Reaction of sodium 2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl) benzenesulfonate with ethylenediamine on Cu(ii) and Ni(ii) centres: Efficient Cu(ii) homogeneous catalysts for cyanosilylation of aldehydes

Article abstract of DOI:10.1039/c6ra12274d

By reacting copper(ii) or nickel(ii) salts with sodium 2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl) benzenesulfonate (NaHL) in an EtOH/H₂O solvent mixture and in the presence of ethylenediamine (en), [Cu(HL)₂(en)₂] (1) or {

Full text of DOI:10.1039/c6ra12274d

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Reaction of sodium 2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)
benzenesulfonate with ethylenediamine on Cu(II) and Ni(II) centres:
efficient Cu(II) homogeneous catalysts for cyanosilylation of aldehydes
Abdallah G. Mahmoud,a,b Kamran T. Mahmudov,*a,c M. Fátima C. Guedes da Silva,*a
Armando J. L. Pombeiro,*a
a Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais,
1049ꢀ001 Lisboa, Portugal
b Department of Chemistry, Faculty of Science, Helwan University, Ain Helwan, Cairo, Egypt
c Department of Chemistry, Baku State University, Z. Xalilov Str. 23, Az 1148 Baku, Azerbaijan
∗Corresponding authors
Eꢀmail addresses:
kamran_chem@mail.ru, kamran_chem@yahoo.com (Kamran T. Mahmudov)
fatima.guedes@tecnico.ulisboa.pt (M. Fátima C. Guedes da Silva)
pombeiro@tecnico.ulisboa.pt (Armando J. L. Pombeiro)
Graphical Abstract
Reaction
of
sodium
2ꢀ(2ꢀ(2,4ꢀdioxopentanꢀ3ꢀylidene)hydrazinyl)benzenesulfonate
with
ethylenediamine on Cu(II) and Ni(II) centres lead to variety of metal complexes which effectively
catalyse the cyanosilylation of aldehydes with trimethylsilyl cyanide.
Abstract
By reacting copper(II) or nickel(II) salts with sodium 2ꢀ(2ꢀ(2,4ꢀdioxopentanꢀ3ꢀylidene)hydrazinyl)
benzenesulfonate (NaHL) in EtOH/H2O solvent mixture and in the presence of ethylenediamine
(en), [Cu(HL)2(en)2] (1) or {[Ni(en)3](HL)2}ꢁC2H5OHꢁ6H2O (2) were synthesized, respectively. In
MeOH, the coordination polymer [Cu(ꢀꢀL1ꢀ1κO,NN’N’’:2κO’)]n (3) was obtained, where L1 refers
to a dianionic ligand species attained via Schiffꢀbase condensation of NaHL with en on the Cu(II)
metal centre, whereas no reaction was obtained in the case of Ni(II). All the compounds were
characterised by IR spectroscopy, ESIꢀMS, elemental and singleꢀcrystal diffraction. The Cu(II)
compounds 1 and 3 act as effective homogenous catalysts for the cyanosilylation reaction of a
variety of aldehydes with trimethylsilyl cyanide affording the corresponding cyanohydrin
trimethylsilyl ethers in high yields (up to 93 %) and at room temperature.
Keywords: Arylhydrazones of βꢀdiketones; CuII and NiII complexes; cyanosilylation of aldehydes.

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1. Introduction
Arylhydrazones of βꢀdiketones (AHBDs) are well known models for the study of E/Z
isomerism as well as azoꢀhydrazone tautomerism.1,2 The molecular structures of AHBDs are
characterized by strong intramolecular N−HꢁꢁꢁO or O−HꢁꢁꢁN resonanceꢀassisted hydrogen bonds
(RAHB), involving a set of conjugated single and double bonds.2 Because of RAHB, the proton
donor and acceptor atoms acquire partial opposite charges and strengthening of Hꢀbond occurs. The
position of the proton designates the nature of the donor functionality, which determines the
reactivity of the AHBD and has an influence on intermolecular forces stabilizing the crystal
structure.3 Thus, RAHB reduces the reactivity of the donor and acceptor sites of AHBD
compounds. For example, the carbonyl group involved in RAHB is not converted into a Schiff base
in the reaction of AHBD with amines, whereas the ammonium salt is isolated.4 A metal centre (for
instance, of Cu2+ or Ni2+) can promote the activation of a carbonyl group of an AHBD in its reaction
with amines, leading to a variety of complexes with different nuclearities and intramolecular nonꢀ
covalent interactions.2
On the other hand, cyanosilylation of carbonyl compounds with trimethylsilyl cyanide
(TMSCN) (Scheme 1) to form new C–C bonds and to protect alcohol functions is an important
reaction as the Oꢀprotected cyanohydrins can be transformed into a variety of building blocks, such
as αꢀhydroxy acids, αꢀhydroxy ketones, αꢀamino acids, βꢀamino alcohols, vicinal diols, 1,2ꢀ
diamines, etc.5 The reaction can be catalysed by various Lewis acids and bases.5 For example,
AlCl3, LaCl3, KCN/18 crownꢀ6, Bu4N+CN–, trimethylsilyl triflate, amines, arsines, phosphines,
phosphazanes, organocatalysts, etc. have been employed for this purpose.5 In particular, the
cyanosilylation of aldehydes does not require a strong Lewis acidity and can be carried out under
mild conditions by using metal complexes as catalysts.6 However, there are only a few metal
complex approaches to this transformation in homogenous catalytic systems.6
Scheme 1. Cyanosilylation of an aldehyde with trimethylsilyl cyanide (TMSCN).
Hence, on the basis of the above considerations, we focused this work on the following
aims: i) to performe the reaction of an AHBD, viz. sodium 2ꢀ(2ꢀ(2,4ꢀdioxopentanꢀ3ꢀylidene)
hydrazinyl)benzenesulfonate (NaHL), with ethylenediamine on Cu(II) and Ni(II) centres to prepare
new stable complexes with strong Lewis acid metal sites; ii) to evaluate the catalytic activity of the
prepared new complexes in the model cyanosilylation of aldehydes with trimethylsilyl cyanide
(TMSCN), for which a high Lewis acid character of the catalyst should constitute a favorable
feature (see below).
2

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2. Results and Discussion
2.1. Synthesis of complexes 1–3
Sodium 2ꢀ(2ꢀ(2,4ꢀdioxopentanꢀ3ꢀylidene)hydrazinyl)benzenesulfonate (NaHL) (Scheme 2)
was synthesized by the JappꢀKlingemann method7 upon reaction between 2ꢀsulfobenzeneꢀ
diazonium chloride and pentaneꢀ2,4ꢀdione in water solution containing sodium hydroxide.
Reactions of copper(II) nitrate hydrate and nickel(II) acetate tetrahydrate with NaHL in the
presence of ethylenediamine (en) in a mixture of EtOH/H2O (1:1, v/v) lead to the mononuclear
compounds [Cu(HLꢀκO)2(en)2] (1) and {[Ni(en)3](HL)2}ꢁC2H5OHꢁ6H2O (2), respectively (routes I
and II in Scheme 2). Oneꢀpot template reaction with copper(II) nitrate hydrate led to the
coordination polymer [Cu(ꢀꢀL1ꢀ1κO,NN’N’’:2κO’)]n (3), where L1 refers to the imino species
derived from nucleophilic attack of en to a carbonyl group of NaHL (route III in Scheme 2). The
formation of a novel Schiff base during complex formation is common.2 We can tentatively explain
the different behaviours of the Cu(II) and Ni(II) salts, as follows: copper(II) is expected to be a
stronger Lewis acid than nickel(II) and thus it can activate more effectively the AHBD ligand
towards a nucleophilic atack of the amine (en) to form the final L1 ligand. Moreover, the acidity of
the en ligand is promoted to a larger extent upon coordination to copper than to nickel, what favours
the formation of water in the condensation reaction. Since Ni(II) is slightly softer than Cu(II) it is
expected that the former prefers coordination to ligands containing softer donor atoms (en).
Compounds 1–3 were characterized by elemental analysis, IR spectroscopy, ESIꢀMS and
singleꢀcrystal Xꢀray diffraction analysis. The IR spectra of both compounds show the ν(NH),
ν(C=O) and ν(C=OꢁꢁꢁH) vibrations at 3245, 1675 and 1639 (for 1), and 3286, 1675 and 1642 cm–1
(for 2) respectively, while for NaHL such bands are observed at 3114, 1679 and 1639 cm–1,
correspondingly.7 For such vibrations, polymer 3 displays values at 3364 and 3287 [ν(NH)], 1674
[ν(C=O)], and 1652 and 1608 [ν(C=N)] cm–1. The ESIꢀMS peaks at 751.42 [Mr+H]+ (for 1), 119.0
[Ni(en)3]2+ and 283.0 [HL]ꢀ (for 2) and 388.8 [Mr+H]+ (for 3) support the formulation of the
compounds.
3

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Scheme 2. Reactions of NaHL with Cu2+ or Ni2+ ions in the presence of ethylenediamine (en).
2.2. Description of the X-ray crystal structures
Crystals of 1−3 suitable for Xꢀray diffraction analysis were obtained upon crystallization
from EtOH/H2O (1:1, v/v) (for 1 and 2) or MeOH (for 3). The molecular structures are shown in
Figure 1 and Hꢀcontacts in Figure S1. Crystallographic data and refinement parameters are given in
Table S1 and selected bond distances and angles in Table S2.
The asymmetric unit of 1 includes a copper cation standing in an inversion centre and bound
to an ethylenediamine molecule and a HL− anion by one of the Oꢀsulfonate atoms. Therefore, the
complex molecule of 1 presents the metal in a slightly distorted octahedral geometry with four Nꢀ
atoms in the equatorial plan and two Oꢀatoms in the apical sites. As a consequence of such a type of
coordination, a RAHB remains, with a regular hydrogen bonding systems of HL−. The structure of 2
comprises two (hydrazinyl)benzenesulfonate anions that coꢀcrystalized with a tris(ethylenediamine)
nickel(II) cation. The anionic ligand in 1, as a whole, deviates from planarity as shown by the
NCCCMe torsion angles of 11.6(3) and ꢀ167.9(2)º, and the angles of 20.06º and 20.34º between the
leastꢀsquare planes of the CMeCO groups, and that of the aromatic ring. Comparing with the
structure of 2, those torsion angles assume values of 4.9(6) and ꢀ175.6(5) in one of the anions, and ꢀ
3.7(6) and ꢀ174.8(4)º in the other; the angles between the afore mentioned planes are as low as
14.68º and 11.49º in one anion and just 4.39º and 6.73º in the other, thus revealing the impact on
coplanarity of coordination of HL− to a metal centre. However, such coordination had no effect
either on the NN (see Table S1) or on the CketoneO bond distances and, in the latter case, the ketone
groups of 1 and 2 not involved in the RAHB present slightly shorter lengths (by ca. 0.016 Å, Table
S1) as comparared to the free ones. In addition, the HL− species in both compounds contains,
besides the Oketone···N RAHB interactions [of 2.579(3) in 1, and 2.566(5) or 2.583(7) Å in 2; see
Figures S1 and S2], also Osulfonyl···N charge assisted hydrogen bondings [CAHB; of 2.970(3) in 1,
4

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and 2.825(5) or 2.924(4) Å in 2; see Figures S1 and S2], which relates to a synergistic mutual
reinforcement of the intramolecular hydrogen bonding.
In the crystal structure of 3, the copper atom has a squareꢀpyramidal coordination sphere (τ5
= 0.05) with the chelating ligand occupying the four equatorial positions and the apical site being
engaged with an Oꢀsulfonyl atom from an adjacent molecule, thus leading to a 1D coordination
polymer that runs along the crystallographic a axis (Figure S1). Each metal cation is thus involved
in two sixꢀmembered and one fiveꢀmembered metallacycles i.e., CuOSC2N, CuN2C2N and
CuNC2N, respectively. The Cu−Oequatorial distance of 1.9667(18) Å in 3 is considerably shorter than
the Cu−Oaxial one, which assume the value of 2.528(2) Å, the latter being identical to that shown by
1 (Table S2). However, the Cu−N bond lenghts in 3 are in the range of 1.928(2) to 1.986(2) Å
(Table S2) and are considerably shorter than those of 1 [avg. 2.012(2) Å]. This can conceivably be
due to the extensive intermolecular hydrogen bond interactions in which compound 1 is involved
and which expands the structure to a 3D network (Figure S4), while in 3 such interactions associate
two infinite chains by means of the amine Hꢀatoms that donate to the viccinal Oꢀsulfonates
(Figures S3 and S4). Despite of that, the intermolecular metal···metal distances are much shorter in
3 [5.407(1) Å] than in 1 [7.4179(4) Å, coincident with the a dimension of the unit cell].
1
2
3
5

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Figure 1. Molecular structures of 1−3 with partial atom numbering schemes. Symmetry codes to
generate equivalent atoms: 1: i) ꢀx,ꢀy,ꢀz; 3: i) 1+x,y,z: ii) ꢀ1+x,y,z. In 2 only one of the components
of the disordered complex cation is shown.
2.3. Catalytic Activity
The catalytic activity of the Cu(II) complexes 1 and 3 in the cyanosilylation reaction was tested
under mild conditions and in air, with benzaldehyde as substrate. Several experimental variables
were explored including catalyst amount, reaction temperature, reaction time, and type of solvent.
These studies were carried out with complex 3 in view of its high solubility in the reaction medium
(methanol) and are shown in Table 1.
Compounds 1 and 3 work as homogeneous catalysts, in methanol, for the conversion of
benzaldehyde into 2ꢀphenylꢀ2ꢀ((trimethylsilyl)oxy)acetonitrile (Scheme 1) at room temperature,
with yields of 86 and 93 %, respectively, after 16 h (Table 1, entries 25 and 6). No other products
were observed.
The plot of yield versus time for the cyanosilylation of benzaldehyde with catalysts 1 (Table
o
1, entries 20ꢀ25) and 3 (Table 1, entries 1ꢀ6) at 25 C, is presented in Figure 2, showing an increase
in the product yield with that factor. Extending the reaction time to 20 h did not increase the yield
significantly.
Table 1. Cyanosilylation of benzaldehyde using 1 and 3 as catalysts.a
Amount of
Catalyst
(mol%)
Time
(h)
Yieldb
(%)
Entry
Catalyst
T (˚C) Solvent
TONc
1
2
3
4
5
6
1
2
4
6
8
5
5
5
5
5
5
25
25
25
25
25
25
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
22.5
40.0
46.5
70.2
77.6
92.6
4.5
8.0
9.3
14.1
15.5
18.5
3
3
3
3
3
3
16
7
8
2
2
1
3
25
25
MeOH
MeOH
23.7
30.0
24.0
10.0
3
3
9
10
11
16
16
16
5
5
5
25
25
25
CH2Cl2
THF
CH3CN
35.9
45.4
29.6
7.2
9.1
5.9
3
3
3
12
13
14
15
16
17
10 min
0.5
1
5
5
5
5
5
5
50
50
50
50
50
50
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
49.5
61.7
63.8
72.9
79.3
82.7
9.9
3
3
3
3
3
3
12.3
12.8
14.6
15.8
16.5
2
4
6
6

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18
19
8
16
5
5
50
50
MeOH
MeOH
84.8
93.4
17.0
18.7
3
3
20
21
22
23
24
25
1
2
4
6
8
5
5
5
5
5
5
25
25
25
25
25
25
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
46.2
51.2
55.6
73.5
82.0
85.5
9.3
1
1
1
1
1
1
10.3
11.1
14.7
16.4
17.1
16
26
27
28
29
16
16
16
16
5
5
ꢀ
25
25
25
25
ꢀ
29.3
34.2
22.1
13.0
5.9
6.9
ꢀ
1
3
-
ꢀ
MeOH
ꢀ
ꢀ
ꢀ
-
Cu(NO3)2·
2.5H2O
2
30
31
16
16
5
5
25
25
MeOH
MeOH
28.9
22.5
5.8
4.5
a Reaction conditions: solvent (2 mL), TMSCN (0.6 mmol) and aldehyde (0.4 mmol), in air. b Determined by
1H NMR analysis of crude products (see Experimental part, Figure S5). c Number of moles of the product 2ꢀ
phenylꢀ2ꢀ((trimethylsilyl)oxy)acetonitrile, per mole of catalyst.
o
Figure 2. Plots of yield vs. time for the cyanosilylation at 25 C of benzaldehyde with TMSCN
using catalysts 1 and 3, in methanol.
The set of experiments with different catalyst 3 loadings keeping the reaction time and temperature
constant (Table 1, entries 2, 7 and 8) indicate that an increase of the catalyst amount from 1 to 5
mol% enhances the total yield from 24 up to ca. 40% (Figure 3ꢀleft), but leads to a significant
decrease of the turnover number TON (moles of product per mole of catalyst) (Figure 3ꢀright).
7

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45
40
35
30
25
20
15
10
5
30
25
20
15
10
5
0
0
0
2
4
6
0
2
4
6
Catalyst amount (mol %)
Catalyst amount (mol %)
Figure 3. Effect of the catalyst 3 amount on the yield (left) and TON (right) for benzaldehyde
cyanosilylation using TMSCN, in methanol.
Concerning the effect of time in the catalytic reaction, by keeping constant the solvent and the
o
o
amount of catalyst 3 at a temperature of 25 C (Table 1, entries 1−6) and 50 C (Table 1, entries
12−19), one can observe that the conversion increases with the temperature (Figure 4). For
example, a yield of 70% is obtained at 25 oC after 6 h (Table 1, entry 4), while a similar yield (73%)
is reached at 50 oC after only 2 h (Table 1, entry 15). However, after 16 h the yield was the same for
both temperatures (93%, Table 1, entries 6 and 19).
Figure 4. Plots of yield vs. time for benzaldehyde cyanosilylation with TMSCN using catalyst 3, in
methanol, at 25 oC and 50 oC (blue round and red square symbols, respectively).
The influence of the solvent, viz. methanol, dichloromethane, tetrahydrofuran (THF) or
acetonitrile, in the catalytic reaction was also assessed, with polymer 3 as catalyst and under the
aforementioned reaction conditions, resulting in yields of 93, 36, 45 and 30%, respectively (Table 1,
entries 6 and 9−11). It is worthwhile to mention that 3 is not soluble in CH2Cl2, THF and in
CH3CN, and thus the catalytic reaction undergoes in a heterogeneous system. Despite the obvious
advantage of the latter type of catalysis in what concerns the catalyst separation from the reaction
medium, the results for the aldehyde conversion in methanol (homogeneous system) are much
8

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better, the reason why this was the chosen solvent. Moreover, under solvent free conditions, only 29
and 34% yields (with 1 and 3, respectively; Table1, entries 26 and 27) were achieved, what may be
a consequence of the heterogeneity of the system in such cases. A couple of blank reactions were
also performed considering not only the absence of metal catalysts, but also the lack of both the
catalyst and the solvent, giving yields of 22 and 13%, respectively (Table1, entries 28 and 29). In
the presence of the Ni(II) complex 2, the catalysis proceeded with only 22.5% yield (Table 1, entry
31).
The study of the influence of the type of aldehyde substrate was also performed, and various
paraꢀsubstituted aromatic aldehydes, as well as aliphatic ones, were used in the catalytic reaction.
In all the cases, the corresponding cyanohydrin trimethylsilyl product was obtained, with yields
ranging from 44 to 97 % (Table 2). Aromatic aldehydes bearing electronꢀdonating substituents
(methoxy or methyl) exhibit relatively lower reactivities (Table 2, entries 1 and 2) as compared to
those having electronꢀwithdrawing groups (bromo, chloro or nitro) (Table 2, entries 4−6),
conceivably resulting from an increase of the substrate electrophilicity in the latter case. A series of
aliphatic aldehydes, viz. acetaldehyde, propionaldehyde and hexanal, were also investigated (Table
2, entries 7−9), the results clearly showing that the aldehyde conversion decreases with the increase
of the size of the aliphatic fragment (98% for acetaldehyde relatively to 65% for hexanal).
Table 2. Cyanosilylation of various aldehydes using TMSCN with catalyst 3a
Entry
Substrate
Yield, %b
44.5
TONc
8.9
1
2
3
4ꢀMethoxybenzaldehyde
4ꢀMethylbenzaldehyde
Benzaldehyde
58.8
92.6
11.8
18.5
4
5
6
7
8
9
4ꢀBromobenzaldehyde
4ꢀChlorobenzaldehyde
4ꢀNitrobenzaldehyde
Acetaldehyde
96.2
96.8
97.4
98.0
89.3
65.4
19.2
19.3
19.5
19.6
17.9
13.1
Propionaldehyde
Hexanal
a Reaction conditions: 5 mol% of catalyst
3, MeOH (2 mL), TMSCN (0.6 mmol) and aldehyde (0.4 mmol).
Reaction time: 16 h. b Determined by 1H NMR analysis of crude products (see Experimental part, Figure S5
and S6). c Number of moles of product per mole of catalyst.
The reaction mechanism is expected to be similar to that reported for related catalytic
systems.6,8 The Lewis acid copper(II) centre of 3 may activate the carbonyl group of the aldehyde
towards the nucleophilic addition of the C≡N group, followed by migration of the silyl group to the
oxygen and subsequent product liberation.
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In comparison to the heterogeneous catalysis, the homogeneous catalysis of aldehyde
cyanosilylation with TMSCN is not usual and scant examples were found in the literature.5,6,9 The
yields observed in this work are comparable with those obtained with other homogeneous metal
complex catalysts, as well as with the chiral oxazaborolidinium ion catalysed cyanosilylation
reaction (Table S3).6a,9 However, in those systems, a longer reaction time, higher or lower (even
negative) temperatures are required, what can be considered as disadvantages in comparison with
our system.
3. Conclusions
Depending on the reaction conditions and on the nature of metal ions, sodium 2ꢀ(2ꢀ(2,4ꢀ
dioxopentanꢀ3ꢀylidene)hydrazinyl)benzenesulfonate reacts with ethylenediamine leading to simple
coordination of this amine or to its template Schiff base condensation and coordination of the
derived species.
The obtained copper(II) complexes, in particular the coordination polymer [Cu(ꢀꢀL1ꢀ
1κO,NN’N’’:2κO’)]n (3), act as homogeneous catalysts, in methanol, for the cyanosilylation of
aldehydes with trimethylsilyl cyanide, achieving excellent yields at room temperature and in
reasonable reaction times. Moreover, it was found that electronꢀwithdrawing substituents on the
aromatic aldehydes promote the reaction yield, while an opposite effect was observed with the
increase of the size of the alkyl group in the aliphatic substrates.
Our protocol is the first example of the application of a Cu(II)ꢀAHBD (arylhydrazone of βꢀ
diketone) complex as a homogeneous catalyst for the cyanosilylation of aldehydes. AHBDs are
handily prepared compounds with easily tunable properties which can be applied to regulate and
optimise the catalytic behaviour of their metal complexes, a direction which desirus to be explored
in further studies.
4. Experimental
4.1. Materials and methods
All the chemicals were obtained from commercial sources and used as received. Infrared spectra
(4000−400 cm−1) were recorded on a Vertex 70 (Bruker) instrument in KBr pellets. Carbon,
hydrogen, and nitrogen elemental analyses were done using a Perkin Elmer 2400 CHN Elemental
Analyzer. Electrospray mass spectra were run with an ionꢀtrap instrument (Varian 500ꢀMS LC Ion
Trap Mass Spectrometer) equipped with an electrospray (ESI) ion source. For electrospray
ionization, the drying gas and flow rate were optimized according to the particular sample with 35
p.s.i. nebulizer pressure. Scanning was performed from m/z 100 to 1200 in methanol solution. The
compounds were observed in the positive mode (capillary voltage = 80–105 V). Catalytic aldehyde
10

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1
conversions were calculated by solution H NMR spectroscopy using a Bruker Avance 400 MHz
spectrometer.
4.2. Synthesis of Complexes
4.2.1. Synthesis of 1
A round bottom flask fitted with a condenser and a magnetic stirrer was charged with 0.5 mmol of
copper(II) nitrate hemi(pentahydrate), 1 mmol of NaHL and 1 mmol of en in a 30 mL mixture of
EtOH/H2O (1:1, v/v). The obtained brown solution was stirred under reflux for 3 h and then left in
open air at room temperature for slow evaporation; green crystals of 1 suitable for Xꢀray
measurements were obtained.
1: Yield, 62 % (based on Cu). Calcd. for C26H38CuN8O10S2 (Mr = 750.30): C 41.62, H 5.11, N
14.93; found C 41.89, H 5.00, N 14.81. ESIꢀMS: m/z: 751.42 [Mr+H]+. IR (KBr): 3340 and 3245 (s,
br) ν(NH), 1675 and 1639 (s) ν(C=O), 1610 (s) ν(C=N) cm–1.
4.2.2. Synthesis of 2
In a round bottom flask fitted with a condenser and a magnetic stirrer, 0.5 mmol of nickel(II)
acetate tetrahydrate were dissolved in a 30 mL mixture of EtOH/H2O (1:1, v/v), then 1 mmol of
NaHL and 1.5 mmol of en were added. The obtained red solution was stirred under reflux for 3 h
and then left in open air at room temperature for slow evaporation; brown crystals of 2 suitable for
Xꢀray measurements were obtained.
2: Yield, 86 % (based on Ni). Calcd. for C30H64N10NiO17S2 (Mr = 959.74): C 37.55, H 6.72, N
14.60; found C 37.60, H 6.70, N 14.87. ESIꢀMS: m/z: 119.0 [Ni(en)3]2+ and 283.0 [HL]ꢀ. IR (KBr):
3335 and 3286 (s, br) ν(NH), 1675 and 1642 (s) ν(C=O), 1605 (s) ν(C=N) cm–1.
4.2.3. Synthesis of 3
In a round bottom flask fitted with a condenser and a magnetic stirrer, 0.5 mmol of NaHL were
dissoved in 20 mL of MeOH. To this stirred solution at ambient temperature were added 0.5 mmol
of copper(II) nitrate hemi(pentahydrate) and 0.5 mmol of en. The reaction mixture was stirred under
solvent reflux for 3 h and left at room temperature for slow evaporation; brown crystals of 3
suitable for Xꢀray measurements were obtained.
3: Yield, 36 % (based on Cu). Calcd. for C13H16CuN4O4S (Mr = 387.90): C 40.25, H 4.16, N 14.44;
found C 40.47, H 3.83, N 14.91. ESIꢀMS: m/z: 388.8 [Mr+H]+. IR (KBr): 3364 and 3287 (s, br)
ν(NH), 1674 (s) ν(C=O), 1652 and 1608 (s) ν(C=N) cm–1.
4.3. X-ray structure determinations
Xꢀray quality single crystals of the compounds were mounted in a nylon loop and measured at 150
K (3) or at room temperature (1 and 2). Intensity data were collected using a Bruker AXSꢀKAPPA
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APEX II (for 3) or a Bruker APEXꢀII PHOTON 100 diffractometer (for 1 and 2) with graphite
monochromated MoꢀKα (λ 0.71069) radiations. Data were collected using phi and omega scans of
0.5° per frame and a full sphere of data was obtained. Cell parameters were retrieved using Bruker
SMART10a software and refined using Bruker SAINT10b on all the observed reflections. Absorption
corrections were applied using SADABS.10b Structures were solved by direct methods by using
SIRꢀ9710c and refined with SHELXLꢀ2014.10d Calculations were performed using the WinGX
System–Version 2014ꢀ1.10e The hydrogen atoms of hydrazine or amine groups were found in the
difference Fourier map and the isotropic thermal parameters were set at 1.5 times the average
thermal parameters of the belonging oxygen or nitrogen atoms, frequently with their distances
restrained by using the DFIX command. Coordinates of hydrogen atoms bonded to carbon atoms
were included in the refinement using the ridingꢀmodel approximation with the Uiso(H) defined as
1.2Ueq of the parent aromatic or methylene atoms. The amine groups in 2 are disordered over two
sites of occupancies 0.71:0.29 and were refined with the use of PART instructions. Probably
because of such disorder, the amine Hꢀatoms were not found but were inserted in calculated
positions and the isotopic thermal parameters were set at 1.5 times the average thermal parameters
of the belonging nitrogen atoms. There were disordered molecules in the structure of 2. All the
attempts made to model them were not successful and they were removed using the SQUEEZE
routine from Platon.10f Considering the number of electrons suppressed (88), the corresponding
volume (374 Å3) and the microanalytical data, the unit cel should contain 1 molecule of ethanol
and 6 water molecules (86 electrons) which were included in the model for final refinement. Least
square refinements with anisotropic thermal motion parameters for all the nonꢀhydrogen atoms and
isotropic ones for the remaining atoms were employed.
4.4. Catalytic activity studies
In typical experiment, to a solution of 1 or 3 (1–5 mol%) in solvent (2 mL) at room temperature was
added aldehyde (0.4 mmol) followed by TMSCN (0.6 mmol). The resulting solution was stirred at
room temperature in normal air for the appropriate time. The reaction mixture was then
concentrated under vacuum, diluted with 3 mL water and extracted with diethyl ether (3x10 mL).
1
After removal of diethyl ether under vacuum, the extract was taken for analysis by HꢀNMR
spectroscopy in CDCl3, to calculate the aldehyde conversion (product yield, since no other products
were formed, Figure S5 and S6). The accuracy of this procedure was verified by repeating a number
1
of the H NMR analyses in the presence of 1,2ꢀdimethoxyethane as internal standard, added to the
CDCl3 solution, what gave product yields similar to those obtained by the above method.
Acknowledgements
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This work has been partially supported by the Foundation for Science and Technology (FCT),
Portugal (UID/QUI/00100/2013). A.G.M. is thankful to the CATSUS doctoral program of FCT for
his PhD fellowship (SFRH/BD/106006/2014). The authors acknowledge the Portuguese NMR
Network (ISTꢀUL Centre) for access to the NMR facility and the IST Node of the Portuguese
Network of Massꢀspectrometry for the ESIꢀMS measurements.
Supporting Information Available: Crystal data, experimental parameters and selected details of
the refinement calculations, selected bond distances and angles, hydrogen bond interactions and
packing diagrams for compounds 1−3, as well as calculation of yield for the catalytic reaction. This
material is available free of charge via the Internet at http://pubs.rsc.org/ or from the authors. CCDC
1456524ꢀ1456526 contain the supplementary crystallographic data for 1−3. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223ꢀ336ꢀ033; or eꢀmail: deposit@ccdc.cam.ac.uk.
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