Half-sandwich and ansa-niobiocenes: Synthesis and reactivity

Article abstract of DOI:10.1016/S0022-328X(97)00720-1

The reaction of [Nb(NMe₂)₃(=N-2,6-iPr₂C₆H₃)] 1 with the cyclopentadienyl-indenyl isopropylidene ligand 2 gave the new half-sandwich niobium complex [Nb(η⁵- C₅H₄R)(NMe<

Full text of DOI:10.1016/S0022-328X(97)00720-1

Journal of Organometallic Chemistry 562 (1998) 71–78
Half-sandwich and ansa-niobiocenes: synthesis and reactivity1
Laurent Djakovitch 2, Wolfgang A. Herrmann *
Anorganisch-chemisches Institut der Technischen Uni6ersita¨t Mu¨nchen, Lichtenbergstrasse 4, D-85747 Garching b. Mu¨nchen, Germany
Received 15 July 1997
Abstract
The reaction of [Nb(NMe2)3(ꢀN-2,6-iPr2C6H3)] 1 with the cyclopentadienyl-indenyl isopropylidene ligand 2 gave the new
half-sandwich niobium complex [Nb(p5- C5H4R)(NMe2)2(ꢀN-2,6-iPr2C6H3)] (R=CMe2C9H7) 3 in high yield. The new ansa-type
niobiocene [Nb(NMe2)(ꢀN-2,6-i-Pr2C6H3)(p5:p1-{C5H4}C(CH3)2{C9H6}] 4 was obtained at higher temperatures by an intramolec-
ular deprotonation with concomitant coordination of the indenyl group. The reactivity of the new ansa-niobiocene 4 towards
electrophilic reagents, giving chloro- and cationic ansa-type niobium complexes is described. © 1998 Elsevier Science S.A. All
rights reserved.
Keywords: Niobium; Amido complexes; Imido complexes; Cationic complexes
1. Introduction
precursors for the ethylene polymerization [5]. In our
continuing research on these systems, we now report
the preparation and the reactions of a niobium ansa-
metallocene based on the cyclopentadienyl-indenyl iso-
propylidene ligand.
Ansa-metallocene complexes have been extensively
developed due to their large application as homoge-
neous Ziegler–Natta polymerization catalyst precursors
for h-olefins using methylaluminoxane (MAO) as co-
catalysts [1,2]. Most of these derivatives are known for
the group 4 transition metals (group of Zr and Ti) [3].
The development of new systems, in order to control
both the stereospecificity and the molecular mass of the
final polymer is a goal of many research groups. Only
recently, ansa-metallocenes of the group 5-elements
(Nb, Ta) attracted increasing interest; niobium and
tantalum complexes have become known as catalyst
precursors for the ‘living polymerization’ of ethylene
[4].
2. Results and discussion
The
[Nb(NMe2)3(ꢀN-2,6-iPr2C6H3)] 1 was treated with an
equimolar amount of the protic ligand
imido-tris-amido-niobium
(V)
complex
C5H5C(CH3)2C9H7 2. Deprotonation by an amido lig-
and of 1 of the cyclopentadiene ring, resulting in its
p5-coordination to the metal centre, occurs smoothly at
1
100°C in toluene [5]. Monitoring the reaction by H
In previous work, we have reported a series of half-
sandwich imido complexes and ansa-metallocenes of
niobium and tantalum that were investigated as catalyst
NMR showed that the reaction is completed within 2 h
without noticeable thermal decomposition of the com-
plex 3. The new half-sandwich niobium complex 3 is
formed quantitatively, and is isolated in good yield
(88%) as a yellow-brown oil (Scheme 1). The complex 3
* Corresponding author. Fax: +49 89 28913473.
1 Dedicated to Professor Bruce King on the occasion of his 60th
birthday.
1
showed characteristic H NMR resonances for the cy-
2 Research Fellow of the Alexander von Humboldt Foundation
(1995–1997).
clopentadienyl ligand which gave as expected two
pseudo-triplets at l=5.77 and 6.05 ppm with a charac-
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00720-1

72
L. Djako6itch, W. A. Herrmann / Journal of Organometallic Chemistry 562 (1998) 71–78
Scheme 1.
3
1
teristic coupling constant J(H,H):2.5 Hz. H NMR
data do not indicate interactions between the metal
centre and the indenyl ligand, i.e. no detectable y-inter-
actions with the vinylic part of the indenyl group.
Investigating the thermal stability of the complex 3
as a singulet, i.e. no H atom is attached to this carbon)
and one signal at l:40 ppm for the ipso-CH of the
1
indenyl group. All the values obtained in H and 13C
NMR are in agreement with the p1-coordination at-
tributed to the indenyl ligand in the complex 4.
Finally the complex 4 was monitored by temperature
1
by H NMR in toluene-D8, it was found that it was
1
quite stable below 100°C even for long reaction times of
several hours. Further reactions were observed at 110°C
in toluene-D8 giving the new ansa-niobiocene 4 in high
programmed H NMR from 20 to 100°C in toluene-D8.
The records showed that from 50°C the broad singulet
observed for the amido ligand becomes sharper to give
at 80°C sharp signal at l=3.34 ppm resulting from a
free rotation of this group. At the same time, the
cyclopentadienyl region is modified. The pseudo-triplet
observed at room temperature at l=5.94 ppm splits
into two pseudo-quartets to give finally at 80°C two
well separated signals at l=5.96 and 6.01 ppm with a
1
yield, characterised by a strong modification in the H
NMR of the cyclopentadienyl region which showed two
pseudo-quartets at l=5.70 and 5.80 ppm plus one
pseudo-triplet at l=5.94 ppm (Scheme 2).
While the coordination of the indenyl group could
directly be studied from the precursor complex 3, we
studied this reaction in a one-pot synthesis. After a
reaction time of 2 h between the niobium (V) complex
1 and the ligand 2 at 100°C in toluene, the mixture was
then refluxed at 110°C for different reaction times.
3
coupling constant J(H, H):2.7 Hz. This modification
of the cyclopentadienyl region results probably from
the free rotation of the amido ligand, which does not
contribute further to the stabilisation of the complex
through donation of nitrogen lone pair.
1
Monitoring the reaction by H NMR, we found that
the indenyl coordination was completed after 7 h with-
out noticeable decomposition of the ansa-niobiocene 4.
The longer reaction time observed for the coordination
of the indenyl ligand versus the cyclopentadienyl ligand
is only due to the difference in pKa between the cy-
clopentadienyl and the indenyl group (respectively 16
and 20) [6]. The new ansa-metallocene 4 was synthe-
sised quantitatively and isolated as a yellow amorphous
powder from heptane in good yield (77%) (Scheme 2).
It is characterised in 1H NMR by two pseudo-quartet at
Treatment of the complex 4 with trimethylsilylchlo-
ride in excess at −78°C in toluene gave after a reaction
time of 2 h at room temperature quantitatively the new
ansa-niobiocene 5 (Scheme 3). The initial yellow solu-
tion of 4 in toluene turned quickly dark red at room
temperature, resulting from the formation of the new
chloro complex 5. The complex 5 was isolated in high
yield (93%) as a micro-crystalline material from a hep-
1
tane solution. It is characterised in H NMR by four
pseudo-quartets in the range from l:5.5 to l=6.3
3
3
l=5.70 and 5.80 ppm with a coupling constant J(H,
ppm with a coupling constant J(H, H):2.5 Hz for
1
H):3.0 Hz plus one pseudo-triplet at l=5.94 ppm
the cyclopentadienyl ligand. In addition, the H NMR
3
with a characteristic coupling constant J(H, H):3.0
showed two signals at l=5.84 and 6.18 ppm for the
resonance of the vinylic CH of indenyl ligand. In the
13C NMR, the cyclopentadienyl ligand gives four sig-
nals in the range from l:98 to 110 ppm for the
resonance of the CH group plus one signal at l:133
ppm for the ipso-C. In addition, the complex 5 is
characterised by resonances from the p3-coordinated
indenyl ligand at l:112–113 ppm as two signals for
the two vinylic CH group plus one signal at l:121
ppm for the ipso-C of the indenyl ligand. All these
values are in agreement with the commonly accepted
values for the p3-coordination of an indenyl ligand [7].
Hz for the cyclopentadienyl region, two broad singulets
at l=3.94 ppm for the ipso-CH of the indenyl function
and l=6.94 ppm for the vinylic-CH of the indenyl
group. In the 13C NMR, the cyclopentadienyl ligand
gives four signals in the range of l:98–108 ppm for
the resonance of the CH group plus one signal at
l:136 ppm for the ipso-C. In addition, the complex 4
is characterised by the resonance of the p1-coordinated
indenyl ligand at l:178 ppm for the carbon coordi-
nated to the metal centre, attribution confirmed by
13C[1H] coupled NMR experiment (this signal appears

L. Djako6itch, W. A. Herrmann / Journal of Organometallic Chemistry 562 (1998) 71–78
73
Scheme 2.
Treatment of the complex 4 with an equimolar
amount of [HNMe3][B(C6H5)4] at −40°C in THF gave
quantitatively, after a reaction time of 12 h at room
temperature, the new cationic ansa-niobiocene 6a
(Scheme 4). The initial yellow-brown solution of 4 in
THF turned slowly red at room temperature, resulting
from the formation of the new cationic complex 6a.
The niobiocene 6a was isolated in good yield (60%) as
a red amorphous material from a pentane-THF solu-
resonance of the CH groups plus one signal at l:136
ppm for the ipso-C and the coordinated amino ligand a
signal at l:41 ppm for the resonance of the methyl
groups. In addition, the complex 6a is characterised by
the resonance of the p3-coordinated indenyl ligand at
l:126 and 133 ppm for the vinylic CH group plus one
signal at l:118 ppm for the ipso-C of the indenyl
ligand. All these values are in agreement with the
p3-coordination of an indenyl ligand [7].
1
tion. It is characterised in H NMR by four pseudo-
Treatment of the complex 4 with equimolar amount
of [HNMe3][Cl] at −40°C in THF gave quantitatively,
after a reaction time of 2 h at room temperature, the
new cationic ansa-niobiocene 6b (Scheme 4). The initial
yellow-brown solution of 4 in THF turned quickly dark
red at room temperature, resulting from the formation
of the new cationic complex 6b isolated in good yield
(73%) as a dark red material from a pentane-THF
quartets in the range from l:6.4 to l=6.8 ppm with
a coupling constant 3J(H, H):2.5 Hz for the cyclopen-
1
tadienyl ligand. In addition, the H NMR showed two
septets at l=3.37 and 4.13 ppm with a coupling con-
3
stant J(H, H):6.5 Hz for the resonance of the CH of
the isopropyl group of the imido ligand, one doublet at
3
l=1.51 ppm with a coupling constant J(H, H):7.1
1
Hz for the resonance of the methyl group of the
coordinated amino ligand. Two signals are observed for
the resonance of vinylic CH groups of the indenyl
ligand, one pseudo-triplet at l=7.03 ppm with a cou-
pling constant 3J(H, H):8.1 Hz and one signal at
l=7.55 ppm (overlapping with another aromatic sig-
nal). In the 13C NMR, the cyclopentadienyl ligand gives
four signals in the range of l:98 to 108 ppm for the
solution. It is characterised in H NMR by four broad
pseudo-quartets in the range from l:6.2 to 6.8 ppm
for the cyclopentadienyl ligand. In addition, the 1H
NMR showed two septets at l=3.08 and 3.97 ppm
with a coupling constant 3J(H, H):7.0 Hz for the
resonance of the CH groups of the isopropyl group of
the imido ligand and one doublet at l=1.28 ppm with
a coupling constant 3J(H, H):6.5 Hz for the reso-

74
L. Djako6itch, W. A. Herrmann / Journal of Organometallic Chemistry 562 (1998) 71–78
Scheme 3.
nance of the methyl group of the coordinated amino
All preparations, manipulations and reactions were
carried out under Argon using standard techniques for
handling air-sensitive materials, such as Schlenk Tech-
niques and Glove-box. Pentane, heptane, THF and
Toluene were freshly distilled over Na/K amalgam un-
der argon from purple benzophenone ketyl before use
(Caution: Solvent should not be distilled to dryness).
Deuterated solvents were dried over Na/K amalgam
and then vacuum transfered and stored under an argon
atmosphere. All glassware were base- and acid-washed,
oven dried and additionally dried under high vaccum.
The cyclopentadienyl-indenyl isopropylidene ligand and
the niobium-trisamido-imido compound [Nb(NMe2)3(ꢀ
N-2,6-iPr2C6H3)] 3 were prepared as reported in the
literature [10,5]. Dimethylfulvene and indene were dis-
tilled before use, and all other chemicals were used as
received.
NMR spectra were recorded with either a JEOL-
LMN-GX 400 or a Bruker AM 400 spectrometer (1H
NMR were referenced to the residual protio-solvent:
C6D6, l=7.15 ppm and D8-THF, l=1.72 and 3.57
ppm; 13C NMR were referenced to the C-signal of the
deutero solvent: C6D6, l=128 ppm and D8-THF, l=
25.3 and 67.4 ppm), Mass spectra (CI) were measured
with a Varian MAT 90 spectrometer, and elemental
analyses were performed in our analytical laboratory.
ligand. One pseudo-triplet at l=6.67 ppm with a cou-
3
pling constant J(H, H):8.3 Hz and one doublet at
3
l=6.99 ppm with a coupling constant J(H, H):8.3
Hz are observed for the resonance of vinylic CH of the
indenyl ligand. In the 13C NMR, the cyclopentadienyl
ligand gives four signals in the range from l:98 to 113
ppm for the resonance of the CH group plus one signal
at l:131 ppm for the ipso-C and the coordinated
amino ligand a signal at l:40 ppm. In addition, the
complex 6b is characterised by the resonance of the
p3-coordinated indenyl ligand at l:121 and 124 ppm
for the vinylic CH plus one signal at l:120 ppm for
the ipso-C of the indenyl ligand. All these values are in
agreement with the p3-coordination of an indenyl lig-
and [7].
Both isolated cationic complexes 6a and 6b are quite
stable under argon, but at room temperature in THF
solution a slow ligand exchange between the amino
group and THF takes place (Scheme 5) giving less
stable complexes 7a–b, which decomposed affording
new unassignable products. Monitoring this reaction by
1H NMR in THF-D8 we showed that after 10 h at r.t.
22% of the amino ligand was exchanged by THF-D8,
characterised by the apparition of a doublet for the free
dimethylamine at l=2.28 ppm with a coupling con-
3
stant J(H, H):6.3 Hz. The low stability of the new
complexes is probably due to a lower contribution of
the coordinated THF to the stabilisation of the cationic
complexes. The rapid decomposition of both 7a and 7b
in solution prevented us from obtaining well defined
data of these compounds.
The new niobium complexes 3–6 are very sensitive to
air, rapidly leading to the formation of white solid
resulting from hydrolysis. They can be stored at room
temperature under argon for several weeks without any
noticeable decomposition.
The catalytic activity of the new ansa-metallocenes of
niobium 3–6 as catalyst precusors for the h-olefin
polymerisation as well as the ethylene/CO copolymeri-
sation using MAO as co-catalysts has to be subject of
further investigations [4]. Their reactivity towards the
insertion reactions by activation of small molecules (e.g.
CO, C2H4,…) [8], and for the selective C–H activation
of hydrocarbons is a promising topic, too [9].
3. Experimental section
1 Preparation of the niobium compound [Nb(p5-
C5H4R)(NMe2)2(ꢀN-2,6-iPr2C6H3)] (R=CMe2C9H7) 3
from [Nb(NMe2)3(ꢀN-2,6-iPr2C6H3)] 1 and the ligand
2.
A solution of the niobium precursor 1 (100 mg, 0.25
mmol) in toluene (10 ml) was treated with a solution of
the ligand 2 (56 mg, 0.25 mmol) in toluene (5 ml) at
−40°C. The mixture was allowed to warm-up to room
temperature, then it was slowly warmed-up to 100°C.
The stirring was continued for 2 h and the solvent was
evaporated. The product of the reaction was dried
under vaccum (10−2 mmHg) for 12 h. Then pentane (5
ml) was added to the residue, the solution filtered
through a glass plug and evaporated under high vac-

L. Djako6itch, W. A. Herrmann / Journal of Organometallic Chemistry 562 (1998) 71–78
75
Scheme 4.
cum to give 127 mg of 3 as a yellow-brown oil. Yield:
and evaporated. The residue was added of heptane (5
ml) and the solution left under argon at −78°C to give
slowly 205 mg of 4 as an amorphous yellow material.
Yield: 77%.
88%.
3
1H NMR, C6D6, 400.13 MHz: 1.26 (d, 12H, J(H,
H)=7.0 Hz, CH(CH3)2); 1.54 (s, 6H, C(CH3)2); 3.15 (s,
12H, N(CH3)2); 3.48 (br. s, 1H, ipsoCH-C9H7); 4.02
(sept., 2H, 3J(H, H)=7.0 Hz, CH(CH3)2); 5.77 (pseudo-
1H NMR, C6D6, 400.13 MHz: 1.16 (d, 6H, 3J(H,
3
H)=7.1 Hz, CH(CH3)2); 1.18 (d, 6H, J(H, H)=7.1
3
t, 2H, J(H, H)=3.0 Hz, C5H4); 6.05 (pseudo-t, 2H,
Hz, CH(CH3)2); 1.68 (s, 3H, C(CH3)2); 1.76 (s, 3H,
C(CH3)2); 3.15 (br.s, 6H, N(CH3)2); 3.94 (br.s, 1H,
3J(H, H)=2.5 Hz, C5H4); 6.58 (m, 1H, vinylCH-C9H7);
6.86 (m, 1H, vinylCH-C9H7); 6.92 (t, 1H, 3J(H, H)=7.5
ipsoCH-C9H6); 4.01 (br. sept., 2H, J(H, H)=7.1 Hz,
3
3
Hz, p-C6H3); 7.07 (d, 2H, J(H, H)=7.5 Hz, m-C6H3);
CH(CH3)2); 5.70 (pseudo-q, 1H, 3J(H, H)=3.1 Hz,
C5H4); 5.80 (pseudo-q, 1H, 3J(H, H)=3.0 Hz, C5H4); 5.
94 (pseudo-t, 2H, 3J(H, H)=3.1 Hz, C5H4); 6.92 (t, 1H,
3J(H, H)=7.5 Hz, p-C6H3); 6.94 (br.s, 1H, vinylCH-
C9H6); 7.05 (d, 2H, 3J(H, H)=7.5 Hz, m-C6H3); 7.11 (t,
3
7.02–7.18 (m, 2H, aromCH-C9H7); 7.23 (d, 1H, J(H,
3
H)=7.5 Hz, aromCH-C9H7); 7.28 (d, 1H, J(H, H)=
7.5 Hz, aromCH-C9H7). 13C{1H} NMR, C6D6, 100.62
MHz: 23.68 (CH(CH3)2); 26.26 (C(CH3)2); 27.72
(CH(CH3)2); 35.77 (C(CH3)2); 37.87 (ipsoC-C9H7); 57.88
(N(CH3)2); 105.88 and 107.32 (C5H4); 121.13, 123.47,
124.63 and 126.01 (aromCH-C9H7); 122.74 (m-C6H3);
123.09 (p-C6H3); 130.86 and 132.84 (vinylCH-C9H7);
133.41 (ipsoC-C5H4); 142.00 (o-C6H3); 142.62 and
144.25 (C-C9H7); 152.06 (ipsoC-C6H3).
3
1H, J(H, H)=7.3 Hz, aromCH-C9H6); 7.23 (t, 1H,
3
3J(H, H)=7.5 Hz, aromCH-C9H6); 7.37 (d, 1H, J(H,
3
H) =7.5 Hz, aromCH-C9H6); 7.48 (d, 1H, J(H, H)=
7.5 Hz, aromCH-C9H6). 13C{1H} NMR, C6D6, 100.62
MHz: 24.16 and 24.57 (CH(CH3)2); 25.99 and 26.54
(C(CH3)2); 27.74 (CH(CH3)2); 35.08 (C(CH3)2); 40.88
(ipsoC-C9H6); 47.85 (N(CH3)2); 98.99, 105.21, 106.13
and 108.93 (C5H4); 119.81, 123.59, 124.33 and 125.96
(aromCH-C9H6); 122.71 (m-C6H3); 123.37 (p-C6H3);
127.42 (vinylCH-C9H6); 136.54 (ipsoC-C5H4); 143.36
(o-C6H3); 145.36 and 148.80 (C-C9H6); 150.53 (ipsoC-
C6H3); 178.36 (ipsoC-vinylC9H6).
C33H46N3Nb - Mass: 577.2748 — Mass Spectra: m/z
(%): [M+] 577.4 (33); [M+ –NMe2] 533.3 (100); [M+
–
HNMe2] 532.3 (58); [M+ –2×NMe2] 489.3 (24). Ele-
mental Analysis [Found (Calc.)]: C: 69.02 (68.60), H:
8.12 (8.03), N: 7.16 (7.28).
2 Preparation of the Niobium compound [Nb(NMe2)
(ꢀN-2,6-i-Pr2C6H3)(p5:p1-{C5H4}C(CH3)2{C9H6}]
4
C31H39N2Nb — Mass: 532.2173 — Mass Spectra:
m/z (%): [M+] 532.7 (100) no fragments. Elemental
Analysis [Found (Calc.)]: C: 69.53 (69.91), H: 7.32
(7.39), N: 5.19 (5.26).
3 Preparation of the Niobium compound [Nb(Cl)(ꢀ
N-2,6-i-Pr2C6H3)(p5:p3-{C5H4} C(CH3)2{C9H6}] 5 from
[Nb(NMe2)(ꢀN-2,6-i-Pr2C6H3)(p5:p1-{C5H4}C
(CH3)2{C9H6}] 4.
A solution of the niobium complex 4 (266 mg, 0.50
mmol) in toluene (10 ml) was treated with a solution of
the Me3SiCl (82 mg, 0.75 mmol) in toluene (5 ml) at
−78°C. The mixture was allowed to warm-up to room
temperature. The stirring was continued for 2 h and the
from [Nb(NMe2)3(ꢀN-2,6-iPr2C6H3)] 1 and the ligand 2.
A solution of the niobium precursor 1 (200 mg, 0.50
mmol) in toluene (10 ml) was treated with a solution of
the ligand 2 (112 mg, 0.50 mmol) in toluene (5 ml) at
−40°C. The mixture was allowed to warm-up to room
temperature, then it was slowly warmed-up to 100°C.
The stirring was continued for 2 h and then the temper-
ature increased up to 110°C. The stirring was main-
tained for 7 h and the solvent was evaporated. The
product of the reaction was dried at r.t. under vacuum
(10−2 mmHg) for 12h. Then pentane (7 ml) was added
to the residue, the solution filtered through a glass plug,

76
L. Djako6itch, W. A. Herrmann / Journal of Organometallic Chemistry 562 (1998) 71–78
Scheme 5.
solvent was evaporated. The product of the reaction
was dried at r.t. under vaccum (10−2 mmHg) for 12 h.
Then pentane (7 ml) was added to the residue, the
solution filtered through a glass plug, and evaporated.
The residue was added of heptane (5 ml) and the
solution left under argon at −78°C to give slowly 243
mg of 5 as a red micro-crystaline material. Yield: 93%.
1H NMR, C6D6, 400.13 MHz: 1.15 (d, 6H, 3J(H,
room temperature. The stirring was continued for 12 h,
and the solution filtered through a glass plug, then the
solvent was evaporated. The product of the reaction
was dried at r.t. under vacuum (10−2 mmHg) for 12 h.
Then THF (4 ml) was added to the residue to give a
dark red solution, to which pentane (1.5 ml) was added.
The solution was left under argon at −78°C to give
247 mg of 6a as an amorphous red material. Yield:
60%.
3
H)=6.6 Hz, CH(CH3)2); 1.31 (d, 6H, J(H, H)=6.4
3
Hz, CH(CH3)2); 1.56 (s, 3H, C(CH3)2); 1.58 (s, 3H,
C(CH3)2); 4.01 (br. sept., 2H, 3J(H, H)=6.6 Hz,
CH(CH3)2); 5.48 (pseudo-q, 1H, 3J(H, H)=2.6 Hz,
C5H4); 5.84 (dq, 1H, 3J(H, H)=12 Hz and 5J(H,
1H NMR, D8-THF, 400.13 MHz: 1.43 (d, 6H, J(H,
3
H)=6.5 Hz, CH(CH3)2); 1.51 (d, 6H, J(H, H)=7.1
Hz, HN(CH3)2); 1.65 (d, 6H, 3J(H, H)=6.5 Hz,
CH(CH3)2); 2.40 (s, 3H, C(CH3)2); 2.50 (s, 3H,
C(CH3)2); 3.37 (sept., 1H, 3J(H, H)=6.5 Hz,
CH(CH3)2); 4.03 (br. s, 1H, HN(CH3)2); 4.13 (sept., 1H,
3J(H, H)=6.5 Hz, CH(CH3)2); 6.45 (pseudo-q, 1H,
3
H)=2.7 Hz, vinylCH-C9H6); 5.92 (pseudo-q, 1H, J(H,
3
H)=2.6 Hz, C5H4); 6. 01 (pseudo-q, 1H, J(H, H)=
2.5 Hz, C5H4); 6.18 (m, 1H, vinylCH-C9H6); 6.29
3
3
(pseudo-q, 1H, J(H, H)=2.6 Hz, C5H4); 6.94 (t, 1H,
3J(H, H)=2.5 Hz, C5H4); 6.54 (pseudo-q, 1H, J(H,
3J(H, H)=7.5 Hz, p-C6H3); 7.02–7.33 (m, 5H, m-C6H3
H)=3.0 Hz, C5H4); 6.66 (pseudo-q, 1H, J(H, H)=2.1
3
3
and aromCH-C9H6); 7.38 (d, 1H, J(H, H)=7.5 Hz,
Hz, C5H4); 6.85 (pseudo-q, 1H, 3J(H, H)=2.5 Hz,
aromCH-C9H6). 13C{1H} NMR, C6D6, 100.62 MHz:
24.01, 24.08, 24.24 and 24.96 (CH(CH3)2); 26.18
(C(CH3)2); 28.02 and 28.25 (CH(CH3)2); 32.03
(C(CH3)2); 98.74, 107.11, 109.38 and 110.01 (C5H4);
112.08 and 112.97 (vinylCH-C9H6); 121.03 (ipsoC-
C9H6); 122.72 (m-C6H3); 123.32 (p-C6H3); 124.40,
125.67, 126.49 and 128.67 (aromCH-C9H6); 132.74 (ip-
soC-C5H4); 142.51 (o-C6H3); 145.05 and 145.66 (C-
C9H6); 152.08 (ipsoC-C6H3).
C5H4); 7.03 (pseudo-t, 1H, J(H, H)=8.1 Hz, vinylCH-
3
3
C9H6); 7.22 (t, 1H, J(H, H)=7.5 Hz, p-C6H3); 7.25
3
(pseudo-t, 4H, J(H, H)=7.5 Hz, p-C6H5B); 7.33 (d,
3
2H, J(H, H)=7.5 Hz, m-C6H3); 7.39 (pseudo-t, 8H,
3
3J(H, H)=7.5 Hz, o-C6H5B); 7.43 (t, 1H, J(H, H)=
7.1 Hz, aromCH-C9H6); 7.55 (m, 2H, aromCH-C9H6
3
and vinylCH-C9H6); 7.71 (d, 1H, J(H, H)=6.5 Hz,
aromCH-C9H6); 7.82 (br. m, 8H, m-C6H5B); 7.88 (d,
1H, 3J(H, H)=7.5 Hz, aromCH-C9H6). 13C{1H}
NMR, D8-THF, 100.62 MHz: 23.91 and 24.30
(CH(CH3)2); 26.41 (C(CH3)2); 27.72 (CH(CH3)2); 34.13
(C(CH3)2); 41.10 (HN(CH3)2); 98.35, 104.27, 105.86 and
108.60 (C5H4); 118.68 (ipsoC-C9H6); 120.86 (p-C6H5B);
121.34 (p-C6H3); 121.84 (m-C6H3); 122.32, 122.94,
123.76 and 127.62 (aromCH-C9H6); 124.72 (m-C6H5B);
126.02 and 133.52 (vinylCH-C9H6); 135.66 (ipsoC-
C5H4); 142.34 (o-C6H3); 143.76 (o-C6H5B); 147.89 and
C29H33NNbCl — Mass: 523.1358 — Mass Spectra:
m/z (%): [M+] 523.4 (100) no fragments. Elemental
Analysis [Found (Calc.)]: C: 65.91 (66.48), H: 6.29
(6.35), N: 2.67 (2.67).
4 Preparation
of
the
Niobium
compound
[Nb(NHMe2)(ꢀN-2,6-i-Pr2C6H3)(p5:p3-{C5H4}
C(CH3)2{C9H6}]+,
[B(C6H5)4]−
6a from
[Nb(NMe2)(ꢀN-2,6-i-Pr2)C6H3)(p5:p1-{C5H4}
C(CH3)2{C9H6}] 4.
1
149.78 (C-C9H6); 151.04 (ipsoC-C6H3); 163.95 (q, J(B,
A solution of the niobium complex 4 (266 mg, 0.50
mmol) in THF (10 ml) was treated with a suspension of
[NHMe3][B(C6H5)4] (190 mg, 0.50 mmol) in THF (5 ml)
at −40°C. The mixture was allowed to warm-up to
C)=49.6 Hz, ipsoC-C6H5B).
C55H60N2NbB — Mass: 852.3905 — Elemental
Analysis [Found (Calc.)]: C: 76.83 (77.43), H: 6.92
(7.09), N: 3.02 (3.29).

L. Djako6itch, W. A. Herrmann / Journal of Organometallic Chemistry 562 (1998) 71–78
77
References
5 Preparation of the Niobium compound [Nb
(NHMe2)(ꢀN-2,6-i-Pr2C6H3)(p5:p3-{C5H4}
C(CH3)2
{C9H6}]+, [Cl]− 6b from [Nb(NMe2)(ꢀN-2,6-i-Pr2C6
[1] W.A. Herrmann, B. Cornils, in: B. Cornils, W.A. Herrmann
(Eds.), Applied Homogeneous Catalysis with Organometallic
Compounds, VCH-Wiley, Weinheim, 1996, p. 9.
H3)(p5:p1-{C5H4} C(CH3)2{C9H6}] 4.
A solution of the niobium complex 4 (266 mg, 0.50
mmol) in THF (10 ml) was treated with a solution of
[NHMe3][Cl] (48 mg, 0.50 mmol) in THF (5 ml) at
−40°C. The mixture was allowed to warm-up to room
temperature. The stirring was continued for 2 h, and
the solution filtered through a glass plug, then the
solvent was evaporated. The product of the reaction
was dried at r.t. under high vacuum (10−2 mmHg) for
12 h. Then THF (4 ml) was added to the residue to give
a dark red solution, to which pentane (2 ml) was added.
The solution was left under argon at −78°C to give
207 mg of 6b as an amorphous dark red material.
Yield: 73%.
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1H NMR, D8-THF, 400.13 MHz: 1.18 (d, 6H, J(H,
3
H)=7.0 Hz, CH(CH3)2); 1.28 (d, 6H, J(H, H)=6.5
Hz, HN(CH3)2); 1.33 (d, 6H, 3J(H, H) =7.0 Hz,
CH(CH3)2); 1.85 (s, 3H, C(CH3)2); 1.98 (s, 3H,
C(CH3)2); 3.05 (sept., 1H, 3J(H, H)=7.0 Hz,
CH(CH3)2); 3.97 (sept., 1H, 3J(H, H)=7.0 Hz,
CH(CH3)2); 4.22 (br. s, 1H, HN(CH3)2); 6.18 (br.
pseudo-q, 1H, C5H4); 6.28 (br. pseudo-q, 1H, C5H4);
6.51 (br. pseudo-q, 1H, C5H4); 6.67 (pseudo-t, 1H, 3J(H,
H)=8.3 Hz, vinylCH-C9H6); 6.80 (br. pseudo-q, 1H,
C5H4); 6.92 (t, 1H, 3J(H, H)=7.5 Hz, p-C6H3); 6.99 (d,
3
1H, J(H, H)=8.3 Hz, vinylCH-C9H6); 7.06 (d, 2H,
3
3J(H, H)=7.5 Hz, m-C6H3); 7.15 (t, 1H, J(H, H)=
3
7.0 Hz, aromCH-C9H6); 7.23 (t, 1H, J(H, H)=7.5 Hz,
aromCH-C9H6); 7.33 (d, 1H, 3J(H, H)=6.9 Hz,
aromCH-C9H6); 7.59 (d, 1H, 3J(H, H)=7.5 Hz,
aromCH-C9H6). 13C{1H} NMR, D8-THF, 100.62
MHz: 21.57 and 22.86 (CH(CH3)2); 25.29 (C(CH3)2);
27.05 (CH(CH3)2); 29.25 (C(CH3)2); 40.38 (HN(CH3)2);
98.28, 106.10, 111.78 and 113.25 (C5H4); 119.88 (ipsoC-
C9H6); 121.55 (m-C6H3); 121.63 (p-C6H3); 116.77,
122.79, 123.52 and 125.18 (aromCH-C9H6); 121.70 and
124.56 (vinylCH-C9H6); 131.11 (ipsoC-C5H4); 142.58
(o-C6H3); 143.94 and 146.42 (C-C9H6); 153.58 (ipsoC-
C6H3).
C31H40N2NbCl — Mass: 568.1936 — Elemental
Analysis [Found (Calc.)]: C: 64.91 (65.47), H: 6.95
(7.09), N: 4.63 (4.93).
Acknowledgements
We are grateful to Professor Dr R. Taube (Technis-
che Universita¨t Mu¨nchen) and Dr W. Baratta (Post-
Doc) for useful discussions, to the Alexander Humboldt
Foundation for a research grant to L.D. and the Tech-
nische Universita¨t of Mu¨nchen for support.

78
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