Synthesis and reactivity of new oxo alkyl or oxo acyl niobocene complexes and crystal structure of Cp′2Nb(=O)(OC(O)CF3) (Cp′=η5-C5H4SiMe3)

Article abstract of DOI:10.1016/S0022-328X(99)00698-1

New alkyl and acyl oxo niobocenes Cp′₂Nb(O)(R) [Cp′=η⁵-C₅H₄SiMe₃; R=CH₂CH₃ (3), CH₂CH₂Ph (4), COCH₂CH₃ (7), COCH₂CH₂Ph (8)] have been synthesized. The oxo alkyl derivatives were obtained by reaction of olefin-hydride complexes Cp′₂Nb(H)(η²-CH₂=CHR) [R=H (1), Ph (2)] with oxygen, whereas the oxo acyl complexes were prepared by reaction of the niobium(III) carbonyl derivatives Cp′₂Nb(CO)(COCH₂CH₂R) [R=H (5), Ph (6)] with oxygen. We have also studied the reaction of Cp′₂Nb(O)(CH₂CH₂R) [R=H (3), Ph (4)] with HBF₄ and CF₃COOH. These reactions afforded Cp′₂NbF(O→BF₃) (9) and Cp′₂Nb(O)[η¹-(O)-OCOCF₃)] (10), respectively. When protonation of oxo acyl niobocenes Cp′₂Nb(O)(COCH₂CH₂R) [R=H (7), Ph (8)] with CF₃COOH was carried out, complex 10 was obtained. Furthermore, carbon dioxide-niobocene derivatives Cp′₂Nb(CO₂)(CH₂CH₂R) [R=H (11), Ph (12)] react with BF₃·Et₂O to yield the fluoro niobocene complex 9. The structure of complex 10 was confirmed by X-ray diffraction. Complex 10 crystallizes in the monoclinic system, in the centrosymmetric P2₁/c space group, with unit cell parameters: a=9.671(1) A?; b=12.935(2) A?, c=18.43(1) A?; β=99.03(2)°; V=2277(1) A?³; δ(Calc.)=1.448 mg m^-3 and R=0.062.

Full text of DOI:10.1016/S0022-328X(99)00698-1

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 598 (2000) 167–173
Synthesis and reactivity of new oxo alkyl or oxo acyl niobocene
complexes and crystal structure of Cp%Nb(ꢀO)(OC(O)CF3)
2
(Cp%=h5-C5H4SiMe3)
Antonio Antin˜olo a, *1, Isabel del Hierro a, Isabel Lo´pez-Solera a,
Santiago Garc´ıa-Yuste a, Antonio Otero a, *2, Mariano Fajardo b, Ana Rodr´ıguez a
a Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica, Facultad de Qu´ımicas, Uni6ersidad de Castilla La Mancha,
E-13071 Ciudad Real, Spain
b Departamento de Qu´ımica Inorga´nica, Campus Uni6ersitario, Uni6ersidad de Alcala´, E-28871 Alcala´ de Henares, Madrid, Spain
Received 12 July 1999; accepted 9 November 1999
Abstract
New alkyl and acyl oxo niobocenes Cp2%Nb(O)(R) [Cp%=h5-C5H4SiMe3; R=CH2CH3 (3), CH2CH2Ph (4), COCH2CH3 (7),
COCH2CH2Ph (8)] have been synthesized. The oxo alkyl derivatives were obtained by reaction of olefin-hydride complexes
Cp2%Nb(H)(h2-CH2ꢀCHR) [R=H (1), Ph (2)] with oxygen, whereas the oxo acyl complexes were prepared by reaction of the
niobium(III) carbonyl derivatives Cp%Nb(CO)(COCH2CH2R) [R=H (5), Ph (6)] with oxygen. We have also studied the reaction
2
of Cp%Nb(O)(CH2CH2R) [R=H (3), Ph (4)] with HBF4 and CF3COOH. These reactions afforded Cp%2NbF(O“BF3) (9) and
2
Cp2%Nb(O)[h1-(O)ꢁOCOCF3)] (10), respectively. When protonation of oxo acyl niobocenes Cp2%Nb(O)(COCH2CH2R) [R=H (7),
Ph (8)] with CF3COOH was carried out, complex 10 was obtained. Furthermore, carbon dioxide–niobocene derivatives
Cp2%Nb(CO2)(CH2CH2R) [R=H (11), Ph (12)] react with BF3·Et2O to yield the fluoro niobocene complex 9. The structure of
complex 10 was confirmed by X-ray diffraction. Complex 10 crystallizes in the monoclinic system, in the centrosymmetric P21/c
3
,
,
,
,
space group, with unit cell parameters: a=9.671(1) A; b=12.935(2) A, c=18.43(1) A; i=99.03(2)°; V=2277(1) A ; l(Calc.)=
1.448 mg m−3 and R=0.062. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Niobium; Alkyl and acyl oxo niobocene
oxo alkyl or acyl niobocenes and the study of their
reactivity toward protic reagents, namely HBF4 or
1. Introduction
CF3COOH and the Lewis acid BF3.
Transition metal complexes bearing oxo or imido
ligands are the focus of continued interest [1]. In con-
nection with our studies on the metal-promoted activa-
tion of unsaturated compounds such as ketenes,
ketenimines, olefins and acetylenes with niobocene
2. Results and discussion
complexes [2], the formation of carbon dioxide–
niobocene complexes was discovered. The reactivity of
this late compound with the Lewis acid B(C6F5)3 al-
lowed us to isolate oxo alkyl niobocene adducts with
B(C6F5)3 [3]. As a continuation of our studies, in this
article we report our results on the formation of new
Oxidation of olefin–hydride niobocenes Cp%Nb(H)-
2
(h2-CH2ꢀCHR) [Cp%=h5-C5H4SiMe3; R=H (1), Ph
(2)] with O2 in hexane at room temperature (r.t.)
yielded a mixture of oxo and peroxo alkyl niobocenes
Cp%Nb(O)(CH2CH2R) [R=H (3), Ph (4)], respectively,
2
and Cp%2Nb(O2)(CH2CH2R) (R=H, Ph). When this
mixture was stirred at 40°C for 4 h, the peroxo alkyl
complexes evolved to the corresponding oxo alkyl
niobocenes, which were isolated as single products (Eq.
(1)).
1 *Corresponding author.
2 *Corresponding author.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00698-1

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A. Antin˜olo et al. / Journal of Organometallic Chemistry 598 (2000) 167–173
Cp%Nb(H)(h2-CH2ꢀCHR)+O2
Taking into account the splitting of HBF4 by oxo
niobocene complexes observed by Bruno et al. [10], we
proposed that these reactions proceed by initial interac-
tion of the Lewis acid BF3 with the oxo group to give
2
R=H (1), Ph (2)
“Cp%Nb(O)(CH2CH2R)
(1)
2
R=H (3), Ph (4)
Nicholas et al. [4] have previously reported the isola-
tion of several alkyl carbon dioxide–niobocene com-
plexes by reaction of CpM2 eNb(CO)(alkyl) with O2. By
contrast, when the reaction was carried out using
carbonyl acyl niobocene derivatives Cp%Nb(CO)-
(COCH2CH2R) [R=H (5), Ph (6)] with O2 in hexane at
the oxo alkyl niobocene Cp%Nb(CH2CH2R)(O“BF3)
2
[R=H (3a), Ph (4a)], which has been observed previ-
ously [3,11]. A possible reaction pathway is shown in
Scheme 1 (see below). There are two possible paths to
explain the presence of the alkane and alkene as reac-
tion byproducts: (a) the usual protonation of the alkyl
group, followed by nucleophilic attack by fluoride; and
(b) b-elimination of the alkyl group to yield the oxo-hy-
dride derivative, which could not be detected (probably
due to its high reactivity), followed by substitution of
the hydride by the fluoride ligand.
2
r.t., the oxo acyl niobocene complexes Cp%Nb(O)-
2
(COCH2CH2R) [R=H (7), Ph (8)] were isolated as
pure compounds (Eq. (2)). The different behavior could
be assigned to the higher electrophilic character of the
acyl group compared with the corresponding alkyl
group, which probably prevents the stabilization of the
corresponding CO2-containing species [3,5,6].
BF3·OEt2 has been used to provide evidence that the
first step of this reaction is not the initial protonation of
the oxo group in the time scale of our experiment, as
has been proposed for complexes Cp*2 Nb(O)(R) (R=
Cp%Nb(CO)(COCH2CH2R)+O2
2
R=H (5), Ph (6)
“Cp%Nb(O)(COCH2CH2R)+CO
(2)
2
H, OMe) [12]. The reaction of Cp%Nb(O)(CH2CH2R)
2
R=H (7), Ph (8)
[R=H (3), Ph (4)] with BF3·OEt2 afforded the same
intermediates 3a and 4a, which rapidly evolved to the
final complex 9 and the corresponding alkene (Eq. (4)).
Protonation reactions of Cp%Nb(O)(CH2CH2R) [R=
H (3), Ph (4)] with an excess of HBF4·Et2O take place
at −78°C in ether. The solution was stirred at r.t. for
2
4 h. In all cases the same complex, Cp%NbF(O“BF3)
Cp2%Nb(O)(CH2CH2R)+BF3·OEt2
2
R=H (3), Ph (4)
(9), was obtained, in which the BF3 moiety is coordi-
nated to the oxygen atom and the R group has been
replaced by the fluoride to give the alkane and alkene
(Eq. (3)). The IR spectrum for compound 9 shows, in
addition to the characteristic bands for Cp at 841 cm−1
and SiMe3 at 1250 cm−1, a broad absorption at 1053
cm−1 corresponding to the BF3 and the w(NbꢁF) vibra-
“Cp%Nb(O“BF3)(CH2CH2R)
2
R=H (3a), Ph (4a)
“Cp%Nb(O“BF3)(F)+CH2ꢀCHR
(4)
2
(9)
The same intermediates can be detected by treatment
of Cp%Nb(CO2)(CH2CH2R) [R=H (11), Ph (12)] with
2
BF3·OEt2 (Scheme 2) (see below), probably due to the
1
tion at 520 cm−1. The H-NMR spectrum shows sig-
rapid decarbonylation reaction of the adducts
Cp%Nb(h2-CO2ꢁBF3)(CH2CH2R) to afford the oxo-
nals at 6.82 (2H), 6.99 (2H), 7.11 (2H) and 7.31 (2H)
ppm for the Cp% groups and a signal at 0.29 ppm for
the SiMe3 group. The 19F-NMR spectrum shows two
signals at −144.44 and −145.46 ppm, corresponding
to (NbꢁF) and BF3, respectively. These data confirm
the proposed structure.
2
alkyl complexes [3].
The reaction of alkyl and acyl derivatives
[Nb(Cp%)2R(O)] [R=Et (3), CH2CH2Ph (4), COCH2-
CH3 (7), COCH2CH2Ph (8)] with an excess of
CF3COOH at −78°C in ether yielded [Nb(Cp%)(O)(h1-
(O)ꢁOCOCF3)] (10) with loss of the R group as either
the alkane or aldehyde in alkyl or acyl derivatives,
respectively (Eq. (5)). The IR spectrum for compound
Cp%Nb(O)(CH2CH2R)+HBF4“Cp%Nb(F)(O“BF3)
2
2
R=H (3), Ph (4)
(9)
(3)
10 shows the characteristic bands for Cp at 839 cm−1
,
The substitution of chloride by fluoride by abstrac-
tion from BF−4 [6] or PF−6 [7] has been observed
previously. When the protonation reaction of the oxo-
alkyl niobocenes with HBF4·OEt2 was monitored by
1H-NMR spectroscopy in an NMR tube in acetone-d6
at low temperature, the loss of the alkyl group as the
corresponding alkane and alkene was detected.
The rapid protonation of these complexes prevents
the isolation of any reaction intermediate. Initially, we
could distinguish two groups of signals, those corre-
sponding to complex 9 and the signals corresponding to
other complexes (3a and 4a, respectively), where the
alkyl group is still coordinated to the niobium atom [8].
This intermediate rapidly affords the final complex 9,
with loss of the alkyl group [9].
w(NbꢀO) at 900 cm−1 and SiMe3 at 1253 cm−1 and
two absorptions at 1717 and 1407 cm−1, corresponding
to the asymmetric and symmetric vibrations, respec-
tively, that are typical for the carboxylate group as a
1
unidentate ligand [13]. The H-NMR spectrum shows
signals at 6.24 (2H), 6.66 (2H) and 6.87 (4H) ppm for
the Cp% group and a signal at 0.24 ppm for the SiMe3
group. The 13C-NMR spectrum confirmed the presence
of the CF3COO− group, with chemical shifts of 158.80
ppm [2J(19F–13C)=40.9 Hz] and 116.19 ppm [1J(19F–
13C)=285.4 Hz]. The 19F-NMR spectrum shows a
unique signal at −75.79 ppm. Similar complexes have
been obtained in our group, namely [Nb(Cp%)L(h1-
(O)ꢁOCOCF3)] (L=CN–xylyl, CO) [14].

A. Antin˜olo et al. / Journal of Organometallic Chemistry 598 (2000) 167–173
169
Cp%Nb(O)(R)
2
CF3COOH. Another pathway, where the initial proto-
nation takes place at the NbꢁC bond, cannot be ex-
cluded.
R=CH CH (3), CH CH Ph (4), COCH CH (7), COCH CH Ph (8)
2
3
2
2
2
3
2
2
+CF3OOH
“Cp%Nb(O)(h1-(O)-OCOCF3)
(5)
2
An X-ray crystal structure determination of complex
[Nb(Cp%)(O)(h1-(O)ꢁOCOCF3)] (10) confirmed the pro-
posed structure. The crystal structure is depicted in Fig.
1 together with the atomic numbering scheme. Selected
bond distances and angles are given in Table 1.
The structure consists of discrete molecules separated
by van der Waals distances. The niobium atom shows
a geometry that is typical for pseudo-tetrahedral
niobocene(V) oxo derivatives. The angle between the
two cyclopentadienyl rings is 127.35(3)°. The environ-
ment of the niobium atom is completed by an oxygen
and a trifluoroacetate group bonded through the oxy-
(10)
The reactions of alkyl derivatives [Nb(Cp%)2(O)-
(CH2CH2R)] [R=H (3), Ph (4)] with CF3COOH
1
were followed by H-NMR spectroscopy in an NMR
tube in acetone-d6. We proposed that these reactions
proceed by initial protonation of the oxo group to
afford cationic intermediates 3b and 4b [15], followed
by the elimination of alkane and the nucleophilic attack
of the CF3COO− ligand to yield complex 10, which has
been previously observed [14] (Scheme 3). The same
intermediate could be obtained by protonation of
[Nb(Cp%)2(CO2)(CH2CH2R)] [R=H (11), Ph (12)] with
Scheme 1.
Scheme 2.

170
A. Antin˜olo et al. / Journal of Organometallic Chemistry 598 (2000) 167–173
Scheme 3.
gen atom to the niobium as a monodentate ligand.
Bond distances are within the normal range found for
these complexes [16], with NbꢁO1 and NbꢁO2 bond
3.1. Preparation of Cp%Nb(O)(CH2CH2R)] [R=H (3),
Ph (4)]
2
A solution of Cp%Nb(H)(h2-CH2ꢀCHR)] [R=H (1),
,
lengths of 1.718(4) and 2.097(5) A, respectively.
2
Ph (2)] (1 mmol) in hexane (30 ml) was stirred for 4 h
at 40°C under dry O2. The solvent was removed under
vacuum and the yellow solid was recrystallized from
hexane (5 ml) at −40°C. The yellow crystals were
filtered off and identified as complexes 3 or 4,
respectively.
3. Experimental
All reactions were performed using standard Schlenk-
tube techniques under a nitrogen atmosphere. Solvents
were distilled from appropriate drying agents. The com-
plexes Cp2%Nb(H)(h2-CH2ꢀCHR) [R=H (1), Ph (2)],
and Cp2%Nb(CO)(COCH2CH2R) [R=H (5), Ph (6)]
were synthesized using previously reported methods [3].
The C and H analyses were carried out using a Perkin–
Elmer 2400B microanalyzer. The infrared spectra were
recorded as Nujol mulls in the range 4000–200 cm−1
using a Perkin–Elmer 883 spectrophotometer. NMR
spectra were recorded on Varian-Unity FT-300 and
Gemini FT-200 spectrometers, and the chemical
shifts were determined by reference to the residual
deuterated solvent peaks for 1H- and 13C-NMR and
externally with CFCl3 for 19F-NMR. When protona-
tions were observed by NMR spectroscopy, CF3COOH
(10%) or HBF4 (10%) was added to an acetone-d6
solution of niobocene complexes in an NMR tube
at −78°C.
Fig. 1. Molecular structure of compound Cp%2Nb(O)(h1-(O)ꢁ
OC(O)CF3) (10). ORTEP, 50% ellipsoids. Disorder and H atoms were
omitted for clarity.

A. Antin˜olo et al. / Journal of Organometallic Chemistry 598 (2000) 167–173
171
Table 1
Complex 8. Yield: 89%. Anal. Calc. for C25-
H35Si2O2Nb: C, 58.13; H, 6.83. Found: C, 57.99; H,
6.45. IR (Nujol) w (cm−1) 1635 (CꢀO), 1597 (Ph), 1245
(SiMe3), 905 (NbꢀO), 838 (C5H4SiMe3). 1H-NMR
(C6D6): l (ppm) 0.20 (s, 18H, SiMe3), 5.50 (2), 5.52 (2),
5.70 (2) 6.12 (2) (m, C5H4SiMe3), 2.91 (A2B2 system,
,
Selected bond lengths (A) and angles (°) for Cp%2Nb(=O)(OC(O)CF3)
(10)
Bond lengths
Nb1ꢁO1
Nb1ꢁO2
C1ꢁO2
C1ꢁO3
C1ꢁC2
1.718(4)
2.097(5)
1.199(9)
1.30(2)
J
AB=6.88 Hz, CH2CH2Ph), 3.55 (A2B2 system, JAB=
6.88 Hz, CH2CH2Ph), 7.20–7.30 (m, CH2CH2Ph).
13C{1H}-NMR (C6D6): l (ppm) −0.85 (SiMe3), 31.23
(CH2CH2Ph), 51.80 (CH2CH2Ph), 107.48, 110.95,
111.10, 119.29 (C5H4SiMe3), 125.99, 128.67, 129.30
(CH2CH2Ph), 143.07 (CipsoꢁPh), 272.99 (h1-C(O)R).
1.56(1)
Bond angles
O1ꢁNb1ꢁO2
Nb1ꢁO2ꢁC1
O2ꢁC1ꢁO3
O2ꢁC1ꢁC2
O3ꢁC1ꢁC2
99.7(2)
133.2(5)
127.4(9)
114.8(8)
113.7(10)
3.1.2. Preparation of [Cp%Nb(F)(O“BF3)] (9)
2
To a solution of Cp%Nb(O)(CH2CH2R) [R=H (3),
2
Ph (4)] (0.4 mmol) in (20 ml) Et2O at −78°C was
added HBF4·OEt2 (10% excess). Immediately a brown
precipitate is formed. The mixture was stirred at r.t. for
4 h. The solid was filtered off, washed with Et2O and
dried under vacuum. Yield 56%. Anal. Calc. for
C16H26Si2BF4ONb: C, 40.85; H, 5.57. Found: C, 40.77;
H, 5.54. IR (Nujol): w (cm−1) 1053 (BF3), 1250 (SiMe3),
841 (C5H4SiMe3), 520 (NbꢁF); 1H-NMR (acetone-d6): l
(ppm) 0.29 (s, 18H, SiMe3), 6.82(2), 6.99(2), 7.11(2),
7.31(2) (m, C5H4SiMe3). 13C{1H}-NMR (acetone-d6): l
(ppm) −0.57 (SiMe3), 113.75, 116.05, 131.42, 132.99
(C5H4SiMe3), 127.71 (Cipso). 19F-NMR (acetone-d6) l
(ppm) −144.44 (NbꢁF), −145.46 (BF3).
Complex 3. Yield: 87%. Anal. Calc. for C18-
H31Si2ONb: C, 52.41; H, 7.58. Found: C, 52.45; H,
7.50. IR (Nujol): w (cm−1) 1245 (SiMe3), 907 (NbꢀO),
1
834 (C5H4SiMe3). H-NMR (acetone-d6): l (ppm) 0.26
(s, 18H, SiMe3), 5.80(2), 5.94(2), 6.16(2) 6.58(2) (m,
C5H4SiMe3), 2.01 [q, J(1H–1H)=7.36 Hz CH2CH3],
1.66 [t, J(1H–1H)=7.36 Hz CH2CH3]. 13C{1H}-NMR
(CDCl3): l (ppm) −0.53 (SiMe3), 20.54 (CH2CH3),
25.00 (CH2CH3), 111.01, 111.27, 114.47, 120.32
(C5H4SiMe3), 120.21 (Cipso).
Complex 4. Yield: 76%. Anal. Calc. for C24-
H35Si2ONb: C, 59.00; H, 7.23. Found: C, 58.99; H,
7.15. IR (Nujol): w (cm−1) 1595 (Ph), 1244 (SiMe3), 906
(NbꢀO), 834 (C5H4SiMe3). 1H-NMR (acetone-d6): l
(ppm) 0.24 (s, 18H, SiMe3), 5.87(2), 6.05(2), 6.26(2)
6.62(2) (m, C5H4SiMe3), 3.08 (m, CH2CH2Ph), 2.19 (m,
CH2CH2Ph), 6.95–7.40 (m, CH2CH2Ph). 13C{1H}-
3.1.3. Preparation of [Cp%Nb(O)(p1-(O)ꢁOCOCF3)]
2
(10)
3.1.3.1. Method A. To a solution of Cp%Nb(O)-
2
NMR (CDCl3):
l (ppm) −0.52 (SiMe3), 34.14
(CH2CH2R) [R=H (3), Ph (4)] (0.4 mmol) in Et2O (20
ml) at −78°C was added trifluoroacetic acid (10%
excess). Immediately a red precipitate was formed. The
mixture was stirred at r.t. for 3 h, then the solid was
filtered off, washed with Et2O and dried under vacuum.
Yield 71%.
(CH2CH2Ph), 42.84 (CH2CH2Ph), 111.27, 111.73,
114.49, 120.01 (C5H4SiMe3), 120.36 (CipsoꢁC5H4SiMe3),
125.20, 127.68, 128.32 (CH2CH2Ph), 147.97 (CipsoꢁPh).
3.1.1. Preparation of Cp%Nb(O)(p1-C(O)CH2CH2R)
2
[R=H (7), Ph (8)]
A solution of Cp%Nb(CO)(h1-C(O)CH2CH2R) [R=
2
H (5), Ph (6)] (0.75 mmol) in hexane (30 ml) was stirred
for 30 min at r.t. under dry O2. The solvent was
removed under vacuum and the yellow solid was recrys-
tallized from hexane (5 ml) at −40°C. The yellow
crystals were filtered off and identified as 7 or 8,
respectively.
3.1.3.2. Method B. To a solution of Cp%Nb(O)(h1-
2
C(O)CH2CH2R) [R=H (5), Ph (6)] (0.4 mmol) in Et2O
(20 ml) at −78°C, trifluoroacetic acid (10% excess) was
added. Immediately a red precipitate was formed. The
mixture was stirred at r.t. for 3 h. The solid was filtered
off, washed with Et2O and dried under vacuum. Yield
83%. Anal. Calc. for C18H26Si2F3O3Nb: C, 43.54; H,
Complex 7. Yield: 92%. Anal. Calc. for C19H31-
Si2O2Nb: C, 51.81; H, 7.10. Found: C, 51.45; H, 7.00.
IR (Nujol) w (cm−1) 1641 (CꢀO), 1247 (SiMe3), 906
5.28. Found: C, 43.10; H, 5.30. IR (Nujol): w (cm−1
)
1717, 1407 (COO), 1253 (SiMe3), 900 (NbꢀO), 839
1
1
(NbꢀO), 835 (C5H4SiMe3). H-NMR (C6D6): l (ppm)
(C5H4SiMe3). H-NMR (acetone-d6): l (ppm) 0.24 (s,
0.19 (s, 18H, SiMe3), 5.16(2), 5.49(2), 5.50(2), 5.65(2)
(m, C5H4SiMe3), 3.33 [q, J(1H–1H)=7.20 Hz,
CH2CH3], 1.20 [t, J(1H–1H)=7.20 Hz, CH2CH3];
13C{1H}-NMR (C6D6): l (ppm) −0.86 (SiMe3), 9.63
(CH2CH3), 43.57 (CH2CH3), 107.25, 110.30, 111.62,
119.16 (C5H4SiMe3), 113.89 (Cipso), 273.22 (h1-C(O)R).
18H, SiMe3), 6.24(2), 6.66(2), 6.87(4) (m, C5H4SiMe3).
13C{1H}-NMR (acetone-d6): l (ppm) −0.60 (SiMe3),
115.62, 118.19, 120.23, 127.76 (C5H4SiMe3), 131.29
(Cipso), 116.19 [q, 1J(19F–13C)=285.4 Hz, CF3COO],
2
158.80 [q, J(19F–13C)=40.9 Hz, CF3COO]. 19F-NMR
(acetone-d6): l (ppm) −75.79 (CF3COO).

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A. Antin˜olo et al. / Journal of Organometallic Chemistry 598 (2000) 167–173
3.2. Crystal structure determination and refinement of
Acknowledgements
complex Cp%Nb(O)(p1-(O)ꢁOCOCF3) (10)
2
We gratefully acknowledge financial support from
the Direccio´n General de Ensen˜anza Superior e Inves-
tigacio´n Cient´ıfica (Grant No. PB-95-0023-C01-C02)
and the University of Alcala´ (Grant No. E005/98).
Diffraction data were obtained at 298 K on a Non-
ius-Mach3 four-circle diffractometer equipped with a
graphite monochromated MoꢁKa radiation source (u=
,
0.7107 A) using an ꢀ/2q scan technique to a maximum
value of 56°. The compound crystallizes in the mono-
clinic group P21/c with Z=4. There is one molecule of
References
Cp%Nb(O)(h1-(O)ꢁOCOCF3) per asymmetric unit.
2
Parameters for the collection and refinement of diffrac-
tion data are contained in Table 2. Data were corrected
for Lorentz and polarization effects and absorption
correction was not necessary (v=6.72 cm−1).
The structure was solved using direct methods [17]
and refinements on F2 was carried out by full-matrix
least-squares analysis (SHELXL-93) [18]. For the disor-
dered atoms in the acetate ligand, occupancies were
refined initially and then fixed at 0.5. The hydrogen
atoms were included in calculated positions and refined
‘riding’ on their parent carbon atoms.
[1] (a) W.A. Nugent, J.M. Mayer, Metal–Ligand Multiple Bonds,
Wiley, New York, 1988. (b) W.A. Nugent, B.L. Haymore,
Coord. Chem. Rev. 31 (1980) 123. (c) D.E. Wigley, Prog. Inorg.
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[2] (a) A. Antin˜olo, M. Fajardo, C. Lo´pez-Mardomingo, A. Otero,
Y. Mourad, Y. Mugnier, J. Sanz-Aparicio, I. Fonseca, F. Flo-
rencio, Organometallics 9 (1990) 2919. (b) A. Antin˜olo, A.
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(1992) 6579.
[5] A similar behaviour was observed when CO2-containing
niobocene adducts were heated. See: P.F. Fu, M.A. Khan, K.M.
Nicholas, Organometallics 10 (1991) 382.
4. Supplementary material
[6] (a) A. Antin˜olo, M. Fajardo, R. Gil-Sanz, C. Lo´pez-Mar-
domingo, P. Mart´ın-Villa, A. Otero, M.M. Kubicki, Y. Mugnier,
S. Elkrami, Y. Mourad, Organometallics 12 (1993) 381. (b) R.J.
Harrison, M.G.H. Wallbridge, E. DeBoer, D.J. Duncalf, A.
McCamley, J. Organomet. Chem. 568 (1998) 271.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 130274 for compound 10.
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 www: http://
www.ccdc.cam.ac.uk).
[7] H. Brunner, G. Gehart, W. Meier, J. Wachter, A. Riedel, S.
Elkrami, Y. Mugnier, B. Nuber, Organometallics 13 (1994) 134.
1
[8] 3a. H-NMR (acetone-d6): l (ppm) 0.32 (s, 18H, SiMe3), 6.36(2),
6.63(2), 6.72(2), 6.80(2) (m, C5H4SiMe3), 2.40 [q, J(1H–1H)=
6.80 Hz, CH2CH3], 1.69 [t, J(1H–1H)=6.80 Hz, CH2CH3]. 4a:
0.31 (s, 18H, SiMe3), 6.47 (2), 6.81 (4), 7.15 (2) (m, C5H4SiMe3),
2.55 (m, CH2CH2Ph), 3.15 (m, CH2CH2Ph), 7.30 (m,
CH2CH2Ph).
Table 2
Crystal analysis parameters of complex 10
[9] CH3CH3. 1H-NMR (acetone-d6): l (ppm) 0.83, s. CH2ꢀCH2:
5.37, s. PhCH2CH3: 1.23 [t, 3H, J(1H–1H)=7.60 Hz,
PhCH2CH3]; 2.65 [q, 2H, J(1H–1H)=7.60 Hz, PhCH2CH3];
7.20–7.50 (m, 5H, PhCH2CH3). PhCHꢀCH2: 5.20 (d, 1H,
PhCHꢀCH2); 5.80 (d, 1H, PhCHꢀCH2); 6.70 (dd, 1H,
PhCHꢀCH2); 7.20–7.50 (m, 5H, PhCHꢀCH2).
Formula
C18H26F3NbO3Si2
496.48
Formula weight
Crystal size (mm)
Habit
0.3×0.2×0.2
Prismatic
Crystal system
Space group
Unit cell dimensions
Monoclinic
P21/c
[10] B. Thiyagarajan, M.E. Kerr, J.C. Bollinger, V.G. Young, J.W.
Bruno, Organometallics 16 (1997) 1331.
[11] P.F. Fu, M.A. Khan, K.M. Nicholas, Organometallics 11 (1992)
2607.
[12] H. Brunner, J.C. Leblanc, D. Lucas, W. Meier, C. Moise, Y.
Mugnier, B. Nuber, S. Rigny, A. Sadorge, J. Wachter, J.
Organomet. Chem. 566 (1998) 203.
[13] A. Antin˜olo, M. Fajardo, S. Garc´ıa-Yuste, I. del Hierro, A.
Otero, S. Elkrami, Y. Mourad, Y. Mugnier, J. Chem. Soc.
Dalton Trans. (1995) 3409.
,
a (A)
9.671(1)
12.935(2)
18.43(1)
99.03(2)
2276.9(13)
4
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Z
v (cm−1
)
6.72
Reflections collected
Observed reflections
Independent reflections
Index range
5492
3090
5492
[14] (a) A. Antin˜olo, F. Carrillo-Hermosilla, M. Fajardo, S. Garc´ıa-
Yuste, A. Otero, S. Camanyes, F. Maseras, M. Moreno, A.
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A. Otero, S. Prashar, E. Villasen˜or, M. Fajardo, Inorg. Chim.
Acta 259 (1997) 101.
05h512, 05k517,
−245l524
0.778 and −0.591
Largest diff. peak and hole
−3
1
,
(e A
R, Rw
)
[15] 3b. H-NMR (acetone-d6): l (ppm) 0.26 (s, 18H, SiMe3), 6.15(2),
0.062, 0.152
6.34(2), 6.54(2), 6.74(2) (m, C5H4SiMe3), 2.21 [q, J(1H–1H)=
7.22 Hz, CH2CH3], 1.69 [t, J(1H–1H)=7.22 Hz, CH2CH3]. 4b:

A. Antin˜olo et al. / Journal of Organometallic Chemistry 598 (2000) 167–173
173
0.26 (s, 18H, SiMe3), 5.87(2), 6.20(2), 6.37(2), 6.46(2) (m,
C5H4SiMe3), 2.40 (m, CH2CH2Ph), 3.03 (m, CH2CH2Ph), 7.20
(m, CH2CH2Ph).
M.P. Diebold, M. Matusz, W.J. Roth, Inorg. Chim. Acta 112
(1986) 147.
[17] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M.C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr.
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[18] G.M. Sheldrick, Program for the Refinement of Crystal Struc-
tures from Diffraction Data, University of Go¨ttingen, Go¨ttin-
gen, Germany, 1993.
[16] (a) A. Antin˜olo, J. Mart´ınez de Llarduya, A. Otero, P. Royo,
A.M. Manotti Lanfredi, A. Tiripicchio, J. Chem. Soc. Dalton
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Eremenko, V.T. Kalinnikov, G.G. Aleksandrov, Y.T.
Struchkov, J. Organomet. Chem. 165 (1979) 39. (c) F.A. Cotton,
.