Hydrazone-Based Ligand with Pyrrolidine Donor and Its Molybdenum(VI) Complex: Synthesis, Structure, and Reactivity

Article abstract of DOI:10.1002/zaac.202000440

The Schiff-base condensation of salicylaldehyde and 4-aminobutanehydrazide hydrochloride leads to the hydrazone-based ligand H₂salhyab containing an amino side chain. The reaction of H₂salhyab ? HCl with bis(acetylacetonato)dioxidomo

Full text of DOI:10.1002/zaac.202000440

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.202000440
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Hydrazone-Based Ligand with Pyrrolidine Donor and Its
Molybdenum(VI) Complex: Synthesis, Structure, and
Reactivity
[a, b]
[a]
[a]
[a]
Simona Nica,
Axel Buchholz, Helmar Görls, and Winfried Plass*
Dedicated to Professor Dr. Peter Klüfers on the Occasion of his 70th Birthday
The Schiff-base condensation of salicylaldehyde and 4-amino-
butanehydrazide hydrochloride leads to the hydrazone-based
pyrrolidine ring leading a new type of tridentate hydrazone
ligand with [NNO] donor set. X-ray crystallography revealed the
ligand H salhyab containing an amino side chain. The reaction
additional coordination of a methanol molecule at the
2
of H salhyab·HCl with bis(acetylacetonato)dioxidomolybdenum
molybdenum(VI) center which leads to the formation of hydro-
gen-bonded dimers of the neutral complex in the crystal
2
leads to the formation of [MoO (salhycab)(MeOH)]
2
(
H salhycab=2-((pyrrolidine-2-ylidenehydrazineylidene)methyl)
structure. The complex [MoO (salhycab)(MeOH)] was found to
2
2
phenol), whereby the amino side chain reacted with the
hydrazide carbonyl group to form a cyclic amidine with a
be an efficient catalyst for the peroxidic oxidation of phenyl
methyl sulfide.
Introduction
Hydrazones are widely used ligand systems due to their
potential in various fields including analytical, sensing, switch-
[12]
Molybdenum has been reported as an important metal in
biological systems and, numerous molybdenum containing
enzymes are known. In particular, the existence of molybde-
num in oxotransferase enzymes has sparked interest in
reactivity and coordination chemistry of cis-dioxidomolybde-
ing, and biological applications.
A specific subgroup of
interest in medicinal and coordination chemistry are the
[
1]
[13]
acylhydrazones,
which in the case of their salicylidene
[14]
derivatives are tridentate chelate ligands. Such N-salicylidene
hydrazides with pendant functionalized side chains (see
Scheme 1) have been introduced as versatility tridentate ligand
systems with [ONO] donor set capable of supporting different
protonation states and various types of transition metal
[
2]
num(VI) complexes. Various molybdenum(VI) complexes have
been reported as efficient catalysts for epoxidation and
[
3]
[4]
hydroxylation of olefins, oxidation of sulfides as well as
[5]
[6]
[14]
alcohols, and as catalysts of oxygen transfer reaction. Among
these applications sulfoxides are of specific interest due to their
complexes. These ligands specifically enable the variation of
[
15]
possible aggregation modes and supramolecular assemblies.
[7]
relevance for pharmaceutical industry and academia.
Although sulfoxidation activity has been reported for different
molybdenum-based catalysts ranging from simple salts and
For molybdenum(VI) complexes with N-salicylidene hydra-
zides that contain an ω-hydroxy side chain, this leads to
intermolecular interactions of the side chain oxygen donor
either as an additional ligand at the molybdenum(VI) center or
[8]
[
9]
[10]
composite metal oxides to heterogeneous materials. How-
ever, the number of documented cis-dioxomolybdenum(VI)
complexes catalyzing the peroxidic oxidation of sulfides is still
[16]
via hydrogen bonding. This is in contrast to vanadium(V)
complexes, for which intramolecular hydrogen bonding inter-
actions of the side chain donor with the oxido groups of the
[11]
rather limited.
[17]
vanadium(V) center were observed. For an ω-amino function-
alized N-salicylidene hydrazide ligand with a long side chain
(R=(CH ) NH , see Scheme 1), however, only intermolecular
[
a] Dr. S. Nica, Dr. A. Buchholz, Dr. H. Görls, Prof. Dr. W. Plass
Institut für Anorganische und Analytische Chemie,
Friedrich-Schiller-Universität Jena,
2
5
2
hydrogen bonding interactions for the vanadium(V) complex
[18]
are found. With this concept, we were also able to generate a
Humboldtstraße 8,
β-amino acid functionalized molybdenum(VI) complex that
07743 Jena, Germany
[19]
efficiently catalyzes the peroxidic oxidation of sulfides.
Fax: +49 3641 948132
Tel: +49 3641 948130
E-mail: sekr.plass@uni-jena.de
b] Dr. S. Nica
[
Present address: Institute of Organic Chemistry, Romanian Acad-
emy, Splaiul Independentei, no. 202B, 060023, Bucharest, Romania
©
2021 The Authors. Zeitschrift für anorganische und allgemeine
Chemie published by Wiley-VCH GmbH. This is an open access
article under the terms of the Creative Commons Attribution
License, which permits use, distribution and reproduction in any
medium, provided the original work is properly cited.
Scheme 1. Representation of N-salicylidene hydrazide ligands with
functionalized side chain and their tautomeric forms.
Z. Anorg. Allg. Chem. 2021, 647, 937–942
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Journal of Inorganic and General Chemistry
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In this work, we present the synthesis and characterization
leads to the formation of a neutral complex, which could be
of an ω-amino N-salicylidene hydrazide ligand with a shortened
side chain (R=(CH ) NH , see Scheme 1) and its complexation
isolated as orange crystalline material. This complex contains
the cyclized amidine derivative H salhycab (2-((pyrrolidine-2-
2
3
2
2
reaction to form a cis-dioxidomolybdenum(VI) complex that
leads to the formation of a cyclic amidine with a pyrrolidine
ring, resulting in a new type of tridentate hydrazone-based
ligand with [ONN] donor set.
ylidene-hydrazineylidene)methyl)phenol) of the employed li-
gand with a pyrrolidine ring leading to a new type of tridentate
hydrazone-based ligand with [ONN] donor set. The formation of
the cyclic amidine seems to be favored by the lengths of the
amino side chain leading to a five membered pyrrolidine ring as
such a cyclization was not observed for derivatives with longer
[18]
Results and Discussion
amino side chain.
This ligand cyclization is supported by
elemental analysis, NMR spectroscopy, and X-ray crystallogra-
phy which also revealed the presence of an additional methanol
molecule coordinated at the molybdenum (VI) center leading to
Synthesis and Characterization
The amino side chain functionalized Schiff base 4-amino-N’-[(2-
the neutral complex [MoO (salhycab)(MeOH)].
2
1
hydroxyphenyl)methylidene]butanohydrazide (H salhyab) was
The H NMR data confirms the formation of the complex
2
synthesized in a two step reaction. First, the carbonic acid
hydrazide was synthesized by reaction of the corresponding
ester with hydrazine hydrate under reflux and continuous
stirring for 12 h. Subsequently, the Schiff base was obtained
by condensation of the carbonic acid hydrazide with salicylalde-
hyde in ethanol and isolated as monohydrochloride salt
and the coordination mode of the cyclized hydrazone-based
pyrrolidine ligand. In particular, the twofold deprotonation of
the ligand is confirmed by the absence of the characteristic NH
[20]
1
and OH resonances in the H NMR spectra of the complex. The
cyclization as well as the coordination of the pyrrolidine donor
at the molybdenum(VI) center is consistent with the observed
downfield shift of the resonance corresponding to the relevant
methylene group from about 2.8 ppm in the hydrochloride of
H salhyab·HCl, as depicted in Scheme 2 (for details see
2
Experimental Section).
+
Such carbonic acid hydrazides are known as tridentate
chelate ligands with [ONO] donor set and, due to their
tautomeric forms, possess a variable protonation state at the
amide function, which allows them to act as mono- or dianionic
the open chain ligand H salhyab·HCl (CH NH ) to about
2
2
3
3.8 ppm in the complex with the coordinated cyclic amidine
2
À
ligand salhycab (CH NÀ Mo). This is also supported by the
2
absence of the NH resonance of the ammonium group at
8.04 ppm (NH3 ). Moreover, for the open chain ligand H salhyab
[21]
+
chelates. The reaction of the hydrochloride salt H salhyab·HCl
2
2
with bis(acetylacetonato)dioxidomolybdenum(VI) in methanol
solution in the presence of one equivalent sodium hydroxide
the azomethine proton (CH=N) gives rise to two resonances at
[22]
8.28 and 8.42 ppm attributed to EÀ Z isomerism, whereas for
the coordinated cyclized H salhycab ligand only one resonance
2
is observed at 8.47 ppm. Interestingly, a much more pro-
[23]
nounced coordination induced shift is observed for compara-
ble molybdenum(VI) and vanadium(V) complexes with carbonic
[
16,22,24]
acid hydrazide ligands that provide an [ONO] donor set.
The presence of the coordinated methanol molecule is
confirmed by the specific resonances of the methyl and OH
protons at 3.16 ppm and 4.08 ppm, respectively, as well as the
1
3
C resonance at 48.6 ppm.
The formation of the cyclic amidine upon coordination at
the molybdenum(VI) center is also evident from the changes
1
3
observed for the relevant C NMR resonances. In particular, the
resonance related to the methylene group next to the terminal
+
ammonium group of H salhyab·HCl (CH NH ) at 38.2 ppm is
2
2
3
found at 58.3 ppm for the corresponding methylene group of
the pyrrolidine ring. In addition, this significant downfield shift
is also consistent with the coordination of the pyrrolidine N
donor at the molybdenum(VI) center. A similar, although less
pronounced, coordination induced shift is observed for the
resonance of the azomethine carbon atom (140.8 and
1
46.3 ppm, EÀ Z isomers) of the uncoordinated open chain
ligand, which is found at 151.5 ppm in the complex with the
cyclic amidine ligand.
[25]
The IR spectrum of the complex [MoO (salhycab)(MeOH)]
2
À 1
contains strong bands at 909 and 930 cm , corresponding to
Scheme 2. Synthesis of H salhyab and the complex
the stretching vibrations of the cis-MoO group. This is in good
agreement with examples reported in literature that also
2
2
[
MoO (salhycab)(MeOH)].
2
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contain a coordinated alcoholic oxygen donor in trans position
to one of the oxido donors at the molybdenum(VI) center.
The strong band assigned to the stretching vibration of the
From the molecular structure it is evident that the
[16,19,26]
molybdenum atom is found in a distorted octahedral geometry,
with the [ONN] donor set of the hydrazone ligand, the
methanol oxygen donor, and the two oxido groups of the cis-
CH=NÀ N=C group, commonly observed in the range from 1600
À 1
2+
to 1625 cm for dianionic carbonic acid hydrazides coordinated
MoO2 moiety forming the coordination sphere. The Mo=O
[
18,22,27]
to metal centers,
is found well within this range for
bond lengths (MoÀ O1 and MoÀ O2) are found in the typical
À 1
[
MoO (salhycab)(MeOH)] at 1606 cm , although in this case an
range of 169–170 pm and also the OÀ MoÀ O bond angle with
2
[
26b,28]
amidine is part of the functional group. The presence of a
coordinated methanol molecule is evident from a broad band
105.19(7)° in the expected range.
Due to the cis config-
uration of the oxido groups, O1 is in an axial position with
respect to the equatorial plane defined by the tridentate ligand
À 1
at 3436 cm .
(O3, N1, and N3), while the second oxido group O2 located in
the equatorial plane is in trans position to the imine donor N1
Structure Description
at a distance of 227.67(15) pm. The dianionic tridentate ligand
2
À
salhycab coordinates in a meridional fashion leading to a five-
and six-membered chelate ring with bite angles of 70.8° and
80.5°, respectively. The two formally anionic donor atoms O3
The neutral complex [MoO (salhycab)(MeOH)] crystallizes in the
monoclinic space group P2 /c (see Experimental Section for
crystallographic details). The molecular structure of the complex
is depicted in Figure 1. Selected bond length and angles for the
first coordination sphere of the molybdenum(VI) center of
2
1
and N3 of the ligand are in trans position with an angle
O3À MoÀ N3 of 147.40(7)° and a MoÀ O3 bond length of
195.38(15) pm, which is somewhat elongated with respect to
the corresponding molybdenum(VI) complexes with N-salicyli-
[
MoO (salhycab)(MeOH)] are summarized in Table 1. The struc-
2
[16,19]
ture shows that the employed ω-amino N-salicylidene hydrazide
dene hydrazide ligands (phenolate MoÀ O 193 pm).
More-
ligand H salhyab was transformed to the cyclic amidine ligand
over, the MoÀ N3 bond length is found at 206.08(18) pm, which
is consistent with the anionic nature of amidate nitrogen donor.
This is supported by the bond lengths for the amidine carbon
atom C8 with 131 and 134 pm for C8À N2 and C8À N3,
respectively, which show that the deprotonated ligand in the
complex corresponds to the tautomeric form with the C=N
double bond of the amidate is in conjugation with the imine
C=N bond of the hydrazone (see Scheme 3). Although a
comparison with coordinated hydrazine amidinate ligands from
literature is not possible, this is supported by the equivalent
observation in the case of the related N-salicylidene hydrazide
ligands, where the corresponding enolate form of the amide
group shows similar bond lengths (CÀ N 131 pm and CÀ O
2
H salhycab upon complexation leading to a pyrrolidine ring in
2
the newly formed hydrazone-based ligand.
[22,29]
1
30 pm),
whereas for complexes with coordinated keto
form a pronounced difference for the bond lengths is observed
[
29]
(
CÀ N 133 pm and CÀ O 127 pm).
The octahedral coordination sphere of the molybdenum
atom is completed by a methanol molecule, which is coordi-
nated in trans position to the oxido group O1 and weakly
Figure 1. Molecular structure of the complex
bounded at the molybdenum(VI) center (MoÀ O1M
[
MoO (salhycab)(MeOH)] together with the atom labeling. Thermal
ellipsoids are drawn at 50% probability level.
2
[30]
2
31.36(14) pm) due to the trans influence of the oxido group.
In the crystal structure the OH group of the coordinated
methanol is involved in hydrogen bonding to a neighboring
complex molecule leading to a dimer of neutral complexes as
depicted in Figure 2.
Table 1. Selected bond lengths (in pm) and angles (in °) for
[
MoO (salhycab)(MeOH)].
2
Mo1À O1
169.85(15)
170.29(15)
195.38(15)
231.39(14)
105.19(7)
96.24(7)
170.80(7)
93.43(6)
100.45(7)
Mo1À N1
227.67(15)
206.08(18)
131.0(3)
134.0(3)
106.46(7)
83.19(6)
77.46(6)
159.02(7)
95.94(7)
147.40(7)
82.14(6)
Mo1À O2
Mo1À N3
Mo1À O3
C8À N2
Mo1À O1M
C8À N3
O1À Mo1À O2
O1À Mo1À O3
O1À Mo1À O1M
O1À Mo1À N1
O1À Mo1À N3
O3À Mo1À N1
N1À Mo1À O1M
N1À Mo1À N3
O2À Mo1À O3
O2À Mo1À O1M
O3À Mo1À O1M
O2À Mo1À N1
O2À Mo1À N3
O3À Mo1À N3
N3À Mo1À O1M
80.48(6)
79.01(5)
70.79(6)
Scheme 3. Tautomeric forms of the protonated ligand H salhycab.
2
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[
MoO (salhycab)(MeOH)] this overoxidation could be reduced
2
by a stepwise addition of the hydrogen peroxide over a period
5 min in the initial phase of the reaction, which leads to the
1
same overall yield, but the amount sulfone formed is reduced
to 10%.
Conclusions
We report the synthesis of a new ω-amino N-salicylidene
hydrazide ligand H salhyab with a short side chain of three
2
methylene groups (R=(CH ) NH , see Scheme 1). This potential
2
3
2
ligand is employed in the synthesis of a molybdenum(VI)
complex. However, this reaction leads to the formation of a
cyclic amidine which is associated with an intramolecular
condensation reaction of the terminal amino and the carbonyl
group of the ligand. As revealed by the crystal structure, the
Figure 2. Hydrogen bonded dimer of [MoO (salhycab)(MeOH)] with
2
an O1M···N2 Distance of 268.8(2) pm (O1MÀ H···N3 179(3)°). Hydro-
gen atoms not involved in hydrogen binding are omitted for clarity.
obtained molybdenum(VI) complex [MoO (salhycab)(MeOH)]
2
Sulfoxidation
contains the new and hitherto unprecedented tridentate
hydrazone-based ligand H salhycab with a cyclic amidine as
2
The cis-dioxidomolybdenum complex [MoO (salhycab)(MeOH)]
part of a pyrrolidine ring and an [ONN] donor set. This new
ligand is coordinated in its dianionic form with the two formally
negative donor groups the phenolate oxygen O3 and the
amidinate nitrogen N3 in trans position at the molybdenum(VI)
center. In the solid state the neutral complex molecules
dimerize via hydrogen bonding between the coordinated
methanol molecule and the non-coordinated amidinate nitro-
gen atom N2. The observed catalytic activity towards the
peroxidic oxidation of sulfides is within the range for reported
complexes with a corresponding N-salicylidene hydrazide back-
bone.
2
was tested for its ability to catalyze the oxidation of sulfides
under homogeneous conditions in solution using methyl
phenyl sulfide (thioanisol) as model substrate (see Scheme 4).
Hydrogen peroxide was used as oxidizing agent in a slight
excess of 1.2 equivalents based on the sulfide substrate. The
reaction was started by the addition of the oxidant to the
solution (dichloromethane/methanol=7:3) of the substrate,
which was cooled to 0°C. The reaction solution containing
1
mol% of catalyst based on the substrate was stirred at room
temperature and monitored by gas chromatography. A control
reaction under the same conditions without any complex
present leads to less than 1% sulfide conversion. After the
reaction the solvent was removed in vacuo and the products Experimental Section
were separated by column chromatography.
Materials and Instrumentation: All reagents were used as received,
without further purification. Abbreviations used throughout the
manuscript: H salhyab=4-amino-N’-[(2-hydroxyphenyl)
methylidene]butanohydrazide and H
denehydrazineylidene)methyl)phenol. Solution NMR spectra ( H
and C) were recorded on Bruker Avance 200 and 400 spectrom-
eters. Elemental analyses (C, H, N) were performed with a Leco
CHNS-932 elemental analyzer. GC measurements were carried out
on an SRI 8610D gas chromatograph using an MXT-1 Restek
column. IR spectra were measured on a Bruker IFS55/Equinox
spectrometer on samples prepared as KBr pellets.
The complex [MoO (salhycab)(MeOH)] functions as an
2
efficient catalyst for the sulfide oxidation. In the presence of
2
1
mol% of complex in a dichlormethane methanol solution
salhycab=2-((pyrrolidin-2-yli-
2
1
mixture an overall yield of 83% was observed after a reaction
time of 18 h, with the sulfoxide being the major product, which
is well within the reported range observed for other molybde-
1
3
[11,16,31]
num(VI) catalysts.
Unfortunately, the reaction also leads to
an overoxidation resulting in the corresponding sulfone at an
amount of 25% of the final product. Although this is a feature
commonly observed for molybdenum(VI) catalysts, it is worth
noting that no such overoxidation is observed for
molybdenum(VI) and vanadium(V) catalysts with related N-
Synthesis of 4-aminobutanehydrazide hydrochloride: To a solu-
tion of ethyl 4-aminobutanoate hydrochloride (7.68 g, 0.05 mmol)
in ethanol (10 mL) hydrazine hydrate (2.50 g, 2.50 mL, 0.05 mmol)
was added under continuous stirring, followed by addition of
ethanol (40 mL) and water (5 mL). The resulting solution was
heated to reflux under continuous stirring overnight. After cooling
to room temperature, diethyl ether (50 mL) was added which
caused a turbid solution. Stirring at room temperature for 12 h
afforded a colorless precipitate. (Note: In the case an oily product is
formed, the reaction mixture was dried in vacuo and subsequently
extracted three times with hot ethanol and precipitated by stirring
with diethyl ether (100 mL)). Yield: 6.45 g (0.04 mol; 84%). Elemen-
[18–19,27b]
salicylidene
hydrazide
ligands.
For
À 1
tal analysis for C H N ClO (M=153.61 g·mol ): calcd: C 31.28, H
4
12
3
Scheme 4. Sulfoxidation of methyl phenyl sulphide with hydrogen
7.87, N 27.36%; found: C 32.20, H 7.68, N 26.37%.
peroxide and 1 mol% of [MoO (salhycab)(MeOH)] as catalyst.
2
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Synthesis of H salhyab·HCl: Salicylaldehyde (2.42 g, 0.02 mol,
2
Table 2. Crystallographic data for [MoO (salhycab)(MeOH)].
2
2.07 mL) was added dropwise to a solution of 4-aminobutanehy-
drazide hydrochloride (3.20 g, 0.02 mol) in absolute ethanol (50 mL)
heated to reflux. The resulting yellow solution was cooled down to
room temperature and subsequently stirred overnight. The formed
precipitate was filtered off and dried in vacuo. Additional material
can be obtained by reducing the solution volume in vacuo to about
half, followed by addition of diethyl ether (100 mL). Total yield:
empirical formula
formula weight/gmol
crystal system
space group
a/pm
C H15MoN O
12 3 4
À 1
361.21
Monoclinic
P2 /c (No. 14)
1
1021.06(3)
1282.03(4)
b/pm
4
2
6
.12 g (0.016 mol; 80%). Elemental analysis for C H N ClO (M=
c/pm
1091.66(2)
90.0
110.274(2)
90.0
11
16
3
2
À 1
57.72 gmol ): calcd: C 51.27, H 6.26, N 16.30%; found: C 51.81, H
α/°
1
.31, N 15.96%. H NMR (400 MHz, dmso-d , ppm): δ=1.80–1.90
β/°
6
3
(m, 2H, CH ), 2.36 and 2.70 (both t, J=7.2 Hz, 2H total, CH CO),
δ/°
2
2
+
3
2
.79–2.85 (m, 2H, CH NH ), 6.87–6.99 (m, 2H, arom. CH), 7.19–7.40
V/nm
1.34048(6)
2
3
+
(m, 1H, arom. CH), 7.46–7.69 (m, 1H, arom. CH), 8.04 (br, 3H, NH3 ),
T/°C
À 90
8
.28 and 8.42 (s, 1H total, CH=N), 10.16, 11.17, 11.29 and 12.02 (NH
Z
4
13
1
À 1
and OH, 2H total). C{ H} NMR (50 MHz, dmso-d , ppm): δ=21.8,
μ(Mo K
α
)/mm
0.996
9330
2762
3055 (0.0235)
1.050
6
+
22.8 (both CH ), 29.0 and 30.6, (CH CO), 38.2 (CH NH ), 116.1,
measured reflections
Data with I >2σ(I)
unique reflections (R
goodness-of-fit on F
Final R indices [all data]
Final R indices [I >2σ(I)]
2
2
2
3
1
16.3, 118.6, 119.2, 120.0, 126.5, 130.6, 130.9, 131.1, 133.1 (all arom.
CH and C), 140.8, 146.5 (both CH=N), 156.4, 157.3, 158.6, 162.5,
int)
À 1
2
1
67.6 (arom. C), 172.9 (C=O). IR (KBr, selected data, cm ): ~n =3461
+
(br, NH3 ), 3169 (br, NH), 1689 (s; C=O), 1621 (s, C=N).
R =0.0284, ωR =0.0635
1
2
R =0.0239, ωR =0.0610
1
2
Synthesis of [MoO (salhycab)(MeOH)]: To a stirred solution of
2
H salhyab·HCl (0.80 g, 3.10 mmol) in methanol (60 mL) was added
2
NaOH (0.12 g, 3.10 mmol), followed by the addition of MoO (acac)
2
2
[
32]
(1.00 g, 3.10 mmol). The resulting red solution was heated under
multiple-scans (SADABS 2016/2).
The structure was solved by
[33]
reflux with continuous stirring for one hour. Subsequently the
volume of the solution was reduced to about half under reduce
pressure and left at room temperature while an orange-reddish
precipitate was formed. The resulting precipitate was filtered off
and the filtrate kept in an open flask at room temperature. Upon
slow evaporation of the solvent suitable orange crystals for X-ray
direct methods (SHELXT) and refined by full-matrix least squares
2 [34]
techniques against F (SHELXL-2018). All hydrogen atoms were
located by difference Fourier synthesis and refined isotropically. All
non-hydrogen atoms were refined anisotropically. A summary of
crystallographic and structure refinement data is given in Table 2.
Crystallographic
data
(excluding
structure
factors)
for
measurement could be isolated. Total yield: 0.72 g (1.99 mmol;
[MoO (salhycab)(MeOH)] has been deposited with the Cambridge
2
À 1
6
4%). Elemental analysis for C H N MoO (M=361.20 gmol ):
Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge
CB21EZ, UK. A copy of the data can be obtained free of charge on
quoting the depository number CCDC-2047182 (E-Mail: depos-
it@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
12
15
3
4
calcd: C 39.90, H 4.19, N 11.63%; found: C 40.20, H 4.16, N 11.55%.
1
H NMR (400 MHz, dmso-d , ppm): δ=2.06–2.14 (m, 2H, CH ), 2.48–
6
2
3
2
5
5
.50 (m, CH C=N, overlap with the solvent signal), 3.16 (d, J=
2
3
.2 Hz, 3H, CH OH), 3.82–3.86 (m, 2H, CH À NÀ Mo), 4.08 (q, J=
3
2
.2 Hz, 1H, CH OH), 6.79–6.98 (m, 2H, arom. CH), 7.36–7.40 (m, 1H,
3
13
arom. CH), 7.53–7.55 (m, 1H, arom. CH), 8.47 (s, 1H, CH=N).
C
1
{
H} NMR (100 MHz, dmso-d , ppm): δ=25.4 (CH ), 26.3 (CH C=N),
6
2
2
Acknowledgements
4
8.6 (CH OH), 58.3 (CH NÀ Mo), 118.1, 120.3, 120.8, 133.3, 133.6 (all
3
2
arom.CH and C), 151.5 (CH=N), 160.2 (arom. CÀ OÀ Mo), 176.5 (C=N)
À 1
Open access funding enabled and organized by Projekt DEAL.
ppm. IR (KBr, selected data, cm ): ~n =3436 (br, OH), 1606 (s,
À C=NÀ N=CÀ ), 930 and 909 (s, MoO2).
Sulfoxidation: The molybdenum complex [MoO (salhycab)(MeOH)]
Keywords: Molybdenum
Sulfoxidation · Crystal structure
·
Hydrazone
·
Schiff base
·
2
(
0.025 mmol) was dissolved at room temperature in a mixture of
CH Cl and CH OH (7:3, 25 mL) and phenyl methyl sulfide (0.29 ml,
2
2
3
2
.5 mmol) was added. The resulting solution was cooled to 0°C and
a slight excess of an aqueous solution of H O 26% (1.2 equiv.,
0
2
2
.35 mL, 3 mmol) was dropwise added to start the reaction. This
[
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Z. Anorg. Allg. Chem. 2021, 937–942
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