A phen-terpy conjugate whose chelate coordination axes are orthogonal to one another and its zinc complex

Article abstract of DOI:10.1039/b511762c

A new highly rigid ditopic ligand has been prepared which consists of a terpy fragment connected through its 4′ position to the 3 position of a phen nucleus via a 1,4-phenylene linker. The chemical structure of the presently reported two-chelate ligand is

Full text of DOI:10.1039/b511762c

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LETTER
www.rsc.org/njc | New Journal of Chemistry
A phen–terpy conjugate whose chelate coordination axes are orthogonal
to one another and its zinc complexw
Benoıt Champin, Valerie Sartor and Jean-Pierre Sauvage*
ˆ
´
Received (in Montpellier, France) 18th August 2005, Accepted 22nd November 2005
First published as an Advance Article on the web 2nd December 2005
DOI: 10.1039/b511762c
7
Holm, which upon lithiation of the brominated precursor and
A new highly rigid ditopic ligand has been prepared which
0
consists of a terpy fragment connected through its 4 position
addition of N,N-dimethylacetamide afforded 2 in 52% yield.
Two parallel reactions were then carried out. On one hand,
azachalcone 3 was obtained by classical aldol condensation of
2 and 4-bromobenzaldehyde, and subsequent dehydration of
to the 3 position of a phen nucleus via a 1,4-phenylene linker.
The chemical structure of the presently reported two-chelate
ligand is such that the coordination axes of the two chelates are
orthogonal to one another. The reaction of this phen–terpy
8
,9
the intermediate (86%). On the other hand, reaction of 2
10
with iodine in pyridine yielded the pyridinium iodide 4
2
1
conjugate with Zn affords in good yield a dimeric structure,
1
as shown by ES-MS and H NMR spectroscopies.
(74%). Precursors 3 and 4 were then allowed to react accord-
8
,11,12
ing to the classical Kro
¨
hnke synthesis
and terpyridine 5
Multisite ligands containing two or several aromatic poly-
imines and their complexes have been extensively used in
relation to electron and energy transfer processes, most of
was obtained in 60% yield. The functionality at the back of the
terpyridine was then modified by changing the bromine atom
for a boronic ester function in the presence of bis(neopentyl
6
13
the time with ruthenium(II) centres and other d transition
1
metals. They have also been utilised extensively to construct
glycolato)diboron according to the well described procedure.
Compound 6 was thus obtained in quantitative yield from 5.
2a
elegant multinuclear architectures such as grids, helical
3
The precursor used for the phenanthroline fragment was
2b,c
2d,e
complexes,
racks,
etc. or new topologies such as knots
3,8-dibromo-1,10-phenanthroline which was synthesized follow-
14,15
4
or rotaxane dimers. As far as we know, two-site ligands
whose chelate coordination axes are orthogonal to one an-
other are not common. Such compounds should favour the
formation of multinuclear complexes with well defined geo-
ing the usual procedure.
It was then dissymetrized by a
5,16
1
statistical Suzuki coupling reaction
on p-anisylboronic
acid, and the mono-coupled product 7 was isolated in 46%
1
3,15,16
yield. A last Suzuki coupling reaction
between 6 and 7
5
metries and nuclearities. Once incorporated in macrocyclic
under classical conditions yielded the phen–terpy conjugate 1
(24%), containing seven conjugated 6-membered aromatic
rings.
systems, they should also allow the synthesis of multi-rota-
xanes. The coordination principle is given in Fig. 1.
21
The present report deals with the synthesis and the proper-
Zn forms stable 5-coordinate complexes and it is most of
the time sufficiently labile to allow formation of coordination
compounds under thermodynamic control. This metal was
thus selected for complexation studies with ligand 1. It should
be noticed that non-distorted trigonal bipyramid geometries,
with their two A and B chelates orthogonal to one another, are
expected to favour formation of 4-metal centre assemblies
similar to that represented in Fig. 1. By contrast, other
0
0
00
ties of such a two-site ligand, containing a 2,2 :6 ,2 -ter-
pyridine unit (terpy ¼ tridentate chelate) attached to a 1,10-
phenanthroline nucleus (phen ¼ bidentate chelate). The rigid
linker used (1,4-phenylene) connects the two chelates via
0
appropriate positions (4 position of terpy and 3 position of
phen) so that the coordination axes are perpendicular to one
another. The phen–terpy ligand 1 is represented in Scheme 1 as
well as the synthetic route leading to it. It should be noticed
that both chelating units are very distinct from one another (A
of Fig. 1 is the phen unit, and B the terpy fragment). If the
complexed metal M has a strong preference for 5-coordinate
situations, M(A)(B) complexes should be strongly favoured
2 2
versus symmetrical complexes of the M(A) or M(B) type.
Compound 2 had previously been made by reacting
6
Grignard reagents with the nitrile derivative. We developed
a new efficient route inspired by the procedure described by
Laboratoire de Chimie Organo-Mine´rale, LC 3-UMR 7177 du CNRS,
Institut de Chimie, Universite´ Louis Pasteur, 4 rue Blaise Pascal, BP
1
032, 67070 Strasbourg Cedex, France. E-mail: sauvage@chimie.
Fig. 1 Formation of M(A)(B) complexes should lead to oriented
cyclic structures. Depending on the coordination sphere geometry of
the transition metal used, various rings and nuclearities could be
obtained.
u-strasbg.fr; Fax: þ33 (0)3 90 24 13 68; Tel: þ33 (0)3 90 24 13 61
w Electronic supplementary information (ESI) available: Structure
and atom numbering for Phen–terpy conjugate 1. See DOI: 10.1039/
b511762c
2
2 | New J. Chem., 2006, 30, 22–25
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major peaks at mass-to-charge (m/z) ratios of 342.6, 506.4, and
4
1
31
8
2
34.6, corresponding to [M] , [M þ OTf] , and [M þ
21
OTf] , respectively, a situation that is consistent with the
proposed dimer compound [Zn ꢁ (1) ] ꢁ 4OTf.
2
2
1
8
DOSY (diffusion-ordered spectroscopy) experiments car-
ried out on a solution of the yellow solid in MeOD (Fig. 3)
revealed unambiguously the presence of a single species,
2
ꢂ1
characterized by its diffusion coefficient (D ¼ 470 mm s
;
2
ꢂ1
monomer 1 in CD
2
Cl
2
: D ¼ 1000 mm s ) and its hydro-
˚
˚
dynamic radius (r
H
¼ 8.5 A; monomer 1: r ¼ 5.3 A).
H
Computational simulation of the hydrodynamic radius of
an ellipsoid object which matches with the experimental value
of the radius enabled us to predict the size of the product in
˚
˚
solution: a ¼ 14 A and b ¼ c ¼ 6 A. The object is thus a prolate
ellipsoid, which is consistent with the proposed dimer com-
pound [Zn ꢁ (1) ] ꢁ 4OTf. The ratio a/b being approximately
2
2
around 2, it would nevertheless be impossible to exclude the
˚
possibility of having an oblate ellipsoid (a ¼ b ¼ 14 A and c ¼
˚
6 A) which would be more consistent with the geometry of the
Scheme 1 Reagents and conditions: (i) 4-bromobenzaldehyde, MeOH
NaOH(aq), 30 min; (ii) I , pyridine, reflux 1 h, rt 14 h; (iii) NH OAc,
AcOH, reflux 7 h, rt 14 h; (iv) Pd(dppf)Cl , KOAc, B neo , dioxane,
0 1C, 18 h; (v) Pd(PPh , Na CO , p-anisylboronic acid, toluene–
O, reflux, 14 h; (vi) Pd(PPh , Na CO , reflux, 30 h.
–
2
4
tetramer species. But considering the results of both ES-MS
and DOSY experiments, we can tell that the sole product
2
2
2
8
H
3
)
4
2
3
formed during the complexation process is the dimer species
1
2
3
)
4
2
3
[
Zn
2
ꢁ (1)
2
] ꢁ 4OTf. Moreover, H NMR clearly shows what was
expected for a dimer species: the geometry around the zinc
5
-coordinate geometries such as, for example, square pyramid
centre is so distorted that the p proton of the phen part of one
2
or distorted trigonal pyramid, should afford smaller rings such
as 3-metal assemblies or even dinuclear species. For entropic
monomer points right into the shielding cone of the central
ring of the terpy fragment of the other monomer, and con-
sequently the p2 proton signal is strongly shifted upfield
(Dd ¼ 2.82 ppm).
2
1
reasons, the reaction between Zn and 1 is expected to lead to
the smallest possible complex, the size of the species obtained
having nevertheless to be compatible with the coordination
constraints imposed by the metal and the ligand. If distortion
In conclusion, a new phen–terpy conjugate 1 has been
synthesized which contains two chelates whose coordination
axes are perpendicular to one another. Whereas the expected
2
1
of Zn coordination sphere and/or of the ligand backbone
costs less than the entropic price needed to build the large ideal
2
1
structure for the Zn complex formed with ligand 1 was that
8
1
4
-metal species, lower nuclearities will be formed. This is the
of a tetramer ([Zn
4
ꢁ (1)
4
]
), a dimer was the sole product
case in the present system. To our surprise, the dimer was the
sole complex formed, without formation of tetramer nor even
trimer complexes. The reaction is represented in Fig. 2 along
with a molecular model (Chem 3D software) of the complex.
observed. The present example tends to indicate that entropy
is a prevailing factor in the complexation process: the reaction
leads to the smallest possible complex in spite of probable
21
distortion of the Zn coordination sphere and constraints
21
The coordination reaction of Zn to 1 was carried out by
mixing equimolar amounts of respectively 1 in CH Cl and
Zn(OTf) in MeOH. The resulting orange solution was al-
within the organic ligand 1. Obviously, the use of other
2
1
2
2
transition metal centres than Zn
with more demanding
2
lowed to stir for 28 hours, the solvent was then evaporated,
the crude mixture was taken up in methanol, filtered, and
the filtrate evaporated to dryness. The dimer complex
4
1
ꢁ 4OTfꢂ was obtained in good yield (78%) as a
[
Zn
2
ꢁ (1)
2
]
yellow solid. It is only sparingly soluble in common organic
solvents. At this stage, it is difficult to know if, in solution, the
2
1
Zn centres are really 5-coordinate or if the counterion (CF -
3
ꢂ
ꢂ
21
SO3 ¼ OTf ) participates in the Zn complexation. The X-
ray structure of a recently published hexanuclear complex with
1
Borromean rings as organic backbone showed that 6-co-
7
21
ꢂ
ordinate Zn
spheres are stable. The dimer complex with two 6-coordinate
complexes with Zn(N) (OTf ) coordination
5
2
1
Zn centres is moreover certainly less strained in terms of
organic ligand distortion than the putative analogous complex
21
in which the Zn centres would be 5-coordinate. The chemi-
4
1
cal structure of [Zn
2
ꢁ (1)
2
]
(M) was proven by electrospray
1
21
Fig. 2 Reaction between 1 and Zn leading to the dimer complex,
ionization mass spectroscopy (ES-MS) and H NMR spectro-
scopies. ES-MS analysis of the yellow solid revealed three
and its molecular model (Chem 3D software).
This journal is ꢀc the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006
New J. Chem., 2006, 30, 22–25 | 23

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temperature. The solvent was removed by rotary evaporation
2 2
and the crude mixture was taken up in CH Cl and washed
with water. The combined organic layers were dried over
Na SO and the solvent evaporated. Chromatography (alumi-
2
4
nium oxide, CH Cl to CH Cl –MeOH (99 : 1)) gave 20 mg
2
2
2
2
1
(
0.032 mmol; 24%) of pure product 1 as a white solid. H
NMR (for atom numbering see ESIw) (300 MHz, CDCl ) d
), 7.08–7.11 (dm,
H, 8.8 Hz, Ho1), 7.67–7.71 (dm, 2H, 8.1 Hz, 2.0 Hz, 0.5 Hz,
3
(
ppm): 2.44 (s, 6H, HCH3), 3.90 (s, 3H, OCH
3
2
H
4
–H
p5–Hp6), 7.91–8.11 (dd, 4H, 8.3 Hz, Ho2–Hm2), 8.34 (d, 1H,
–H
), 9.42
4
00), 7.72–7.75 (dm, 2H, 8.8 Hz, Hm1), 7.88 (d, 2H, 1.5 Hz,
H
2
.3 Hz, Hp7), 8.46 (d, 1H, 2.3 Hz, Hp4), 8.57 (m, 2H, H
00), 8.75 (s, 2H, H 0
.56–8.58 (d, 2H, 7.4 Hz, H –H –H
5
6
00),
6
8
3
3
3
0
1
3
(
d, 1H, 2.25 Hz, H ), 9.50 (d, 1H, 2.25 Hz, H ). C NMR
p9 p2
0
(
300 MHz, CDCl ) d (ppm): 160.07 (i); 156.19 (2 ); 153.80 (2);
3
0
1
1
1
1
49.62 (6); 149.43 (4 ); 149.36 (p9); 149.30 (p2); 146.02 (p12);
45.40 (p3); 144.72 (p11); 138.68 (y); 137.44 (4); 135.46 (p8);
34.92 (x); 133.57 (5); 133.41 (p4); 132.59 (p7); 130.00 (p);
28.69 (m1); 128.67 (p14); 128.37 (p13); 128.21 (o2); 127.97
0
(
(
(
m2); 127.24 (p6); 127.06 (p5); 120.96 (3); 118.16 (3 ); 114.78
3 3
o1); 55.47 (OCH ); 18.48 (CH ). EI-MS, m/z exp.: 622.254
1, calc. for [M þ H]: 622.260). DOSY (CD
2 2
Cl , 500 MHz):
2
˚
D ¼ 1000 mm /s; r
H
¼ 5.3 A.
.
.
Dimer [Zn
pended in 0.25 mL of CH
CH OH (23.8 mg in 1 mL) was prepared, and 0.25 mL were
2
(1)
2
] 4OTf. Phen–terpy conjugate 1 was sus-
Fig. 3 DOSY experiment on the dimer complex in MeOD, and zoom
on the aromatic region of the spectrum. Apart from the MeOH broad
signals, a single product is present.
2
Cl . A solution of Zn(OTf) in
2
2
3
added to the ligand suspension, which became clear and
orange. The reaction mixture was allowed to stir for 28 h,
the solvent was then evaporated and the crude mixture taken
up in methanol, filtered, and the filtrate evaporated to dryness
stereoelectronic requirements, making distortion more diffi-
cult, should favour formation of trimers or tetramers.
1
yielding [Zn ꢁ (1) ] ꢁ 4OTf as a yellow solid (10.5 mg; 78%). H
2
2
NMR (500 MHz, CD OD) d (ppm): 2.37 (s, 6H, H
), 4.02
CH3
3
Experimental
(s, 3H, OCH
o1), 7.64–7.66 (dm, 2H, 8.0 Hz, Hm2), 8.12 (m, 2H, H
.16 (dm, 2H, 8.0 Hz, Ho2), 8.20 (m, 4H, Hp5–Hp6–Hm1), 8.25
(m, 2H, H –H ), 8.44–8.46 (d, 1H, Hp9), 8.76–8.78 (d, 2H, 8.1
Hz, H –H ), 8.94 (m, 1H, Hp4), 9.04 (s, 2H, H –H ), 9.39 (s,
1H, Hp7). EI-MS, m/z exp.: 342.592 (calc. for [Zn
3
), 6.68 (s, 1H, Hp2), 7.35–7.37 (d, 2H, 8.85 Hz,
H
4
), 8.14–
General
8
1
13
H, C NMR and DOSY spectra were acquired either on a
Bruker AVANCE 300 (300 MHz) or a Bruker AVANCE 500
500 MHz) spectrometer, using the deuterated solvent as the
6
0
6
0
0
0
5
3
3
3
4
1
(
2
(1)
, OTf] : 506.438); 834.681
, 2OTf] : 834.637). DOSY (CD OD, 500
2
]
:
31
lock and residual solvent as the internal reference. Mass
spectra were obtained by using a Bruker MicroTOF spectro-
2 2
342.590); 506.439 (calc. for [Zn (1)
2
1
(calc. for [Zn
(1)
2
2
3
2
ꢂ1
˚
meter (ES-MS). Pd(PPh
products.
3
)
4
and Zn(OTf)
2
were commercial
MHz): D ¼ 470 mm s ; r ¼ 8.5 A.
H
Acknowledgements
Syntheses
We thank the Region Alsace and the CNRS for financial
´
Phen–terpy conjugate 1. To a degassed solution of 3-bromo-
-(4-methoxyphenyl)-1,10-phenanthroline (7, 49 mg; 0.134
support to BC.
8
mmol) and Pd(PPh3)4 (7.8 mg; 0.007 mmol) in 10 mL of
toluene were added, under argon, 1 mL of a degassed solution
0
References
of 2 M aqueous Na
2
CO
3
and a solution of 4 -(4-(neopentyl
0
1
For a few representative publications on multi-ligands and their
complexes, see: (a) J.-P. Sauvage, J.-P. Collin, J.-C. Chambron, S.
Guillerez, C. Coudret, V. Balzani, F. Barigelletti, L. De Cola and
L. Flamigni, Chem. Rev., 1994, 94, 993–1019; (b) S. Encinas, A. M.
Barthram, M. D. Ward, F. Barigelletti and S. Campagna, Chem.
Commun., 2001, 277–278; (c) C. Ringenbach, A. De Nicola and R.
Ziessel, J. Org. Chem., 2003, 68, 4708–4719; (d) E. C. Constable, R.
0
0
0
00
glycolatoboron)phenyl)-5,5 -dimethyl-2,2 :6 ,2 -terpyridine (6,
2 mg; 0.138 mmol) in 5 mL of toluene. It is very important to
6
respect the following sequence in the additions: (a) dibromo-
phenanthroline in toluene, (b) 3 vacuum–argon cycles, (c)
addition of the catalyst, (d) 3 vacuum–argon cycles, (e) addi-
W. Handel, C. E. Housecroft, A. Farran Morales, B. Ventura, L.
`
tion of the degassed solution of Na
2
CO
3
, (f) 3 vacuum–argon
Flamigni and F. Barigelletti, Chem. Eur. J., 2005, 11, 4024–4034;
e) S. Ghumaan, B. Sarkar, S. Patra, K. Parimal, J. van Slageren,
J. Fiedler, W. Kaim and G. Kumar Lahiri, Dalton Trans., 2005,
706–712; (f) S.-H. Hwang, C. N. Moorefield, F. R. Fronczek,
cycles, (g) addition of the degassed solution of the boronic
ester. The reaction was monitored by TLC, and after 30 h
reflux, the reaction mixture was allowed to cool to room
(
2
4 | New J. Chem., 2006, 30, 22–25
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˚
¨
8 P. Korall, A. Borje, P.-O. Norrby and B. Akermark, Acta Chem.
Scand., 1997, 51, 760–766.
9 G. W. V. Cave and C. L. Raston, J. Chem. Soc., Perkin Trans. 1,
2001, 3258–3264.
O. Lukoyanova, L. Echegoyen and G. R. Newkome, Chem.
Commun., 2005, 713–715; (g) P. Wang, C. N. Moorefield and G.
R. Newkome, Angew. Chem., Int. Ed., 2005, 44, 1679–1683; (h)
E. C. Glazer, D. Magde and Y. Tor, J. Am. Chem. Soc., 2005, 127,
4
190–4192.
10 P. Baret, J. Einhorn, G. Gellon and J.-L. Pierre, Synthesis, April,
1998, 431–435.
¨ ¨
11 (a) F. Krohnke, Chem. Ber., 1961, 94, 690–698; (b) F. Krohnke,
2
(a) P. N. W. Baxter, J.-M. Lehn, J. Fischer and M.-T. Youinou,
Angew. Chem., Int. Ed. Engl., 1994, 33, 2284; (b) J.-M. Lehn, A.
Rigault, J. Siegel, J. Harrowfield, B. Chevrier and D. Moras, Proc.
Natl. Acad. Sci. USA, 1987, 84(9), 2565–2569; (c) T. M. Garret, U.
Koert, J.-M. Lehn, A. Rigault, D. Meyer and J. Fischer, J. Chem.
Soc., Chem. Commun., 1990, 557; (d) G. S. Hanan, C. R. Arana,
J.-M. Lehn and D. Fenske, Angew. Chem., Int. Ed. Engl.,
1995, 34(10), 1122–1124; (e) P. N. W. Baxter, G. S. Hanan and
J.-M. Lehn, Chem. Commun., 1996, 2019.
(a) J.-P. Sauvage, Acc. Chem. Res., 1990, 23, 319; (b) C.
Dietrich-Buchecker and J.-P. Sauvage, New J. Chem., 1992, 16,
Angew. Chem., Int. Ed. Engl., 1963, 2, 380.
12 (a) I. Maeba, J. Chem. Soc., Perkin Trans. 1, 1991, 939; (b) S. N.
Kilenyi, Comprehensive Organic Synthesis, Pergamon Press, 1991,
vol. 7, pp. 657–659.
13 C. J. Aspley and J. A. G. Williams, New J. Chem., 2001, 25,
1136–1147.
14 Y. Saitoh, T. Koizumi, K. Osakada and T. Yamamoto, Can. J.
Chem., 1997, 75, 1336.
3
4
´
15 C. Dietrich-Buchecker, M. C. Jimenez and J.-P. Sauvage, Tetra-
hedron Lett., 1999, 40, 3395.
2
77–285.
(a) M.-C. Jime
Cian, Angew. Chem., Int. Ed., 2000, 39(7), 1295–1298; (b) M.-C.
Jimenez-Molero, C. Dietrich-Buchecker and J.-P. Sauvage, Chem.
´
nez, C. Dietrich-Buchecker, J. P. Sauvage and A. De
16 N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457.
17 K. S. Chichak, S. J. Cantrill, A. R. Pease, S.-H. Chiu, G. W. V.
Cave, J. L. Atwood and J. F. Stoddart, Science, 2004, 304(5675),
1308–1312.
´
Eur. J., 2002, 8(6), 1456–1466.
5
6
7
M. Fujita, M. Tominaga, A. Hori and B. Therrien, Acc. Chem.
Res., 2005, 38, 371–380.
T. A. Crabb and G. C. Heywood, Org. Magn. Reson., 1982, 20(4),
18 For similar use of DOSY NMR to determine the nature of the
chemical species formed in solution, see: (a) A. Hori, K. Kuma-
zawa, T. Kusukawa, D. Kumar Chand, M. Fujita, S. Sakamoto
and K. Yamaguchi, Chem. Eur. J., 2001, 7(19), 4142–4149; (b) A.
Hori, K.-I. Yamashita, T. Kusukawa, A. Akasaka, K. Biradha and
M. Fujita, Chem. Commun., 2004, 1798–1799.
2
42–248.
J. E. Parks, B. E. Wagner and R. H. Holm, J. Organomet. Chem.,
973, 56, 53–66.
1
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