Conversion of hydrazides into: N, N ′-diacylhydrazines in the presence of a ruthenium(II)-arene complex

Article abstract of DOI:10.1039/c7nj00965h

Mono and dinuclear p-cymene-ruthenium(ii) complexes [RuCl(L¹)(η⁶-p-cymene)]Cl, where L¹ is propionic acid hydrazide (1) and [Ru₂Cl₂(L²)(η⁶-p-cymene)₂], where H₂L² is N¹,N²-dipropionylhydrazine (2), were prepared by a reaction of [RuCl₂(η⁶-p-cymene)]₂ with the corresponding ligand precursor. Upon the reaction of [RuCl₂(η⁶-p-cymene)]₂ with butyric acid hydrazide and pentanoic acid hydrazide in a 1:1 molar ratio in situ formation of tetradentate bridging ligands, N¹,N²-dibutanoylhydrazine and N¹,N²-dipentanoylhydrazine, respectively, occurred and the dinuclear complexes [Ru₂Cl₂(L³)(η⁶-p-cymene)₂] (3) and [Ru₂Cl₂(L⁴)(η⁶-p-cymene)₂] (4) were isolated. The compounds were characterised by elemental analysis, ESI-mass spectrometry, IR and 1D and 2D NMR spectroscopies. The structures of all complexes were established using single crystal X-ray crystallography. According to these data in both the mono- and dinuclear complexes the ruthenium atoms adopt the usual three-leg piano-stool geometry which is common for this type of complexes. Combining DFT calculations with the characterisation of the final products using X-ray diffraction, a possible reaction mechanism was discussed.

Full text of DOI:10.1039/c7nj00965h

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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Conversion of hydrazides into N,N'-diacylhydrazines in the presence of ruthenium(II)ꢀarene
complex
Stefan Nikolića, Ivanka Ćirića, Alexander Rollerb, Vladimir Lukesc, Vladimir B. Arionb, Sanja
GrgurićꢀŠipkad
aInovative Centre, Faculty of Chemistry, University of Belgrade, Studentski trg 12ꢀ16, 11 000
Belgrade, Serbia
bInstitute of Inorganic Chemistry, University of Vienna, Währinger Str. 42, 1090 Vienna, Austria
cInstitute of Physical Chemistry and Chemical Physics, Slovak University of Technology in
Bratislava, Radlinského 9, SKꢀ812 37 Bratislava, Slovakia
dFaculty of Chemistry, University of Belgrade, Studentski trg 12ꢀ16, 11000 Belgrade, Serbia
Abstract
Mono and dinuclear pꢀcymeneꢀruthenium(II) complexes [RuCl(L1)(η6ꢀpꢀcymene)]Cl, where L1 is
propionic acid hydrazide (1) and [Ru2Cl2(L2)(η6ꢀpꢀcymene)2], where H2L2 is N1,N2ꢀ
dipropionylhydrazine (2) were prepared by reaction of [RuCl2(η6ꢀpꢀcymene)]2 with the
corresponding ligand precursor. Upon the reaction of [RuCl2(η6ꢀpꢀcymene)]2 with butyric acid
hydrazide and pentanoic acid hydrazide in 1:1 molar ratio in situ formation of tetradentate bridging
ligands, N1,N2ꢀdibutanoylhydrazine and N1,N2ꢀdipentanoylhydrazine, respectively, occurred and the
dinuclear complexes [Ru2Cl2(L3)(η6ꢀpꢀcymene)2] (3) and [Ru2Cl2(L4)(η6ꢀpꢀcymene)2] (4) were
isolated. The compounds were characterised by elemental analysis, ESIꢀmass spectrometry, IR, 1D
and 2D NMR spectroscopies. Single crystals of [3][RuCl2(η6ꢀpꢀcymene)]2 were grown from a
mixture of N1,N2ꢀdibutanoylhydrazine and excess [RuCl2(η6ꢀpꢀcymene)]2. The structures of all
complexes were established by single crystal Xꢀray crystallography. According to these data in both
the monoꢀ and dinuclear complexes the ruthenium atoms adopt the usual „threeꢀleg pianoꢀstool”
geometry which is common for this type of complexes. Combining DFT calculations with the
characterization of final products by Xꢀray singleꢀcrystal diffraction, possible reaction mechanism
was discussed.
Introduction
1

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Dinuclear metal complexes, called also "clips" represent building blocks for the
multifunctional supramolecular systems with diverse potential applications.1,2,3 In recent years,
dinuclear and polynuclear ruthenium complexes incorporating diꢀ and tridentate bridging ligands
have received considerable attention because of their possible applications in homogeneous
catalysis, as multielectron storage systems4 and as antitumour agents.5 Through the choice of
chelating bridging linkers and introduction of various functional groups the reactivity of the metal
center can be tuned. Recent efforts have focused on attempts to optimise the biological properties of
arene rutheniumꢀassemblies.6 Of note is also the design and synthesis of new polynuclear ruthenium
complexes with structural diversity.7
A large number of the reported complexes in the literature is formed by selfꢀassembly
reactions.8
The approach often includes in situ reactions of the starting building blocks in the presence
of metal ions with formation of new organic product (ligand) isolated as a metal complex. An
advantage of this approach is the one step reaction to metal complex which does not need the direct
ligand synthesis followed by complex formation reaction. The main disadvantage is the difficulty in
isolation of the organic product formed. One possibility is via demetallation, which, however, not
always is easily accomplished, and is mainly developed for firstꢀrow transition metals. Depending
on the nature of ligating atoms, both chelating and bridging ligands can be formed, leading to the
compounds of varying nuclearities.9
We have been interested in the reactions of the chlorido bridged arene ruthenium complex
[RuCl2(η6ꢀpꢀcymene)]2 with a variety of different ligand precursors.10 A number of mononuclear
areneꢀruthenium(II) complexes with caprylic acid hydrazide (a hydrazide with a long hydrocarbon
chain) and isonicotinic acid hydrazide (a hydrazide with an aromatic pyridine ring), have been
reported.11 Xꢀray structure analysis confirmed the coordination of caprylic acid hydrazide in a
bidentate manner through the hydrazide moiety.
In order to examine the effect of the hydrocarbon chain length on both physicochemical and
cytotoxic properties of pꢀcymene ruthenium complexes attempts to prepare new mononuclear
complexes of aliphatic hydrazides were undertaken. While the reaction of [RuCl2(η6ꢀpꢀcymene)]2
with propionic acid hydrazide afforded the expected product, with butyric acid hydrazide and
pentanoic acid hydrazide dinuclear complexes with the bridging, in situ formed N1,N2ꢀ
2

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dibutanoylhydrazine and N1,N2ꢀdipentanoylhydrazine were isolated. The dimeric complex with
N1,N2ꢀdibutanoylhydrazine was also obtained by the reaction of starting dinuclear complex with a
priori prepared N1,N2ꢀdibutanoylhydrazine. The corresponding dinuclear complex with N1,N2ꢀ
dipropionylhydrazine was prepared by the reaction of starting complex with a priori synthesised
N1,N2ꢀdipropionylhydrazine.
Transformation of hydrazides into N,N’ꢀdiacylhydrazines is a wellꢀknown reaction in
organic chemistry and usually demands oxidation agents like oxone,12 selenium based compounds,13
iodine,14 iodobenzene diacetate,15 sodium perborate,16 or mercury(II) acetate.17 Microwave
irradiation is also efficient.18 Depending on the nucleophile present in reaction mixture, hydrazide
can be transformed into aldehyde, carboxylic acid or ester.19 This kind of transformations is also
performed in the presence of thallium,20 or transition metal ions, e.g, lead,21 copper,22 iron23 or
manganese.24 In the present study this transformation occurred in the presence of ruthenium arene
complex. The reaction is presumably facilitated by the coordination of butyric ꢀ or pentanoic acid
hydrazide to ruthenium centre.
All new complexes were characterised by elemental analysis, 1H and 13C NMR, UV–vis and
ESIꢀmass spectrometry, as well as by single crystal Xꢀray crystallography. On the basis of
spectroscopic characterization and DFT calculations, a mechanism of in situ transformation was
proposed.
Results and discussion
Synthesis of the ligand precursors and ruthenium(II)ꢀarene complexes
Disubstituted acyl hydrazines H2L2 and H2L3 were obtained by condensation of hydrazides with the
corresponding acyl chlorides, in the presence of potassium carbonate in water as shown in Scheme
1. The products precipitated directly from the reaction mixture or after evaporating the solvent
under reduced pressure.
3

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Scheme 1
Surprisingly, the reaction of butyric acid hydrazide and pentanoic acid hydrazide with
[RuCl2(η6ꢀpꢀcymene)]2 afforded N,N'ꢀdiacylhydrazines H2L3 and H2L4 isolated as dinuclear
ruthenium(II) complexes 3 and 4, respectively. Unlike, in the case of the propionic acid hydrazide,
formation of N1,N2ꢀdipropionylhydrazine H2L2 as ruthenium(II)ꢀarene complex was not observed.
Instead, complex 1 (Scheme 2) was isolated. However, dinuclear species 2 was obtained from a
priori synthesised H2L2 and [RuCl2(η6ꢀpꢀcymene)]2 in 1:1 molar ratio. The complex 3 prepared
from H2L3 and ruthenium(II)ꢀpꢀcymene dimer was identical to that prepared from butyric acid
hydrazide and [RuCl2(η6ꢀpꢀcymene)]2.
4

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Scheme 2
Spectroscopy
The infrared spectra of the ligand precursors and the corresponding Ru(II) complexes were
compared in order to gain preliminary information about the coordination mode of the ligands to the
metal centre. The major changes are noticed in NꢀH stretching region of asymmetric and symmetric
vibrations in the spectra of N,N'ꢀdiacylhydrazines H2L2ꢀ4 and those of 2ꢀ4. Spectra of H2L2ꢀ4 contain
a strong sharp band at 3200 cm−1 and this band is missing in the spectra of 2ꢀ4. The C=O vibrations
in IR spectra of H2L2ꢀ4 are in the range 1585ꢀ1598 cm−1, while those of the corresponding
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complexes 2ꢀ4 are shifted markedly (1528ꢀ1539 cm−1). Similar observations are of note for L1 and
1. These data suggest coordination of L1ꢀL4 to ruthenium(II) via both carbonyl group and nitrogen
atom.
The 1H NMR spectra of the complexes show a characteristic pattern originating from the pꢀ
cymene moiety. In the spectra of complexes 2ꢀ4 proton signals from the aromatic ring are separated
in two groups, one at around 5.35 ppm corresponding to three protons and another at around 5.00
ppm corresponding to one proton. A different pattern is observed in spectrum of 1, where signals at
5.97 ppm correspond to two protons and resonances at 5.78 and 5.72 ppm to the other two protons.
Isopropyl group from pꢀcymene shows a characteristic pattern for this type of ruthenium complexes.
In the spectrum of 1, signals for methylene group of L1 are split into two multiplets at 2.49
and 2.26 ppm. The methyl group from the ligand appears at 1.15 ppm. In the spectra of 2 and 3
signals of aliphatic protons of ligands have different shifts compared to these of the free proligand.
H2L2 has two signals (CH2 and CH3 proton signals) and H2L3 has three (two CH2 and CH3 proton
resonances), as expected. Upon coordination to ruthenium centre, all signals from the ligands are
wellꢀseparated. In spectrum of 2 terminal methyl protons resonate at 1.28 and 1.24 ppm. One CH2
group is split into two multiplets at 2.90 and 2.69 ppm. Another CH2 group appears at 3.71 ppm as a
quartet. These resonances were also assigned by COSY and HSQC NMR measurements. In the
spectrum of 3 the first two CH2 groups are split into two multiplets at 2.82 and 2.66 ppm, whereas
further CH2 groups are centred at around 1.81 ppm as a multiplet, and both terminal methyl groups
are seen at 1.01 ppm as a triplet. The spectrum of 4 shows a triplet at 0.97 ppm from terminal
methyl groups, multiplets at 1.39, 1.77 and 2.70 ppm from three (distant and nearest) CH2 groups.
The reason why distant CH2 groups are at the same place may be in the length of aliphatic chain of
the ligand and consequently the fact that the coordination has little effect on remote protons.
13
The C NMR spectra of 2 ꢀ 4 are also in agreement with proposed structures. Resonances
in the δ range 78.84–101.84 ppm belong to aromatic carbons. Methine carbon of isopropyl group is
found at around 30 ppm and its methyl groups carbons at around 22 ppm, while methyl group
carbon in para position to isopropyl group is seen at around 18 ppm. Carbons from the ligand in 1
are at 173.75 (carbonyl group), 24.36 (CH2 group) and 9.47 ppm (CH3 group). In 2 carbon of
carbonyl group is located at 174.38 ppm, carbon from CH2 groups are at 58.14 ppm and 27.35 ppm,
and methyl carbons are found at 18.29 and 11.74 ppm. The 13C NMR spectrum of 3 provides
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resonances for carbons of the ligand at 173.75 ppm for carbonyl group, at 36.31 ppm resonates the
carbon from nearest CH2 group, at 20.70 ppm the carbon from more distant CH2 group and terminal
13
methyl groups are seen in C NMR spectrum at 14.39 ppm. Complex 4 shows a signal at 173.88
ppm (C=O), at 34.06 from closer CH2 group, at 29.65, 29.29, 22.52 and 22.12 ppm from remote
CH2 group and methyl carbon at 14.03 ppm.
The ESI mass spectrum of 1 recorded in the positive ion mode showed a peak with m/z
359.04 attributed to the [MꢀCl]+. Complexes 2ꢀ4 exhibit peaks attributed to the [MꢀCl]+ at m/z
649.21, 677.08 and 704.13, respectively.
Xꢀray crystallography
The results of Xꢀray diffraction studies of 1, 2·2EtOH, [3][RuCl2(η6ꢀpꢀcymene)]2 and 4 are shown
in Figures 1−4. Each ruthenium atom has the typical “three leg pianoꢀstool’’ geometry, which is
common for a large number of ruthenium(II) arene species. Despite the presence of one stereogenic
centre in 1 or two stereogenic centres in 2 ꢀ 4, the complexes are not chiral and crystallise in
centrosymmetric space groups P21/c, and Pꢀ1, respectively.
Figure 1. ORTEP view of one of the two crystallographically independent cations [RuCl(L1)(η6ꢀpꢀ
cymene)]+ in 1 with thermal ellipsoids at 50% probability level. Selected bond distances (Å) and
angles (deg): Ru2−O2 = 2.0880(17), Ru2−N3 = 2.115(2), Ru2−Cl2 = 2.4028(7), Ru2−C17 =
2.198(3), Ru2−C18 = 2.176(3), Ru2−C19 = 2.159(3), Ru2−C20 = 2.166(3), Ru2−C21 = 2.145(3),
Ru2−C22 = 2.171(3), N3−N4 1.423(3), C14−O2 1.250(3), O2−Ru2−N3 77.63(7).
The N−N bond lengths in all three complexes correspond to typical single bonds. The C−O
bond length in 1 has predominantly a double bond character, while in 2ꢀ4 the electronic
delocalisation is slightly more pronounced leading to elongation of these by ca. 0.04 Å. The bond
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lengths around ruthenium(II) are wellꢀcomparable to those in other related monoꢀ and dinuclear pꢀ
cymene ruthenium complexes.22
Figure 2. ORTEP view of 2 with thermal ellipsoids at 50% probability level. Selected bond
distances (Å) and angles (deg): Ru−O1 = 2.0534(7), Ru−N1i = 2.0994(8), Ru−Cl1 = 2.4290(3),
Ru−C4 = 2.1841(10), Ru−C5 = 2.1674(10), Ru−C6 = 2.2010(10), Ru−C7 = 2.2164(10), Ru−C8 =
2.2024(10), Ru−C9 = 2.1466(10), N1−N1i = 1.4345(16), C1−O1 = 1.2934(12), O1−Ru−N1i
76.03(3).
The Ru···Ru distances in 2 and 3 are of 4.9498(2) and 4.9356(3) Å. These are wellꢀ
comparable to that of 4.9411(5) Å in a related dinuclear pꢀcymene ruthenium complex with diethylꢀ
1,2ꢀdiazenedicarboxylate.11
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Figure 3. ORTEP view of [3][RuCl2(η6
ꢀpꢀcymene)]2 with thermal ellipsoids at 50% probability
level. Selected bond distances (Å) and angles (deg): Ru1−O1 = 2.0678(15), Ru−N2 = 2.1006(17),
Ru1−Cl1 = 2.4176(6), Ru1−C9 = 2.208(2), Ru1−C10 = 2.197(2), Ru1−C11 = 2.172(2), Ru1−C12 =
2.201(2), Ru1−C13 = 2.187(2), Ru1−C14 = 2.201(2), O1−Ru1−N2 76.12(6); Ru2−O2 =
2.0639(15), Ru2−N1 = 2.0949(18), Ru2−Cl2 = 2.4102(6), Ru2−C19 = 2.172(2), Ru2−C20 =
2.158(2), Ru2−C21 = 2.191(2), Ru2−C22 = 2.222(2), Ru2−C23 = 2.202(2), Ru2−C24 = 2.151(2),
N1−N2 = 1.433(3), C4−O1 = 1.287(3), C5−O2 = 1.289(3), O2−Ru2−N1 76.11(6); Ru3−Cl3 =
2.4423(6), Ru3−Cl3i = 2.4424(5), Ru3−Cl4 = 2.4087(6), Ru3−C29 = 2.205(2), Ru3−C30 =
2.178(2), Ru3−C31 = 2.145(2), Ru3−C32 = 2.168(2), Ru3−C33 = 2.148(2), Ru3−C34 = 2.158(2).
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Figure 4. ORTEP view of 4 with thermal ellipsoids at 50% probability level. Selected bond
distances (Å) and angles (deg): Ru1a−O1a = 2.0619(18), Ru1a−N1a = 2.091(2), Ru1a−Cl1a =
2.4135(7), Ru1a−C6a = 2.171(2), Ru1a−C7a = 2.147(3), Ru1a−C8a = 2.188(3), Ru1a−C9a =
2.216(3), Ru1a−C10a = 2.187(2), Ru1a−C11a = 2.185(2), O1a−Ru1a−N1a 76.04(8); Ru1b−O1b =
2.065(2), Ru1b−N1b = 2.087(2), Ru1b−Cl1b = 2.4244(8), Ru1b−C6b = 2.180(3), Ru1b−C7b =
2.175(2), Ru1b−C8b = 2.188(2), Ru1b−C9b = 2.204(3), Ru1b−C10b = 2.186(3), Ru1b−C11b =
2.187(3), N1a−N1b = 1.428(3), C1a−O1a = 1.292(3), C1b−O1b = 1.349(9), O1b−Ru1b−N1b
76.17(8).
It is apparent from the crystal structures (vide infra) that the formation of H2L2 and H2L3
takes place via the nucleophilic attack of the NH2 group of the neighboring molecule of hydrazide
on coordinated C=O group of hydrazide, followed by release of N2H4 and formation of N,N'ꢀ
diacylhydrazine bound to two ruthenium(II) centres with formation of the dinuclear complexes 3
and 4.
It is well established that transition metals increase the polarity of C=O bonds upon
coordination and in such a way facilitate the subsequent reactions like hydrolysis, esterification or
transamination.25 The IR stretching vibrations and 13C NMR signal of C=O group are shifted to
lower wavenumbers and higher chemical shifts in comparison to proligand, indicating the
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polarisation of C=O bond making it more reactive for nucleophilic attack of amine nitrogen of
neighbouring hydrazide molecule.
A certain view on the possible reaction pathway (Scheme 3) can be deduced from the quantum
chemical calculations which were performed for the reaction of [RuCl2(η6ꢀpꢀcymene)]2 complex
(R1) with the butyric acid hydrazide (R2). If we suppose that the initial reaction step starts with the
coordination of R2 molecule to the metal atom, the energetically preferred intermediate Ia has only
one Ru···Cl···Ru bridge stabilising the bisꢀarene complex and it exhibits one bond between the
C=O group and Ru atom at 2.207 Ǻ. The second direct addition of reactant molecule (R2´) to the Ia
seems to be less preferable due to the steric reasons. The better steric conditions and the structural
stability of reaction complex presumably ensure the consecutive elimination of two HCl molecules
as shown in Scheme 3. The formed intermediate IIIa is stabilised via two bonds occurring between
the N1 atom and both ruthenium atoms. The corresponding bond lengths are of 1.943 Ǻ for N1‒Ru
and 2.133 Ǻ for N1‒Ru´. The bond length C=O‒Ru is shortened (2.087 Ǻ) compared to that in Ia.
The second addition of R2´ molecule results in the intermediate IVa, where a new bond C´=O´‒Ru´
is formed. The two bond lengths Ru‒O and Ru´···O´are of 2.086 and 2.082 Ǻ, respectively. The
hydrogen transfer from the hydrazine moiety to the neighbouring one in IVa leads to a stable
intermediate Va. Finally, the abstraction of hydrazine molecule terminates the reaction and the final
product P is generated. A view of the B3LYP optimal structures of all identified intermediates and
their electronic energies are presented in Fig. S15. It should be also noted that calculated bond
distances and angles in the DFT optimized structure satisfactorily agree with those from Xꢀray
diffraction of 3 within ± 0,034 Å (see Table S1).
From the thermodynamic point of view, the Gibbs free energy (ꢀrG) of the reaction can be
calculated as the difference of Gibbs free energies of products and reactants
ꢀrG = G(P)+ 2 × G(HCl) + G(N2H2) – G(R1) – 2 × G(R2) (1)
The B3LYP energy for the gasꢀphase is 102 kJ·mol–1 what indicates the endothermic character of
the studied reaction. This resulting energy is obtained as the sum of the reaction Gibbs free energies
connected with the proposed individual reaction steps (see Scheme 3). The strongest endothermic
character has the addition of R2´ molecule to the IIIa intermediate. On the other hand, the final
dichloridoꢀbridged product formation after hydrazine elimination from the intermediate V is
strongly exothermic. Nevertheless, it should be noted that the heat of solvation of hydrogen chloride
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and hydrazine molecule in real environment will affect the final energy balance of chemical
reaction.
12

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A tentative mechanism is purposed shown in Scheme 3.
Scheme 3. The proposed reaction pathway, the B3LYP optimal geometries of predicted
intermediates and the Gibbs free energies of individual reaction steps; cyan spheres indicate
ruthenium atoms, violet – chloride, blue – nitrogen, red – oxygen, green – carbon.
Experimental
Material and methods
RuCl3·3H2O was purchased from Johnson Matthey (London, United Kingdom). [RuCl2(η6ꢀpꢀ
cymene)]2 was prepared according to a published procedure.26
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Propionyl and butyryl chloride were purchased from Acros, butyric acid hydrazide and pentanoic
acid hydrazide from Alfa Aesar, and propionic acid hydrazide from Sigma Aldrich. Solvents of p.a.
quality were from Acros or Sigma Aldrich, and were used without additional purification.
Elemental analysis was carried out with Elemental Vario EL III microanalyser. Infrared spectra
1
were recorded on a Nicolet 6700 FTꢀIR spectrometer using ATR or KBr pellet technique. H and
13C NMR spectra were recorded on a Varian Geminiꢀ200 spectrometer (at 200 and 50 MHz,
respectively) and on a Bruker Ultrashield Advance III spectrometer (at 500 and 125 MHz,
respectively) employing indicated solvents (vide infra) using TMS as the internal standard.
Chemical shifts (δ) are expressed in ppm and coupling constants J in Hz.
ESI mass spectra of ligand precursors and ruthenium complexes were recorded on 6210 Timeꢀofꢀ
Flight LCꢀMS instrument (G1969A, Agilent Technologies) in positive ion mode and on Bruker
Daltonics HCT 6000 mass spectrometer in positive ion mode by using as solvents CH3CN/H2O or
CH3CN.
Synthesis of ligand precursors
N1,N2ꢀdipropionylhydrazine H2L2. Propionyl chloride (840 mg, 793 ꢁl, 9.08 mmol) was added
dropwise over 30 min to a stirred solution of propionic acid hydrazide (200 mg, 2.27 mmol) and
potassium carbonate (627 mg, 4.54 mmol) in water (4 ml) at 0 °C. The mixture was stirred at 0°C
for 2 h and at room temperature for 1 h. The solvent was removed under reduced pressure and the
residue was purified by column chromatography on silica by using DCM/MeOH (1/4) as eluent.
Yield: 190 mg (58%). IR (ATR): 3215 (s), 3046 (w), 2974 (m), 2938 (m), 1598 (s), 1489 (s), 1218
1
(m), 1073 (w), 883 (w), 654 (m). H NMR (500 MHz, DMSO) δH 9.64 (NH, s, 1H), 2.14 – 2.08
(H2, q, J = 7.5 Hz, 2H), 1.03 – 0.97 (H3, t, J = 7.5 Hz, 2H). 13C NMR (125 MHz, DMSO) δC
171.89 (C1), 26.38 (C2), 9.67 (C3). (+)ESIꢀMS (m/z): [M+Na]+ 167.14.
N1,N2ꢀdibutanoylhydrazine H2L3. nꢀButyryl chloride (1.03 g, 9.67 mmol) was added dropwise over
30 min to a stirred mixture of butyric acid hydrazide (290 mg, 2.84 mmol) and potassium carbonate
(782 mg, 5.68 mmol) in water (3 ml) at 0 °C. The reaction mixture was stirred at 0 °C for 2 h. The
product was filtered off, recrystallised from ethanol (3 ml) and dried in air. Yield: 112 mg (23%).
Anal. calcd for C8H16N2O2: C, 55.79; H, 9.36; N, 16.27. Found: C, 55.65; H, 9.38; N, 16.33. IR
(ATR): 3206 (s), 3055 (w), 2964 (s), 2933 (m), 2870 (w), 1591 (s), 1503 (s), 1483 (s), 1437 (m),
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1201 (m), 1093 (w), 663 (m), 607 (w). 1H NMR (500 MHz, DMSOꢀd6) δH 9.62 (s, 1H), 2.07 (H2, t,
J = 7 Hz, 2H), 1.57 – 1.48 (H3, m, 2H), 0.87 (H4, t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, CDCl3)
δC 171.00 (C1), 35.09 (C2), 18.50 (C3), 13.52 (C4). (+)ESIꢀMS (m/z): [M+Na]+ 195.12; [2M+Na]+
367.26.
Synthesis of ruthenium(II) complexes
[RuCl(propionylhydrazine)(η6ꢀpꢀcymene)]Cl (1). To a warm suspension of [RuCl2(η6ꢀpꢀcymene)]2
(49.9 mg, 0.081 mmol) in isopropanol (7 ml) was added dropwise a suspension of propionic acid
hydrazide (16.3 mg, 0.16 mmol) in isopropanol (3 ml). The mixture was stirred at room temperature
for 3 h and allowed to stand in the fridge for 10 days. The product was filtered off, washed with
isopropanol, diethyl ether and dried in vacuo. Yield: 34 mg (59%). Anal. calcd for
C13H22Cl2N2ORu: C, 39.60; H, 5.62; N, 7.10. Found: C, 39.92; H, 5.36; N, 7.00. IR (ATR): 3211
(m), 3107 (m), 3052 (s), 2981 (s), 2958 (s), 2873 (s), 2775 (s), 2737 (s), 2654 (m), 1639 (s), 1569
1
(s), 1467 (m), 1381 (w), 1330 (w), 1291 (m), 1233 (s), 1090 (w), 885 (w), 785 (w), 551 (w). H
NMR (500 MHz, CDCl3) δH 12.08 (NH, s, 1H), 10.76 (NH from NH2, d, J = 8.5 Hz, 1H), 6.47 (NH
from NH2, d, J = 8.5 Hz, 1H), 5.98 (H5, d, J = 6.0 Hz, 2H), 5.95 (H6, d, J = 5.5 Hz, 1H) 5.79 (H5',
d, J = 6.0 Hz, 1H), 5.73 (H6', d, J = 6.0 Hz, 1H), 2.90 (H9, hept, J = 7.0 Hz, 1H), 2.54 – 2.46 (H2,
hept, J = 7.5 Hz 1H), 2.45 – 2.36 (H2, hept, J = 8.0 Hz 1H), 2.26 (H8, s, 3H), 1.33 (H10, d, J = 7.0
Hz, 3H), 1.30 (H10', d, J = 7.0 Hz, 3H), 1.15 (H3, t, J = 7.6 Hz, 3H). 13C NMR (125 MHz, CDCl3)
δC 181.33 (C1), 102.18 (C7), 95.98 (C4), 83.11 (C5), 82.97 (C5'), 79.93 (C6), 79.58 (C6'), 31.01
(C9), 24.63 (C2), 22.65 (C10), 22.23 (C10'), 18.36 (C8), 9.47 (C3). (+)ESIꢀMS (m/z): ([MꢀCl]+)
359.04.
[Ru2Cl2(N1,N2ꢀdipropionylhydrazine)(η6ꢀpꢀcymene)2] (2). To [RuCl2(η6ꢀpꢀcymene)]2 (62 mg, 0.101
mmol) in DCM (4 ml) was added N1,N2ꢀdipropionylhydrazine (18 mg, 0.125 mmol) in ethanol (4
ml). The orange solution was stirred at room temperature for 4 h. Next day, the solution was
concentrated, the product was filtered off, washed with Et2O and dried. Yield: 46 mg (66%). A
single crystal suitable for Xꢀray diffraction analysis was obtained by slow evaporation of the mother
liquor. Anal. calcd for C26H38Cl2N2O2Ru2: C, 45.68; H, 5.60; N, 4.10. Found: C, 45.59; H, 5.57; N,
4.02. IR (ATR): 3391 (m), 3209 (m), 3055 (s), 3031 (s), 2965 (s), 2875 (s), 2781 (m), 1697 (m),
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1639 (s), 1570 (m), 1539 (s), 1464 (s), 1396 (s), 1234 (m), 1088 (w), 880 (w). 1H NMR (500 MHz,
CDCl3): δH 5.35 (H7, 7', 8', dt, J1 = 16.5, J2 = 6.0 Hz, 3H), 4.99 (H8, d, J = 5.5 Hz, 1H), 3.71 (H4,
q, J = 7.0 Hz, 2H), 2.90 (H2, m, 1H), 2.74 – 2.65 (H2, H11, m, 2H), 2.20 (H10, s, 3H), 1.28 (H1, t,
13
J = 7.5 Hz, 3H), 1.24 (H5, t, J = 7.0 Hz, 3H), 1.16 (H12, 12', dd, J1 = 14.0, J2 = 6.5 Hz, 6H). C
NMR (125 MHz, CDCl3) δC 174.38 (C3), 101.19 (C9), 98.49 (C6), 83.34 (C7), 80.49 (C8), 80.42
(C7'), 79.98 (C8'), 58.14 (C4), 30.43 (C11), 27.35 (C2), 22.40 (C12), 22.08 (C12'), 18.51 (C10),
18.29 (C5), 11.74 (C1). (+)ESIꢀMS (m/z): ([MꢀCl]+) 649.21.
[Ru2Cl2(N1,N2ꢀdibutanoylhydrazine)(η6ꢀpꢀcymene)2] (3) – Direct reaction. To a suspension of
[RuCl2(η6ꢀpꢀcymene)]2 (51 mg, 0.083 mmol) in ethanol (8 ml) was added a suspension of N1,N2ꢀ
dibutanoylhydrazine (14 mg, 0.083 mmol) in ethanol (3 ml) at room temperature. The mixture was
stirred at room temperature for 6 h and allowed to stand in the fridge for 7 days. The product was
filtered off, washed with EtOH, diethyl ether and dried in vacuo. Yield: 35 mg (59%). Anal. calcd
for C28H42Cl2N2O2Ru2: C, 47.25; H, 5.95; N, 3.94. Found: C, 47.50; H, 7.61; N, 3.56. IR (ATR):
3554 (m), 3495 (m), 3449 (s), 3032 (s), 2961 (s), 2928 (s), 2871 (s), 1529 (s), 1466 (m), 1390 (s),
1094 (w), 1041 (m), 880 (m). 1H NMR (500 MHz, CDCl3) δH 5.37 – 5.29 (H9, 9', 10', m, 3H), 4.99
(H10, d, J = 5.5 Hz, 1H), 2.83 (H3 and H5, m, 1H), 2.74 – 2.61 (H3 and H5, H13, m, 2H), 2.19
(H12, s, 3H), 1.88 – 1.74 (H2 and H6, m, 2H), 1.17 (H14, H14', dd, J = 14.5, 7.0 Hz, 6H), 1.01
(H1 and H7, t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, CDCl3) δC 173.75 (C4), 101.85 (C11), 98.10
(C8), 83.10 (C9), 80.96 (C9'), 80.73 (C10'), 79.84 (C10), 36.31 (C3, C5), 30.61 (C13), 22.62 (C14),
22.11 (C14'), 20.70 (C12), 18.59 (C2, C6), 14.39 (C1, C7). (+)ESIꢀMS (m/z): ([MꢀCl]+) 677.08;
([Mꢀ2Cl]2+) 321.06.
[Ru2Cl2(N1,N2ꢀdibutanoylhydrazine)(η6ꢀpꢀcymene)2] (3) – In situ formation of ligand. To a solution
of butyric acid hydrazide (33 mg, 0.32 mmol) in ethanol (3 ml) was added a warmed solution of
[RuCl2(η6ꢀpꢀcymene)]2 (100 mg, 0.16 mmol) in ethanol (8 ml). The mixture was stirred at room
temperature for 16 h and allowed to stand in the fridge for 4 days. The product was filtered off,
washed with cold ethanol, diethyl ether and dried in vacuo. Yield: 25.6 mg (44%). Anal. calcd for
C28H42Cl2N2O2Ru2: C, 47.25; H, 5.95; N, 3.94. Found: C, 47.50; H, 7.61; N, 3.56. IR (ATR): 3554
(m), 3495 (m), 3449 (s), 3032 (s), 2961 (s), 2928 (s), 2871 (s), 1529 (s), 1466 (m), 1390 (s), 1094
1
(w), 1041 (m), 880 (m). H NMR (500 MHz, CDCl3) δH 5.37 – 5.29 (H9, 9', 10', m, 3H), 4.99
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(H10, d, J = 5.5 Hz, 1H), 2.83 (H3 and H5, m, 1H), 2.74 – 2.61 (H3 and H5, H13, m, 2H), 2.19
(H12, s, 3H), 1.88 – 1.74 (H2 and H6, m, 2H), 1.17 (H14, H14', dd, J = 14.5, 7.0 Hz, 6H), 1.01
(H1 and H7, t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, CDCl3) δC 173.75 (C4), 101.85 (C11), 98.10
(C8), 83.10 (C9), 80.96 (C9'), 80.73 (C10'), 79.84 (C10), 36.31 (C3, C5), 30.61 (C13), 22.62 (C14),
22.11 (C14'), 20.70 (C12), 18.59 (C2, C6), 14.39 (C1, C7). (+)ESIꢀMS (m/z): ([MꢀCl]+) 677.08.
[Ru2Cl2(N1,N2ꢀdipentanoylhydrazine)(η6ꢀpꢀcymene)2] (4) – In situ formation of ligand. To a
solution of [RuCl2(η6ꢀpꢀcymene)]2 (64 mg, 0.1 mmol) in methanol (8 ml) at room temperature, a
solution of pentanoic acid hydrazide (24.6 mg, 0.2 mmol) in methanol (2 ml) was added dropwise.
Reaction mixture was stirred for 2.5 h and then left to stand in the fridge for 7 days. The resulting
product was filtered off, washed with cold MeOH and dried in air. Yield: 39 mg (53%). Anal. calcd
for C30H46Cl2N2O2Ru2: C, 48.71; H, 6.27; N, 3.79. Found: C, 46.65; H, 6.11; N, 3.17. IR (ATR):
3053 (s), 3032 (s), 2961 (s), 2924 (s), 2869 (s), 1536 (s), 1496 (m), 1468 (s), 1389 (s), 1056 (m),
1
1034 (m), 878 (m). H NMR (200 MHz, CDCl3) δH 5.32 (H11, 11', 12', m, 3H), 4.98 (H12, d, J =
5.8 Hz, 1H), 2.87 (H15, m, 1H), 2.66 (H4 and H6, m, 2H), 2.18 (H14, s, 3H), 1.77 (H3 and H7, m,
2H), 1.43 (H2 and H8, m, 2H), 1.17 (H16, H16', t, J = 6.6 Hz, 6H), 0.97 (H1 and H9, t, J = 8.2 Hz,
13
3H). C NMR (50 MHz, CDCl3) δC 173.88 (C5), 101.83 (C13), 98.11 (C10), 83.03 (C11), 81.27
(C11'), 80.50 (C12), 79.81 (C12'), 34.06 (C4, C6), 30.59 (C15), 29.65 (C3), 29.29 (C7), 22.93 (C16,
C16'), 22.52 (C2), 22.12 (C8), 18.56 (C14), 14.03 (C1, C9). (+)ESIꢀMS (m/z): ([MꢀCl]+) 704.13.
Xꢀray crystallography. Xꢀray diffraction measurements were performed on a Bruker X8 APEXII
CCD and Bruker D8ꢀVenture diffractometers. Single crystals were positioned at 40, 34, 35 and 34
mm from the detector and 1784, 1630, 1832 and 2626 frames were measured, each for 10, 30 and
10 s over 1° scan width for 1, 2·2EtOH, 3·0.5[RuCl2(η6ꢀpꢀcymene)]2, and 4 respectively. The data
were processed using SAINT software.27 Crystal data, data collection parameters, and structure
refinement details are given in Table 1. The structures were solved by direct methods and refined by
fullꢀmatrix leastꢀsquares techniques. Nonꢀhydrogen atoms were refined with anisotropic
displacement parameters. Hydrogen atoms were inserted in calculated positions and refined with a
riding model. The following computer programs and hardware were used: structure solution,
SHELXSꢀ2013 and refinement, SHELXLꢀ2013;28 molecular diagrams, ORTEP;29 computer, Intel
CoreDuo. Disorder observed for pꢀcymene and alkyl chain of L1 in 1 was resolved by applying
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SADI and EADP restraints and DFIX constraints implemented in SHELXL. Crystallographic data
for these complexes have been deposited with the Cambridge Crystallographic Data Center as
supplementary publications no. CCDCꢀ1492601, ꢀ1492600, ꢀ1492602 and ꢀ1492599. Copy of the
data can be obtained free of charge on application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (email: deposit@ccdc.cam.ac.uk).
Table 1. Crystal Data and Details of Data Collection for 1, 2·2EtOH, 3·0.5[RuCl2(
η
6ꢀpꢀcymene)]2 and 4
3·0.5[RuCl2(η6ꢀpꢀcymene)]2
compound
empirical formula C13H22Cl2N2ORu
2·2EtOH
C30H50Cl2N2O4Ru2 C38H56Cl4N2O2Ru3
1
4
C30H50Cl2N2O4Ru2
fw
394.30
P21/c
775.76
Pꢀ1
1017.86
Pꢀ1
775.76
Pꢀ1
space group
13.8233(6)
20.4127(9)
12.0459(5)
103.277(2)
9.0536(4)
9.0906(4)
9.9218(4)
88.9010(11)
88.7726(11)
85.6563(11)
813.93(6)
1
9.916(1)
12.3781(5)
16.9971(7)
76.132(2)
78.331(2)
88.314(2)
1983.2(2)
2
9.6072(5)
9.7722(5)
17.7727(8)
α
b, Å
c, Å
, Å
α, °
95.264(2)
90.765(2)
93.160(2)
1658.71(14)
2
β
, °
γ
, °
V [Å3]
3308.2(2)
8
Z
0.71073
1.583
0.71073
1.583
0.71073
1.705
0.71073
1.553
λ
ρ
[Å]
calcd, g cm−3
crystal size, mm
T [K]
0.30 × 0.19 × 0.08 0.25 × 0.21 × 0.11 0.19 × 0.13 × 0.05
0.16 × 0.16 × 0.07
100(2)
1.107
0.0335
0.0822
100(2)
100(2)
100(2)
, mm−1
1.265
1.128
1.433
ꢁ
R1
wR2
GOFc
a
0.0315
0.0843
1.044
0.0148
0.0386
0.0224
0.0551
b
1.048
1.032
2 2
1.058
a R1 = Σ||Fo| − |Fc||/Σ|Fo|. b wR2 = {Σ[w(Fo − Fc2)2]/Σ[w(Fo ) ]}1/2. c GOF = {Σ[w(Fo − Fc2)2]/(n − p)}1/2,
2
2
where n is the number of reflections and p is the total number of parameters refined.
Computational Details. The quantum chemical calculations were performed using Gaussian 09
program package.30 The optimal geometries of the studied molecules were calculated in the gasꢀ
phase by DFT method with B3LYP (Becke’s three parameter Lee–Yang–Parr) functional31,32
without any constraints (energy cutꢀoff of 10−5 kJ mol−1, final RMS energy gradient under 0.01 kJ
mol−1 A−1). For all calculations, the SVP/FitSVP basis set was employed.33,34 The optimised
structures were confirmed to be real minima by frequency analysis (no imaginary frequencies). The
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enthalpies and Gibbs free energies were evaluated 298.15 K. Visualisation of the obtained
theoretical results was done by Molekel program package.35
Conclusion
The formation of N,N'ꢀdiacylhydrazines from hydrazides in the presence of [RuCl2(η6ꢀpꢀcymene)]2,
isolated as dinuclear ruthenium(II) complexes was confirmed by spectroscopic and Xꢀray
diffraction methods. A tentative mechanism of these reactions is proposed. The carbon atom of
carbonyl group of butyricꢀ or pentanoic acid hydrazide undergoes nucleophilic attack by NH2 group
of another substituted hydrazine, followed by a loss of hydrazine and formation of N,N'ꢀ
diacylhydrazine capable to link two ruthenium ions. Xꢀray crystallography of dinuclear complexes
confirmed their pseudoꢀtetrahedral geometry which is characteristic for all η6ꢀarene ruthenium
complexes. The preparation of these dinuclear ruthenium complexes emphasize the usefulness of in
situ formation of ligands in preparation of new compounds. The further effort will be directed
towards synthesis of higher nuclearity discrete metallaꢀassemblies.
ACKNOWLEDGEMENTS
This work was supported by the Ministry of Science of the Republic of Serbia, grant numbers
172035. The authors acknowledge the support of the FP7 RegPot project FCUB ERA GA No.
256716. We also acknowledge the bilateral AustrianꢀSerbian mobility grant “New potential
anticancer drugs based on organoruthenium compounds with organic coꢀligands”, No. 451ꢀ03ꢀ
01039/2015ꢀ09/03 (Serbia) and (SRBꢀ08/2016ꢀ2017, OeAD, Austria).
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Formation of new tetradentate bridging ligands was triggered by the presence of starting diruthenium complexe
resulting in the formation of new diruthenium assemblies.