Carborane-functionalized polyaza aromatic ligands: Synthesis, crystal structure and a copper(II) complex

Article abstract of DOI:10.1021/om051058v

A consecutive aromatic nucleophilic substitutions of hydrogen in 1,2,4-triazine 4-oxides and an aza Diels-Alder reaction is a versatile route to carborane-functionalized bi- and terpyridines and their 1,2,4-triazine analogues. The heterocycles facilitate

Full text of DOI:10.1021/om051058v

2972
Organometallics 2006, 25, 2972-2977
Carborane-Functionalized Polyaza Aromatic Ligands: Synthesis,
Crystal Structure, and a Copper(II) Complex
Anton M. Prokhorov,† Dmitry N. Kozhevnikov,*,†,‡ Vladimir L. Rusinov,†
Oleg N. Chupakhin,‡ Ivan V. Glukhov,§ Mikhail Yu. Antipin,§ Olga N. Kazheva,|
Anatolii N. Chekhlov,| and Oleg A. Dyachenko|
Urals State Technical UniVersity, Mira 19, Ekaterinburg 620002, Russia, Institute of Organic Synthesis,
Ural Branch of Russian Academy of Sciences, S. KoValeVsloy 22, Ekaterinburg 620219, Russia, Institute of
Organoelement Compounds, Russian Academy of Sciences, X-ray Crystallography Laboratory, ul. VaViloVa
28, Moscow 119991, Russia, and Institute of Problem of Chemical Physics, Russian Academy of Sciences,
X-ray Crystallography Laboratory, pr. SemenoVa 1, ChernogoloVka 142432, Russia
ReceiVed December 10, 2005
A consecutive aromatic nucleophilic substitutions of hydrogen in 1,2,4-triazine 4-oxides and an aza
Diels-Alder reaction is a versatile route to carborane-functionalized bi- and terpyridines and their 1,2,4-
triazine analogues. The heterocycles facilitate deboronation of the substituted carboranes, and the carborane
moiety has a significant influence on the coordination properties of the ligands as well.
Polypyridines (i.e. 2,2′-bipyridines, 2,2′:6′,2′′-terpyridines,
ridines due to the steric and electronic influence of a carborane
moiety.9 However, one of the most appropriate methods for the
synthesis of C-heteroaryl carboranes (i.e. condensation of
haloheteroarenes with C-copper10 or C-lithium9,11 carboranes)
is limited by the starting materials. In this paper we describe
some of our studies in ligand design and initial studies of
coordination properties of new carborane-functionalized poly-
pyridines.
We chose to use the available 3-pyridyl-1,2,4-triazine 4-oxides6a
as precursors to the cluster-functionalized ligands. The triazine
1 is expected to react with nucleophiles at the 5-site with
concomitant loss of the N-oxygen in the presence of acylating
agents.7
Lithiation of 1-phenyl-1,2-dicarba-closo-dodecaborane gener-
ated 2-lithium-1-phenyl-1,2-dicarba-closo-dodecaborane in situ,
and this was reacted with the 1,2,4-triazine 4-oxide 1 in THF.
Treatment of the reaction mixture with N,N-dimethylcarbamyl
chloride resulted in the formation of 1-(1,2,4-triazin-5-yl)-1,2-
dicarba-closo-dodecaborane (2a) as an air-stable yellow solid
in 56% yield (Scheme 1). The reaction is expected to proceed
by addition of the nucleophile at the 5-site of the 1,2,4-triazine
ring followed by aromatization of the intermediate σ adducts.12
To provide the latter step, an O-acylation of the σ adduct is
usually used to eliminate an acid molecule instead of water.
Only smoothly acylating agents can be used in the reaction
described: dimethylcarbamyl chloride or acetic anhydride (the
former gave better yields). Acetyl chloride has to be avoided
phenanthrolines, and their aza analogues) are undoubtedly
among the most widely used ligands in coordination and
supramolecular chemistry.1 It has been shown in numerous
studies that transition-metal polypyridine complexes have vari-
ous applications: from catalysis2 and photocatalysis3 to analyti-
cal reagents4 and selective extracting agents in the separation
of lanthanides and actinides in the management of nuclear
wastes.5 We have been developing strategies for the synthesis
of functionalized aza aromatic ligands and their metallo
complexes.6 Our approach combines two general features of
the 1,2,4-triazines: (1) a susceptibility to nucleophilic aromatic
substitution reactions7 and (2) the relatively easy transformation
of 1,2,4-triazines to pyridines via an aza Diels-Alder reaction.8
In particular, we decided to obtain carborane-functionalized
ligands of the pyridine and 1,2,4-triazine series, since they are
expected to exhibit properties different from “typical” polypy-
* To whom correspondence should be addressed. Tel/fax: +7 343
3740458. E-mail: dnk@htf.ustu.ru.
† Urals State Technical University.
‡ Institute of Organic Synthesis, Ural Branch of Russian Academy of
Sciences.
§ Institute of Organoelement Compounds, Russian Academy of Sciences.
| Institute of Problem of Chemical Physics, Russian Academy of Sciences.
(1) (a) Lehn, J.-M. Supramolecular Chemistry-Concepts and Perspec-
tiVes; VCH: Weinheim, Germany, 1995. (b) Ward, M. D. Chem. Soc. ReV.
1995, 121. (c) Constable, E. C. Prog. Inorg. Chem. 1994, 42, 67.
(2) Chelucci, G.; Thummel, R. P. Chem. ReV. 2002, 102, 3129.
(3) Ziessel, R. In Photosensitization and Photocatalysis Using Inorganic
and Organic Compounds; Kalyanasundaram, K., Gra¨tzel, M., Eds.; Kluwer
Academic: Dordrecht, The Netherlands, 1993; p 217.
(8) (a) Pabst, G. R.; Pfu¨ller, O. C.; Sauer, J. Tetrahedron 1999, 55, 8045.
(b) Stanforth, S. P.; Tarbit, B.; Watson, M. D. Tetrahedron 2004, 60, 8893.
(c) Kozhevnikov, V. N.; Kozhevnikov, D. N.; Shabunina, O. V.; Rusinov,
V. L.; Chupakhin, O. N. Tetrahedron Lett. 2005, 46, 1791. (d) Branowska,
D.; Rykowski, A.; Wysocki, W. Tetrahedron Lett. 2005, 46, 6223.
(9) (a) Armspach, D.; Constable, E. C.; Housecroft, C. E.; Neuburger,
M.; Zehnder, M. New J. Chem. 1996, 20, 331. (b) Armspach, D.; Constable,
E. C.; Housecroft, C. E.; Neuburger, M.; Zehnder, M. Supramol. Chem.
1996, 7, 97. (c) Armspach, D.; Constable, E. C.; Housecroft, C. E.;
Neuburger, M.; Zehnder, M. J. Organomet. Chem. 1998, 550, 193.
(10) Coult, R.; Fox, M. A.; Gill, W. R.; Herbertson, P. L.; MacBride, J.
A. H.; Wade, K. J. Organomet. Chem. 1993, 462, 19.
(4) Croot, P. L.; Hunter, K. A. Anal. Chim. Acta 2000, 406, 289-295.
(5) Kolarik, Z.; Mullich, U.; Gassner, F. SolVent Extr. Ion Exch. 1999,
17, 23.
(6) (a) Kozhevnikov, V. N.; Kozhevnikov, D. N.; Nikitina, T. V.;
Rusinov, V. L.; Chupakhin, O. N.; Zabel, M.; Koenig., B. J. Org. Chem.
2003, 68, 2882. (b) Kozhevnikov, V. N.; Kozhevnikov, D. N.; Rusinov, V.
L.; Chupakhin, O. N.; Koenig, B. Synthesis 2003, 2400. (c) Kozhevnikov,
V. N.; Kozhevnikov, D. N.; Shabunina, O. V.; Rusinov, V. L.; Chupakhin,
O. N. Tetrahedron Lett. 2005, 46, 1791. (d) Kozhevnikov, V. N.;
Kozhevnikov, D. N.; Prokhorov, A. M.; Ustinova, M. M.; Rusinov, V. L.;
Chupakhin, O. N. Tetrahedron Lett. 2006, 47, 869.
(7) (a) Neunhoeffer, H. In ComprehensiVe Heterocyclic Chemistry II;
Katrizky, A. R., Rees, C. W., Scriven, E. F. V., Eds.; Pergamon Press:
Oxford, U.K., 1996; Vol. 6, p 50. (b) Kozhevnikov, D. N.; Rusinov, V. L.;
Chupakhin, O. N. AdV. Heterocycl. Chem. 2002, 82, 261.
(11) Hawthorne, M. F.; Maderma, A. Chem. ReV. 1999, 99, 3421.
(12) Chupakhin, O. N.; Prokhorov, A. M.; Kozhevnikov, D. N.; Rusinov,
V. L.; Glukhov, I. A.; Starikova, Z. A.; Olshevskaya, V. A.; Kalinin, V.
N.; Antipin, M. Yu. Russ. Chem. Bull. (Engl. Transl.) 2004, 53, 1223.
10.1021/om051058v CCC: $33.50 © 2006 American Chemical Society
Publication on Web 05/13/2006

Carborane-Functionalized Polyaza Aromatic Ligands
Organometallics, Vol. 25, No. 12, 2006 2973
Scheme 1
because it induces 1,2,4-triazine ring contraction to give
are almost perpendicular to the C-C bond of the carborane (the
torsion angles are 78.92 and 89.32°, respectively).
carboranyltriazolines.12 The 1H and 13C NMR spectra of 2a and
1
elemental analysis confirmed the proposed structure. The H
As an additional confirmation, we carried out the straight-
forward synthesis of 2a via the well-studied reaction of
nucleophilic substitution of the cyano group in 5-cyano-1,2,4-
triazines with carbanions.14 All spectroscopic data for the
product of the reaction of 1-lithio-2-phenyl-1,2-dicarba-closo-
dodecaborane with 5-cyano-6-phenyl-3-(pyridyl-2)-1,2,4-triazine
(3) were identical with those of triazinylcarborane 2a.
The reaction of triazine 1 with lithiated 1-methyl-1,2-dicarba-
closo-dodecaborane under the conditions mentioned above
yielded the methylcarboranyltriazine 2b (Scheme 1). Spectro-
scopic data and elemental analysis were consistent with the
formulation of 2b.
NMR spectrum of 2a showed typical signals for the two phenyls
and the 2-pyridyl moiety and a broad multiplet for the B-H
protons as well. The absence of a low-field singlet indicated
the H-5 substitution. Elemental analysis confirmed loss of the
N-oxygen atom. Both the 11B and 13C NMR spectra of 2a were
in accord with a 1,2-disubstituted closo-dodecaborane. In
particular, the 11B NMR spectrum exhibited two signals indica-
tive of the most deshielded atoms, B-3 and B-6 (δ -3.5 and
-1.4), and broad signal for the remaining boron atoms. The
13C NMR spectrum of 2a was fully consistent with the presence
of two phenyl groups, pyridyl, 1,2,4-triazine, and closo-
carborane.
We found that the triazinylcarborane 2a very easily underwent
a decapping process in polar solvents in the presence of water
under neutral conditions. The zwitterionic 1,2,4-triazinyl-nido-
carborane 4 was obtained in quantitative yield at room temper-
ature by dissolving 2a in DMSO containing 5-10% of water.
Single crystals of compound 2a suitable for X-ray diffraction
were grown from acetonitrile. The molecular structure of 2a is
shown in Figure 1, and selected bond distances are given in
the figure caption. The structural parameters for the ordered
closo-dodecaborane cage are unexceptional.13 The pyridyltri-
azine fragment is approximately planar, while the torsion angle
between the 1,2,4-triazine ring and the aromatic substituent is
56.28°. 1,2,4-Triazine ring and phenyl binding to the cluster
1
The structure of 4 was defined by H and 11B NMR spectros-
1
copy. The H NMR spectrum of 4 showed signals typical of
phenyl groups and 2-pyridyl. The most diagnostic feature is the
observation of a bridging hydrogen (highest field broad signal,
δ -2.75) and an acid proton (lowest field broad signal, δ 10.2
ppm) of the deboronated nido-carborane. All signals of the 11
B
NMR spectrum of 4 are shifted to higher field (highest field
resonance δ -33.6) in comparison with 2a, which provides
additional evidence for the formation of an anionic nido cluster.9
Single-crystal X-ray diffraction studies of compound 4
revealed the molecular structure shown in Figure 2. The bridging
hydrogen atom binds to boron atoms next to the carbon bound
to phenyl. The geometry of the phenylpyridyltriazine moiety
of 4 is very similar to that of 2a, except for N-protonation of
the pyridyl group. The 1,2,4-triazine ring is perpendicular to,
while phenyl is nearly coplanar with, the open face of the cluster.
A similar zwitterion formation was found to occur in the
deboronation of terpyridylcarborane.9 However, we were lucky
1
to observe the decapping process liVe with H NMR spectros-
copy. Thus, the appearance and rise of three new signals in the
1H NMR spectra of 2a solution in wet DMSO-d6 (1% of water)
were clearly observed in 5 min after dissolving 2a at room
Figure 1. Molecular structure of 2a. Hydrogens are omitted.
Selected bond lengths (Å): C(1)-C(13) ) 1.522(3), C(1)-C(2)
) 1.725(3), C(1)-B(3) ) 1.724(3), C(1)-B(4) ) 1.701(4), C(1)-
B(5) ) 1.706(3), C(1)-B(6) ) 1.737(3), C(2)-B(3) ) 1.733(4),
C(2)-B(6) ) 1.733(3), C(2)-B(7) ) 1.714(3), C(2)-B(11) )
1.707(3), C(2)-C(31) ) 1.498(3). Selected torsion angles (deg):
C(2)-C(1)-C(13)-N(14) ) 97.4(2), C(1)-C(2)-C(31)-C(36) )
89.3(2).
(13) Beaudet, R. A. In AdVances in Boron and the Boranes; Liebman,
J. F.., Greenberg, A., Williams, R. E., Eds.; VCH: New York, 1988; p
417.
(14) Konno, S.; Ohba, S.; Agata, M.; Aizawa, V.; Sagi, M.; Yamanaka,
H. Heterocycles 1987, 26, 3259.

2974 Organometallics, Vol. 25, No. 12, 2006
ProkhoroV et al.
Figure 3. Molecular structure of [Cu2(2b)2Cl4]. Selected bond
lengths (Å): N(2)-Cu ) 2.029(2), N(7)-Cu ) 2.054(3), Cu-Cl-
(1) ) 2.2523(11), Cu-Cl(2) ) 3.4131(14),
Figure 2. Molecular structure of 4. Hydrogens are omitted.
Selected bond lengths (Å): C(1)-C(12) ) 1.513(4), C(1)-C(2)
) 1.596(4), C(1)-B(5) ) 1.655(4), C(2)-B(3) ) 1.614(5), C(2)-
C(18) ) 1.497(4). Selected torsion angles (deg): C(1)-C(2)-
C(18)-C(23) ) 58.4(4), C(2)-C(1)-C(12)-C(17) ) 35.6(4).
Scheme 2
temperature. Full conversion of 2a to 4 under the conditions
discussed occurred in 30 h. Resonances for a bridging hydrogen
(highest field broad signal, δ -2.75) and an acid proton (lowest
field broad signal, δ 10.2 ppm) indicated formation of the
zwitterion 4. The third signal (sharp singlet, δ 4.61) was a
puzzle; it could not be explained in terms of structures 2 and 4.
However, the full equation of the decapping reaction shows that
formation of the zwitterion 4 in the presence of water is
accompanied by elaboration of boric acid and molecular
hydrogen (Scheme 2). The resonance of the latter could be the
signal observed. However, we were surprised that it was not
easy to find literature data on the chemical shift for such a simple
molecule. Only in a recent issue of J. Am. Chem. Soc. did we
find a resonance for o-hydrogen (o-H2) in polar solvents
observed around δ 4.6.15 To remove all doubt, we bubbled
gaseous hydrogen through DMSO-d6 in an NMR tube and
observed the same signal (δ 4.61).
Figure 4. Crystal structure of [Cu2(2b)2Cl4].
Increasing the water concentration significantly increases the
rate of the decapping reaction. Full conversion of 2a to 4
occurred in 3-4 h at room temperature in a DMSO-water
mixture (5:1).
Figure 5. Chains of [Cu2(2b)2Cl4] along the a axis.
The triazines 2 are potential N,N-chelating ligands; nitrogen
atoms of the 1,2,4-triazine and pyridine moieties can act as donor
atoms in transition-metal coordination. However, the N-4 atom
of the 1,2,4-triazine is obviously hindered by the bulk carborane
moiety. Thus, reaction of 2b with copper(II) chloride resulted
in the complex [Cu2(2b)2Cl4], where N-2 but not N-4 is
coordinated to the metal. Single-crystal X-ray diffraction studies
of the complex revealed the molecular structure shown in Figure
3. Complex [Cu2(2b)2Cl4] is a dinuclear centrosymmetric dimer.
Each Cu atom is chelated by bidentate 2b. In addition, two
bridging and one exocyclic chloride anion complete the five-
coordinated square-pyramidal structure of each copper(II) center.
In the crystal state the complex [Cu2(2b)2Cl4] forms chains along
the a axis due to intermolecular interactions Cu‚‚‚Cl(2*) of
length 3.413(1) Å, less than the sum of the van der Waals radii
of Cu and Cl (3.7 Å) (Figures 4 and 5). The structure of the
ligand 2b in the complex is very similar to that of 2a.
The electron-withdrawing closo-carborane moiety had to
facilitate transformation of the 1,2,4-triazine ring to pyridine
via an inverse electron-accepting aza Diels-Alder reaction.
Indeed, refluxing the triazines 2a,b with 2,5-norbornadiene in
toluene yielded the 6-(closo-carboranyl)-2,2′-bipyridines 5a,b
1
(Scheme 3). The structures of the latter were defined by H,
13C, and 11B NMR spectroscopy. The most indicative feature
is the observation of H-4 and H-3 protons of the new pyridine
(15) Matsumoto, M.; Espenson, J. H. J. Am. Chem. Soc. 2005, 127,
11447.

Carborane-Functionalized Polyaza Aromatic Ligands
Organometallics, Vol. 25, No. 12, 2006 2975
Scheme 3
of view, the rates of the decapping of both compounds have to
be approximately equal. Moreover, taking into consideration
that pyridine is more basic than 1,2,4-triazine, the easiest
deboronation can be expected for carboranylbipyridine 5a, but
experimental data do not confirm this consideration. On the other
hand, a significant difference in the electron-withdrawing
properties of these heterocyclic systems is a more plausible
argument. It is known16 that introduction of an electron-
withdrawing substituent renders the carborane cage susceptible
to removal of a boron vertex. The influence of the heterocycle
attached to the carborane may be directly quantified by a
comparison of the carborane carbon C-1′ resonances in com-
pounds 2a and 5a. In the triazine 2a C-1′ is observed at δ 86.6,
whereas in the pyridine 5a C-1′ is observed at δ 69.5. This
indicates a stronger deshielding effect of the more π-deficient
1,2,4-triazine in comparison with pyridine. Obviously, a nu-
cleophilic attack on the carborane binding to 1,2,4-triazine has
to be more facilitated. Indeed, the decapping of the triazine 2a
proceeds in a DMSO-water mixture (5:1) at room temperature
in 4 h, while the same reaction of the pyridine 5a was observed
only after 24 h of heating at 100 °C.
ring as two doublets at δ 7.5 and 8.3 (J ) 8.0 Hz) and two
additional signals in the 13C NMR spectra of 5a,b in comparison
with those of 2a,b. Transformation of the triazine ring to
pyridine did not actually change the 11B NMR spectra.
The carboranylbipyridine 5a underwent a deboronation reac-
tion similar to that of carboranyltriazine 2a, but at a significantly
decreased rate: just prolonged heating (not less than 24 h) of
5a at 90 °C in DMSO/water (5:1) gave the nido-carboranyl-
2,2′-bipyridine 6 (Scheme 3). The observation of the 11B
resonance of 6 shifting to higher field (highest field resonance,
δ -33.5) in comparison with 5a provided evidence for the
formation of an anionic nido cluster. Moreover, the 11B NMR
spectrum of 6 became more complicated: for 5a, chemical shifts
of all boron atoms except B-3 and B-6 are very close and are
represented by one broad singlet, whereas for 6, the shifts are
more different because of deboronation and carborane cage
symmetry breakdown.9 X-ray diffraction studies revealed the
structure of the zwitterion 6, shown in Figure 6. The molecular
structure of bipyridine 6 is very similar to that of triazine 4.
The approximately planar bipyridinium cation adopts a cis
conformation of the two pyridine rings about the interannular
bond. Molecules of 6 form stacks with alternation of the anionic
carborane moiety of one molecule and the cationic bipyridine
residue of the next molecule.
The suggested approach is appropriate for the synthesis of
tricyclic azines bearing two carborane cages. The reaction of
the bis(1,2,4-triazinyl)pyridine N,N′-dioxide 7 with o-carboranes
under the conditions mentioned above resulted in the bis[5-
carboranyl-1,2,4-triazinyl]pyridines 8a,b. The dicarboranyltri-
azine 8b was transformed to the 6,6′′-bis(2-methyl-o-carboran-
1-yl)-2,2′:6′,2′′-terpyridine 9 through the aza Diels-Alder
reaction of 8 with 2,5-norbornadiene in a way similar to that
for the monocarboranyltriazines 2 (Scheme 4). Compounds 8a,b
1
and 9 exhibited the expected spectroscopic properties. The H
NMR spectra of 8a,b and 9 are in accord with the presence of
two carborane moieties in the molecules. The 1H NMR spectrum
of 9 showed signals typical for the terpyridine moiety, indicating
that both triazine rings transformed to pyridine rings via the
reaction with norbornadiene. Elemental analysis confirmed the
proposed structures.
Conclusions
The deboronation reactions of 2a and 5a can be considered
as a process facilitated by the basicity of pyridine or triazine
groups. The heterocycles can serve as intramolecular bases,
generating hydroxides as deboronating agents. From this point
In conclusion, we have shown that carboranyl-functionalized
aza aromatic ligands may be obtained using a consecutive
nucleophilic aromatic substitution and aza Diels-Alder reaction.
The method is limited by aryl substituents in 1,2,4-triazine/
pyridine rings because of limitations of the method for the
synthesis of the starting 6-(hetero)aryl-3-pyridyl-1,2,4-triazine
4-oxides.6a Carborane-functionalized pyridyl-1,2,4-triazines are
interesting ligands for transition metals due to the electronic
and steric influence of the carborane cage. The easy deborona-
tion reaction extends this approach to new compounds.
Experimental Section
General Remarks. The manipulations were performed under
an atmosphere of dry argon using vacuum-line and standard Schlenk
techniques. All reagents were obtained from commercial suppliers
and used without further purification. Solvents were dried by
standard methods and distilled under nitrogen before use. The
starting compounds 1, 3, and 7 were prepared according to methods
reported in the literature.6a The C, H, and N analyses were carried
out with a Perkin-Elmer PE 2400 microanalyzer. Mass spectra were
determined with a Varian CH-5 mass spectrometer. NMR spectra
were recorded on a Bruker DPX-300 instrument at 300 MHz (1H),
Figure 6. Molecular structure of 6. Hydrogens are omitted.
Selected bond lengths (Å): C(1)-C(12) ) 1.503(4), C(1)-C(2)
) 1.579(4), C(2)-C(18) ) 1.486(4), C(1)-B(5) ) 1.623(5), C(2)-
B(3) ) 1.614(4). Selected torsion angles (deg): C(1)-C(2)-
C(18)-C(23) ) 61.5(4), C(2)-C(1)-C(12)-C(17) ) 46.2(4).
(16) Schaeck, J. J.; Kahl, S. B. Inorg. Chem. 1999, 38, 204.

2976 Organometallics, Vol. 25, No. 12, 2006
ProkhoroV et al.
Scheme 4
75.4 MHz (13C), or 128.4 MHz (11B), using SiMe4 (1H and 13C
NMR) and BF3‚Et2O (11B NMR) as standards.
mL) was added, and the resulting solution was kept at room
temperature for 4 h. Next, 10 mL of water was added, and the
yellow precipitate was filtered off and recrystallized from aceto-
Preparation of 1-(3,6-Disubstituted 1,2,4-triazin-5-yl)-1,2-
dicarba-closo-dodecaboranes (2). tert-Butyllithium (1.6 M pentane
solution, 2.5 mL) was added to a solution of the carborane (4 mmol)
in 20 mL of THF at room temperature. The resulting solution of
carboranyllithium was added dropwise to a suspension of the 1,2,4-
triazine 4-oxide 1 (1.0 g, 4 mmol) in THF (10 mL) at -50 °C, and
the mixture was stirred for 20 min. When the mixture had become
clear, dimethylcarbamyl chloride (0.37 mL, 4 mmol) was added.
The solvent was removed, and the residue was treated with toluene
(20 mL). The toluene solution was separated from the solids, and
the solvent was removed. The residue was treated with acetonitrile
(1 mL), and pale yellow crystals were filtered off. All of the
products were recrystallized from acetonitrile.
1-[6-Phenyl-3-(2-pyridyl)-1,2,4-triazin-5-yl]-2-phenyl-1,2-di-
carba-closo-dodecaborane (2a). Yield: 1.03 g, 56%. Mp: 227
°C. 1H NMR (CDCl3; δ): 1.20-3.20 (m, 10H, B-H), 7.10-7.30
(m, 7H), 7.40-7.60 (m, 4H), 7.97 (m, 1H, Py), 8.42 (m, 1H, Py),
8.92 (m, 1H, Py). 13C NMR (CDCl3; δ): 81.6 (carborane C-2′),
86.6 (carborane C-1′), 124.4 (Py), 126.1 (Py), 128.3, 128.5, 129.6,
129.9, 130.4, 130.5, 130.8, 134.7, 137.3 (Py), 145.0, 150.8 (Py),
151.3 (Py), 158.1, 159.00. 11B{1H} NMR (CDCl3): -10.3 (8B),
-3.5 (1B), -1.4 (1B). Anal. Calcd for C22H24B10N4: C, 58.39; H,
5.35; N, 12.38. Found: C, 58.33; H, 5.37; N, 12.26.
1
nitrile. Yield: 380 mg, 85%. Mp: >300 °C dec. H NMR (δ):
-2.85 (br s, 1H, carborane bridge H), 0.20-3.00 (m, 9H, B-H),
6.47-6.91 (m, 5H, Ph), 7.30-7.49 (m, 5H, Ph), 8.05 (m, 1H, Py),
8.59 (m, 1H, Py), 8.74 (m, 1H, Py), 8.92 (m, 1H, Py), 10.21 (br s,
1H). 11B{1H} NMR (CDCl3; δ): -33.6 (2B), -31.6 (1B), -21.8
(2B), -11.8 (2B), -7.4 (1B), -2.4 (1B). Anal. Calcd for
C22H25B9N4‚CH3CN: C, 59.58; H, 5.83; N, 14.48. Found: C, 59.49;
H, 5.81; N, 14.60. MS (EI-MS): m/z 442 [M+].
Preparation of Carboranylbipyridines 5a,b. The carboranyl-
triazines 2a,b (1 mmol) and 2,5-norbornadiene (0.54 mL, 5 mmol)
were dissolved in toluene (20 mL) and heated at reflux for 5 h.
The solvent was removed under reduced pressure, the residue was
treated with acetonitrile, and the resulting solids were filtered off.
1-(5-Phenyl-2,2′-bipyridin-6-yl)-2-phenyl-1,2-dicarba-closo-
dodecaborane (5a). Yield: 410 mg, 90%. Mp: 183 °C. 1H NMR
(δ): 1.20-3.50 (m, 10H, B-H), 6.91 (m, 2H), 7.18-7.38 (m, 5H),
7.41-7.52 (m, 4H), 7.55 (d, 2H, J ) 8.0 Hz), 8.08 (m, 1H, Py),
8.27 (d, 1H, J ) 8.0 Hz), 8.33 (m, 1H, Py), 8.69 (m, 1H, Py). 13
C
NMR (CDCl3; δ): 47.4 (carborane C2′), 69.5 (carborane C1′),
122.3, 123.1, 123.6, 123.9, 124.0, 124.6, 125.3, 128.2, 128.6, 129.2,
157.1, 160.6, 164.0. 11B{1H} NMR (CDCl3): -10.4 (8B), -3.5
(1B), -1.4 (1B). Anal. Calcd for C24H26B10N2: C, 63.97; H, 5.82;
N, 6.22. Found: C, 63.83; H, 5.87; N, 6.26.
1-(5-Phenyl-2,2′-bipyridin-6-yl)-2-methyl-1,2-dicarba-closo-
dodecaborane (5b). Yield: 398 mg, 90%. Mp: >300 °C. 1H NMR
(DMSO-d6; δ): 1.88 (s, 3H, CH3), 1.20-3.20 (m, 10H, B-H),
7.3-7.5 (m, 6H), 7.77 (d, 1H, J ) 8 Hz), 8.03 (m, 1H, H-4′), 8.38
(m, 1H, H-3′), 8.50 (d, 1H, J ) 8 Hz), 8.72 (m, 1H, H-6′). 13C
NMR (CDCl3; δ): 47.4 (carborane C2′), 69.5 (carborane C1′),
122.3, 123.1, 123.6, 123.9, 124.0, 124.6, 125.3, 128.2, 128.6, 129.2,
157.1, 160.6, 164.0. 11B{1H} NMR (CDCl3; δ): -10.05 (8B),
-3.59 (1B), -1.39 (1B). Anal. Calcd for C19H24B10N2: C, 58.74;
H, 6.23; N, 7.21. Found: C, 58.73; H, 6.27; N, 7.33.
Preparation of 1-(5-Phenyl-2,2′-bipyridin-6-yl)-2-phenyl-1,2-
dicarba-nido-undecaborane (6). The bipyridylcarborane 5a (450
mg, 1 mmol) was dissolved in 5 mL of DMSO; then 1 mL of water
was added, and the resulting solution was kept at 90 °C for 24 h.
Next, 10 mL of water was added, and the precipitate was filtered
off and recrystallized from acetonitrile. Yield: 380 mg, 86%. Mp:
> 300 °C dec. 1H NMR (δ): -2.75 (br s, 1H), 0.00-3.00 (m, 9H,
B-H), 6.65-6.90 (m, 5H, Ph), 6.97 (m, 2H), 7.20-7.35 (m, 3H),
7.53 (d, 1H, J ) 8.0 Hz, H-4), 7.72 (m, 1H, H-5′), 8.22 (d, 1H, J
) 8.0 Hz, H-3), 8.29 (m, 1H, H-4′), 8.65 (d, 1H, H-3′), 8.82 (m,
1H, H-6′), 11.00 (br s, 1H). 11B{1H} NMR (CDCl3): -33.52 (2B),
1-[6-Phenyl-3-(2-pyridyl)-1,2,4-triazine-5-yl]-2-methyl-1,2-di-
carba-closo-dodecaborane (2b). Yield: 900 mg, 48%. Mp: 183
1
°C. H NMR (CDCl3; δ): 1.86 (s, 3?, CH3), 1.20-3.20 (m, 10H,
B-H), 7.46 (m, 2H), 7.50-7.65 (m, 4H), 7.98 (m, 1H), 8.58 (m,
1H), 8.95 (m, 1H). Anal. Calcd for C17H22B10N4: C, 52.29; H, 5.68;
N, 14.35. Found: C, 52.33; H, 5.48; N, 14.36.
Reaction of 5-Cyano-1,2,4-triazine (3) with Carborane. tert-
Butyllithium (1.6 M pentane solution, 2.5 mL) was added to a
solution of the phenylcarborane (880 mg, 4 mmol) in 20 mL of
THF at room temperature. The resulting solution of carboranyl-
lithium was added dropwise to a solution of the cyanotriazine 3
(1036 mg, 4 mmol) in THF (10 mL) at -50 °C; the mixture was
stirred for 25 min, and acetic acid (0.24 mL, 4 mmol) was added.
The solvent was removed, and the residue was treated with toluene
(20 mL). The toluene solution was separated from the solids, and
the solvent was removed. The residue was treated with acetonitrile
(1 mL), and pale yellow crystals were filtered off and recrystallized
from acetonitrile to give the carboranyltriazine 2a. Yield: 864 mg,
47%.
1-[6-Phenyl-3-(2-pyridyl)-1,2,4-triazin-5-yl]-2-phenyl-1,2-di-
carba-nido-undecaborane (4). The triazinyl-closo-carborane 2a
(452 mg, 1 mmol) was dissolved in DMSO (5 mL); then water (1

Carborane-Functionalized Polyaza Aromatic Ligands
Organometallics, Vol. 25, No. 12, 2006 2977
Table 1. Crystal Data and Structure Refinement Details for 2a, 4, 6, and [Cu2(2b)2Cl4]
2a
4
6
[Cu2(2b)2Cl4]
chem formula
fw
C22H24B10N4
452.55
120(2)
0.710 73
tetragonal
P43
11.231(1)
11.231(1)
19.104(2)
90
90
90
2409.8(5)
4
C24H28B9N5
483.80
120(2)
0.710 73
monoclinic
P21/n
10.885(3)
17.343(6)
14.540(5)
90
105.938(10)
90
2639.5(2)
4
1.217
C24H27B9N2
440.77
120(2)
0.710 73
monoclinic
P21/c
10.574(2)
15.120(2)
14.707(2)
90
96.781(4)
90
2335.0(7)
4
1.254
C34H44B20Cl4Cu2N8
1049.85
293
0.710 73
triclinic
P1h
T, K
wavelength, Å
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
7.341(2)
12.045(2)
14.775(3)
84.33(2)
76.13(2)
79.00(2)
1243.1(5)
1
Z
d
calcd (g cm-3
)
1.247
6.8
1.40
µ (mm-1
F(000)
)
6.8
1008
12 971
4926
384
6.7
920
12 163
4510
360
1.108
936
530
no. of rflns collected
no. of indep rflns
no. of params
R (I > 2σ(I))
R1
9659
3467
4609
3173
365
367
0.0487
0.0940
0.0487
0.0940
0.0629
0.0995
0.035
0.070
wR2
-31.94 (1B), -21.72 (2B), -12.60 (2B), -8.77 (1B), -2.76 (1B).
Anal. Calcd for C24H27B9N2 (440.78): C, 65.40; H, 6.17; N, 6.36.
Found: C, 65.49; H, 6.11; N, 6.49. MS (EI-MS): m/z 440 [M+].
2,6-Bis[6-phenyl-5-(2-phenyl-1,2-dicarba-closo-dodecaboran-
1-yl)-1,2,4-triazin-3-yl]pyridine (8a). tert-Butyllithium (1.6 M
pentane solution. 2.5 mL, 4 mmol) was added to a solution of
phenylcarborane (880 mg, 4 mmol) in 20 mL of THF at room
temperature. The resulting solution of carboranyllithium was added
dropwise to a suspension of the 1,2,4-triazine 4-oxide 7 (842 mg,
2 mmol) in THF (10 mL) at -50 °C, and the mixture was stirred
for 20 min. When the mixture had become clear, dimethylcarbamyl
chloride (0.37 mL, 4 mmol) was added. The solvent was removed,
and the residue was treated with toluene (30 mL). The toluene
solution was separated from the solids, and the solvent was
removed. The residue was treated with acetonitrile (1 mL), and
pale yellow crystals were filtered off and recrystallized from
acetonitrile. Yield: 332 mg, 20%. Mp: 262 °C. 1H NMR (CDCl3;
δ): 1.20-3.20 (m, 20H, B-H), 7.13-7.65 (m, 20H, Ph), 8.35 (t,
1H, J ) 8.0 Hz, Py), 8.62 (d, 2H, J ) 8.0 Hz, Py). Anal. Calcd for
C39H43B20N7: C, 56.71; H, 5.25; N, 11.87. Found: C, 56.83; H,
5.39; N, 11.96.
2,6-Bis[5-(2-methyl-1,2-dicarba-closo-dodecaboran-1-yl)-6-
phenyl-1,2,4-triazin-3-yl]pyridine (8b). tert-Butyllithium (1.6 M
pentane solution, 5 mL, 8 mmol) was added to a solution of
methylcarborane (1264 mg, 8 mmol) in 30 mL of THF at room
temperature. The resulting solution of carboranyllithium was added
dropwise to a suspension of the 1,2,4-triazine 4-oxide 7 (1684 mg,
4 mmol) in THF (20 mL) at -50 °C, and the mixture was stirred
for 20 min. When the mixture became clear, dimethylcarbamyl
chloride (0.74 mL, 8 mmol) was added. The solvent was removed,
and the residue was treated with toluene (30 mL). The toluene
solution was separated from the solids, and the solvent was
removed. The residue was treated with acetonitrile (1 mL), and
pale yellow crystals were filtered off and recrystallized from
acetonitrile. Yield: 1.48 g, 53%. Mp: >300 °C. 1H NMR (CDCl3;
δ): 1.93 (s, 6H, carborane CH3), 1.20-3.20 (m, 20H, B-H), 7.49-
7.65 (m, 10H, Ph), 8.29 (t, 1H, J ) 7.9 Hz, Py), 8.85 (d, 2H, J )
7.9 Hz, Py). Anal. Calcd for C29H39B20N7: C, 49.62; H, 5.60; N,
13.97. Found: C, 49.46; H, 5.76; N, 13.82.
δ): 1.20-3.20 (m, 20H, B-H), 1.82 (s, 6H), 7.25 (m, 4H), 7.47
(m, 6H), 7.69 (d, 2H, J ) 7.8 Hz), 8.14 (t, 1H, J ) 8.0 Hz), 8.60
(d, 2H, J ) 7.8 Hz), 8.64 (d, 2H, J ) 8.0 Hz). Anal. Calcd for
C33H43B20N3: C, 56.79; H, 6.21; N, 6.02. Found: C, 56.70; H,
6.37; N, 6.16.
Complex [Cu2(2b)2Cl4]. A solution of CuCl2‚2H2O (34 mg, 0.20
mmol) in acetonitrile (20 mL) was added to a solution of the ligand
(78 mg, 0.20 mmol) in acetonitrile (30 mL). The mixture was slowly
concentrated over a few days to about 20 mL. Dark green crystals
(50 mg, 47%) were filtered off. Anal. Calcd for C34H44B20Cl4-
Cu2N8: C, 38.90; H, 4.22; N, 10.67. Found: C, 39.06; H, 4.35; N,
10.91.
X-ray Structure Determinations of 2a, 4, 6, and [Cu2(2b)2Cl4].
Crystals suitable for X-ray diffraction analysis were obtained by
slow solvent (MeCN) evaporation from saturated solutions of 2a,
4, 6, and [Cu2(2b)2Cl4] in acetonitrile. Data collection, crystal, and
refinement parameters are collected in Table 1. Diffraction data
for 2a, 4, and 6 were recorded on a Bruker Smart 1000 diffracto-
meter and for complex [Cu2(2b)2Cl4] on an Enraf-Nonius CAD-4
diffractometer (in all cases ω/2θ scans, Mo KR radiation). The
structures were solved by direct methods. Isotropic least-squares
refinement on F2 was performed. During the final stages of the
refinements, all positional parameters and the anisotropic temper-
ature factors of all non-H atoms were refined. The H atoms were
geometrically placed, and their coordinates were refined riding on
their parent atoms with common isotropic thermal parameters. All
calculations were performed using SHELXTL 5.1 (for 2a, 4, and
6) and SHELXL97 (for the complex [Cu2(2b)2Cl4]).17
Acknowledgment. This work was supported by the Russian
Foundation for Basic Researches (Grant Nos. 05-03-32134 and
06-03-33123). We thank V. N. Kalinin for supplying carboranes.
Supporting Information Available: Crystallographic data for
the structures of 2a, 4, 6 and the complex [Cu2(2b)2Cl4] as CIF
files. This material is available free of charge via the Internet at
http://pubs.acs.org. These data have also been deposited with the
Cambridge Crystallographic Data Center as Supplementary Nos.
CCDC 210343-210345 and 284092. Copies of the data can be
obtained free of charge on application to the CCDC (e-mail:
deposit@ccdc.cam.ac.uk).
Preparation of 6,6′′-Bis(2-methyl-1,2-dicarba-closo-dodecabo-
ran-1-yl)-5,5′′-diphenyl-2,2′:6′,2′′-terpyridine (9). The carbora-
nyltriazine 8b (702 mg, 1 mmol) and 2,5-norbornadiene (1.08 mL,
10 mmol) were dissolved in toluene (30 mL) and heated to reflux
over 6 h. The solvent was removed under reduced pressure, the
residue was treated with acetonitrile, and the resulting solids were
filtered off. Yield: 630 mg, 91%. Mp: >300 °C. 1H NMR (CDCl3;
OM051058V
(17) (a) Sheldrick, G. M. SHELXTL 5.1; University of Go¨ttingen,
Go¨ttingen, Germany, 1998. (b) Sheldrick, G. M. SHELXL-97; University
of Go¨ttingen, Go¨ttingen, Germany, 1997.