Synthesis of multifunctional ligands: A 2,9-diaryl-1,10-phenanthroline/2,2′:6′,2″-terpyridine conjugate

Article abstract of DOI:10.1016/S0040-4039(01)00279-9

The synthesis of a ligand including a 1,10-phenanthroline and a 2,2′:6′,2″-terpyridine separated by a 1,3-phenylene spacer is presented. The different aromatic carbon-carbon bonds have been generated by reactions with organolithium compounds, and by Stille and Suzuki couplings.

Full text of DOI:10.1016/S0040-4039(01)00279-9

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 2779–2781
Synthesis of multifunctional ligands: a
2,9-diaryl-1,10-phenanthroline/2,2%:6%,2¦-terpyridine conjugate
Nicolas Belfrekh, Christiane Dietrich-Buchecker* and Jean-Pierre Sauvage
Laboratoire de Chimie Organo-Mine´rale, UMR 7513 du CNRS, Universite´ Louis Pasteur, Faculte´ de Chimie,
4, rue Blaise Pascal, 67070 Strasbourg Cedex, France
Received 22 January 2001; accepted 19 February 2001
Abstract—The synthesis of a ligand including a 1,10-phenanthroline and a 2,2%:6%,2¦-terpyridine separated by a 1,3-phenylene
spacer is presented. The different aromatic carbonꢀcarbon bonds have been generated by reactions with organolithium
compounds, and by Stille and Suzuki couplings. © 2001 Elsevier Science Ltd. All rights reserved.
Multifunctional ligands incorporating several coordina-
tion sites are of special interest in coordination chem-
istry because they are useful building blocks in the
templated synthesis of multicomponent molecular
assemblies,1 including motors and machines,1,2 or topo-
logical non-trivial compounds, like catenanes, rotax-
anes and knots.3,4 In particular, 1,10-phenanthroline
and 2,2%:6%,2¦-terpyridine moieties have been extensively
used in the design of such ligands using either Cu(I) or
Fe(II) as templating species.5,6 We would now like to
report a convenient directed synthesis of a dissymmetri-
cal ligand containing two different chelates: a 1,10-
phenanthroline and a 2,2%:6%,2¦-terpyridine connected
by a 1,3-phenylene spacer. In previous work, the meta-
phenylene spacer has been shown to favour the forma-
tion of helical arrangements7 and, when used as a
bridge, to insure a significant level of electronic
communication.8
chloropyridine required for the preparation of boronic
ester 2 (pathway A). This same bromine will be selec-
tively involved in the Suzuki coupling reaction afford-
ing 4 (pathway B). Therefore, both intermediates 6 and
4 still bear an intact 2-chloro substituent and have been
later converted into the trimethylstannanes 8 and 7,
respectively, required for the further CꢀC coupling
reactions (routes C,D and D,E, respectively). Taking
advantage of this striking difference of reactivity, we
were able to build in both a parallel and convergent
way the differently substituted phenanthroline and the
immediate precursor to the terpyridine, which is only
formed in the ultimate connection step (F). Our syn-
thetic strategy, based on a cascade like successive for-
mation of the different carbonꢀcarbon bonds of ligand
10, is depicted in Fig. 1.
Compound 1 was selectively lithiated at the 5 position
with butyllithium in ether at −78°C; further treatment
with B(OMe)3 at −78°C and transesterification with
2,2-dimethylpropane-1,3-diol gave 2 in 74% yield.11
Reaction of 2 with 1 equiv. of the 2,9-disubstituted
phenanthroline 3,12 under Suzuki cross-coupling condi-
tions,13 afforded compound 6 in 55% yield. The chlo-
rine of compound 6 was then converted into a
trimethylstannyl group by reaction of a suspension of 6
The main difficulty of the synthesis of such a ligand is
related to its unsymmetrical feature. The use of the
non-symmetrical single synthon 5-bromo-2-chloropy-
ridine 19 (Fig. 1) associated with that of NaSnMe3
10
appeared highly beneficial. Indeed, the key synthon 1
bears one bromine and one chlorine which differ
strongly in reactivity. Due to this large difference of
reactivity, only the bromine in the 5-position leads, by
interconversion with butyllithium, to the 5-lithio-2-
10
with a solution of NaSnMe3 in DME. A very short
filtration over dry alumina gave stannane derivative 8
in 80% yield.
Reaction of 1 with 1 equiv. of the ester of p-
methoxyphenylboronic acid,14 under Suzuki cross-cou-
pling conditions (Pd[P(C6H5)3]4 in toluene, aqueous
Na2CO3, 60°C, 40 h), afforded pyridine derivative 4 in
Keywords: 1,10-phenanthroline; 2,2%:6%,2¦-terpyridine; Stille and
Suzuki couplings.
* Corresponding author. Fax: +33 3 90 24 13 68; e-mail: dietrbuc@
chimie.u-strasbg.fr
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00279-9

2780
N. Belfrekh et al. / Tetrahedron Letters 42 (2001) 2779–2781
Br
Cl
N
1
O
H3CO
B
O
A
B
5
O
Cl
B
H3CO
Cl
N
N
O
2: 74%
4: 70%
N
N
D
C
Br
3
H3CO
N
N
N
H3CO
Sn(CH3)3
Cl
N
6: 55%
H3CO
7: 70%
D
E
N
N
N
N
H3CO
Sn(CH3)3
N
Br
9: 50%
8: 80%
H3CO
OCH3
F
Rxn
N
N
N
N
N
H3CO
10: 83%
Figure 1. Conditions: (A) (1) BuLi, Et2O, −78°C, 6 h, (2) B(OMe)3, Et2O, −78°C to rt, 12 h, (3) 2,2-dimethylpropane-1,3-diol,
Et2O, 1 h, 0°C, (4) methanesulfonic acid, Et2O, 0°C, 30 min; (B) 2% Pd[P(C6H5)3]4, C6H5CH3, 2 M Na2CO3, 60°C, 40 h; (C) 2%
Pd[P(C6H5)3]4, C6H5CH3, 2 M Na2CO3, 110°C, 7 h; (D) NaSnMe3, DME, −13°C to rt, 15 h; (E) 2,6-dibromopyridine (1 equiv.),
1% Pd[P(C6H5)3]4, C6H5CH3, 110°C, 15 h; (F) 2% Pd[P(C6H5)3]4, C6H5CH3, 110°C, 15 h.
70% yield. Conversion of the chlorine of 4 into a
trimethylstannyl group with NaSnMe3 in DME gave
stannane derivative 7 after a short column over alu-
mina. The latter was reacted with 1 equiv. of 2,6-dibro-
mopyridine to afford the bipyridine 9 in 50% yield.15 In
a final step, reaction of stannane 8 and bipyridine 9,
under Stille16 cross-coupling conditions, afforded ligand
1017 in 83% yield.
sis of a functionalised bischelate ligand that can be
obtained on a gram scale.
Acknowledgements
The authors would like to thank the CNRS for finan-
cial support and the French Ministry of National Edu-
cation for a fellowship to N.B.
In conclusion, we have developed a convenient synthe-

N. Belfrekh et al. / Tetrahedron Letters 42 (2001) 2779–2781
2781
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