Novel synthesis of indazoles from (η6-arene)tricarbonylchromium complexes

Article abstract of DOI:10.1016/S0022-328X(00)00215-1

Indazole chromium complexes and some of its derivatives were synthesised by two strategies: (1) by cyclisation of [η ⁶-2-(2′-phenylhydrazine)-1,3-dioxolane]tricarbonylchromium (2) in acidic conditions which was converted into σ-complex (11); (2) by thermolysis of Cr(CO)₆ with 1-bis(trimethylsilyl)methylindazole (3) and 2-bis(trimethylsilyl)methyl-3-trimethyl-silylindazole (4), using bulky protecting groups at N(1) or simultaneously at N(2) and C(3), to afford [η⁶-1-bis(trimethylsilyl)methylindazole]tricarbonylchromium (14) and [η ⁶-2-bis(trimethylsilyl)methyl-3-trimethylsilylindazole] tricarbonylchromium (15), respectively. The deprotonation of complex 14 followed by electrophilic quench occurs at the C(4) and C(7) positions in a ratio of 3:1 and with complex 15 the deprotonation was completely regioselective at the C(7) position. The position of this substitution was confirmed by n.O.e. difference spectroscopy and X-ray crystal structure determination of the [η ⁶-2-bis(trimethylsilyl)methyl-7-methyl-3-trimethylsilylindazole] tricarbonylchromium (5). These complexes were decomplexed to produce new substituted indazole derivatives in good yield.

Full text of DOI:10.1016/S0022-328X(00)00215-1

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 604 (2000) 157–169
6
Novel synthesis of indazoles from (h -arene)tricarbonylchromium
complexes
a,
a
b
M. Rute G. da Costa *, M. Jo a˜ o M. Curto , Stephen G. Davies ,
c
c
a,b
M. Teresa Duarte , C. Resende , F a´ tima C. Teixeira
a
Departamento de Tecnologia de Ind u´ strias Qu ´ı micas, Instituto Nacional de Engenharia e Tecnologia Industrial,
Estrada do Pa c¸ o do Lumiar 22, 1649-038 Lisbon, Portugal
b
The Dyson Perrins Laboratory, Uni6ersity of Oxford, South Parks Road, Oxford OX1 3QY, UK
c
Centro de Qu ´ı mica Estrutural, Complexo I, Instituto Superior T e´ cnico, A6. Ro6isco Pais, 1049-001 Lisbon, Portugal
Received 29 February 2000; accepted 3 April 2000
Abstract
6
Indazole chromium complexes and some of its derivatives were synthesised by two strategies: (1) by cyclisation of [h -2-(2%-
phenylhydrazine)-1,3-dioxolane]tricarbonylchromium (2) in acidic conditions which was converted into s-complex (11); (2) by
thermolysis of Cr(CO)6 with 1-bis(trimethylsilyl)methylindazole (3) and 2-bis(trimethylsilyl)methyl-3-trimethyl-silylindazole (4),
6
using bulky protecting groups at N(1) or simultaneously at N(2) and C(3), to afford [h -1-bis(trimethyl-
6
silyl)methylindazole]tricarbonylchromium (14) and [h -2-bis(trimethylsilyl)methyl-3-trimethylsilylindazole]tricarbonylchromium
(
15), respectively. The deprotonation of complex 14 followed by electrophilic quench occurs at the C(4) and C(7) positions in a
ratio of 3:1 and with complex 15 the deprotonation was completely regioselective at the C(7) position. The position of this
6
substitution was confirmed by n.O.e. difference spectroscopy and X-ray crystal structure determination of the [h -2-
bis(trimethylsilyl)methyl-7-methyl-3-trimethylsilylindazole]tricarbonylchromium (5). These complexes were decomplexed to pro-
duce new substituted indazole derivatives in good yield. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Indazoles; Arene complexes; Hetero arene complexes; Chromium
(
Rannunculaceae) and are used for the treatment of
1. Introduction
various diseases [4]. Although the indazole ring system
is not abundant in nature, a number of its derivatives
have been synthesised and several display a wide variety
of applications in the fields of agriculture, industry and
biology, while some are effective pharmacophores in
medicinal chemistry [1,2,5,6]. From literature results, it
appears that changes in the basicity–acidity of 1H- and
The annular tautomerism of indazole (1) concerns
the position of the NH proton, the benzenoid 1H-tau-
tomer (1a) being always more stable than the quinonoid
H-tautomer (1b) (Scheme 1) [1–3].
The two known examples of natural products con-
2
taining an indazole ring nucleus — nigellicine and
nigellidine — were isolated from Nigella sati6e Linn.
2
H-indazole derivatives dramatically changes their bio-
logical activity [6i].
There are three classical ways to prepare indazoles
and several improved syntheses have been developed.
These syntheses proceed from benzene derivatives,
where the pyrazole ring was generated by ring closure
[1,7].
Scheme 1. Annular tautomerism of indazole (Benzenoid 1H-indazole
tautomer (1a); quinonoid 2H-indazole tautomer (1b)).
The indazole ligand has been used as a nitrogen s
donor in organometallic chemistry [2,8–14] and until
now there are no reports of indazole–chromium com-
plexes. The tricarbonylchromium complexes of hetero-
*
Corresponding author.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00215-1

158
M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
2
. Results and discussion
Our initial efforts to form an indazole–chromium
complex focused on the cyclisation of a di-substituted
aromatic complex. Different cyclisation approaches to
the synthesis of indazole proceed from benzene deriva-
tives, where the pyrazole moiety was generated by ring
closure [1,7]. So logical disconnection of the indazole
tricarbonylchromium complex was examined, assuming
that the starting material must coordinate to tricar-
bonylchromium moiety very easily and the resulting
complex must be a stable di-substituted aromatic
Scheme 2. Reagents and conditions: (i) HOCH CH OH, p-
2
2
TsOH·H O, C H ; (ii) Cr(CO) , Bu O:THF (10:1).
2
6
6
6
2
complex.
The
6
retrosynthetic
analysis
from
(h -inda-
zole)tricarbonylchromium (6) shown that the best route
for disconnection starts from 2-fluorobenzaldehyde
6
(
7). As (h -2-fluorobenzaldehyde)tricarbonylchromium
Scheme 3. Reagents and conditions: (i) NH NH H O, THF, D.
2
2.
2
complex can not be prepared by direct complexation
with Cr(CO) , we synthesised 2-(2%-fluorophenyl)-1,3-
dioxolane (8) according to the literature [23]. Thermoly-
sis of Cr(CO)6 with 2-(2%-fluorophenyl)-1,3-dioxolane
6
cycles were prepared for the first time by Fischer [15].
There are a large of known tricarbonylchromium com-
plexes from heterocycles, but usually involve only one
heteroatom [16–22]. These heterocyclic p-complexes are
difficult to prepare because the nitrogen lone pair of
electrons compete with the carbocyclic ring in coordina-
tion to the metal, forming s-coordinated complexes. In
the complexation of condensed heterocycles with two
heteroatoms, such as benzoxazole and benzimidazole,
Toma observed that the main product was the
(
4
8) gave, after work-up, complex 9 as a yellow solid in
4% yield (Scheme 2). Spectroscopic data for this com-
plex are in agreement with those reported in the litera-
ture [23]. Tricarbonylchromium complexes of phenyl
halides undergo nucleophilic substitution (ipso substitu-
tion) of halogen by nucleophiles, therefore the reaction
of complex 9 and hydrazine gave, after work-up, chro-
matography and recrystallisation, complex 2 as yellow
crystals in 15% yield (Scheme 3).
To improve the yield of this nucleophilic substitution,
distinct conditions were used which are described in
Table 1. The best conditions for the substitution reac-
tion in order to obtain compound 2 were achieved
when this reaction was carried out with 2.5 equivalents
of hydrazine and refluxed over 2 days (Table 1). Using
complex 9 with hydrazine in the presence of potassium
tert-butoxide, complex 10 was isolated in 96% yield
(Scheme 4) and was totally characterised.
NꢀCr(CO) complex [18].
5
To the best of our knowledge we report herein the
first examples of indazole–chromium complexes syn-
thesised by formation of a pyrazole ring via cyclisation
6
of [h -2-(2%-phenylhydrazine)-1,3-dioxolane]tricarbonyl-
chromium (2) or by p-coordination of the tricar-
bonylchromium moiety to the arene ring of 1-bis-
(
trimethylsilyl)methylindazole (3) and 2-bis(trimethyl-
silyl)methyl-3-trimethylsilylindazole (4), using bulky
TMS groups.
After the preparation of the p-complexes we exam-
ined their deprotonation–electrophilic sequences to af-
ford new indazole derivatives, following decomplexa-
tions. In addition, we disclosed the details of the crystal
structure of complex 5 which showed its exclusive re-
gioselectivity at C(7).
Subsequent research was directed towards formation
of the pyrazole ring of indazole by a cyclisation reac-
tion. Using a solution of complex 2 in CH Cl and a
2
2
catalytic quantity of (9)-camphorsulfonic acid, after 5
min, the colour of the mixture changed from yellow to
1
red. The H-NMR spectrum of the crude reaction
Table 1
Experimental conditions for the synthesis of complex 2
Hydrazine (equivalents)
Base
Reaction time (h)
Yield of 2 (%)
1
2
2
5
1
.5
.0
.5
18
48
48
72
96
15
29
54
31
26
.5
NaHCO3 (2 equivalents)

M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
159
no p-complex was present and confirmed the presence
of a s-complex 11. This cyclisation reaction was re-
peated using p-toluenesulfonic acid, after work-up com-
plex 11 was isolated in 64% yield.
To confirm the nature of complex 11 obtained by the
procedures described above, an ether solution of this
complex was exposed to air and light. The colourless
®
Scheme 4. Reagents and conditions: (i) NH NH H O, THF; (ii)
t-BuOK, 18 h, D.
solution was filtered through Celite and the solvent
2
2.
2
1
removed to afford a colourless oil and its H-NMR
spectrum proved it to be identical with the 1H-indazole
reported in the literature [13].
The formation of the indazole by cyclisation of com-
plex 2 was observed, but the transference of the
chromium fragment to the nitrogen atom makes this
route unsuccessful for the synthesis of the p-complex 6.
Hence, any approach to the synthesis of an indazole
p-complex could be via the preparation of a protected
indazole to prevent s-complexation.
Strategies for the formation of p-complexes of pyridi-
nes [20,21], thiophenes [22], benzothiazoles and benzim-
idazoles [24] have demonstrated the usefulness of
alkylsilyl groups or other bulky groups. Thus, a similar
strategy was envisaged to increase steric hindrance at
the nitrogen atoms of indazole.
Scheme 5. Reagents and conditions: (i) CSA, CH Cl , r.t.
2
2
N-Methylation of indazole (1) with n-BuLi–MeI at
−
78°C afforded a mixture of 1-methylindazole (12)
and 2-methylindazole (13) which were separated by
chromatography, giving white crystals in 58 and 40%
yield, respectively (Scheme 6), whose the unambiguous
assignment was carried out by H- and C-NMR spec-
tra [3,25–30].
Scheme 6. Reagents and conditions: (i) n-BuLi or NaH; (ii) MeI.
1
13
This reaction was also carried out using NaH as a
deprotonating agent, in which case compounds 12 and
1
3 were isolated in 52 and 40% yield, respectively.
To protect both nitrogen lone pair of electrons, a
Scheme 7. Reagents and conditions: (i) t-BuLi; (ii) TMSCl.
subsequent deprotonation of 1-methylindazole (12) and
-methylindazole (13) with base, followed by elec-
trophilic quench with TMSCl was developed.
mixture showed only the presence of the s-complex 11.
2
The mixture was purified by column chromatography
to give yellow crystals of compound 11 in 62% yield
Thus, 1-methylindazole (12) reacted with t-BuLi (3.5
1
(
Scheme 5). The H-NMR spectrum of this yellow
equivalents)–TMSCl at
bis(trimethylsilyl)methylindazole (3) in 73% yield
Scheme 7) which is in agreement with Tertov’s results
−78°C to form 1-
1
s-complex was identical to the H-NMR spectrum of
the same complex when the free indazole is submitted
to direct complexation with Cr(CO)6 in which the
chromium moiety is s-bonded to the nitrogen lone pair
of electrons. This lone pair is in the same plane as the
pyrazole ring and it has a greater tendency to coordi-
nate to the chromium moiety. The carbon signals on
(
1
[31], who has used n-BuLi at −15°C. The H-NMR
spectrum of 3 shows a singlet at l 0.06 attributed to
two TMS groups and one proton singlet at l 3.55
attributed to a methine proton which confirms this
deprotonation. The presence of a proton singlet at l
7.94 confirms that the H(3) position was not silylated.
2-Methylindazole (13) also reacted with t-BuLi–TM-
SCl in the above experimental conditions to form 2-
bis(trimethylsilyl)methyl-3-trimethylsilylindazole (4) as
a colourless oil in 98% yield. The metallation occurred
simultaneously at two adjacent non-equivalent groups
1
3
the C-NMR spectrum were only very slightly shifted
relative to the free indazole, except a slight deshielding
of the C(3) signal (l 142.16) compared with the free
ligand (l 135.2) [13]. Infrared analysis showed the
presence of the extremely strong carbonyl stretching
−
1
frequencies at 1970 and 1903 cm
and the presence of
1
the pentacarbonylchromium fragment was also con-
(Scheme 8). These observations were confirmed by H-
+
13
firmed by mass spectrometry (m/z=310, M ). All
and C-NMR spectroscopies which showed the pres-
spectroscopic data for this complex showed clearly that
ence of the TMS signals, with the C(3) signal appearing

160
M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
1
as a Cipso (l 132.84). Similar results were documented
by Tertov [31] who found that 1-methylindazole (12)
was metallated by n-BuLi (−15°C) at the N-methyl
group and 2-methylindazole (13) was only lithiated at
the 3-position. Using t-BuLi we also observed metalla-
tion of the N-methyl group of the 2-methylindazole
H-NMR spectra analysis of these complexes showed
four up-field resonances relative to the carbocyclic pro-
tons, strong evidence for the presence of a p-complex
13
with the carbocyclic ring. C-NMR spectra also con-
firmed these attributions.
As expected from the literature [16], the complexa-
tion occurred on the carbocyclic ring rather than to the
pyrazole ring. These reactions also showed that the use
of sterically demanding TMS groups provide ample
steric hindrance at the nitrogen lone pair and promote
p-complexation on the carbocyclic ring, eliminating the
possibility of s-coordination with nitrogen. The p-
bonding of the tricarbonylchromium fragment to the
carbocyclic ring of the protected indazoles described
here, is consistent with the behaviour of other con-
densed heterocycles, such as indole [16], quinaldine [17],
benzothiophene [16,19] and benzofuran [16].
The tricarbonylchromium unit in these p-complexes
creates the potential for promoting substitution in the
carbocyclic ring. This enables proton abstraction to
occur in conditions under which the uncomplexed sub-
strate is unreactive. Subsequent efforts were directed
towards the investigation of the effect of deprotonation
agents upon complexes 14 and 15.
(
13).
Directed complexation of compound 3 and 4 with
Cr(CO) under reflux afforded complexes 14 and 15 in
6
6
0 and 92% yield, respectively, Bu O–n-heptane being
2
the most effective solvent systems (Schemes 9 and 10).
Scheme 8. Reagents and conditions: (i) t-BuLi; (ii) TMSCl.
Scheme 9. Reagents and conditions: (i) Cr(CO) , Bu O–n-heptane
6
2
Treatment of complex 14 with n-BuLi–TMEDA in
(1:1), D, 6 days.
1
THF, followed by MeI quenching gave a red oil. H-
NMR spectrum of the crude reaction mixture showed
the presence of complexes 16, 17 and 18 in a ratio 6:2:3
(
Scheme 11). Column chromatography allowed isola-
tion of 4- and methine-substituted indazole complex 17
in 11% yield. However, despite careful and repeated
attempts to separated complexes 16 and 18, only the
major 4-substituted indazole 16 was isolated in 24%
yield, after repeated recrystallisations.
Scheme 10. Reagents and conditions: (i) Cr(CO) , Bu O–n-heptane
6
2
(1:1), D, 6 days.
The structure of complex 16 was assigned to a 4-sub-
stituted indazole complex by nuclear Overhauser effect
(
n.O.e) difference spectroscopy. Irradiation of the CH3
protons at the 4-position results in the enhancement in
the H(5) and H(3) resonances (Fig. 1). All the data for
this complex were consistent with the proposed
structure.
The structure assignment of complex 17 was based
1
on its H-NMR spectrum which showed the presence of
three contiguous protons in the complexed arene ring,
one proton singlet at l 7.86 attributed to H(3) of the
pyrazole nucleus and two singlets each one relative to
three protons at l 2.04 and the other at l 2.63 due to
two new methyl groups. The C-NMR spectrum, with
the characteristic carbon signal at high field attributed
to C(7), is similar to that of complex 16 and similar to
literature data [3].
Scheme 11. Reagents and conditions: (i) n-BuLi–TMEDA; (ii) MeI.
13
Complex 18 could not be isolated pure, but the
H-NMR spectrum of its mixture with complex 16
1
allowed to assign complex 18 as the 7-substituted
Fig. 1. n.O.e. difference spectroscopy of complex 16.
isomer.

M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
161
plexed indazole [32], this strategy allowed the formation
of the 4-substituted indazole derivatives and no 5-sub-
stituted derivative was produced [1,2].
The first strategy for the deprotonation–electrophilic
quench sequence outlined for complex 14 was extended
to complex 15. Lithiation of complex 15 with n-BuLi–
TMEDA or n-BuLi, followed by MeI quench, afforded
only the 7-substituted indazole complex 5 (Scheme 12).
With n-BuLi–TMEDA the yield of the complex 5 was
much better (81%) than in n-BuLi (20%).
1
The H-NMR spectrum of complex 5 indicated the
presence of three contiguous protons in the complexed
homocyclic ring and a three protons singlet at l 2.67
due to the new methyl substituent in complex 5. The
structure of complex 5 was initially assigned by n.O.e.
difference spectroscopy. Irradiation of the methyl pro-
tons of the electrophile at l 2.72 results in the enhance-
ment of the H(6) resonance and no enhancement in the
resonance of the TMS protons at C(3) (Fig. 2). These
observations were only consistent with a 7-substituted
indazole complex derivative.
+
Scheme 12. Reagents and conditions: (i) n-BuLi–TMEDA; (ii) E .
Fig. 2. n.O.e. difference spectroscopy of complex 5.
At the single crystal X-ray structure analysis of com-
plex 5, two geometrically identical molecules were
found in the asymmetric unit. Fig. 3a shows the molec-
ular diagram while Table 2 displays selected bond
lengths and angles. The coordination geometry around
the chromium is the usual for these (h -
arene)tricarbonylchromium complexes, the so called
three legged piano stool. The indazole ring is planar
This deprotonation–methylation sequence was re-
peated in the absence of TMEDA by a similar proce-
dure. Analysis of the crude product by H-NMR
1
spectroscopy demonstrated that only complexes 16 and
18 were formed in a ratio 3:1. Under these experimental
6
conditions, the deprotonation–methylation sequence of
complex 14 resulted in 4- and 7-substituted indazoles,
16 and 18, respectively, the 4-substituted complex being
with maximum deviations of 90.049(7) A to the mean
,
least squares plane. Atoms C(8), C(9), H(9) and Si(1)
are also in the plane of the ring. The chromium is at an
the major complex. Presumably, the steric effect of the
bulky bis(trimethylsilyl)methyl group present in com-
plex 14 generates steric hindrance and disfavours de-
protonation at the 7-position, with deprotonation of
average distance of 1.758(4) A
ring, even though atoms C(3a) and C(7a) present a
slight longer bonding distance, 2.319(5) and 2.329(6) A
,
from the carbocyclic
4-position predominating. In contrast to the uncom-
,
,
Fig. 3. (a) Molecular diagram of complex 5 and (b) view of the molecule showing the relative positions of carbonyl ligands to the carbocyclic ring.

162
M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
Table 2
C(3) position, with the methine proton in the same
direction of the 3-substituent (Fig. 3a).
Selected bond lengths (A) and angles (°) for complex 5
,
A view of the structure from the uncomplexed face of
the indazole complex 5 shows the tricarbonylchromium
tripod with respect to the carbocyclic ring, rotated
away from the ideally staggered conformation, with the
carbonyl groups located between C(5) and C(6) and
near C(4) and C(7) (Fig. 3b). This is indicative of
enhanced electron deficiency at C(4) and C(7) and thus
enhanced the anion stabilisation at these centers [34].
The origins of the regioselective deprotonation can
be rationalised in terms of chelation control and steric
effect. Coordination of the lithium cation to the nitro-
gen lone pair of electrons at N(1) could increase the
acidity of the 7-position, giving rise to selective removal
of the proximal C(7) hydrogen to produce the corre-
sponding stabilised anion. The deprotonation of the
C(4) position is precluded in this case, because the very
bulky TMS group at C(3) position prevent approach of
the bases employed to the C(4) hydrogen. The selected
deprotonation–electrophilic sequence of complex 15
leads to a total regioselectivity at C(7), in contrast to
the deprotonation of complex 14 and the electrophilic
substitution of the uncomplexed 2H-indazole [1,32].
With the structure of complex 5 established, the
lithiated complex was treated with other electrophiles
Bond length
Cr(1)ꢀC(20)
Cr(1)ꢀC(21)
Cr(1)ꢀC(19)
Cr(1)ꢀC(5)
Cr(1)ꢀC(6)
Cr(1)ꢀC(4)
Cr(1)ꢀC(7)
Cr(1)ꢀC(3a)
Cr(1)ꢀC(7a)
C(3)ꢀN(2)
C(3)ꢀC(3a)
C(3a)ꢀC(7a)
C(7a)ꢀN(1)
C(7a)ꢀC(7)
C(7)ꢀC(6)
1.827(7)
1.832(7)
1.846(7)
2.198(6)
2.201(6)
2.224(6)
2.261(6)
2.319(5)
2.329(6)
1.354(7)
1.421(7)
1.428(7)
1.344(7)
1.425(7)
1.386(8)
1.489(9)
1.404(9)
1.397(8)
1.365(6)
1.462(7)
C(7)ꢀC(8)
C(6)ꢀC(5)
C(5)ꢀC(4)
N(1)ꢀN(2)
N(2)ꢀC(9)
Bond angles
C(20)ꢀCr(1)ꢀC(21)
C(20)ꢀCr(1)ꢀC(19)
C(21)ꢀCr(1)ꢀC(19)
C(3)ꢀN(2)ꢀC(9)
N(1)ꢀN(2)ꢀC(9)
N(2)ꢀC(9)ꢀSi(3)
N(2)ꢀC(9)ꢀSi(2)
Si(3)ꢀC(9)ꢀSi(2)
86.7(3)
90.0(3)
86.9(3)
129.2(4)
115.1(4)
111.0(4)
109.5(4)
120.4(3)
(ClCO
complexes 19 and 20 (Scheme 12). In both cases the
-substituted complex 19 and 20 were isolated in pure
Me and ClCO Et) to give substituted indazole
2
2
7
form by column chromatography in 25 and 26% yield,
respectively. The corresponding decomplexed indazoles
2
1 and 22 were also isolated in 33 and 40% yield,
respectively. These compounds were fully characterised
and data are in agreement with the proposed structures.
Complexes 16 and 5 were subject to decomplexation
reactions, by exposing ether solutions of both com-
plexes to air and light until the yellow colour of the
solutions disappeared. Filtration to remove chromiu-
m(III) residues, followed by evaporation of the filtrate
afforded the decomplexed indazoles 23 and 24, respec-
tively (Schemes 13 and 14). C-NMR spectroscopy
showed the absence of the carbonyl signals and infrared
analyses confirmed the removal of the tricar-
bonylchromium moiety in both cases.
Scheme 13. Reagents and conditions: (i) hw, O2.
13
Scheme 14. Reagents and conditions: (i) hw, O2.
Desilylation at the C(3), N(2) or N(1) positions of
these compounds can easily be carried out by known
procedure to afford the corresponding free indazole
derivatives [35].
respectively (see Table 2). All the distances within the
carbocyclic ring are as found in other related com-
pounds [13,19,33].
The results of X-ray structural analysis of complex 5
clearly confirmed that substitution occurred at the C(7)
position and the carbocyclic ring was h -coordinated to
3
. Conclusions
6
the tricarbonylchromium fragment. It could also be
seen that the most stable conformation of complex 5 is
the one where the two TMS substituents at N(2) are in
opposite direction with respect to the TMS group at the
We reported the synthesis of the first indazole
chromium complexes. The cyclisation of [h -2-(2%-
phenylhydrazine) - 1,3 - dioxolane]tricarbonylchromium
6
(
2) afforded the indazole s-complex (11) only.

M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
163
6
The p-complexes [h -1-bis(trimethylsilyl)methylinda-
recorded on a Kratos 25 RF, a VG MicromassLab
ZAB 1F, a VG MassLab 20–250 or an APCI
Plataform spectrometer. High resolution mass spectra
(HRMS) were obtained on a VG AutoSpect instru-
ment. Elemental analysis were performed on a Carlo
Erba 1106 elemental analyser.
6
zole]tricarbonylchromium (14) and [h -2-bis(trimethyl-
silyl)methyl - 3 - trimethylsilylindazole]tricarbonylchro-
mium (15) were successfully prepared for the first time
via direct complexation of hindered silylated com-
pounds 3 and 4, respectively.
6
Establishment of experimental conditions of deproto-
nation–electrophilic sequence of complexes 14 and 15
allowed to determine their regioselectivity. In complex
[2-(2%-Fluorophenyl)-1,3-dioxolane] (8) and [h -2-(2%-
fluorophenyl)-1,3-dioxolane]-tricarbonylchromium (9)
were prepared according to the literature [23] and the
spectroscopic data were identical with those reported.
1
4 the nature of carbanion and the steric hindrance of
substituents on the indazole created more than one
position for electrophilic attack on the indazole com-
plex, the 4-substituted complex 16 being the major
complex formed. In complex 15 we have established the
exclusive C(7) funcionalisation which will allow the
development of the synthesis of a great variety of C(7)
functionalised indazoles.
6
4.1. [p -2-(2%-Phenylhydrazine)-1,3-dioxolane]-
tricarbonylchromium (2)
To a solution of complex 9 (201 mg, 0.66 mmol) in
THF (40 ml) was added hydrazine hydrate (0.08 ml,
1.65 mmol) and the mixture was heated at reflux for 2
days. The solution was filtered through silica, eluted
with ethyl acetate and the solvents were removed in
vacuo to give a yellow oil. Column chromatography
(petrol–ether (7:3)), followed by recrystallisation from
ether–petrol, gave complex 2 (113 mg, 54%) as yellow
crystals. M.p. 120–121°C. IR wmax (KBr): 3412, 3323
(NꢀH), 3096 (CꢀH)Ar, 2975, 2908 (CꢀH), 1964, 1867,
4. Experimental
All the reactions involving air sensitive reagents and
organometallic complexes, as well as their purification,
were performed under an atmosphere of dry nitrogen
and all solvents were degassed before use. All solvents
were distilled under a nitrogen atmosphere. Diethyl
−
1
1
1830 (CꢁO), 1638, 1546, 1485 cm
(300 MHz, CDCl ): l 3.53 (2H, br s, NH ), 4.05 (2H,
m, OCH CH O), 4.26 (2H, m, OCH CH O), 4.81 (1H,
(CꢂC). H-NMR
3
2
2
2
2
2
ether (referred to ether), THF, dibutyl ether (Bu O) and
t, J 6.3, 4-H or 5-H), 5.55 (1H, d, J 6.9, 3-H or 6-H),
5.68 (1H, t, J 6.3, 5-H or 4-H), 5.72 (1H, s, OCHO),
5.84 (1H, d, J 6.3, 6-H or 3-H), 6.29 (1H, br s, NH).
2
dioxane were distilled from Na–benzophenone ketyl.
CH Cl was distilled from calcium hydride. ‘Petroleum
2
2
13
ether’ (petrol) refers to the fraction distilling between 40
and 60°C and was redistilled before use. Reagents were
used as purchased and when necessary were purified
according to standard procedures [36]. n-BuLi was used
as a 1.3–1.6 M solution in hexane and t-BuLi as a
C-NMR (75 MHz, CDCl ): l 65.00 (OCH CH O),
3 2 2
65.46 (OCH CH O), 73.69, 82.19, 95.80, 96.90, 100.74
2
2
(Ar:C3ꢀC6, OꢀCHꢀO), 89.92 (Ar:C1, Cipso), 132.91
+
(Ar:C2, C ), 234.11 (CO). m/z (EI): 316 (M , 11%),
ipso
+
+
+
260 (M −2CO, 3%), 232 (M −3CO, 3%), 180 [M
−Cr(CO) , 1%], 52 (Cr , 100%). Anal. Found: C,
+
1.0–1.7 M solution in hexane and were titrated immedi-
3
ately before use. NaH was used as 60% dispersion in
mineral oil, which was washed with petrol and dried in
vacuo before use. Column chromatography was per-
formed on silica gel (230–400 Mesh) under a positive
pressure of nitrogen. Melting points were determined
on a Reichert Thermovar or on a Gallenkamp melting
point apparatus and are uncorrected. Infrared spectra
were recorded using a Perkin–Elmer 172SX Fourier
45.81; H, 3.69; N, 8.86. Calc.: C, 45.58; H, 3.82; N,
8.86%.
6
4.2. [p -2-(2%-tert-Butoxyphenyl)-1,3-dioxolane]-
tricarbonylchromium (10)
To a solution of potassium tert-butoxide (518 mg,
4.86 mmol) in THF (20 ml) at 0°C, was added hy-
drazine hydrate (0.15 ml, 3.09 mmol), followed by
addition of complex 9 (468 mg, 1.54 mmol) in THF (30
ml). This mixture was heated at reflux for 18 h. The
resulting solution was filtered through silica, eluted with
ethyl acetate and the solvents were removed in vacuo to
give complex 10 (529 mg, 96%) as yellow crystals. M.p.
91–92°C. IR wmax (KBr): 3085 (CꢀH)Ar, 2977, 2931,
2895 (CꢀH), 1972, 1884, 1864 (CꢁO), 1523, 1504, 1477
1
Transform or a Perkin–Elmer 781 instrument. H-
NMR spectra were recorded at 200 MHz on a Varian
Gemini 200 or a Bruker AC 200 spectrometer, or at 300
MHz on a General Electrical QE-300 spectrometer.
1
3
C-NMR spectra were recorded at 75 MHz on a
General Electrical QE-300 spectrometer or a Bruker
WH 300 spectrometer, or at 125 MHz on a Bruker
AMX 500 spectrometer. NMR spectra were recorded in
−
1
1
CDCl , using tetramethylsilane (lH 0.00 ppm) or resid-
cm
(CꢂC). H-NMR (300 MHz, CDCl ): l 1.47 [9H,
3
3
ual CHCl (lH 7.26 ppm; lC 77.0 ppm) as internal
s, OC(CH ) ], 3.98–4.20 (4H, m, OCH CH O), 4.85
3
3 3 2 2
standard. Chemical shifts (l) are reported in ppm and
coupling constants (J) in Hz. Mass spectra (m/z) were
(1H, t, J 6.3, ArH, 4-H or 5-H), 5.24 (1H, d, J 6.6,
ArH, 3-H or 6-H), 5.49 (1H, dt, J 6.3 and 1.2, ArH,

164
M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
5
3
-H or 4-H), 5.84 (1H, dd, J 6.3 and 1.2, ArH, 6-H or
-H), 5.86 (1H, s, OCHO). C-NMR (75 MHz,
4.6. Preparation of 1-methylindazole (12) and
2-methylindazole (13) using two different processes
13
CDCl ): l 28.75 [OC(CH ) ], 65.64 (OCH CH O),
3
3 3
2
2
8
8
2.09, 84.68, 92.82, 94.23, 98.38 (Ar:C3ꢀC6, OꢀCHꢀO),
4.6.1. Using n-BuLi as base
2.22 [OC(CH ) , C ], 97.09 (Ar:C1, Cipso) 140.03
n-BuLi (9.0 ml, 11.70 mmol) was added dropwise to
a solution of indazole (1) (1.07 g, 9.02 mmol) in THF
(50 ml) at −78°C. After 30 min, the reaction mixture
was warmed to 0°C, stirred over 15 min and then
recooled to −78°C. After 15 min, excess MeI (1.7 ml,
3
3
ipso
+
(
Ar:C2, C ), 232.80 (CO). m/z (EI): 358 (M , 22%),
ipso
+
+
3
02 (M −2CO, 6%), 274 (M −3CO, 17%), 173
+
(
C H O Cr , 100%). Anal. Found: C, 53.38; H, 4.87.
7 5 2
Calc.: C, 53.64; H, 5.06%
2
7.3 mmol) was added and the reaction mixture was
1
4
(
.3. Preparation of (p -indazole)pentacarbonylchromium
allowed to warm slowly to r.t. and stirred overnight.
After quenching with methanol (1 ml), the solvent was
removed under reduced pressure. The residue was redis-
solved in ether, filtered through a plug of magnesium
sulfate and silica and the solvent removed in vacuo.
Purification of the resulting pale yellow oil by column
chromatography (petrol–ether (3:2)) gave the known
1-methylindazole (12) (690 mg, 58%), followed by 2-
methylindazole (13) (481 mg, 40%), both as white crys-
11) 6ia cyclisation of complex 2
To a solution of complex 2 (40 mg, 0.13 mmol) in
CH Cl (10 ml) was added (9)-camphorsulfonic acid
5 mg). After stirring for 5 min at r.t., the solvent was
2
2
(
evaporated. The residue was redissolved in ether,
filtered through a plug of silica and the solvent was
removed in vacuo. Purification of the resulting yellow
oil by column chromatography (petrol–ether (1:1))
gave compound 11 (15 mg, 62%) as yellow crystals.
M.p. (dec.) 113°C. IR wmax (KBr): 3470 (NꢀH), 3078
talline solids. Compound 12: M.p. 58°C ([27] 60–61°C).
1
H-NMR (300 MHz, CDCl ): l 3.99 (3H, d, J 1.2,
3
NCH ), 7.07–7.13 (1H, m, ArH), 7.31–7.34 (2H, m,
3
−
1
(
(
(
7
(
(
(
2
2
1
CꢀH)Ar, 1970 and 1903 (CꢁO), 1629, 1510, 1439 cm
ArH), 7.68 (1H, d, J 8.1, ArH), 7.95 (1H, s, 3-H).
1
13
CꢂC, CꢂN). H-NMR (300 MHz, CDCl ): l 7.20–7.24
C-NMR [29] (75 MHz, CDCl ): l 35.20 (NCH ),
3
3
3
1H, m, ArH), 7.46 (1H, m, ArH), 7.48 (1H, m, ArH),
108.66 (Ar:C7), 120.18 (Ar:C5), 120.80 (Ar:C4), 123.77
(Ar:C3a), 125.94 (Ar:C6), 132.44 (Ar:C3), 139.62
(Ar:C7a). m/z (EI): 132 (M , 100%). Compound 13:
M.p. 56°C ([27] 56°C). H-NMR (300 MHz, CDCl ): l
4.19 (3H, s, NCH ), 7.07 (1H, t, J 7.5, ArH), 7.27 (1H,
.68 (1H, d, J 8.2, ArH), 8.08 (1H, d, J 1.5, 3-H), 9.89
1H, br s, NH). C-NMR (125 MHz, CDCl ): l 108.94
Ar:C7), 119.87, 122.50, 128.58 (Ar:C4ꢀC6), 123.44
Ar:C3a), 141.31 (Ar:C7a), 142.16 (Ar:C3), 214.20,
20.02 (CO). m/z (EI): 310 (M , 1%), 198 (M −4CO,
%), 170 (M −5CO, 11%), 118 [M −Cr(CO) ,
00%]. Anal. Found: C, 46.21; H, 1.92; N, 8.84. Calc.:
1
3
+
3
1
3
3
+
+
t, J 7.5, ArH), 7.63 (1H, d, J 7.8, ArH), 7.70 (1H, d, J
8.4, ArH), 7.85 (1H, s, 3-H). m/z (EI): 132 (M , 100%).
+
+
+
5
C, 46.47; H, 1.95; N, 9.03%.
4.6.2. Using NaH as base
A solution of indazole (1) (1.93 g, 8.72 mmol) in
THF (10 ml) was added to a suspension of NaH (1.27
g, 42.3 mmol) in THF (25 ml). When no further gas
was evolved, the mixture was cooled to 0°C and MeI
(2.7 ml, 43.1 mmol) was added. The reaction mixture
was stirred at r.t. overnight. Ether (150 ml) was added
to the reaction mixture and the resulting solution
1
4
.4. Preparation of (p -indazole)pentacarbonylchromium
(
11) from indazole (1)
A solution of indazole (1) (500 mg, 4.23 mmol) and
Cr(CO) (1.12 g, 5.08 mmol), in Bu O (50 ml) and THF
5 ml), was heated at reflux for 4 days. The resulting
yellow solution was filtered through silica, washed ini-
tially with petrol (100 ml) and then CH Cl (200 ml) to
yield a yellow solution. Evaporation of solvents in
vacuo and recrystallisation from ether–n-hexane gave
compound 11 (679 mg, 52%) as a yellow solid. M.p.
6
2
(
®
filtered through Celite . After evaporation of the sol-
vents the resulting mixture was purified by column
chromatography (petrol–ether (3:2)) to give 1-
methylindazole 12 (630 mg, 52%) and 2-methylindazole
13 (460 mg, 40%), both as white crystalline solids.
2
2
(
dec.) 113°C. All spectroscopic data were identical to
the previously described.
4.7. 1-[bis(Trimethylsilyl)methyl]indazole (3)
4
.5. Decomplexation of
t-BuLi (10.9 ml, 18.09 mmol) was added dropwise to
a solution of compound 12 (680 mg, 5.15 mmol) in THF
1
(p -indazole)pentacarbonylchromium (11)
(
20 ml). After stirring at −78°C for 2 h, TMSCl
A solution of complex 11 (30 mg, 0.097 mmol) in
(2.6 ml, 20.49 mmol) was added and the reaction was
stirred at −78°C for 1.5 h. Work-up was performed
using the same procedure as in Section 4.6.1. Purifica-
tion of the resulting orange oil by column chromatog-
raphy (petrol–ether (9:1)) gave compound 3 (1.03 g,
ether (15 ml) was exposed to air and sunlight. After 5
®
days, filtration through Celite and evaporation of the
solvent gave indazole (1) (10 mg, 88%) identical with an
authentic sample.

M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
165
7
3
1
3%) as white crystals. M.p. 58°C. IR wmax (KBr): 3057,
{CH[Si(CH ) ] }, 76.59 (Ar:C7), 84.86, 89.17, 90.15
3 3 2
041 (CꢀH)Ar, 2955, 2898, 2876 (CꢀH), 1614, 1496,
(Ar:C4ꢀC6), 94.11 (Ar:C3a), 118.38 (Ar:C7a), 134.23
−
1
1
+
+
462, 1416 cm
(CꢂC, CꢂN). H-NMR (300 MHz,
(Ar:C3), 232.60 (CO). m/z (APCI ): 413 (MH , 18%),
+
+
CDCl ): l 0.06 {18H, s, CH[Si(CH ) ] }, 3.55 {1H, s,
CH[Si(CH ) ] }, 7.04–7.09 (1H, m, ArH), 7.29–7.30
357 (MH −2CO, 20%), 329 (MH −3CO, 27%), 277
3
3 3 2
+
[MH −Cr(CO) , 100%]. Anal. Found: C, 49.52; H,
3
3 2
3
(
3
{
2H, m, ArH), 7.69 (1H, d, J 8.1, ArH), 7.94 (1H, s,
5.65; N, 6.60. Calc.: C, 49.49; H, 5.86; N, 6.79%.
1
3
-H).
C-NMR (125 MHz, CDCl3):
l
−0.45
6
CH[Si(CH ) ] }, 43.09 {CH[Si(CH ) ] }, 109.37
4.10. {p -2-[bis(Trimethylsilyl)methyl]-3-
3
3 2
3 3 2
(
(
2
Ar:C7), 119.54, 120.80, 125.13 (Ar:C4ꢀC6), 131.22
Ar:C3), 123.14 (Ar:C3a), 139.86 (Ar:C7a). m/z (EI):
trimethylsilylindazole}tricarbonylchromium (15)
+
+
+
76 (M , 26%), 261 (M −Me, 21%), 203 (M −
A mixture of compound 4 (1.61 g, 4.61 mmol) and
+
+
SiMe , 70%), 73 (SiMe , 100%) (HRMS Found: MH ,
2
Cr(CO)6 (1.52 g, 6.92 mmol) in Bu O (50 ml) and
3
3
2
+
77.154870; C H N Si . Calc.: MH , 277.155631).
n-heptane (50 ml) was heated at reflux for 6 days. The
solution was treated as in procedure of Section 4.4 to
afford a red oil. Recrystallisation from ether–petrol
gave compound 15 (2.05 g, 92%) as red crystals. M.p.
1
4
24
2
2
4
.8. 2-[bis(Trimethylsilyl)methyl]-3-trimethylsilyl-
indazole (4)
1
69–170°C. IR wmax (KBr): 2958, 2901 (CꢀH), 1958,
−1
A solution of 2-methylindazole (13) (481 mg, 3.64
mmol) in THF (20 ml) was treated with t-BuLi (7.7 ml,
1875, 1860 (CꢁO), 1554, 1494, 1437 cm
(CꢂC, CꢂN).
0.05 [9H, s,
1
H-NMR (200 MHz, CDCl3):
l
12.78 mmol) and TMSCl (1.85 ml, 14.58 mmol) accord-
CHSi(CH ) ], 0.12 [9H, s, CHSi(CH ) ], 0.54 [9H, s,
3 3 3 3
ing to the procedure in Section 4.7 to afford an orange
oil. Column chromatography (petrol–ether (19:1)) gave
compound 4 (1.25 g, 98%) as a colourless oil. IR wmax
Si(CH ) ], 3.66 {1H, s, CH[Si(CH ) ] }, 5.29 (1H, t, J
3 3 3 3 2
6.7, 5-H or 6-H), 5.51 (1H, t, J 6.7, 6-H or 5-H), 6.34
(1H, d, J 6.8, 4-H or 7-H), 6.47 (1H, d, J 6.9, 7-H or
13
(
1
(
film): 3090, 3046 (CꢀH)Ar, 2955, 2900 (CꢀH), 1617,
4-H).
C-NMR (125 MHz, CDCl3):
l
−0.84
−
1
1
579, 1544, 1489, 1450 cm
(CꢂC, CꢂN). H-NMR
[CHSi(CH ) ], −0.45 [CHSi(CH ) ], 0.61 [Si(CH ) ],
3
3
3 3
3 3
300 MHz, CDCl ): l 0.08 {18H, s, CH[Si(CH ) ] },
52.15 {CH[Si(CH ) ] }, 82.49, 85.03, 89.30, 92.34
3
3 3 2
3 3 2
0
7
9
.50 [9H, s, Si(CH ) ], 3.74 {1H, s, CH[Si(CH ) ] },
(Ar:C4ꢀC7), 103.47 (Ar:C3a), 126.88 (Ar:C7a), 138.21
3
3
3 3 2
+
.02 (1H, m, ArH), 7.21 (1H, m, ArH), 7.71 (1H, d, J
(Ar:C3), 233.55 (CO). m/z (EI): 484 (M , 1%), 400
13
+
+
.3, ArH), 7.74 (1H, d, J 9.0, ArH). C-NMR (125
−0.68 {CH[Si(CH ) ] }, 1.14
(M −3CO, 10%), 348 [M −Cr(CO) , 10%], 333
3
+
MHz, CDCl3):
l
(348-Me, 21%), 275 (348-SiMe , 34%), 73 (SiMe ,
3 3 2
3
3
[
1
(
3
Si(CH ) ], 49.49 {CH[Si(CH ) ] }, 117.26, 120.19,
100%). Anal. Found: C, 49.78; H, 6.75; N, 5.76. Calc.:
C, 49.56; H, 6.65; N, 5.78%.
3
3
3 3 2
20.66, 123.70 (Ar:C4ꢀC7), 129.32 (Ar:C3a), 132.84
+
Ar:C3), 148.85 (Ar:C7a). m/z (EI): 348 (M , 30%),
+
+
6
33 (M −Me, 85%), 275 (M −SiMe , 69%), 73
4.11. {p -1-[bis(Trimethylsilyl)methyl]-4-
3
+
(
SiMe , 100%) (HRMS Found: MH , 349.195256;
methylindazole}tricarbonylchromium (16),
3
+
6
C H N Si . Calc.: MH , 349.195160).
{p -1-[1%,1%-bis(trimethylsilyl)ethyl]-4-methylindazole}-
1
7
32
2
3
6
tricarbonylchromium (17) and {p -1-[bis(trimethyl-
6
4
.9. {p -1-[bis(Trimethylsilyl)methyl]indazole}-
silyl)methyl]-7-methylindazole}tricarbonyl-
tricarbonylchromium (14)
chromium (18)
A mixture of compound 3 (758 mg, 2.75 mmol) and
4.11.1. Reaction of complex 14 with n-BuLi–TMEDA
and MeI
Cr(CO)6 (1.00 g, 4.55 mmol) in Bu O (50 ml) and
2
n-heptane (50 ml) was heated at reflux for 6 days. The
solution was treated as in procedure of Section 4.4 to
afford a red oil. Column chromatography [petrol–ether
n-BuLi (0.23 ml, 0.315 mmol) was added dropwise to
a solution of complex 14 (100 mg, 0.242 mmol) and
TMEDA (0.11 ml, 0.726 mmol) in THF (20 ml), at
−78°C. After stirring at −78°C for 1.5 h, MeI (0.05
ml, 0.726 mmol) was added. The solution was stirred at
−78°C for 3 h and subsequently was allowed to warm
slowly to r.t. and stirred overnight. Work-up was per-
formed using the same procedure as in Section 4.6.1 to
afford a red oil. Column chromatography [n-hexane–
CH Cl (10:1)] led to the isolation of two fractions.
(
9:1)], followed by recrystallisation from ether–n-hex-
ane, gave complex 14 (678 mg, 60%) as orange crystals.
M.p. (dec.) 155°C. IR wmax (KBr): 3090 (CꢀH)Ar, 2956,
2
1
901 (CꢀH), 1948, 1880, 1858 (CꢁO), 1555, 1515, 1465,
−1 1
446, 1429, 1402 cm
(CꢂC, CꢂN). H-NMR (300
MHz, CDCl ): l 0.03 [9H, s, CHSi(CH ) ], 0.17 [9H, s,
3
3 3
CHSi(CH ) ], 3.35 {1H, s, CH[Si(CH ) ] }, 5.28 (1H, t,
3
3
3 3 2
2
2
J 6.6, 5-H or 6-H), 5.37 (1H, t, J 6.6, 6-H or 5-H), 6.00
Recrystallisation of the first fraction from petrol gave
complex 17 (12 mg, 11%) as orange crystals. Repeated
recrystallisation of the second fraction from petrol gave
complex 16 (25 mg, 24%) as orange crystals, with the
(
4
1H, d, J 6.6, 4-H or 7-H), 6.23 (1H, d, J 6.6, 7-H or
-H), 7.85 (1H, s, 3-H). C-NMR (125 MHz, CDCl3):
13
l −0.52 [CHSi(CH ) ], 0.05 [CHSi(CH ) ], 44.01
3
3
3 3

166
M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
mother liquors enriched in complex 18. Complex 16:
tallisation from ether–n-hexane, gave complex 5 (99
mg, 81%) as red crystals. M.p. (dec.) 147–148°C. IR
o
M.p. (dec.) 164–165 C. IR w
(KBr): 2958, 2359
max
−
1
(
CꢀH), 1951, 1860 (CꢁO), 1547, 1470, 1434 cm (CꢂC,
wmax (KBr): 2960, 2917, 2849 (CꢀH), 1946, 1875, 1858
1
−1
CꢂN). H-NMR (200 MHz, CDCl ): l 0.04 [9H, s,
(CꢁO), 1567, 1539, 1463, 1422 cm
(CꢂC, CꢂN).
0.07 [9H, s,
3
1
CHSi(CH ) ], 0.18 [9H, s, CHSi(CH ) ], 2.63 (3H, s,
H-NMR (200 MHz, CDCl3):
l
3
3
3 3
CH ), 3.36 {1H, s, CH[Si(CH ) ] }, 5.12 (1H, d, J 5.9,
CHSi(CH ) ], 0.13 [9H, s, CHSi(CH ) ], 0.53 [9H s,
3
3 3 2
3 3 3 3
5
7
−
-H), 5.41 (1H, t, J 6.6, 6-H), 5.87 (1H, d, J 6.9, 7-H),
Si(CH ) ], 2.67 (3H, s, CH3), 3.66 {1H, s,
3 3
1
3
.90 (1H, s, 3-H). C-NMR (125 MHz, CDCl ): l
CH[Si(CH ) ] }, 5.28 (1H, t, J 6.4, 5-H), 5.38 (1H, d, J
3
3 3 2
13
0.44 [CHSi(CH ) ], 0.15 [CHSi(CH ) ], 18.39 (CH ),
5.9, 6-H), 6.20 (1H, d, J 6.6, 4-H). C-NMR (125 MHz,
CDCl ): l −0.79 [CHSi(CH ) ], −0.40 [CHSi(CH ) ],
3
3
3 3
3
44.10 {CH[Si(CH ) ] }, 74.71 (Ar:C7), 89.47, 90.75
3 3 2
3
3 3
3 3
(
Ar:C5,C6), 95.98 (Ar:C4), 101.51 (Ar:C3a), 119.13
0.57 [Si(CH ) ], 16.94 (CH ), 52.24 {CH[Si(CH ) ] },
3 3 3 3 3 2
(
4
Ar:C7a), 133.46 (Ar:C3), 232.90 (CO). m/z (CI/NH ):
83.61, 89.59, 92.83 (Ar:C4ꢀC6), 98.90 (Ar:C7), 103.58
3
+
+
27 (MH , 9%), 291 [MH ꢀCr(CO) , 100%]. Anal.
(Ar:C3a), 128.08 (Ar:C7a), 138.14 (Ar:C3), 234.01
3
+
+
+
Found: C, 50.67; H, 6.00; N, 6.51. Calc.: C, 50.68; H,
(CO). m/z (APCI ): 499 (MH , 100%), 363 [MH
6
.14; N, 6.57%.
Complex 17: M.p. (dec.) 146°C. IR wmax (KBr): 2973
ꢀCr(CO) , 39%]. Anal. Found: C, 50.31; H, 7.02; N,
3
5.72. Calc.: C, 50.57; H, 6.87; N, 5.62%.
−
1
(
(
CꢀH), 1947, 1877, 1856 (CꢁO), 1541, 1468, 1438 cm
1
6
CꢂC, CꢂN). H-NMR (200 MHz, CDCl ): l −0.03
4.13. {p -2-[bis(Trimethylsilyl)methyl]-7-methoxy-
3
[9H, s, C(Me)Si(CH ) ], 0.19 [9H, s, C(Me)Si(CH ) ],
carbonyl-3-trimethylsilylindazole}-tricarbonylchromium
(19) and 2-[bis(trimethylsilyl)methyl]-7-
3
3
3 3
2.04 [3H, s, C(CH )Si(CH ) ], 2.63 (3H, s, CH ), 5.00
3 3 3 3
(
(
(
1H, d, J 5.9, 5-H or 7-H), 5.44 (1H, t, J 7.0, 6-H), 6.20
methoxycarbonyl-3-trimethylsilylindazole (21)
13
1H, d, J 7.2, 7-H or 5-H), 7.86 (1H, s, 3-H). C-NMR
125 MHz, CDCl ): l −1.21 [C(Me)Si(CH ) ], 0.32
A solution of complex 15 (122 mg, 0.253 mmol) and
3
3 3
[
C(Me)Si(CH ) ], 16.28 (CH ), 18.52 (CH ), 51.40
TMEDA (0.11 ml, 0.759) in THF (20 ml) was treated
3
3
3
3
[
C(Me)(SiMe ) ],
76.45
(Ar:C7),
88.27,
92.16
with n-BuLi (0.23 ml, 0.323 mmol) and ClCO Me (0.06
3
2
2
(
(
Ar:C5,C6), 95.60 (Ar:C4), 102.45 (Ar:C3a), 121.75
ml, 0.759 mmol) according to the procedure in Section
4.11.1 to afford an orange oil. Column chromatography
[n-hexane–ether (10:1)], followed by recrystallisation
from petrol, gave complex 19 (34 mg, 25%) as brown
crystals and compound 21 (34 mg, 33%) as white
crystals. Complex 19: M.p. (dec.) 121–122°C. IR wmax
(KBr): 2958, 2903 (CꢀH), 1951, 1894, 1871 (CꢁO), 1715
+
Ar:C7a), 133.07 (Ar:C3), 233.06 (CO). m/z (APCI ):
+
+
+
4
ꢀ
41 (MH , 10%), 413 (MH ꢀCO, 6%), 305 [MH
+
Cr(CO) , 7%] (HRMS Found: MH , 441.113437;
3
+
1
C H CrN O Si . Calc.: MH , 441.112185). H-NMR
1
9
28
2
3
2
1
spectrum of complex 18 in the mixture: H-NMR (200
MHz, CDCl ): l 0.08 [9H, s, CHSi(CH ) ], 0.20 [9H, s,
CHSi(CH ) ], 2.80 (3H, s, CH3), 3.86 {1H, s,
3
3 3
−
1
(CꢂO), 1633, 1539, 1501, 1435 cm
(CꢂC, CꢂN).
3
3
1
CH[Si(CH ) ] }, 5.11 (1H, d, J 5.6, 4-H or 6-H), 5.29
H-NMR (200 MHz, CDCl3):
l
0.05 [9H, s,
3
3 2
(
1H, t, J 6.1, 5-H), 6.09 (1H, d, J 5.9, 6-H or 4-H), 7.88
CHSi(CH ) ], 0.14 [9H, s, CHSi(CH ) ], 0.55 [9H s,
3 3 3 3
(
1H, s, 3-H).
Si(CH ) ], 3.66 {1H, s, CH[Si(CH ) ] }, 4.03 (3H, s,
3 3 3 3 2
CO CH ), 5.29 (1H, t, J 6.6, 5-H), 6.38 (1H, d, J 6.3,
2
3
1
3
4.11.2. Reaction of complex 14 with n-BuLi and MeI
4-H or 6-H), 6.50 (1H, d, J 6.7, 6-H or 4-H). C-NMR
(125 MHz, CDCl ): l −0.91 [CHSi(CH ) ], −0.57
A solution of complex 14 (60 mg, 0.145 mmol) in
3
3 3
THF (10 ml) was treated with n-BuLi (0.14 ml, 0.189
mmol) and MeI (0.03 ml, 0.435 mmol) according to the
procedure in Section 4.11.1 to afford a red oil. Column
[CHSi(CH ) ],
0.59
[Si(CH3)3],
52.33,
52.51
3
3
[CH(Si(CH ) ) , CO CH ], 80.72 (Ar:C7), 86.91, 87.39,
3
3 2
2
3
94.66 (Ar:C4ꢀC6), 101.55 (Ar:C3a), 126.03 (Ar:C7a),
139.00 (Ar:C3), 167.56 (CO Me), 232.14 (CO). m/z
chromatography [n-hexane–CH Cl2 (10:1)], followed
2
2
+
+
by a series of recrystallisations from petrol, gave com-
plex 16 (19 mg, 31%) as orange crystals. The mother-
liquors were enriched in complex 18.
(CI/NH ): 543 (MH , 62%), 407 [MH ꢀCr(CO) ,
3
3
+
100%]
(HRMS
Found:
MH ,
543.125209;
+
C H N Si CrO . Calc.: MH , 543.125893). Com-
22
34
2
3
5
pound 21: M.p. 49–50°C. IR wmax (KBr): 2957, 2902
6
−1
4
3
.12. {p -2-[bis(Trimethylsilyl)methyl]-7-methyl-
-trimethylsilylindazole}tricarbonylchromium (5)
(CꢀH), 1712 (CꢂO), 1606, 1553, 1436 cm
(CꢂC,
1
CꢂN). H-NMR (200 MHz, CDCl ): l 0.10 {18H, s,
3
CH[Si(CH ) ] }, 0.52 [9H, s, Si(CH ) ], 3.74 {1H, s,
3
3 2
3 3
A solution of complex 15 (139 mg, 0.287 mmol) and
TMEDA (0.13 ml, 0.861 mmol) in THF (20 ml) was
CH[Si(CH ) ] }, 4.00 (3H, s, CO CH ), 7.09 (1H, t, J
8.4, 5-H), 7.95–8.03 (2H, m, 4-H and 6-H). C-NMR
3 3 2 2 3
13
treated with n-BuLi (0.27 ml, 0.373 mmol) and MeI
(125 MHz, CDCl ): l −0.78 {CH[Si(CH ) ] }, 1.09
3
3 3 2
(
0.05 ml, 0.861 mmol) according to the procedure in
[Si(CH ) ], 50.20 {CH[Si(CH ) ] }, 51.59 (CO CH ),
3 3 3 3 2 2 3
Section 4.11.1 to afford a red oil. Column chromatog-
118.84 (Ar:C7), 119.38, 126.20, 128.53 (Ar:C4ꢀC6),
130.95, 135.46 (Ar:C3,C3a), 145.97 (Ar:C7a), 167.95
raphy [n-hexane–CH Cl (10:1)], followed by recrys-
2
2

M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
167
+
+
®
(
CO Me). m/z (APCI ): 407 (MH , 100%) (HRMS
days, filtration through Celite and evaporation of the
solvent gave colourless oil. Column chromatography
[petrol–ether (10:1)] gave compound 23 (5 mg, 75%) as
white crystals. M.p. 52–53°C. IR wmax (KBr): 3048
(CꢀH)Ar, 2958, 2901, 2877, 2857 (CꢀH), 1605, 1586,
2
+
Found: MH , 407.201594; C H N O Si . Calc.:
19
34
2
2
3
+
MH , 407.200639).
6
4
.14. {p -2-[bis(Trimethylsilyl)methyl]-7-etoxy-
−
1
1
1
505, 1459, 1416 cm
(CꢂC, CꢂN). H-NMR (200
MHz, CDCl ): l 0.06 {18H, s, CH[Si(CH ) ] }, 2.59
3H, s, CH ), 3.54 {1H, s, CH[Si(CH ) ] }, 6.84 (1H, d,
3 3 3 2
J 6.6, ArH), 7.13–7.25 (2H, m, ArH), 7.95 (1H, s,
C-NMR (125 MHz, CDCl3):
CH[Si(CH ) ] }, 18.60 (CH ), 43.15 {CH[Si(CH ) ] },
06.95 (Ar:C7), 119.54, 125.27 (Ar:C5, C6), 123.61,
24.02 (Ar:C4,C3a), 130.03 (Ar:C3), 139.78 (Ar:C7a).
m/z (APCI ): 291 (MH , 100%) (HRMS Found:
carbonyl-3-trimethylsilylindazole}tricarbonyl–
chromium (20) and 2-[bis(trimethylsilyl)methyl]-7-
etoxycarbonyl-3-trimethylsilylindazole (22)
3
3 3 2
(
13
3
{
1
1
-H).
l
−0.47
A solution of complex 15 (116 mg, 0.240 mmol) and
TMEDA (0.10 ml, 0.720 mmol) in THF (20 ml) was
treated with n-BuLi (0.22 ml, 0.312 mmol) and
3 3 2
3
3 3 2
ClCO Et (0.07 ml, 0.720 mmol) according to the proce-
2
+
+
dure in Section 4.11.1 to afford a red–brown oil.
Column chromatography [n-hexane–ether (10:1)], fol-
lowed by recrystallisation from petrol, gave complex 20
+
+
MH , 291.170450; C H N Si . Calc.: MH ,
15 26
2
2
2
91.171281).
(
(
34 mg, 26%) as red–brown crystals and compound 22
40 mg, 40%) as white crystals. Complex 20: M.p. (dec.)
4
.16. 2-[bis(Trimethylsilyl)methyl]-7-methyl-3-
1
1
cm
0
0
3
46–147°C. IR wmax (KBr): 2958, 2903 (CꢀH), 1960,
trimethylsilylindazole (24)
896, 1865 (CꢁO), 1708 (CꢂO), 1636, 1541, 1502, 1438
−
1
1
(CꢂC, CꢂN). H-NMR (200 MHz, CDCl ): l
3
A solution of complex 5 (53 mg, 0.106 mmol) in ether
.06 [9H, s, CHSi(CH ) ], 0.14 [9H, s, CHSi(CH ) ],
3 3 3 3
(
20 ml) was exposed to air and sunlight. After 10 days,
.55 [9H s, Si(CH ) ], 1.46 (3H, t, J 7.2, CO CH CH ),
3
3
2
2
3
®
filtration through Celite and evaporation of the sol-
vent gave a pale yellow oil. Column chromatography
.68 {1H, s, CH[Si(CH ) ] }, 4.43–4.60 (2H, m,
3
3 2
CO CH CH ), 5.30 (1H, t, J 6.6, 5-H), 6.40 (1H, d, J
2
2
3
[petrol–ether (10:1)] gave compound 24 (29 mg, 76%)
6
.4, 4-H or 6-H), 6.50 (1H, d, J 6.8, 6-H or 4-H).
as a colourless oil. IR w (film): 3045 (CꢀH)Ar, 2956,
2
MHz, CDCl ): l 0.08 {18H, s, CH[Si(CH ) ] }, 0.49
1
3
max
−1
C-NMR (125 MHz, CDCl ): l −0.86 [CHSi(CH ) ],
3
3 3
1
900 (CꢀH), 1567 cm
(CꢂC, CꢂN). H-NMR (200
−
0.51
[CHSi(CH ) ],
0.67
[Si(CH3)3],
14.62
3
3
3
3 3 2
(
CO CH CH ),
52.50
{CH[Si(CH ) ] },
61.62
2
2
3
3 3 2
[9H, s, Si(CH ) ], 2.59 (3H, s, CH ), 3.71 {1H, s,
3 3 3
(
CO CH CH ), 81.12 (Ar:C7), 86.85, 87.42, 94.88
2 2 3
CH[Si(CH ) ] }, 6.89–6.96 (2H, m, ArH), 7.54–7.59
(1H, m, ArH). C-NMR (125 MHz, CDCl
{CH[Si(CH ) ] }, 1.08 [Si(CH ) ], 17.09 (CH ), 49.43
3
3 2
(
(
Ar:C4ꢀC6), 101.80 (Ar:C3a), 126.00 (Ar:C7a), 139.00
Ar:C3), 167.26 (CO Et), 232.19 (CO). m/z (APCI ):
13
+
3
): l −0.69
2
+
+
3
3 2
3 3
3
5
57 (MH , 97%), 421 [MH ꢀCr(CO) , 100%]. Anal.
3
{
1
CH[Si(CH ) ] }, 118.09, 120.44, 122.72 (Ar:C5ꢀC7),
3
3 2
Found: C, 49.56; H, 6.54; N, 4.89. Calc.: C, 49.61; H,
.52; N, 5.03%. Compound 22: M.p. 97–98°C. IR wmax
KBr): 2956, 2903 (CꢀH), 1701 (CꢂO), 1606, 1552,
27.41, 128.87 (Ar:C7, C3a), 132.80 (Ar:C3), 148.83
6
(
1
+
+
(
Ar:C7a). m/z (APCI ): 363 (MH , 100%) (HRMS
+
+
−
1
1
Found: MH , 363.212280; C H N Si . Calc.: MH ,
479, 1457 cm
(CꢂC, CꢂN). H-NMR (200 MHz,
18 34 2 3
3
63.210810).
4.17. Crystal structure determination of complex (5)
CDCl ): l 0.09 {18H, s, CH[Si(CH ) ] }, 0.51 [9H s,
Si(CH ) ], 1.45 (3H, t, J 7.1, CO CH CH ), 3.74 {1H, s,
CH[Si(CH ) ] }, 4.46 (2H, q, J 7.1, CO CH CH ), 7.08
3
3 3 2
3
3
2
2
3
3
3 2
2
2
3
(
(
1H, t, J 8.1, 5-H), 7.94 (1H, d, J 8.2, 4-H or 6-H), 8.01
1H, d, J 7.1, 6-H or 4-H). C-NMR (125 MHz,
1
3
4
.17.1. Crystal data
CDCl ): l −0.30 {CH[Si(CH ) ] }, 1.57 [Si(CH ) ],
3
3 3 2
3 3
C H Cr N O Si , M=997.54. Data was collected
42
68
2
4
6
6
1
5.08 (CO CH CH ), 50.57 {CH[Si(CH ) ] }, 61.08
2 2 3 3 3 2
at r.t. Triclinic, with cell dimensions a=9.995(2), b=
5.982(3), c=17.651(4) A, h=81.11(2), i=75.03(2)
and k=82.52(2)°, space group P-1, V=2679(1) A
Z=2 (with two molecules in the asymmetric unit),
(
(
(
CO CH CH ), 119.64 (Ar:C7), 119.83, 126.51, 129.16
2 2 3
1
,
Ar:C4ꢀC6), 131.44, 133.95 (Ar:C3,C3a), 146.41
3
,
,
+
+
Ar:C7a), 167.98 (CO Et). m/z (APCI ): 421 (MH ,
2
100%). Anal. Found: C, 57.23; H, 8.81; N, 6.50. Calc.:
−3
−1
dcalc=1.237 g cm , v=0.534 mm , F(000)=1056.
0130 reflections were collected from which 8987 were
C, 57.09; H, 8.62; N, 6.66%).
1
independent (R =0.0350) and used in the structure
int
4.15. 1-[bis(Trimethylsilyl)methyl]-4-methylindazole (23)
refinement. Two molecules were found in the asymmet-
ric unit. Final R values are: R [I\2|(I)]=0.0700,
1
A solution of complex 16 (10 mg, 0.023 mmol) in
ether (10 ml) was exposed to air and sunlight. After 6
wR2 [I\2|(I)]=0.1828, R1 (all data)=0.1167, wR2
(all data)=0.2161.

168
M.R.G. da Costa et al. / Journal of Organometallic Chemistry 604 (2000) 157–169
Krapcho, S.N. Haydar, J. Heterocyclic. Chem. 34 (1997) 1637.
q) T. Morie, H. Harada, S. Kato, Synth. Commun. 27 (1997)
59. (r) H. Harada, T. Morie, Y. Hirokawa, S. Kato, Tetrahe-
5
. Supplementary material
(
5
Full details of data collection and refinement, tables
dron Asymm. 8 (1997) 2367.
of final atomic coordinates, anisotropic thermal
parameters for all non-hydrogen atoms, hydrogen
atomic coordinates, complete tables for bond lengths
and angles as well as torsion angles have been deposited
with the Cambridge Crystallographic Data Centre,
CCDC No. 141004 for complex 5. Copies of this infor-
mation may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
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