Solvent-free synthesis of bis(2,2′:6′,2″-terpyridin- 4′-yl)amine and its metal complexes

Article abstract of DOI:10.1055/s-2008-1072574

The key compound bis(2,2′:6′,2″-terpyridin-4′-yl) amine was prepared in one step starting from 4′-amino-2,2′:6′, 2″-terpyridine and 4′-bromo-2,2′:6′,2″-terpyridine in quantitative yield. In addition, we have established an easy and efficient route for the

Full text of DOI:10.1055/s-2008-1072574

1
514
SHORT PAPER
Solvent-Free Synthesis of Bis(2,2¢:6¢,2¢¢-terpyridin-4¢-yl)amine and Its Metal
Complexes
B
R
is(2,2
¢
:6
¢
,2¢¢-ter
e
¢
-y
z
l)amine an
a
d Its Metal
-
C
omplex
A
es li Fallahpour*
Institute of Organic Chemistry, University of Zurich UZH, Winterthurerstrasse 190, 8057 Zurich, Switzerland
Fax +41(61)3639869; E-mail: Reza.Fallahpour@oci.uzh.ch
Received 6 January 2008; revised 13 February 2008
Abstract: The key compound bis(2,2¢:6¢,2¢¢-terpyridin-4¢-yl)amine
was prepared in one step starting from 4¢-amino-2,2¢:6¢,2¢¢-terpyri-
dine and 4¢-bromo-2,2¢:6¢,2¢¢-terpyridine in quantitative yield. In ad-
dition, we have established an easy and efficient route for the
synthesis of the bromoterpyridine compound. Using the novel
ligand, two ruthenium complexes were also prepared.
N
N
i)
N
NH2
N
Br
Key words: aminoterpyridine, bromoterpyridine, amino-bridged
N
N
terpyridine, metallodendrimers
1
2
Scheme 1 Reagents and conditions: (i) 48% HBr, Br , NaNO , 0 °C,
2
2
Dendrimers, in principal, and in particular metalloden-
drimers, belong to a rapidly growing field within su-
3
0 min, 59%.
1
pramolecular chemistry. The metal centers are
When we reacted 1 and 2 to prepare our desired ligand 3
in acetonitrile or dimethyl sulfoxide in the presence of a
base, even in the form of a metal complex, the reaction
failed. However, when 1 and 2 were reacted in a melt at
2
incorporated into the dendrimers for electron transfer or
3
as a chromophore. Although 2,2¢:6¢,2¢¢-terpyridine (tpy)
ligands do not exhibit the desired photochemical proper-
ties with transition metals, e.g., with ruthenium(II); the
geometric and stereochemical advantages of the tpy
ligand make it an interesting molecule. 2,2¢:6¢,2¢¢-Terpyri-
dine seems to be among the most versatile ligands for
complex formation with transition metals. Most work in
this field has been concerned with attaching functional
2
40 °C, compound 3 only was formed, the remainder of
the product mixture was unreacted starting materials.
Hence, this is a clean reaction and the yield is quantitative
with respect to the reacted compounds. The turnover of
the reaction is more than 98%, but it is not dependant on
the reaction time or the ratio of the starting materials. The
reaction of 1 and 2 in the ratio of 1:1 gave only compound
4
groups directly to C4¢ of the 2,2¢:6¢,2¢¢-terpyridine. We
have also been involved in the functionalization of oli-
gopyridines and have developed methods to achieve this
3
; when two or more equivalents of 2 were reacted with 1,
product 3 was again isolated in quantitative yield
Scheme 2).
5
goal. In addition, we have also reported the preparation of
(
6
2
,2¢:6¢,2¢¢-terpyridine 1¢-oxides. We now wish to report
the synthesis of an amine-bridged tpy ligand 3 and its ru-
thenium(II) complexes.
N
H
N
N
In the series of amino-substituted terpyridine ligands only
two compounds, 4¢-amino-2,2¢:6¢,2¢¢-terpyridine (tpy-
N
i)
N
5
c
5c
1
+
2
NH , 1) and 4¢-(dimethylamino)-2,2¢:6¢,2¢¢-terpyridine
2
have been reported previously; both tpy ligands have been
incorporated into metal-bonded complexes.
N
N
4
¢-Amino-2,2¢:6¢,2¢¢-terpyridine (1) was converted into 4¢-
3
bromo-2,2¢:6¢,2¢¢-terpyridine (tpy-Br, 2) using standard
methodology (Scheme 1). This method allows also the
6
Scheme 2 Reagents and conditions: (i) neat, 240 °C, 16 h, 100%.
preparation of halogen-substituted symmetric and asym-
metric terpyridine ligands.
Due to the symmetry of the molecule, only five signals
would be expected (and are observed) in the H NMR
spectrum of bis(2,2¢:6¢,2¢¢-terpyridin-4¢-yl)amine (3).
Compound 3 was compared with 4¢-amino-2,2¢:6¢,2¢¢-
terpyridine (1). In deuterochloroform solution H3¢ was
shifted to low field and was observed as a singlet at d =
1
We became interested in the amine-bridged tpy ligand 3,
firstly, due to the possibility of functionalization of the
amine nitrogen atom to form a trisubstituted amine as a
core for dendrimers.
8
.33 (Dd = 0.59) while H6 (d = 8.68, Dd = 0.06) and H3
SYNTHESIS 2008, No. 10, pp 1514–1516
x
x.
x
x
.
2
0
0
8
Advanced online publication: 07.04.2008
DOI: 10.1055/s-2008-1072574; Art ID: Z00408SS
Georg Thieme Verlag Stuttgart · New York
(d = 8.65, Dd = 0.07) were slightly shifted to low field, re-
spectively. In the Maldi-TOF mass spectrum of 1, parent
©

SHORT PAPER
Bis(2,2¢:6¢,2¢¢-terpyridin-4¢-yl)amine and Its Metal Complexes
1515
H
N
4+
N
N
N
N
N
N
N
N
N
N
i)
[
X-tpy(RuCl3)]
+
3
Ru
Ru
N
N
X
X
X = Cl
4
5
X = OH
Scheme 3 Reagents and conditions: (i) [RuCl (Cl-tpy)], N-ethylmorpholine, MeOH, 64 °C, 1 h, 4 (61%); [RuCl (HO-tpy)], N-ethylmorpho-
3
3
line, MeOH, 64 °C, 1 h, 5 (54%).
ion peaks were observed at m/z = 479. All the analytical All of the starting oligopyridines and the novel amine bridged 3 and
catalysts are currently available from HetCat, Switzerland
and spectroscopic data are in accord with the proposed
formulation and structure.
(www.hetcat.com).
Two ruthenium complexes of this ligand were prepared by 4¢-Bromo-2,2¢:6¢,2¢¢-terpyridine (2)
standard methods, to exemplify its reactivity and prop- 4¢-Amino-2,2¢:6¢,2¢¢-terpyridine (1, 500 mg, 2.01 mmol) was dis-
solved in 48% HBr (10 mL). Br (0.4 mL) was added at 0 °C fol-
erties (Scheme 3). Compound 3 was reacted with
trichloro(4¢-hydroxy-2,2¢:6¢,2¢¢-terpyridine)ruthenium
2
lowed by NaNO (500 mg) in H O (2 mL) and the mixture was
stirred for 30 min. The soln was neutralized by adding NaOH (2.0
g) in H O (5 mL). The aqueous phase was then extracted with
CH Cl (3 × 30 mL). The combined organic phases were dried
MgSO ) and solvent was removed. Compound 2 was purified by
2
2
5
c
[
RuCl (HO-tpy)]
and trichloro(4¢-chloro-2,2¢:6¢,2¢¢-
3
5
c
2
terpyridine)ruthenium [RuCl (Cl-tpy)] in methanol to
3
2
2
obtain the complexes 4 and 5 in 61% and 54% yield, re-
(
4
spectively. Both complexes 4 and 5 are symmetric and ex- chromatography (silica gel, CH Cl –hexane, 1:1); yield: 0.37 g
2
2
1
hibit ten signals in the H NMR spectra, each five for 4 (59%); mp 135 °C.
1
and 4¢-hydroxy-2,2¢:6¢,2¢¢-terpyridine or 4¢-chloro-
2
2
H NMR (CDCl ): d = 8.71 (m, 2 H, H6), 8.64 (s, 2 H, H3¢), 8.57 (d,
3
,2¢:6¢,2¢¢-terpyridine. In complex 5, H3¢¢¢ of 4¢-hydroxy- J = 7.80 Hz, 2 H, H3), 7.86 (ddd, J = 8.30, 7.80, 1.95 Hz, 2 H, H4),
,2¢:6¢,2¢¢-terpyridine was observed at d = 8.23 while in 7.35 (ddd, J = 8.30, 7.80, 1.95 Hz, 2 H, H5).
13
complex 4 it was observed at d = 8.87, which is consistent
C NMR (CDCl ): d = 156.47, 154.93, 149.20, 136.93, 135.06,
3
with the electron-releasing and -withdrawing groups; H3¢ 124.23, 124.20, 121.40.
of the 4¢-aminoterpyridine was observed at d = 8.85 for 4
and at d = 8.69 for 5.
MS (Maldi-TOF): m/z = 312.
Anal. Calcd for C H BrN : C, 57.72; H, 3.23; N, 13.46. Found: C,
1
5
10
3
Ruthenium(II) complexes 4 and 5 are electrochemically 57.61; H, 3.35; N, 13.22.
active in acetonitrile solution, each exhibiting a wave cor-
Bis(2,2¢:6¢,2¢¢-terpyridin-4¢-yl)amine (3)
responding to the ruthenium(II)/ruthenium(III) process.
The potential of the ruthenium(II) complexes 4 and 5 (vs
ferrocene-ferrocenium internal reference) are 0.93 and
A mixture of 4¢-bromo-2,2¢:6¢,2¢¢-terpyridine (2, 100 mg, 0.32
mmol) and 4¢-amino-2,2¢:6¢,2¢¢-terpyridine (1, 100 mg, 0.40 mmol)
was heated at 240 °C in a closed glass ampoule for 20 h. After cool-
ing to r.t. the black residue was dissolved in MeOH (50 mL). The
organic solvent was removed. Chromatographic separation (alumi-
na, CH Cl –hexane, 1:1) gave the first fraction, compound 2, fol-
0
.89 V, respectively, which are comparable with other ru-
thenium complexes of tpy ligands.
2
2
In conclusion, we have shown an easy and efficient
solvent-free synthesis of 4¢-bromo-2,2¢:6¢,2¢¢-terpyridine
lowed by compound 3. As a last fraction compound 1 was collected.
The separation was made easy, since compound 3 reacts with
iron(II) to give a blue complex while 1 and 2 give purple complexes.
(
2) and bis(2,2¢:6¢,2¢¢-terpyridin-4¢-yl)amine (3) and metal
complexes 4 and 5 of 3. Both compounds are interesting Compound 3 was recrystallized (EtOH) to give a yellow microcrys-
starting materials in coordination and dendrimer chemis- talline solid; yield: 150 mg (100%, with respect to reacted 2); mp
1
95–196 °C.
try.
IR (KBr): 3423 (m), 1607 (m), 1578 (s), 1528 (s), 1430 (m), 1342
–
1
(
m), 1293 (m), 1231 (m), 999 (m), 786 cm (m).
All reagents were used as supplied. Silica gel (0.060–0.200 mm)
was supplied from Merck and aluminum oxide (type 507 C neutral;
1
H NMR (CDCl ): d = 8.68 (d, J = 7.80 Hz, 4 H, H6), 8.65 (d,
3
J = 8.30 Hz, 4 H, H3), 8.33 (s, 4 H, H3¢), 7.87 (ddd, J = 8.30, 7.80,
1
s, 1 H, NH).
1
1
00–125 mesh) from Fluka. Melting points were measured on Bü-
.95 Hz, 4 H, H4), 7.34 (ddd, J = 8.30, 7.80, 1.95, 4 H, H5), 6.68 (br
chi 535 and are not corrected. IR spectra were recorded on a Matt-
son Genesis Fourier-transform spectrophotometer with samples in
compressed KBr discs. UV spectra were measured on Perkin-Elmer
H NMR (CD OD): d = 8.62 (d, J = 7.80 Hz, 4 H, H6), 8.57 (d,
3
1
13
lambda 19. H and C NMR spectra were recorded on Bruker AM
50 spectrometer and referenced against TMS. TOF (Maldi) spectra
J = 8.30 Hz, 4 H, H3), 8.24 (s, 4 H, H3¢), 7.97 (ddd, J = 8.30, 7.80,
1
2
.95 Hz, 4 H, H4), 7.44 (ddd, J = 8.30, 7.80, 1.95 Hz, 4 H, H5).
were recorded using a PerPespective Biosystems Voyagers-RP Bio-
spectrometry Workstation. Electrochemical measurements were
performed with an Ecochemie Autolab PGSTAT 20 potentiostat.
1
3
C NMR (CDCl ): d = 156.93, 156.12, 154.48, 149.06, 136.75,
3
1
23.78, 121.35, 109.58.
Synthesis 2008, No. 10, 1514–1516 © Thieme Stuttgart · New York

1
516
R.-A. Fallahpour
SHORT PAPER
MS (EI): m/z (%) = 479 (54, M), 401 (100, M – pyridine), 374 (12),
97 (5), 240 (19), 200 (12), 78 (9, pyridine).
MS (Maldi-TOF): m/z = 1759 [M + 4 PF ], 1469 [M + 2 PF ], 1179
[M], 930 [M – tpyOH], 829 [M – Ru(tpy-OH)].
6
6
2
Anal. Calcd for C H N ·H O: C, 72.42; H, 4.66; N, 19.71. Found:
C, 72.17; H, 4.62; N, 19.34.
UV (MeCN): lmax = 272, 303, 352, 509 nm; lmin 277, 347, 400 nm.
30
21
7
2
Anal. Calcd for C H F N O P Ru ·H O (1778.13): C, 40.53; H,
6
0
43 24 13
2
4
2
2
2
.55; N, 10.24. Found: C, 39.88; H, 2.99; N, 10.81.
Synthesis of Ruthenium(II) Complexes 4 and 5; General Proce-
dure
o
CV: E = 0.89 V.
Terpyridine 3 (20 mg) and N-ethylmorpholine (0.1 mL) were added
to a suspension of [RuCl (Cl-tpy)] or [RuCl (HO-tpy)] (1 mol
3
3
Acknowledgment
equiv) in MeOH (20 mL) and the mixture was heated for 1 h. The
resulting soln was filtered through Celite, and then excess NH PF
4
6
I would like to thank Professor J. S. Siegel and the University of
Zurich.
was added to the filtrate. This was collected by filtration and washed
with ice-cold MeOH (5 mL), H O (5 mL), and Et O (5 mL) and air
2
2
dried. Purification was performed by chromatography (silica gel,
MeCN–NH , 30:1). Both complexes were further purified by re- References
3
crystallization (diffusion of Et O into the MeCN soln).
2
(1) (a) Topics in Current Chemistry, Vol. 197; Vögtle, F., Ed.;
Springer Verlag: Berlin, 1998. (b) Topics in Current
Chemistry, Vol. 210; Vögtle, F., Ed.; Springer Verlag:
Berlin, 2000. (c) Topics in Current Chemistry, Vol. 212;
Vögtle, F., Ed.; Springer Verlag: Berlin, 2001.
Ruthenium Complex 4.
Yield: 45 mg (61%).
1
H NMR (CD CN): d = 8.87 (s, 4 H, H3¢¢¢), 8.85 (s, 4 H, H3¢), 8.56
3
(
d, J = 7.80 Hz, 4 H, H3¢¢), 8.53 (d, J = 7.80 Hz, 4 H, H3), 7.99 (ddd,
(
(
(
2) Chow, H.-F.; Mong, T. K.-K.; Nongrum, M. F.; Wan, C.-W.
Tetrahedron 1998, 54, 8543.
3) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni,
S. Chem. Rev. 1996, 96, 759.
J = 8.30, 7.80, 1.95 Hz, 4 H, H4¢¢), 7.93 (ddd, J = 8.30, 7.80, 1.95
Hz, 4 H, H4), 7.67 (d, J = 5.35 Hz, 4 H, H6¢¢), 7.40 (d, J = 5.35 Hz,
4
H, H6), 7.30 (ddd, J = 8.30, 7.80, 1.95 Hz, 4 H, , H5¢¢), 7.18 (ddd,
J = 8.30, 7.80, 1.95 Hz, 4 H, H5).
4) (a) Potts, K. Bull. Soc. Chim. Belg. 1990, 99, 741.
(b) Ziessel, R. Synthesis 1999, 1839. (c) Constable, E. C.
Chem. Commun. 1997, 1073. (d) Grosshenny, V.; Ziessel,
R. J. Organomet. Chem. 1993, C19-C22, 453. (e) Pabst, G.
R.; Sauer, J. Tetrahedron 1999, 55, 5067. (f) Càrdenas, D.
J.; Sauvage, J.-P. Synlett 1996, 916.
(5) (a) Fallahpour, R.-A.; Constable, E. C. J. Chem. Soc., Perkin
Trans. 1 1997, 2263. (b) Fallahpour, R.-A.; Neuburger, M.;
Zehnder, M. Polyhedron 1999, 18, 2445. (c) Fallahpour, R.-
A. Eur. J. Inorg. Chem. 1998, 1205. (d) Fallahpour, R.-A.;
Neuburger, M.; Zehnder, M. New J. Chem. 1999, 23, 53.
MS (Maldi-TOF): m/z = 1506 [M + 2 PF ], 1361 [M + PF ], 1216
6
6
[
M], 1181 [M – Cl], 949 [M – tpyCl], 848 [M – Ru(tpy-Cl)].
UV (MeCN): lmax = 275, 305, 350, 507 nm; lmin = 280, 347, 394
nm.
Anal. Calcd for C H Cl F N P Ru ·2 H O (1833.04): C, 40.53;
6
0
41
2
24 13
4
2
2
H, 2.55; N, 10.24. Found: C, 40.01; H, 3.01; N, 9.68.
o
CV: E = 0.93 V.
Ruthenium Complex 5
Yield: 40 mg (54%).
(
e) Fallahpour, R.-A.; Neuburger, M.; Zehnder, M. Synthesis
1
999, 1051. (f) Fallahpour, R.-A. Synthesis 2000, 1138.
1
H NMR (CD CN): d = 8.69 (s, 4 H, H3¢), 8.54 (d, J = 7.80 Hz, 4 H,
3
(g) Fallahpour, R.-A. Synthesis 2000, 1665. (h) Fallahpour,
R.-A. Helv. Chim. Acta 2000, 83, 384. (i) Fallahpour, R.-
A.; Neuburger, M. Helv. Chim. Acta 2001, 84, 710.
3
H3), 8.45 (d, J = 7.80 Hz, 4 H, H ¢¢), 8.23 (s, 4 H, H3¢¢¢), 7.94 (m, 8
H, H4, H4¢¢), 7.56 (d, J = 5.35 Hz, 4 H, H6), 7.50 (d, J = 5.35 Hz, 4
H, H6¢¢), 7.23 (m, H4, H4¢¢, 8 H).
(
j) Fallahpour, R.-A. Synthesis 2003, 153.
6) Fallahpour, R.-A.; Neuburger, M. Eur. J. Org. Chem. 2001,
853.
(
1
Synthesis 2008, No. 10, 1514–1516 © Thieme Stuttgart · New York