Synthesis of N,N′-bis and N,N,N′,N′-tetra-[(3,5-di- substituted-1-pyrazolyl)methyl]para-phenylenediamines: New candidate ligands for metal complex wires

Article abstract of DOI:10.1016/j.tet.2006.01.034

A series of tridentate ligands N,N-bis-[(di-substituted-1-pyrazolyl)methyl] arylamines 2-3a,b and benzylamine 4a,b, tetradentate N,N′-bis-[(di- substituted-1-pyrazolyl)methyl]para-phenylenediamines 7a,b and hexadentate N,N,N′,N′-tetra-[(di-substituted-1-p

Full text of DOI:10.1016/j.tet.2006.01.034

Tetrahedron 62 (2006) 3123–3127
Synthesis of N,N0-bis and N,N,N0,N0-
tetra-[(3,5-di-substituted-1-pyrazolyl)methyl]-
para-phenylenediamines: new candidate ligands
for metal complex wires
Maria Daoudi,a Najib Ben Larbi,a Abdelali Kerbal,a Brahim Bennani,b Jean-Pierre Launay,c
e,
Jacques Bonvoisin,c Taibi Ben Haddad, and Pierre H. Dixneuf
*
*
a
´ `
Laboratoire de Chimie Organique, Faculte des Sciences Dhar Mehraz, 30000 Fes, Maroc
b
´ ´
Departement de Chimie, Ecole Normale Superieure, Bensouda, 30000 Fes, Maroc
`
cCENS, CNRS, 29 rue Jeanne Marvig, 31 055 Toulouse Cedex 04, France
´ ´
Laboratoire d’Activation Moleculaire, Faculte des Sciences, 60000 Oujda, Maroc
d
e
´
Institut de Chimie de Rennes, Campus de Beaulieu, UMR 6509 CNRS-Universite de Rennes, 35042 Rennes, France
Received 15 November 2005; revised 8 January 2006; accepted 10 January 2006
Available online 3 February 2006
Abstract—A series of tridentate ligands N,N-bis-[(di-substituted-1-pyrazolyl)methyl]arylamines 2–3a,b and benzylamine 4a,b, tetradentate
N,N0-bis-[(di-substituted-1-pyrazolyl)methyl]para-phenylenediamines 7a,b and hexadentate N,N,N0,N0-tetra-[(di-substituted-1-pyrazolyl)-
methyl]para-phenylenediamines 8a,b has been prepared in good yield by condensation of arylamines, benzylamine or para-
phenylenediamine with N-hydroxymethyl disubstituted pyrazoles 1a,b. The synthesis and characterisation of these various polydentate
ligands are described.
q 2006 Elsevier Ltd. All rights reserved.
1. Introduction
In search of new terminal coordinating groups to study
intramolecular electron transfers, we have considered the
case of polydendate pyrazole ligands. Such compounds are
particularly interesting as ligands for the building of
polynuclear complexes as models for bioinorganic
systems2 as well as for the discovery of new catalyst
precursors.3
Polymetallic complexes with suitable polydentate bridging
ligands can be useful models of molecular wires.1 By
reference to macroscopic electrical devices, the concept of
a wire is fundamentally based on intramolecular electron
transfer that occurs in its simplest form in mixed-valence
complexes.Bimetallicmetalcomplexeswithsuitablebridging
ligands can be useful models to study electronic interaction or
electron transfer rates with distance including in biological
electron transfer.1 Another interesting use of long distance
coordinating ligands is the electronic communication between
remote metallic atoms and the development of molecular
switches, that is, molecules able to promote or block
intramolecular electron transfer.1 This development clearly
requires the mastering of long distance electron transfer
The flexibility of the pyrazolic N-coordinating groups of the
tridentateligandscouldallowthemtoactasmeridional4,5 oras
facial ligands6,7 when coordinating to transition metal
complexes (Scheme 1).
In the case of polydentate ligands, they could coordinate in
facial and meridional fashion as proposed in Scheme 1, such
as by combination of bis-tridentate ligands with Ru2C metal
sites. In contrast, with bis-bidentate ligand, the four nitrogen
atoms cannot coordinate to the same metal atom and are
expected to lead to polymeric metal complex.8–11
˚
(over 15–20 A).
Keywords: Polydentate N-ligands; Pyrazoles; Pyrazol-1-ylmethanol;
p-Phenylenediamine.
Corresponding authors. Tel.: C33 223236280; fax: C33 223236939
(P.H.D.); tel.: C212 61753135; fax: C212 56500603 (T.B.H.); e-mail
addresses: tbenhadda@yahoo.fr; pierre.dixneuf@univ-rennes1.fr
To gain insight into the coordination behaviour of larger
ligand systems containing at the same time pyrazolyl
nitrogen groups and electron releasing amine N-donor
*
0040–4020/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.01.034

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M. Daoudi et al. / Tetrahedron 62 (2006) 3123–3127
R
R
H3C
CH3
R
R
N
NN
CH3
H3C
N
N
N
N
N
N
N
Metal
N
N
N
Metal
N
Metal
n
n
N
N
N
N
N
H3C
N
CH3
R
CH3
H3C
R
R
R
R
CH3
R
CH3
N
N
N
N
Metal
NH
N
Metal
R
NH
NH
N
Metal
NH
n
n
N
N
H3C
H3C
R
Scheme 1. Examples of possible polymetallic wires.
atoms we have developed initial work on tridentate N,N-bis-
[(3,5-dimethyl-1-pyrazolyl)methyl] alkylamines.12
R
R
R
N
N
N
N
N
N
N
N
HN
N
NH
N
In the present paper, we report the synthesis of a family of
tridentate, tetradentate, bis-bidentate and bis-tridentate
ligands containing pyrazol groups bridged by aminomethyl
groups, with the general topology shown in Figure 1, on
reaction of (pyrazol-1-yl)methanol and primary amines.
N
R
N
N
N
R
R
Figure 1.
R
R
R
H3C
CH3
CH3
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
CH3
H3C
CH3
R
R
R
3a–b
4a–b
2a–b
NH2
NH2
NH2
R
R
H3C
H3C
N
N
N
N
N
N
R
R
CH3CO2NH4
H3C
CH3CO2NH4
N
N
H
X
N
N
N
N
N
OH
N
H3C
H3C
R
R
1a–b
5a–b
6a–b
H2
N
NH2
H2
N
NH2
R
R
R
H3C
CH3
H3C
N
N
N
N
N
N
N
H
N
N
N
H
N
N
N
N
N
N
CH3
H3C
CH3
R
R
R
7a
8a–b
Scheme 2. Synthesis of tridentate (2–4), tetradentate (6a–b), bis-bidentate (7a) and bis-tridentate (8a–b) N-ligands with [RZ–CH3 (a), –CO2CH3 (b)].

M. Daoudi et al. / Tetrahedron 62 (2006) 3123–3127
3125
2. Results and discussion
3.2. Synthesis of compounds 2–8.
On the basis of our initial work for the synthesis of
compounds 2a12 the new tridentate ligands 2b, 3a,b, 4a,b
were prepared on reaction of (3,5-dimethyl-1H-pyrazol-1-
yl)methanol 1a and methyl 1-(hydroxymethyl)-5-methyl-
1H-pyrazole-3-carboxylate 1b, respectively, with aniline,
p-methylaniline or benzylamine. The tridentate compounds
2–4 were easily prepared from the condensation of 2 equiv
of 1-(hydroxymethyl)-3,5-dimethyl-pyrazole 1a or
1-(hydroxymethyl)-3-methoxycarbonyl-5-methyl-pyrazole
1b with 1 equiv of arylamine under mild conditions (room
temperature), using anhydrous acetonitrile as solvent. The
reaction is very slow but selective at room temperature.
Thus after 4–5 days of stirring at room temperature the
derivatives 2b (94%), 3a (74%), 3b (64%), 4a (77%) and 4c
(53%) were isolated (Scheme 2).
General procedure for the synthesis of 2–4 and 6. The
products were prepared by the addition of arylamine
(p-R-C6H4NH2), and (C6H5CH2NH2) or ammonium
acetate to 1a or 1b. To a solution of the substituted
hydroxymethylpyrazole 1a (1.26 g, 10 mmol) or 1b
(1.70 g, 10 mmol) in acetonitrile (25 ml) was added the
desired amine (5 mmol) and the mixture was continued at
room temperature for 4–5 days. The formed compound
was precipitated by addition of cold water to acetonitrile
solution, washed with hexane and dried under vacuum.
Compounds 2–4 and 6 were obtained as white solids
(60–94% yield).
General procedure for the synthesis of 7–8. The products
7–8 were prepared by the addition of p-phenylenediamine
(NH2–C6H4–NH2) to 1a or 1b. To a solution of the
substituted hydroxymethylpyrazole 1a (1.26 g, 10 mmol)
or 1b (1.70 g, 10 mmol) in acetonitrile (25 ml) was added
p-phenylenediamine (2.5 mmol) for 8 or (5 mmol) for 7 and
the mixture and the stirring was continued at room
temperature for 4–5 days. The product was precipitated by
simple addition of cold water, washed with hexane and dried
under vacuum. The compounds 7–8 were obtained as white
solids (60–67%).
Tetradentate molecules 6a,b have been prepared using
ammonium acetate as the source of ammonia as outlined in
Scheme 2. In this way, the reaction of 1a–b with ammonium
acetate in acetonitrile could not be stopped to afford the
expected tridentate ligands 5a,b with central N–H group,
and the tetradentate compounds 6a,b were directly obtained.
The reaction of precursors 1a,b with the p-phenylene-
diamine in CH3CN at room temperature produces bis-
bidentate ligand 7a and bis-tridentate ligands 8a,b. This
reaction selectivity is simply controlled by the use of 2 and
4 equiv of 1a–b, respectively, with respect to p-phenylene-
diamine, and 7a (61%), 8a (67%) and 8b (73%) were
isolated after 5 days of stirring at room temperature
(Scheme 2). The crystal structure of hexadentate compound
8a was recently reported and confirmed the molecular
structure.13
3.2.1. N,N-Bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]
aniline (2a). Yield 65%. Mp 85 8C (mp lit.16Z83 8C). IR
(KBr, y cmK1): 3260 (]C–H Ar), 3080 (C–H Me), 1600
(C]C), 1500, 1470 (C]N); 1500, 1350, 1290, 1230, 1170,
1110, 1050. 1H NMR (60 MHz, CDCl3) d ppm: 7.00 (m, 5H,
0
Ph), 5.75 (s, 2H, pyrazol–H4,4 ), 5.40 (s, 4H, NCH2N), 2.30
(s, 6H, CH3), 2.10 (s, 6H, CH3). MS (DCI/NH3, CH2Cl2):
Calcd for [M]C C18H23N5: 310. Found [MCH]C (m/z)Z
311 (45%).
By comparison with various bis-bidentate and bis-tridentate
ligands for the synthesis of known bimetallic or poly-
metallic complexes in the literature,14,15 we describe here
bis-bidentate and bis-tridentate compounds, for which the
synthesis is relatively easy. Their synthesis from p-phenyl-
enediamine could certainly be generalised to a large variety
of other aromatic diamines.
3.2.2. Methyl-1-[({[3-(methoxycarbonyl)-5-methyl-1H-
pyrazol-1-yl]methyl}anilino)methyl]-5-methyl-1H pyra-
zole-3-carboxylate (2b). Yield 94%. Mp 124–126 8C. IR
(KBr, y cmK1): 3200 (CH, Ar), 2920 (CH), 1730
(C]O), 1600 (C]C), 1490 (C]N), 1460, 1420, 1230.
1H NMR (250 MHz, CDCl3) d 0 ppm: 6.70–7.45 (m, 5H,
C6H5), 6.5 (s, 2H, pyrazol–H4,4 ), 5.65 (s, 4H, NCH2N),
3.90 (s, 6H, OCH3), 2.05 (s, 6H, pyrazol–CH3). MS
(MeOH/GLY): Calcd for [M]C C20H23N5O4: 397. Found
[MCH]C (m/z)Z398 (19%). Elemental analysis for
C20H23N5O4 Calcd (Found): C 60.45 (60.48), H 5.79
(5.81), N 17.63 (17.56).
3. Experimental
3.1. General methods
3.2.3. (3,5-Dimethyl-1H-pyrazol-1-yl)-N-[(3,5-dimethyl-
1H-pyrazol-1-yl)methyl]methanamine (3a). Yield 74%.
Mp 108–109 8C. IR (KBr, y cmK1): 3025 (]C–H Ar), 2950
Infrared spectra were recorded on a PYE Unicam SP3-300
1
spectrometer as KBr pellets. The H and 13C NMR spectra
1
were recorded on Varian EM 360 (operating at 60 MHz for
1H) or/and Bruker spectrometer (250 and 400 MHz) using
TMS as internal standard. Chemical shifts are reported
downfield from the standard in ppm. The FAB mass spectra
were obtained on a NERMANG R10-LOC instrument. For
the chemical ionisation (DCI/NH3/CH3), the compounds
were dissolved in DMSO or MeOH and dispersed in a
matrix solution, currently the 3-nitrobenzyl (MNBA) or
Glycerol (GLY). Elemental analyses were performed by the
Service Central d’Analyse du CNRS LCC (Toulouse).
(CH), 1720/1600 1500/1472 (C]N). H NMR (60 MHz,
CDCl3) d ppm: 6.8, 7.3 (m, 4H, Ph), 5.90 (s, 2H, pyrazol–
0
H
4,4 ), 5.60 (s, 4H, 2NCH2N), 2.25 (s, 15H, CH3-PhCCH3-
pz). MS (DCI/NH3, CH2Cl2): Calcd for [M]C C19H25N5:
323. Found [MCH]C (m/z)Z324 (23%).
3.2.4. (3-(Methoxycarbonyl)-5-methyl-1H-pyrazol-
1-yl)methyl]methanamine (3b). Yield 64%. 1H NMR
(400 MHz, CDCl3) d ppm: 7.10 (d, 2H,0 C6H5), 6.90 (d,
2H, C6H5), 6.50 (s, 2H, pyrazol–H4,4 ), 5.70 (s, 4H,

3126
M. Daoudi et al. / Tetrahedron 62 (2006) 3123–3127
2NCH2N), 3.95 (s, 6H, 2OCH3), 2.30 (s, 3H, CH3-ph), 2.10
(s, 6H, pyrazol–CH3). MS (CI/CH3): Calcd for [M]%C
C21H25N5O4: 411. Found [MCH]%C (m/z)Z412 (4.92%).
3.2.10. N,N,N0,N0-Tetrakis[(3,5-dimethyl-1H-pyrazol-1-
yl)methyl]-1,4-benzenediamine (8a). Yield 67%. Mp
174–176 8C. IR (KBr, y cmK1): 2980 (C–H), 1590
1
(C]C), 1220, 1170, 1490. H NMR (250 MHz, CDCl3)
d ppm: 7 (s, 4H, Ph), 5.8 (s, 4H, pyrazol), 5.5 (s, 8H,
NCH2N), 2.3 (s, 12H, CH3), 2.0 (s, 12H, CH3). MS
Calcd for [M]C C34H40N10O8: 716; [MCNaC]% (m/z)Z
739, 613, 585, 460. MS (FAB!0, MeOH/GLY): Calcd
for [M]%C C30H40N10: 540. Found [MCH]%C (m/z)Z541
(11.5%). Elemental analysis for C30H40N10 Calcd
(Found): C 65.66 (65.82), H 7.40 (6.98), N 25.90
(25.24).
3.2.5. (3,5-Dimethyl-1H-pyrazol-1-yl)-N-[(3,5-dimethyl-
1H-pyrazol-1-yl)methyl]benzylamine (4a). Yield 65%.
Mp 73 8C. IR (KBr, y cmK1): 3085 (]C–H aromat),
2930 (CH), 1550 (C]C), 1450 (C]N), 1380,
1310, 1100, 1000, 960, 800, 750. 1H (60 MHz, CDCl3)
4,40
d ppm: 7.4 (s, 5H, C6H5), 5.9 (s, 2H, pz, C ), 5
(s, 2N–CH2–N), 3.9 (s, 2H, ph-CH2–N), 2.3 (s, 6H, 2CH3,
3,30
5,50
C
), 2.1 (s, 6H, 2CH3, C ). MS (DCI/NH3): Calcd for
[M]%C C19H25N5: 323. Found [MCH]%C (m/z)Z324
(92.5%), 228 (100%), 137 (21.7%), 120 (37.5%), 114
(42.5%).
3.2.11. Methyl-1-[(4-(bis{[3-(methoxycarbonyl)-5-methyl-
1H-pyrazol-1-yl]methyl}amino){[3-(methoxycarbonyl)-
5-methyl-1H-pyrazol-1-yl]methyl}anilino)methyl]-5-
methyl-1H-pyrazole-3-carboxylate (8b). Yield 73.5%.
Mp 196–198 8C. IR (KBr, y cmK1): 3140 (]CH), 2990
(CH), 1730 (C]O), 1540 (C]C), 1480 (C]N), 1450,
1410. 1H NMR (250 MHz, CDCl3) d ppm: 7.3 (s, 4H,
Ph), 6.6 (s, 4H, pyrazol), 5.6 (s, 8H, 4N–CH2–N), 4.0 (s,
12H, 4O–CH3), 2.2 (s, 12H, 4CH3). MS (FAB!0,
DMSO/MNBA): Calcd for [M]C C34H40N10O8: 716;
[MCNa]%C (m/z)Z739 (100%). Elemental analysis for
C30H40N10O8 Calcd (Found): C 56.97 (56.62), H 5.63
(5.51), N 19.54 (19.47).
3.2.6. (-3-(Methoxycarbonyl)-5-methyl-1H-pyrazol-1-
yl)methyl]]benzylamine (4b). Yield 65%. Mp 85 8C. IR
(KBr, y cmK1): 3025 (]CH aromat), 2950 (CH), 1750
(C]O), 1600, 1450 (C]C), 1310, 1220 (C–O), 940,
820, 780. 1H (400 MHz, CDCl3) d ppm: 7.4. (s, 5H,
C6H5), 5.2 (s, 4H, 2NCH2N), 3.9 (s, 6H, 2O–CH3), 3.8
(s, 2H, ph-CH2–N), 2.1 (s, 6H, 2CH3, C5,5 ). C13
(400 MHz, CDCl3) d ppm: 163.04 (CO2Me), 142.62–
0
0
0
0
140.69 (ph), 130.1 (C3,3 ), 122.85 (C5,5 ), 108.83 (C4,4 ),
66.73 (N–CH2–N), 0 52.04 (O–CH3), 20.84 (ph-CH2–N),
11.08 (CH3–CH35,5 ). Elemental analysis for C21H25N5O4
Calcd (Found): C 61.31 (61.48), H 6.08 (6.20), N 17.03
(17.40). MS (CI/CH3): Calcd for [M]%C C21H25N5O6:
411. Found [MCC2H5]%C (m/z)Z440 (5%).
Acknowledgements
´
This work was supported by the ‘Projet Global d’Universite
Mohamed Prenier/LAM’ Grant.
3.2.7. (3,5-Dimethyl-1H-pyrazol-1-yl)-N-[(3,5-dimethyl-
1H-pyrazol-1-yl)methyl] amine (6a). Yield 77%. Mp 94–
96 8C. IR (KBr, y cmK1): 3000 (]C–H aromat), 290 (CH),
1560, 1440 (C]N), 1400, 1350, 1290, 1230, 1160, 1050,
830, 690. 1H (60 MHz, CDCl3) d ppm: 5.70 (s, 3H, pz, H4),
5.00 (s, NCH2N), 2.10 (s, 9H, 3CH3), 1.90 (s, 9H, 3CH3).
MS (DCI/NH3): Calcd for [M]%C C18H27N7: 341. Found
[MCH]%C (m/z)Z342 (100%).
References and notes
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3.2.8. (-3-(Methoxycarbonyl)-5-methyl-1H-pyrazol-1-
yl)methyl]] amine (6b). Yield 53%. IR (KBr, y cmK1):
3080 (]C–H aromat), 2940 (CH), 1730 (C]O), 1450
(C]N), 1380, 1330, 1240, 1180, 1120, 1040, 830, 800. 1H
(400 MHz, CDCl3) d ppm: 6.50 (s, 3H, pz, H4), 5.20 (s, 6H,
3NCH2N), 3.90 (s, 9H, 3O–CH3), 1.90 (s, 9H, 3CH3). C13
(400 0MHz, CDCl3) d p0pm: 162.67 (CO2Me0)0 , 142.85
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4150–4156.
00
00
0
(C3,3 ,3 ), 141.13 (C5,5 ,5 ), 109.15 (C4,4 ,4 ), 00 63.55
0
(N–CH2–N), 52.04 (O–CH3); 10.09 (CH3–C5,5 ,5 ). MS
(CI/CH3): Calcd for [M]%C C21H27N7O6: 473. Found
[MH]%C (m/z)Z474 (3%).
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1689–1694.
3.2.9. N,N0 Bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-
1,4-benzenediamine (7a). Yield 61.5%. Mp 158–160 8C.
IR (KBr, y cmK1): 3300 (–NH), 2920 (]CH), 1520
(C]C), 1450 (C]N), 1380, 1180. NMR 1H (60 MHz,
CDCl3) d ppm: 6.65 (s, 4H, Ph), 5.7 (s, 2H, pyrazol–C4),
5.4 (s, 4H, NCH2N), 4.4 (s, 2H, Ph-N–H), 2.2 (s, 6H,
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0
0
CH3, C3,3 ), 2.1 (s, 6H, CH3, C5,5 ). MS (DCI/NH3,
CH2Cl2): Calcd for [M]C C18H24N6: 324.219. Found
[MCH]%C (m/z)Z325 (2.52%).
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´
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