated as air-sensitive
solids after the appropriate work up.
CH COCH
3
[Nb(h5-C5H4SiMe3)2(H)3]+B(C6F5)3 ꢀꢀꢀꢀꢀꢀꢁ3
−H
2
[(h5-C5H4SiMe3)2Nb][(CH3)2CHO)B(C6F5)3]
(4)
The same process in a non-coordinative solvent, such
as toluene, afforded a mixture of intractable products
that were not characterized. Complex 10 is soluble in
acetone and THF, partially soluble in toluene, and
insoluble in alkanes. It was stable for several days in
solution or in the solid state under an inert atmosphere
and was crystallized from acetone. However, unfortu-
nately the crystals obtained in this way were not suit-
able for study by means of X-ray crystal diffractometric
methods.
Nb(h5-C5H4SiMe3)2(H)(L)+BF3·Et2O
“[(h5-C5H4SiMe3)2(L)Nb(m-H)BF3)+Et2O
(2)
4a: X=H, L=CNXylyl; 5a: X=H, L=CNCy; 6a:
X=H, L=CO.

A. Antin˜olo et al. / Journal of Organometallic Chemistry 609 (2000) 123–129
125
accordance with the data reported, we propose the
structural disposition depicted in Fig. 1 for the differ-
ent classes of zwitterionic compounds. The formation
of the hydride-containing complexes can be considered
as the result of an electrophilic attack of the Lewis
acid B(C6F5)3 or BF3 on the Nb–H bond, to give a
well known three-center two-electron Nb–H–B bond
[6b].
The new families of niobocene complexes were char-
acterized by spectroscopic methods. The IR spectra of
complexes 1–9 exhibit the characteristic band of the
ancillary ligand L, wCO for CO at ca. 1900 cm−1 or
wCN for RNC at ca. 2100 cm−1, which are typical of a
terminal ligand and indicate that no interactions be-
tween this ligand and the Lewis acid B(C6F5)3 take
place. The absence of the band corresponding to
w(Nb–H) in the spectra of complexes 1a–6a and the
presence of a band at ca. 2260 cm−1 are noteworthy,
and these can be ascribed to w(Nb–H–B); in the spec-
tra of complexes 7a–9a the w(B–H) of the
[HB(C6F5)3]− appears as a band at ca. 2400 cm−1
[11]. The NMR spectra of 1–9 also provide informa-
A comparable situation, where the bridging chloride
ligand would act as a Lewis base toward the Lewis
acid B(C6F5)3 could be considered for complexes 1b–
3b. Spectroscopic data will also be considered for
1
complex 10. The H-NMR and 11B-NMR spectra, re-
spectively, exhibit the characteristic resonances for an
isopropoxide group and a single signal. In addition,
the 19F-NMR spectrum displays the three characteris-
tic resonances of the C6F5 group, indicating that the
three groups are equivalent even when the spectrum
was recorded at −90°C. The formation of 10 can be
envisaged on the basis of the steps outlined in Scheme
1.
1
tive data. Firstly, the H-NMR spectra of 1a–6a do
not exhibit the expected resonance for the bridging
hydride, and this is probably due to both its coupling
with the 11B atom and the high quadrupolar moments
of the 93Nb and 11B nuclei. However, their 11B-NMR
1
spectra show a doublet at ca. −20 ppm, J(B–H)=85
Hz, by virtue of coupling between the boron atom and
the proposed bridging hydride atom. This value is
intermediate between that corresponding to a genuine
bridging B–H (1J(B–H):60 Hz) and a terminal B–H
The first step would correspond to the formation of
a typical adduct between both B(C6F5)3 and acetone
[14]. After this, an interaction between this adduct,
through the electron deficient carbon atom, and an
Nb–H bond would take place to give an ion pair,
which would evolve with the elimination of H2 to give
rise to the final product 10. One question to be consid-
ered is the exact nature of the interaction between the
proposed anion [((CH3)2CHO)B(C6F5)3]− with the
proposed highly electron deficient niobocene species
[(h5-C5H4SiMe3)2Nb]+. Two possibilities have been de-
picted in Scheme 1. The first implies an interaction
through two fluorine atoms of one C6F5 group, a
possibility that has previously been described in some
cationic zirconocene complexes [15]. In the second
possibility, such an interaction would take place alter-
natively through the oxygen atom of the isopropoxide
group. In light of the 19F-NMR spectrum recorded at
low temperature (−90°C), where the three C6F5
groups are equivalent (see above), we are tempted to
propose the second interaction as the more probable,
although the first type of interaction cannot be defini-
tively ruled out.
1
(1J(B–H):100 Hz) bond [12]. Although the H-NMR
spectra of the ion pairs 7a–9a and 9b do not exhibit
the expected resonance of the [HB(C6F5)3]− anion,
again probably due to the effects discussed above,
their 11B-NMR spectra display the corresponding reso-
nance as a broad doublet at ca. −20 ppm (1J(B–H)
=
95 Hz) [11c]. Three characteristic resonances for the
C6F5 groups of the B(C6F5)3 moieties [13] in com-
plexes 1–3 and 7–9 and only one resonance for the
BF3 group in complexes 4a–6a were observed in the
19F-NMR spectra, indicating that in complexes con-
taining a bridging hydride or halide Nb–X–B (X=H,
Cl) a free rotation around the X–B bond occurs (see
below) making the C6F5 and F groups equivalent. In
In conclusion, a study into the reaction of electron-
rich, coordinatively saturated niobocene complexes
with two strong Lewis acids, namely B(C6F5)3 and
BF3, has been undertaken, and new families of zwitte-
rionic complexes resulting from the interaction of
these acids with the Nb–X bonds and ion pairs have
been isolated and characterized. Finally, an interesting
reaction between a trihydride niobocene and B(C6F5)3
has also been considered, giving rise to an ion pair in
which the presence of a highly electron poor [(h5-
C5H4SiMe3)2Nb]+ moiety is proposed.
Fig. 1. Proposed structure for niobocene complexes containing a
bridging hydride or halide.

126
A. Antin˜olo et al. / Journal of Organometallic Chemistry 609 (2000) 123–129
Scheme 1. Proposed reaction pathway for the formation of complex 10.
3. Experimental
3.2. Preparation of complexes 1–3
The strong Lewis acid B(C6F5)3 (0.30 g, 0.59 mmol)
was added to a solution of [Nb(h5-C5H4SiMe3)2(H)-
(CNXylyl)] (0.29 g, 0.59 mmol) in toluene (ca. 50 ml) at
−78°C. The resulting mixture was stirred for 10 min
and then allowed to warm up to r.t. After that time a
deep red solution had formed and this was stirred for 2
h. The solvent was removed under vacuum to give a
deep red oily solid, which was washed with ca. 10 ml of
hexane to yield the deep red solid [(h5-C5H4SiMe3)2-
(CNXylyl)Nb(m-H)B(C6F5)3] (1a) (0.43 g, 72%). Com-
plexes 2a–3a were prepared in a similar manner to 1a.
Yields of 70 and 69% were obtained for 2a and 3a,
respectively.
3.1. General
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.
The following compounds: Nb(h5-C5H4SiMe3)2(H)-
(CNXylyl),
Nb(h5-C5H4SiMe3)2(H)(CNCy),
Nb-
(h5-C5H4SiMe3)2(H)(CO),
Nb(h5-C5H4SiMe3)2(Cl)-
(CNXylyl), Nb(h5-C5H4SiMe3)2(Cl)(CNCy), Nb(h5-
C5H4SiMe3)2(Cl)(CO), [Nb(h5-C5H4SiMe3)2(H)3] and
B(C6F5)3 were prepared as described earlier [13,16–20].
CNXylyl, CNCy, CO and BF3·OEt2 were used as re-
ceived (Aldrich). IR spectra were recorded on a
The method of preparation for the complexes 1b–3b
was similar to 1a and gave green solids. Yields of
around 70% were found in all cases.
Perkin–Elmer PE 883 IR spectrophotometer. H-, 13C-,
1
11B- and 19F-NMR spectra were recorded using a
Varian FT-300 spectrometer at 300, 75, 96 and 282
MHz, respectively. 1H and 13C chemical shifts were
determined by reference to the residual deuterated sol-
vent signal and those of 11B and 19F with respect to
l=0 for BF3·OEt2 and CFCl3, respectively. Micro-
analyses were carried out using a Perkin–Elmer 2400
CHN analyzer.
3.2.1. Complex 1a
IR (nujol) wCN 2058 cm−1, w(Nb–H–B) 2280 cm−1
,
1657, 1525, 1467, 1096, 980 cm−1 B(C6F5)3, 1260 cm−1
1
SiMe3. H-NMR (acetone-d6, in ppm): l=0.12 (s, 18
H, SiMe3), 5.58 (2 H), 5.78 (2 H), 5.83 (2 H), 6.32 (2 H)
(m, C5H4), 2.48 (s, 6 H, MeCNR), 7.21 (m, 3 H,
C6H3CNR). 13C{1H}-NMR (acetone-d6, in ppm): l=
−0.1 (SiMe3), 99.8, 102.1 (C1), 103.7, 104.5, 112.1

A. Antin˜olo et al. / Journal of Organometallic Chemistry 609 (2000) 123–129
127
(C5H4), 18.5 (MeCNR), 228.6 (CNR), 139.0, 142.0,
147.0, 150.0 B(C6F5)3. 19F-NMR (acetone-d6, in ppm):
l= −129.8 (br.s. 6 F, o-F), −161.70 (t, 3 F, 3JFF=18
Hz, p-F), −164.0 (br. s. 6 F, m-F) B(C6F5)3 11B{1H}-
NMR (acetone-d6, in ppm): l= −19.8 B(C6F5)3. Anal.
Calc. for C43H36BF15NNbSi2: C, 50.98; H, 3.55; N,
1.48. Found: C, 50.71; H, 3.25; N, 1.28%.
tone-d6, in ppm): l=0.12 (s, 18 H, SiMe3), 5.34
(2 H), 5.54 (2 H), 5.64 (2 H), 6.12 (2 H) (m, C5H4),
4.50 (m, CNCy), 1.30–1.85 (m, CNCy). 13C{1H}-
NMR (acetone-d6, in ppm): l=0.0 (SiMe3), 95.2
(C1), 99.5, 103.5, 103.9, 110.5 (C5H4), 57.2 (CNC6H11),
134.6, 139.5, 146.4, 150.9 B(C6F5)3. 19F-NMR (acetone-
d6, in ppm):l= −131.4 (br.s. 6 F, o-F), −157.5 (t, 3
F, 3JFF=19 Hz, p-F), −162.8 (br. s. 6 F, m-F)
B(C6F5)3. 11B{1H}-NMR (acetone-d6, in ppm): l=1.2
B(C6F5)3. Anal. Calc. for C41H37BClF15NNbSi2: C,
49.36; H, 3.35; N, 1.34. Found: C, 48.52; H, 3.23; N,
1.32%.
3.2.2. Complex 2a
IR (nujol) wCN 2280 cm−1, w(Nb–H–B) 2290 cm−1
,
1657, 1525, 1467, 1096, 980 cm−1 B(C6F5)3, 1253 cm−1
1
SiMe3. H-NMR (acetone-d6, in ppm): l=0.11 (s, 18
H, SiMe3), 5.32 (2 H), 5.55 (2 H), 5.67 (2 H), 6.12 (2 H)
(m, C5H4), 1.5 (m, CNCy). 13C{1H}-NMR (acetone-d6,
in ppm): l=1.0 (SiMe3), 99.9, 96.8 (C1), 103.9, 104.3,
110.8 (C5H4), 68.4 (CNC6H11), 225.7 (CNC6H11), 135.0,
140.0, 147.0, 152.0 B(C6F5)3. 19F-NMR (acetone-d6, in
ppm): l= −129.7 (br. s. 6 F, o-F), −161.8 (t, 3 F,
3JFF=18 Hz, p-F), −164.5 (br. s. 6 F, m-F) B(C6F5)3.
11B{1H}-NMR (acetone-d6, in ppm): l= −20.3
B(C6F5)3. Anal. Calc. for C41H38BF15NNbSi2: C, 49.75;
H, 3.88; N, 1.41. Found: C, 48.52; H, 3.23; N, 1.32%.
3.2.6. Complex 3b
IR (nujol) wCO 1946 cm−1, 1645, 1517, 1471, 1090,
977 cm−1 B(C6F5)3, 1285 cm−1 SiMe3. H-NMR (ace-
1
tone-d6, in ppm): l=0.21 (s, 18 H, SiMe3), 5.71 (2 H),
5.92 (2 H), 5.95 (2 H), 6.28 (2 H) (m, C5H4). 13C{1H}-
NMR (acetone-d6, in ppm): l=0.1 (SiMe3), 97.9 (C1),
99.1, 104.6, 106.9, 110.2 (C5H4), 250.0 (CO), 135.0,
139.9, 146.3, 151.1 B(C6F5)3. 19F-NMR (acetone-d6, in
ppm): l= −131.4 (br. s. 6 F, o-F), −157.4 (t, 3 F,
3JFF=18 Hz, p-F), −162.8 (br. s. 6 F, m-F) B(C6F5)3.
11B{1H}-NMR (acetone-d6, in ppm): l=1.3 B(C6F5)3.
Anal. Calc. for C35H26BClF15NbOSi2: C, 44.57; H,
2.76. Found: C, 45.31; H, 2.88%.
3.2.3. Complex 3a
IR (nujol) wCO 1920 cm−1, w(Nb–H–B) 2285 cm−1
,
1657, 1525, 1467, 1096, 980 cm−1 B(C6F5)3, 1249 cm−1
1
SiMe3. H-NMR (acetone-d6, in ppm): l=0.23 (s, 18
H, SiMe3), 5.20 (2 H), 5.59 (2 H), 5.62 (2 H), 6.00 (2 H)
(m, C5H4). 13C{1H}-NMR (acetone-d6, in ppm): l=
0.53 (SiMe3), 98.56, 100.91 (C1), 102.54, 105.98, 110.75
(C5H4), 252.00 (CO), 136.00, 141.00, 147.00, 150.00
B(C6F5)3. 19F-NMR (acetone-d6, in ppm): l= −129.90
(br.s. 6 F, o-F), −161.70 (t, 3 F, 3JFF=18.30 Hz, p-F),
−164.53 (br. s. 6 F, m-F) B(C6F5)3. 11B{1H}-NMR
(acetone-d6, in ppm): l= −20.20 B(C6F5)3. Anal. Calc.
for C35H27BF15NbOSi2: C, 46.25; H, 2.97. Found: C,
45.81; H, 2.35%.
3.3. Preparation of complexes 4a–6a
To a solution of [Nb(h5-C5H4SiMe3)2(H)(CNXylyl)]
(0.28 g, 0.57 mmol) in toluene (ca. 40 ml) was added
BF3·Et2O (90 ml, 0.57 mmol) by a microsyringe at
−78°C. The resulting mixture was stirred for 10 min
and then allowed to warm up to r.t. After that time a
deep red solution had formed and this was stirred for 2
h. The solvent was removed in vacuo to give a deep red
oily solid, which was washed with ca. 10 ml of cool
hexane to yield the deep red solid 4a (0.25 g, 78%).
Complexes 5a and 6a were prepared in a similar man-
ner to 4a. Yields of 72 and 75% were found for 5a and
6a, respectively.
3.2.4. Complex 1b
IR (nujol) wCN 2204 cm−1, 1644, 1515, 1466, 1093,
1
975 cm−1 B(C6F5)3, 1252 cm−1 SiMe3. H-NMR (ace-
tone-d6, in ppm): l=0.12 (s, 18 H, SiMe3), 5.59 (2 H),
5.78 (2 H), 5.87 (2 H), 6.34 (2 H) (m, C5H4), 2.48 (s, 6
H, MeCNR), 7.15 (m, 3 H, C6H3CNR). 13C{1H}-NMR
(acetone-d6, in ppm): l= −0.1 (SiMe3), 99.0, 99.8 (C1),
103.7, 104.5, 112.1 (C5H4), 19.2 (MeCNR), 134.9,
137.4, 139.7, 142.2 B(C6F5)3. 19F-NMR (acetone-d6, in
ppm): l= −131.5 (br. s. 6 F, o-F), −158.5 (t, 3 F,
3JFF=18 Hz, p-F), −163.2 (br. s. 6 F, m-F) B(C6F5)3.
11B{1H}-NMR (acetone-d6, in ppm): l=1.0 B(C6F5)3.
Anal. Calc. for C43H35BClF15NNbSi2: C, 49.36; H,
3.35; N, 1.34. Found: C, 50.01; H, 3.25; N, 1.28%.
3.3.1. Complex 4a
IR (nujol) wCN 2084 cm−1, wB–F(BF3) 1050 cm−1
,
1
1262 cm−1 SiMe3. H-NMR (acetone-d6, in ppm): l=
0.12 (s, 18 H, SiMe3), 5.57 (2 H), 5.77 (2 H), 5.86 (2 H),
6.32 (2 H) (m, C5H4), 2.49 (MeCNR), 7.20 (m, 3 H,
C6H3CNR). 13C{1H}-NMR (acetone-d6, in ppm): l=
0.4 (SiMe3), 100.2, 102.2 (C1), 104.1, 105.0, 112.5
(C5H4), 19.6 (MeCNR), 235.0 (CNR). 19F-NMR (ace-
tone-d6, in ppm): l= −147.1 BF3. 11B{1H}-NMR
(acetone-d6, in ppm): l=4.9 BF3. Anal. Calc. for
C25H35BF3NNbSi2: C, 51.61; H, 3.51; N, 1.36. Found:
C, 50.89; H, 3.98; N, 1.42%.
3.2.5. Complex 2b
IR (nujol) wCN 2171 cm−1, 1646, 1518, 1471, 1088,
1
980 cm−1 B(C6F5)3, 1254 cm−1 SiMe3. H-NMR (ace-

128
A. Antin˜olo et al. / Journal of Organometallic Chemistry 609 (2000) 123–129
3.3.2. Complex 5a
3.4.2. Complex 8a
IR (nujol) wCN 2270 cm−1, wB–F(BF3) 1048 cm−1
,
IR (nujol) wCN 2100 cm−1, wB–H 2389 cm−1, 1640,
1258 cm−1 SiMe3. H-NMR (acetone-d6, in ppm): l=
0.11 (s, 18 H, SiMe3), 5.30 (2 H), 5.53 (2 H), 5.66 (2 H),
6.12 (2 H) (m, C5H4), 1.6 (m, CNCy). 13C{1H}-NMR
(acetone-d6, in ppm): l=0.6 (SiMe3), 100.3, 101.4 (C1),
103.6, 105.6, 110.9 (C5H4), 70.0 (CNCy), 238.0
(CNCy). 19F-NMR (acetone-d6, in ppm): l= −147.5
BF3. 11B{1H}-NMR (acetone-d6, in ppm): l=4.5 BF3.
Anal. Calc. for C23H38BF3NNbSi2: C, 50.64; H, 6.97;
N, 2.57. Found: C, 50.21; H, 7.22; N, 2.89%.
1511, 1463, 1089, 976 cm−1 B(C6F5)3, 1254 cm−1
1
1
SiMe3. H-NMR (acetone-d6, in ppm): l=0.23 (s, 18
H, SiMe3), 5.62 (4 H), 5.89 (4 H) (pst, C5H4), 1.60 (m,
CNCy). 13C{1H}-NMR (acetone-d6, in ppm): l=0.8
(SiMe3), 98.2, 97.2 (C1), 102.3 (C5H4), 69.0 (CNCy),
230.0 (CNCy), 135.0, 139.0, 147.0, 151.0 B(C6F5)3.
19F-NMR (acetone-d6, in ppm): l= −129.6 (br.s. 6 F,
3
o-F), −162.0 (t, 3 F, JFF=18 Hz, p-F), −164.6 (br.
s. 6 F, m-F) B(C6F5)3. 11B{1H}-NMR (acetone-d6, in
ppm): l= −20.4 B(C6F5)3. Anal. Calc. for
C48H11BF15N2NbSi2: C, 52.45; H, 4.46; N, 2.55. Found:
C, 52.10; H, 4.59; N, 2.89%.
3.3.3. Complex 6a
IR (nujol) wCO 1920 cm−1, wB–F(BF3) 1052 cm−1
,
1250 cm−1 SiMe3. H-NMR (acetone-d6, in ppm): l=
0.25 (s, 18 H, SiMe3), 5.21 (2 H), 5.52 (2 H), 5.61 (2 H),
5.96 (2 H) (m, C5H4). 13C{1H}-NMR (acetone-d6, in
ppm): l= −0.18 (SiMe3), 90.5, 93.5 (C1), 96.8, 100.8,
101.5 (C5H4), 252.8 (CO). 19F-NMR (acetone-d6, in
ppm): l= −147.7 BF3. 11B{1H}-NMR (acetone-d6, in
ppm): l=2.2 BF3. Anal. Calc. for C27H27BF3NbOSi2:
C, 43.97; H, 2.87. Found: C, 42.51; H, 5.51%.
1
3.4.3. Complex 9a
IR (nujol) wCO 1935 cm−1, wB–H 2410 cm−1, 1641,
1510, 1493, 1096, 978 cm−1 B(C6F5)3, 1247 cm−1
1
SiMe3. H-NMR (acetone-d6, in ppm): l=0.22 (s, 18
H, SiMe3), 5.21 (2 H), 5.52 (2 H), 5.71 (4 H), 5.98 (4 H)
(spt, C5H4). 13C{1H}-NMR (acetone-d6, in ppm): l=
0.5 (SiMe3), 98.5, 99.0 (C1), 102.0 (C5H4), 248.0 (CO),
135.0, 139.0, 141.0, 151.0 B(C6F5)3. 19F-NMR (acetone-
d6, in ppm): l= −129.7 (br. s. 6 F, o-F), −162.0 (t, 3
F, 3JFF=18 Hz, p-F), −164.5 (br. s. 6 F, m-F)
B(C6F5)3. 11B{1H}-NMR (acetone-d6, in ppm): l=
−20.4 B(C6F5)3. Anal. Calc. for C36H27BF15NbO2Si2:
C, 46.15; H, 2.88. Found: C, 46.32; H, 2.61%.
3.4. Preparation of complexes 7–9
To a solution of [(h5-C5H4SiMe3)2(CNXylyl)Nb(m-
H)(B(C6F5)3)] (1a) (0.60 g, 0.59 mmol) in toluene (ca.
50 ml) at r.t., was added CNXylyl (0.08 g, 0.59 mmol).
The resulting mixture was stirred for 2 days. The color
of the solution changed from deep red to orange–red
and the precipitation of an orange–red solid was ob-
served. This solid was filtered off and washed with ca.
10 ml of hexane to yield the complex [Nb(h5-
C5H4SiMe3)2(CNXylyl)2][HB(C6F5)3] (7a) (0.46 g, 68%).
Complexes 8a, 9a and 9b were prepared in a similar
manner to 7a. For complexes, 9a and 9b the corre-
sponding solutions of 3a and 3b were saturated with
CO. Yields into the range of 65–70% were found for
8a, 9a and 9b.
3.4.4. Complex 9b
IR (nujol) wCO 2057 cm−1, 1645, 1519, 1471, 1082,
980 cm−1 B(C6F5)3, 1258 cm−1 SiMe3. H-NMR (ace-
1
tone-d6, in ppm): l=0.32 (s, 18 H, SiMe3), 6.16 (4 H),
6.23 (4 H), (pst, C5H4). 13C{1H}-NMR (acetone-d6, in
ppm): l=0.5 (SiMe3), 98.5, 99.0 (C1), 102.0 (C5H4),
248.0 (CO), 135.7, 140.1, 146.6, 151.3 B(C6F5)3. 19F-
NMR (acetone-d6, in ppm): l= −129.7 (br. s. 6 F,
3
o-F), −162.0 (t, 3 F, JFF=19 Hz, p-F), −164.5 (br.
s. 6 F, m-F) B(C6F5)3. 11B{1H}-NMR (acetone-d6, in
ppm): l=1.0 B(C6F5)3. Anal. Calc. for C36H26BClF15-
NbO2Si2: C, 44.52; H, 2.68. Found: C, 45.02; H, 2.88%.
3.4.1. Complex 7a
IR (nujol) wCN 2124 cm−1, wB–H 2381 cm−1, 1640,
1511, 1463, 1089, 976 cm−1 B(C6F5)3, 1251 cm−1
1
SiMe3. H-NMR (acetone-d6, in ppm): l=0.25 (s, 18
3.5. Preparation of complex 10
H, SiMe3), 5.74 (4 H), 5.99 (4 H) (pst, C5H4), 2.46 ((s,
6H, MeCNR), 7.24 (m, 3 H, C6H3CNR). 13C{1H}-
NMR (acetone-d6, in ppm): l=0.0 (SiMe3), 97.2, 98.1
(C1), 102.2 (C5H4), 19.1 (MeCNR), 226.1 (CNR),
135.0, 139.0, 147.0, 151.0 B(C6F5)3. 19F-NMR (acetone-
d6, in ppm): l= −131.4 (br.s. 6 F, o-F), −157.4 (t, 3
F, 3JFF=18 Hz, p-F), −162.8 (br. s. 6 F, m-F)
B(C6F5)3. 11B{1H}-NMR (acetone-d6, in ppm): l=
−20.4 B(C6F5)3. Anal. Calc. for C52H45BF15N2NbSi2:
C, 54.64; H, 3.97; N, 2.45. Found: C, 55.21; H, 3.71; N,
2.89%.
To a solution of [Nb(h5-C5H4SiMe3)2(H)3] (0.30 g,
0.81 mmol) in acetone (ca. 50 ml) at −78°C, was
added (0.41 g, 0.81 mmol) of B(C6F5)3. The resulting
mixture was stirred for 15 min during which time it was
allowed to warm up to r.t. The solution was stirred at
r.t. for a further 2 h. The final color of the solution was
yellow. The solvent was removed in vacuo to give a
yellowish–white solid, which was washed with ca. 10 ml
of pentane to yield the complex [(h5-C5H4SiMe3)2Nb]-
[(CH3)2CHO)B(C6F5)3] (10) (0.61 g, 80%).

A. Antin˜olo et al. / Journal of Organometallic Chemistry 609 (2000) 123–129
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3.5.1. Complex 10
IR (nujol) 1640, 1511, 1463, 1045, 976 cm−1
B(C6F5)3, 1250 cm−1 SiMe3. H-NMR (acetone-d6, in
ppm): l=0.31 (s, 18 H, SiMe3), 5.46 (2 H), 5.60 (2 H),
1
3
6.66 (2 H), 6.76 (2 H) (m, C5H4), 1.15 [d, 6 H, JHH=6
Hz, (CH3)2CH], 3.90 [m, 1H, (CH3)2CH]. 13C{1H}-
NMR (acetone-d6, in ppm): l= −0.2 (SiMe3), 109.9,
110.7, 117.6, 118.4, 122.4 (C1) (C5H4), 248.0 (CO), 25.0
[(CH3)2CH], 88.0 [(CH3)2CH], 135.0, 139.0, 141.0,
151.0 B(C6F5)3. 19F-NMR (acetone-d6, in ppm): l=
3
−128.9 (br. s. 6 F, o-F), −157.5 (t, 3 F, JFF=18 Hz,
p-F), −162.2 (br. s. 6 F, m-F) B(C6F5)3. 11B{1H}-
NMR (acetone-d6, in ppm): l= −5.2 B(C6F5)3. Anal.
Calc. for C37H35BF15NbOSi2: C, 44.30; H, 3.90. Found:
C, 44.50; H, 3.71%.
Acknowledgements
The authors gratefully acknowledge financial support
from the Direccio´n General de Ensen˜anza Superior e
Investigacio´n Cient´ıfica (grant no. PB-95-0023-C01) of
Spain.
[9] A. Antin˜olo, F. Carrillo-Hermosilla, B. Chaudret, M. Fajardo, J.
Ferna´ndez-Baeza, M. Lanfranchi, H.H. Limbach, M. Maurer,
A. Otero, M.A. Pellinghelli, Inorg. Chem. 35 (1996) 7873.
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