New reactivity of Cp′2NbH3, Cp′ = η5-C5H4SiMe3. Synthesis, electrosynthesis and reactivity of new carboxylato niobocene complexes

Article abstract of DOI:10.1016/j.jorganchem.2005.04.003

A new family of niobium bidentate carboxylato-containing niobocene complexes, mononuclear Cp2′Nb(κ2-O,O′OOC(C6H5))(3), binuclear [(Cp2′Nb)2(1,4-(κ2-O,O′OOC)2(C6H4))](4)and[(Cp2′Nb)2(1, 3-(κ2-O,O′OOC)2(C6H4))](5) and trinuclear [(Cp2′Nb)3(1,3,5- (κ2-O,O′OOC)3(C6H3))](6), have been prepared by the reaction of Cp2′NbH3(1) and the corresponding carboxylic acid, namely (C ₆H₅)COOH, (1,4-COOH)₂(C₆H ₄), (1,3-COOH)₂(C₆H₄) and (1,3,5-COOH)₃(C₆H₃). Complexes 3, 4, 5 and 6 have been prepared by an alternative route involving a two-electron reduction of Cp2′NbCl2(2) in the presence of the appropriate molar ratios of the corresponding carboxylic acids. Furthermore, the reaction of complexes 3, 4 and 6 with 2,6-Me₂C₆H₃NC (xylylNC) in the molar ratios 1:1, 1:2 and 1:3, respectively, resulted in opening of the bidentate carboxylato ligand to give the monodentate carboxylato-containing complexes [Cp2′Nb(κ1-OOOC(C6H5))(xylylNC)](7),[(Cp2′Nb(xylylNC))2(1, 4-(κ1-OOOC)2(C6H4))](8)and[(Cp2′Nb(xylylNC))3(1,3,5-(κ1-OOOC) 3(C6H3))](9). Similarly, complex [(Cp2′Nb(η1-C,κ1-SCS2))3(1,3,5- (κ1-OOOC)3(C6H3))](10) was prepared by reaction of 6 with the appropriate amount of CS₂. Complexes 7, 8 and 9 can be prepared in an alternative way by reaction of [Cp2′Nb(H)(xylylNC)] with the corresponding carboxylic acids. The structures of all complexes have been established by spectroscopic techniques. In addition, the X-ray molecular structure of 4 was determined by a single-crystal X-ray diffraction study.

Full text of DOI:10.1016/j.jorganchem.2005.04.003

Journal of Organometallic Chemistry 690 (2005) 3134–3141
www.elsevier.com/locate/jorganchem
New reactivity of Cp20 NbH3; Cp0 ¼ g5-C5H4SiMe3. Synthesis,
electrosynthesis and reactivity of new carboxylato
niobocene complexes
,a
a
Antonio Antin˜olo , Santiago Garcıa-Yuste , Isabel Lopez-Solera ,
a
*
´
Antonio Otero , Juan Carlos Perez-Flores , Isabel del Hierro ,
´
a,
a
b
*
´
´ `
Laurent Salvi , Helene Cattey , Yves Mugnier
c
c
c
a
´ ´ ´ ´ ´
Departamento de Quımica Inorganica, Organica y Bioquımica y Bioquımica, Facultad de Quimica, Universidad de Castilla-La Mancha,
13071 Ciudad Real, Spain
´ ´ ´
Departamento de Tecnologıa Quımica, Ambiental y de los Materiales, ESCET, Universidad Rey Juan Carlos, 28933 Mostoles (Madrid), Spain
b
c
` ` ´ ´ ´
Laboratoire de Synthese et Electrosynthese Organometalliques, LSEO UMR 5188 Faculte des Sciences Mirande, 9 Allee Alain Savary,
21000 Dijon, France
Received 25 January 2005; revised 5 April 2005; accepted 6 April 2005
Available online 23 May 2005
Abstract
A
new family of niobium bidentate carboxylato-containing niobocene complexes, monon0uclear Cp02Nbðj2-O;
O0AOOCðC6H5ÞÞ ð3Þ, binuclear ½ðCp20 NbÞ ð1; 4-ðj2-O; O0AOOCÞ ðC6H4ÞÞꢀ ð4Þ and ½ðCp02NbÞ ð1; 3-ðj2-O; O AOOCÞ ðC6H4ÞÞꢀ ð5Þ
and trinuclear ½ðCp02NbÞ ð1; 3; 5-ðj2-O; O0A2OOCÞ ðC6H3ÞÞꢀ ð6Þ, have been prepared by the reaction of Cp20 NbH3 ð1Þ and the corre-
2
2
2
3
3
sponding carboxylic acid, namely (C6H5)COOH, (1,4-COOH)2(C6H4), (1,3-COOH)2(C6H4) and (1,3,5-COOH)3(C6H3). Complexes
3, 4, 5 and 6 have been prepared by an alternative route involving a two-electron reduction of Cp0 NbCl2 ð2Þ in the presence of the
2
appropriate molar ratios of the corresponding carboxylic acids. Furthermore, the reaction of complexes 3, 4 and 6 with 2,6-
Me2C6H3NC (xylylNC) in the molar ratios 1:1, 1:2 and 1:3, respectively, resulted in opening of the bidentate carboxylato ligand
to give the monodentate carboxylato-containing complexes ½Cp02Nbðj1-OAOOCðC6H5ÞÞðxylylNCÞꢀ ð7Þ; ½ðCp20 NbðxylylNCÞÞ
2
ð1; 4-ðj1-OAOOCÞ ðC6H4ÞÞꢀ ð8Þ and ½ðCp20 NbðxylylNCÞÞ ð1; 3; 5-ðj1-OAOOCÞ ðC6H3ÞÞꢀ ð9Þ. Similarly, complex ½ðCp02Nbðg1-C;
2
3
3
j1-SACS2ÞÞ ð1; 3; 5-ðj1-OAOOCÞ ðC6H3ÞÞꢀ ð10Þ was prepared by reaction of 6 with the appropriate amount of CS2. Complexes
3
3
7, 8 and 9 can be prepared in an alternative way by reaction of ½Cp02NbðHÞðxylylNCÞꢀ with the corresponding carboxylic acids.
The structures of all complexes have been established by spectroscopic techniques. In addition, the X-ray molecular structure of
4 was determined by a single-crystal X-ray diffraction study.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Niobocene; Carboxylato; Synthesis; Electrosynthesis
1. Introduction
great depth. This complex constitutes an interesting
example of a trihydride complex that exhibits the phe-
nomenon of exchange coupling [1], with unusual
1J(H,H) couplings that vary with temperature [2]. In
the last 15 years we have focused our attention on the
study of the reactivity of 1, e.g., with p-acid ligands to
give different families of complexes Cp02NbHðLÞ;
L ¼ p-acid ligand [3], in E–H (E = Si, Ge, H)
In previous studies we have investigated the chemical
behaviour of the trihydride complex Cp0 NbH3 ð1Þ in
2
*
Corresponding author. Fax: +34 92 629 5318.
E-mail addresses: antonio.antinolo@uclm.es (A. Antin˜olo),
antonio.otero@uclm.es (A. Otero).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.04.003

A. Antin˜olo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141
3135
∆
activation processes [4] and with Lewis acids, such as
3 Cp'2NbH3 + (1,3,5-(HOOC)3(C6H3))
[M(PPh3)][PF6], M = Cu, Ag, Au to give a broad class
of heterobimetallic species [5]. A few years ago, we pre-
pared a formato niobocene complex Cp02Nbðj2-O;
O0AOOCHÞ by carbon dioxide insertion into the nio-
bium-hydrogen bond of Cp02NbH3. The formato com-
plex could also be obtained from the two-electron
reduction of Cp02NbCl2 in the presence of formic acid
[6].0 In addition, an acetato-containing complex, namely
Cp2Nbðj2-O; O0AOOCMeÞ, was also chemically and
electrochemically prepared [6]. Other authors have pre-
pared O-bound carboxylato complexes by the insertion
of carbon dioxide into M–C bonds [7]. More recently,
electrochemical and spectroscopic studies on dicarboxy-
lato-containing niobocene complexes were carried out
[8]. As a continuation of our interest in the chemistry
of Cp02NbH3, we report here its behaviour towards
mono-, bi- and trinuclear aromatic carboxylic
acids. These reactions led to the isolation of new
carboxylato niobocene0 complexes, 0 namely Cp02Nb
ðj2O; O0AOOCRÞ; ½ðCp2NbÞ ðj2-O; O AOOCÞ Rꢀ; and
- 6 H2
O
2
ð3Þ
C
O
O
C
Cp'2Nb
C
O
O
O
'
p
C
b
N
2
6
The different complexes were isolated as green air-sen-
sitive solids. The evolution of H2 was detected in all of the
experiments. Complexes 4, 5 and 6 were isolated as the
only carboxylato-containing species even when niobo-
cene:carboxylic acid molar ratios lower than 2:1 or 3:1
were employed, indicating that the formation of either
the corresponding binuclear or trinuclear species is ther-
modynamically favoured. The formation of those com-
plexes could take place through the elimination of H2
and the formation of a very reactive sixteen-electron
monohydride niobocene species, which has previously
been proposed in several cases [9]. All the complexes de-
scribed in this work were spectroscopically characterized.
The most prominent features in the IR spectra are the
COꢁ2 stretching frequencies of the carboxylato group
and our attention was focused upon these. The usual ap-
proach in this respect has been to relate the D values (the
separation between masymðCOꢁÞ and msymðCOꢁÞ) with the
2
2
½ðCp02NbÞ ðj2-O; O0AOOCÞ Rꢀ, which can also be
3
3
formed from the reduction of Cp02NbCl2 in the presence
of the appropriate carboxylic acid. Several aspects con-
cerning the reactivity of these systems are also discussed.
2
2
mono- or bidentate character of the ligands [10]. The IR
spectra of complexes 3, 4, 5 and 6 showed the masym
ðCOꢁÞ and msymðCOꢁÞ absorptions to have D values of
2. Results and discussion
2
2
We are currently interested in studying the reactiv-
ity of Cp0NbH3 towards different classes of carboxylic
acids. With this aim in mind, four types of carboxylic
acid, namely benzoic, (C6H5)COOH, terephthalic,
(1,4-COOH)2(C6H4), isophthalic, (1,3-COOH)2(C6H4)
and 1,3,5-phenyltricarboxylic, (1,3,5-COOH)3(C6H3),
were selected. The standard reaction procedure in-
volved heating at ca. 60 ꢁC a stirred THF solution
of 1 with the appropriate carboxylic acid. This meth-
od allowed the isolation of the carboxylato-containing
complexes after an appropriate work-up procedure
(Eqs. (1)–(3)).
95, 117, 121 and 74 cmꢁ1, respectively, which are consis-
tent with the presence of a bidentate carboxylato li-
gand[10]. Moreover, the 1H and 13C NMR data confirm
the bidentate coordination. In fact, the observation of
two and three signals for each cyclopentadienyl ring in
the H and 13C NMR spectra, respectively, (see Section
1
4) indicate the presence of a symmetrical environment.
In addition, the 13C NMR spectra contain signals for
the carboxylato carbon atoms at d 190.1, 205.5, 188.9
and 187.6 for complexes 3, 4, 5 and 6, respectively. In or-
der to confirm the proposed structural disposition for
these complexes, the X-ray crystal molecular structure
of 4 was determined. The molecular structure and atom-
ic numbering scheme are shown in Fig. 1. Selected bond
lengths and angles for 4 are given in Table 1.
The structure of 4 consists of a symmetric binuclear
niobium complex. The metal atoms are bound to two
cyclopentadienyl rings in a g5 mode and to two oxygen
atoms from the chelating carboxylato group. The six-
membered aromatic ring and the two carboxylato
groups are coplanar, although the niobium atom is out
of the plane defined by O1, O2, C1, C2, C3 and C4
∆
Cp'2NbH3
+
HOOC(C6H5)
- 2 H2
O
ð1Þ
ð2Þ
Cp'2Nb
C
O
3
∆
2 Cp'2NbH3 + (1,X-(HOOC)2(C6H4))
- 4 H2
˚
(by 0.156(6) A). The two oxygen atoms of the bidentate
carboxylato ligand have similar Nb–O bond distances
˚
(2.220(4) and 2.230(4) A for O1 and O2, respectively)
and these values are in reasonable agreement with those
O
O
NbCp'2
Cp'2Nb
C
C
O
O
X=4,4 X=3,5

3136
A. Antin˜olo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141
Fig. 1. Molecular structure and atom-labelling scheme for complex 4, with thermal ellipsoids at 30% probability.
Table 1
The same complexes can be prepared in an alternative
˚
way by reaction of the complex ½Cp02NbðHÞðxylylNCÞꢀ
[3] with the appropriate molar ratios of the correspond-
ing carboxylic acids. Finally, complex ½Cp02Nb
ððg1-C; j1-SACS2ÞÞ ð1; 3; 5-ðj1-OAOOCÞ ðC6H3ÞÞꢀ ð10Þ
Selected bond lengths (A) and angles (ꢁ) for 4
Nb1–O1
Nb1–O2
O1–C1
O2–C1
C1–C2
2.220(4)
2.230(4)
1.262(7)
1.261(7)
1.501(8)
3
3
was also prepared by the reaction of 6 with CS2. The dif-
ferent monodentate carboxylato-niobocene complexes
were isolated as either air-sensitive green (for 7, 8 and
9) or non-air-sensitive brown (for 10) solids. The differ-
ent complexes were spectroscopically characterized. The
O1–Nb1–O2
C1–O1–Nb1
C1–O2–Nb1
O1–C1–O2
O1–C1–C2
O2–C1–C2
58.9(2)
90.5(4)
90.1(4)
120.3(5)
120.0(6)
119.7(6)
IR spectra of complexes 7–10 show the masymðCOꢁÞ
2
and msymðCOꢁÞ absorptions to have D values of 262,
2
245, 242 and 230 cmꢁ1, respectively, which are consis-
tent with the presence of a bidentate carboxylato ligand
[10]. In accordance with the lack of symmetry in the pro-
posed structures (see Fig. 2), the 1H and 13C NMR spec-
tra of these complexes show four and five resonances for
each cyclopentadienyl ring. The carbon resonances for
the carboxylato ligands appear at d 175.6, 174.2, 174.4
and 182.2, respectively, for 7–10. In addition, in these
spectra the carbon resonances for the ancillary ligands,
namely 2,6-Me2C6H3NC and CS2, appear at d 208.2,
209.9, 212.5 and 250.2, respectively.
reported for the carboxylato ligands [11]. The cyclopen-
tadienyl groups are in a typical eclipsed fashion with re-
spect to each other and the SiMe3 groups are in a trans
disposition.
Reactions of complexes 3, 4 and 6 with 2,6-
Me2C6H3NC (xylylNC), in the appropriate molar ratios
led to a change from a bidentate to a monodentate carb-
oxylato unit due to coordination of the incoming ligand.
These reactions led to the isolation of new complexes
after the appropriate work-up procedure (Eqs. (4)–(6)).
Cp02Nbðj2-O; O0AOOCðC6H5ÞÞ þ xylylNC
! ½Cp02Nbðj1-OAOOCðC6H5ÞÞðxylylNCÞꢀ
ð4Þ
ð7Þ
SiMe3
O
SiMe3
½ðCp02NbÞ ð1; 4-ðj2-O; O0AOOCÞ ðC6H4ÞÞꢀ þ 2xylylNC
O
O
2
2
C
C
! ½ðCp02NbðxylylNCÞÞ ð1; 4-ðj1-OAOOCÞ ðC6H4ÞÞꢀ
O
S
2
2
Nb
Nb
ð8Þ
CNXylyl
C
S
ð5Þ
(a)
(b)
SiMe3
SiMe3
½ðCp02NbÞ ð1; 3; 5-ðj2-O; O0AOOCÞ ðC6H3ÞÞꢀ þ 3xylylNC
3
3
! ½ðCp02NbðxylylNCÞÞ ð1; 3; 5-ðj1-OAOOCÞ ðC6H3ÞÞꢀ
Fig. 2. (a) Proposed structure for complex 7. An analogous structural
situation may be displayed for 8 and 9. (b) Analogous trinuclear
disposition with an g1-C, j1-S–CS2 ancillary ligand proposed for
complex 10.
3
3
ð9Þ
ð6Þ

A. Antin˜olo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141
3137
Cl
2.1. Electrochemical studies
+ 1/2 H2
Cp'2Nb
Cp'2NbCl
+ HOOC(C6H5)
O
C
O
ð9Þ
Electrochemical studies on Cp0 NbCl2 ð2Þ in the pres-
2
ence of the appropriate carboxylic acids were carried
out. Rotating disk electrode (RDE) voltammetry was
performed on the complex in THF in the presence of
0.2 mol Lꢁ1 NaBPh4 as a supporting electrolyte. Com-
plex 2 was found to exhibit a reduction wave A and
an oxidation wave E0 (Fig. 3(a)). Wave A corresponds
to the one-electron reduction of 2 to give Cp02NbCl, as
mentioned previously [12]. When the process was re-
peated in the presence of one equivalent of
(C6H5)COOH the RDE voltammogram was unchanged;
however, when the electrolysis was performed on a car-
bon gauze electrode at ꢁ1.50 V (versus an SCE elec-
trode) corresponding to the plateau of wave A, a
quantity of electricity close to two equivalent of elec-
trons per mole of 2 was consumed. The RDE voltammo-
gram of the resulting solution showed one well-defined
oxidation wave F0 at ꢁ0.510 V (Fig. 3(b)). This electro-
generated product corresponds to complex 3. The for-
mation of this complex can be rationalized in terms of
the following global reaction (Eq. (7)):
Cl
Cp'2Nb
2Cp'2NbCl +
O
C
O
ð10Þ
O
Cp'2Nb
C
Cp'2NbCl2 +
O
3
Cp02NbCl would react with the carboxylic acid to give a
paramagnetic niobium(IV) complex, namely Cp02NbCl
ðj1-O; O0AOOCðC6H5ÞÞ, with elimination of H2 (Eq.
(9)). This intermediate would then be reduced by
Cp02NbCl to give 3 and the regeneration of 2 (yield
50%, Eq. (10)). These results imply that reaction (10)
should be markedly faster than reaction (9). In cyclic
voltammetry studies, 3 exhibited an F/F0 reversible sys-
tem (Fig. 4), which can be described by the following
reaction (Eq. (11)):
-1e-
O
O
Cp'2Nb
C
Cp'2Nb
C
O
ð11Þ
+1e-
O
Cp02NbCl2 þ HOOCðC6H5Þ þ 2eꢁ ! ½ðCp02NbÞ
3'
3
ðj2-O; O0AOOCðC6H5ÞÞꢀ þ 1=2H2 þ 2Clꢁ
ð7Þ
However, under different experimental conditions
(i.e., THF/NaBPh4 or THF/Bu4NPF6), the electrooxida-
tion process of 3 at the potential of the wave F0 leads to
partial regeneration of 2 according to the following pro-
cess (Eq. (12)):
When one equivalent of (C6H5)COOH was added to a
solution containing Cp20 NbCl (obtained from the one-
electron reduction of 2 in THF in the presence of 0.2
mol Lꢁ1 NaBPh4), a fast reaction occurred to give 3
and the regeneration of 50% of 2 (identified by its reduc-
tion wave A and by ESR spectroscopy). This result ex-
O
O
Cp'2NbCl2 + (C6H5)COO-
C
- 1e- + 2 Cl-
Cp'2Nb
ð12Þ
plains the consumption of
2
electrons in the
Even when the electrolysis of 3 was carried out a
low temperature, the stabilization of 30 was not possi-
ble. Finally, complexes 4, 5, and 6, with dicarboxylic
and tricarboxylic acids, were similarly electrogenerated
electrolysis of 2 in the presence of one equivalent of
the acid. These electrochemical results can be rational-
ized according to the processes represented in the Eqs.
(8)–(10):
from Cp0 NbCl2 ð2Þ and the appropriate molar ratios
2
2Cp02NbCl2 þ 2eꢁ ! 2Cp02NbCl þ 2Clꢁ
ð8Þ
of the carboxylic acids (see Table 2). In cyclic
20 µA
c
F'
E'
E (V/ECS)
b
-1.5
-1
-0.5
0
0.5
A
a
Fig. 3. RDE voltammogram of (a, m) Cp02NbCl2 2 in THF containing 0.2 mol Lꢁ1 of NaBPh4; (b, h) after adding one equivalent of benzoic acid and
a 2 eꢁ reduction at ꢁ1.50 V on carbon electrode (scan rate: 20 mV sꢁ1).

3138
A. Antin˜olo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141
F'
5 µA
E (V/ECS)
-1.1
-0.85
-0.6
-0.35
-0.1
F
Fig. 4. Cyclic voltammogram of 3 on carbon electrode in THF containing 0.2 mol Lꢁ1 of NaBPh4 (scan rate: 100 mV sꢁ1; starting potential: ꢁ1 V).
˚
solvents were dried over 4 A molecular sieves and
Table 2
Half-wave potential of the F/F0 system, obtained on carbon electrode
degassed prior to use. Carboxylic acids, namely
C6H5(COOH), [1,4-(HOOC)2(C6H4)], [1,3-(HOOC)2-
(C6H4)], [1,3,5-(HOOC)2(C6H3)], and carbon disulphide
were used as purchased from Aldrich. NMR spectra
were recorded on a Varian Unity 300 (300 MHz for
1H, 75 MHz for 13C) spectrometer. Chemical shifts were
measured relative to partially deuterated solvent peaks
and are reported relative to TMS. IR spectra were re-
corded on a Perkin–Elmer 883 spectrometer in Nujol
mulls over CsI windows.
(scan rate: 20 mV sꢁ1) in THF/NaBPh4
Complex
E1/2 (V)
4
5
6
ꢁ0.482
ꢁ0.479
ꢁ0.456
voltammetry experiments, these complexes also exhibit
the reversible F/F0 system at the potential values indi-
cated in Table 2.
4.1. Electrochemical experiments
3. Conclusions
All manipulations were performed using Schlenk tech-
niques in an atmosphere of dry oxygen-free argon gas
and using dry solvents. The supporting electrolyte was
degassed under vacuum before use and then solubilized
at a concentration of 0.2 mol Lꢁ1. Voltammetric analyses
were carried out in a standard three-electrode cell with a
Princeton Applied Research, Model 263A. The reference
electrode was a saturated calomel electrode (SCE) sepa-
rated from the solution by a sintered glass disk. The aux-
iliary electrode was a platinum wire. For all voltammetric
measurements, the working electrode was a vitreous car-
bon electrode (/ = 3 mm). A CTV101 Speed Control unit
The interaction of Cp20 NbH3 with carboxylic acids
was studied. The liberation of H2 and the subsequent
formation of new carboxylato-containing niobocenes,
which were alternatively prepared by an electrochemical
method, was observed. In addition, the reactivity of
these complexes towards xylylNC and CS2 was studied.
It was found that a bidentate ! monodentate conver-
sion of the coordination mode of the carboxylato ligand
occurred.
ꢀ
was used to adjust the rotation speed ðx ¼ 500 rpmÞ of
4. Experimental
the EDI101 electrode (Radiometer). In these conditions,
when operating in THF, the formal potential for the fer-
rocene+/ꢁ couple is found to be +0.56 V versus SCE. The
controlled potential electrolysis was performed with an
Amel 552 potentiostat coupled with an Amel 721 elec-
tronic integrator. High scale electrolyses were performed
in a cell with three compartments separated with fritted
glasses of medium porosity. A carbon gauze was used
as the working electrode, a platinum plate as the coun-
ter-electrode and a saturated calomel electrode as the ref-
erence electrode.
General procedures. All reactions were carried out
using Schlenk techniques. Oxygen and water were ex-
cluded by the use of vacuum lines supplied with purified
N2. Toluene was distilled from sodium. Pentane was dis-
tilled from sodium/potassium alloy. Diethyl ether and
THF were distilled from sodium benzophenone. All sol-
vents were deoxygenated prior to use. Complexes
Cp0 NbðHÞ and Cp0 NbðHÞðCNð2; 6-Me2C6H3ÞÞ were
2
3
2
prepared as described in the literature [2,3]. Deuterated

A. Antin˜olo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141
3139
4.2. Synthesis of Cp02Nb(j2-O,O0AOOC(C6H5)) (3)
6: IR (Nujol/PET cmꢁ1) mðCOOaꢁsymÞ 1605, ðCOOꢁsym
Þ
1
1531. H NMR (C6D6): d ꢁ0.02 (s, 54H, SiMe3), 4.06,
5.58 (12 H each a complex signal, C5H4SiMe3), 8.40 (s,
3H, C6H3). 13C{1H} NMR (C6D6): d 0.3 (SiMe3), 94.5
(C1, C5H4), 104.7, 107.5 (C2–5, exact assignment not pos-
sible, C5H4SiMe3), 132.2 and 132.5 (C6H3), 187.6
(COOꢁ). Anal. Calc. for C57H100Nb3O6Si6: C, 52.30;
H, 6.19. Found: C, 52.12; H, 6.10%.
A mixture of Cp0 NbH3 ð1Þ (0.28 g; 0.75 mmol) and
2
the carboxylic acid C6H5(COOH) (0.15 g; 0.75 mmol)
was stirred with dry THF (30 mL) at 50 ꢁC for 5 h.
The solution became dark green in colour and the sol-
vent was evaporated to dryness under vacuum. The dark
green oily residue was extracted with hexane (10 mL).
The resulting solution was filtered and evaporated to
dryness. Complex 3 was isolated as a dark green solid
(90% yield): IR (Nujol/PET cmꢁ1) ðmCOOaꢁsymÞ 1634,
ðCOOꢁsymÞ 1539. 1H NMR (C6D6): d 0.06 (s, 18H,
4.4. Synthesis of [Cp02Nb(j1-OAOOC(C6H5))
(xylylNC)] [(7)]
SiMe3), 4.18, 5.69 (4H each
a
complex signal,
4.4.1. Method A
C5H4SiMe3), 6.87 (t, JH–H = 7.4 Hz, 1H, Hp C6H5),
A mixture of ½Cp02NbðHÞðxylylNCÞꢀ (0.75 g; 2.25
mmol) and the carboxylic acid C6H5(COOH) (0.27 g;
2.25 mmol) was stirred with dry THF (30 mL) at room
temperature for 3 h. The solution became green in col-
our and the solvent was evaporated to dryness under
vacuum. The green oily residue was extracted with hex-
ane (10 mL). The resulting solution was filtered and
evaporated to dryness. Complex 7 was isolated as a
green solid (90% yield).
3
3
3
6.90 (t, JH–H = 7.5 Hz, 2H, HmC6H5), 7.78 (d, JH–H
= 7.5 Hz, 2H, Ho C6H5). 13C{1H}NMR (C6D6): d 0.4
(SiMe3), 94.0 (C1, C5H4SiMe3), 104.3, 108.2 (C2–5, exact
assignment not possible, C5H4SiMe3), 127.0, 128.0,
132.7 (C6H5), 190.1 (COOꢁ). Anal. Calc. for
C23H34NbSi2O2: C, 56.56; H, 6.35. Found: C, 56.11;
H, 6.19%.
4.3. Synthesis of [(Cp02Nb)2(1,4-(j2-O,O0AOOC)2(C6-
H4))] (4), [(Cp02Nb)2(1,3-(j2-O,O0AOOC)2(C6H4))]
(5) and [(Cp20 Nb)3(1,3,5-(j2-O,O0AOOC)3(C6H3))]
(6)
4.4.2. Method B
A
mixture of Cp02Nbðj2-O; O0AOOCðC6H5ÞÞ ð3Þ
(0.13 g; 0.75 mmol) and CN(2,6-Me2C6H3) (0.06 g;
0.75mmol) was stirred with dry THF (30 mL) at room
temperature for 3 h. The solution became green in col-
our and the solvent was evaporated to dryness under
vacuum. The green oily residue was extracted with hex-
ane (10 mL). The resulting solution was filtered and
evaporated to dryness. Complex 7 was isolated as a
green solid (82% yield): IR (Nujol/PET cmꢁ1) m(C„N)
2068, ðCOOꢁasymÞ 1712, ðCOOsꢁymÞ 1450. 1H NMR
(C6D6): d 0.02 (s, 18H, SiMe3), 2.35 (s, 6H, CN(2,6-
Me2C6H3)), 4.99, 5.19, 5.57, 5.86 (2 H each a complex
signal, C5H4SiMe3), 6.64 (s, 3H, CN(2,6-Me2C6H3)),
A mixture of Cp0 NbH3 ð1Þ (0.28 g; 0.75 mmol) and
2
the corresponding carboxylic acid [1,4-(HOOC)2(C6H4)]
(0.15 g; 0.75 mmol) was stirred with dry THF (30 mL) at
50 ꢁC for 5 h. The solution became dark green in colour
and the solvent was evaporated to dryness under vac-
uum. The dark green oily residue was extracted with
hexane (10 mL). The resulting solution was filtered
and evaporated to dryness. Complex 4 was isolated as
a dark green solid (90% yield). Complexes 5 and 6 were
prepared in a similar way.
4: IR (Nujol/PET cmꢁ1) mðCOOaꢁsymÞ 1646, ðCOOꢁsym
Þ
7.00 (t, JH–H = 7.3 Hz, 2H, Hm C6H5), 7.13 (t,
3
3
1
1529. H NMR (CO(CD3)2): d ꢁ0.03 (s, 36H, SiMe3),
4.52, 5.83 (8 H each a complex signal, C5H4SiMe3),
7.50 (s, 4H, HoC6H4). 13C{1H}NMR (CO(CD3)2): d
3JH–H = 7.3 Hz, 1H, Hp C6H5) 8.14 (d, JH–H = 7 Hz,
2H, HoC6H5). 13C{1H}NMR (C6D6): d 0.1 (SiMe3),
19.1 (CN(2,6-Me2C6H3)), 93.9 (C1, C5H4), 96.7, 101.1,
104.2, 109.6 (C2–5, exact assignment not possible,
C5H4SiMe3), 126.5, 129.8, 130.3 and 130.7 (CN(2,6-
Me2C6H3)), 132.9, 133.1 and 135.3 (C6H5), 175.6
(COOꢁ), 208.2 (CN(2,6-Me2C6H3)). Anal. Calc. for
C32H43NNb2O2Si4: C, 62.04; H, 6.46; N, 2.26. Found:
C, 61.89; H, 6.32; N, 2.32%.
0.4 (SiMe3), 96.0 (C1, C5H4SiMe3), 105.1, 108.1 (C2–5
,
exact assignment not possible, C5H4SiMe3), 128.7 and
135.9 (C6H4), 205.5 (COOꢁ). Anal. Calc. for
C40H62Nb2Si4O4: C, 54.24; H, 5.65. Found: C, 53.97;
H, 5.55%.
5: IR (Nujol/PET cmꢁ1) mðCOOaꢁsymÞ 1648, ðCOOꢁsym
Þ
1
1527. H NMR (C6D6): d 0.00 (s, 36H, SiMe3), 4.12,
5.62 (8 H each a complex signal, C5H4SiMe3), 6.72 (t,
4.5. Synthesis of [[(Cp02Nb(xylylNC))2(1,4-[(j1-OA
OOC)2(C6H4))] (8)
3
3JH–H = 8.0 Hz, 1H, Hm C6H4), 7.70 (d, JH–H = 7.7
Hz, 2H, HoC6H4), 8.31 (s, 1H, HoC6H4). 13C{1H}NMR
(C6D6): d 0.4 (SiMe3), 94.5 (C1, C5H4), 104.6, 107.5
(C2–5, exact assignment not possible, C5H4SiMe3),
127.0, 129.0, 132.2 and 132.5 (C6H4), 188.9 (COOꢁ).
Anal. Calc. for C40H62Nb2Si4O4: C, 54.24; H, 5.65.
Found: C, 54.04; H, 5.55%.
A
mixture of ½ðCp02NbÞ ð1; 4-ðj2-O; O0AOOCÞ
2
2
ðC6H4ÞÞꢀ ð4Þ (0.13 g; 0.75 mmol) and (CN(2,6-
Me2C6H3)) (0.19 g; 1.50 mmol) was stirred with dry
THF (30 mL) at room temperature for 3 h. The solution
became green in colour and the solvent was evaporated

3140
A. Antin˜olo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141
1
to dryness under vacuum. The green oily residue was ex-
tracted with hexane (10 mL). The resulting solution was
filtered and evaporated to dryness. Complex 8 was iso-
lated as a green solid (82% yield): IR (Nujol/PET
cmꢁ1) m(CN) 2062, ðCOOaꢁsymÞ 1698, ðCOOꢁsymÞ 1453.
1H NMR (CO(CD3)2): d 0.12 (s, 36H, SiMe3), 2.23 (s,
12H, CN(2,6-Me2C6H3)), 5.21, 5.45, 5.55, 5.95 (4H,
each a complex signal, C5H4SiMe3), 6.80 (s, 6H,
CN(2,6-Me2C6H3)), 8.19 (s, 4H, C6H4). 13C{1H}NMR
(CO(CD3)2): d 0.3 (SiMe3), 19.2 (CN(2,6-Me2C6H3)),
94.9, 97.2, 101.7, 110.3 (C2–5, exact assignment not pos-
sible, C5H4SiMe3), 104.7 (C1, C5H4), 128.6, 128.7, 128.9
and 129.7 (C6H4), 127.2, 130.2, 133.4 and 138.9
(CN(2,6-Me2C6H3)), 174.2 (COOꢁ), 209.9 (CN(2,6-
Me2C6H3)). Anal. Calc. for C58H80N2Nb2O4Si4: C,
60.00; H, 6.38; N, 2.69. Found: C, 59.56; H, 6.09; N,
2.41%.
(C@S) 1151. H NMR (C6D6): 0.06 (s, 54H, SiMe3),
5.91, 6.20, 6.28, 6.44 (6 H each a complex signal,
C5H4SiMe3), 8.83 (s, 3H, C6H3). 13C{1H}NMR
(C6D6): d 0.2 (SiMe3), 94.5 (C1, C5H4), 102.3, 104.7,
106.8, 107.5 (C2–5, exact assignment not possible,
C5H4SiMe3), 134.0 (C6H3), 136.9 (C6H5), 182.2
(COOꢁ), 250.2 (CS2). Anal. Calc. for C60H100Nb3O6S6-
Si6: C, 48.00; H, 1.93. Found: C, 48.43; H, 2.10%.
4.8. X-ray Structure determination for compound 4
Intensity data for compound 4 were collected on a
NONIUS-MACH3 diffractometer equipped with a
graphite
monochromator
(Mo Ka
radiation,
˚
k = 0.71073 A) using an x/2h scan technique. The final
unit cell parameters were determined from 25 well-
centered reflections and refined by least-squares method.
Absorption correction was made. The crystal data and
details of the data collection and structure analysis are
summarized in Table 3.
4.6. Synthesis of [(Cp20 Nb(xylylNC))3(1,3,5-(j1-O,-
OOC)3(C6H3))] (9)
The structure was solved by direct methods using
SHELXS computer program [13] and refined on F2 by
full-matrix least-squares (SHELXL-97) [14]. All non-
hydrogen atoms were refined with anisotropic thermal
parameters for all compounds. The hydrogen atoms
were included in calculated positions and were refined
with an overall isotropic temperature factor using a rid-
ing model. Weights were optimized in the final cycles.
A mixture of ½ðCp20 NbÞ ð1; 3; 5-ðj2-O; O0AOOCÞ
3
3
ðC6H3ÞÞꢀ ð6Þ (0.16 g; 0.75 mmol) and CN(2,6-Me2C6H3)
(0.29 g; 2.25 mmol) was stirred with dry THF (30 mL) at
room temperature for 3 h. The solution became green in
colour and the solvent was evaporated to dryness under
vacuum. The green oily residue was extracted with hex-
ane (10 mL). The resulting solution was filtered and
evaporated to dryness. Complex 9 was isolated as a
green solid (87% yield): IR (Nujol/PET cmꢁ1) m(C„N)
2046, ðCOOꢁasymÞ 1629, ðCOOsꢁymÞ 1387. 1H NMR
(C6D6): d 0.10 (s, 54H, SiMe3), 2.43 (s, 18H, CN(2,6-
Me2C6H3)), 5.05, 5.21, 5.51, 5.73 (6H, each a complex
signal, C5H4SiMe3), 6.80 (m, 9H, CN(2,6-Me2C6H3)),
8.82 (s, 3H, C6H3). 13C{1H} NMR (C6D6): d 0.3
(SiMe3), 19.4 (CN(2,6-Me2C6H3)), 93.9, 96.6, 100.8,
109.9 (C2–5, exact assignment not possible, C5H4SiMe3),
104.6 (C1, C5H4), 127.5 and 129.2 (C6H3), 133.1, 133.6
and 137.3 (CN(2,6-Me2C6H3)), 174.4 (COOꢁ), 212.5
(CN(2,6-Me2C6H3)). Anal. Calc. for C84H127N3Nb3O6-
Si6: C, 59.25; H, 6.35; N, 2.82. Found: C, 59.43; H,
6.55; N, 2.71%.
Table 3
Crystal data and structure refinement for 4
Formula
Fw
T (K)
C40H56Nb2O4Si4
889.03
200(2)
Triclinic
Crystal system
Space group
Unit cell dimensions
ꢀ
P1
˚
a (A)
7.470(1)
10.763(1)
˚
b (A)
˚
c (A)
14.456(1)
103.33(1)
a (ꢁ)
b (ꢁ)
c (ꢁ)
96.92(1)
91.48(1)
1121.0(2)
3
˚
V (A )
4.7. Synthesis of [(Cp02Nb(g1-C,j1-SACS2))3(1,3,5-
(j1-OAOOC)3(C6H3))] (10)
Z
1
1.332
Dc (g cmꢁ3
)
l (mmꢁ1
F(000)
Crystal dimensions (mm)
)
0.653
466
A mixture of [(Nb(g5-C5H4SiMe3)2)3(1,3,5-(j2-O,O–
OOC)3(C6H3))] (6) (0.16 g; 0.75 mmol) and an equimo-
lecular quantity of CS2 (0.14 mL; 2.25 mmol) was stirred
with dry THF (30 mL) at room temperature for 3 h. The
solution became green in colour and the solvent was
evaporated to dryness under vacuum. The green oily res-
idue was extracted with hexane (10 mL). The resulting
solution was filtered and evaporated to dryness. Com-
plex 10 was isolated as a brown solid (70% ꢁyield): IR
(Nujol/PET cmꢁ1) mðCOOaꢁsymÞ 1638, ðCOOsymÞ 1408,
0.2 · 0.2 · 0.3
2.14 to 28.11
h Range (ꢁ)
Index ranges
ꢁ9 6 h 6 9, ꢁ14 6 k 6 13,
0 6 l 6 19
5611
Number of reflections measured
Number of independent reflections
Number of observed reflections
Goodness-of-fit on F2
5401
3071
0.987
R1 = 0.0649, wR2 = 0.1287
Final R indices [I > 2r(I)]
Largest difference peak and hole (e A
ꢁ3
˚
)
0.761/ꢁ0.765
2
2 0.5
R1 = RiFo| ꢁ |Fci/R|Fo|; wR2 ¼ ½R½wðF 2o ꢁ F c2Þ ꢀ=R½wðF o2Þ ꢀꢀ
.

A. Antin˜olo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141
3141
[4] A. Antinolo, F. Carrillo-Hermosilla, A. Castel, M. Fajardo, J.
Fernandez-Baeza, M. Lanfranchi, A. Otero, M.A. Pellinghelli,
G. Rima, J. Satge, E. Villasenor, Organometallics 17 (1998)
1523.
C16 and C17 are in disordered positions (0.54 and 0.63
population, respectively).
Crystallographic data for the structural analysis of 4
have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC Number 256606. Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44 1223 336033; e-mail: deposit@ccdc.
cam.ac.uk or http://www.ccdc.cam.ac.uk).
[5] A. Antinolo, F. Carrillo-Hermosilla, B. Chaudret, M. Fajardo, S.
Garcia-Yuste, F.J. Lahoz, M. Lanfranchi, J.A. Lopez, A. Otero,
M.A. Pellinghelli, Organometallics 14 (1995) 1297.
[6] A. Antinolo, M. Fajardo, S. Garcia-Yuste, I. del Hierro, A.
Otero, S. Elrami, Y. Mourad, Y. Mugnier, J. Chem. Soc., Dalton
Trans. (1995) 3409.
[7] (a) D.J. Darensbourg, M. Pala, J. Am. Chem. Soc. 107 (1985)
5687;
(b) D.J. Darensbourg, R.K. Hanckel, C.G. Bauch, M. Pala, D.
Simmons, J.N. White, J. Am. Chem. Soc. 107 (1985) 7463;
(c) D.J. Darensbourg, H.P. Wiegreffe, P.H. Wiegreffe, J. Am.
Chem. Soc. 112 (1990) 9252;
Acknowledgements
We gratefully acknowledge financial support from
(d) B.P. Sullivan, T.J. Meyer, Organometallics 5 (1986) 1500.
[8] D. Lucas, T.Z. Modarres, Y. Mugnier, A. Antinolo, A. Otero,
M. Fajardo, J. Organomet. Chem. 629 (2001) 54.
[9] A. Antinolo, F. Carrillo-Hermosilla, M. Fajardo, S. Garcia-
Yuste, A. Otero, J. Organomet. Chem. 482 (1994) 93.
[10] G.B. Deacon, R.J. Phillips, Coord. Chem. Rev. 33 (1980)
227.
´
´
´
the Direccion General de Investigacion Cientıfica, Spain
(MEC, Grant No. BQU2002-04638-CO2-02) and the
Junta de Comunidades de Castilla-La Mancha (Grant
Nos, PAC-02-003, GC-02-010 and PAI-02-016).
[11] A.A. Pasynskii, Y.V. Skiripkin, I.L. Emerenko, V.T. Kalinnikov,
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