Zirconium hydrazinediido complexes derived from cyclic hydrazines and their role in the catalytic synthesis of 1,7-annulated indoles

Article abstract of DOI:10.1021/om301235d

Reaction of cyclic 1,1′-disubstituted hydrazines with the bis(dimethylamido)zirconium complex [Zr{(N^Xyl)₂N _py} (NMe₂)₂] (1) in the presence of dmap yielded the hexacoordinate zirconium hydrazinediido

Full text of DOI:10.1021/om301235d

Note
pubs.acs.org/Organometallics
Zirconium Hydrazinediido Complexes Derived from Cyclic
Hydrazines and Their Role in the Catalytic Synthesis of 1,7-Annulated
Indoles
Solveig A. Scholl, Hubert Wadepohl, and Lutz H. Gade*
Anorganisch-Chemisches Institut, Universitat Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
̈
S
* Supporting Information
ABSTRACT: Reaction of cyclic 1,1′-disubstituted hydrazines with the
bis(dimethylamido)zirconium complex [Zr{(NXyl)2Npy} (NMe2)2] (1)
in the presence of dmap yielded the hexacoordinate zirconium
hydrazinediido complexes [Zr{(NXyl)2Npy}(NNC9H10)(dmap)2] (2)
and [Zr{(NXyl)2Npy}(NNC12H8)(dmap)2] (3). Hydrazinediides are
thought to be key intermediates in the zirconium-catalyzed reaction of
cyclic 1,1′-disubstituted hydrazines and disubstituted alkynes to yield
1,7-annulated indoles. Their basic structural motif is found in 5-HT3 receptor antagonists such as Cilansetron.
ecent studies of transformations of the MN−NR2 unit
in group 4 metal hydrazinediides1 have established the
R
potential addition of unsaturated molecules at the highly polar
MN bond as well as the facile fragmentation of the N−N
bond. Both processes may occur sequentially or almost
concomitantly and may lead to the combined formation and
scission of several chemical bonds in one process. These
include stoichiometric transformations which involve formal
insertions into the N−N bond, such as those reported by
Mountford et al.2 as well as the titanium-catalyzed syntheses of
N-heterocycles developed by Odom, Beller, and others.3−5
Recently we reported a zirconium-catalyzed multistep
reaction leading to indoles,6 which involves hydrazinediido
complexes as key species (Chart 1).7 Closer inspection of the
polycyclic indole derivatives, we aimed to prepare such
hydrazides derived from cyclic hydrazines (B). Moreover, we
set out to investigate whether a catalytic transformation
involving in situ prepared hydrazides of this type would give
access to a target compound related to A.
RESULTS AND DISCUSSION
■
Reaction of the bis(dimethylamido)zirconium complex 1 with 1
molar equiv of the annulated hydrazine in the presence of an
excess of DMAP yielded the hexacoordinate zirconium
hydrazinediido complexes [Zr{(NXyl)2Npy}(NNC9H10)-
(dmap)2] (2) and [Zr{(NXyl)2Npy}(NNC12H8)(dmap)2]
(3) (Scheme 1).
Chart 1
The detailed structures of both complexes 2 and 3 were
established by X-ray diffraction and are depicted in Figure 1.
The coordination geometry is distorted octahedral with the
amido groups of the facial-coordinating tripodal ligand and the
DMAP nitrogens lying in a common plane. The hydrazinediido
ligand adopts an essentially linear coordination geometry. The
Zr−N(4) and the N(4)−N(5) bond lengths are in good
agreement with those found for other zirconium hydrazinediido
complexes reported by Bergman and ourselves.6−8
mechanism revealed a non-Fischer-type pathway including
combined N−N bond cleavage and N−C coupling, which was
first demonstrated by Bergman in 1991 in a stoichiometric
transformation of [Cp2Zr(N2Ph2)(dmap)] (Cp = C5H5, dmap
= 4-dimethylaminopyridine).8
The indole ring system is one of the most important building
blocks in natural bioactive products and in today’s pharma-
ceuticals.9 In particular, 1,7-annulated indole derivatives such as
the prototypical Cilansetron (A) display high activity as 5-HT3
receptor antagonists and are being clinically tested for the
treatment of symptoms in the gastrointestinal system such as
irritable bowel syndrome (IBS).10
The amidozirconium complex [Zr(NXyl)2Npy(NMe2)2] (1)
was tested as a catalyst for the formation of 1,7-annulated
indoles, starting from the corresponding hydrazines and
disubstituted alkynes (Table 1).11 The reactions were carried
out at 80 °C in toluene using a catalyst loading of 10 mol %. As
To extend our previous synthetic strategy based on the
reactivity of zirconium hydrazinediido complexes to annulated
Received: December 20, 2012
Published: January 27, 2013
© 2013 American Chemical Society
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dx.doi.org/10.1021/om301235d | Organometallics 2013, 32, 937−940

Organometallics
Note
Scheme 1. Synthesis of the Cyclic Zirconium Hydrazinediido
Complexes 2 and 3 from the Bis(dimethylamido)zirconium
Precursor 1
Table 1. Zirconium-Catalyzed Synthesis of Annulated
Heterocycles
a
Figure 1. Molecular structures of 2 (top) and 3 (bottom). Selected
bond lengths (Å) and angles (deg) are as follows. 2: Zr−N(1)/N(2) =
2.201(2)/2.193(2), Zr−N(3) = 2.449(2), Zr−N(4) = 1.875(2), Zr−
N(6) = 2.405(2), N(4)−N(5) = 1.377(2); N(3)−Zr-N(4) =
166.83(7), N(4)−Zr−N(6) = 88.40(7), Zr−N(4)−N(5) = 172.1(2).
3: Zr−N(1)/N(2) = 2.197(2)/2.182(2), Zr−N(3) = 2.447(3), Zr−
N(4) = 1.883(3), Zr−N(6) = 2.400(2), N(4)−N(5) = 1.362(4);
N(3)−Zr−N(4) = 166.9(1), N(4)−Zr−N(6) = 96.2(1), Zr−N(4)−
N(5) = 174.7(2).
a
Reaction conditions: 1.2 mmol of alkyne, 1.44 mmol of hydrazine, 10
mol % of [Zr(NXyl)2Npy(NMe2)2], 24 h in 2 mL of toluene at 80 °C.
b
c
1
Determined by H NMR spectroscopy. Yields of isolated products
d
determined after chromatographic workup. Major isomer is shown.
shown in Table 1, a variety of 1,7-annulated indoles could be
isolated in moderate yields, probably due to the ring strain in
these tricyclic N-heterocycles.
Notably, the best yields for each hydrazine derivative were
obtained in combination with 2-butyne. For unsymmetrically
disubstituted alkynes the indole with a bulkier substituent at the
3-position was the major product (Table 1, Ind2, Ind4, Ind6,
Ind9, Ind11, and Ind13). This was established unambiguously
by X-ray diffraction of Ind4 (Figure 2).12 In general, sterically
bulky substituents at the CC triple bond, such as an aryl ring,
lead to better regioselectivities. This is further enhanced by the
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Organometallics
Note
EXPERIMENTAL SECTION
■
Preparation of [Zr(NXyl)2Npy(NNC9H10)(DMAP)2]. Zr-
(NXyl)2Npy(NMe2)2] (200.00 mg, 0.36 mmol), DMAP (134.00 mg,
1.08 mmol), and 3,4-dihydroquinolin-1(2H)-amine (54.00 mg, 0.36
mmol) were dissolved in toluene (4 mL). After the mixture stood in a
refrigerator at −30 °C for 2 days, a brown solid precipitated as thin
needles. The solvent was removed by filtration, and the crude product
was washed with pentane (3 mL) to give [Zr(NXyl)2Npy(NNC9H10)-
(DMAP)2] as brown needles. Yield: 243.0 mg (0.28 mmol, 79%).
Single crystals for X-ray diffraction were obtained from these needles.
1H NMR (399.89 MHz, C6D6, 296 K): δ 1.55 (s, 3H, C-CH3), 1.82
Figure 2. Molecular structures of annulated indoles Ind3 (left) and
Ind4 (right) (only one of the two independent molecules is shown).
Selected bond lengths (Å) and angles (deg) are as follows; data for the
second independent molecule for Ind4 are given in brackets. Ind3:
N(1)−C(11) = 1.392(2), C(11)−C(10) = 1.378(2), C(10)−C(8) =
1.440(2); C(9)−N(1)−C(11) = 108.3(1), C(8)−C(9)−N(1) =
109.0(1); C(9)−C(8)−C(10) = 106.9(1). Ind4: N(1)−C(11) =
1.382(2) [1.379(2)], C(11)−C(10) = 1.394(2) [1.396(2)], C(10)−
C(8) = 1.445(2) [1.444(2)]; C(9)−N(1)−C(11) = 108.9(1)
[109.3(1)], C(8)−C(9)−N(1) = 109.1(1) [108.9(1)], C(9)−C(8)−
C(10) = 106.1(1) [106.2(1)].
3
(quint, 2H, JHH = 5.7 Hz, NCH2CH2), 2.31 (s, 12H, CH3 (Xylyl)),
3
2.32 (s, 12H, N(CH3)2 DMAP), 2.65 (t, JHH = 6.2 Hz, 2H,
2
N(CH2)2CH2), 3.46−3.51 (m, 2H, CHH), 3.85 (d, JHH = 14.7 Hz,
2H, CHH), 4.07 (t, 3JHH = 5.7 Hz, 2H, NCH2), 5.71 (d, 3JHH = 6.7 Hz,
4H, CHar DMAP), 6.23−6.34 (m, 2H, CHarHydrazine, H5py), 6.39 (s, 2H,
CHxyl), 6.73−6.79 (m, 1H, H3py), 6.91−7.00 (m, 2H, CHarHydrazine
,
3
H4py), 7.32 (s, 4H, CHxyl), 7.68 (d, JHH = 5.4 Hz, 1H, CHarHydrazine),
3
7.78 (d, JHH = 8.1 Hz, 1H, CHarHydrazine), 8.32 (d, 3JHH = 5.4 Hz, 1H,
3
H6py), 8.53 (d, JHH = 6.4 Hz, 4H, CHar DMAP). 13C{1H} NMR
(100.56 MHz, C6D6, 296 K): δ 22.4 (NCH2CH2), 22.5 (CH3 (Xylyl)),
27.8 (C-CH3), 28.9 (N(CH2)2CH2), 38.9 (N(CH3)2), 43.5 (C-CH3),
54.4 (NCH2), 62.7, 63.8 (CH2), 106.6 (CHar DMAP), 112.7
(CHarHydrazine), 114.0, 114.2 (CHar Xylyl), 116.3 (C-NMe2), 120.1
(C5py), 120.5 (CHarHydrazine), 127.0, 127.1 (C4py, CHarHydrazine), 136.3
(C-CH3 Xylyl), 147.4 (CHarHydrazine), 150.5 (C6py), 152.4
(CHarHydrazine), 154.1 (Cq Hydrazine), second Cq n.o., 165.9 (C2py),
presence of a secondary alkyl substituent at the hydrazine N
atom (Table 1, Ind6 and Ind9). We note that a ring expansion
of the annulated hydrazine from six to eight resulted in lower
yields (Table 1, Ind14 and Ind15).13 Unfortunately, all
attempts to obtain tetracyclic indole derivatives starting from
the hydrazine employed in the synthesis of complex 3 gave no
detectable quantities of the target species and only led to
nonspecific degradation. This is propably due to the increased
ring strain in such tetracycles.
On the basis of our previous detailed mechanistic work on
the formation of simple indoles we propose an analogous
mechanistic non-Fischer type pathway, as presented in Scheme
2.6
C3py and C -N n.o; IR (Nujol, NaCl, cm−1): v 2924 s, 2854 s, 2725 w,
̃
ar
1597 m, 1539 m, 1299 m, 1225 m, 1198 w, 1170 m, 1002 m, 939 m,
813 m, 803 w, 690 m. Anal. Calcd for C48H59N9Zr·1.5(toluene): C,
70.69; H, 7.26; N, 12.79. Found: C, 70.40; H, 7.24; N, 12.89.
Preparation of [Zr(NXyl)2Npy(NNC12H10)(DMAP)2]. 9H-Carbazol-
9-amine (16.70 mg, 91.74 mmol), DMAP (33.58 mg, 275.23 mmol),
and [Zr(NXyl)2Npy(NMe2)2] (50 mg, 91.74 mmol) were dissolved in
toluene. After standing at room temperature for 24 h, decoloration of
the formerly red solution was noticed as well as the formation of red
1
needles. Yield: 70.0 mg (79.06 mmol, 86%). H NMR (C6D6, 600.13
MHz, 296 K): δ 1.46 (s, 3 H, C−CH3), 1.91 (s, 3 H,
N(CH3)2(DMAP)), 2.02 (s, 3 H, CH3 (Xylyl)), 2.37 (s, 3 H, CH3
(Xylyl)), 2.19 (bs, 9 H, N(CH3)2(DMAP)), 3.51 (d, 3JHH = 12.3 Hz, 1
Scheme 2. Proposed Simplified Mechanistic Cycle for the
Catalytic Transformation of Tricylic Heterocycles
3
H, CHH), 3.55 (s, 6 H, CH3 (Xylyl)), 3.78 (d, JHH = 12.2 Hz, 1 H,
CHH), 3.82 (d, 3JHH = 12.2 Hz, 1 H, CHH), 3.92 (d, 3JHH = 12.8 Hz, 1
H, CHH), 5.44 (t, 3JHH = 6.5 Hz, 1 H, H5py), 5.58 (d, 3JHH = 7.8 Hz, 4
H, CHar DMAP), 6.41 (s, 1 H, CHXyl), 6.25 (s, 1 H, CHXyl), 6.54 (m, 3
3
H, CHXyl), 6.58 (t, JHH = 7.8 Hz, 1 H, H4py), 6.80 (s, 1 H, CHXyl),
6.84 (d, 3JHH = 8.2 Hz, 1 H, H3py), 7.01 (t, 3JHH = 7.4 Hz, 2 H, HCarb),
3
7.20−7.11 (m, 3 H, HCarb, H6py), 7.49 (d, JHH = 8.2 Hz, 2 H, HCarb),
7.93 (d, 3JHH = 7.6 Hz, 2 H, HCarb), 8.46−8.38 (m, 4 H, CHar DMAP).
13C{1H} NMR (C6D6, 150.92 MHz, 296 K): δ 22.0 (CH3 (Xylyl)),
27.1 (C-CH3), 38.8 (N(CH3)2), 45.9 (C-CH3), 63.0 (CH2), 106.6
(CHar DMAP), 110.1 (CCarb), 113.9 (Co/Cp (Xylyl)), 117.5 (Co/Cp
(Xylyl)), 119.2 (CCarb), 119.8 (C5py), 120.0 (CCarb), 120.2 (CCarb),
124.9 (CCarb), 136.3 (Cm (Xylyl)), 142.2 (CCarb), 150.1 (CHar DMAP),
153.2 (CHar DMAP), 164.7 (C2py), n. o. Ci(Xyl). DMAP, IR (Nujol,
NaCl, cm−1): ν
̃
3356 w, 2920 s, 2852 s, 2724 w, 1617 m, 1261 m, 1226
w, 1094 m, 1016 m, 863 w, 802 m. Anal. Calcd for
C48H59N9Zr·(toluene): C, 71.13; H, 6.69; N, 12.87. Found: C,
70.64; H, 6.83; N, 12.97.
General Procedure for Zirconium-Catalyzed Synthesis of
Tricyclic Heterocycles. If not stated otherwise, a sample of the
alkyne (1.20 mmol), the particular hydrazine (1.44 mmol), and the
precatalyst [Zr(NXyl)2Npy(NMe2)2] (0.12 mmol, 10 mol %) were
dissolved in toluene and stirred at 80 °C for 24 h. At this stage
complete conversion of the starting materials was confirmed by GC-
MS analysis. The reaction mixture was subsequently filtered through a
silica column and washed with dichloromethane. After all volatiles
were removed, the crude product was subjected to column
chromatography. In the case of regioisomers the ratio was determined
In conclusion, we succeeded in extending the scope of the
zirconium-catalyzed indole synthesis to annulated tricyclic
target compounds in moderate yields. Attempts to extend the
synthetic concept to more highly condensed systems were
unsuccessful. This represents a limitation of the chosen
approach.
1
by H NMR spectroscopy of the isolated product.
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Organometallics
Note
X-ray Diffraction Studies: Crystal Data. 2·1.5(toluene):
C58.50H71N9Zr, M = 991.46, monoclinic, a = 18.8426(2) Å, b =
15.3591(2) Å, c = 18.8516(2) Å, β = 105.363(1)°, V = 5260.8(1) Å3, T
= 115(1) K, space group P21/n, Z = 4, Cu Kα λ radiation, λ = 1.5418
Å, 59622 reflections measured, 9353 unique (Rint = 0.0507), final R
values (Fo > 4σ(Fo)) R(F) = 0.0331, Rw(F2) = 0.0740.
3·2(toluene): C65H73N9Zr, M = 1071.54, monoclinic, a =
11.0816(1) Å, b = 15.8271(2) Å, c = 17.4213(2) Å, β =
106.928(1)°, V = 2923.12(7) Å3, T = 110(1) K, space group P21, Z
= 2, Cu Kα λ radiation, λ = 1.5418 Å, 47425 reflections measured,
11106 unique (Rint = 0.0631), final R values (Fo > 4σ(Fo)) R(F) =
0.0394, Rw(F2) = 0.1027; absolute structure parameter −0.004(8).
Electron density attributed to disordered toluene was removed from
the structure with the BYPASS procedure.14
Ind3: C15H19N, M = 213.31, orthorhombic, a = 7.8641(1) Å, b =
9.0823(1) Å, c = 16.9708(2) Å, V = 1212.12(3) Å3, T = 115(1) K,
space group P212121, Z = 4, Cu Kα λ radiation, λ = 1.5418 Å, 22409
reflections measured, 2368 unique (Rint = 0.0565), final R values (Fo >
4σ(Fo)) R(F) = 0.0280, Rw(F2) = 0.0691; absolute structure parameter
0.1(2).
Ind4: C18H17N, M = 247.32, orthorhombic, a = 8.455(4) Å, b =
14.579(6) Å, c = 21.010(9) Å, V = 2589.7(18) Å3, T = 100(2) K, space
group P212121, Z = 8, Mo Kα λ radiation, λ = 0.71073 Å, 68299
reflections measured, 8955 unique (Rint = 0.0297), final R values (Fo >
4σ(Fo)) R(F) = 0.0387, Rw(F2) = 0.1009; absolute structure parameter
−0.2(4).
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ASSOCIATED CONTENT
* Supporting Information
Text giving general experimental procedures and CIF files
giving crystallographic data for 2, 3, Ind3, and Ind4. This
material is available free of charge via the Internet at http://
pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*Fax: (+49) 6221-545609. Tel: (+49) 6221-548444. E-mail:
lutz.gade@uni-hd.de.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
́
2009, 48, 9608−9644. (b) Kruger (nee Alex), K.; Tillack, A.; Beller,
This work has been supported by the Deutsche Forschungsge-
meinschaft (SFB 623, TP A7). We thank Sabine Stolz, Jan
Wenz, and Mario Wiesenfeldt for help with the synthetic work.
̈
M. Adv. Synth. Catal. 2008, 350, 2153−2167.
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P. J.; Tipker, J.; Tulp, M. Th. M.; Mol, F.; Olivier, B.; de Jonge, A. J.
Med. Chem. 1993, 36, 3693−3699. (b) Shi, Z.; Zhang, C.; Li, S.; Pan,
D.; Ding, S.; Cui, Y.; Jiao, N. Angew Chem., Int. Ed. 2009, 48, 4572−
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W. Appl. no. 88201253.7, EP no. 0297651. (d) Hamminga, D.; Haeck,
H. H.; van Wijngaarden, I.; Wouters, W. Appl. no. 88202800.4, EP no.
0322016. (e) Hamminga, D.; van Wijngaarden, I.; Haeck, H. H.;
Wouters, W. Appl. no. 89203204.6, EP no. 0375045.
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