Building functionality into 4′-hydrazone derivatives of 2,2′:6′,2″-terpyridine

Article abstract of DOI:10.1002/hlca.200900132

The syntheses of the five 2,2′:6′,2″-terpyridine (tpy) ligands 5-9 functionalized in the 4′-position with a hydrazone substituent RR′C=N-NH (R=R′=Me; R=H, R′=4-BrC₆H₄ , 4-O₂NC₆H₄, 4-MeOC₆H<

Full text of DOI:10.1002/hlca.200900132

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Helvetica Chimica Acta – Vol. 92 (2009)
Building Functionality into 4’-Hydrazone Derivatives of
2,2’:6’,2’’-Terpyridine
by Jonathon E. Beves, Edwin C. Constable*, Catherine E. Housecroft*, Markus Neuburger,
Silvia Schaffner, and Jennifer A. Zampese
Department of Chemistry, University of Basel, Spitalstrasse 51, CH-4056 Basel
(phone: þ 41-61-2671008; fax: þ 41-61-2671018; e-mail: Catherine.Housecroft@unibas.ch)
This article is dedicated to our friend and colleague Jean-Claude Bꢀnzli on the occasion of his
65th birthday
The syntheses of the five 2,2’:6’,2’’-terpyridine (tpy) ligands 5 – 9 functionalized in the 4’-position
with a hydrazone substituent RR’C¼NꢀNH (R ¼ R’ ¼ Me; R ¼ H, R’ ¼ 4-BrC6H4, 4-O2NC6H4, 4-
MeOC6H4, or 3,5-(MeO)2C6H3) are described. Protonation of the tpy domain of the ligands is facile.
Solution behaviour has been studied by NMR and electronic spectroscopies. Representative structural
data are presented for neutral and monoprotonated ligands, and illustrate that H-bonding involving the
formal amine NH unit is a dominant structural motif in all cases.
Introduction. – There has been a long-standing interest in hydrazones and their
metal complexes, largely through their applications in analytical chemistry [1][2],
organic synthesis [3][4], biologically related areas [5 – 9] and sensors, optoelectronic
and polymeric materials [10 – 17]. Hydrazone units attached to ligand scaffolds are
relatively rigid spacers and have been incorporated into supramolecular assemblies
including helical wires [18][19], grids [20 – 26], and coordination polymers containing
interconnected metallomacrocycles [27]. The assembly of this last example depended
upon the hydrazone unit acting as a nonlinear spacer, and upon the incorporation of a
peripheral metal-binding domain, in this case, pyridine. We recently reported the family
of 4’-substituted 2,2’:6’,2’’-terpyridine (tpy) ligands 1 – 4 (Fig. 1), and described the
effects that varying the R and R’ substituents had on their solution behaviour (in
particular rotation about the CpyridineꢀNamine bond) and packing interactions in the solid
state [28]. The synthesis of these hydrazones was by the well-documented acid-
catalysed condensation of a hydrazine (4’-hydrazino-2,2’:6’,2’’-terpyridine or 4’-(1-
methylhydrazino)-2,2’:6’,2’’-terpyridine [29 – 31]) with an aldehyde or ketone. This
methodology is readily adapted to the preparation of other 4’-hydrazone derivatives of
tpy with pendant functionalities. We report here the synthesis of five new members of
this series of compounds, along with solution behaviour and structural data for
representative neutral and monoprotonated ligands.
Results. – The experimental strategy that we have previously established for the
synthesis of 4’-hydrazone derivative 1 involves the reaction of 4’-hydrazino-2,2’:6’,2’’-
terpyridine with PhCHO in MeOH in the presence of a few drops of concentrated
ꢀ 2009 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Fig. 1. Structures of ligands 1 – 9 and atom labelling for NMR spectroscopic assignments
H2SO4. This results in the formation of the bright yellow methyl sulfate salt of [H21]2þ
(structurally confirmed for the chloride salt). Subsequent treatment of [H21][MeO-
SO3]2 with NaBF4 or K2CO3 results in the formation of [H1][BF4] or 1, respectively
[28]. This same sequence of reactions has been used to isolate 2 – 4 and their mono- and
diprotonated derivatives [28], as well as 4’-(3,5-dimethyl-1H-pyrazol-1-yl)-2,2’:6’,2’’-
terpyridine and its monoprotonated analogue [32]. The reaction of acetone with 4’-
hydrazino-2,2’:6’,2’’-terpyridine in MeOH in the presence of concentrated H2SO4
produced bright yellow [H25][MeOSO3]2, formulated by analogy with the fully
characterized diprotonated derivatives of compounds 1 – 4. Treatment of [H25][MeO-
SO3]2 with NaBF4 led to the formation of [H5][BF4], the electrospray mass spectrum
(ESI-MS) of which showed peaks at m/z 304.1, 326.1, and 629.0 assigned to [H5]þ, [5 þ
1
Na]þ, and [(5)2Na]þ. In the H-NMR spectrum, the signals assigned to H-atoms HA3
and HB3 are broad (Fig. 2,a), consistent with protonation restricting rotation about the
Cpy(ring A)ꢀCpy(ring B) bonds. We have already presented a detailed study of the
affects of protonation on the energy barriers to rotation about the Cpy(ring
A)ꢀCpy(ring B) and Cpy(ring B)ꢀNamine bonds [28].
Treatment of [H25][MeOSO3]2 with K2CO3 gave 5 in good yield as an off-white
solid. The ESI-MS exhibited a base peak at m/z 304.1 assigned to [H5]þ. The 1H- and
13C-NMR spectra were fully assigned by 2D-techniques, the HMe-a and HMe-b signals
being distinguished by the observation of a NOESY cross-peak between the signals for
the NH and HMe-a H-atoms. The symmetrical appearance of the tpy region of the
1H-NMR spectrum (Fig. 2,b) was evidence for there being free bond rotation about the
CpyꢀNamine bond on the NMR timescale, and the well-resolved signals for HB3 and HA3
confirmed that rotation about the Cpy(ring A)ꢀCpy(ring B) bonds was no longer

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Fig. 2. Part (d(H) 9.0 – 7.0) of the room-temperature 500-MHz 1H-NMR spectra of a) a (D6)DMSO
solution of [H5][BF4], and b) a CDCl3 solution of 5 (* ¼ residual solvent peak). For H-atom numbering,
see Fig. 1.
restricted. Large pale yellow, X-ray-quality blocks of 5 were grown by slow evaporation
of a CDCl3 solution of the compound. The molecular structure of 5 is shown in Fig. 3,
and selected bond parameters (which are unexceptional) are given in the caption. All
the C- and N-atoms of the Me2C¼NNHꢀ (ring B) unit are within 0.2 ꢂ of the least-
squares plane through the 11 C- and N-atoms which comprise this unit. The tpy unit
adopts the expected s-trans,s-trans-configuration, but one pyridine ring is twisted
significantly out of the plane of the other two (angles between least squares planes of
rings containing N(1) and N(2), and N(3) and N(2) are 17.94(3) and 1.42(4)8, resp.).
The deviation from planarity is associated with the intermolecular interactions.
Molecules associate in pairs by virtue of the H-bonds shown in Fig. 4,a (N(4)H(1) ···
N(1i) ¼ 2.75, N(4) ··· N(1i) ¼ 3.570(1) ꢂ, N(4)ꢀH(1) ··· N(1i) ¼ 1548; C(7)H(71) ···
N(1i) ¼ 2.75, C(7) ··· N(1i) ¼ 3.580(1) ꢂ, N(4)ꢀH(1) ··· N(1i) ¼ 1468; symmetry code,
see Fig. 4 caption). The centrosymmetric dimer forms a V-shaped motif, and these
assemble into a herringbone architecture (Fig. 4,b), reminiscent of that adopted by
compound 1 in the solid state [28].
The reaction of a slight excess of 4-bromobenzaldehyde, 4-nitrobenzaldehyde, 4-
methoxybenzaldehyde, or 3,5-dimethoxybenzaldehyde with 4’-hydrazino-2,2’:6’,2’’-
terpyridine in MeOH or EtOH (see Exper. Part) in the presence of a few drops of
concentrated H2SO4 led to the bright yellow methyl sulfate or ethyl sulfate salts of
[H26]2þ, [H27]2þ, [H28]2þ, or [H29]2þ. These compounds were difficult to fully
characterize, and were typically used directly for the syntheses of the neutral ligands.
In the case of [H27][EtOSO3]2, an analytically pure sample was obtained. The 1H-NMR
spectrum in (D6)DMSO solution showed two sets of Et signals, d(H) 3.73 and 1.10, and
d(H) 3.44 and 1.06. The latter pair of signals was assigned to EtOH [33] and the former
to the ethyl sulfate anion. The persistant appearance of EtOH can be explained by

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Fig. 3. Molecular structure of 5 with thermal ellipsoids plotted at 50% probability level. Selected bond
parameters: N(5)ꢀC(16) ¼ 1.280(1), N(4)ꢀN(5) ¼ 1.3775(9), N(4)ꢀC(8) ¼ 1.3693(9), C(16)ꢀC(17) ¼
1.496(1),
C(16)ꢀC(18) ¼ 1.498(1) ꢂ;
N(5)ꢀC(16)ꢀC(17) ¼ 124.77(7),
N(5)ꢀC(16)ꢀC(18) ¼
117.18(8), C(17)ꢀC(16)ꢀC(18) ¼ 118.05(8), N(4)ꢀN(5)ꢀC(16) ¼ 116.87(7), N(5)ꢀN(4)ꢀC(8) ¼
119.41(6)8.
Fig. 4. a) H-Bonded interactions between pairs of molecules of 5 (symmetry code i ¼ ꢀx, y, 3/2 ꢀ z).
b) Packing of dimeric motifs. N-Atoms are shown in black.
hydrolysis of the anion by residual H2O in the (D6)DMSO solvent, and this
phenomenon was consistently observed for methyl sulfate salts of [H21]2þ, [H22]2þ,
[H23]2þ, or [H24]2þ [28]. In the aromatic region of the spectrum of [H27][EtOSO3]2, the

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signal for HB3 was extremely broad, and that for HA3 appeared as a broadened d (see
earlier discussion).
The exchange of the [MeOSO3]ꢀ or [EtOSO3]ꢀ ion for [BF4]ꢀ allowed the
monoprotonated 4’-hydrazone derivatives of tpy to be isolated. This was confirmed by a
structural determination of [H9][BF4], single crystals of which were grown by slow
evaporation of a MeOH/H2O 10 :1 solution of the compound. The structure of the
[H9]þ cation is shown in Fig. 5. The s-cis,s-cis-conformation of the tpy unit is consistent
with that observed in [H1][PF6], [H2][BF4], and [H3][MeOSO3] [28] but contrasts
with the s-cis,s-trans-arrangement adopted by the [Htpy]þ cations in [Htpy][CF3SO3]
[34] and [Htpy][ReO4] [35]. The difference appears to arise from the H-bonding
ability of the NH H-atom in the hydrazone derivatives. In [H9][BF4], the [BF4]ꢀ anion
is H-bonded to the H(4)N(4) unit (N(4)H(4) ··· F(1) ¼ 1.95, N(4) ··· F(1) ¼ 2.858(3) ꢂ,
N(4)ꢀH(4) ··· F(1) ¼ 1698), and there are supporting CꢀH ··· F interactions to the
same anion (C(4)H(41) ··· F(2) ¼ 2.53, C(4) ··· F(2) ¼ 3.521(4) ꢂ, C(4)ꢀH(41) ···
F(2) ¼ 1668; C(7)H(71) ··· F(2) ¼ 2.26, C(7) ··· F(2) ¼ 3.251(3) ꢂ, C(7)ꢀH(71) ···
F(2) ¼ 1668). The latter nonclassical H-bonds are only switched on if the tpy unit is
in an s-cis,s-cis conformation which results in the favourable NH ··· N H-bonds shown in
Fig. 5. In the crystal lattice, the cations are organized in ribbon-like assemblies,
supported by the nonclassical H-bonds shown in Fig. 6. The arene rings in one ribbon
are p-stacked over the tpy domains of an adjacent ribbon (separation of 3.3 ꢂ), and
stacks of infinite ribbons assemble into a pleated sheet with the least-squares plane
through one ribbon subtending an angle of 1368 with the next.
Fig. 5. Molecular structure of [H9]þ in [H9][BF4] with thermal ellipsoids plotted at 50% probability
level. Selected bond parameters: N(5)ꢀC(16) ¼ 1.284(3), N(4)ꢀN(5) ¼ 1.378(2), N(4)ꢀC(8) ¼
1.346(3), C(16)ꢀC(17) ¼ 1.461(3), C(19)ꢀO(1) ¼ 1.360(3), C(20)ꢀO(1) ¼ 1.393(4), C(22)ꢀO(2) ¼
1.365(3), C(23)ꢀO(2) ¼ 1.414(4) ꢂ; N(5)ꢀC(16)ꢀC(17) ¼ 121.9(2), N(4)ꢀN(5)ꢀC(16) ¼ 114.1(2),
N(5)ꢀN(4)ꢀC(8) ¼ 120.5(2),
C(20)ꢀO(1)ꢀC(19) ¼ 118.6(2),
C(23)ꢀO(2)ꢀC(22) ¼ 118.4(2)8.
H-Bonds: N(2)H(2) ··· N(1) ¼ 2.23, N(2) ··· N(1) ¼ 2.653(3) ꢂ, N(2)ꢀH(2) ··· N(1) ¼ 1078; N(2)H(2)
··· N(3) ¼ 2.25, N(2) ··· N(3) ¼ 2.636(2) ꢂ, N(2)ꢀH(2) ··· N(3) ¼ 1058.

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Fig. 6. Ribbon assembly of [H9]þ cations in [H9][BF4]. H-Bonds: O(2) ··· H(211ii)C(21ii) ¼ 2.44,
O(2) ··· C(21ii)H(211ii) ¼ 3.425(4) ꢂ,
O(2) ··· C(21ii)ꢀH(211ii) ¼ 1638;
N(1) ··· H(11i)C(21i) ¼ 2.63,
N(1) ··· C(21i) ¼ 3.555(4) ꢂ, N(1) ··· H(11i)ꢀC(21i) ¼ 1538. Symmetry codes: i ¼ ꢀx, 1 ꢀ y, 1 ꢀ z;
ii ¼ 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
Treatment of each of the methyl sulfate or ethyl sulfate salts of [H26]2þ, [H27]2þ,
[H28]2þ, or [H29]2þ with K2CO3 gave, after workup, neutral ligands 6 – 9 in moderate to
1
good yields. All solution H- and 13C-NMR spectra were recorded in (D6)DMSO and
were assigned by 2D-techniques. The NMR spectroscopic characterization of these
compounds is significantly easier than that of the protonated species since the spectra
are well resolved at room temperature, with the exception of the signal for H-atom HB3
which is broad in all cases. This is consistent with hindered rotation about the Cpy(ring
1
B)ꢀNamine bond. For 6, the H-NMR spectrum was recorded in both (D6)DMSO and
CDCl3. Whereas the signal for HB3 is broad in (D6)DMSO, it is sharp in CDCl3,
indicating that the energy barrier to rotation about the Cpy(ring B)ꢀNamine bond is
lower in CDCl3 than in (D6)DMSO. The solvent dependence of the dynamic process
can be attributed to H-bonding between a (D6)DMSO and the NH in 6 which hinders
bond rotation, an observation upon which we have previously commented with respect
to compounds 1 – 3 [28]. Consistent with the environment of the NH being solvent
dependent, the signal for this H-atom shifts from d(H) 11.21 in (D6)DMSO to 8.21 in
CDCl3. The chemical shift for the N¼CH H-atom is also sensitive to solvent, appearing
at d(H) 7.64 in CDCl3 and 8.02 in (D6)DMSO. Other signals in the spectrum are little
affected.
Single crystals of 6 · H2O were grown by slow evaporation of a CHCl3 solution of
the compound. The compound crystallizes in space group P – 1. The asymmetric unit
contains two independent molecules which encapsulate two H2O molecules within a H-
bonded motif (Fig. 7); the O-attached H-atoms were located from the difference map.
The tpy adopts the usual s-trans,s-trans-configuration, and the combination of two
pyridine acceptors and two NH donors in a pair of ligands with the NH groups facing
one another is ideally set up to host two H2O molecules. One H2O H-atom (H(101))
remains free to act as a H-bond donor to a similar motif stacked above the first one. The
four aromatic rings in each molecule of 6 are not coplanar and deviate from a plane by
between 13.3(1)8 (angle between the least squares planes between rings containing
atoms N(1) and N(2)) and 22.4(1)8 (angle between rings containing N(7) and C(39)).
The ((6)2 · 2 H2O) motifs align into parallel sheets, with the preferred orientations of
the aromatic rings optimizing short intermolecular CꢀH ··· N, CꢀH ··· Br, and N ··· Br
contacts (Br(1) ··· N(6ii) ¼ 3.417(3), Br(2) ··· N(3iii) ¼ 3.341(2) ꢂ; symmetry codes:

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Fig. 7. The asymmetric unit of the solid-state structure of 6 · H2O with thermal ellipsoids plotted at 50%
probability level. Selected bond parameters: N(4)ꢀC(8) ¼ 1.376(3), N(9)ꢀC(30) ¼ 1.370(3),
N(4)ꢀN(5) ¼ 1.362(3), N(9)ꢀN(10) ¼ 1.368(3), N(5)ꢀC(16) ¼ 1.291(3), N(10)ꢀC(38) ¼ 1.282(3),
Br(1)ꢀC(20) ¼ 1.897(3), Br(2)ꢀC(42) ¼ 1.898(3) ꢂ; N(5)ꢀN(4)ꢀC(8) ¼ 121.8(2), C(16)ꢀN(5)ꢀ
N(4) ¼ 114.1(2), N(10)ꢀN(9)ꢀC(30) ¼ 122.5(2), C(38)ꢀN(10)ꢀN(9) ¼ 113.6(2)8. H-Bonding:
N(4)H(4)B ··· O(1) ¼ 2.06, N(4) ··· O(1) ¼ 2.930(3) ꢂ, N(4)ꢀH(4B) ··· O(1) ¼ 1708; O(1)H(100) ···
N(8) ¼ 2.16(4), O(1) ··· N(8) ¼ 2.923(3) ꢂ, O(1)ꢀH(100) ··· N(8) ¼ 160(4)8; O(2)H(201) ··· O(1) ¼
2.12(5), O(2) ··· O(1) ¼ 2.904(3) ꢂ, O(2)ꢀH(201) ··· O(1) ¼ 173(3)8; N(9)H(9B) ··· O(2) ¼ 1.98,
N(9) ··· O(2) ¼ 2.855(3) ꢂ, N(9)ꢀH(9B) ··· O(2) ¼ 1788; O(2)H(200) ··· N(1) ¼ 2.11(2), O(2) ··· N(1) ¼
2.880(3) ꢂ, O(2)ꢀH(200) ··· N(1) ¼ 165(4)8. Atom H(101) is H-bonded to an adjacent motif (see text):
O(1)H(101) ··· N(3i) ¼ 2.11(4), O(1) ··· N(3i) ¼ 2.859(3) ꢂ, O(1)ꢀH(101) ··· N(3i) ¼ 157(3)8. Symmetry
code i ¼ ꢀx, 1 ꢀ y, 1 ꢀ z.
ii ¼ ꢀ1 þ x,1 þ y, z; iii ¼ 1 þ x, ꢀ 1 þ y, z) both within and between the sheets. Short
N ··· Br contacts stabilizing solid-state structures are not uncommon [36].
X-Ray-quality crystals of the NO2 derivative 7 were grown by slow evaporation of a
CHCl3 solution of the compound. The asymmetric unit contains two independent
molecules, one of which is shown in Fig. 8. Each molecule is close to planar. With the
exception of the atoms of the NO2 groups, the maximum deviation from the least-
squares plane through one molecule is 0.24 ꢂ, and 0.19 ꢂ for the second. Each NO2
unit is twisted only slightly out of the plane of the aromatic ring to which it is attached
(3.28 for molecule A and 4.18 for B). The angle between the least-squares planes
through the two independent molecules is 70.68. Each molecule is involved in the same
types of intermolecular interactions: NHamine ··· Onitro H-bonds and p-stacking of
aromatic rings. The former is responsible for the assembly of planar ribbons which run
parallel to the b axis, and the latter for the stacking of the ribbons into a herringbone
assembly (Fig. 9).
In addition to our interest in using compounds 1 – 9 as ligands in supramolecular
assemblies, the electronic spectroscopic properties of these phenylhydrazone deriva-
tives are of interest in their own right. Like [H21][MeOSO3]2, each of the methyl sulfate

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Fig. 8. The structure of one of the two independent molecules (A) of 7 with thermal ellipsoids plotted at
50% probability level. Selected bond parameters: N(4)ꢀC(8) ¼ 1.384(3), N(4)ꢀN(5) ¼ 1.358(3),
N(5)ꢀC(16) ¼ 1.288(3), C(16)ꢀC(17) ¼ 1.463(3), O(1)ꢀN(6) ¼ 1.231(3), O(2)ꢀN(6) ¼ 1.219(3) ꢂ;
N(5)ꢀN(4)ꢀC(8) ¼ 118.7(2), C(16)ꢀN(5)ꢀN(4) ¼ 117.6(2), O(1)ꢀN(6)ꢀO(2) ¼ 122.8(2)8. Bond
parameters for the second molecule (B) are similar.
Fig. 9. Packing of molecules of 7; the unit cell is viewed down the b axis. Crystallographically independent
molecules A and B are shown in pale and dark grey, respectively.
or ethyl sulfate salts of [H25]2þ, [H26]2þ, [H27]2þ, [H28]2þ, or [H29]2þ is bright yellow,
while the neutral hydrazones, with the exception of 7, are off-white or pale yellow. The
NO2 derivative 7 is orange. The conversion of diprotonated to neutral ligands was
carried out with K2CO3, but the addition of a stronger base such as KOtBu results in the

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deprotonation of the NH group. Compound 1 is the parent for the series of derivatives
6 – 9, and titration of aqueous NaOH solution into a DMSO solution of [H21][MeO-
SO3]2 (2.9 · 10ꢀ5 mol dmꢀ3) is accompanied by a decrease in intensity of the absorption
at 356 nm and a shift to 344 nm. If the base is changed to KOtBu, a new absorption
appears at 459 nm when the base is present in excess, a consequence of the extended
conjugation that is possible once the NH group is deprotonated. This is a general
observation for compounds 1, 6, 8, and 9. Addition of excess KOtBu to a DMSO
solution of orange 7 (2.2 · 10ꢀ5 mol dmꢀ3) results in the loss of the absorption at 400 nm
and appearance of an absorption (e ¼ 34000 dm3 molꢀ1 cmꢀ1) at 646 nm leading to an
intense red colour consistent with extension of the p-system from the tpy to NO2
domains once the NH group is deprotonated.
Conclusions. – We described the syntheses of five 2,2’:6’,2’’-terpyridine ligands
functionalized in the 4’-position with a hydrazone substituent RR’C¼NꢀNH (R ¼
R’ ¼ Me (5); R ¼ H, R’ ¼ 4-BrC6H4 (6), 4-O2NC6H4 (7), 4-MeOC6H4 (8), or 3,5-
(MeO)2C6H3 (9)). These extend our previously reported series of ligands in this family.
Protonation of the tpy domain of 5 – 9 is facile, and the solution behaviour of the
ligands was studied by NMR and electronic spectroscopies. In the solid state, the tpy
domains in 5, 6 · H2O, and 7 adopt the expected s-trans,s-trans-conformation, while
protonation causes a switch to an s-cis,s-cis-arrangement, exemplified in [H9][BF4]. In
the solid state, H-bonding involving the NH unit is important in all the structures. In a
future paper, we will report the synthesis, structures, and spectroscopic properties of
homoleptic complexes of iron(II) and ruthenium(II) containing ligands 1 – 9.
We thank the Swiss National Science Foundation and the University of Basel for financial support.
Experimental Part
General. 1H- and 13C-NMR Spectra: Bruker-Avance-DRX 500 spectrometer; d in ppm rel. to Me4Si
as internal standard, J in Hz. ESI-MS: Finnigan-MAT-LCQ mass spectrometer; in m/z (rel. %).
[H25][MeOSO3]2. Acetone (0.5 ml, 7 mmol) was added to 4’-hydrazino-2,2’:6’,2’’-terpyridine (0.20 g,
0.76 mmol) in hot MeOH. A few drops of conc. H2SO4 were added to the soln., and a yellow precipitate
formed which dissolved within a few min. The soln. was heated under reflux for 3 h, and then cooled to r.t.
At this stage, only a small amount of solid was present. The addition of Et2O yielded a bright yellow,
hygroscopic solid which was collected by filtration and washed with EtOH/Et2O: [H25][MeOSO3]2
(0.30 g, ca. 75%). Yellow solid. A pure sample was not obtained, and the compound was used without
further purification.
[H5][BF4]. A sample of [H25][MeOSO3]2 was dissolved in a minimum amount of hot H2O, and a
large excess of solid NaBF4 was added. After stirring at r.t. for 1 h, a yellow-green solid formed which was
1
collected and washed well with H2O and cold EtOH. H-NMR (500 MHz, (D6)DMSO, 295 K): 10.94
(br., NH); 8.90 (d, J ¼ 4.4, 2 H, HA6); 8.41 (br., HA3); 8.18 (t, J ¼ 7.2, HA4); 8.03 (br., 2 H, HB3); 7.74 (m,
2 H, HA5); 2.14 (s, Me); 2.08 (s, Me). ESI-MS: 304.1 ([H5]þ; calc. 304.4), 326.1 ([5 þ Na]þ; calc. 326.1),
629.0 ([(5)2 þ Na]þ; calc. 629.3).
Propane-2-one 2-([2,2’:6’,2’’-Terpyridin]-4’-yl)hydrazone (5). [H25][MeOSO3]2 (0.20 g, 0.38 mmol)
was dissolved in H2O (30 ml) and sat. aq. KHCO3 soln. was added to give a colorless soln. This was
extracted with CHCl3 (4 ꢁ 100 ml), dried (MgSO4), and the residue recrystallized from MeOH/CHCl3: 5
(0.092 g, 79%). Off-white solid. 1H-NMR (500 MHz, CDCl3, 295K): 8.69 (d, J ¼ 3.2, 2 H, HA6); 8.61 (d,
J ¼ 7.9, 2 H, HA3); 8.10 (s, 2 H, HB3); 7.83 (t, J ¼ 7.7, 2 H, HA4); 7.48 (s, NH); 7.31 (dd, J ¼ 5.2, 5.8, 2 H, HA5);
2.09 (s, Meb); 1.88 (s, Mea). 1H-NMR (500 MHz, (D6)DMSO, 295 K): 9.62 (s, NH); 8.68 (ddd, J ¼ 4.6, 1.3,

Helvetica Chimica Acta – Vol. 92 (2009)
2223
0.6, 2 H, HA6); 8.58 (d, J ¼ 7.8, 2 H, HA3); 8.16 (s, 2 H, HB3); 7.96 (td, J ¼ 7.7, 1.7, HA4); 7.45 (ddd, J ¼ 7.5, 4.8,
1.1, 2 H, HA5); 2.03 (s, Meb); 1.96 (s, Mea). 13C-NMR (125 MHz, CDCl3, 295K): 156.7 (CA2/B2); 156.2
(CA2/B2); 153.32 (CB4); 149.0 (CA6); 146.5 (C¼N); 136.8 (CA4); 123.6 (CA5); 121.4 (CA3); 104.9 (CB3); 25.3
(CMe-b); 14.2 (CMe-a). 13C-NMR (125 MHz, (D6)DMSO, 295 K): 155.8 (CA2); 155.1 (CB2); 153.7 (CB4);
149.0 (CA6); 147.6 (C¼N); 137.1 (CA4); 124.0 (CA5); 120.6 (CA3); 104.1 (CB3); 25.1 (CMe-b); 17.0 (CMe-a).
ESI-MS: 304.1 ([5 þ H]þ; calc. 304.4). Anal. calc. for C18H17N5 · 0.33 CH3OH: C 69.57, H 6.00, N 21.93;
found: C 69.95, H 5.66, N 21.81.
[H26][MeOSO3]2. The 4-bromobenzaldehyde (0.15 g, 0.81 mmol) was added to 4’-hydrazino-
2,2’:6’,2’’-terpyridine (0.20 g, 0.76 mmol) in hot MeOH. A few drops of conc. H2SO4 were added, and a
bright orange precipitate immediately formed. The suspension was heated under reflux for 3 h, then
cooled to r.t. After cooling, a bright yellow precipitate had formed which was collected by filtration and
washed with EtOH: [H26][MeOSO3]2 (0.36 g, ca. 55%). Yellow solid. The compound was used without
further purification.
[H6][BF4]. A sample of [H26][MeOSO3]2 was dissolved in a minimum amount of hot H2O, and
NaBF4 was added, and a yellow-green precipitate formed immediately. ESI-MS: 432.0 ([H6]þ; calc.
431.3). Anal. calc. for C22H17BBrF4N5 · 2.5 H2O: C 46.92, H 3.94, N 12.44; found: C 47.18, H 3.78, N 12.53.
[C(E)]-4-Bromobenzaldehyde 2-([2,2’:6’,2’’-Terpyridin]-4’-yl)hydrazone (6). [H26][MeOSO3]2
(0.20 g, 0.31 mmol) was dissolved in H2O (10 ml), and sat. aq. KHCO3 soln. (20 ml) was added. The
resulting pale yellow suspension was extracted into CH2Cl2 (3 ꢁ 50 ml), and the yellow soln. was dried
(MgSO4). Evaporation gave 6 as a sticky yellow solid which was purified by column chromatography
1
(short column, alumina, CH2Cl2/MeOH 99 :1): 6 (0.051 g, 39%). Yellow needles. H-NMR (500 MHz,
CDCl3, 295 K): 8.71 (d, J ¼ 4.1, 2 H, HA6); 8.61 (d, J ¼ 7.9, 2 H, HA3); 8.21 (s, NH); 8.15 (s, 2 H, HB3); 7.85
(t, J ¼ 7.7, 2 H, HA4); 7.64 (s, N¼CH); 7.58 (d, J ¼ 7.4, 2 H, HC2); 7.50 (d, J ¼ 7.4, 2 H, HC3); 7.33 (t, J ¼ 5.5,
1
2 H, HA5). H-NMR (500 MHz, (D6)DMSO, 295 K): 11.21 (s, NH); 8.73 (d, J ¼ 4.6, 2 H, HA6); 8.61 (d,
J ¼ 7.9, 2 H, HA3); 8.15 (br. s, 2 H, HB3); 8.02 (s, N¼CH); 7.99 (td, J ¼ 7.8, 1.7, 2 H, HA4); 7.70 (d, 8.7, 2 H,
H
C2); 7.67 (d, J ¼ 8.7, 2 H, HC3); 7.48 (ddd, J ¼ 7.4, 4.9, 0.9, 2 H, HA5). 13C-NMR (125 MHz, CDCl3, 295 K):
156.6 (CA2); 152.3 (CB2); 149.1 (CA6); 139.0 (C¼N); 137.0 (CA4); 133.6 (CC1); 131.9 (CC3); 128.3 (CC2);
123.9 (CA5); 123.3 (CC4); 121.6 (CA3); 105.0 (CB3). 13C-NMR (125 MHz, (D6)DMSO, 295 K): 155.6
(CC2/B2) 155.5 (CA2/B2); 152.5 (CB4); 149.2 (CA6); 139.5 (C¼N); 137.2 (CA4); 134.2 (CC1); 131.8 (CC3); 128.1
(CC2); 124.2 (CA5); 122.0 (CC4); 120.7 (CA3); 103.8 (CB3). ESI-MS: 432.0 ([6 þ H]þ; calc. 432.1). Anal.
calc. for C22H16N5Br· 0.33 H2O: C 60.57, H 3.85, N 16.05; found: C 60.77, H 3.86, N 15.61.
[H27][EtOSO3]2. The 4-nitrobenzaldehyde (0.15 g, 0.99 mmol) was added to 4’-hydrazino-2,2’:6’,2’’-
terpyridine (0.21 g, 0.80 mmol) in hot EtOH. A few drops of conc. H2SO4 were added, and a yellow-
orange precipitate immediately formed. The suspension was heated under reflux for 3 h, then cooled to
r.t. Filtration yielded a bright yellow powder which was washed with EtOH: [H27][EtOSO3]2 (0.43 g,
1
87%). H-NMR (500 MHz, (D6)DMSO, 295 K): 11.9 (br., NH); 8.82 (d, J ¼ 4.1, 2 H, HA6); 8.66 (br. d,
J ¼ 7.4, 2 H, HA3); 8.34 (d, J ¼ 8.8, 2 H, HC2); 8.25 (s, N¼CH); 8.17 (br., HB3); 8.11 (m, 4 H, HC3þA4); 7.63
(m, 2 H, HA5); 3.73 (q, J ¼ 7.13, MeCH2, see text); 1.10 (t, J ¼ 7.12, MeCH2, see text). Anal. calc. for
C26H26N6O10S2 · H2O: C 46.98, H 4.25, N 12.64; found: C 46.97, H 4.12, N 12.61.
[H7][BF4]. [H27][EtOSO3]2 (0.20 g, 0.31 mmol) was dissolved in a minimum amount of hot H2O,
and excess NaBF4 was added. The yellow-green solid that formed was collected by filtration and washed
well with H2O and cold EtOH: [H7][BF4] (0.081 g, 54%). Yellow solid. ESI-MS: 397.1 ([H7]þ; calc.
397.2).
[C(E)]-4-Nitrobenzaldehyde 2-([2,2’:6’,2’’-Terpyridin]-4’-yl)hydrazone (7). [H27][EtOSO3]2
(0.20 g, 0.31 mmol) was dissolved in H2O (50 ml). Solid K2CO3 (5g) was added, and the suspension
was extracted into CH2Cl2 (3 ꢁ 150 ml), washed with H2O (2 ꢁ 250 ml), and dried (MgSO4). The solvent
was evaporated to give an orange powder which was recrystallized twice from EtOH/CH2Cl2: 7 (0.052 g,
1
41%). Orange needles. H-NMR (500 MHz, (D6)DMSO, 295 K): 11.52 (s, NH); 8.74 (d, J ¼ 3.8, 2 H,
HA6); 8.62 (d, J ¼ 7.9, 2 H, HA3); 8.33 (d, J ¼ 8.8, 2 H, HC2); 8.20 (br. s, 2 H, HB3); 8.14 (s, HC¼N); 8.00 (m,
4 H, HA4þC3); 7.50 (ddd, J ¼ 7.6, 4.9, 1.1, 2 H, HA5). 13C-NMR (125 MHz, (D6)DMSO, 295 K): 155.7
(CA2/B2); 155.4 (CA2/B2); 152.2 (CB4); 149.2 (CA6); 147.0 (CC4); 141.4 (CC1); 138.2 (C¼N); 137.3 (CA4); 127.0
(CC2); 124.3 (CA5/C3); 124.2 (CA5/C3); 120.8 (CA3); 103.7 (CB3). ESI-MS: 397.1 ([7 þ H]þ; calc. 397.4). Anal.
calc. for C22H16N6O2: C 66.66, H 4.07, N 21.20; found: C 66.51, H 4.10, N 21.00.

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Helvetica Chimica Acta – Vol. 92 (2009)
[H28][MeOSO3]2. The 4-methoxybenzaldehyde (0.11 g, 0.81 mmol) was added to 4’-hydrazino-
2,2’:6’,2’’-terpyridine (0.20 g, 0.76 mmol) in hot MeOH. A few drops of conc. H2SO4 were added,
resulting in the formation of an orange precipitate. The suspension was heated under reflux for 3 h, then
cooled to r.t. [H28][MeOSO3]2 precipitated, was collected by filtration, washed with EtOH, and isolated
as an orange powder (0.46 g, 99%). The compound was used without further purification.
[H8]BF4. A sample of [H28][MeOSO3]2 was dissolved in a minimum amount of hot H2O. Addition
of a large excess of solid NaBF4 yielded a yellow precipitate. ESI-MS: 382.1 ([H8]þ; calc. 382.2). Anal.
calc. for C23H20BF4N5O · 0.75 H2O: C 57.22, H 4.49, N 14.51; found: C 57.33, H 4.32, N 14.51.
[C(E)]-4-Methoxybenzaldehyde 2-([2,2’:6’,2’’-Terpyridin]-4’-yl)hydrazone (8). [H28][MeOSO3]2
(0.20 g, 0.33 mmol) was dissolved in hot H2O (20 ml), and solid K2CO3 (5 g) was added, to give a
milky suspension. CH2Cl2 (100 ml) was added, and the biphasic mixture was sonicated for 1 h. The aq.
layer was extracted with CH2Cl2 (2 ꢁ 100 ml), the combined org. phase washed with H2O (2 ꢁ 100 ml)
and dried (Na2SO4), the solvent evaporated, and the residue purified by column chromatography (short
column, alumina, CH2Cl2/MeOH 99 :1): 8 (0.093 g, 74%). Pale yellow solid. 1H-NMR (500 MHz,
(D6)DMSO, 295 K): 10.97 (s, NH); 8.72 (d, J ¼ 4.4, 2 H, HA6); 8.60 (d, J ¼ 7.9, 2 H, HA3); 8.12 (s, 2 H,
HB3); 8.00 (s, HC¼N); 7.98 (t, J ¼ 7.5, 2 H, HA4); 7.69 (d, J ¼ 8.5, 2 H, HC2); 7.48 (dd, J ¼ 6.9, 5.4, 2 H,
HA5); 7.05 (d, J ¼ 8.8, 2 H, HC3); 3.81 (s, Me). 13C-NMR (125 MHz, (D6)DMSO 295 K): 160.1 (CC4);
156.6 (CA2); 156.4 (CB2); 152.7 (CB4); 149.1 (CA6); 140.7 (C¼N); 137.2 (CA4); 127.8 (CC2); 127.5 (CC1);
124.1 (CA5); 120.7 (CA3); 114.4 (CC3); 103.7 (CB3); 55.3 (MeO). ESI-MS: 382.2 ([H8]þ; calc. 382.2). Anal.
calc. for C23H19N5O · 0.25 H2O: C 71.58, H 5.09, N 18.15; found: C 71.60, H 5.19, N 17.84.
[H29][MeOSO3]2. The 3,5-dimethoxybenzaldehyde (0.15 g, 0.90 mmol) was added to 4’-hydrazino-
2,2’:6’,2’’-terpyridine (0.20 g, 0.76 mmol) in hot MeOH. A few drops of H2SO4 were added to the soln.,
and a bright yellow precipitate formed after a few seconds. The suspension was heated under reflux for
3 h and then cooled to r.t. [H29][MeOSO3]2 (0.30 g, ca. 62%) was isolated as a yellow powder, after
filtration and washing with EtOH. The compound was used without further purification.
[H9][BF4]. A sample of [H29][MeOSO3]2 was dissolved in a minimum amount of hot H2O, and solid
NaBF4 was added. After stirring at r.t. for 1 h, a yellow-green solid had formed which was collected by
filtration and washed well with H2O and cold EtOH. ESI-MS: 412.1 ([H9]þ), 411.2, 434.4 ([9 þ Naþ];
calc. 434.2), 845.0 ([(9)2 þ Naþ]; calc. 845.3). Anal. calc. for C24H22BF4N5O2 · 3 H2O: C 52.19, H 4.93, N
12.68; found: C 52.44, H 4.20, N 12.60.
[C(E)]-3,5-Dimethoxybenzaldehyde 2-([2,2’:6’,2’’-Terpyridin]-4’-yl)hydrazone (9). Solid K2CO3
(5 g) was added to a suspension of [H29][MeOSO3]2 (0.20 g, 31 mmol) in H2O (50 ml). CH2Cl2
(100 ml) was added, and the mixture was sonicated for 1 h. The org. phase was washed with H2O (2 ꢁ
1
100 ml) and dried (MgSO4) and the solvent evaporated: 9 (0.11 g, 86%). Off-white powder. H-NMR
(500 MHz, (D6)DMSO, 295K): 11.15 (s, NH); 8.73 (d, J ¼ 4.1, 2 H, HA6); 8.60 (d, J ¼ 7.9, 2 H, HA3); 8.15
(br. s, 2 H, HB3); 7.98 (t, J ¼ 7.7, 2 H, HA4); 7.97 (s, HC¼N); 7.47 (dd, J ¼ 6.6, 5.4, 2 H, HA5); 6.91 (s, 2 H,
HC2); 6.56 (s, 1 H, HC4); 3.82 (s, 2 Me). 13C-NMR (125 MHz, (D6)DMSO, 295 K): 160.8 (CC2); 155.5
(CA2þB2); 152.6 (CB4); 149.2 (CA6); 140.5 (C¼N); 137.2 (CA4); 136.9 (CC1); 124.2 (CA5); 120.7 (CA3); 104.4
(CA2); 103.8 (CB3); 100.7 (CC4); 55.3 (MeO). ESI-MS: 412.2 ([H9]þ; calc. 412.2). Anal. calc. for
C24H21N5O2 · 0.5 CH3OH: C 68.83, H 5.42, N 16.38; found: C 68.56, H 5.40, N 16.06.
Crystal-Structure Determinations. General. Data were collected on a Bruker-Nonius-Kappa-CCD or
Stoe-IPDS instrument; data reduction, solution, and refinement used the programs COLLECT [37],
SIR92 [38], DENZO/SCALEPACK [39], and CRYSTALS [40], or Stoe-IPDS software [41] and
SHELXL97 [42], structures were analysed by Mercury v. 2.2 [43]. ORTEP Diagrams were drawn with
ORTEP-3 for Windows [44]. Crystallographic data were deposited with the Cambridge Crystallographic
Data Centre, deposition numbers CCDC 726089 – 726092 for 5, 6 · H2O, 7, and [H9][BF4]. These data can
be obtained free of charge via www.ccdc.ac.uk/data_request/cif.
Crystal Data of 5. C18H17N5, Mr 303.37, yellow block; monoclinic, space group C2/c; a ¼ 12.200(2),
b ¼ 12.502(3), c ¼ 20.658(4) ꢂ, b ¼ 91.55(3)8, V ¼ 3149.9(11) ꢂ3, Z ¼ 8, Dcalc. ¼ 1.279 Mg mꢀ3
;
m(MoKa) ¼ 0.080 mmꢀ1, T 173 K, 6762 reflections collected. Refinement of 5339 reflections (208
parameters) with I > 2s(I) converged at final R1 ¼ 0.0511 (R1 all data ¼ 0.0593), wR2 ¼ 0.0570 (wR2 all
data ¼ 0.0664), Rint ¼ 0.065, g.o.f. ¼ 1.0386.

Helvetica Chimica Acta – Vol. 92 (2009)
2225
Crystal Data of 6 · H2O. C22H18BrN5O, Mr 448.31, yellow block; triclinic, space group P – 1; a ¼
11.147(2), b ¼ 12.328(3), c ¼ 15.273(3) ꢂ, a ¼ 95.93(3), b ¼ 102.46(3), g ¼ 104.38(3)8, V¼
1957.7(8) ꢂ3, Z ¼ 4, Dcalc. ¼ 1.521 Mg mꢀ3; m(MoKa) ¼ 2.124 mmꢀ1, T 200(2) K, 40694 reflections
collected, merging r¼ 0.0927. Refinement of 535 parameters with 9413 independent reflections against
F2 converged at final R1 ¼ 0.0527 (R1 all data ¼ 0.0669), wR2 ¼ 0.1144 (wR2 all data ¼ 0.1207), g.o.f. ¼
1.185.
Crystal Data of 7. C22H16N6O2, Mr 396.41, orange block; monoclinic, space group P21/c; a ¼
19.617(4), b ¼ 17.698(3), c ¼ 11.301(2) ꢂ, b ¼ 105.66(3)8, V¼ 3777.9(12) ꢂ3, Z ¼ 8, Dcalc. ¼ 1.394 Mg
mꢀ3; m(MoKa) ¼ 0.094 mmꢀ1, T 223(2) K, 47531 reflections collected, merging r¼ 0.0699. Refinement of
557 parameters with 6671 independent reflections against F2 converged at final R1 ¼ 0.0635 (R1 all data ¼
0.0851), wR2 ¼ 0.1193 (wR2 all data ¼ 0.1268), g.o.f. ¼ 1.237.
Crystal Data of [H9][BF4]. C24H22BF4N5O2, Mr 499.27, colorless plate; monoclinic, space group C2/
c; a ¼ 32.0072(8), b ¼ 7.0994(2), c ¼ 25.6676(6) ꢂ, b ¼ 122.985(1)8, V¼ 4892.4(2) ꢂ3, Z ¼ 8, Dcalc.
¼
1.356 Mg mꢀ3; m(MoKa) ¼ 0.109 mmꢀ1, T 173 K, 5619 reflections collected. Refinement of 3282
reflections (326 parameters) with I > 1.8s(I) converged at final R1 ¼ 0.0564 (R1 all data ¼ 0.0996), wR2 ¼
0.0654 (wR2 all data ¼ 0.0916), Rint ¼ 0.022, g.o.f. ¼ 1.1042.
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Received April 16, 2009