Sandwich and half-sandwich niobium imido complexes: X-ray crystal structure of [Nb(=NAr)Cp′2Cl] (Cp′=η5-C5H4SiMe3, Ar=C6H4OMe-4)

Article abstract of DOI:10.1016/S0022-328X(99)00208-9

The imido niobium complexes [Nb(=NAr)Cl₃(dme)] (Ar=C₆H₄Me-4 (1), C₆H₄OMe-4 (2)) have been prepared and characterised. The half-sandwich complex [Nb(=NBu^t)CpCl₂] (3) (Cp=η⁵-C₅H₅) has been synthesised by a new method via the reaction of NaCp and [Nb(=NBu^t)Cl₃(py)₂] and in a similar manner the novel complex [Nb(=NC₆H₄Me-4)CpCl₂] (4) was prepared by the reaction of NaCp with 1. The preparation of [Nb(=NBu^t)Cp′Cl₂] (5) (Cp′=η⁵-C₅H₄SiMe₃) yielded an essentially inseparable mixture of 5 and [Nb(=NBu^t)Cp′₂Cl] (6). The imido niobocene(V) complex 6 was prepared and isolated as the unique product by a new synthetic pathway via the reaction of two equivalents of LiCp′ and [Nb(=NBu^t)Cl₃(py)₂] and in a similar manner the novel complexes [Nb(=NAr)Cp′₂Cl] (Ar=C₆H₄Me-4 (7), C₆H₄OMe-4 (8)) were prepared. The molecular structure of 8 has been determined by X-ray diffraction studies. The mixed metallocene complex [Nb(=NBu^t)CpCp′Cl] (9) was prepared by the reaction of Li(C₅H₄SiMe₃) and 3. The alkylation of 6-8 by ClMgCH₂CH=CH₂ yielded the η¹-allyl complexes [Nb(=NR)Cp′₂(CH₂CH=CH₂)] (R=Bu^t (10), C₆H₄Me-4 (11), C₆H₄OMe-4 (12)).

Full text of DOI:10.1016/S0022-328X(99)00208-9

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 585 (1999) 154–161
Sandwich and half-sandwich niobium imido complexes: X-ray crystal
structure of [Nb(ꢀNAr)Cp%Cl] (Cp%=h5-C5H4SiMe3,
2
Ar=C6H4OMe-4)
Antonio Antin˜olo a, Mariano Fajardo b, Carmen Huertas a, Antonio Otero a,*,
Sanjiv Prashar a, Ana M. Rodriguez a
a Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica, Facultad de Qu´ımicas, Campus Uni6ersitario,
Uni6ersidad de Castilla-La Mancha, E-13071 Ciudad Real, Spain
b Departamento de Qu´ımica Inorga´nica, Campus Uni6ersitario, Uni6ersidad de Alcala´, Alcala´ de Henares E-28871 Madrid, Spain
Received 9 March 1999; received in revised form 8 April 1999
Abstract
The imido niobium complexes [Nb(ꢀNAr)Cl3(dme)] (Ar=C6H4Me-4 (1), C6H4OMe-4 (2)) have been prepared and character-
ised. The half-sandwich complex [Nb(ꢀNBut)CpCl2] (3) (Cp=h5-C5H5) has been synthesised by a new method via the reaction
of NaCp and [Nb(ꢀNBut)Cl3(py)2] and in a similar manner the novel complex [Nb(ꢀNC6H4Me-4)CpCl2] (4) was prepared by the
reaction of NaCp with 1. The preparation of [Nb(ꢀNBut)Cp%Cl2] (5) (Cp%=h5-C5H4SiMe3) yielded an essentially inseparable
mixture of 5 and [Nb(ꢀNBut)Cp%2Cl] (6). The imido niobocene(V) complex 6 was prepared and isolated as the unique product by
a new synthetic pathway via the reaction of two equivalents of LiCp% and [Nb(ꢀNBut)Cl3(py)2] and in a similar manner the novel
complexes [Nb(ꢀNAr)Cp%2Cl] (Ar=C6H4Me-4 (7), C6H4OMe-4 (8)) were prepared. The molecular structure of 8 has been
determined by X-ray diffraction studies. The mixed metallocene complex [Nb(ꢀNBut)CpCp%Cl] (9) was prepared by the reaction
of Li(C5H4SiMe3) and 3. The alkylation of 6–8 by ClMgCH2CHꢀCH2 yielded the h1-allyl complexes
[Nb(ꢀNR)Cp2%(CH2CHꢀCH2)] (R=But (10), C6H4Me-4 (11), C6H4OMe-4 (12)). © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Niobium; Imido; Allyl; Niobocene; Half-sandwich
synthesised by either the reaction of [{Cp%NbCl}2]
2
1. Introduction
with the amine or by heating a toluene solution of
[NbCp%(PhNCO)Cl] [2]. [Nb(ꢀNBut)Cp2Cl] was pre-
2
Half-sandwich complexes are well known in nio-
pared by the reaction of NaCp with the half-sand-
bium imido chemistry [1]. The principle synthetic
wich complex Nb(ꢀNBut)CpCl2 (Cp=h5-C5H5) [3].
route is the reaction of [Nb(h5-C5R5)Cl4] with the ap-
propriate amine, H2NR%, or NR%(SiMe3)2 to yield
[Nb(ꢀNR%)(h5-C5R5)Cl2]. Bent imido metallocene com-
plexes of niobium to date have not been widely stud-
ied and have generally been prepared by various
The
hydrazido
complexes
[Nb(ꢀNNMe2)(h5-
C5H4R)2Cl] (R=H, Me) were prepared in a similar
manner from their half-sandwich analogue [4]. Mixed
cyclopentadienyl (Cp) niobocene imide complexes
have been reported in two cases, namely [Nb(ꢀ
NNMe2)Cp(h5-C5H4Me)Cl] [4] and [Nb(ꢀNBut)Cp(h5-
C5Me5)Cl] [3b]. Ansa-complexes of the type
[Nb(ꢀNR)Cp{(h5-C5H4)CMe2(h1-C5H4)}] have also
been reported [4,5]. This paper will focus on the syn-
thesis and structural details of new families of half-
sandwich and sandwich niobium imido complexes.
methods. [Nb(ꢀNPh)Cp%Cl] (Cp%=h5-C5H4SiMe3) was
2
* Corresponding author. Fax: +34-926-295318.
E-mail address: aotero@qino-cr.uclm.es (A. Otero)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00208-9

A. Antin˜olo et al. / Journal of Organometallic Chemistry 585 (1999) 154–161
155
2. Results and discussion
The preparation of the niobium imido complexes
[Nb(ꢀNAr)Cl3(dme)] (Ar=C6H4Me-4 (1), C6H4OMe-4
(2)) was carried out by a modification of the method
reported for the synthesis of other niobium and tanta-
lum halide imido compounds [6]. In this reaction (Eq.
(1)) the pyridine acts as a base, dme as a donating
ligand and ZnCl2 abstracting halide and forming an
insoluble salt, in CH2Cl2, with HPy+ thus facilitating
its removal. The complexes 1 and 2 were isolated as red
air-sensitive solids and were characterised by spectro-
Scheme 1.
1
scopic methods. Their H-NMR spectra showed clearly
the inequivalence of the methyl and methylene groups
of the dme adduct (see Section 3) suggesting, for an
octahedral disposition, that this ligand is bonded to the
metal centre by two Nb–O links in which one oxygen
atom is located cis to the imide group and the other
oxygen atom trans (Fig. 1). This has previously been
observed in other complexes of this type [6,7].
(2)
Using this same method the half-sandwich imido
complex [Nb(ꢀNC6H4Me-4)CpCl2] (4) was prepared
(Eq. (3)). Complex 4 was characterised by spectroscopic
1
methods. In the H spectrum of 4 two singlets at 2.12
and 5.75 ppm corresponding to the methyl protons of
p-tolyl and the Cp protons, respectively and two dou-
blets at 6.46 and 6.88 ppm associated with the phenylic
protons of the p-tolyl group were observed. The inte-
grals of these signals are in agreement with the mono-
substitution of the Cp ligand (see Section 3).
(1)
The half-sandwich niobium imido complex
[Nb(ꢀNBut)CpCl2] (3) was prepared by the reaction of
[Nb(ꢀNBut)Cl3(py)2] [8] and NaCp in THF (Eq. (2))
and isolated in yields of 80%. This complex was previ-
ously prepared by the addition of NH(But)(SiMe3) to
[NbCpCl4] and the subsequent elimination of SiMe3Cl
and HCl [1a]. The reaction depicted in Eq. (2) offers an
alternative and more facile route to 3 as both starting
components, NaCp and [Nb(ꢀNBut)Cl3(py)2], are easily
prepared.
(3)
In order to prepare the half-sandwich complex
[Nb(ꢀNBut)Cp%Cl2] (5) using the trimethylsilyl substi-
tuted Cp ligand, the reaction of one equivalent of LiCp%
with [Nb(ꢀNBut)Cl3(py)2] was carried out. When this
reaction mixture in THF was stirred at room tempera-
ture (r.t.) for 24 h, a yellow oil was isolated which, by
1H-NMR spectroscopy, was shown to be a mixture, in
proportion ca. 1:1, of 5 and the disubstituted analogue
[Nb(ꢀNBut)Cp%Cl] (6). The reaction was repeated at
2
low temperature and only stirred for 2 h. After appro-
priate work up the only product isolated was that of 6.
With this observation we propose that the reaction
initially commences with the rapid formation of the
bis-Cp complex 6. This is then followed by the slow
reaction of 6 with [Nb(ꢀNBut)Cl3(py)2], which yields
the half-sandwich complex 5. The direct reaction of 6
with [Nb(ꢀNBut)Cl3(py)2], stirred in THF for 24 h at
r.t. yielded 5 and endorses the proposed mechanism
(Scheme 1).
Complex 5 was characterised by spectroscopic meth-
ods. H-NMR spectroscopy showed that only one Cp%
Fig. 1. Proposed structure of [Nb(ꢀNAr)Cl3(dme)] (Ar=C6H4Me-4
(1), C6H4OMe-4 (2)).
1

156
A. Antin˜olo et al. / Journal of Organometallic Chemistry 585 (1999) 154–161
ligand was incorporated in 5 and this was confirmed by
the AA%BB% system observed for the Cp% ring protons,
two multiplets at 6.11 and 6.35 ppm. The symmetry of
5 means that for the Cp% ring protons that H2 and H5,
and H3 and H4 become equivalent. In the case of the
bis-Cp% complex 6 an ABCD system is observed due to
the inequivalency of the Cp% ring protons although a
plane of symmetry makes the two Cp% rings equivalent,
thus giving four multiplets for the eight ring protons.
Complex 6 can be synthesised directly by the reaction
of two equivalents of LiCp% with [Nb(ꢀNBut)Cl3(py)2]
plexes, linear Nb–N–Cipso geometries are observed (see
Table 2). However, in 8, the angle Nb(1)–N(1)–C(1),
163.0(2)° deviates from linear. The bent arrangement
could indicate that the imido nitrogen is sp2-hybridised,
but in such a case the anisole substituent would be
orientated out of the equatorial plane towards one of
the Cp ligands [9]. However, the phenyl substituent of
the imido group is situated practically in the equatorial
plane. The phenyl plane forms an angle of 175.81(9)°
with the equatorial plane defined by the atoms Cl(2)–
Nb(1)–N(1)
similar
to
that
observed
in
[Nb(ꢀNPh)Cp%Cl] [2] and [Ta(ꢀNPh)(h5-C5Me5)2H] [9].
1
in yields of ca. 80%. H-NMR spectroscopy shows 6 to
2
Deviation from linear of the Nb–N–Cipso angles has
been reported for some niobocene imido complexes and
is normally in the range of 12–15° (see Table 2). These
complexes in general contain aryl-imido and/or steri-
be the unique product isolated after work up. This
compound was previously prepared by either the reac-
tion of [{NbCp%Cl}2] with the amine or by heating a
2
toluene solution of [NbCp%(ButNCO)Cl] [2]. The
2
cally
demanding
ligands.
In
the
case
of
niobocene(V) imido complexes [Nb(ꢀNAr)Cp%Cl]
2
[Nb(ꢀNPh)Cp%Cl] extended-Hu¨ckel MO calculations es-
(Ar=C6H4Me-4 (7), C6H4OMe-4 (8)) were synthesised
2
tablished that the imido bond angles for ‘linear imide’
in this class of complexes can vary until 140° with little
effect on the Nb–N bonding [2]. Therefore we propose
that in 8 the nitrogen atom is sp-hybridised and that the
two limiting descriptions proposed by Bercaw and co-
workers [9a], for [Ta(ꢀNPh)(h5-C5Me5)2H] may explain
the true bonding situation.
in a similar manner (Eq. (4)) and characterised by
1
spectroscopic methods. Their H-NMR spectra showed
them to be unique complexes and were similar to the
spectrum recorded for 6, namely four multiplets for the
Cp% ring protons and a singlet corresponding to the
SiMe3 groups. In addition the expected signals for the
aryl-imido group were observed.
,
The Nb(1)–N(1) bond distance of 1.787(3) A is at
the upper limit for those observed for niobium imido
,
complexes (1.73–1.80 A) (see Table 2) and is indicative
of a Nb–N triple bond. The formal electron count is 20
(4)
The molecular structure of 8 was established by
X-ray crystal studies. The molecular structure and
atomic numbering scheme are shown in Fig. 2. Selected
bond lengths and angles are given in Table 1.
Suitable X-ray-quality crystals of 8 were obtained by
the slow evaporation of a toluene solution. The com-
pound crystallises in the P21/n space group, monoclinic
and with four molecules in the unit cell. The structure
consists of a typical bent metallocene with distances
between the metal atom and the centroids of the Cp
,
rings of 2.189(1) and 2.1880(5) A and the angle
Cent(1)–Nb(1)–Cent(2) 125.23(2)°. The orientation of
the Cp rings is between eclipsed and staggered as
indicated by the value of the torsion angle Si(3)–
Cent(1)–Cent(2)–Si(4) of 24°.
The imide ligand is able to act as either a two or four
electron donor. In the first case the nitrogen atom
would be sp2-hybridised and therefore results in the
bending back of the imide substituent. In the second
case the nitrogen would be sp-hybridised and the
metal–nitrogen-substituent angle linear. In the struc-
tures previously reported for niobocene imido com-
Fig. 2. Molecular structure and atom-labelling scheme for
[Nb(ꢀNAr)Cp%2Cl] (8) (Cp%=h5-C5H4SiMe3, Ar=C6H4OMe-4).

A. Antin˜olo et al. / Journal of Organometallic Chemistry 585 (1999) 154–161
157
Table 1
Selected bond lengths (A) and angles (°) for complex 8
Table 3
a
,
Comparison of Nb–Cent distances in selected Cp%-containing
niobocene complexes
Nb(1)–N(1)
1.787(3)
2.457(3)
2.189(1)
2.188(1)
2.506(3)
2.539(4)
2.544(4)
2.429(4)
2.458(4)
Nb(1)–C(21)
Nb(1)–C(22)
Nb(1)–C(23)
Nb(1)–C(24)
Nb(1)–C(25)
N (1)–C(1)
C(4)–O(1)
2.486(3)
2.527(4)
2.553(4)
2.480(4)
2.429(4)
1.379(4)
1.370(4)
1.423(6)
Nb(1)–Cl(2)
Nb(1)–Cent(1)
Nb(1)–Cent(2)
Nb(1)–C(11)
Nb(1)–C(12)
Nb(1)–C(13)
Nb(1)–C(14)
Nb(1)–C(15)
Compound
Average Nb–Cent a Ref.
,
(A)
[Nb(ꢀNC6H4OMe-4)Cp%2Cl] (8) 2.189
This work
[2]
[14]
[17]
[14]
[Nb(ꢀNPh)Cp2% Cl]
[{NbCp2% Cl}2(m-1,3-N2C6H4)]
[Nb(ꢀO)Cp2% Me]
2.180
2.188
2.181
2.121
2.07
C(7)–O(1)
[NbCp2% Cl(h2-N,C-OCNPh)]
[{NbCp2% Cl}2]
[2]
Cent(1)–Nb(1)–Cent(2) 125.23(2) Cent(2)–C(21)–Si(3) 173.1(3)
[NbCp2% Cl2]
[NbCp2% (C6F5)(CO)]
2.079
2.04
[17,18]
[17]
Cent(1)–Nb(1)–Cl(2)
Cent(1)–Nb(1)–N(1)
Cent(2)–Nb(1)–Cl(2)
Cent(2)–Nb(1)–N(1)
N(1)–Nb(1)–Cl(2)
104.26(4) Nb(1)–N(1)–C(1)
108.67(9) C(4)–O(1)–C(7)
105.36(4) C(5)–C(4)–O(1)
109.56(9) C(3)–C(4)–O(1)
100.82(10) N(1)–C(1)–C(2)
163.0(2)
117.7(3)
124.8(3)
116.0(3)
121.7(3)
120.5(3)
a Cent, the centroid of the C5 ring.
Cent(1)–C(11)–Si(4)
173.0(3)
N(1)–C(1)–C(6)
(9) was prepared by the addition of LiCp% to a THF
solution of 3 (Eq. (5)). The reaction always gave,
regardless of the excess of LiCp% used, an essentially
inseparable mixture, which by NMR spectroscopy was
shown to contain only 3 and the title complex. Com-
a Cent(1) and Cent(2) are the centroids of the Cp rings C(11)–C(15)
and C(21)–C(25), respectively.
electrons and this fact may have an effect in the length-
ening of the Nb–Cent distances of these formally ‘20-
electron’ complexes in comparison to their 18- and
17-electron analogues (see Table 3). Indeed such length-
ening has also been observed in metallocene imidos of
titanium [10] and molybdenum [11]. The bonding in the
‘19-electron’ vanadium complex [V(ꢀNC6H3Me2-
2,6)(h5-C5Me5)2] has previously been studied by MO
calculations and led to the proposal that the surplus
electrons in these ‘high electron’ complexes are located
in essentially ligand based orbitals and thus the 18-elec-
tron rule is not violated [12]. Similar calculations have
been carried out for ’20-electron’ osmium complexes
[Os(NR)3] [13].
1
plex 9 was characterised by H- and 13C-NMR spec-
troscopy. Four multiplets (5.75, 5.80, 6.18 and 6.23
ppm) and a singlet (0.28 ppm) pertaining to the Cp%
ligand and a singlet (5.88 ppm) corresponding to the Cp
1
ligand were observed in the H-NMR spectrum of 9.
(5)
The mixed sandwich complex [Nb(ꢀNBut)CpCp%Cl]
Table 2
Selected structural data of niobocene imido complexes
Cent c–Nb–Cent (°)
125.23
Nb–N–C (°)
Nb–N (A)
Ref.
,
[Nb(ꢀNC6H4OMe-4)Cp%2Cl] (8)
[(Nb(ꢀNPh)Cp%2Cl]
[{NbCp2% Cl}2(m-1,3-N2C6H4)]
163.0(2)
165.1(2)
1.787(3)
1.792(2)
This work
[2]
124.9
124.5, 125.6
121.21
114.2
113.3
113.4
167(2), 168(2)
178.8(2)
167.71(7)
178.4(3)
178.3(2)
171.8(2)
167.5(1)
166.8(1)
173.6(4), 179.4(5)
1.75(2), 1.76(2)
1.756(3)
1.777(1)
1.762(3)
1.765(2)
1.770(2)
1.798(2)
1.803(2)
1.789(4), 1.737(6)
[14]
[15]
[16]
[16]
[16]
[16]
[5b]
[5b]
[Nb(ꢀNBut){(h5-C5H4)2(m-SiMe2)}Cl]
[Nb(ꢀNSiMe3){(h5-C5H4)2(m-CMe2)}Cl]
[Nb(ꢀNBut){(h5-C5H4)2(m-Cme2)}Cl]
[Nb(ꢀNBut){(h5-C5H4)2(m-Cme2)}Br]
[Nb(ꢀNBut){(h5-C5H4)2(m-Cme2)}I]
[Nb(ꢀNAr*){(h5-C5H4)2(m-CMe2)}Cl] a
114.2
Not reported
[Nb(ꢀNAr*){(h5-C5H4)2(m-CMe2)}(NMe2){B(C6H5)4}] a Not reported
[Nb(ꢀNBut)Cp2Cl] b
122.7, 124.0
[3a]
a Ar, C6H3Pri2-2,6.
b Two independent molecules exist in the unit cell.
c Cent, the centroid of the C5 ring.

158
A. Antin˜olo et al. / Journal of Organometallic Chemistry 585 (1999) 154–161
Complexes 6–8 can be considered as 20-electron
spectrometers and referenced to the residual deuterated
solvent. Microanalyses were carried out with a Perkin–
Elmer 2400 microanalyzer. [Nb(ꢀNBut)Cl3(py)2] was
prepared as described earlier [8]. NbCl5, H2N(C6H4Me-
4), H2N(C6H4OMe-4) and THF solutions of
ClMgCH2CHCH2 were purchased from Aldrich and
used directly.
complexes and therefore it is not surprising that their
reaction with the allyl Grignard reagent ClMg-
CH2CHCH2 yielded only the h1-allyl complexes
[Nb(ꢀNR)Cp%(CH2CHꢀCH2)] (R=But (10), C6H4Me-4
2
(11), C6H4OMe-4 (12) (Eq. (6)). This phenomenon is
1
clearly illustrated by H-NMR spectroscopy in which
the signals and couplings normally associated with an
h1-allyl system (e.g. [Nb(ꢀNBut){(h5-C5H4)2(m-SiMe2)}
(h1-CH2CHCH2)] [15], [Nb(ꢀO)Cp%(h1-CH2CHCH2)]
3.2. Synthesis of [Nb(ꢀNC6H4Me-4)Cl3(dme)] (1)
2
[19] and [Nb(ꢀNBut)Cp(h1-CH2CHCH2)Cl] [19]) are
observed (see Section 3), namely, three signals corre-
sponding to the CH2 bonded to the metal centre, the
central group CH and the olefinic protons for the
terminal CH2. The various coupling constants are given
in Table 4.
To a mixture of NbCl5 (3.68 g, 14.00 mmol) and
ZnCl2 (3.82 g, 28.00 mmol) in CH2Cl2 (150 ml) was
added dme (2.5 ml). To this mixture, at −30°C, was
then added a solution of H2NC6H4Me-4 (1.33 g, 14.00
mmol) and pyridine (2.26 cm3, 28.00 mmol) in CH2Cl2
(50 cm3). This resultant mixture was allowed to stir at
r.t. for 16 h. The suspension was allowed to decant and
filtered. Solvent was removed, from the filtrate, under
reduced pressure to yield a red solid of the title complex
(5.15 g, 96%). Crystals were obtained by cooling (−
30°C) a CH2Cl2/hexane solution of 1. IR (Nujol mull):
1
wNbꢀN 1255 cm−1. H-NMR (C6D6, 200 MHz): l 1.95
(s, 3H, NC6H4Me), 2.88 (2H), 2.93 (2H) (t,
CH3OCH2CH2OCH3), 3.13 (3H), 3.42 (3H) (s,
CH3OCH2CH2OCH3), 6.71 (2H), 7.34 (2H) (J 8.14 Hz)
(d, NC6H4Me). 13C{1H}-NMR (CDCl3, 300 MHz): l
21.27 (NC6H4Me), 62.73, 68.54 (CH3OCH2CH2OCH3),
70.85, 75.34 (CH3OCH2CH2OCH3), 125.13, 125.82
(Cipso), 128.88, 137.67 (Cipso) (NC6H4Me). Anal. Calc.
for C11H17Cl3NNbO2: C, 33.49; H, 4.34; N, 3.55.
Found: C, 33.25; H, 4.12; N, 3.76%.
(6)
In conclusion, we have reported the synthesis and
characterisation of various sandwich and half-sandwich
niobium imido complexes and the reactivity of the
former with the allyl Grignard reagent ClMgCH2-
CHCH2. The X-ray structure of [Nb(ꢀNC6H4OMe-
4)Cp%Cl] (8) confirms that in this type of formally
2
‘20-electron’ complexes that there is a lengthening of
the Centroid–Nb distance in order to recover the more
stable eighteen electron core.
3.3. Synthesis of [Nb(ꢀNC6H4OMe-4)Cl3(dme)] (2)
The synthesis of 2 was carried out in an identical
manner to that of 1. NbCl5 (2.99 g, 11.07 mmol), ZnCl2
(3.02 g, 22.14 mmol), dme (2.0 cm3), H2NC6H4O-
Me-4 (1.36 g, 11.07 mmol) and pyridine (1.79 ml,
22.14 mmol). Yield 4.16 g, 92%. IR (Nujol mull):
3. Experimental
3.1. General procedures
All operations were performed under an inert atmo-
sphere using standard vacuum-line (Schlenk) techniques
or a Vac glovebox. Solvents were purified by distillation
from appropriate drying agents and degassed before
use. IR spectra were recorded on a Perkin–Elmer PE
883 IR spectrophotometer. 1H and 13C spectra were
recorded on Varian FT-300 and Varian Gemini FT-200
wNbꢀN 1235 cm−1 1H-NMR (C6D6, 200 MHz):
.
l 3.08 (s, 3H, NC6H4OMe), 2.85 (2H), 2.90 (2H)
(t, CH3OCH2CH2OCH3), 3.13 (3H), 3.41 (3H)
(s, CH3OCH2CH2OCH3), 6.45 (2H), 7.37 (2H) (J
9.0 Hz) (d, NC6H4OMe). 13C{1H}-NMR (CDCl3,
300 MHz):
l 55.52 (NC6H4OMe), 62.70, 68.40
(CH3OCH2CH2OCH3), 70.83, 75.29 (CH3OCH2CH2-
Table 4
Coupling constants for the h1-allyl complexes 10–12
3J(1H–1H) (Hz)
2Jgem(1H–1H) (Hz)
3Jcis(1H–1H) (Hz)
3Jtrans(1H–1H) (Hz)
[Nb(ꢀNBut)Cp2% (h1-CH2CHCH2)] (10)
8.5
8.1
8.3
2.5
2.5
2.4
9.9
9.9
10.0
16.9
16.8
16.8
[Nb(ꢀNC6H4Me-4)Cp2% (h1-CH2CHCH2)] (11)
[Nb(ꢀNC6H4OMe-4)Cp2% (h1-CH2CHCH2)] (12)

A. Antin˜olo et al. / Journal of Organometallic Chemistry 585 (1999) 154–161
159
OCH3), 113.43, 119.48 (Cipso), 126.97, 138.05 (Cipso
)
(NC6H4OMe). Anal. Calc. for C11H17Cl3NNbO3: C,
32.18; H, 4.17; N, 3.41. Found: C, 32.04; H, 4.11; N,
3.58%
3.7. Synthesis of [Nb(ꢀNBut)Cp%Cl] (6)
2
3.7.1. Method A
To a solid mixture of LiCp% (1.92 g, 13.30 mmol) and
[Nb(ꢀNBut)Cl3(py)2] (2.85 g, 6.65 mmol) was added
THF (150 ml). The yellow solution was allowed to stir
at r.t. for 16 h. Solvent was removed under reduced
pressure and hexane (150 ml) added and the mixture
was filtered. Solvent was removed, from the filtrate, to
give a yellow oil. Cooling (−30°C) a hexane (30 ml)
solution of this oil yielded yellow crystals of 6 (2.31 g,
73%).
3.4. Synthesis of [Nb(ꢀNBut)CpCl2] (3)
To a solid mixture of NaCp (0.92 g, 10.50 mmol) and
[Nb(ꢀNBut)Cl3(py)2] (4.50 g, 10.50 mmol) was added
THF (150 ml). The mixture was allowed to stir, at r.t.
for 16 h. Solvent was removed under reduced pressure
and the resulting residue extracted in hexane (3×150
ml). The removal of hexane, in vacuo, yielded a yellow
crystalline solid of 3 (2.66 g, 84%).
3.7.2. Method B
The synthesis was carried out in an identical manner
to Method A except the reaction was carried out at 0°C
and only stirred for 2 h. LiCp% (0.96 g, 6.65 mmol) and
[Nb(ꢀNBut)Cl3(py)2] (2.85 g, 6.65 mmol). Yield (with
reference to LiCp%) 1.09 g, 69%.
3.5. Synthesis of [Nb(ꢀNC6H4Me-4)CpCl2] (4)
The synthesis of 4 was carried out in an identical
manner to that of 3. NaCp (0.67 g, 7.60 mmol) and 1
(3.00 g, 7.60 mmol). Yield 1.82 g, 72%. IR (Nujol mull):
3.8. Synthesis of [Nb(ꢀNC6H4Me-4)Cp%Cl] (7)
1
wNbꢀN 1254 cm−1. H-NMR (C6D6, 200 MHz): l 2.12
2
(s, 3H, NC6H4Me), 5.75 (s, 5H, C5H5), 6.46 (2H), 6.88
(2H) (J 8.1 Hz) (d, NC6H4Me). 13C{1H}-NMR (CDCl3,
300 MHz): l 25.36 (NC6H4Me), 115.47 (C5H5), 126.05,
129.38 (Cipso), 130.95, 140.93 (Cipso) (NC6H4Me). Anal.
Calc. for C12H12Cl2NNb: C, 43.15; H, 3.62; N, 4.19.
Found: C, 42.90; H, 3.52; N, 4.07%
The synthesis of 7 was carried out in an identical
manner to that of 6 (Method A). LiCp% (1.54 g, 10.64
mmol) and 1 (2.10 g, 5.32 mmol). Yield 1.82 g, 67%. IR
1
(Nujol mull): wNbꢀN 1258 cm−1. H-NMR (C6D6, 200
MHz): l 0.23 (s, 18H, SiMe3), 2.10 (s, 3H, NC6H4Me),
5.51 (2H), 5.96 (2H) 6.25 (2H) 6.33 (2H) (m,
C5H4SiMe3), 6.45 (2H), 6.89 (2H) (J 9.10 Hz) (d,
NC6H4Me). 13C{1H}-NMR (acetone-d6, 300 MHz): l
−0.25 (SiMe3), 20.8 (NC6H4Me), 116.0, 116.9, 117.8,
118.0, 122.0 (C1) (C5H4SiMe3), 126.8, 126.1 (Cipso),
3.6. Synthesis of [Nb(ꢀNBut)Cp%Cl2] (5)
3.6.1. Method A
To a solid mixture of LiCp% (0.84 g, 5.83 mmol) and
[Nb(ꢀNBut)Cl3(py)2] (2.50 g, 5.83 mmol) was added
THF (150 ml). The yellow solution was allowed to stir
at r.t. for 16 h. Solvent was removed under reduced
pressure and hexane (150 ml) added and the mixture
was filtered. Solvent was removed, from the filtrate, to
give a yellow oil. H-NMR spectroscopy showed this
oil to be uniquely a mixture (ca. 1:1) of the title
complex 5 and 6.
130.2, 130.3 (Cipso
C23H33ClNNbSi2: C, 54.37; H, 6.55; N, 2.76. Found: C,
54.11; H, 6.39; N, 2.81%
) (NC6H4Me). Anal. Calc. for
3.9. Synthesis of [Nb(ꢀNC6H4OMe-4)Cp%Cl] (8)
2
1
The synthesis of 8 was carried out in an identical
manner to that of 6 (Method A). LiCp% (1.58 g, 10.96
mmol) and 2 (2.25 g, 5.48 mmol). Yield 2.13 g, 74%. IR
(Nujol mull): wNbꢀN 1296 cm−1. H-NMR (C6D6, 200
1
3.6.2. Method B
MHz):
l
0.23 (s, 18H, SiMe3), 3.21 (s, 3H,
To a solid mixture of [Nb(ꢀNBut)Cl3(py)2] (1.30 g,
3.03 mmol) and 6 (1.44 g, 3.03 mmol) was added THF
(150 ml). The yellow solution was allowed to stir at r.t.
for 16 h. Solvent was removed under reduced pressure
and hexane (150 ml) added and the mixture was
filtered. Solvent was removed, from the filtrate, to give
NC6H4OMe), 5.56 (2H), 5.99 (2H) 6.26 (2H) 6.33 (2H)
(m, C5H4SiMe3), 6.47 (2H), 6.67 (2H) (J 8.9 Hz) (d,
NC6H4OMe). 13C{1H}-NMR (acetone-d6, 300 MHz): l
0.2 (SiMe3), 55.8 (NC6H4OMe), 112.0, 113.2, 114.0,
114.1 (C1), 115.2 (C5H4SiMe3), 120.2, 118.8 (Cipso),
120.4, 127.5 (Cipso) (NC6H4OMe). Anal. Calc. for
C23H33ClNNbOSi2: C, 52.71; H, 6.35; N, 2.67. Found:
C, 52.43; H, 6.25; N, 2.71%
1
a yellow oil. H-NMR spectroscopy showed this oil to
be uniquely a mixture (ca. 1:1) of the title complex 5
and 6. 1H-NMR (C6D6, 200 MHz): l 0.20 (s, 9H,
SiMe3), 1.02 (s, 9H, CMe3), 6.11 (2H), 6.35 (2H) (m,
C5H4SiMe3). 13C{1H}-NMR (C6D6, 300 MHz): l 0.51
(SiMe3), 30.4 (CMe3), 70.1 (CMe3), 110.4, 112.4, 116.0
(C1) (C5H4SiMe3).
3.10. Synthesis of [Nb(ꢀNBut)CpCp%Cl] (9)
To a solid mixture of LiCp% (0.56 g, 3.85 mmol) and
3 (1.05 g, 3.50 mmol) was added THF (150 ml). The

160
A. Antin˜olo et al. / Journal of Organometallic Chemistry 585 (1999) 154–161
yellow solution was heated, under reflux, for 8 h. The
solvent was removed under reduced pressure and hex-
ane (150 ml) added and the mixture was filtered. The
solvent was removed from the filtrate to give a yellow
oil. 1H-NMR spectroscopy showed this oil to be
uniquely a mixture (ca. 1:1) of the title complex 9 and
(C5H4SiMe3), 105.21 (CH2CHꢀCH2), 149.96 (CH2CHꢀ
CH2), 126.35, 129.10, 129.96 (Cipso), 139.03 (Cipso
(NC6H4Me). Anal. Calc. for C26H38NNbSi2: C, 60.79;
)
H, 7.46; N, 2.73. Found: C, 60.48; H, 7.35; N, 2.84%
3.13. Synthesis of [Nb(ꢀNC6H4OMe-4)Cp%(p1-CH2CH
2
1
3. H-NMR (C6D6, 200 MHz): l 0.28 (s, 9H, SiMe3),
ꢀCH2)] (12)
0.94 (s, 9H, CMe3), 5.88 (s, 5H, C5H5), 5.75 (1H), 5.80
(1H), 6.18 (1H), 6.23 (1H) (m, C5H4SiMe3): 13C{1H}-
NMR (C6D6, 300 MHz,) l 0.53 (SiMe3), 30.0 (CMe3),
69.8 (CMe3), 105.28, 114.89, 117.20 (C1), 122.34, 125.65
(C5H4SiMe3).
The synthesis of 12 was carried out in an identical
manner to that of 10. A 2 M solution of ClMgCH2-
CHꢀCH2 in THF (0.62 ml, 1.24 mmol) and 8 (0.54 g,
1.03 mmol). Yield 0.34 g, 61%. IR (Nujol mull): wNbꢀN
1285 cm−1. 1H-NMR (C6D6, 200 MHz): l 0.14 (s, 18H,
SiMe3), 3.32 (s, 3H, NC6H4OMe), 2.82 (d, 2H,
CH2CHꢀCH2) 3J(1H–1H) 8.3 Hz, 4.84 (cis), 5.01
3.11. Synthesis of [Nb(ꢀNBut)Cp%(p1-CH2CHꢀCH2)
2
(10)
2
(trans) (dd, 2H, CH2CHꢀCH2) Jgem(1H–1H) 2.4,
A 2 M solution of ClMgCH2CHꢀCH2 in THF (0.66
ml, 1.32 mmol) was added to a stirring solution of 6
(0.52 g, 1.10 mmol) in THF (50 ml) at −30°C and
allowed to stir for 3 h at this temperature. Solvent was
removed in vacuo and the remaining yellow oil ex-
tracted in hexane (50 ml). Solvent was removed in
vacuo and the remaining yellow oil extracted in hexane.
A yellow crystalline solid was obtained by concentrat-
ing (15 ml) and cooling (−30°C) the solution (0.29 g,
3
3Jcis(1H–1H) 10.0, Jtrans(1H–1H) 16.8 Hz, 5.53 (2H),
5.70 (2H), 5.91 (2H), 5.99 (2H) (m, C5H4SiMe3), 6.53
(m, 1H, CH2CHꢀCH2), 6.48 (2H), 6.68 (2H) (J 9.0 Hz)
(d, NC6H4OMe). 13C{1H}-NMR (C6D6, 300 MHz): l
0.48 (SiMe3), 57.42 (NC6H4OMe), 38.12 (CH2CHꢀ
CH2), 105.99, 110.42, 112.17 (C1), 119.70, 120.61
(C5H4SiMe3), 103.85 (CH2CHꢀCH2), 148.63 (CH2CHꢀ
CH2), 124.32, 125.67 (Cipso), 130.17, 131.42 (Cipso
)
(NC6H4OMe). Anal. Calc. for C26H38NNbOSi2: C,
58.96; H, 7.23; N, 2.64. Found: C, 58.63; H, 7.31; N,
2.62%
55%). IR (Nujol mull): wNbꢀN 1240 cm−1 1H-NMR
.
(C6D6, 200 MHz): l 0.22 (s, 18H, SiMe3), 0.96 (s, 9H,
3
CMe3), 2.75 (d, 2H, CH2CHꢀCH2) J(1H–1H) 8.5 Hz,
4.83 (cis), 5.02 (trans) (dd, 2H, CH2CHꢀCH2)
3.14. Crystallography
3
3
2Jgem(1H–1H) 2.5, Jcis(1H–1H) 9.9, Jtrans(1H–1H) 16.9
Hz, 5.76 (2H), 5.77 (2H), 5.95 (2H), 6.06 (2H) (m,
C5H4SiMe3), 6.55 (m, 1H, CH2CHꢀCH2). 13C{1H}-
NMR (C6D6, 300 MHz): l 0.57 (SiMe3), 30.92 (CMe3),
37.45 (CH2CHꢀCH2), 70.72 (CMe3), 106.81, 111.64,
118.88, 124.73, 109.91 (C1) (C5H4SiMe3), 104.18
(CH2CHꢀCH2), 151.29 (CH2CHꢀCH2). Anal. Calc. for
C23H40NNbSi2: C, 57.59; H, 8.41; N, 2.92. Found: C,
57.61; H, 8.52; N, 2.81%
Diffraction data for 8 were obtained at 298 K on a
Nonius-Mach3 diffractometer with graphite monochro-
matized Mo–Ka radiation using a v/2q scan technique.
Cell parameters were determined by a least-squares fit
on 25 reflections. Data were corrected for Lorentz and
polarization effects and absorption correction was not
required because the variation in integrated c-scan
intensities was B10%. The structure was solved by a
combination of direct methods [20] and Fourier synthe-
sis and then refined by full-matrix least-squares on F2
[21]. Anisotropic thermal parameters were considered
for all non-hydrogen atoms, while hydrogen atoms
were included in calculated position but not refined.
Final disagreement indices are R1=0.0325, wR2=
0.0814, largest difference peak and hole 0.319 and
3.12. Synthesis of
[Nb(ꢀNC6H4Me-4)Cp%(p1-CH2CHꢀCH2)] (11)
2
The synthesis of 11 was carried out in an identical
manner to that of 10.
A
2
M
solution of
ClMgCH2CHꢀCH2 in THF (0.77 ml, 1.54 mmol) and 7
(0.65 g, 1.28 mmol). Yield 0.38 g, 58%. IR (Nujol mull):
−0.333 e A−3. Details are given in Table 5.
,
1
wNbꢀN 1260 cm−1. H-NMR (C6D6, 200 MHz): l 0.14
(s, 18H, SiMe3), 2.09 (s, 3H, NC6H4Me), 2.82 (d, 2H,
CH2CHꢀCH2) 3J(1H–1H) 8.1 Hz, 4.83 (cis), 5.00
2
(trans) (dd, 2H, CH2CHꢀCH2) Jgem(1H–1H) 2.5,
4. Supplementary material
3
3Jcis(1H–1H) 9.9, Jtrans(1H–1H) 16.8 Hz, 5.52 (2H),
5.65 (2H), 5.91 (2H), 5.98 (2H) (m, C5H4SiMe3), 6.52
(m, 1H, CH2CHꢀCH2), 6.49 (2H), 6.89 (2H) (J 8.0 Hz)
(d, NC6H4Me). 13C{1H}-NMR (C6D6, 300 MHz): l
0.26 (SiMe3), 20.92 (NC6H4Me), 37.23 (CH2CHꢀ
CH2), 110.82, 113.71, 113.98 (C1), 116.18, 119.28
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CSD-115349 for compound 8. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2

A. Antin˜olo et al. / Journal of Organometallic Chemistry 585 (1999) 154–161
161
Table 5
Gibson, J.A.K. Howard, C. Lehmann, A.D. Poole, U. Siemeling,
J. Chem. Soc. Dalton Trans. (1998) 103. (i) M.L.H. Green, J.T.
James, J.F. Saunders, J. Souter, J. Chem. Soc. Dalton Trans.
(1997) 1281.
Crystal data and structure refinement for complex 8
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system, space group
C23H33ClNNbOSi2
524.04
293(2)
0.71070
[2] A. Antin˜olo, P. Espinosa, M. Fajardo, P. Go´mez-Sal, C. Lo´pez-
Mardomingo, A. Martin-Alonso, A. Otero, J. Chem. Soc. Dal-
ton Trans. (1995) 1007.
[3] (a) A.N. Chernega, M.L.H. Green, A.G. Suarez, J. Chem. Soc.
Dalton Trans. (1993) 3031. (b) S. Schmidt, J. Sundermeyer, J.
Organomet. Chem. 472 (1994) 127.
,
Monoclinic, P21/n
Unit cell dimensions
,
a (A)
7.335(9)
17.219(3)
20.682(9)
99.42(7)
2577(3)
4
1.351
6.78
1088
0.4×0.2×0.2
05h59, 05k522, −275l526
6200/0/262
R1=0.0325, wR2=0.0814
,
b (A)
[4] M.L.H. Green, J.T. James, A.N. Chernega, J. Chem. Soc. Dal-
ton Trans. (1997) 1719.
,
c (A)
i (°)
[5] (a) W.A. Hermann, W. Baratta, E. Herdtweck, Angew. Chem.
Int. Ed. Engl. 35 (1996) 1951. (b) W.A. Hermann, W. Baratta, E.
Herdtweck, J. Organomet. Chem. 541 (1997) 445. (c) A.N.
Chernega, M.L.H. Green, A.G. Suarez, Can. J. Chem. 73 (1995)
1157.
[6] A.V. Korolev, A.L. Rheingold, D.S. Williams, Inorg. Chem. 36
(1997) 2647.
[7] K.S. Heinseiman, V.M. Miskowski, S.J. Geib, L.C. Wang, M.D.
Hopkins, Inorg. Chem. 36 (1997) 5530.
3
,
Volume (A )
Z
Dcalc (g cm−3
)
Absorption coefficient (cm−1
F(000)
)
Crystal size (mm)
Index ranges
Data/restraints/parameters
Final R indices [I\2|(I)]
[8] J. Sundermeyer, J. Putterlik, M. Foth, J.S. Field, N. Ramesar,
Chem. Ber. 127 (1994) 1201.
[9] (a) G. Parkin, A. van Asselt, D.J. Leahy, L.R. Whinnery, N.G.
Hua, R.W. Quan, L.M. Henling, W.P. Schaefer, B.D. Santar-
siero, J.E. Bercaw, Inorg. Chem. 31 (1992) 82. (b) K.A.
Jørgensen, Inorg. Chem. 32 (1993) 1521.
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http//www.ccdc.cam.ac.uk).
[10] S.C Dunn, P. Mountford, D.A. Robson, J. Chem. Soc. Dalton
Trans. (1997) 293.
Acknowledgements
[11] J.C. Green, M.L.H. Green, J.T. James, P.C. Konidaris, G.H.
Maunder, P. Mountford, J. Chem. Soc. Chem. Commun. (1992)
1361.
[12] J.H. Osborne, A.L. Rheingold, W.C. Trogler, J. Am. Chem. Soc.
107 (1985) 7945.
[13] M.H. Schofield, T.P. Kee, J.T. Anhaus, R.R. Schrock, K.H.
Johnson, W.M. Davis, Inorg. Chem. 30 (1991) 3595.
[14] A. Antin˜olo, F. Carrillo-Hermosilla, A. Otero, M. Fajardo, A.
Garce´s, P. Go´mez-Sal, C. Lo´pez-Mardomingo, A. Mart´ın, C.
Miranda, J. Chem. Soc. Dalton Trans. (1998) 59.
[15] A. Antin˜olo, A. Otero, S. Prashar, A.M. Rodriguez,
Organometallics 17 (1998) 5454.
We gratefully acknowledge financial support from
the Direccio´n General de Ensen˜anza Superior e Inves-
tigacio´n Cient´ıfica, Spain (Grant no. PB 95-0023-C02-
01), and for a postdoctoral grant to S.P. under the
Programa Nacional de Formacio´n de Personal
Investigador.
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[1] See for example: (a) D.N. Williams, J.P. Mitchell, A.D. Poole,
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.