The synthesis of alkyl niobocene imido complexes and the X-ray crystal structure of [Nb(=O)Cp2Me] (Cp=η5-C5H5)

Article abstract of DOI:10.1016/S0022-328X(01)01056-7

The following new niobium imido complexes containing alkyl ligands have been prepared and characterised: [Nb(=NBu^t)Cp₂Et] (1), [Nb(=NBu^t)Cp₂(CH₂SiMe₃)] (2), [Nb(=NAr)Cp₂Me] (3),

Full text of DOI:10.1016/S0022-328X(01)01056-7

Journal of Organometallic Chemistry 631 (2001) 151–156
www.elsevier.com/locate/jorganchem
The synthesis of alkyl niobocene imido complexes and the X-ray
crystal structure of [Nb(ꢀO)Cp2Me] (Cp=h5-C5H5)
Antonio Antin˜olo, Isabel Lo´pez-Solera, Antonio Otero *, Sanjiv Prashar
Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica, Facultad de Qu´ımicas, Campus Uni6ersitario, Uni6ersidad de Castilla-La Mancha,
13071 Ciudad Real, Spain
Received 17 April 2001; accepted 29 May 2001
Abstract
The following new niobium imido complexes containing alkyl ligands have been prepared and characterised: [Nb(ꢀNBut)Cp2Et]
(1), [Nb(ꢀNBut)Cp2(CH2SiMe3)] (2), [Nb(ꢀNAr)Cp2Me] (3), [Nb(ꢀNAr)Cp2Et] (4), [Nb(ꢀNAr)Cp2(CH2Ph)] (5),
[Nb(ꢀNAr)Cp2(CH2SiMe3)] (6), [Nb(ꢀNAr)Cp2(CH2CHꢀCH2)] (7) (Cp=h5-C5H5, Ar=C6H4Me-4). The synthetic pathway to
these complexes is by the reaction of the appropriate magnesium reagent MgRCl with the metallocene complexes
[Nb(ꢀNBut)Cp2Cl] or [Nb(ꢀNAr)Cp2Cl]. The hydrolysis of 3 gave the oxo-alkyl complex [Nb(ꢀO)Cp2Me] (8). The molecular
structure of 8 has been determined by X-ray diffraction studies. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Niobium; Imido; Alkyl; Niobocene; Oxo
1. Introduction
2. Results and discussion
Half sandwich complexes are well known in niobium
imido chemistry [1] and to a lesser degree so are their
metallocene counterparts [2]. Our previous studies in
the chemistry of niobium imido complexes have been
centred on substituted metallocene [3], ansa-metal-
locene [4] and alkynyl [5] derivatives. However, in spite
of the broad scope of this chemistry only a handful of
alkyl-containing niobocene imido complexes have pre-
viously been reported [2a,b,4a,6]. Following our re-
search in this field, we have explored the preparation of
new alkyl-containing niobocene species with the non-
substituted cyclopentadienyl ring and this work is fo-
cussed on the synthesis of alkyl niobocene imido
complexes and the preparation and X-ray crystal struc-
ture characterisation of an oxo-alkyl niobocene
complex.
The complexes [Nb(ꢀNBut)Cp2Et] (1), and
[Nb(ꢀNBut)Cp2(CH2SiMe3)] (2) (Cp=h5-C5H5), were
prepared by the reaction of [Nb(ꢀNBut)Cp2Cl] and
MgRCl in THF (Eq. (1)). The methyl and benzyl
derivatives have previously been described by Green et
al. [2a].
(1)
Compounds 1 and 2 were isolated as yellow air-sensi-
tive crystalline solids which were characterised by
NMR spectroscopy. The expected singlet signals for the
1
Cp and But groups in the H-NMR spectra of 1 and 2
were observed. In the case of 2 only a singlet was
observed for the NbꢁCH2 protons indicating their
1
equivalency. In the H-NMR spectrum of 1 the ethyl
group displays an A3BC pattern (JAB=7.0 Hz, JAC
7.5 Hz, JBC=14.0 Hz), similar to that reported previ-
=
* Corresponding author. Tel.: +34-26-295326; fax: +34-26-
295318.
E-mail address: aotero@qino-cr.uclm.es (A. Otero).
ously in three ethyl complexes of niobium [4a,7]. This
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01056-7

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A. Antin˜olo et al. / Journal of Organometallic Chemistry 631 (2001) 151–156
observation indicates the inequivalency of the methyl-
ene protons due to either H-bonding interactions C−
H···N between the alkyl and imido groups, which
restrict rotation about the NbꢁC bond or the presence
of an unusually weak agostic interaction between an
a-hydrogen atom of the ethyl group and the metal
centre. The latter explication is favoured because in
complexes that do not contain electronegative ligands,
e.g. [NbCp2(Et)(RCꢂCR)], the same phenomenon of
possible agostic interactions is observed in the NMR
spectra [7b]. However, it must be pointed out that in
the 13C-NMR spectrum of 1 we were unable to distin-
indicating free rotation of the niobium–carbon bond in
solution. This is also observed in 7 which, furthermore,
shows an AB system for the terminal olefinic protons of
the h1-allyl group (see Section 3) similar to that previ-
ously reported for other h1-allyl niobium complexes
[3d,8].
IR spectroscopy of 1–7 showed a band between 1245
and 1300 cm−1 characteristic of the terminal imido
ligand [1a]. Several vibrational spectroscopic studies of
Group 5 imido complexes have been reported in the
literature [9].
It was found that when 3 reacted with moist O2, the
subsequent hydrolysis reaction took place at the Nb–N
and not the Nb–C bond of the alkyl group. The
oxo-alkyl complex, [Nb(ꢀO)Cp2Me] (8), was isolated by
recrystallisation from a hexane solution. The amine,
H2NC6H4Me-4, was identified by 1H-NMR spec-
troscopy to be the by-product of this reaction (Eq. (3)).
1
guish the two J(13C–1H) constants corresponding to
the CH2 group.
The complexes [Nb(ꢀNAr)Cp2Me] (3), [Nb(ꢀNAr)-
Cp2Et] (4), [Nb(ꢀNAr)Cp2(CH2Ph)] (5), [Nb(ꢀNAr)-
Cp2(CH2SiMe3)]
(6),
and
[Nb(ꢀNAr)Cp2(CH2-
CHꢀCH2)] (7) (Ar=C6H4Me-4), were prepared in a
similar manner to their But analogues 1 and 2 by the
reaction of [Nb(ꢀNAr)Cp2Cl] and MgRCl in THF (Eq.
(2)).
(3)
The molecular structure of 8 was established by
X-ray crystal studies. The molecular structure and the
atom-numbering scheme are shown in Fig. 1 Selected
bond lengths and angles are given in Table 1. This
complex was previously synthesised via the decomposi-
tion of [NbCp2(Me)(ONCH3)] [10]. Several oxo-
niobocene complexes have also been reported [11].
Suitable X-ray quality crystals of 8 were obtained by
the slow evaporation of a hexane solution. The com-
pound crystallises in, P21 space group, monoclinic and
with four distinct molecules in the asymmetric unit. The
niobium atom shows a geometry that is typical for
pseudo-tetrahedral niobocene derivatives. The structure
consists of a typical bent metallocene with distances
between the metal atom and the centroids of the Cp
(2)
Compounds 3–7 were isolated as orange or red
air-sensitive crystalline solids. Their H-NMR spectra
were similar to those recorded for 1 and 2. In 4 the
ethyl group displays the same A3BC pattern observed
for 1. In the H-NMR spectra of compounds 5 and 6,
the CH2 protons of the alkyl group are equivalent
1
1
,
rings of between 2.175 and 2.189 A and the angle
Cent(1)ꢁNb(1)ꢁCent(2) between 127.0 and 128.3°. The
environment of the niobium atom is completed by an
oxygen atom and the carbon atom of the methyl group.
The structure of 8 is similar to that reported for
[Nb(ꢀO)(h5-C5H4SiMe3)2Me] [11h] and [Nb(ꢀO)(h5-
C5H4Me)2(CH2SiMe3)] [11f,g]. The NbꢁO (1.744–1.746
,
,
A) and NbꢁCH3 (2.230–2.247 A) bond distances in 8
are longer and comparable, respectively, to the corre-
sponding bonds found in [Nb(ꢀO)Cp2{C7H5(CF3)2}]
,
[11d] (1.63(3) and 2.27(4) A), containing a s-bonded
substituted norbornadienyl ligand. The lesser d-electron
density on the metal determining the reduced double-
bond character of the NbꢁO distance in 8 can be
Fig. 1. Molecular structure and atom-labelling scheme for
[Nb(ꢀO)Cp2Me] (8), with thermal ellipsoids at 10% probability.

A. Antin˜olo et al. / Journal of Organometallic Chemistry 631 (2001) 151–156
153
Table 1
,
to 2.72 A [13]. The C−H···O angles (153.0–170.7°)
show a linear disposition.
,
Selected bond lengths (A) and bond angles (deg) for [Nb(ꢀO)Cp2Me]
(8)
In conclusion we report the synthesis of new alkyl
niobocene imido complexes by the reaction of the ap-
propriate halide niobocene imido complexes with the
corresponding Grignard reagents, the reactivity of one
of these complexes with O2 to give an oxo-containing
niobocene species as well as the X-ray crystal structure
of the isolated oxo-niobocene complex [Nb(ꢀO)Cp2Me].
a
b
c
d
Bond lengths
Nb(1)ꢁCent(1)
Nb(1)ꢁCent(2)
Av. Nb(1)ꢁC(11–15)
Av. Nb(1)ꢁC(16–20)
Nb(1)ꢁC(1)
2.186
2.178
2.479
2.469
2.182
2.189
2.473
2.476
2.179
2.186
2.469
2.474
2.185
2.175
2.475
2.463
2.247(8) 2.230(8) 2.237(8) 2.239(8)
1.744(5) 1.746(5) 1.746(5) 1.746(5)
Nb(1)ꢁO(1)
3. Experimental
Bond angles
Cent(1)ꢁNb(1)ꢁCent(2) 127.0
C(1)ꢁNb(1)ꢁCent(1)
C(1)ꢁNb(1)ꢁCent(2)
O(1)ꢁNb(1)ꢁCent(1)
O(1)ꢁNb(1)ꢁCent(2)
C(1)ꢁNb(1)ꢁO(1)
128.3
102.1
102.9
110.8
110.8
95.7(3)
128.0
102.2
103.3
110.6
111.0
95.6(3)
127.2
102.5
104.0
110.4
111.4
95.5(3)
102.6
103.8
110.7
111.4
95.5(3)
3.1. General procedures
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 letters a, b, c and d refer to the four distinct molecules in the
asymmetric unit. Cent(1) and Cent(2) are the centroids of
C(11)ꢁC(15) and C(16)ꢁC(20), respectively.
IR spectra were recorded on a Perkin–Elmer PE 883
IR spectrophotometer. H- and 13C-NMR spectra were
1
recorded on Varian FT-300 and Varian Gemini FT-200
spectrometers and referenced to the residual deuteriated
solvent. Microanalyses were carried out with a Perkin–
Elmer 2400 microanalyser. Tethrahydrofuran or Et2O
solutions of MgRCl (R=Me, Et, CH2Ph, CH2SiMe3
and CH2CHꢀCH2) were purchased from Aldrich and
used directly. [NbCp2(ꢀNBut)Cl] [2a] was prepared as
described earlier. [Nb(ꢀNAr)Cp2Cl] was prepared by
the reaction of two equivalents of NaCp with
[Nb(ꢀNAr)Cl3(DME)] in THF (key data: 1H-NMR
(200 MHz, C6D6): l 2.16 (s, 3H, NC6H4CH3), 5.80 (s,
10H, C5H5), 6.49 (2H), 6.94 (2H) (d, NC6H4CH3) (J=
8.1 Hz)).
attributable to the smaller s-donating character of the
methyl group with respect to that of the norbornadienyl
ligand. The greater steric demand of this latter ligand
seems to explain the larger OꢁNbꢁC angle (99(5)°)
compared with that observed in 8 (95.5–95.7°). A
comparison of 8 with related oxo-niobocene complexes
is given in Table 2.
Hydrogen bond interactions between oxygen and
CꢁH groups have been reported [12]. We have found
that this kind of interaction also exists in niobocene
complexes that have previously been described by our
research group [11h]. The crystal is stabilised by an
extensive hydrogen-bonding network (see Table 3 and
Fig. 2). Each oxygen is involved in two hydrogen bonds
with the cyclopentadienyl ring protons of other
molecule. The C−H···O hydrogen bond distances are
3.2. Synthesis of [Nb(ꢀNBut)Cp2Et] (1)
A 2 M solution of MgEtCl in Et2O (0.64 ml, 1.28
mmol) was added to
a
stirring solution of
[Nb(ꢀNBut)Cp2Cl] (0.35 g, 1.07 mmol) in THF (25 ml)
at −78 °C. The yellow solution was allowed to warm
,
between 2.42 and 2.52 A, slightly shorter than the sum
of the van der Waals radii of H and O which is equal
Table 2
Comparison of structural data of oxo-niobocene complexes
,
Complex
NbꢀO (A)
CpꢁNbꢁCp (°)
OꢁNbꢁX (°)
Ref.
[Nb(ꢀO)Cp2Cl]
1.737(6)
1.63(3)
128.2(1)
127.2
129.1(1)
131.0(1)
126.5(5)
136.3
98.4
99(5)
99.6
97.3(1)
95.0(6)
97.9(1)
95.6(3)
99.7(2)
98.95(7)
98.41(4)
[11c]
[11d]
[11e]
[11f,g]
[11h]
[11i]
This work
[11j]
[11k]
[11k]
[Nb(ꢀO)Cp2{C7H5(CF3)2}]
[Nb(ꢀO)(h5-C5H4Me)2Cl]
[Nb(ꢀO)(h5-C5H4Me)2(CH2SiMe3)]
[Nb(ꢀO)(h5-C5H4SiMe3)2Me]
[Nb(ꢀO)(h5-C5Me5)2(OC(O)H)]
1.732(1)
1.741(3)
1.720(7)
1.738(3)
1.745(5)
1.718(4)
1.7366(17)
1.7413(11)
a
[Nb(ꢀO)Cp2Me]
127.6
[Nb(ꢀO)(h5-C5H4SiMe3)2(OC(O)CF3)]
[Nb(ꢀO)(h5-C5H4Pri)2Cl]
127.35(3)
129.22(6)
129.28(7)
[Nb(ꢀO)(h5-C5H4But)(h5-C5H4Me)Cl]
a Average value.

154
A. Antin˜olo et al. / Journal of Organometallic Chemistry 631 (2001) 151–156
Table 3
,
Hydrogen bond distances (A) and bond angles (°) for 8
a
D−H···A
d(DꢁH)
d(H···A)
d(D···A)
Ú(DHA)
Symmetry
C(14A)−H(14A)···O(1C)
C(15A)−H(15A)···O(1A)
C(14B)−H(14B)···O(1D)
C(15B)−H(15B)···O(1B)
C(14C)−H(14C)···O(1A)
C(15C)−H(15C)···O(1C)
C(14D)−H(14D)···O(1B)
C(15D)−H(15D)···O(1D)
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.93
2.51
2.43
2.51
2.43
2.51
2.43
2.52
2.42
3.37(1)
3.34(1)
3.37(1)
3.35(1)
3.37(1)
3.35(1)
3.37(1)
3.34(1)
153.5
167.0
153.1
170.7
153.3
171.0
153.0
167.8
−x, y+1/2, 1−z
x−1, y, z
1−x, y+1/2, −z
x−1, y, z
1−x, y−1/2, 1−z
x+1, y, z
2−x, y−1/2, −z
x+1, y, z
a Symmetry operation for A.
to room temperature (r.t.) and stirred for 15 h. Solvent
was removed in vacuo and the remaining yellow oil
extracted in hexane (50 ml). A yellow crystalline solid
was obtained by concentrating (5 ml) and cooling (−
30 °C) the solution (0.25 g, 74%). IR (Nujol mull,
3.5. Synthesis of [Nb(ꢀNAr)Cp2Et] (4)
The synthesis of 4 was carried out in an identical
manner to that of 1 with a 2 M solution of MgEtCl in
Et2O (0.54 ml, 1.08 mmol) and [Nb(ꢀNAr)Cp2Cl] (0.33
g, 0.90 mmol). Yield 0.24 g, 75%. IR (Nujol mull,
1
cm−1): wNbꢀN 1280. H-NMR (200 MHz, C6D6): l 0.94
1
(s, 9H, C(CH3)3), 1.80 (q, 2H, CH2CH3), 1.88 (t, 3H,
CH2CH3), 5.49 (s, 10H, C5H5). 13C{1H}-NMR (300
MHz, C6D6): l 19.80 (CH2CH3), 22.39 (CH2CH3),
31.05 (C(CH3)3), 69.42 (C(CH3)3), 107.59 (C5H5). Anal.
Found: C, 59.28; H, 7.41; N, 4.33. Calc. for
C16H24NNb: C, 59.45; H, 7.48; N, 4.33%.
cm−1): wNbꢀN 1290. H-NMR (200 MHz, C6D6): l 1.80
(q, 2H, CH2CH3), 1.93 (t, 3H, CH2CH3), 2.17 (s, 3H,
NC6H4CH3), 5.43 (s, 10H, C5H5), 6.48 (2H), 6.94 (2H)
(d, NC6H4CH3) (J=8.20 Hz). 13C{1H}-NMR (300
MHz, C6D6): l 20.94 (CH2CH3), 26.76 (CH2CH3),
22.45 (NC6H4CH3), 107.63 (C5H5), 118.71, 129.07,
129.72 (CMe), 132.45 (CN) (NC6H4CH3). Anal.
Found: C, 63.61; H, 6.12; N, 4.00. Calc. for
C19H22NNb: C, 63.87; H, 6.21; N, 3.92%.
3.3. Synthesis of [Nb(ꢀNBut)Cp2(CH2SiMe3)] (2)
The synthesis of 2 was carried out in an identical
manner to that of 1 with a 1 M solution of
Mg(CH2SiMe3)Cl in Et2O (1.20 ml, 1.20 mmol) and
[Nb(ꢀNBut)Cp2Cl] (0.33 g, 1.00 mmol). Yield 0.23 g,
61%. IR (Nujol mull, cm−1): wNbꢀN 1290. 1H-NMR
(200 MHz, C6D6): l 0.32 (s, 9H, CH2SiMe3), 0.60 (s,
2H, CH2SiMe3), 0.91 (s, 9H, C(CH3)3), 5.58 (s, 10H,
C5H5). 13C{1H}-NMR (300 MHz, C6D6): l 3.85
(SiMe3), 30.77 (C(CH3)3), 30.9 (CH2), 69.34 (C(CH3)3),
107.80 (C5H5). Anal. Found: C, 56.37; H, 7.84; N, 3.63.
Calc. for C18H30NNbSi: C, 56.68; H, 7.93; N, 3.67%.
3.6. Synthesis of [Nb(ꢀNAr)Cp2(CH2Ph)] (5)
The synthesis of 5 was carried out in an identical
manner to that of 1 with a 1 M solution of
3.4. Synthesis of [Nb(ꢀNAr)Cp2Me] (3)
The synthesis of 3 was carried out in an identical
manner to that of 1 with a 3 M solution of MgMeCl in
THF (0.36 ml, 1.08 mmol) and [Nb(ꢀNAr)Cp2Cl] (0.33
g, 0.90 mmol). Yield 0.24 g, 77%. IR (Nujol mull,
1
cm−1): wNbꢀN 1300. H-NMR (200 MHz, C6D6): l 0.95
(s, 3H, Me), 2.16 (s, 3H, NC6H4CH3), 5.43 (s, 10H,
C5H5), 6.47 (2H), 6.93 (2H) (d, NC6H4CH3) (J=8.26
Hz). 13C{1H}-NMR (300 MHz, C6D6): l 3.95 (Me),
20.75 (NC6H4CH3), 108.69 (C5H5), 118.55, 129.00
(CMe), 129.25, 131.52 (CN) (NC6H4CH3). Anal.
Found: C, 62.79; H, 5.76; N, 4.01. Calc. for
C18H20NNb: C, 62.98; H, 5.87; N, 4.08%.
Fig. 2. Hydrogen bonding in [Nb(ꢀO)Cp2Me] (8).

A. Antin˜olo et al. / Journal of Organometallic Chemistry 631 (2001) 151–156
155
Mg(CH2Ph)Cl in Et2O (1.10 ml, 1.10 mmol) and
[Nb(ꢀNAr)Cp2Cl] (0.34 g, 0.92 mmol). Yield 0.32 g,
82%. IR (Nujol mull, cm−1): wNbꢀN 1260. 1H-NMR
(200 MHz, C6D6): l 2.18 (s, 3H, NC6H4CH3), 3.15 (s,
2H, CH2Ph), 5.35 (s, 10H, C5H5), 6.54 (2H), 6.96 (2H)
(d, NC6H4CH3) (J=8.3 Hz), 6.86–6.99, 7.19–7.37 (m,
5H, CH2Ph). 13C{1H}-NMR (300 MHz, C6D6): l 22.75
(NC6H4CH3), 34.87 (CH2Ph), 109.33 (C5H5), 121.67
(C1), 128.00, 129.18, 130.31 (CH2Ph), 118.95, 129.00,
129.97 (CMe), 132.75 (CN) (NC6H4CH3). Anal.
Found: C, 68.51; H, 5.70; N, 3.33. Calc. for
C24H24NNb: C, 68.74; H, 5.77; N, 3.34%.
(−30 °C) the solution (0.12 g, 75%). IR (Nujol mull,
1
cm−1): wNbꢀO 910. H-NMR (200 MHz, C6D6): l 1.06
(s, 3H, Me), 5.47 (s, 10H, C5H5). 13C{1H}-NMR (300
MHz, C6D6): l 3.16 (Me), 107.50 (C5H5). Anal. Found:
C, 51.73; H, 5.07. Calc. for C11H13NbO: C, 51.99; H,
5.16%.
3.10. X-ray crystal structure determination for
[Nb(ꢀO)Cp2Me] (8)
Intensity data were collected on a NONIUS-MACH3
diffractometer equipped with a graphite monochroma-
,
tor Mo–Ka radiation (u=0.71073 A) using the ꢀ–2q
3.7. Synthesis of [Nb(ꢀNAr)Cp2(CH2SiMe3)] (6)
scan technique. The final unit cell parameters were
determined from 25 well-centred peaks and refined by
least-squares method. The structures were solved by
direct methods using the SHELXS computer program
[14] and refined on F2 by full-matrix least-squares
The synthesis of 6 was carried out in an identical
manner to that of 1 with a 1 M solution of
Mg(CH2SiMe3)Cl in Et2O (1.10 ml, 1.10 mmol) and
[Nb(ꢀNAr)Cp2Cl] (0.34 g, 0.92 mmol). Yield 0.26 g,
67%. IR (Nujol mull, cm−1): wNbꢀN 1270. 1H-NMR
(200 MHz, C6D6): l 0.29 (SiMe3), 0.66 (s, 2H,
CH2SiMe3), 2.12 (s, 3H, NC6H4CH3), 5.51 (s, 10H,
C5H5), 6.50 (2H), 6.94 (2H) (d, NC6H4CH3) (J=8.3
Hz). 13C{1H}-NMR (300 MHz, C6D6): l 3.39 (SiMe3),
31.9 (CH2SiMe3), 20.93 (NC6H4CH3), 108.24 (C5H5),
119.47, 129.15, 130.12 (CMe), 131.53 (CN)
(NC6H4CH3). Anal. Found: C, 60.46; H, 6.70; N, 3.31.
Calc. for C21H28NNbSi: C, 60.71; H, 6.79; N, 3.37%.
(
SHELXL-97) [15]. All non-hydrogen atoms were refined
with anisotropic thermal parameters. The hydrogen
atoms were included in calculated positions and
were refined with an overall isotropic temperature
factor using a riding model. Weights were optimised
in the final cycles. Crystallographic data are given in
Table 4.
Table 4
Crystal data and structure refinement parameters for [Nb(ꢀO)Cp2Me]
(8)
3.8. Synthesis of [Nb(ꢀNAr)Cp2(CH2CHꢀCH2)] (7)
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
C11H13NbO
254.12
293(2)
Monoclinic
P21
The synthesis of 7 was carried out in an identical
manner to that of 1 with a 2 M solution of
Mg(CH2CHCH2)Cl in THF (0.56 ml, 1.12 mmol) and
[Nb(ꢀNAr)Cp2Cl] (0.34 g, 0.93 mmol). Yield 0.27 g,
77%. IR (Nujol mull, cm−1): wNbꢀN 1245. 1H-NMR
(200 MHz, C6D6): l 2.17 (s, 3H, NC6H4CH3), 2.68 (d,
2H, CH2ꢁCHꢀCH2) 3J(1H–1H)=8.3 Hz, 4.78 (cis),
,
a (A)
6.366(1)
,
b (A)
15.803(1)
20.506(1)
2062.9(4)
2
1.636
1.123
,
c (A)
3
2
,
4.91 (trans) (dd, 2H, CH2ꢁCHꢀCH2) Jgem(1H–1H)=
V (A )
Z
3
3
2.5 Hz, Jcis(1H–1H)=9.9 Hz, Jtrans(1H–1H)=16.8
Hz, 5.45 (s, 10H, C5H5), 6.40 (m, 1H, CH2ꢁCHꢀCH2),
6.44 (2H), 6.95 (2H) (d, NC6H4CH3) (J=8.2 Hz).
Dcalc (g cm−3
)
Absorption coefficient (mm−1
F(000)
)
1024
13C{1H}-NMR
(300
MHz,
C6D6):
l
21.50
Crystal size (mm)
Theta range for data collection (°)
Index ranges
0.2×0.1×0.1
2.37–27.98
−85h58, 05k520,
05l527
5271
(NC6H4CH3), 36.93 (CH2ꢁCHꢀCH2), 107.79 (C5H5),
102.96 (CH2ꢁCHꢀCH2), 155.31 (CH2ꢁCHꢀCH2),
120.03, 129.15, 130.03 (CMe), 131.53 (CN)
(NC6H4CH3). Anal. Found: C, 64.79; H, 5.93; N, 3.77.
Calc. for C20H22NNb: C, 65.05; H, 6.00; N, 3.79%.
Reflections measured
Reflections observed
Independent reflections
Final R indices [I\2|(I)]
4142
5147
R1=0.0301 a,
wR2=0.0592 b
−0.1(6)
3.9. Synthesis of [Nb(ꢀO)Cp2Me] (8)
Flack parameter
Goodness-of-fit on F2
1.037
Largest difference peak and hole
0.678 and −0.809
A solution of 3 (0.24 g, 0.70 mmol) in hexane (25 ml)
was stirred for 30 min at r.t., under 1 atm of O2. A
colour change was observed from red to yellow. Crys-
tals were obtained by concentrating (5 ml) and cooling
−3
,
(e A
)
a R1=ꢀ ꢁ ꢁFoꢁ−ꢁFcꢁ ꢁ/ꢀ ꢁFoꢁ.
b wR2=[ꢀ [w(Fo2−Fc2)2]/ꢀ [w(F2o)2]]0.5
.

156
A. Antin˜olo et al. / Journal of Organometallic Chemistry 631 (2001) 151–156
(c) Z. Modarres, D. Lucas, Y. Mugnier, A. Antin˜olo, A. Otero,
4. Supplementary material
M. Fajardo, A. Garces, C. Lo´pez-Mardomingo, J. Organomet.
Chem. 548 (1997) 309;
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 161085 for compound 8.
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).
(d) A. Antin˜olo, M. Fajardo, C. Huertas, A. Otero, S. Prashar,
A.M. Rodriguez, J. Organomet. Chem. 585 (1999) 154.
[4] (a) A. Antin˜olo, A. Otero, S. Prashar, A.M. Rodriguez,
Organometallics 17 (1998) 5454;
(b) A. Antin˜olo, I. Lo´pez-Solera, I. Orive, A. Otero, S. Prashar,
A.M. Rodriguez, E. Villasen˜or, Organometallics 20 (2001) 71.
[5] A. Antin˜olo, M. Fajardo, C. Lo´pez-Mardomingo, I. Lo´pez-Sol-
era, A. Otero, Y. Pe´rez, S. Prashar, Organometallics (2001), in
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[6] (a) A. Antin˜olo, F. Carrillo-Hermosilla, A. Otero, M. Fajardo,
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(b) M.J. Humphries, M.L.H. Green, R.E. Douthwaite, L.H.
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(b) H. Yasuda, H. Yamamoto, T. Arai, A. Nakamura, J. Chen,
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Acknowledgements
We gratefully acknowledge financial support from
the Direccio´n General de Ensen˜anza Superior e Inves-
tigacio´n Cient´ıfica, Spain (Grant. No. PB 98-0159-C02-
01-02), and a fellowship to S.P. under the Programa
Nacional de Formacio´n de Personal Investigador.
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M.D. Hopkins, Inorg. Chem. 36 (1997) 5530.
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(1980) 1888.
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