A Synthesis of Conjugatively Bridged Bis- and Tris-5-(2,2′-Bipyridines): Multitopic Metal Ion-Binding Modules for Supramolecular Nanoengineering

Article abstract of DOI:10.1021/jo990665n

An efficient preparation of linear and curved bis- and branched tris-5-(2,2′-bipyridines) of nanoscopic dimensions possessing rigid conjugated bridges is presented. The synthesis, which avoids the need of protection/deprotection methodology, utilizes central bridge precursors which are outwardly diand trifunctionalized with a 5-(2-chloropyridine) synthon via a chemoselective palladium-catalyzed Sonogashira or Negishi cross-coupling protocol to yield the bridged linear (5a-c, 5f,g) and curved (6, 7) bis- and branched (8) tris-5-(2-chloropyridines). Under more forcing conditions, the ethynebridged 5-(2-chloropyridines) undergo the Stille cross-coupling reacton with 2-trimethylstannylpyridines to afford the conjugatively bridged linear (1a,b, 1g-j) and curved (2a,b, 3a,b) bis- and branched, (4a,b) tris-5-(2,2′-bipyridines) in good overall yields. The phenyl- and biphenyl-bridged linear bis-5-(2,2′-bipyridines) (1c-f) were best prepared from the bis-5-(2-bromopyridines) (5d,e) to ensure completion of the Stille cross-coupling reactions. The Stille cross-couplings showed a marked substituent effect in which the terminally phenylated bis- and tris-5-(2,2′-bipyridines) were formed in higher yields than the methyl-substituted analogues with the same bridge. The advantages of the methodology lie in its synthetic convenience and adaptibility for creating multitopic metal ion-binding scaffolds with a potentially very large variety of bridging units and substituents on the terminal pyridine rings. The bridged 5-(2-chloropyridines) may also serve as precursors for the fabrication of metal ion-coordinated conjugated polymers.

Full text of DOI:10.1021/jo990665n

J . Org. Chem. 2000, 65, 1257-1272
1257
A Syn th esis of Con ju ga tively Br id ged Bis- a n d
Tr is-5-(2,2′-Bip yr id in es): Mu ltitop ic Meta l Ion -Bin d in g Mod u les for
Su p r a m olecu la r Na n oen gin eer in g
P. N. W. Baxter
Laboratoire de Chimie Supramole´culaire, Institut Le Bel, Universite´ Louis Pasteur, 4 rue Blaise Pascal,
F-67000 Strasbourg, France
Received April 21, 1999
An efficient preparation of linear and curved bis- and branched tris-5-(2,2′-bipyridines) of nanoscopic
dimensions possessing rigid conjugated bridges is presented. The synthesis, which avoids the need
of protection/deprotection methodology, utilizes central bridge precursors which are outwardly di-
and trifunctionalized with a 5-(2-chloropyridine) synthon via a chemoselective palladium-catalyzed
Sonogashira or Negishi cross-coupling protocol to yield the bridged linear (5a -c, 5f,g) and curved
(6, 7) bis- and branched (8) tris-5-(2-chloropyridines). Under more forcing conditions, the ethyne-
bridged 5-(2-chloropyridines) undergo the Stille cross-coupling reacton with 2-trimethylstannylpy-
ridines to afford the conjugatively bridged linear (1a ,b, 1g-j) and curved (2a ,b, 3a ,b) bis- and
branched, (4a ,b) tris-5-(2,2′-bipyridines) in good overall yields. The phenyl- and biphenyl-bridged
linear bis-5-(2,2′-bipyridines) (1c-f) were best prepared from the bis-5-(2-bromopyridines) (5d ,e)
to ensure completion of the Stille cross-coupling reactions. The Stille cross-couplings showed a
marked substituent effect in which the terminally phenylated bis- and tris-5-(2,2′-bipyridines) were
formed in higher yields than the methyl-substituted analogues with the same bridge. The advantages
of the methodology lie in its synthetic convenience and adaptibility for creating multitopic metal
ion-binding scaffolds with a potentially very large variety of bridging units and substituents on
the terminal pyridine rings. The bridged 5-(2-chloropyridines) may also serve as precursors for the
fabrication of metal ion-coordinated conjugated polymers.
In tr od u ction
oligomers has been successfully exploited for the con-
struction of a range of nanosized hydrocarbon molecular
architectures such as rings, cages, and dendritic macro-
molecules.8 These have also enjoyed uses as modules for
crystal engineering,9 liquid crystals,10 and organic an-
tenna arrays.11
Organic polymers and oligomers which possess elec-
tronically conjugated backbones currently fulfill a pivotal
role in the design and generation of new materials.1a-e
The unique physicochemical properties exhibited by such
systems have encouraged the development of a cornuco-
pia of technologically diverse and industrially important
applications. For example, oligo- and polythiophenes,
pyrroles, pyridines, quinolines, benzobisthiazoles, phe-
nylenes, and similar substrates incorporating alternate
ethene or ethyne groups have been demonstrated to
function as organic electronic conductors and photocon-
ductors,1a-e,2a,b electroluminescent materials for light-
emitting diodes,3 field-effect transistors,4 laser emitters,5a-c
NLO substrates,6a,b and materials with high tensile
strength and heat resistance.7 Within the field of na-
noengineering, the structural rigidity of phenylacetylene
In light of the aforementioned considerations, conju-
gated organic polymers and oligomers which incorporate
metal ions as integral structural units would represent
especially interesting synthetic targets with respect to
materials science applications. Substrates of this type
would be expected to display a rich variety of physico-
chemical properties in addition to those discussed above,
such as, for example, multiple redox behavior and optical,
magnetic, mechanical, sensing, and catalytic activity.
Other possibilities concern the unique characteristics of
particular metal ions, which may be harnessed to fine-
tune the electronic properties of the conjugated organic
component in order to perform a desired function.
(1) (a) Handbook of conducting polymers, 2nd ed.; Skotheim, T. A.,
Ed.; Dekker: New York, 1997. (b) Conjugated Conducting Polymers;
Kies, H., Ed.; Springer Series in Solid-State Physics; Springer: Berlin,
1992; Vol. 102. (c) Conjugated polymers; Bre´das, J . L., Sylbey, R., Eds.;
Kluwer: Dordrecht, The Netherlands, 1991. (d) Miller, J . S. Adv.
Mater. 1993, 5, 671. (e) Yamamoto, T. J . Synth. Org. Chem. J pn. 1995,
53, 999.
(2) (a) Kanatzidis, M. G. Chem. Eng. News, 1990, 36. (b) Roncali, J .
Chem. Rev. 1992, 92, 711.
(3) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int.
Ed. Engl. 1998, 37, 402.
The preparation of conjugated organic structures com-
prising electronically communicating metal ions therefore
requires the prior incorporation of metal ion-binding
sites, which cause minimum disruption of the conjugation
pathway and which are able to function as ligands to a
wide variety of metal cations. An ideal candidate for this
purpose is the 2,2′-bipyridine moiety which adopts a rigid,
(4) Horowitz, G. Adv. Mater. 1998, 10, 365.
(5) (a) Berggren, M.; Dodabalapur, A.; Bao, Z.; Slusher, R. E. Adv.
Mater. 1997, 9, 968. (b) Kallinger, C.; Hilmer, M.; Haugeneder, A.;
Perner, M.; Spirkl, W.; Lemmer, U.; Feldmann, J .; Scherf, U.; Mu¨llen,
K.; Gombert, A.; Wittwer, V. Adv. Mater. 1998, 10, 920. (c) J ohansson,
N.; Salbeck, J .; Bauer, J .; Weisso¨rtel, F.; Bro¨ms, P.; Andersson, A.;
Salaneck, W. R. Adv. Mater. 1998, 10, 1136.
(6) (a) Nalwa, H. S. Adv. Mater. 1993, 5, 341. (b) Bre´das, J . L.;
Adant, C.; Tackx, P.; Persoons, A.; Pierce, B. M. Chem. Rev. 1994, 94,
243.
(7) Osaheni, J . A.; J enekhe, S. A. Chem. Mater. 1992, 4, 1282 and
references therein.
(8) Moore, J . S. Acc. Chem. Res. 1997, 30, 402.
(9) Venkataraman, D.; Gardner, G. B.; Lee, S.; Moore, J . S. J . Am.
Chem. Soc. 1995, 117, 11600.
(10) Zhang, J .; Moore, J . S. J . Am. Chem. Soc. 1994, 116, 2655.
(11) Devadoss, C.; Bharathi, P.; Moore, J . S. J . Am. Chem. Soc. 1996,
118, 9635.
10.1021/jo990665n CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/12/2000

1258 J . Org. Chem., Vol. 65, No. 5, 2000
Baxter
conjugated planar conformation when complexed.12 It is
characterized by an extensive coordination chemistry and
a rich electro- and photophysical behavior of its metal
complexes.12,13a,b A limited number of recent reports
describing the preparation of conjugated organic poly-
mers incorporating the 2,2′-bipyridine ligand and some
of its metal complexes have shown that materials of this
type do indeed display interesting properties such as
unusual photophysics,14 redox activity,15 metal ion-
sensing,16a-c and photocatalytic,17 photoconductive,18 and
photorefractive19 behavior. However, despite such prom-
ising investigative potential, a study of the properties of
conjugated oligomeric architectures of nanometric dimen-
sions, possessing spatially precisely defined arrays of
metal ions other than short, linear binuclear complexes,
has received little attention.20a-e This may in part result
from the circuitous synthetic procedures and solubility
problems associated with the preparation of oligomeric
structures of appropriate geometries with the inclusion
of large numbers of metal ion-binding sites.
and aryldi- and -triethyne-bridged bis- and tris-5-(2,2′-
bipyridines) were selected as model targets for this study
owing to their ease of construction, enhanced conjugation,
and the favorable solubility characteristics of the smaller
ligand architectures.22a-e Specifically, the construction
sequence starts with a central bridging scaffold or core
which is outwardly chemoselectively functionalized with
2-chloropyridine units. These are then reacted further
with appropriately substituteded pyridine derivatives to
form the metal ion-binding 2,2′-bipyridine moieties in the
last step of the synthesis.
This method of preparation of bridged 5-(2,2′-bipy-
ridines) has many advantages in terms of brevity and
adaptibility which are detailed as follows: (i) Tempera-
ture-controllable chemoselective reactions are used for
ligand construction, which avoid the need for protection/
deprotection steps. In principle, the reaction sequence
could be iterated through multiple cycles to generate
larger multitopic oligomers if, for example, trialkylsilyl-
ethyne-substituted pyridines were used to form the
bipyridine units. (ii) The methodology avoids the need
for the prior syntheses of unsymmetrically functionalized
2,2′-bipyridines. In the case where differing combinations
of bridging groups and terminal pyridine functionalities
are required, a new bipyridine synthesis would have to
be accomplished for each bridge/terminal functionality
combinaton. This would involve time-consuming and
repetitive multistep syntheses. (iii) Formation of the
bipyridine units in the final step of the synthesis permits
direct incorporation of a wide variety of terminal sub-
stituents into the bridged 5-(2,2′-bipyridine) products by
way of readily accessible and appropriately functionalized
pyridine synthons. Solubilizing substituents may thus be
readily introduced, thereby avoiding the solubility prob-
lems which are frequently encountered with higher
molecular weight oligomers incorporating aromatic and
heterocyclic rings.23 Also, in cases where terminal sub-
stituents may complicate workup conditions, this problem
will only be encountered in the last synthetic step. (iv)
The halopyridyl-functionalized bridging units will serve
as monomers for the generation of 2,2′-bipyridine-
incorporated polymers, thereby maximizing the synthetic
utility of the bridged 5-(2,2′-bipyridine) precursors.
Subsequent experimental investigations fully justified
the above considerations and showed that the bridged
bis- and tris-5-(2,2′-bipyridines) 1a -j, 2a ,b , 3a ,b , and
Syn th esis
Liga n d Design . High molecular weight organic oli-
gomeric and dendritic materials are most frequently
constructed using two main design strategies, i.e., that
of convergent and divergent syntheses which may be used
separately or in combination. In the convergent approach,
a section or segments of the desired architecture are
prepared initially and then connected together to a
central core unit in the final step of the synthesis. In the
divergent approach, the target molecule is built out-
wardly in sequence from a difunctionalized or multiply
functionalized core. A combination of the two strategies
results in molecular doubling at each iteration, enabling
the creation of very high molecular weight oligomers and
normally requires extensive use of protection/deprotec-
tion methodology.
As a first step toward the creation of nanosized
coordination arrays based upon rigid, conjugated organic
frameworks possessing multitopic metal ion-binding
domains, the divergent approach21 was envisioned as
providing the shortest preparative pathway to materials
of this type. Structurally simple ethyne, phenyl, biphenyl,
(12) Constable, E. C. Adv. Inorg. Chem. 1989, 34, 1.
(13) (a) Kalyanasundaram, K. Photochemistry of polypyridine and
porphyrin complexes; Academic Press: London, 1992. (b) Balzani, V.;
J uris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem. Rev. 1996,
96, 759.
(14) Ley, K. D.; Whittle, C. E.; Bartberger, M. D.; Schanze, K. S. J .
Am. Chem. Soc. 1997, 119, 3423.
(15) Grosshenny, V.; Harriman, A.; Gisselbrecht, J .-P.; Ziessel, R.
J . Am. Chem. Soc. 1996, 118, 10315.
(16) (a) Swager, T. M.; Zhu, S. S. J . Am. Chem. Soc. 1997, 119,
12568. (b) Wang, B.; Wasielewski, M. R. J . Am. Chem. Soc. 1997, 119,
12. (c) Kimura, M.; Horai, T.; Hanabusa, K.; Shirai, H. Adv. Mater.
1998, 10, 459.
(17) Yamamoto, T.; Maruyama, T.; Zhou, Z.-hua.; Ito, T., Fukuda,
T.; Yoneda, Y.; Begum, F.; Ikeda, T.; Sasaki, S.; Takezoe, H.; Fukuda,
A.; Kubota, K. J . Am. Chem. Soc. 1994, 116, 4832.
(18) Peng, Z.; Yu, L.; J . Am. Chem. Soc. 1996, 118, 3777.
(19) Peng, Z.; Gharavi, A. R.; Yu, L.; J . Am. Chem. Soc. 1997, 119,
4622.
(20) For reports on the syntheses of bis-2,2′-bipyridines with short
conjugated bridges, and the properties of their dinuclear metal
complexes see; (a) Kocian, O.; Mortimer, R. J .; Beer, P. D. Tetrahedron
Lett. 1990, 31, 5069. (b) Benniston, A. C.; Goulle, V.; Harriman, A.;
Lehn, J .-M.; Marczinke, B. J . Phys. Chem. 1994, 98, 7798. (c) Baba,
A. I.; Ensley, H. E.; Schmehl, R. H. Inorg. Chem. 1995, 34, 1198. (d)
Strouse, G. F.; Schoonover, J . R.; Duesing, R.; Boyde, S.; J ones, J r. W.
E.; Meyer, T. J . Inorg. Chem. 1995, 34, 473. (e) Harriman, A.; Ziessel,
R. J . Chem. Soc., Chem. Commun. 1996, 1707 and references therein.
(21) For a discussion concerning generalized strategies for oligomer
synthesis, see for example: Moore, J . S.; Prince, R. B. In Materials
Science and Technology, A Comprehensive Treatment; Synthesis of
Polymers; Cahn, R. W., Haasen, P., Kramer, E. J ., Eds.; Schlu¨ter, A.-
D., Vol. Ed.; Wiley-VCH: 1999, pp 13-36.
(22) For early reports on the direct ethynylation of brominated 2,2′-
bipyridines using the Sonogashira protocol, see: (a) Butler, I. R.; Soucy-
Breau, C. Can. J . Chem. 1991, 69, 1117. (b) Suffert, J .; Ziessel, R.
Tetrahedron Lett. 1991, 32, 757. This methodology has been extended
to the syntheses of linear, terminally unfunctionalized bis-(2,2′-
bipyridine) ligands bearing ethyne and diethyne bridges via a more
convergent approach. (c) Ziessel, R. Suffert, J .; Youinou, M.-T. J . Org.
Chem. 1996, 61, 6535. (d) Grosshenny, V.; Romero, F. M.; Ziessel, R.
J . Org. Chem. 1997, 62, 1491. An identical methodology has been
communicated to yield terminally unfunctionalized aryldiethyne-
bridged bis(2,2′-bipyridines), but full product characterization and
experimental details were not reported. (e) El-Ghayoury, A.; Ziessel,
R. Tetrahedron Lett. 1997, 38, 2471.
(23) It must be emphasized that the poor solubility expected of larger
ligand architectures may not necessarily hamper the processibility and
usefulness of the resulting metal complexes. In the case of ligand
scaffolds coordinated by charge-neutral metal complexes, ancillary
metal-bound ligands may act as the solubilizing components. For ionic
complexes, the couterions may endow solubility-enhancing properties
to the resulting superstructure.

Synthesis of Bis- and Tris-5-(2,2′-Bipyridines)
J . Org. Chem., Vol. 65, No. 5, 2000 1259
Ta ble 1. Syn th esis a n d Str u ctu r e of Con ju ga tively Br id ged Lin ea r Bis-5-(2,2′-bip yr id in es)
a
The length (including van der Waals surfaces) is defined as the Me-Me distance for 1b, 1d , 1f, 1h , and 1j, and the distance between
the para hydrogens of the terminal phenyl substituents in 1a , 1c, 1e, 1g, and 1i. Distances between the metal ion-binding sites are
included in parentheses. The lengths were calculated for the linear bridged bis-5-(2,2′-bipyridines) with the all-planar, all-transoid
conformations shown above, in the gas phase, using the MM3 force field with MacroModel version 5.5 (Columbia University, New York).
4a ,b could be rapidly constructed in relatively few steps
starting from the common building block, 2-chloro-5-
iodopyridine (9) (Table 1, Schemes 1-3). Pyridine 9 was
selected for two reasons. First, the 5-iodo substituent is
more reactive toward palladium-catalyzed organometallic
cross-coupling reactions than the 2-chloro group. This
ensures preferential chemoselective reactivity at the
5-position rather than the normally more reactive 2-posi-
tion to yield the bridged bis-2-chloropyridine precursors
5a -c, 5f,g, and 6-8.24 These can be further homologated
to the desired bridged bis-5-(2,2′-bipyridines) via a Stille
cross-coupling reaction with 2-trialkylstannylpyridines
under more forcing conditions in the last step of the
synthesis.25a,b Second, 9 could be prepared in two steps
from 2-aminopyridine on a 50-100 g scale and in high
overall yield by electrophilic iodination followed by a
diazotization-chlorination protocol.26a-c The bridged bis-
5-(2,2′-bipyridine) terminal pyridine ring substituents
chosen for this study were 5′-methyl and 6′-phenyl
groups. These were selected to investigate the influence
of widely differing steric and electronic substituent effects
upon the Stille cross-coupling reactions.
Syn th esis of Con ju ga tively Br id ged Bis- a n d Tr is-
5-(2-ch lor opyr idin es). 1, 2-bis[5-(2-chloropyridyl)]ethyne
(5a ) comprises a single acetylene connecting the pyridine
rings and therefore represents the shortest bridged
bischloropyridine prepared in this study. Previous reports
on the syntheses of dibromo-, dimethoxy-, and dithi-
omethoxy-substituted analogues of 5a employed Wad-
sworth-Emmons and McMurry methodology to give first
the corresponding 1,2-bis[5-(2-bromopyridyl)], 1, 2-bis-
[5-(2-methoxypyridyl)]- and 1,2-bis[5-(2-thiomethoxypy-
ridyl)]ethenes. This required the initial preparation of
the appropriately substituted pyridine-5-carboxaldehydes
and diethyl [5-methyl-(2-bromopyridyl)]phosphonate.
Treatment of the ethenes with bromine followed by
dehydrobromination with potassium tert-butoxide af-
forded the 1,2-bis[5-(2-bromopyridyl)]-, 1,2-bis[5-(2-meth-
oxypyridyl)]-, and 1,2-bis[5-(2-thiomethoxypyridyl)]ethynes
(24) 2-Chloro-3-iodopyridine and 2,6-dimethyl-3-iodo-4-chloropyri-
dine are both reported to undergo selective palladium-catalyzed
ethynylation at the 3-iodo substituent: Sakamoto, T.; Kondo, Y.;
Watanabe, R.; Yamanaka, H. Chem. Pharm. Bull. 1986, 34, 2719.
(25) For examples of 2,2′-bipyridine syntheses via Stille cross-
couplings with 2-chloropyridines, see for example: (a) Ghadiri, M. R.;
Soares, C.; Choi, C. J . Am. Chem. Soc. 1992, 114, 825. (b) Zhang, B.;
Breslow, R. J . Am. Chem. Soc. 1997, 119, 1676.
(26) (a) Clayton, S. C.; Regan, A. C. Tetrahedron Lett. 1993, 34, 7493.
(b) Hama, Y.; Nobuhara, Y.; Aso, Y.; Otsubo, T.; Ogura, F. Bull. Chem.
Soc. J pn. 1988, 61, 1683. (c) Magidson, O.; Menschikoff, G. Chem. Ber.
1925, 58, 113.

1260 J . Org. Chem., Vol. 65, No. 5, 2000
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Sch em e 1a
a
Reaction conditions and yields: (i) Pd(PPh3)4, DMF, 105 °C, 24 h (77%); (ii) 1 equiv of n-BuLi, THF, -90 °C, then ZnCl2; (iii) PdH2(PPh3)2,
THF, 20 °C (68%, 5b; 58%, 5c); (iv) POBr3, 170 °C, 15-20 h (77%, 5d , 90%, 5e); (v) PdCl2(PPh3)2, CuI, Et3N and/or Py, 25-70 °C, 48 h
(68%, 5f; 78%, 5g); (vi) PdCl2(PPh3)2, CuI, Et3N, TMS(ethyne), 20 °C, 48 h (94%); (vii) 0.01 M aqueous NaOH, THF, MeOH, 20 °C, 24 h
(82-95%); (viii) Pd2(dba)3, CuI, PPh3, Et3N, 40 °C, 14 h (75%); (xv) PdCl2(PPh3)2, CuI, Et3N, 20-75 °C, 48 h (59%); (x) see (xv) (94%).
Sch em e 2
readily accessible starting materials. 1,2-Bis(tributyl-
stannyl)ethyne (10) has been demonstrated to function
as an acetylene synthon for the generation of a range of
symmetrically substituted diphenylethynes via the Stille
cross-coupling protocol.28 Using this methodology, reac-
tion of g2 equiv of 9 with 10 in the presence of a catalytic
amount of Pd(PPh3)4 in toluene solution gave a 63%
isolated yield of 5a . Changing the solvent to DMF
resulted in an increase in yield to 77% after an identical
workup procedure. Product 5a can therefore be prepared
in three steps from commercially available materials in
high overall yield. This result represents a considerable
in moderate overall yields.27 However, the circuitous
routes to the substituted pyridine precursors and lack of
adaptability for variation in structure of the bridging unit
suggested the necessity of a more general approach from
(27) Windscheif, P.-M.; Vo¨gtle, F. Synthesis 1994, 87.
(28) Cummins, C. H. Tetrahedron Lett. 1994, 35, 857.

Synthesis of Bis- and Tris-5-(2,2′-Bipyridines)
J . Org. Chem., Vol. 65, No. 5, 2000 1261
Sch em e 3
synthetic improvement over the previously reported
methodology for the generation of substituted bis(py-
ridyl)ethynes and may provide a general method of access
to functionalized bisheterocyclic ethynes.
Parallel experimental investigations showed 2-chloro-
5-ethynylpyridine (15b) to be an excellent synthon for
introducing the 5-ethynyl-2-chloropyridyl group into
halogenated aromatic substrates via the Sonogashira
protocol.31 15b could be conveniently prepared in two
steps from 9, first upon reaction of a 1:1 ratio of
(trimethylsilyl)ethyne and 9 with catalytic quantities of
PdCl2(PPh3)2 and CuI in triethylamine to yield 2-chloro-
(5-trimethylsilylethynyl)pyridine (15a ). Second, aqueous
hydroxide mediated hydrolytic deprotection of 15a af-
forded 15b in 77-89% overall yield from 9. Therefore,
to explore the possible advantages of using 15b in place
of the dialkynyl precursors for the syntheses of bridged
5-(2-chloropyridines), it was decided to prepare the
acutely bent bridged bis-5-(2-chloropyridine) 6 via 15b.
However, the reaction between 1,2-dibromobenzene and
g2 equiv of 15b at 70 °C using conditions similar to those
used for the preparation of 5f, 7, and 8 above provided
only a poor (<20%) yield of 6 after workup. A significant
improvement in the isolated yield of 6 to 75% was finally
The Sonogashira cross-coupling protocol was found to
provide the shortest and most convenient route to the
linear 1,4-diethynylphenyl- and 4,4′-diethynyl-1,1′-biphen-
yl-bridged bis-5-(2-chloropyridines) 5f and 5g, and the
curved 1,3-diethynylphenyl-bridged bis-5-(2-chloropyri-
dine) 7.29 Thus, reaction of g2 equiv of 9 with the readily
accessible terminal diethynes 13a ,b and 16 in the pres-
ence of catalytic quantities of PdCl2(PPh3)2 and CuI
afforded the bridged bis-5-(2-chloropyridines) 5f, 5g, and
7 in 68%, 78%, and 59% isolated yields, respectively. The
reactions yielding 5f and 7 were conducted in triethyl-
amine and that of 5g was conducted in pyridine-
triethylamine (1:4.5) to avoid precipitation of semireacted
species. The yields were unoptimized and the products
easily purified by recrystallization from the appropriate
solvent. Interestingly, the Sonogashira methodology could
also be successfully applied to the synthesis of the
branched species 1,3,5-tris(5-ethynyl-2-chloropyridyl)-
benzene (8). Reaction of 1,3,5-triethynylbenzene (17) with
g3 equiv of 9 under conditions identical to those used
for the preparation of 5f and 7 afforded 8 in 94% isolated
yield.30
(30) Syntheses of 1,3,5-tris(pyridylethynyl)benzenes appear to be
rare in the literature. For a preparation of 1,3,5-tris(4-pyridylethynyl)-
benzene, see: Anderson, H. L.; Walter, C. J .; Vidal-Ferran, A.; Hay,
R. A.; Lowden, P. A.; Sanders, J . K. M. J . Chem. Soc., Perkin Trans. 1
1995, 2275.
(31) The reaction of 15b with iodobenzene and 1-bromo-4-(trimeth-
ylsilylethynyl)benzene under Sonogashira conditions provided the
respective2-chloro-5-(ethynylphenyl)pyridineand2-chloro-5-(1-ethynyl-4-tri-
methylsilylethynylphenyl)pyridine in >70% isolated yields: P. N. W.
Baxter, unpublished results.
(29) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 50, 4467.

1262 J . Org. Chem., Vol. 65, No. 5, 2000
Baxter
obtained upon using 1,2-diiodobenzene (14) in place of
the dibromo analogue, changing the catalyst system to a
1:4.6:1 ratio of Pd2(dba)3/PPh3/CuI, reducing the reaction
temperature to 40 °C, and reducing the reaction time
from 48 to 14 h.
The syntheses of the 1,4-phenyl- and 4,4′-(1,1′-biphen-
yl) bridged bis-5-(2-chloropyridines) 5b and 5c relied
upon the utilization of an efficient chemoselective het-
eroaryl-aryl cross-coupling strategy. The three currently
most widely used methods for sp2-sp2 carbon-carbon
bond formation between unsymmetrically substituted
cross-coupling reaction with 2-trialkylstannylpyridines
to give substituted 2,2′-bipyridines.25a,b The temperature-
dependent reactivity of the 2-chloropyridyl group there-
fore allows the sequential homologative construction of
oligopyridyl structures while avoiding the need for in-
troducing additional functional group protection/depro-
tection steps. The synthetic economy of this approach
provided a rapid and efficient method of access to a wide
range of conjugatively bridged 5-(2,2′-bipyridines) via
multiple Stille cross-couplings with the bridged 5-(2-
chloropyridine) precursors.
aromatic substrates comprise the palladium-catalyzed
Thus, reaction between the ethyne-containing bridged
bis-5-(2-chloropyridines) 5a , 5f,g, and 7 and an excess
of 2-trimethylstannyl-6-phenylpyridine (18a ) or 2-tri-
methylstannyl-5-methylpyridine (18b) with Pd(PPh3)4 as
catalyst and at a temperature of greater than 120 °C
afforded the linearly bridged bis-5-(2,2′-bipyridines) 1a ,b
and 1g-j, and curved 3a and 3b in good yields. The
products were obtained in higher purity and about 10%
higher yields when trimethylstannylpyridines were used
in place of their tri-n-butylstannyl analogues. In the
majority of examples investigated, the use of toluene as
reaction solvent provided products of higher purity than
DMF, although the yields were unaffected. In cases
where the limited solubility of the product precluded
purification by column chromatography, solvent washing
and recrystallizations sufficed to yield material of ana-
lytical purity. During the course of each reaction, color
darkening and sometimes palladium mirror formation
occurred. Catalyst decomposition was therefore taking
place, and resulted in part from the relatively high
temperatures employed. However, the product yields
remained unchanged upon adding extra catalyst or by
continual infusion of the catalyst into the reaction
mixture over a 24 h period. Changing the catalyst from
Pd(PPh3)4 to PdCl2(PPh3)2 or Pd2(dba)3/AsPh3 (1:8) also
had no affect upon the product yield, although the latter
system exhibited marked reaction rate enhancements.36
33
Stille,32a-d Suzuki,32b-d,
and transmetalation cross-
coupling protocols.32b-d The latter transmetalation meth-
odology was selected as the preferred route to 5b and 5c
as it avoids the need for prior isolation and purification
of the metalated aromatic component. The metalated
entity is normally generated in situ upon reaction
between an initially formed aryllithium species and a
zinc, magnesium, or copper salt. The metalate is then
added directly to the aryl or heteroaryl halide and
palladium catalyst to give finally the cross-coupled
product in the same pot. An experimental investigation
into the reactivity of metalated 9 with aryl iodides
showed the organozincate (Negishi) adaptation to be the
most superior transmetalation methodology owing to its
mild reaction conditions and freedom from side reac-
tions.34 Thus, the iodine substituent of 9 can be cleanly
chemoselectively lithiated at low temperature with 1
equiv of n-butyllithium to give 2-chloro-5-lithiopyridine,
and this can be converted to 2-chloro-5-chlorozincatopy-
ridine (11) upon addition of 1 equiv of ZnCl2 in Et2O
solution. The zincate 11, which is stable at ambient
temperature, then underwent a palladium-catalyzed
double cross-coupling reaction with 0.5 equiv of the
diiodides 12a and 12b to afford 5b and 5c in 68% and
58% isolated yields, respectively. The reaction proceeds
efficiently without the need for external heating and
appears to be unreactive toward the 2-chloro substituents
of 11, 5b, and 5c.35
Studies concerning the influence of additives on the
Stille cross-coupling reaction have demonstrated that the
presence of LiCl,37a,b transition metal salts,38 and oxides39
can cause significant increases in product yields. In an
attempt to improve the yields of 2b and 3b, the reactions
were therefore repeated under identical conditions in the
presence of excess LiCl. However, after identical workup
procedures the reactions conducted with added LiCl did
not show any significant increase in the isolated yield of
the respective bridged bis-5-(2,2′-bipyridines). The origin
of the moderate yield of 2b may derive in part from the
enhanced reactivity of aryl-1,2-diethynes toward ther-
mally induced cyclizations and polymerizations.40a-c How-
ever, the presence of LiCl did influence the yield of 2a ,
which increased from 46% to 64% when excess LiCl was
added to the reaction mixture. The yields of 4a and 4b
were also sensitive to the presence of LiCl, and increased
Having defined optimal reaction pathways for the
syntheses of the bridged bis- and tris-5-(2-chloropy-
ridines) 5a -c, 5f,g, and 6-8, an exploration into their
use as precursor substrates for the preparation of ter-
minally substituted bridged bis-5-(2,2′-bipyridines) was
next undertaken.
Syn th esis of Sym m etr ica lly Su bstitu ted Con ju -
ga tively Br id ged Bis- a n d Tr is-5-(2,2′-bip yr id in es).
The successful synthesis of the bridged bis- and tris-5-
(2-chloropyridines) relies upon the fact that the 2-chloro
substituent of 9 and its bridged derivatives is relatively
unreactive toward cross-coupling chemistry at temper-
atures between 20 and 70 °C, in the presence of the
conventional triphenylphosphine-ligated palladium cata-
lysts.24 At higher temperatures, the unactivated 2-chlo-
ropyridyl group can be induced to undergo the Stille
(32) (a) Mitchell, T. N. Synthesis 1992, 803. (b) Kalinin, V. N.
Synthesis, 1992, 413. (c) Undheim, K.; Benneche, T. Adv. Heterocycl.
Chem. 1995, 62, 305. (d) Stanforth, S. P. Tetrahedron 1998, 54, 263.
(33) Yang, Y.; Martin, A. R. Acta Chem. Scand. 1993, 47, 221.
(34) Negishi, E.; King, A. O.; Okukado, N. J . Org. Chem. 1977, 42,
1821.
(35) If the Sonogashira and Negishi cross-coupling reactions with
13a and 12a , respectively, are performed using 2-bromo-5-iodopyridine
in place of 9, then chemoselectivity is lost and product mixtures are
obtained, which arise from reaction at both the 2- and 5-pyridine ring
positions.
(36) For a detailed investigation into the influence of the catalyst
upon the rate, yield, and temperature dependence of the Stille cross-
coupling reaction, see: Farina, V.; Krishnan, B. J . Am. Chem. Soc.
1991, 113, 9585.
(37) (a) Fujita, M.; Oka, H.; Ogura, K. Tetrahedron Lett. 1995, 36,
5247. (b) Echavarren, A. M.; Stille, J . K. J . Am. Chem. Soc. 1987, 109,
5478 and references therein.
(38) Evans, D. A.; Black, W. C. J . Am. Chem. Soc. 1993, 115, 4497.
(39) Gronowitz, S.; Bjo¨rk, P.; Malm, J .; Ho¨rnfeldt, A.-B. J . Orga-
nomet. Chem. 1993, 460, 127.

Synthesis of Bis- and Tris-5-(2,2′-Bipyridines)
J . Org. Chem., Vol. 65, No. 5, 2000 1263
Sch em e 4
from, respectively, 73% and 64% to 83% and 76% when
repeated with added LiCl.
the 2-trimethylstannylpyridine and yield of bridged bis-
5-(2,2′-bipyridine) in all cases studied. For a given
bridging unit, Stille cross-couplings with 18a gave con-
sistently higher yields of bis-2,2′-bipyridines with 6-phen-
yl substituents on the terminal pyridine rings, compared
to the analogous reactions with 18b. The origin of this
phenomenon may be related to the rate of catalyst
destruction via coordination to the product as it is formed
during the course of the reaction. In the case of reactions
with 18a , the o-phenyl substituent may sterically disfavor
binding of the product to the catalyst. This would result
in an increased catalyst lifetime, thereby allowing the
formation of larger amounts of product. Electronic factors
may also be operative.
Syn th esis of Un sym m etr ica lly Su bstitu ted 1,4-
P h en yl-Br id ged Bis-5-(2,2′-bip yr id in es). The marked
reluctance of 5b and 5c to undergo Stille cross-couplings
at both chlorine substituents suggested that the condi-
tions of this reaction may possibly be adjusted to provide
access to 1,4-phenylene-bridged 5-(2-chloropyridine)-5-
(2,2′-bipyridyl) species in synthetically useful yields. The
remaining halogen would then be available for further
homologations to unsymmetrically substituted bridged
bis-2,2′-bipyridines or longer entities. The 2-trimethyl-
stannylpyridines 18c and 18d and bis-2-chloropyridine
5b were chosen for this investigation because they
afforded reaction products of sufficient solubility to be
separated by column chromatography. However, only low
yields (e15%) of monocoupled products were obtained
from the Pd(PPh3)4-catalyzed reaction between 1:1 equiv
of 18c, 18d , and 5b. The yields of monocoupled products
increased to 30% when an excess of 18c and 18d and
30-50 mol % Pd(PPh3)4 were used, but this was clearly
wasteful in 2-trimethylstannylpyridines and catalyst.
When the 1:1 stoichiometric reactions were repeated
using 5d in place of 5b, slightly higher yields of mono-
coupled products 19 (36%) and 20 (33%) resulted (Scheme
4). Although the yield enhancement of 19 and 20 origi-
nated directly from the greater reactivity of 5d , the
product distributions showed no preferential selectivity
for monocoupling. The monocoupled products 19 and 20
underwent clean Pd(PPh3)4-catalyzed reactions with 18a
in refluxing toluene to give, respectively, the unsym-
metrically substituted 22 and 23 in high yield.
Initial investigations into the syntheses of the bis-5-
(2,2′-bipyridines) with 1,4-phenyl and 4,4′-biphenyl bridges
revealed that the Stille cross-coupling reactions between
5b, 5c, and 18b afforded the methyl-substituted 1d and
1f in only e20% yields. The crude reaction products
comprised mainly of unreacted 5b, 5c, and bridged 5-(2-
chloropyridine)-5-(2,2′-bipyridyl) species arising from
reactions of 1:1 stoichiometry between 18b and the
bridged bis-2-chloropyridines 5b and 5c. It was therefore
decided to prepare all the 1,4-phenyl- and 4,4′-biphenyl
bridged bis-5-(2,2′-bipyridines) from the more reactive
dibromo-substituted analogues 5d and 5e. Thus, heating
5b and 5c in excess POBr3 resulted in efficient halogen
metathesis to give the dibromo adducts 5d and 5e.
Finally, reaction of 5d and 5e with more than 2 equiv of
18a and 18b in the presence of catalytic quantities of
Pd(PPh3)4 afforded 1c-f in 63-71% isolated yields. DMF
and xylene were used as solvents in these examples to
achieve higher reflux temperatures and thereby drive the
reactions to completion. The lower reactivity of 5b,c
toward the Stille cross-coupling reaction with 18a com-
pared to the bis- and tris-5-(2-chloropyridines) incorpo-
rating ethyne moieties in their bridges (5a , 5f,g, 6-8) is
currently unclear, but may result from insufficient
electronic activation of the 2-chloropyridyl groups.41
Particularly noteworthy is that a correlation exists
between the position and identity of the substituent on
(40) Yield reductions have also been observed in the Sonogashira-
type synthesis of a phenyl-1,2-bis(meso-ethynylporphyrin) system: (a)
Arnold, D. P.; Nitschinsk, L. J . Tetrahedron Lett. 1993, 34, 693. For
investigations on the thermal rearrangements of phenyl-1,2-ethynes,
see: (b) Semmelhack, M. F.; Neu, T.; Foubelo, F. Tetrahedron Lett.
1992, 33, 3277. (c) J ohn, J . A.; Tour, J . M. Tetrahedron 1997, 53, 15515.
(41) The bis- and tris-5-(2-chloropyridines) incorporating ethyne
moieties in their bridges will be expected to experience an increased
electronic communication between the 2-chloro groups of the terminal
pyridine rings in the case of 5a and 5f, and to a lesser extent 6-8.
The 2-chloro groups of the 5-(2-chloropyridines) 5f,g, and 6-8 would
also be strongly electronically linked to the bridging phenyl and
biphenyl rings. Both situations would result in
a net electron-
withdrawing effect upon the 2-chloro substituents of 5a , 5f,g, and 6-8.
It is well documented that the rates and yields of Stille cross-coupling
reactions with aryl- and vinyltrialkyltin reagents are enhanced by the
presence of electron-withdrawing substituents on the aryl-halide
component. See for example: (a) Stille, J . K. Angew. Chem., Int. Ed.
Engl. 1986, 25, 516. (b) McKean, D. R.; Parrinello, G.; Renaldo, A. F.;
Stille, J . K. J . Org. Chem. 1987, 52, 422. The lower reactivity of 5b
and 5c toward double Stille cross-couplings with 18b may therefore
result from a lack of reactivity enhancement of the chlorine groups,
due to poorer electronic communication through the phenyl and
biphenyl bridges. In this case, catalyst decomposition effectively
competes with bis-5-(2,2′-bipyridine) formation.
Ch a r a cter iza tion a n d P r op er ties
Sp ectr oscop ic Ch a r a cter iza tion of th e Con ju ga -
tively Br id ged Bis- a n d Tr is-5-(2,2′-bip yr id in es). The

1264 J . Org. Chem., Vol. 65, No. 5, 2000
Baxter
1H NMR spectra of all the bridged 2,2′-bipyridines were
in accordance with their proposed structures and were
assigned on the basis of COSY, ROESY, and/or NOESY
measurements and spectral comparisons. The 13C NMR
spectra of the majority of compounds studied were free
from overlapping resonances and exhibited the expected
number of bands. The resonances due to the ethyne
bridging carbons were also clearly identifyable in 1a ,b
as a single band, and as two bands of low-medium
intensity in 1g-j, 2a ,b, 3a ,b, and 4a ,b between 82 and
103 ppm. The determination of NMR spectra of the
higher molecular weight linear bridged bis-5-(2,2′-bipy-
ridines) was impeded by the poor solubility of these
substrates in most organic solvents. However, the use of
CDCl2CDCl2 at elevated temperatures and/or CF3COOD
at ambient temperature caused rapid solubilization of the
products and enabled the recording of clean NMR spec-
be expected to comprise a total of 18 magnetically and
chemically inequivalent resonances. In CDCl3 solution,
14 bands are observed, 3 of which consist of overlapping
multiplets assigned to the inner pyridine H6′/6′′′ and H4′/
4′′′pairs, and the terminal phenylpyridine H5/bridging
phenyl H2′′,6′′;3′′,5′′ protons. The H3′′′′,4′′′′,5′′′′,6′′′′ pro-
tons of the terminal unsubstituted pyridine ring were
readily assignable through COSY cross-peaks and their
characteristic splitting patterns, comprising a doublet of
triplets, a triplet, a quartet, and a doublet of doublets,
respectively. The terminal phenylpyridine H4 was also
identifiable as the typically simple triplet at 7.92 ppm,
and H5 and H3 through COSY cross-peaks with H4. The
remaining doublets corresponding to the inner pyridine
H3′ and H3′′′ protons were identified on the basis of the
presence of COSY cross-peaks with the H6′/6′′′ and H4′/
4′′′ multiplets. However, these two signals could not be
unambiguously assigned for the above-mentioned rea-
sons. A tentative assignment was made possible through
comparison with the 1H NMR spectrum of 21. The
chemical shifts of the terminal unsubstituted pyridine
ring protons, the inner pyridine H6′/6′′′ and H4′/4′′′pairs,
and the more upfield of the pair of bands corresponding
to the H3′ and H3′′′ protons were virtually identical to
those of the terminal and inner pyridine ring protons of
21 in CDCl3 solution. The identical values of the chemical
shifts of the inner pyridine H3′ (8.52 ppm) of 21 and the
band at 8.52 ppm in the spectrum of 23 suggested that
the latter band originated from H3′′′ and the resonance
at 8.75 ppm from H3′ of the inner pyridine ring adjacent
1
tra. Comparison of the H NMR spectra of the terminally
substituted bridged bis-5-(2,2′-bipyridines) revealed some
general, solvent-independent correlations which aided
spectral interpretations and assignments. These are
briefly discussed below.
In the 1H NMR spectra of the terminally phenyl-
substituted bridged bis-2,2′-bipyridines 1a , 1c, 1e, 1g,
1i, 2a , 3a , 4a , 22, and 23, the ortho, meta, and para
protons of the phenyl substituent invariably appeared as
a well-separated group of signals comprising a doublet
and two triplets in a 2:2:1 ratio. The bands also exhibited
the characteristic fine-structured splitting patterns re-
sulting from second-order >3J couplings. The doublet
corresponding to the ortho protons was always situated
further downfield than the two triplets arising from the
meta and para protons. The stronger deshielding expe-
rienced by the ortho protons evidenced their close prox-
imity to the adjacent terminal pyridine ring nitrogen lone
pair. In the 1H NMR spectra of all 2,2′-bipyridines
studied, the H6′ (1a -j, 2a ,b, 3a ,b, 4a ,b, 19-21) and H6′/
6′′′ (22, 23) protons of the inner pyridine rings were the
most deshielded and gave the furthest downfield situated
signals. The inner pyridine H4′ of 1a -i, 2a ,b, 3a ,b, 4a ,b,
and 19-21 and H4′/4′′′ of 22 and 23 also followed a
similar trend in that they were more deshielded than the
corresponding terminal pyridine H4 and H4/4′′′′ protons.
In 1j the H4 and H4′ signals were overlapping. In
contrast, the bands assigned to the terminal pyridine ring
H5 protons of 1a , 1c, 1e, 1g, 1i, 2a , 3a , 4a , and 19-21
and H5/5′′′′ protons of 22 and 23 were always the most
upfield positioned and shielded of the pyridine ring
signals.
1
to the terminal phenylpyridine. In the H NMR spectra
of 2a ,b, an unambiguous assignment of the bridging
phenyl H3′′,6′′ and H4′′,5′′ protons was not possible owing
to a lack of ROESY and COSY cross-peaks with the inner
pyridine H4′ and H6′ protons. The more downfield of the
bridging phenyl multiplets was therefore assigned to the
H3′′,6′′ protons adjacent to the ethyne groups, as these
would be expected to be the most sensitive to the
inductive electron-withdrawing influence of the 2,2′-
bipyridine moieties.
The EI and FAB mass spectra were also in agreement
with the proposed structural formulas of all compounds
investigated. In the case of the less soluble bridged
5-(2,2′-bipyridines), optimal conditions for recording mass
spectra were afforded by FAB using CF3COOH as matrix.
The bridged 5-(2,2′-bipyridines) proved to be particularly
stable materials under mass-spectral conditions, giving
predominantly M and M + 1 clusters with little or no
fragmentation.
Compounds 19, 20, 22, and 23 afforded the most
1
complex H NMR spectra of the 2,2′-bipyridines investi-
gated. In the case of 19, 20, and 23, a completely
unambiguous assignment was not possible owing to an
absence of interpyridine ring proton cross-peaks in their
ROESY and NOESY spectra. Assignments of the inner
pyridine and bromopyridine ring protons of 19 and 20
The solid-state infrared spectra of the bridged 5-(2,2′-
bipyridines) studied exhibited a considerable variation
in complexity throughout the fingerprint region, and were
characteristic for each compound. The vibrational modes
of the pyridine ring CC, CN, and CH bonds were clearly
distinguishable as medium to very strong intensity bands
in all cases. However, the stretching vibrational mode of
the ethynyl bridge was only observed in 1h -j, at 2215-
2213 cm-1, and 4a ,b at 2207 and 2208 cm-1, respectively,
as bands of weak intensity.
1
were therefore made instead by comparison with the H
NMR spectrum of 5d . In the spectra of 19 and 20, three
relatively upfield shifted signals from protons of the same
ring at 8.65, 7.79, and 7.58-7.59 ppm occurred at
chemical shifts similar to those of the H6, H4, and H3
bromopyridine ring protons of 5d at 8.66, 7.87, and 7.66
ppm, respectively. These were therefore assigned to the
H6′′′, H4′′′, and H3′′′ protons of the bromopyridine ring
of 19 and 20, and the remaining peaks to H6′, H4′, and
The UV/vis spectra of the bridged 5-(2,2′-bipyridines)
all display intense absorption envelopes between 258 and
373 nm, which arise predominantly from π f π* elec-
tronic transitions originating from the pyridyl and phenyl
1
H3′ of the inner pyridine rings. The H NMR of 23 would

Synthesis of Bis- and Tris-5-(2,2′-Bipyridines)
J . Org. Chem., Vol. 65, No. 5, 2000 1265
F igu r e 1. UV/vis spectra of 1:1 stoichiometric mixtures of 9.1
× 10-6 mol dm-3 solutions of 1h with, respectively, Zn(CF3-
SO3)2, Cd(CF3SO3)2, and Hg(CF3SO3)2 in 1:2 CHCl3/MeOH.
F igu r e 2. UV/vis spectra of 1:1 stoichiometric mixtures of 9.1
× 10-6 mol dm-3 solutions of 1h with, respectively, Sc(CF3-
SO3)3, [Cu(MeCN)4](CF3SO3), and Hg(CF3SO3)2 in 1:2 CHCl3/
MeOH.
rings.42a,b In particular, a band associated with the
presence of a terminal phenyl substituent is always
present in the spectra of 1a , 1c, 1e, 1g, 1i, 2a , 3a , 4a ,
22, and 23, at 262-270 nm. The lowest energy absor-
bances of all compounds investigated are exhibited by 1g
and 1h at 373 and 371 nm, respectively, indicating that
they possess bridging units with the most extended
electronic delocalization.
Meta l Ion Com p lexa tion Beh a vior of 1h . Ligands
incorporating bridging units with maximal conjugation
are expected to exhibit the most interesting physico-
chemical properties with respect to metal ion coordina-
tion. In the case of 1 g,h , it was suspected that metal
ion-binding would cause shifts in the absorption enve-
lopes to values characteristic of the electronic and
coordination preferences of particular classes of metal
cations. An investigation into the complexation behavior
of 1h was therefore undertaken to evaluate its potential
for the spectroscopic sensing of colorless metal ions.
The results of this study are summarized in Figures 1
and 2, and show that the absorption maxima of 1h shift
to lower energy in the event of metal ion complexation,
F igu r e 3. Titration comprising incremental additions of Hg-
(CF3SO3)2 into 9.1 × 10-6 mol dm-3 solutions of 1h in 1:2
CHCl3/MeOH. The 1h :Hg2+ stoichiometric ratio is indicated
for each curve. The UV/vis spectrum of an equivalent concen-
tration of a 1:1 stoichiometric mixture of 2,2′-bipyridine:Hg2+
in 1:2 CHCl3/MeOH is also included for comparison.
and exhibit the greatest changes in the presence of Sc3+
Cu+, Zn2+, Cd2+, and Hg2+. Stoichiometric 1:1 mixtures
of 1h with the triflate salts of Na+, Mg2+, Ba2+, Ag+, Mn2+
,
,
lower energy and the concomitant development of a pale
yellow coloration. This behavior may originate from
incomplete coordination of both the 2,2′-bipyridine moi-
eties of 1h at a 1:2 ratio of 1h :Hg2+. The presence of an
excess of Hg2+ may thus be necessary to saturate all the
metal ion-binding sites of 1h in a dilute environment.
Interactions between the Hg2+ cations and the 1, 4-di-
ethynylphenyl bridge of 1h may also possibly contribute
to the observed spectral shifts at higher [Hg2+]. From the
titration, the lower limit for the detection of Hg2+ was
Tl+, Pb2+, La3+, and Eu3+ at equivalent concentrations
yielded spectra which were essentially identical to that
of the free, uncomplexed ligand. This suggests that either
a negligible or zero degree of binding between 1h and
the latter cations was operative at high dilution in 1:2
CHCl3/MeOH.
Of particular interest is that the greatest complexation-
induced spectral shift for all cations investigated occurs
in the presence of Hg2+. The incremental addition of Hg2+
into solutions of 1h (Figure 3) resulted in the progressive
disappearance of the free ligand absorption at 350 nm,
and an increase in intensity and a shift to lower energy
of the band at 371 nm. Increasing the relative [Hg2+] to
greater than 2 equiv with respect to the [1h ] resulted in
a continued shift of the latter absorption maximum to
estimated to be at a [Hg2+] of 5 × 10-6 mol dm-3
.
Comparison of the spectra obtained from 1:1 stoichio-
metric mixtures of 1h :Hg2+ and 2,2′-bipyridine:Hg2+ at
identical concentrations strikingly demonstrated the
effect of conjugation enhancement on the spectroscopic
properties of metal ion complexes of 1h . The 1:1 mixture
of 2,2′-bipyridine:Hg2+ yielded a spectrum with only a
weak and poorly defined absorption envelope at 285 nm.
The conjugated 1,4-diethynylphenyl bridge has therefore
completely transformed the electronic nature of the
(42) For an assignment of the UV absorption spectrum of 2,2′-
bipyridine, see: (a) Gondo, Y.; Kanda, Y. Bull. Chem. Soc. J pn. 1965,
38, 1187. (b) Supramolekulare Chemie; Vo¨gtle, F., Ed.; B. G. Teubner:
Stuttgart, 1989, Chapter 2, p 33 and references therein.

1266 J . Org. Chem., Vol. 65, No. 5, 2000
Baxter
appended 2,2′-bipyridine units and significantly contrib-
utes to the spectroscopic behavior of 1h .
coordinating polymers and copolymers with unusual and
intriguing optical, sensing, mechanical, and electronically
conducting properties. The bridged 5-(2,2′-bipyridines)
will be capable of forming an extensive range of multi-
nuclear transition metal complexes, such as, for example,
unusual cyclometalated species with 1a , 1c, 1e, 1g, 1i,
2a , 3a , and 4a , metalloclefts with 2a ,b, metallomacro-
cycles with 3a ,b, and dendritic entities in the case of
4a ,b. A multitude of functions may be envisioned for
these materials, especially within the supramolecular
arena, such as electronically controllable catalysts, mo-
lecular electronics device components, and precursors to
metallo-assembled nanoarchitectures. Many of these
ligands may also display metal ion-sensing capabilities,
as in the case of 1h . Optimization of these properties via
additional structural refinements may afford a poten-
tially new class of analytical reagents for the spectro-
photometric detection of toxic metals.
Ligand 1h therefore possesses potential for the spec-
trophotometric detection of Zn2+, Cd2+, and Hg2+ in the
presence of group 1 and 2, lanthanides, main group, and
specific “colorless” transition metal ions. The introduction
of further structural modifications into 1h and related
ligands may be expected to maximize the selectivity and
sensitivity toward specific metal ions, and thereby afford
a new class of sensing materials for metallic environ-
mental toxins.
Con clu sion
In conclusion, the work presented above describes a
convenient synthesis of linear (1a -j, 21-23) and curved
(2a ,b, 3a ,b) bis-5-(2,2′-bipyridines) and branched tris-5-
(2,2′-bipyridines) (4a ,b) incorporating rigid conjugated
bridging units, which avoids the use of protection/
deprotection steps. The ligands 1a -j, 3a ,b, 4a ,b, and 21-
23 are of nanoscopic dimensions and lie within the size
range of 20-35 Å (including van der Waals surfaces). In
the initial stage of the syntheses, a central preformed
bridging module with n g 2 outwardly positioned reactive
sites is functionalized with pyridine synthon 9 to yield
the bridged bis-5-(2-chloropyridine) precursors 5a -c,
5f,g, and 6-8. The success of this methodology relies
upon the fact that the 2-chloro substituent of 9 is
unreactive to ambient temperature organometallic cross-
coupling protocols such as the Sonogashira and Negishi
reactions. This enabled a facile regioselective reaction at
the 5-position of 9, and its chlorozincate 11 with ethynyl-
and diiodoaryl-functionalized bridging units. The reactiv-
ity of the 2-chloropyridyl group can then be “switched
on” at higher temperatures, and thereby induced to
participate in the Stille cross-coupling reaction with
trialkylstannylpyridines to afford the desired bridged
5-(2,2′-bipyridines). The 1,4-phenyl- and 4,4′-(1,1′-biphen-
yl)-bridged bis-5-(2,2′-bipyridines), on the other hand,
were best prepared from the bis-5-(2-bromopyridines)
5d ,e, owing to the lower reactivity of the corresponding
bis-2-chloropyridines 5b,c. The Stille cross-coupling yields
also showed a marked sensitivity to the type of substitu-
ent on the trimethylstannylpyridine, and in some cases
to the presence of additives such as LiCl. In all cases
investigated, reactions with identical bridging units gave
higher Stille cross-coupling product yields with the
phenyl-substituted 18a .
The synthetic methodology described above therefore
provides a platform for the future construction of rigid
nanosized and polymeric organic scaffolds with metal ion-
binding capabilities, for which many diverse materials
applications await discovery in the 21st century.
Exp er im en ta l Section
Gen er a l Meth od s a n d Sta r tin g Ma ter ia ls. Standard
inert atmosphere and Schlenk techniques were employed for
reactions conducted under dinitrogen and argon. All solvents
used for the palladium-catalyzed coupling reactions were
freshly redistilled under dry, oxygen-free argon over the
appropriate drying agent before use. Elemental analyses were
performed by the Service de Microanalyse, Institut de Chimie,
1
Universite´ Louis Pasteur. The H and 13C NMR spectra of 1h ,
recorded in 20% D2O/CF3COOD, were referenced to the
trimethylsilyl peak of added sodium 3-(trimethylsilyl)-1-pro-
panesulfonate (TSPSA). 1,4-Diethynylbenzene,43 4,4′-bisethy-
nyl-1,1′-biphenyl,43 1,2-diiodobenzene,44 1,3-diethynylben-
zene,45 1,3,5-trisethynylbenzene,46 Pd(PPh3)4,47 Pd2(dba)3,48 and
2-trimethylstannylpyridine (18d )49 were prepared according
to published procedures. 2-Trimethylstannyl-6-phenylpyridine
(18a ), 2-trimethylstannyl-5-methylpyridine (18b), and 2-tri-
methylstannyl-6-methylpyridine (18c) were prepared in the
same way as 18d .
1,2-Bis[5-(2-ch lor op yr id yl)]eth yn e (5a ). To a mixture of
2-chloro-5-iodopyridine (9) (1.004 g, 4.19 × 10-3 mol), 1,2-bis-
(tri-n-butyltin)ethyne (10) (1.27 g, 2.10 × 10-3 mol), and 0.38
g of Pd(PPh3)4 under an atmosphere of argon was added via
syringe 15 mL of dry dimethylformamide. The mixture was
then heated and stirred in a bath at 105 °C for 24 h, during
which time the reaction mixture became dark-brown in color.
After heating, all solvent was removed under reduced pressure
and the residue column chromatographed on alumina (stan-
dardized activity II-III), using 75:25 CH2Cl2/hexane as eluant.
The product 5a thus obtained was further purified by suspen-
sion in 5 mL of MeOH followed by brief ultrasonication,
filtration under vacuum, washing of the isolated solid with
MeOH, and finally air-drying to yield 0.402 g (77%) of 5a as a
cream-colored microcrystalline solid. Analytically pure 5a (mp
229-230 °C) could be obtained upon sublimation under
The economy and adaptability of the synthetic proce-
dures detailed above make possible the formation of bis-
and tris-5-(2-chloropyridines) and 5-(2,2′-bipyridines)
incorporating a potentially very large variety of bridging
moieties in addition to those already investigated. In
particular, the synthesis provides a convenient method
of access to conjugatively bridged 5-(2,2′-bipyridines)
possessing substituents on the outer pyridine rings. This
option is important for the additional modulation and
control of the physicochemical properties of these materi-
als, and also for synthetic elaboration and incorporation
into larger architectures.
(43) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627.
(44) Shuttleworth, R. G.; Rapson, W. S.; Stewart, E. T. J . Chem.
Soc. 1944, 71.
(45) Neenan, T. X.; Whitesides, G. M. J . Org. Chem. 1988, 53, 2489.
(46) Weber, E.; Hecker, M.; Koepp, E.; Orlia, W.; Czugler, M.;
Cso¨regh, I. J . Chem. Soc., Perkin Trans. 2 1988, 1251.
(47) Coulson, D. R.; Satek, L. C.; Grim, S. O. Inorg. Synth. 1990,
28, 107.
(48) Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J . J .; Ibers, J . A. J .
Organomet. Chem. 1974, 65, 253.
The conjugatively bridged 5-(2-halopyridines) and 5-(2,2′-
bipyridines) constitute a reservoir of structural building
blocks which can be expected to find many uses in
materials science and nanotechnology. For example, the
bridged 5-(2-halopyridines) 5a -g and 6-8 may function
as substrates for the tailored engineering of metal ion-
(49) J utzi, P.; Gilge, U. J . Organomet. Chem. 1983, 246, 163.

Synthesis of Bis- and Tris-5-(2,2′-Bipyridines)
J . Org. Chem., Vol. 65, No. 5, 2000 1267
vacuum at 110-130 °C/5 × 10-7 mmHg. 1H NMR (CDCl3, 500
4J 4,6 ) 2.6 Hz, 2H; H4), 7.76 (d, 3J 2′,3′;6′,5′ ) 8.5 Hz, 4H; biphenyl
(inner) H2′,6′), 7.67 (d, 3J 3′,2′;5′,6′ ) 8.5 Hz, 4H; biphenyl (outer)
4
5
MHz, 25 °C): δ (ppm) 8.55 (dd, J 6,4 ) 2.3 Hz, J 6,3 ) 0.7 Hz,
3
4
3
5
2H; H6), 7.77 (dd, J 4,3 ) 8.3 Hz, J 4,6 ) 2.4 Hz, 2H; H4), 7.36
H3′,5′), 7.44 (dd, J 3,4 ) 8.2 Hz, J 3,6 ) 0.7 Hz, 2H; H3). 13C
NMR (CDCl3, 125.8 MHz, 25 °C): δ (ppm) 150.5, 147.9, 140.3,
137.0, 135.8, 135.0, 127.8, 127.6, 124.3. UV/vis (CHCl3): λ (nm)
(ꢀ, M-1 cm-1) 303 (51 868). EIMS: m/z 376 (M+, 100). Anal.
Calcd for C22H14Cl2N2: C, 70.04; H, 3.74; N, 7.43. Found: C,
69.88; H, 3.80; N, 7.24.
(dd, J 3,4 ) 8.3 Hz, J 3,6 ) 0.7 Hz, 2H; H3). 13C NMR (CDCl3,
125.8 MHz, 25 °C): δ (ppm) 152.1, 151.3, 140.9, 124.1, 118.3,
89.0 (CtC). UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 276sh
(22 374), 285sh (25 522), 294 (27 951), 302 (25 896), 312
(26 643). EIMS: m/z 248 (M+, 100). Anal. Calcd for C12H6-
Cl2N2: C, 57.86; H, 2.43; N, 11.25. Found: C, 58.01; H, 2.49;
N, 11.31.
3
5
1,4-Bis[5-(2-br om op yr id yl)]ben zen e (5d ). An intimate
mixture of 5b (0.255 g, 8.47 × 10-4 mol) and POBr3 (9.0 g) in
a flask fitted with a CaCl2 drying tube was heated in a bath
at 170 °C with stirring for 20 h. After the mixture was cooled
to ambient temperature, the resulting black solid was broken
up, added to excess crushed ice/water, and vigorously stirred
until all the ice had melted and the suspended solid homog-
enized. More ice was added and the mixture adjusted to pH
14 by the dropwise addition of 10% aqueous NaOH. The
mixture was stirred for a further 6 h, and then the suspended
solid isolated by filtration under vacuum, washed with distilled
water, and air-dried. The solid was then Soxhlet extracted with
boiling CHCl3 for 48 h. Removal of the solvent from the extract
on a water bath yielded 0.246 g of crude 5d as a khaki solid.
The product was purified by sublimation under vacuum at 150
°C/2 × 10-6 mmHg, and finally by boiling the sublimate in
MeOH, isolating the solid by vacuum filtration, washing with
MeOH, and drying under dynamic vacuum to yield 0.224 g
1,4-Bis[5-(2-ch lor op yr id yl)]ben zen e (5b). To 9 (2.5 g,
1.04 × 10-2 mol) in a dried argon-filled flask equipped with
an alcohol thermometer and argon/vacuum septum inlet
adaptor was added 37 mL of THF via syringe. The solution
was cooled to an internal temperature of -95 °C (liquid N2/
hexane bath), and then 1.6 M n-BuLi (6.51 mL, 1.04 × 10-2
mol) was added by syringe to the stirred solution of 9 at such
a rate as to maintain the reaction temperature below -90 °C.
During addition, the reaction solution became dark brown in
color, and a suspended brown solid formed. The stirred mixture
was subsequently allowed to warm to -83 °C over 0.75 h and
then recooled to -96 °C. A solution of ZnCl2 (1.0 M in Et2O;
11 mL, 1.10 × 10-2 mol) was then syringed into the reaction
solution at such a rate as to maintain the temperature at e-80
°C. The resulting pale brown solution of 11 was allowed to
warm to ambient temperature with stirring over 1.5 h. To
PdCl2(PPh3)2 (0.24 g, 3.42 × 10-4 mol) in a dried, argon-filled
flask were added 38 mL of THF and (n-Bu)2AlH (1.0 M in
hexane; 0.7 mL, 7.0 × 10-4 mol) by syringe, and the resulting
dark brown-green mixture was stirred for 0.25 h. 1,4-Diiodo-
benzene (12a ; 1.70 g, 5.15 × 10-3 mol) was then added to the
catalyst mixture, and after being stirred for 0.1 h the solution
of 11 was cannulated into the reaction flask. The mixture was
stirred for 48 h at ambient temperature. During this time, a
faun-colored suspended solid developed. All solvent was then
distilled off under reduced pressure, 100 mL of a saturated
aqueous disodium-EDTA solution added to the residue, and
the mixture vigorously stirred for 3 h. The suspended solid
was collected by filtration under vacuum, washed with distilled
water, and air-dried. The solid was then suspended in Et2O
(20 mL), briefly ultrasonicated, isolated by vacuum filtration,
washed with Et2O, and air-dried. After the Et2O washing, the
product was sublimed under vacuum at 210-240 °C/1 × 10-6
mmHg to yield 1.069 g (68%) of 5b. Analytically pure product
could be obtained upon boiling the sublimate in 20 mL of
MeOH, isolation of the solid by vacuum filtration followed by
washing with MeOH, and then finally recrystallization from
2-methoxyethanol to yield 5b (mp 261-264 °C) as colorless
microcrystals. 1H NMR (CDCl3, 300 MHz, 25 °C): δ (ppm) 8.65
(dd, 4J 6,4 ) 2.6 Hz, 5J 6,3 ) 0.7 Hz, 2H; H6), 7.89 (dd, 3J 4,3 ) 8.3
1
(77%) of 5d (mp 291-293 °C) as a white amorphous solid. H
NMR (CDCl2CDCl2, 300 MHz, 25 °C): δ (ppm) 8.66 (d, 4J 6,4
)
3
4
2.3 Hz, 2H; H6), 7.87 (dd, J 4,3 ) 8.3 Hz, J 4,6 ) 2.6 Hz, 2H;
3
H4), 7.70 (s, 4H; phenyl H2′,3′,5′,6′), 7.66 (d, J 3,4 ) 8.4 Hz,
2H; H3). UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 275sh (35 421),
293 (44 797). EIMS: m/z 390 (M+, 100). HRMS (FAB+,
CHCl3): calcd for C16H10Br2N2 388.9262, found 388.9274.
4,4′-Bis[5-(2-br om op yr id yl)]-1,1′-bip h en yl (5e). Com-
pound 5e was prepared as described for 5d above from 5c
(0.322 g, 8.53 × 10-4 mol) and 11.2 g of POBr3. After workup,
the solid isolated from the CHCl3 Soxhlet extraction was
washed with CH2Cl2 and sublimed under vacuum at 265 °C/2
× 10-6 mmHg to yield 0.360 g (90%) of 5e as a white powder
1
(mp > 320 °C). H NMR (CDCl2CDCl2, 500 MHz, 100 °C): δ
4
5
(ppm) 8.69 (dd, J 6,4 ) 2.6 Hz, J 6,3 ) 0.7 Hz, 2H; H6), 7.82
(dd, 3J 4,3 ) 8.2 Hz, 4J 4,6 ) 2.6 Hz, 2H; H4), 7.81 (d, 3J 2′,3′; 6′,5′
)
8.2 Hz, 4H; biphenyl (inner) H2′,6′), 7.70 (d, 3J 3′,2′;5′,6′ ) 8.1 Hz,
4H; biphenyl outer) H3′,5′), 7.61 (dd, 3J 3,4 ) 8.2 Hz, 5J 3,6 ) 0.7
Hz, 2H; H3). 13C NMR (CDCl2CDCl2, 125.8 MHz, 100 °C): δ
(ppm) 148.4, 141.3, 140.5, 136.7, 136.0, 135.5, 128.1, 127.9,
127.6. UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 304 (60 118).
FABMS: m/z 466 (M+, 100). Anal. Calcd for C22H14Br2N2: C,
56.68; H, 3.03; N, 6.01. Found: C, 56.95; H, 3.06; N, 5.93.
1,4-Bis(5-eth yn yl-2-ch lor op yr id yl)ben zen e (5f). To a
mixture of 9 (1.223 g, 5.11 × 10-3 mol), 1,4-diethynylbenzene
(13a ; 0.320 g, 2.54 × 10-3 mol), and PdCl2(PPh3)2 (0.073 g, 1.04
× 10-4 mol) under an argon atmosphere was added 50 mL of
Et3N via syringe, and the mixture was stirred for 0.2 h. A
solution of CuI (0.040 g, 2.10 × 10-4 mol) in 10 mL of Et3N
was then added via syringe and the mixture stirred at 25-30
°C for 24 h and finally at 70 °C for 24 h. During the course of
the reaction a flocculent dark-brown solid formed which
changed in color to pale yellow-brown. After heating, all
solvent was removed under reduced pressure, and the remain-
ing solid suspended in 50 mL of acetone, followed by brief
ultrasonication, reisolation by vacuum filtration, washing with
acetone, and air-drying. Further purification was achieved
upon recrystallization first from 70 mL of pyridine and then
toluene to which 0.266 g of decolorizing charcoal had been
added. The product 5f, 0.600 g (68%), was isolated after
washing with toluene and air-drying as pale yellow flakes.
Analytically pure 5f (mp 281-283 °C) could be obtained upon
sublimation under vacuum at 207 °C/1 × 10-6 mmHg. 1H NMR
4
Hz, J 4,6 ) 2.6 Hz, 2H; H4), 7.68 (s, 4H; phenyl H2′,3′,5′,6′),
3
5
7.44 (dd, J 3,4 ) 8.3 Hz, J 3,6 ) 0.7 Hz, 2H; H3). 13C NMR
(CDCl3, 75 MHz, 25 °C): δ (ppm) 150.7, 147.9, 137.0, 136.6,
134.7, 127.8, 124.4. UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 273sh
(27 525), 291 (34 140). EIMS: m/z 300 (M+, 100). Anal. Calcd
for C16H10Cl2N2: C, 63.81; H, 3.35; N, 9.30. Found: C, 63.84;
H, 3.30; N, 9.10.
4,4′-Bis[5-(2-ch lor opyr idyl)]-1,1′-biph en yl (5c). This com-
pound was prepared in a manner identical to that of 5b. Thus,
11 was generated from 9 (2.0 g, 8.35 × 10-3 mol), n-BuLi (1.6
M; 5.3 mL, 8.48 × 10-3 mol), and ZnCl2 (1.0 M in Et2O; 8.5
mL, 8.5 × 10-3 mol) in 50 mL of anhydrous THF. The catalyst
mixture was prepared from PdCl2(PPh3)2 (0.20 g, 2.85 × 10-4
mol) and (n-Bu)2AlH (1.0 M; 0.58 mL, 5.8 × 10-4 mol) in 20
mL of THF. 4,4′-Diiodo-1,1′-biphenyl (12b; 1.6 g, 3.94 × 10-3
mol) was then added to the catalyst followed by 11. The
suspended solid from the Na2EDTA treatment was filtered off,
washed with distilled water and MeOH, and air-dried. Final
purification was achieved by boiling the product in 150 mL of
CHCl3, filtering the cooled mixture under vacuum, washing
with CHCl3, and sublimation under vacuum at 218 °C/2 × 10-6
mmHg to yield 0.862 g (58%) of analytically pure 5c as a white
powder (mp 285-302 °C, continual softening to an opaque
melt). 1H NMR (CDCl3, 500 MHz, 25 °C): δ (ppm) 8.68 (dd,
4J 6,4 ) 2.6 Hz, 5J 6,3 ) 0.7 Hz, 2H; H6), 7.91 (dd, 3J 4,3 ) 8.3 Hz,
4
(CDCl2CDCl2, 500 MHz, 100 °C): δ (ppm) 8.58 (d, J 6,4 ) 2.2
3
4
Hz, 2H; H6), 7.80 (dd, J 4,3 ) 8.2 Hz, J 4,6 ) 2.4 Hz, 2H; H4),
3
7.60 (s, 4H; phenyl H2′,3′,5′,6′), 7.37 (d, J 3,4 ) 8.2 Hz, 2H;
H3). 13C NMR (CDCl2CDCl2, 125.8 MHz, 100 °C): δ (ppm)
152.1, 150.9, 140.8, 131.8, 123.9, 123.0, 119.1, 93.3 (CtC), 87.1
(CtC). UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1): 312sh (62 089),

1268 J . Org. Chem., Vol. 65, No. 5, 2000
Baxter
326 (77 989), 346 (51 727), 371 (4256). EIMS: m/z 348 (M+,
100). Anal. Calcd for C20H10Cl2N2: C, 68.79; H, 2.89; N, 8.02.
Found: C, 68.89; H, 2.88; N, 7.91.
1,3,5-Tr is(5-eth yn yl-2-ch lor op yr id yl)ben zen e (8). Com-
pound 8 was prepared in the same way as 5f, from 9 (1.440 g,
6.01 × 10-3 mol), 17 (0.300 g, 2.0 × 10-3 mol), PdCl2(PPh3)2
(0.100 g, 1.42 × 10-4 mol) in 45 mL of Et3N, and CuI (0.070 g,
3.67 × 10-4 mol) in 3 mL of Et3N. All solvent was removed
from the completed reaction under reduced pressure and the
remaining khaki solid dissolved in 40 mL of CH2Cl2 and flash
column chromatographed on silica, eluting with CH2Cl2, to
yield 0.913 g (94%) of 8 as a pale yellow solid. Analytically
pure 8 (mp 243-245 °C) could be obtained upon further
recrystallization from MeCN followed by sublimation under
vacuum. 1H NMR (CDCl3, 500 MHz, 25 °C): δ (ppm) 8.55 (dd,
4J 6,4 ) 2.3 Hz, 5J 6,3 ) 0.7 Hz, 3H; H6), 7.76 (dd, 3J 4,3 ) 8.3 Hz,
4J 4,6 ) 2.4 Hz, 3H; H4), 7.70 (s, 3H; phenyl H2′,4′,6′), 7.36 (dd,
3J 3,4 ) 8.3 Hz, 5J 3,6 ) 0.7 Hz, 3H; H3). 13C NMR (CDCl3, 125.8
MHz, 25 °C): δ (ppm) 152.2, 151.1, 140.9, 134.7, 124.1, 123.4,
118.6, 91.5 (CtC), 86.4 (CtC). UV/vis (CHCl3): λ (nm) (ꢀ, M-1
cm-1) 276 (63 766), 293 (93 458), 302 (87 660), 311 (96 982),
4,4′-Bis(5-eth yn yl-2-ch lor op yr id yl)-1,1′-bip h en yl (5g).
Compound 5g was prepared in the same way as 5f, from 9
(0.355 g, 1.48 × 10-3 mol), 13b, (0.15 g, 7.42 × 10-4 mol), PdCl2-
(PPh3)2 (0.020 g, 2.85 × 10-5 mol) in 9 mL of pyridine, and
CuI (0.013 g, 6.83 × 10-5 mol) in 2 mL of Et3N. The solid
isolated by filtration of the cooled reaction mixture was washed
with pyridine and recrystallized from toluene to which 0.15 g
of decolorizing charcoal had been added. The crystals thus
obtained were isolated by vacuum filtration, washed with
toluene, and dried under vacuum to yield 0.245 g (78%) of 5g
as lemon-yellow needles. Analytically pure 5g (mp 302-304
°C) could be obtained by further recrystallization from CHCl3
followed by sublimation under vacuum at 230 °C/2 × 10-6
mmHg. 1H NMR (CDCl2CDCl2, 500 MHz, 100 °C): δ (ppm)
4
3
4
8.59 (d, J 6,4 ) 2.2 Hz, 2H; H6), 7.82 (dd, J 4,3 ) 8.2 Hz, J 4,6
) 2.3 Hz, 2H; H4), 7.69 (d, J 2′,3′;6′,5′ ) 8.7 Hz, 4H; biphenyl
337 (2591). EIMS: m/z 483 (M+, 100). Anal. Calcd for C27H12
-
3
(inner) H2′,6′), 7.67 (d, 3J 3′,2′;5′,6′ ) 8.8 Hz, 4H; biphenyl (outer)
H3′,5′), 7.37 (d, 3J 3,4 ) 8.3 Hz, 2H; H3). 13C NMR (CDCl2CDCl2,
125.8 MHz, 100 °C): δ (ppm) 152.1, 150.7, 140.8, 140.7, 132.4,
127.0, 123.8, 121.9, 119.0, 93.7 (CtC), 86.0 (CtC). UV/vis
(CHCl3): λ (nm) (ꢀ, M-1 cm-1) 330 (86 211). EIMS: m/z 424
(M+, 100). Anal. Calcd for C26H14Cl2N2: C, 73.42; H, 3.32; N,
6.59. Found: C, 73.39; H, 3.34; N, 6.75.
Cl3N3: C, 66.90; H, 2.50; N, 8.67. Found: C, 66.86; H, 2.77;
N, 8.69.
Gen er a l P r oced u r e for Stille Cou p lin g Rea ction s. The
appropriate quantities of bis- and tris-5-(2-halopyridines)
5a ,d -g and 6-8), bromopyridines 19 and 20, trimethylstan-
nylpyridine 18a -d , Pd(PPh3)4, and LiCl in the case of 2a and
4a ,b were refluxed in toluene, xylene, or DMF at 120-160 °C
for 24-72 h under an atmosphere of argon. The solvent was
then removed under reduced pressure on a water bath, and
unless otherwise stated, MeOH was added to the residue, the
suspension briefly ultrasonicated and filtered under vacuum,
and the isolated solid washed with excess MeOH and air-dried.
Further purifications are described for each compound.
1,2-Bis[5-(6′-ph en yl-2,2′-bipyr idyl)]eth yn e (1a). 5a (0.111
g, 4.46 × 10-4 mol), 18a (0.510 g, 1.60 × 10-3 mol), and Pd-
(PPh3)4 (0.035 g, 3.03 × 10-5 mol) in 13 mL of toluene were
refluxed for 48 h at 135 °C. After removal of solvent, the
residue was dissolved in 25 mL of hot CHCl3 and chromato-
graphed on a column of alumina (standardized activity II-
III), using CHCl3 as eluant. The product thus obtained was
suspended in 30 mL of Et2O, briefly ultrasonicated, isolated
by filtration under vacuum, washed with Et2O, and dried
under vacuum to yield 0.172 g (79%) of 1a (mp 260-261 °C)
as a cream-colored microcrystalline solid. 1H NMR (CDCl3, 500
MHz, 25 °C): δ (ppm) 8.88 (dd, 4J 6′,4′ ) 2.1 Hz, 5J 6′,3′ ) 0.8 Hz,
1,2-Bis(5-eth yn yl-2-ch lor op yr id yl)ben zen e (6). Com-
pound 6 was prepared in the same way as 5f from 1,
2-diiodobenzene (14; 0.236 g, 7.15 × 10-4 mol), 15b (0.197 g,
1.43 × 10-3 mol), Pd2(dba)3 (0.028 g, 3.06 × 10-5 mol), PPh3
(0.037 g, 1.41 × 10-4 mol), and CuI (0.006 g, 3.15 × 10-5 mol)
in 7 mL of Et3N at 40 °C for 14 h. After removal of solvent,
the residue was dissolved in 25 mL of CH2Cl2 and extracted
twice with distilled water. The organic layer was subsequently
dried (MgSO4) and filtered, and the solvent reduced in volume
to 8 mL on a water bath. The CH2Cl2 solution was then flash
chromatographed on a column of silica, eluting with CH2Cl2,
and the isolated product boiled in 5 mL of hexane, filtered
under vacuum, washed with 2 mL of hexane, and air-dried.
Final purification was achieved upon sublimation under
vacuum (135 °C/2 × 10-6 mmHg), to yield 0.187 g (75%) of 6
(mp 153-154 °C) as a cream-colored solid. 1H NMR (CDCl3,
4
5
500 MHz, 25 °C): δ (ppm) 8.54 (dd, J 6,4 ) 2.3 Hz, J 6,3 ) 0.7
3
4
Hz, 2H; H6), 7.74 (dd, J 4,3 ) 8.2 Hz, J 4,6 ) 2.3 Hz, 2H, H4),
7.59 (m, 2H; phenyl H6′,3′), 7.39 (m, 2H; phenyl H4′,5′), 7.34
3
5
2H; H6′), 8.69 (dd, J 3′,4′ ) 8.2 Hz, J 3′,6′ ) 0.8 Hz, 2H; H3′),
(dd, J 3,4 ) 8.3 Hz, J 3,6 ) 0.7 Hz, 2H; H3). 13C NMR (CDCl3,
125.8 MHz, 25 °C): δ (ppm) 152.0, 150.8, 140.7, 132.1, 128.9,
124.8, 124.1, 119.1, 92.1 (CtC), 88.9 (CtC). UV/vis (CHCl3):
λ (nm) (ꢀ, M-1 cm-1) 275 (44 049), 301 (27 472), 318 (24 287),
8.42 (dd, J 3,4 ) 7.8 Hz, J 3,5 ) 0.9 Hz, 2H; terminal pyridine
3
5
3
4
3
H3), 8.16 (dm, J o,m ) 7.1 Hz, 4H; phenyl H-ortho), 8.01 (dd,
3J 4′,3′ ) 8.2 Hz, J 4′,6′ ) 2.1 Hz, 2H; H4′), 7.91 (t, J 4,3;4,5 ) 7.8
4
3
Hz, 2H; terminal pyridine H4), 7.80 (dd, 3J 5,4 ) 7.8 Hz, 4J 5,3
)
339sh (9615). EIMS: m/z 348 (M+, 100). Anal. Calcd for C20H10
-
0.9 Hz, 2H; terminal pyridine H5), 7.53 (tm, 3J m,o;m,p ) 7.4 Hz,
3
Cl2N2: C, 68.79; H, 2.89; N, 8.02. Found: C, 68.96; H, 3.04;
N, 8.24.
4H; phenyl H-meta), 7.46 (tt, J p,m ) 7.3 Hz, 2H; phenyl
H-para). 13C NMR (CDCl3, 125.8 MHz, 25 °C): δ (ppm) 156.6,
1, 3-Bis(5-eth yn yl-2-ch lor op yr id yl)ben zen e (7). Com-
pound 7 was prepared in the same way as 5f, from 9 (1.14 g,
4.76 × 10-3 mol), 16 (0.30 g, 2.38 × 10-3 mol), PdCl2(PPh3)2
(0.100 g, 1.42 × 10-4 mol) in 45 mL of Et3N, and CuI (0.070 g,
3.67 × 10-4 mol) in 3 mL of Et3N. After removal of solvent,
the product was briefly ultrasonicated in 60 mL of acetone,
stirred for 5 h, and then filtered under vacuum and the solid
collected, washed with acetone, and air-dried. The khaki solid
was then recrystallized from 25 mL of boiling toluene to which
0.20 g of decolorizing charcoal had been added. The product
was isolated by vacuum filtration, washed with cold toluene,
and dried under vacuum to yield 0.489 g (59%) of 7 (mp 215-
155.5, 155.0, 151.6, 139.4, 139.2, 137.8, 129.1, 128.8, 127.0,
120.6, 119.7, 90.5 (CtC). UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1
)
267 (37 214), 340 (66 832), 359 (52 514). FABMS: m/z 487 ([M
+ H]+, 100). Anal. Calcd for C34H22N4: C, 83.93; H, 4.56; N,
11.51. Found: C, 83.78; H, 4.63; N, 11.53.
1,2-Bis[5-(5′-m eth yl-2,2′-bipyr idyl)]eth yn e (1b). 5a (0.151
g, 6.06 × 10-4 mol), 18b (0.398 g, 1.56 × 10-3 mol), and Pd-
(PPh3)4 (0.030 g, 2.59 × 10-5 mol) in 7 mL of toluene were
refluxed for 24 h at 140 °C. After removal of solvent, the
residue was dissolved in CHCl3 and twice column chromato-
graphed on alumina (basic, activity IV), using CHCl3 as eluant.
The product thus obtained was suspended in Et2O, briefly
ultrasonicated, and filtered under vacuum and the isolated
solid washed with Et2O and dried under vacuum to yield 0.139
1
217 °C) as golden needles. H NMR (CDCl3, 500 MHz, 25 °C):
4
3
δ (ppm) 8.54 (d, J 6,4 ) 2.2 Hz, 2H; H6), 7.76 (dd, J 4,3 ) 8.2
4
1
Hz, J 4,6 ) 2.4 Hz, 2H; H4), 7.72 (t, 1H; phenyl H2′), 7.54 (m,
g (63%) of 1b (mp 279-281 °C) as colorless needles. H NMR
3J 4′,5′;6′,5′ ) 7.8 Hz, 2H; phenyl H4′,6′), 7.39 (t, J 5′,4′;5′,6′ ) 7.8
(CDCl3, 500 MHz, 25 °C): δ (ppm) 8.82 (dd, J 6′,4′ ) 2.1 Hz,
3
4
Hz, 1H; phenyl H5′), 7.34 (d, 3J 3,4 ) 8.2 Hz, 2H; H3). 13C NMR
(CDCl3, 125.8 MHz, 25 °C): δ (ppm) 152.1, 150.7, 140.9, 134.7,
132.0, 128.8, 124.0, 122.8, 119.0, 92.5 (CtC), 85.5 (CtC). UV/
vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 273 (50 756), 289 (66 065),
301 (59 860), 309 (61 856), 333 (6966), 345 (4540). EIMS: m/z
348 (M+, 100). Anal. Calcd for C20H10Cl2N2: C, 68.79; H, 2.89;
N, 8.02. Found: C, 68.88; H, 2.86; N, 8.08.
5J 6′,3′ ) 0.8 Hz, 2H; H6′), 8.51 (d, J 6,4 ) 2.2 Hz, 2H;
4
3
5
methylpyridine H6), 8.40 (dd, J 3′,4′ ) 8.3 Hz, J 3′,6′ ) 0.8 Hz,
2H; H3′), 8.32 (d, 3J 3,4 ) 8.1 Hz, 2H; methylpyridine H3), 7.95
(dd, J 4′,3′ ) 8.2 Hz, J 4′,6′ ) 2.1 Hz, 2H; H4′), 7.64 (dd, J 4,3
8.1 Hz, J 4,6 ) 2.2 Hz, 2H; methylpyridine H4), 2.41 (s, 6H;
CH3). 13C NMR (CDCl3, 125.8 MHz, 25 °C): δ (ppm) 155.4,
152.8, 151.6, 149.8, 139.4, 137.5, 133.9, 121.0, 120.1, 119.3,
3
4
3
)
4

Synthesis of Bis- and Tris-5-(2,2′-Bipyridines)
J . Org. Chem., Vol. 65, No. 5, 2000 1269
90.3 (CtC), 18.4 (CH3). UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1
326sh (63 594), 336 (69 272), 355 (52 365). FABMS: m/z 363
([M + H]+, 100). Anal. Calcd for C24H18N4: C, 79.54; H, 5.01;
N, 15.46. Found: C, 79.63; H, 4.92; N, 15.41.
)
25 °C): δ (ppm) 158.0, 148.4, 144.9, 144.3, 143.7, 143.1, 142.7,
140.7, 134.7, 132.1, 130.8, 130.1, 129.3, 128.9 (two bands),
128.5, 128.4, 126.3. UV/vis (CHCl3, [1e] e 5 × 10-6 mol dm-3):
λ (nm) (ꢀ, M-1 cm-1) 268 (30 672), 334 (49 509). FABMS: m/z
615 ([M + H]+, 100). Anal. Calcd for C44H30N4: C, 85.97; H,
4.92; N, 9.11. Found: C, 86.03; H, 5.09; N, 9.29.
1,4-Bis[5-(6′-p h en yl-2,2′-b ip yr id yl)]b en zen e (1c). 5d
(0.160 g, 4.10 × 10-4 mol), 18a (0.524 g, 1.65 × 10-3 mol), and
Pd(PPh3)4 (0.033 g, 2.86 × 10-5 mol) in 15 mL of toluene were
refluxed at 136 °C for 48 h. After removal of solvent and
treatment with MeOH, the product was recrystallized from
100 mL of boiling toluene and dried under vacuum to yield
0.158 g (71%) of 1c (mp 312-314 °C) as cream-colored flakes.
1H NMR (CF3COOD), 500 MHz, 25 °C): δ (ppm) 9.63 (d, 4J 6′,4′
4,4′-Bis[5-(5′-m eth yl-2,2′-bip yr id yl)]-1,1′-bip h en yl (1f).
5e (0.118 g, 2.53 × 10-4 mol), 18b (0.260 g, 1.02 × 10-3 mol),
and Pd(PPh3)4 (0.030 g, 2.60 × 10-5 mol) in 10 mL of xylene
were heated for 72 h at 150 °C. After removal of solvent and
treatment with MeOH, the product was recrystallized from
90 mL of boiling pyridine to yield 0.078 g (63%) of 1f (mp >
320 °C) as a cream-colored solid. 1H NMR (CF3COOD), 500
3
) 1.8 Hz, 2H; H6′ inner pyridine), 9.20 (dd, J 4′,3′ ) 8.4 Hz,
3
4
4J 4′,6′ ) 2.1 Hz, 2H; H4′ inner pyridine), 9.01 (t, J 4,3;4,5 ) 8.1
MHz, 60 °C): δ (ppm) 9.75 (d, J 6′,4′ ) 2.2 Hz, 2H; H6′), 9.39
3
3
4
4
Hz, 2H; phenylpyridine H4), 8.93 (d, J 3′,4′ ) 8.4 Hz, 2H; H3′
(dd, J 4′,3′ ) 8.5 Hz, J 4′,6′ ) 2.2 Hz, 2H; H4′), 9.31 (dd, J 6,4 )
5
3
4
inner pyridine), 8.74 (dd, J 3,4 ) 7.9 Hz, J 3,5 ) 0.9 Hz, 2H;
1.3 Hz, J 6,3 ) 0.6 Hz, 2H; methylpyridine H6), 9.05 (m, 4H;
3
4
3
phenylpyridine H3), 8.67 (dd, J 5,4 ) 8.3 Hz, J 5,3 ) 0.9 Hz,
2H; phenylpyridine H5), 8.26 (s, 4H; central phenyl H2′′,3′′,
5′′,6′′), 8.14 (dm, 3J o,m ) 7.2 Hz, 4H; terminal phenyl H-ortho),
methylpyridine H3, inner pyridine H3′), 8.98 (d, J 4,3 ) 8.3
3
Hz, 2H; methylpyridine H4), 8.37 (d, J 2′′,3′′;6′′,5′′ ) 8.6 Hz, 4H;
3
biphenyl (inner) H2′′,6′′), 8.32 (d, J 3′′,2′′;5′′,6′′ ) 8.6 Hz, 4H;
3
7.99 (tt, J p,m ) 7.5 Hz, 2H; terminal phenyl H-para), 7.91 (t,
biphenyl (outer) H3′′,5′′), 3.16 (s, 6H; CH3). 13C NMR (CF3-
COOD, 125.8 MHz, 60 °C): δ (ppm) 149.1, 144.3, 144.2, 144.0,
143.7, 143.5, 143.4, 141.1, 141.0, 132.4, 129.2, 128.3, 127.6,
127.3, 17.5 (CH3). UV/vis (CHCl3, [1f] < 2 × 10-6 mol dm-3):
λ (nm) (ꢀ, M-1 cm-1) 330 (78 909). FABMS: m/z 491 ([M + H]+,
100). Anal. Calcd for C34H26N4: C, 83.24; H, 5.34; N, 11.42.
Found: C, 83.09; H, 5.32; N, 11.41.
3J m,o;m,p ) 7.7 Hz, 4H; terminal phenyl H-meta). 13C NMR (CF3-
COOD, 125.8 MHz, 25 °C): δ (ppm) 157.6, 148.3, 144.4, 144.0,
143.7, 142.8, 142.2, 136.0, 134.7, 130.8, 130.1, 129.5, 128.6,
128.4, 128.1, 125.7. UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 265
(44 852), 332 (89 654). FABMS: m/z 539 ([M + H]+, 100). Anal.
Calcd for C38H26N4: C, 84.73; H, 4.87; N, 10.40. Found: C,
84.95; H, 5.00; N, 10.43.
1,4-Bis[5-eth yn yl(6′-ph en yl-2,2′-bipyr idyl)]ben zen e (1g).
5f (0.152 g, 4.35 × 10-4 mol), 18a (0.520 g, 1.64 × 10-3 mol),
and Pd(PPh3)4 (0.046 g, 3.98 × 10-5 mol) in 17 mL of toluene
were refluxed at 136 °C for 48 h. After cooling, the reaction
mixture was filtered under vacuum, washed with toluene, and
air-dried. The product was then dissolved in 80 mL of boiling
toluene to which 0.1 g of decolorizing charcoal had been added,
gravity filtered, and left to cool. The crystalline solid which
formed on standing was isolated by filtration under vacuum,
washed with toluene, and dried under vacuum to yield 0.164
g (64%) of 1g (mp 285-286 °C) as slightly green flourescent
plates. 1H NMR (CDCl2CDCl2, 500 MHz, 70 °C): δ (ppm) 8.91
1,4-Bis[5-(5′-m et h yl-2,2′-b ip yr id yl)]b en zen e (1d ). 5d
(0.152 g, 3.90 × 10-4 mol), 18b (0.390 g, 1.52 × 10-3 mol), and
Pd(PPh3)4 (0.032 g, 2.77 × 10-5 mol) in 18 mL of xylene were
refluxed at 160 °C for 48 h. After removal of solvent and
treatment with MeOH, the product was recrystallized from
boiling pyridine, washed with CH2Cl2, and dried under vacuum
to yield 0.104 g (64%) of 1d (mp > 320 °C) as a cream-colored
microcrystalline solid. 1H NMR (CF3COOD), 500 MHz, 25
°C): δ (ppm) 9.34 (dd, 4J 6′,4′ ) 2.2 Hz, 5J 6′,3′ ) 0.4 Hz, 2H; H6′),
3
4
8.96 (dd, J 4′,3′ ) 8.4 Hz, J 4′,6′ ) 2.2 Hz, 2H; H4′), 8.87 (m,
4J 6,4 ) 1.9 Hz, 2H; methylpyridine H6), 8.63 (m, 3J 4,3 and J 3′,4′
3
4
5
3
) 8.2 Hz, 4H; methylpyridine H4, inner pyridine H3′), 8.55
(dd, J 6′,4′ ) 2.2 Hz, J 6′,3′ ) 0.9 Hz, 2H; H6′), 8.68 (dd, J 3′,4′ )
5 3 4
3
(d, J 3,4 ) 8.3 Hz, 2H; H3), 7.99 (s, 4H; phenyl H2′′,3′′,5′′,6′′),
8.2 Hz, J 3′,6′ ) 0.9 Hz, 2H; H3′), 8.48 (dd, J 3,4 ) 7.8 Hz, J 3,5
2.70 (s, 6H; CH3). 13C NMR (CF3COOD, 125.8 MHz, 25 °C): δ
(ppm) 149.5, 145.0, 144.1, 144.0, 143.7, 142.8, 141.8, 140.8,
135.9, 129.5, 128.1, 127.7, 17.6 (CH3). UV/vis (CHCl3): λ (nm)
(ꢀ, M-1 cm-1) 326 (67 198). FABMS: m/z 415 ([M + H]+, 100).
Anal. Calcd for C28H22N4: C, 81.13; H, 5.35; N, 13.52. Found:
C, 81.16; H, 5.40; N, 13.59.
) 0.9 Hz, 2H; terminal pyridine H3), 8.20 (dm, 3J o,m ) 7.7 Hz,
3
4
4H; terminal phenyl H-ortho), 8.03 (dd, J 4′,3′ ) 8.2 Hz, J 4′,6′
3
) 2.1 Hz, 2H; H4′), 7.94 (t, J 4,3;4,5 ) 7.8 Hz, 2H; terminal
3
4
pyridine H4), 7.83 (dd, J 5,4 ) 7.8 Hz, J 5,3 ) 1.0 Hz, 2H;
terminal pyridine H5), 7.65 (s, 4H; central phenyl H2′′,3′′,5′′,6′′),
7.57 (tm, 3J m,o;m,p ) 7.4 Hz, 4H; terminal phenyl H-meta), 7.50
3
4,4′-Bis[5-(6′-p h en yl-2,2′-bip yr id yl)]-1,1′-bip h en yl (1e).
5e (0.100 g, 2.15 × 10-4 mol), 18a (0.300 g, 9.43 × 10-4 mol),
and Pd(PPh3)4 (0.021 g, 1.82 × 10-5 mol) in 9 mL of DMF were
heated at 150 °C for 72 h. After cooling, the mixture was
filtered under vacuum and the solid collected, washed with
MeOH, and air-dried. The solid was then Soxhlet extracted
with 400 mL of boiling pyridine for 48 h, and the extract twice
gravity filtered, boiled down to 190 mL, and left to stand for
24 h. The solid which formed was isolated by filtration under
vacuum, washed with pyridine, and dried under vacuum to
yield 0.086 g (65%) of 1e as pale yellow microcrystals.
Analytically pure 1e was obtained by dissolving the product
in 8 mL of concentrated aqueous HCl to which 0.40 g of
decolorizing charcoal had been added and briefly boiling the
mixture followed by filtration through a G3 glass frit. The
filtrate was then diluted with distilled water until precipitation
ceased, adjusted to pH 7 with dilute aqueous NaOH, and boiled
for 0.5 h. The product was isolated by filtration under vacuum,
washed with distilled water, and dried under vacuum at 100
°C/2 × 10-6 mmHg to yield 1e (mp > 320 °C) as a white
amorphous solid. 1H NMR (CF3COOD), 500 MHz, 25 °C): δ
(tt, J p,m ) 7.3 Hz, 2H; terminal phenyl H-para). 13C NMR
(CDCl2CDCl2, 125.8 MHz, 70 °C): δ (ppm) 156.8, 155.5, 155.2,
151.7, 139.4, 139.3, 137.6, 131.8, 129.1, 128.8, 127.1, 123.2,
120.6, 120.5, 120.1, 119.9, 93.2 (CtC), 88.9 (CtC). UV/vis
(CHCl3): λ (nm) (ꢀ, M-1 cm-1): 266 (32 749), 353 (84 595), 373
(59 344). FABMS: m/z 587 ([M + H]+, 100%). Anal. Calcd for
C
42H26N4: C, 85.98; H, 4.47; N, 9.55. Found: C, 85.89; H, 4.64;
N, 9.54.
1,4-Bis[5-eth yn yl(5′-m eth yl-2,2′-bipyr idyl)]ben zen e (1h ).
5f (0.127 g, 3.64 × 10-4 mol), 18b (0.344 g, 1.34 × 10-3 mol),
and Pd(PPh3)4 (0.032 g, 2.77 × 10-5 mol) in 16 mL of toluene
were refluxed at 140 °C for 48 h. After removal of solvent and
treatment with MeOH, the product was recrystallized from
50 mL of toluene to which 0.15 g of decolorizing charcoal had
been added. The solid thus obtained was finally sublimed
under vacuum at 250 °C/2 × 10-6 mmHg and the sublimate
suspended in acetone, briefly ultrasonicated, isolated by filtra-
tion under vacuum, washed with acetone, and dried under
vacuum to yield 0.093 g (55%) of 1h (mp 295-297 °C) as a
light-sensitive pale yellow-green solid. 1H NMR (CDCl2CDCl2,
500 MHz, 100 °C): δ (ppm) 8.87 (d, 2H; inner pyridine H6′),
3
4
3
(ppm) 9.52 (s, 2H; H6′), 9.17 (dd, J 4′,3′ ) 8.4 Hz, J 4′,6′ ) 1.5
8.59 (s, 2H; methylpyridine H6), 8.50 (d, J 3′,4′ ) 8.2 Hz, 2H;
3
Hz, 2H; H4′), 8.92 (t, J 4,3;4,5 ) 8.1 Hz, 2H; terminal pyridine
inner pyridine H3′), 8.41 (d, 3J 3,4 ) 8.0 Hz, 2H; methylpyridine
H3), 7.97 (dd, 3J 4′,3′ ) 8.2 Hz, 4J 4′,6′ ) 2.1 Hz, 2H; inner pyridine
H4′), 7.70 (dd, 3J 4,3 ) 8.1 Hz, 4J 4,6 ) 2.1 Hz, 2H; methylpyridine
3
3
H4), 8.84 (d, J 3′,4′ ) 8.4 Hz, 2H; H3′), 8.62 (d, J 3,4 ) 7.7 Hz,
2H; terminal pyridine H3), 8.58 (d, 3J 5,4 ) 8.3 Hz, 2H; terminal
pyridine H5), 8.08-8.02 (m, 12H; central biphenyl H2′′,6′′;3′′,5′′,
1
H4), 7.63 (s, 4H; phenyl H2′′,3′′,5′′,6′′), 2.46 (s, 6H; CH3). H
3
and terminal phenyl H-ortho), 7.89 (t, J p,m ) 7.5 Hz, 2H;
NMR (CF3COOD/20% D2O, 500 MHz, 25 °C): δ (ppm) 9.00
3
4
5
terminal phenyl H-para), 7.80 (t, J m,o;m,p ) 7.8 Hz, 4H;
(dd, J 6′,4′ ) 1.9 Hz, J 6′,3′ ) 0.7 Hz, 2H; inner pyridine H6′),
terminal phenyl H-meta). 13C NMR (CF3COOD, 125.8 MHz,
8.74 (dm, J 6,4 ) 1.2 Hz, 2H; methylpyridine H6), 8.57 (dd,
4

1270 J . Org. Chem., Vol. 65, No. 5, 2000
Baxter
3J 4,3 ) 8.4 Hz, 4J 4,6 ) 1.3 Hz, 2H; methylpyridine H4), 8.49 (d,
methylcyclohexane to which 0.09 g of decolorizing charcoal had
been added prior to filtration, to yield 0.107 g (64%) of 2a (mp
230-231 °C) as fibrous cream-colored needles. 1H NMR
3
3J 3,4 ) 8.4 Hz, 2H; methylpyridine H3), 8.36 (dd, J 4′,3′ ) 8.3
4
3
Hz, J 4′,6′ ) 2.0 Hz, 2H; inner pyridine H4′), 8.30 (dd, J 3′,4′
)
5
4
8.4 Hz, J 3′,6′ ) 0.6 Hz, 2H; inner pyridine H3′), 7.67 (s, 4H;
phenyl H2′′,3′′,5′′,6′′), 2.70 (s, 6H; CH3). 13C NMR (CF3COOD/
20% D2O, 125.8 MHz, 25 °C): δ (ppm) 154.7, 152.4, 147.6,
146.9, 146.1, 145.5, 144.7, 135.8, 129.5, 128.0, 126.7, 126.6,
101.2 (CtC), 89.1 (CtC). 20.7 (CH3). UV/vis (CHCl3): λ (nm)
(ꢀ, M-1 cm-1) 350 (98 621), 371 (64 037). FABMS: m/z 463 ([M
+ H]+, 100). Anal. Calcd for C32H22N4: C, 83.09; H, 4.79; N,
12.11. Found: C, 83.17; H, 5.07; N, 12.19.
(CDCl3, 500 MHz, 25 °C): δ (ppm) 8.89 (dd, J 6′,4′ ) 2.1 Hz,
3
5
5J 6′,3′ ) 0.9 Hz, 2H; H6′), 8.69 (dd, J 3′,4′ ) 8.2 Hz, J 3′,6′ ) 0.8
3
4
Hz, 2H; H3′), 8.41 (dd, J 3,4 ) 7.8 Hz, J 3,5 ) 0.9 Hz, 2H;
3
phenylpyridine H3), 8.16 (dm, J o,m ) 7.0 Hz, 4H; terminal
3
4
phenyl H-ortho), 8.01 (dd, J 4′,3′ ) 8.2 Hz, J 4′,6′ ) 2.1 Hz, 2H;
3
H4′), 7.90 (t, J 4,3;4,5 ) 7.8 Hz, 2H; phenylpyridine H4), 7.79
3
4
(dd, J 5,4 ) 7.8 Hz, J 5,3 ) 0.9 Hz, 2H; phenylpyridine H5),
3
7.66 (m, 2H; central phenyl H3′′,6′′), 7.51 (tm, J m,o;m,p ) 7.4
4,4′-Bis[5-eth yn yl(6′-p h en yl-2,2′-bip yr id yl)]-1, 1′-bip h e-
n yl (1i). 5g (0.100 g, 2.35 × 10-4 mol), 18a (0.400 g, 1.26 ×
10-3 mol), and Pd(PPh3)4 (0.035 g, 3.03 × 10-5 mol) in 10 mL
of toluene were refluxed at 135 °C for 60 h. A suspended solid
remained present throughout the reaction period. After re-
moval of solvent, the residue was worked up as described for
1d , with the exception that the boiling pyridine solution prior
to gravity filtration contained 0.1 g of decolorizing charcoal.
The product 1i (0.112 g, 72%) was isolated as lemon-yellow
microcrystalline flakes, pure by 1H NMR. Analytically pure
material was obtained upon boiling in 25 mL of concentrated
aqueous HCl and adding 125 mL of distilled water. Boiling
was continued for 0.1 h and the mixture allowed to cool to
ambient temperature. The suspended solid was then isolated
by filtration under vacuum, washed with distilled water, air-
dried, and finally recrystallized from boiling pyridine (mp 313-
316 °C). 1H NMR (CDCl2CDCl2, 500 MHz, 120 °C): δ (ppm)
Hz, 4H; terminal phenyl H-meta), 7.44 (tt, 3J p,m ) 7.3 Hz, 2H;
terminal phenyl H-para), 7.40 (m, 2H; central phenyl H4′′,5′′).
13C NMR (CDCl3, 125.8 MHz, 25 °C): δ (ppm) 156.6, 155.4,
155.0, 151.5, 139.3, 139.2, 137.8, 132.1, 129.1, 128.7, 128.6,
127.0, 125.3, 120.7, 120.6, 120.1, 119.7, 92.0 (CtC), 90.8 (Ct
C). UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 262sh (50 536), 270
(51 046), 322 (76 097), 350sh (41 926). FABMS m/z 587 ([M +
H]+, 100). Anal. Calcd for C42H26N4: C, 85.98; H, 4.47; N, 9.55.
Found: C, 85.80; H, 4.61; N, 9.61.
1,2-Bis[5-eth yn yl(5′-m eth yl-2,2′-bipyr idyl)]ben zen e (2b).
6 (0.100 g, 2.86 × 10-4 mol), 18b (0.232 g, 9.06 × 10-4 mol),
and Pd(PPh3)4 (0.020 g, 1.73 × 10-5 mol) in 5.5 mL of toluene
were refluxed at 120 °C for 24 h. After removal of solvent and
treatment with MeOH, the brown solid was chromatographed
on alumina (standardized activity II-III), using CH2Cl2 as
eluant, and the isolated product suspended in 3 mL of acetone.
The mixture was briefly ultrasonicated, filtered under vacuum,
washed with acetone, and air-dried to yield 0.070 g (52%) of
2b as a pale-yellow microcrystalline solid. Analytically pure
product was obtained upon sublimation under vacuum (2 ×
10-4 mmHg/220 °C, with some decomposition), and brief
ultrasonication of the sublimate in acetone followed by filtra-
tion under vacuum, washing with acetone, and drying under
vacuum to yield 2b (mp 246-247 °C) as a cream-colored
4
5
8.94 (dd, J 6′,4′ ) 2.1 Hz, J 6′,3′ ) 0.8 Hz, 2H; H6′), 8.69 (dd,
5
3
3J 3′,4′ ) 8.2 Hz, J 3′,6′ ) 0.8 Hz, 2H; H3′), 8.51 (dd, J 3,4 ) 7.8
4
3
Hz, J 3,5 ) 0.9 Hz, 2H; phenylpyridine H3), 8.20 (dm, J o,m
)
7.1 Hz, 4H; terminal phenyl H-ortho), 8.06 (dd, 3J 4′,3′ ) 8.2 Hz,
4J 4′,6′ ) 2.1 Hz, 2H; H4′), 7.95 (t, J 4,3;4,5 ) 7.8 Hz, 2H;
3
3
4
phenylpyridine H4), 7.84 (dd, J 5,4 ) 7.8 Hz, J 5,3 ) 0.9 Hz,
2H; phenylpyridine H5), {7.74 (dm, 3J ) 8.6 Hz, 4H) and 7.70
(dm, 3J ) 8.6 Hz, 4H), biphenyl H2′′,6′′;3′′,5′′}, 7.57 (tm, 3J m,o;m,p
1
powder. H NMR (CDCl3, 500 MHz, 25 °C): δ (ppm) 8.84 (dd,
3
5
) 7.4 Hz, 4H; terminal phenyl H-meta), 7.51 (tt, J p,m ) 7.5
4J 6′,4′ ) 2.1 Hz, J 6′,3′ ) 0.9 Hz, 2H; inner pyridine H6′), 8.51
Hz, 2H; terminal phenyl H-para). 13C NMR (CDCl2CDCl2,
125.8 MHz, 120 °C): δ (ppm) 156.8, 155.3, 151.6, 140.6, 139.5,
139.1, 137.4, 132.3, 129.0, 128.6, 127.0, 126.9, 122.4, 120.5,
120.3, 119.9, 93.5 (CtC), 87.8 (CtC). UV/vis (CHCl3, [1i] e 5
× 10-6 mol dm-3), λ (nm) (ꢀ, M-1 cm-1) 263 (41 931), 351
(91 836). FABMS: m/z 663 ([M + H]+, 100). Anal. Calcd for
(m, 2H; methylpyridine H6), 8.39 (dd, J 3′,4′ ) 8.2 Hz, J 3′,6′
)
3
5
3
5
0.9 Hz, 2H; inner pyridine H3′), 8.31 (dd, J 3,4 ) 8.0 Hz, J 3,5
3
) 0.2 Hz, 2H; methylpyridine H3), 7.95 (dd, J 4′,3′ ) 8.2 Hz,
4J 4′,6′ ) 2.1 Hz, 2H; inner pyridine H4′), 7.63 (dm, J 4,3 ) 8.1
3
Hz, 2H; methylpyridine H4), 7.62 (m, 2H; central phenyl
H3′′,6′′), 7.38 (m, 2H; central phenyl H4′′,5′′), 2.40 (s, 6H; CH3).
13C NMR (CDCl3, 125.8 MHz, 25 °C): δ (ppm) 155.3, 152.9,
151.5, 149.8, 139.3, 137.5, 133.8, 132.1, 128.6, 125.3, 121.0,
120.2, 119.7, 91.9 (CtC), 90.8 (CtC), 18.3 (CH3). UV/vis
(CHCl3): λ (nm) (ꢀ, M-1 cm-1) 258 (26 445), 274 (27 773), 315
(78 492), 348 (37 154). FABMS: m/z 463 ([M + H]+, 100). Anal.
Calcd for C32H22N4: C, 83.09; H, 4.79; N, 12.11. Found: C,
83.26; H, 4.75; N, 12.21.
C
48H30N4: C, 86.98; H, 4.56; N, 8.45. Found: C, 86.91; H, 4.58;
N, 8.53.
4,4′-bis[5-eth yn yl(5′-m eth yl-2,2′-bip yr id yl)]-1,1′-bip h e-
n yl (1j). 5g (0.080 g, 1.88 × 10-4 mol), 18b (0.270 g, 1.05 ×
10-3 mol), and Pd(PPh3)4 (0.023 g, 1.99 × 10-5 mol) in 8 mL of
DMF were heated at 150 °C for 48 h. Upon cooling to ambient
temperature, a solid formed which was isolated by fitration
under vacuum, washed with DMF, and twice recrystallized
from 4 mL portions of boiling DMF to yield 0.04 g (40%) of 1j
(mp > 320 °C) after drying under vacuum as a khaki-yellow
powder. 1H NMR (CF3COOD), 500 MHz, 25 °C): δ (ppm) 9.19
1,3-Bis[5-eth yn yl(6′-ph en yl-2,2′-bipyr idyl)]ben zen e (3a).
7 (0.140 g, 4.01 × 10-4 mol), 18a (0.365 g, 1.15 × 10-3 mol),
and Pd(PPh3)4 (0.036 g, 3.12 × 10-5 mol) in 10 mL of toluene
were refluxed at 136 °C for 48 h. After removal of solvent and
treatment with MeOH, the solid was chromatographed on
silica, eluting first with CHCl3 and then 1% MeOH/CHCl3, and
the product collected in a single fraction (200 mL). Decolorizing
charcoal (0.1 g) was added, the mixture stirred and refluxed
for 0.25 h and then gravity filtered, and all solvent removed
from the filtrate by distillation on a water bath. The remaining
buff-colored solid was then dissolved in 220 mL of boiling
acetone and gravity filtered and the solvent reduced in volume
to 12 mL by rotary evaporation on a water bath. The product
was isolated by filtration under vaccum, washed with acetone,
and dried under vacuum to yield 0.178 g (76%) of 3a (mp 228-
230 °C) as a cream-colored microcrystalline solid. A product
of microanalytical purity was obtained upon recrystallization
from toluene. 1H NMR (CDCl3, 500 MHz, 25 °C): δ (ppm) 8.86
4
(d, J 6′,4′ ) 1.5 Hz, 2H; H6′), 8.98 (s, 2H; methylpyridine H6),
3
3
4
8.75 (dd, J 4,3 and J 4′,3′ ) 8.4 Hz, J 4′,6′ ) 1.5 Hz, 4H;
3
methylpyridine H4, inner pyridine H4′), 8.66 (d, J 3,4 ) 8.3
Hz, 2H; methylpyridine H3), 8.61 (d, 3J 3′,4′ ) 8.4 Hz, 2H; inner
pyridine H3′), 7.81 (s, 8H; biphenyl H2′′,6′′;3′′,5′′), 2.83 (s, 6H;
CH3). 13C NMR (CF3COOD, 125.8 MHz, 25 °C): δ (ppm) 149.5,
148.2, 147.3, 143.6, 143.1, 142.9, 141.5, 140.7, 133.3, 128.4,
127.6, 127.1, 126.6, 120.6, 102.2 (CtC), 82.6 (CtC), 17.6 (CH3).
UV/vis (CHCl3, [1j] e 5 × 10-6 mol dm-3), λ nm (ꢀ, M-1 cm-1
)
350 (85 954). FABMS: m/z 539 ([M + H]+, 100). Anal. Calcd
for C38H26N4: C, 84.73; H, 4.86; N, 10.40. Found: C, 84.91; H,
4.87; N, 10.22.
1,2-Bis[5-eth yn yl(6′-ph en yl-2,2′-bipyr idyl)]ben zen e (2a).
6 (0.100 g, 2.86 × 10-4 mol), 18a (0.329 g, 1.03 × 10-3 mol),
LiCl (0.380 g, 8.96 × 10-3 mol), and Pd(PPh3)4 (0.020 g, 1.73
× 10-5 mol) in 10 mL of toluene were refluxed at 130 °C for
48 h. After removal of solvent, the residue was briefly
ultrasonicated in 20 mL of Et2O and filtered under vacuum
and the collected solid resuspended in 15 mL of MeOH and
refiltered under vacuum. The isolated solid was washed with
MeOH and then acetone and recrystallized from boiling
4
3
(d, J 6′,4′ ) 2.1 Hz, 2H; H6′), 8.67 (d, J 3′,4′ ) 8.2 Hz, 2H; H3′),
8.40 (d, 3J 3,4 ) 7.7 Hz, 2H; phenylpyridine H3), 8.16 (dm, 3J o,m
3
) 7.2 Hz, 4H; terminal phenyl H-ortho), 7.99 (dd, J 4′,3′ ) 8.2
4
3
Hz, J 4′,6′ ) 2.1 Hz, 2H; H4′), 7.91 (t, J 4,3;4,5 ) 7.8 Hz, 2H;
phenylpyridine H4), 7.83 (m, 1H; central phenyl H2′′), 7.80
3
3
(d, J 5,4 ) 7.8 Hz, 2H; phenylpyridine H5), 7.59 (dd, J 4′′,5′′;6′′,5′′
) 7.7 Hz, 4J 4′′,2′′;6′′,2′′ ) 1.6 Hz, 2H; central phenyl H4′′,6′′), 7.53

Synthesis of Bis- and Tris-5-(2,2′-Bipyridines)
J . Org. Chem., Vol. 65, No. 5, 2000 1271
3
(tm, J m,o;m,p ) 7.4 Hz, 4H; terminal phenyl H-meta), 7.46 (tt,
eluting with CHCl3. The product thus obtained was briefly
ultrasonicated in 3 mL of cold 1,4-dioxane, filtered under
vacuum, washed with ice cold 1,4-dioxane, and dried under
vacuum to yield 0.054 g (76%) of 4b (mp 302-303 °C) as a
3J p,m ) 7.3 Hz, 2H; terminal phenyl H-para), 7.42 (t, 3J 5′′,4′′;5′′,6′′
) 7.6 Hz, 1H; central phenyl H5′′). 13C NMR (CDCl3, 125.8
MHz, 25 °C): δ (ppm) 156.7, 155.0, 154.6, 151.3, 139.7, 139.1,
137.8, 134.8, 131.9, 131.8, 129.2, 128.8, 127.0, 123.1, 120.9,
120.7, 120.1, 119.8, 92.6 (CtC), 87.1(CtC). UV/vis (CHCl3):
λ (nm) (ꢀ, M-1 cm-1) 269 (64 264), 330 (122 284), 343 (109 094).
FABMS: m/z 587 ([M + H]+, 100). Anal. Calcd for C42H26N4:
C, 85.98; H, 4.47; N, 9.55. Found: C, 86.09; H, 4.39; N, 9.49.
1,3-Bis[5-eth yn yl(5′-m eth yl-2,2′-bipyr idyl)]ben zen e (3b).
7 (0.141 g, 4.04 × 10-4 mol), 18b (0.300 g, 1.17 × 10-3 mol),
and Pd(PPh3)4 (0.018 g, 1.56 × 10-5 mol) in 7 mL of toluene
were refluxed at 140 °C for 48 h. After removal of solvent, the
residue was chromatographed on alumina (basic, activity IV),
eluting with CHCl3. The product was then sublimed under
vacuum at 230 °C/6 × 10-6 mmHg and the sublimate sus-
pended in acetone, briefly ultrasonicated, isolated by filtration
under vacuum, washed with acetone, and dried under vacuum
to yield 3b (0.077 g, 41%) as a white solid. Analytically pure
3b could be obtained by boiling in excess MeCN, isolation by
vacuum filtration, followed by recrystallization from 4 mL of
toluene, and drying under vacuum to yield 3b (mp 287-288
1
cream-colored powder. H NMR (CDCl3, 500 MHz, 25 °C): δ
4
5
(ppm) 8.81(dd, J 6′,4′ ) 2.1 Hz, J 6′,3′ ) 0.8 Hz, 3H; H6′), 8.52
4
5
(dd, J 6,4 ) 1.4 Hz, J 6,3 ) 0.8 Hz, 3H; methylpyridine H6),
8.40 (dd, 3J 3′,4′ ) 8.2 Hz, 5J 3′,6′ ) 0.8 Hz, 3H; H3′), 8.32 (d, 3J 3,4
3
) 8.2 Hz, 3H; methylpyridine H3), 7.93 (dd, J 4′,3′ ) 8.2 Hz,
4J 4′,6′ ) 2.1 Hz, 3H; H4′), 7.75 (s, 3H; phenyl H2′′,4′′,6′′), 7.64
(m, 3J 4,3 ) 8.1 Hz, 4J 4,6 ) 2.2 Hz, 3H; methylpyridine H4), 2.41
(s, 9H; CH3). 13C NMR (CDCl3, 125.8 MHz, 25 °C): δ (ppm)
155.4, 152.8, 151.7, 149.8, 139.4, 137.5, 134.5, 133.9, 123.7,
120.9, 120.1, 119.3, 91.3 (CtC), 88.0 (CtC), 18.4 (CH3). UV/
vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 325 (179 505), 342 (146 303).
EIMS: m/z 654 (M+, 100). Anal. Calcd for C45H30N6: C, 82.55;
H, 4.62; N, 12.84. Found: C, 82.60; H, 4.84; N, 12.87.
2-Ch lor o-5-(tr im eth ylsilyleth yn yl)p yr id in e (15a ). To a
mixture of 9 (1.703 g, 7.11 × 10-3 mol), PdCl2(PPh3)2 (0.040 g,
5.70 × 10-5 mol), and CuI (0.036 g, 1.89 × 10-4 mol) were
added consecutively 25 mL of Et3N and (trimethylsilyl)ethyne
(0.700 g, 7.13 × 10-3 mol), and the reaction was stirred at
ambient temperature for 48 h. After removal of solvent, the
residue was boiled in 25 mL of hexane. The hexane extract
was flash chromatographed on a column of silica, eluting with
5% Et2O/hexane, to yield an oil which solidified upon cooling
after removal of solvent by distillation on a water bath. The
solid was subsequently dried under vacuum (20 °C/0.1 mmHg)
to yield 1.400 g (94%) of 15a (mp 58-59 °C) as volatile colorless
crystals. The product could also be readily sublimed under
vacuum (50 °C/0.1 mmHg). 1H NMR (CDCl3, 300 MHz, 25
1
°C) as colorless microcrystals. H NMR (CDCl3, 500 MHz, 25
°C): δ (ppm) 8.80 (dd, 4J 6′,4′ ) 2.1 Hz, 5J 6′,3′ ) 0.9 Hz, 2H; H6′),
8.52 (m, 4J 6,4 ) 2.2 Hz, 5J 6,3 ) 0.8 Hz, 2H; methylpyridine H6),
8.38 (dd, 3J 3′,4′ ) 8.3 Hz, 5J 3′,6′ ) 0.9 Hz, 2H; H3′), 8.31 (d, 3J 3,4
3
) 8.1 Hz, 2H; methylpyridine H3), 7.93 (dd, J 4′,3′ ) 8.2 Hz,
4J 4′,6′ ) 2.1 Hz, 2H; H4′), 7.79 (td, 4J 2′′,4′′; 2′′,6′′ ) 1.6 Hz, 5J 2′′,5′′
)
3
4
0.5 Hz, 1H; phenyl H2′′), 7.64 (dd, J 4,3 ) 8.1 Hz, J 4,6 ) 2.3
Hz, 2H; methylpyridine H4), 7.56 (m, 3J 4′′,5′′; 6′′,5′′ ) 7.7 Hz, 4J 4′′,2′′;
3
) 1.7 Hz, 2H; phenyl H4′′,6′′), 7.40 (td, J 5′′,4′′;
) 7.8
6′′,2′′
5′′,6′′
5
4
3
Hz, J 5′′,2′′ ) 0.6 Hz, 1H; phenyl H5′′), 2.41 (s, 6H; CH3). 13C
NMR (CDCl3, 125.8 MHz, 25 °C): δ (ppm) 155.1, 152.8, 151.6,
149.6, 139.4, 137.6, 134.8, 133.9, 131.7, 128.7, 123.2, 121.0,
120.1, 119.6, 92.3 (CtC), 87.2 (CtC), 18.4 (CH3). UV/vis
(CHCl3): λ (nm) (ꢀ, M-1 cm-1) 323 (10 1580), 339 (85 044).
FABMS: m/z 463 ([M + H]+, 100). Anal. Calcd for C32H22N4:
C, 83.09; H, 4.79; N, 12.11. Found: C, 83.23; H, 5.01; N, 11.91.
1,3,5-Tr is[5-e t h yn yl(6′-p h e n yl-2,2′-b ip yr id yl)]b e n -
zen e (4a ). 8 (0.100 g, 2.08 × 10-4 mol), 18a (0.366 g, 1.15 ×
10-3 mol), LiCl (0.736 g, 1.74 × 10-2 mol), and Pd(PPh3)4 (0.031
g, 2.68 × 10-5 mol) in 10 mL of toluene were refluxed at 134
°C for 48 h. The product precipitated from solution during
reflux. After removal of solvent and treatment with MeOH,
the solid was recrystallized from toluene containing 0.1 g of
decolorizing charcoal, washed with acetone, and air-dried to
yield 4a (0.146 g, 83%) as a cream-colored powder (mp g 292
°C with gradual decomposition). A product of microanalytical
purity was obtained upon further recrystallization from tolu-
ene. 1H NMR (CDCl2CDCl2, 500 MHz, 25 °C): δ (ppm) 8.91
°C): δ (ppm) 8.45 (d, J 6,4 ) 2.3 Hz, 1H; H6), 7.67 (dd, J 4,3 )
4 3
8.3 Hz, J 4,6 ) 2.3 Hz, 1H; H4), 7.26 (d, J 3,4 ) 8.3 Hz, 1H;
H3), 0.25 (s, 9H; CH3). 13C NMR (CDCl3, 75 MHz, 25 °C): δ
(ppm) 152.4, 150.6, 141.2, 123.7, 119.2, 100.0 (CtC), 99.6 (Ct
C), -0.3 (CH3). UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 255
(20 368), 259sh (19 222), 278 (6227), 285 (6621), 294sh (4821).
EIMS: m/z 209 (M+, 15). Anal. Calcd for C10H12ClNSi: C,
57.26; H, 5.77; N, 6.68. Found: C, 57.27; H, 5.73; N, 6.72.
2-Ch lor o-5-eth yn ylp yr id in e (15b). To a solution of 15a
(0.400 g, 1.91 × 10-3 mol) in THF (20 mL) and MeOH (15 mL)
was added a solution of NaOH (0.430 g, 1.08 × 10-2 mol) in
distilled water (2 mL), and the reaction was stirred at ambient
temperature for no longer than 24 h. Saturated aqueous NaCl
(30 mL) was then added and the mixture extracted with 3 ×
60 mL portions of Et2O. The organic extracts were combined,
dried (MgSO4), and filtered and the solvent distilled off at
atmospheric pressure on a water bath at 55 °C. The remaining
solid was sublimed under vacuum at 52 °C/0.1 mmHg to yield
15b (82-95%) as volatile, pungent-smelling colorless crystals
(mp 81-82 °C). 1H NMR (CDCl3, 300 MHz, 25 °C): δ (ppm)
4
5
(dd, J 6′,4′ ) 1.9 Hz, J 6′,3′ ) 0.5 Hz, 3H; inner pyridine H6′),
3
5
4
3
4
8.69 (dd, J 3′,4′ ) 8.4 Hz, J 3′,6′ ) 0.5 Hz, 3H; inner pyridine
H3′), 8.44 (d, 3J 3,4 ) 7.6 Hz, 3H; phenylpyridine H3), 8.18 (dm,
8.48 (d, J 6,4 ) 2.2 Hz, 1H; H6), 7.70 (dd, J 4,3 ) 8.3 Hz, J 4,6
3
) 2.3 Hz, 1H; H4), 7.29 (d, J 3,4 ) 8.3 Hz, 1H; H3), 3.25 (s,
3J o,m ) 7.1 Hz, 6H; terminal phenyl H-ortho), 8.06 (dd, J 4′,3′
1H; HCtC). 13C NMR (CDCl3, 75 MHz, 25 °C): δ (ppm) 152.6,
151.1, 141.4, 123.8, 118.1, 81.7 (CtC), 79.1 (CtC). UV/vis
(CHCl3): λ (nm) (ꢀ, M-1 cm-1) 275sh (3860), 281 (4509), 289
(3480). EIMS: m/z 137 (M+, 100). Anal. Calcd for C7H4ClN:
C, 61.12; H, 2.93; N, 10.18. Found: C, 61.36; H, 2.94; N, 10.17.
1-[5-(6′-Meth yl-2,2′-bip yr id yl)]-4-[5-(2-br om op yr id yl)]-
ben zen e (19). 5d (0.233 g, 5.97 × 10-4 mol), 18c (0.195 g,
7.62 × 10-4 mol), and Pd(PPh3)4 (0.040 g, 3.46 × 10-5 mol) in
20 mL of toluene were refluxed at 135 °C for 36 h. After
removal of solvent, the residue was chromatographed on
alumina (standardized activity II-III), eluting with CH2Cl2.
Unreacted 5d eluted first followed by 19. After removal of
solvent by distillation on a water bath, the 5d and 19 thus
obtained were separately suspended in 20 mL of MeOH, briefly
ultrasonicated, isolated by vacuum filtration, washed with
MeOH, and air-dried to yield 5d (0.027 g) and 19 (0.077 g,
3
) 8.2 Hz, 4J 4′,6′ ) 2.1 Hz, 3H; inner pyridine H4′), 7.95 (t, 3J 4,3;4,5
) 7.8 Hz, 3H; phenylpyridine H4), 7.87 (s, 3H; central phenyl
3
4
H2′′,4′′,6′′), 7.83 (dd, J 5,4 ) 7.9 Hz, J 5,3 ) 0.7 Hz, 3H;
phenylpyridine H5), 7.56 (tm, J m,o;m,p ) 7.4 Hz, 6H; terminal
3
phenyl H-meta), 7.50 (tm, 3J p,m ) 7.3 Hz, 3H; terminal phenyl
H-para). 13C NMR (CDCl2CDCl2, 125.8 MHz, 25 °C): δ (ppm)
156.6, 155.4, 154.9, 151.8, 139.7, 139.1, 138.0, 134.9, 129.4,
129.0, 127.1, 123.7, 120.9, 120.7, 120.0, 119.7, 91.8 (CtC), 88.2
(CtC). UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 270 (65 152), 290
(57 976), 332 (118 375), 346 (108 621). FABMS: m/z 841 ([M
+ H]+, 100). Anal. Calcd for C60H36N6: C, 85.69; H, 4.31; N,
9.99. Found: C, 85.75; H, 4.54; N, 10.16.
1,3,5-Tr is[5-e t h yn yl(5′-m e t h yl-2,2′-b ip yr id yl)]b e n -
zen e (4b). 8 (0.052 g, 1.08 × 10-4 mol), 18b (0.220 g, 8.60 ×
10-4 mol), LiCl (0.140 g, 3.30 × 10-3 mol), and Pd(PPh3)4 (0.018
g, 1.56 × 10-5 mol) in 8 mL of toluene were refluxed at 140 °C
for 24 h. Further portions of 18b (0.150 g, 5.86 × 10-4 mol)
and Pd(PPh3)4 (0.018 g, 1.56 × 10-5 mol) were added, and
stirring was continued at 140 °C for an additional 24 h. After
removal of solvent and treatment with MeOH, the product was
chromatographed on alumina (standardized activity II-III),
36% based on reacted 5d ) (mp 237-240 °C) as white solids.
4
1H NMR (CDCl3, 300 MHz, 25 °C): δ (ppm) 8.95 (dd, J 6′,4′
)
2.4 Hz, 5J 6′,3′ ) 0.8 Hz, 1H; inner pyridine H6′), 8.65 (dd, 4J 6′′′,4′′′
5
) 2.6 Hz, J 6′′′,3′′′ ) 0.6 Hz, 1H; bromopyridine H6′′′), 8.52 (dd,
3J 3′,4′ ) 8.2 Hz, J 3′,6′ ) 0.8 Hz, 1H; inner pyridine H3′), 8.22
5
3
3
(d, J 3,4 ) 7.8 Hz, 1H; methylpyridine H3), 8.04 (dd, J 4′,3′
)

1272 J . Org. Chem., Vol. 65, No. 5, 2000
Baxter
1
8.2 Hz, 4J 4′,6′ ) 2.4 Hz, 1H; inner pyridine H4′), 7.79 (dd, 3J 4′′′,3′′′
) 8.2 Hz, 4J 4′′′,6′′′ ) 2.6 Hz, 1H; bromopyridine H4′′′), 7.77 (dm,
3J 2′′,3′′;6′′,5′′ ) 8.4 Hz, 2H; phenyl (inner) H2′′,6′′), 7.73 (t, 3J 4,3;4,5
(87%) of 22 (mp 275-276 °C) as a hard white solid. H NMR
4
(CF3COOD, 500 MHz, 25 °C): δ (ppm) 9.53 (d, J 6′,4′;6′′′,4′′′
)
3
4
2.1 Hz, 2H; H6′,6′′′), 9.14 (dd, J 4′′′,3′′′ ) 8.4 Hz, J 4′′′,6′′′ ) 2.2
3
3
4
) 7.7 Hz, 1H; methylpyridine H4), 7.68 (dm, J 3′′,2′′;5′′,6′′ ) 8.5
Hz, 1H; H4′′′), 9.09 (dd, J 4′,3′ ) 8.4 Hz, J 4′,6′ ) 2.2 Hz, 1H;
Hz, 2H, phenyl (outer) H3′′,5′′), 7.58 (dd, 3J 3′′′,4′′′ ) 8.2 Hz, 5J 3′′′,6′′′
H4′), 8.91 (t, J 4,3;4,5 ) 8.1 Hz, 1H; phenylpyridine H4), 8.84
3
3
3
) 0.7 Hz, 1H; bromopyridine H3′′′), 7.20 (d, J 5,4 ) 7.6 Hz,
(t, J 4′′′′,3′′′′;4′′′′,5′′′′ ) 8.1 Hz, 1H; methylpyridine H4′′′′), 8.83 (dd,
5
3
1H; methylpyridine H5), 2.66 (s, 3H; CH3). 13C NMR (CDCl3,
125.8 MHz, 25 °C): δ (ppm) 158.1, 155.8, 155.2, 148.4, 147.5,
141.2, 138.0, 137.1, 136.8, 136.2, 135.3 (2 peaks), 135.0, 128.1,
127.9, 127.7, 123.4, 121.2, 118.1, 24.7 (CH3). UV/vis (CHCl3):
λ (nm) (ꢀ, M-1 cm-1) 314 (58 056). EIMS: m/z 401 (M+, 100).
Anal. Calcd for C22H16BrN3: C, 65.68; H, 4.01; N, 10.45.
Found: C, 65.62; H, 3.97; N, 10.24.
3J 3′,4′ ) 8.4 Hz, J 3′,6′ ) 0.5 Hz, 1H: H3′), 8.80 (dd, J 3′′′,4′′′
)
5
3
8.4 Hz, J 3′′′,6′′′ ) 0.4 Hz, 1H; H3′′′), 8.65 (dd, J 3,4 ) 7.9 Hz,
4J 3,5 ) 1.0 Hz, 1H; phenylpyridine H3), 8.61 (d, J 3′′′′,4′′′′ ) 7.9
3
Hz, 1H; methylpyridine H3′′′′), 8.57 (dd, 3J 5,4 ) 8.3 Hz, 4J 5,3
)
1.0 Hz, 1H; phenylpyridine H5), 8.24 (d, 3J 5′′′′,4′′′′ ) 7.8 Hz, 1H;
methylpyridine H5′′′′), 8.17 (s, 4H; central phenyl H2′′,6′′;3′′,5′′),
3
8.06 (dd, J o,m ) 8.4 Hz, 2H; terminal phenyl H-ortho), 7.91
1-[5-(2,2′-Bipyr idyl)]-4-[5-(2-br om opyr idyl)]ben zen e (20)
a n d 1,4-Bis-5-(2,2′-bip yr id yl)ben zen e (21). 5d (0.305 g, 7.82
× 10-4 mol), 18d (0.224 g, 9.26 × 10-4 mol), and Pd(PPh3)4
(0.054 g, 4.67 × 10-5 mol) in 25 mL of toluene were refluxed
at 135 °C for 36 h. After removal of solvent, 25 mL of Et2O
was added and the mixture briefly ultrasonicated, filtered
under vacuum, washed with Et2O, and air-dried. The solid was
then chromatographed on alumina (basic, activity IV), eluting
with CH2Cl2. Unreacted 5d eluted first followed by 20 and
finally 21. 5d was further purified by brief ultrasonication in
Et2O, isolation by suction filtration, and drying under vacuum
to yield 0.043 g of 5d . Pure 20 (0.087 g, 33% based on reacted
5d ) was obtained in a manner identical to that described for
5d , and 21 (0.033 g, 13% based on reacted 5d ) (mp 299-303
°C) after washing with acetone and drying under vacuum.
Microanalytically pure 20 (mp 217-219 °C) was obtained upon
recrystallization from toluene and drying under vacuum at 120
°C/2 × 10-6 mmHg.
(tt, 3J p,m ) 7.5 Hz, 1H; terminal phenyl H-para), 7.83 (t, 3J m,o;m,p
) 7.7 Hz, 2H; terminal phenyl H-meta), 3.17 (s, 3H; CH3). 13
C
NMR (CF3COOD, 125.8 MHz, 25 °C): δ (ppm) 158.8, 157.5,
148.6, 148.3, 144.9, 144.2, 144.1, 143.9, 143.1, 143.0, 142.6,
142.3, 141.7, 136.3, 135.7, 134.7, 130.9, 130.8, 130.2, 129.5 (two
bands), 128.4, 128.3 (two bands), 127.9, 125.8, 125.5, 19.6
(CH3). UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1) 266 (32 301), 329
(99 214). EIMS: m/z 476 (M+, 100). Anal. Calcd for C33H24N4:
C, 83.17; H, 5.08; N, 11.76. Found: C, 83.34; H, 5.00; N, 11.82.
1-[5-(6′-P h en yl-2,2′-bip yr id yl)]-4-[5-(2,2′-bip yr id yl)]ben -
zen e (23). 20 (0.070 g, 1.80 × 10-4 mol), 18a (0.240 g, 7.55 ×
10-4 mol), and Pd(PPh3)4 (0.030 g, 2.60 × 10-5 mol) in 12 mL
of toluene were refluxed at 136 °C for 48 h. After removal of
solvent and treatment with MeOH, the solid was recrystallized
from 5 mL of boiling toluene. Upon cooling, 10 mL of hexane
was added to complete crystallization. The product was
isolated by filtration under vacuum, washed with 1:1 toluene/
hexane, and dried under vacuum to yield 0.060 g (72%) of 23
as cream-colored microcrystals. Microanalytically pure 23 (mp
277-278 °C) was obtained upon further recrystallization from
toluene and drying under vacuum at 120 °C/2 × 10-6mmHg.
1H NMR (CDCl3), 500 MHz, 25 °C): δ (ppm) 9.00 (m, 2H; inner
1
Da ta for 20. H NMR (CDCl3), 500 MHz, 25 °C): δ (ppm)
4
5
8.96 (dd, J 6′,4′ ) 2.4 Hz, J 6′,3′ ) 0.8 Hz, 1H; inner pyridine
3
4
5
H6′), 8.71 (dq, J 6,5 ) 4.8 Hz, J 6,4 ) 1.8 Hz, J 6,3 ) 0.9 Hz,
1H; terminal pyridine H6), 8.65 (dd, 4J 6′′′,4′′′ ) 2.6 Hz, 5J 6′′′,3′′′
0.7 Hz, 1H; bromopyridine H6′′′), 8.51 (dd, 3J 3′,4′ ) 8.2 Hz, 5J 3′,6′
)
3
5
pyridines H6′, H6′′′), 8.75 (dd, J 3′,4′ ) 8.2 Hz, J 3′,6′ ) 0.7 Hz,
3
4
5
3
4
) 0.8 Hz, 1H; H3′), 8.45 (dt, J 3,4 ) 7.9 Hz, J 3,5; J 3,6 ) 1.1
1H; inner pyridine H3′), 8.72 (dq, J 6′′′′,5′′′′ ) 4.8 Hz, J 6′′′′,4′′′′
)
3
4
1.7 Hz, 5J 6′′′′,3′′′′ ) 0.9 Hz, 1H; terminal unsubstituted pyridine
Hz, 1H; terminal pyridine H3), 8.07 (dd, J 4′,3′ ) 8.3 Hz, J 4′,6′
3
3
5
) 2.4 Hz, 1H; inner pyridine H4′), 7.85 (qd, J 4,3 ) 7.9 Hz,
H6′′′′), 8.52 (dd, J 3′′′,4′′′ ) 8.2 Hz, J 3′′′,6′′′ ) 0.6 Hz, 1H; inner
3J 4,5 ) 7.6 Hz, J 4,6 ) 1.8 Hz, 1H; terminal pyridine H4), 7.79
4
3
4
5
pyridine H3′′′), 8.46 (dt, J 3′′′′,4′′′′ ) 7.9 Hz, J 3′′′′,5′′′′; J 3′′′′,6′′′′
)
(dd, 3J 4′′′,3′′′ ) 8.3 Hz, 4J 4′′′,6′′′ ) 2.6 Hz, 1H; bromopyridine H4′′′),
7.78 (d, 3J 2′′,3′′;6′′,5′′ ) 8.6 Hz, 2H; phenyl inner H2′′,6′′), 7.69 (d,
3J 3′′,2′′;5′′,6′′ ) 8.6 Hz, 2H; phenyl outer H3′′,5′′), 7.59 (dd, 3J 3′′′,4′′′
3
0.9 Hz, 1H; terminal unsubstd. pyridine H3′′′′), 8.43 (dd, J 3,4
4
) 7.8 Hz, J 3, ) 0.9 Hz, 1H; terminal phenylpyridine H3),
5
8.18 (d, 3J o,m ) 7.6 Hz, 2H; terminal phenyl H-ortho), 8.10 (m,
5
3
) 8.2 Hz, J 3′′′,6′′′ ) 0.7 Hz, 1H; bromopyridine H3′′′), 7.34 (qd,
2H; inner pyridines H4′, H4′′′), 7.92 (t, J 4,3;4,5 ) 7.8 Hz, 1H;
3J 5,4 ) 7.5 Hz, J 5,6 ) 4.8 Hz, J 5,3 ) 1.2 Hz, 1H; terminal
pyridine H5). 13C NMR (CDCl3, 125.8 MHz, 25 °C): δ (ppm)
155.7, 155.3, 149.3, 148.4, 147.5, 141.2, 137.8, 137.0, 136.8,
136.3, 135.5, 135.3, 135.1, 128.1, 127.9, 127.7, 123.8, 121.1.
UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1): 312 (48 369). EIMS:
m/z 389 (M+, 100). Anal. Calcd for C21H14BrN3: C, 64.96; H,
3.63; N, 10.82. Found: C, 64.94; H, 3.84; N, 10.62.
3
4
3
terminal phenylpyridine H4), 7.86 (td, J 4′′′′,3′′′′;4′′′′,5′′′′ ) 7.7 Hz,
4J 4′′′′,6′′′′ ) 1.8 Hz, 1H; terminal unsubstituted pyridine H4′′′′),
7.82-7.79 (m, 5H; terminal phenylpyridine H5 and central
3
phenyl H2′′,6′′;3′′,5′′), 7.53 (t, J m,o;m,p ) 7.5 Hz, 2H; terminal
phenyl H-meta), 7.46 (tt, J p,m ) 7.3 Hz, 1H; terminal phenyl
3
3
3
4
H-para), 7.34 (qd, J 5′′′′,4′′′′ ) 7.5 Hz, J 5′′′′,6′′′′ ) 4.8 Hz, J 5′′′′,3′′′′
) 1.2 Hz, 1H; terminal unsubstituted pyridine H5′′′′). 13C NMR
(CDCl3, 125.8 MHz, 25 °C): δ (ppm) 156.5, 155.8, 155.5, 155.4,
155.2, 149.3, 147.6, 147.4, 139.3, 137.7, 137.6, 137.4, 137.0,
135.7, 135.13, 135.06, 129.1, 128.7, 127.8, 127.0, 123.8, 121.3,
121.1, 120.4, 119.3. UV/vis (CHCl3): λ (nm) (ꢀ, M-1 cm-1): 267
(22 174), 328 (64 079). FABMS m/z: 463 ([M + H]+, 100). Anal.
Calcd for C32H22N4: C, 83.09; H, 4.79; N, 12.11. Found: C,
83.10; H, 4.66; N, 12.18.
1
Da ta for 21. H NMR (CDCl3), 500 MHz, 25 °C): δ (ppm)
3
8.99 (s, 2H; inner pyridine H6′), 8.72 (m, J 6,5 ) 4.0 Hz, 2H;
3
terminal pyridine H6), 8.52 (d, J 3′,4′ ) 8.2 Hz, 2H; inner
3
pyridine H3′), 8.46 (d, J 3,4 ) 7.9 Hz, 2H; terminal pyridine
H3), 8.09 (dd, 3J 4′,3′ ) 8.2 Hz, 4J 4′,6′ ) 2.3 Hz, 2H; inner pyridine
3
4
H4′), 7.85 (td, J 4,3;4,5 ) 7.7 Hz, J 4,6 ) 1.7 Hz, 2H; terminal
3
pyridine H4), 7.80 (s, 4H; phenyl H2′′,3′′,5′′,6′′), 7.34 (dd, J 5,4
3
) 6.7 Hz, J 5,6 ) 5.1 Hz, 2H; terminal pyridine H5). 13C NMR
(CDCl3, 125.8 MHz, 25 °C): δ (ppm) 155.8, 155.2, 149.3, 147.5,
137.4, 137.0, 135.7, 135.1, 127.8, 127.7, 123.8, 121.1. UV/vis
(CHCl3): λ (nm) (ꢀ, M-1 cm-1) 323 (67 088). EIMS: m/z 386
(M+, 100). Anal. Calcd for C26H18N4: C, 80.81; H, 4.69; N,
14.50. Found: C, 80.54; H, 4.93; N, 14.60.
Ack n ow led gm en t is made to the Colle`ge de France
for financial support, to Professor J .-M. Lehn for labora-
tory facilities, and to Roland Graff for the 1H NMR
COSY, NOESY, and ROESY measurements.
1-[5-(6′-P h en yl-2,2′-bip yr id yl)]4-[5-(6′-m eth yl-2,2′-bip y-
r id yl)]ben zen e (22). 19 (0.077 g, 1.91 × 10-4 mol), 18a (0.228
g, 7.17 × 10-4 mol), and Pd(PPh3)4 (0.026 g, 2.25 × 10-5 mol)
in 12 mL of toluene were refluxed at 135 °C for 48 h. After
removal of solvent and treatment with MeOH, the solid was
washed with MeOH and air-dried. The product was then
recrystallized from 23 mL of boiling toluene to yield 0.079 g
Su p p or tin g In for m a tion Ava ila ble: Full experimental
details and complete product infrared and mass spectral data.
This material is available free of charge via the Internet at
http://pubs/acs/org.
J O990665N