Synthesis of monophosphonic acid ligands with a phenanthroline core

Article abstract of DOI:10.1016/j.tetlet.2004.07.067

The efficient synthesis of two diimine ligands incorporating one benzyl phosphonate group and a phenanthroline core is described. These functionalized ligands constitute a new type of linkers in hybrid organic-inorganic materials based on inorganic oxides and metallic complexes.

Full text of DOI:10.1016/j.tetlet.2004.07.067

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 7805–7807
Synthesis of monophosphonic acid ligands with a
phenanthroline core
a,
Cedric R. Mayer, Maryline Herve, Helene Lavanant and Francis Secheresse
a
b
a
*
´
´
´ `
´
a
´
Institut Lavoisier, UMR 8637 CNRS, Universite de Versailles, 45 avenue des Etats-Unis, 78000 Versailles, France
b
´
Laboratoire de Spectrometrie de Masse Bio-Organique, UMR CNRS 6014, INSERM-IFRMP23, CRUS,
ˆ ´
Batiment IRCOF, Universite de Rouen, 76821 Mont St Aignan Cedex, France
Received 8 June 2004; accepted 15 July 2004
Abstract—The efficient synthesis of two diimine ligands incorporating one benzyl phosphonate group and a phenanthroline core is
described. These functionalized ligands constitute a new type of linkers in hybrid organic–inorganic materials based on inorganic
oxides and metallic complexes.
Ó 2004 Elsevier Ltd. All rights reserved.
The synthesis of hybrid organic–inorganic materials
based on inorganic oxides and metallic complexes is
an expanding field of investigation. Indeed, the ability
to attach metallic polypyridyl complexes to oxide sur-
faces in controlled architectures (distance, orientation,
compacity and rigidity) is essential for the design of
new composite systems. Hybrid organic–inorganic
materials are known to favour the combination of both
the properties of the inorganic and organic moieties;1
the linker used between these two systems however,
plays a major role. Presently, one of the most studied
hybrid systems results from the entrapment of polypyr-
idyl complexes, either by attachment on oxide solid sur-
face such as semi-conductor (for the development of
molecular level devices)2 or by incorporation in a phos-
phonate framework (for supported homogenous cataly-
sis)3 or in nanocrystalline films of TiO2 for their utility in
dye sensitized solar cells.4 It appears however that the
synergy between the complex and the host is stronger
with a covalent grafting.
heterovacant POM.6 Eventually, the covalent incorpo-
ration of a POM in a material should result in the for-
mation of a new hybrid material that would most
likely benefit the large panel of applications of POMs,
in particular their numerous electronic properties.7 This
challenge however requires the control of the linking
between the metallic complex and POM moieties
(Scheme 1).
Indeed, this link must incorporate three important fea-
tures: (i) an electrophilic group such as a phosphonate
group to ensure the bonding with the POM, (ii) a small
aliphatic group between the electrophilic part and the
chelating part and (iii) a strong rigid chelating group
such as polypyridyls. Among the polypyridyl library,
the phenanthroline seems the more adapted, and more
especially the 9,10-phenanthroline-5,6-dione. It behaves
as a good organic block likely to easily condense with
another organic block possessing either a benzaldehyde
group8 or an ortho-diaminoaromatic group. The struc-
tural modification of 9,10-phenanthroline compounds
We are currently investigating the synthesis of hybrid
materials based on polyoxometalate (POMs) clusters.5
The synthesis of such hybrid systems, necessitates the
pre-functionalization of the POM cluster the main
method consisting in grafting electrophilic groups on a
N
N
N
Oxo-metallic
surface
N
N
M
N
Keywords: Phosphonic acids; Polyridyls; Pyrazine; Imidazole; Hetero-
cyclic compounds.
Linker
Scheme 1. Schematic representation of an example of hybrid system.
*
Corresponding author. Tel.: +33 1 39254397; fax: +33 1 339254381;
e-mail: cmayer@chimie.uvsq.fr
0040-4039/$ - see front matter Ó 2004Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.07.067

7806
C. R. Mayer et al. / Tetrahedron Letters 45 (2004) 7805–7807
has been the object of numerous studies due to their rich
coordination chemistry. In fact, the large variety of
complexes based on phenanthroline or polypyridyl
derivatives allows the formation of many different
molecular systems with various applications ranging
from metallo-supramolecular chemistry,9 metal sen-
sors,10 molecular electronics11 and photosensitizers.12
Another interest of this work was to test different organic
blocks that would include one monophosphonate
group and thus to devise an efficient route to diversify
the nature of the link. Although, different bipyridils lig-
ands with two phosphonate groups are described in the
literature, only few results are related to the monofunc-
tionalization of polypyridyls ligands. Gra¨tzel and co-
workers reported monophosphonate terpyridines13 and
recently Schmehl and co-workers reported a bipyridyl
monofunctionalization with phenylphosphonate.14 The
key feature of our approach was to functionalize the
phenanthroline by only one monophosphonic acid.
The functionalization by a bisphosphonic acid would
most probably lead to the formation of oligomeric spe-
cies, as it is the case for the reaction of an aromatic bis-
phosphonic acid with a divacant POM.15 This work
presents the synthesis of two modified benzylphospho-
nates and their condensation with 9,10-phenanthroline-
5,6-dione. We thus describe here the synthesis of two
diimine ligands functionalized with one phosphonic
acid substituent. The first organic-phosphonate block
(OPB) we used is 4-(diethoxyphosphorylmethyl)-1,2-di-
reaction was performed in ethanol with Pd on activated
carbon and with excess of hydrazine monohydrate, at
reflux overnight, resulting in the deprotection of the
amino group and accompanied with the reduction of
the nitro group into a second amino group. The conden-
sation with 9,10-phenanthroline-5,6-dione was then car-
ried out in refluxed ethanol. The hydrolysis was
achieved by the McKenna method17 or in a 12M HCl
aqueous solution to give the pure product 2-(dihydroxy-
phosphorylmethyl)-pyrido[3,2-a:20,30-c]phenazine (LI)
in good yield (Scheme 2A).18
Two precursors were considered for the synthesis of
compound 7, para-4-bromomethyl-xylene or a-bromo-
p-tolunitrile. Starting from para-4-bromomethyl-xylene,
the first step consisted in the preparation of 4-(diethoxy-
phosphorylmethyl)-1-methyl-phenyl
7
using
the
Arbuzov method.19 The second step consisted in the
bromination of para-methyl group by N-bromosuccin-
imide (NBS) in CCl4 and dibenzoylperoxide (DBPO)
as radical initiator. The formation of the aldehydic
groups was obtained by the protocol of Nace and
Monagle in DMSO in the presence of NaHCO3.20 The
second method proceeded in two steps from commercial
a-bromo-p-tolunitrile. First the a-bromo-p-tolualdehyde
was formed as described by Wen et al.21 and the ex-
pected compound 7 was then obtained by reaction with
triethylphosphite. Compound 7 was recovered in acetic
acid with NH4OAc through the protocol of Steck and
Day.8 However, in these conditions solely one of the
ester functions of the phosphonate groups was hydrolyzed
as observed by 1H NMR or ESI-MS. An additional
reaction was therefore carried out in 12M HCl aqueous
solution to form the final product (4-(dihydroxyphos-
phorylmethyl)-phenyl)-phenanthrimidazole (LII) in
good yield (Scheme 2B).18
´
amino-phenyl (3) and the second OPB corresponds to
4-(diethoxyphosphorylmethyl)-1-benzaldehyde (7). The
synthesis of the latter product was recently described,16
herein, two alternative syntheses are proposed.
The preparation of compound 3 from 4-(diethoxyphos-
phorylmethyl)-1-amino-phenyl (1) proceeded in four
steps. The first reaction achieved the protection of the
amino group using phthalic anhydride in acetic acid
solution. After evaporation, precipitation and drying,
this compound was added to a mixture of HNO3/
H2SO4 at ꢀ5°C. The pure product compound 2 was
recovered by precipitation in cooled water. The last
In conclusion, we described an efficient method for the
preparation of two new phosphonic acid chelating
ligands: 2-(dihydroxyphosphorylmethyl)-pyrido[3,2-a:
20,30-c]phenazine (LI) and (4-(dihydroxyphosphoryl-
methyl)-phenyl)-phenanthrimidazole (LII). We recently
A-
PhthN
O2N
H2N
H2N
N
N
N
N
N
N
N
N
c
d
PO3Et2
e
a,b
H2N
PO3Et2
PO3Et2
PO3Et2
PO3H2
1
2
3
4
L I
B-
f
PO Et
Br
PO3Et2
3
2
g
i
H
O
H
N
5
H
N
j
N
N
N
N
k
PO3Et2
O
O
N
P
N
PO3H2
h
HO
N
OEt
C
7
Br
Br
H
8
6
L II
Scheme 2. Reagents and conditions : (a) phthalic anhydride; (b) HNO3/H2SO4, ꢀ5°C; (c) N2H4, Pd/C; (d) 1,10-phenanthrolinedione; (e) HCl 12M
reflux; (f) NBS, DBPO, hm; (g) NaHCO3, DMSO; (h) DIBALH; (i) P(OC2H5)3; (j) 1,10-phenanthrolinedione, NH4OAc, CH3COOH; (k) HCl 12M
reflux.

C. R. Mayer et al. / Tetrahedron Letters 45 (2004) 7805–7807
7807
5. Mayer, C. R.; Neveu, S.; Cabuil, V. Angew. Chem. Int.,
Ed. 2002, 41, 501.
6. See for example: Mayer, C. R.; Herson, P.; Thouvenot, R.
Inorg. Chem. 1999, 38, 6152.
7. Special issue in Chem. Rev. 1998, 98.
described the functionalization of POM by compound
5.22 The grafting of these ligands on other POM frame-
works and their interaction with TiO2 surface are cur-
rently under investigation.
8. Steck, E. A.; Day, A. R. J. Am. Chem. Soc. 1943, 65, 452.
9. Lehn, J. M. Supramolecular Chemistry, Concept and
Perspectives; VCH: Weinheim, 1995.
Acknowledgements
10. Walters, K. A.; Trouillet, L.; Guillerez, S.; Schanze, K. S.
Inorg. Chem. 2000, 39, 5496.
11. Peng, Z.; Gharavi, A. R.; Yu, L. J. Am. Chem. Soc. 1997,
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12. Hara, K.; Sugihara, H.; Tachibana, Y.; Islam, A.;
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2001, 17, 5992.
We gratefully acknowledge Ally Aukoulo (Laboratoire
de Chimie Inorganique, UMR CNRS 8613, ICMMO,
Orsay) for fruitful discussion. We thank Vincent
Steinmetz for mass spectrometry measurements.
13. Zakeeruddin, S. M.; Nazeeruddin, M. K.; Pechy, P.;
Rotzinger, F. P.; Humphry-Baker, R.; Kalyanasundarm,
K.; Gra¨tzel, M. Inorg. Chem. 1997, 36, 5937.
14. Montalti, M.; Wadhwa, S.; Kim, W. Y.; Kipp, R. A.;
Schmehl, R. H. Inorg. Chem. 2000, 39, 76.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
2004.07.067. The general procedure and mass spectrum
are detailed in Supplementary data.
´
15. Mayer, C. R.; Herve, M.; Lavanant, H.; Blais, J.-C.;
´
Secheresse, F. Eur. J. Inorg. Chem. 2004, 5, 973.
16. Loewe, R. S.; Ambroise, A.; Muthukumaran, K.; Pad-
maja, K.; Lysenko, A. B.; Mathur, G.; Li, Q.; Bocian, D.
F.; Misra, V.; Lindsey, J. S. J. Org. Chem. 2004, 69, 1453.
17. McKenna, C. E.; Higa, M. T.; Cheung, N. H. Tetrahedron
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4. Zabri, H.; Gillaizeau, I.; Bignozzi, C. A.; Caramori, S.;
Charlot, M.-F.; Cano-Boquera, J.; Odobel, F. Inorg.
Chem. 2003, 42, 6655.
18. For general procedure see Supplementary data.
19. Bhattacharya, A. K.; Thyagarajan, G. Chem. Rev. 1981,
81, 415.
20. Nace, H. R.; Monagle, J. J. J. Org. Chem. 1959, 24, 1792.
21. Wen, L.; Li, M.; Schlenoff, J. B. J. Am. Chem. Soc. 1997,
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´
22. Mayer, C. R.; Marrot, J.; Secheresse, F. J. Mol. Struct.
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