Novel cage-like hexanuclear nickel(II) silsesquioxane. Synthesis, structure, and catalytic activity in oxidations with peroxides

Article abstract of DOI:10.3390/molecules21050665

New hexanuclear nickel(II) silsesquioxane [(PhSiO_1.5)₁₂(NiO)₆(NaCl)] (1) was synthesized as its dioxane-benzonitrile-water complex (PhSiO_1,5)₁₂(NiO)₆(NaCl)(C₄H₈O₂)₁₃(PhCN)₂(H₂O)₂ and studied by X-ray and topological analysis. The compound exhibits cylinder-like type of molecular architecture and represents very rare case of polyhedral complexation of metallasilsesquioxane with benzonitrile. Complex 1 exhibited catalytic activity in activation of such small molecules as light alkanes and alcohols. Namely, oxidation of alcohols with tert-butylhydroperoxide and alkanes with meta-chloroperoxybenzoic acid. The oxidation of methylcyclohexane gave rise to the isomeric ketones and unusual distribution of alcohol isomers.

Full text of DOI:10.3390/molecules21050665

molecules
Article
Novel Cage-Like Hexanuclear Nickel(II)
Silsesquioxane. Synthesis, Structure, and Catalytic
Activity in Oxidations with Peroxides
Alexey N. Bilyachenko 1 *, Alexey I. Yalymov , Lidia S. Shul’pina , Dalmo Mandelli ,
,2,
1
1
3
1
,4
1
1
1
Alexander A. Korlyukov , Anna V. Vologzhanina , Marina A. Es’kova , Elena S. Shubina ,
Mikhail M. Levitsky 1 and Georgiy B. Shul’pin
5,6,
*
1
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov Str. 28,
19991 Moscow, Russia; alexyalymov@gmail.com (A.I.Y.); shulpina@ineos.ac.ru (L.S.S.);
1
alex@xrlab.ineos.ac.ru (A.A.K.); vologzhanina@mail.ru (A.V.V.); marinaeskovskaya@gmail.com (M.A.E.);
shu@ineos.ac.ru (E.S.S.); levitsk@ineos.ac.ru (M.M.L.)
Inorganic Chemistry Department, People’s Friendship University of Russia, Miklukho-Maklay Str. 6,
2
3
4
5
6
1
17198 Moscow, Russia
Center of Natural and Human Sciences, Federal University of ABC (UFABC), Santa Adélia Street, 166,
Bangu, Santo André, SP 09210-170, Brazil; dalmo.mandelli@ufabc.edu.br
Chemistry Department, Russian National Research Medical University, Ostrovitianov str. 1,
1
17997 Moscow, Russia
Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina, dom 4,
19991 Moscow, Russia
1
Chair of Chemistry and Physics, Plekhanov Russian University of Economics, Stremyannyi pereulok,
dom 36, 117997 Moscow, Russia
*
Correspondence: bilyachenko@ineos.ac.ru (A.N.B.); shulpin@chph.ras.ru (G.B.S.);
Tel.: +7-499-135-9369 (A.N.B.); +7-495-939-7317 (G.B.S.)
Academic Editor: Maxim L. Kuznetsov
Received: 12 April 2016; Accepted: 13 May 2016; Published: 19 May 2016
Abstract: New hexanuclear nickel(II) silsesquioxane [(PhSiO1.5)12(NiO) (NaCl)] (
1) was synthesized
6
as its dioxane-benzonitrile-water complex (PhSiO1,5)12(NiO) (NaCl)(C H O ) (PhCN) (H O) and
6
4
8
2 13
2
2
2
studied by X-ray and topological analysis. The compound exhibits cylinder-like type of molecular
architecture and represents very rare case of polyhedral complexation of metallasilsesquioxane with
benzonitrile. Complex
1 exhibited catalytic activity in activation of such small molecules as light
alkanes and alcohols. Namely, oxidation of alcohols with tert-butylhydroperoxide and alkanes with
meta-chloroperoxybenzoic acid. The oxidation of methylcyclohexane gave rise to the isomeric ketones
and unusual distribution of alcohol isomers.
Keywords: metal silsesquioxane; X-ray analysis; topological analysis; oxidation; alkanes; alcohols;
meta-chloroperoxybenzoic acid (MCPBA)
1
. Introduction
Cage-like metallasilsesquioxanes (CLMSs) [
metal silicate-like) cores and organic environments, have been thoroughly investigated in the line of
their potential application in catalysis [14 17]. Nevertheless, their capacities as catalysts of oxidation
1–13], being a family of polyhedra with inorganic
(
–
processes remain in the shadow until recent past. Then, some of us reported the first examples of
the oxidation reactions catalyzed by copper(II) silsesquioxanes, possessing different types of cage
geometry, namely cooling tower [18,19], globule [19,20], sandwich [20], and cylinder [21].
To use the advantage of good solubility of cage metallasilsesquioxanes in organic solvents and the
ability of bringing unusual effects in the catalytic act due to specific structures of catalytic centers [19
]
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we decided to study some other (not copper-containing) types of CLMSs. Here we present preliminary
results on first examination of new Ni(II)-CLMS under oxidation conditions.
2
. Results and Discussion
2
.1. Synthesis
Recently, some of us reported on ability of 1,4-dioxane molecules to serve as bridging linkers,
combining individual CLMSs into an entire supramolecular system [20], and we were interested in
the synthesis of new dioxane-CLMS complexes. Performing the synthesis of Ni-phenylsilsesquioxane
[
starting from PhSi(OEt) ] in dioxane-containing media allowed us to isolate (in 20% yield)
3
a new cage-like hexanuclear product [(PhSiO1.5)12(NiO) (NaCl)] (1) in the form of its adduct with
6
dioxane/benzonitrile/water solvating ligands (PhSiO1,5)12(NiO) (NaCl)(C H O ) (PhCN) (H O)
6
4
8
2 13
2
2
2
(Scheme 1).
Scheme 1. Synthesis of compound 1.
2
.2. Structure
The age skeleton of the product belongs to a CLMS of the cylinder type [9], characterized by the
presence of three layers: two 12-membered siloxane cycles mutually connected through a metal-oxide
(
Ni O ) cycle (Figure 1; see Supplementary Materials for more details).
6
6
Figure 1. Molecular structure of compound
counter ion Na are omitted for clarity.
1 (A—side view, B—top view). Solvating ligands and
+
The inner void of the cylinder moiety contains a chloride anion which occupies the
crystallographic center of inversion. Each Ni(II) ion of
The axial positions of the octahedron are occupied by a Cl anion and oxygen or nitrogen atoms of
1
adopts distorted octahedral coordination.
-
coordinated dioxane and benzonitrile molecules, respectively. Four nickel ions of 1 are coordinated
by dioxane molecules, while the remaining two ions are bonded to benzonitrile molecules (Figure 2).
Possibly, the donor ability of solvent molecules can govern the strength of Ni¨ ¨ ¨ Cl coordination bond
and distortion of cylindric shape as consequence. Indeed, Ni¨ ¨ ¨ Cl distances are noticeably different
[
2.7231(7), 2.8269(8) and 2.9474 Å]. It is noteworthy, that shortest Ni¨ ¨ ¨ Cl distances correspond to
nickel atoms coordinated by dioxane molecules.

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Figure 2. Structures
A and B: compound 1 with solvating ligands (side and top views, respectively).
Ph groups at silicon atoms are omitted for clarity; structures
C and D is the illustration of distorted
-
octahedral coordination of nickel ion. The anion Cl and the oxygen atom of the coordinated dioxane
molecule occupy an axial position, while the oxygen atoms of siloxanolate cycles form the equatorial
plane of the coordinating octahedron.
This is just the second evidence that benzonitrile ligands could participate in aggregation of
a CLMS structure. The first observation of such unusual coordination was presented by some of us [21
for the copper-containing CLMS.
]
2
.3. Topological Analysis and Supramolecular Assembly
Following the procedure of a metal cluster notation [22] implemented into the ToposPro package
the Samara Center for Theoretical Materials Science, Samara, Russia) [23] we obtained that nickel
atoms in compound form in terms of the NDk-m notation the discrete 5M6-1clusters, where 5
is the coordination number of topologically non-equivalent nodes, M denotes a discrete cluster,
is the number of metal atoms in the cluster, and 1 is a classification number to distinguish
(
1
6
topologically-distinct clusters with equal NDk parameters. A database of topological representations
of polynuclear nickel compounds [24] contains representatives of the nickel clusters with the
´ 2´
M6-1 topology, and µ6-coordinated Hal and S anions; recently, some of us have synthesized
5
2
´
a nickel-silsesquioxane encapsulating the O anion [13]. Nevertheless, to our knowledge, complex
1
is only the sixth known representative of Ni clusters with the 5M6-1 topology.
6
An additional attractive feature of synthesized complex is a formation of supramolecular structure
where cage components are assembled into infinite chains (Figure 3) via H-bonds between water
molecules bonded to sodium anions and oxygen atoms of siloxane cycles. The r(O¨ ¨ ¨ O) and
=OHO are
˝
˝
equal to 3.364(6)–3.488(6) Å and 135.7 –149.0 . The connection between ions is additionally supported

Molecules 2016, 21, 665
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by C-H¨ ¨ ¨ O interactions between 1,4-dioxane and silsesquioxane as short as 3.62(2) and 3.91(2) Å
for r(O¨ ¨ ¨ C). As a consequence, cylinder cage fragments and complex cations Na(H O) (O C H )
2
2
2
4
8 2
share the same pseudo two-fold axis parallel to the [100]-crystallographic direction. The chains are
packed as the hexagonal rod packing, with the distances between two-fold axes of 16.1 and 16.3 Å
and non-parallel disposition of Ni metal rings. Only weak C-H¨ ¨ ¨ O and C-H¨ ¨ ¨ π bonding between
6
neighboring chains, or chains and solvent molecules, were found. Worth noting is that the shortest
distance between two oxygen atoms of 1,4-dioxanes connected with Ni is equal to 8.6 Å, which is only
1
slightly longer than the distance between nitrogen atoms of 4,4 -bipyridine, at 7.1 Å. In principle, this
means that bipyridine and its analogues can be used to obtain coordination polymers connected by
linkers through d-metals even for bulky phenylsilsesquioxanes. This opportunity will be a subject of
our further investigations.
Figure 3. Crystal packing of 1.

Molecules 2016, 21, 665
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2
.4. Oxidations Catalyzed by Compound 1
Nickel complexes are known to catalyze certain oxidation reactions of hydrocarbons [25
–37] and
alcohols [38
various oxidants. It turned out that
with hydrogen peroxide in acetonitrile solution. In contrast to H O , tert-butyl hydroperoxide oxidizes
–
44] by peroxides. We have tested the catalytic effect of compound
1 in oxidations with
1
does not catalyze the oxidation of 1-phenylethanol or alkanes
2
2
˝
´6
´1
1
-phenylethanol at 70 C to afford acetophenone in 90% yield (initial reaction rate W = 7
initial TOF = 50 h ) after 24 h. The kinetic curves of acetophenone accumulation shown in Figure 4
ˆ
10 M s ;
0
´
1
indicate the pronounced catalytic effect of compound 1.
0
.4
PhC(=O)Me in the
presence of 1
PhCH(OH)Me in the
absence of 1
0
0
.3
.2
PhCH(OH)Me in the
presence of 1
PhC(=O)Me in
the presence of
Ni(NO3)2
0
.1
0
PhC(=O)Me in the
absence of 1
0
8
16
Time (h)
24
Figure 4. Formation of acetophenone with time in the 1-phenylethanol (0.33 M) oxidation with tert-butyl
hydroperoxide (TBHP; 70%, aqueous, 1.65 M) in the absence and in the presence of compound
1
´
10 M), as well as in the presence of Ni(NO ) . Solvent was acetonitrile (total volume of the
3 2
4
(5
ˆ
˝
reaction solution was 5 mL); temperature was 70 C.
As can be expected, alkanes are less reactive in comparison with alcohols and only
meta-choroperoxybenzoic acid (m-CPBA) turned out to be a good oxidant. Certain complexes of
transition metals have been previously reported to oxidize alkanes with m-CPBA [27
–29,32–34,36,45–47].
Complex exhibited activity in the oxidation of cyclohexane with m-CPBA (Table 1). It can be seen
1
˝
that at 20 C the reaction deceased after 15 min. The ketone/alcohol ratio is not changed in the
chromatograms made before and after reduction of samples with triphenylphosphine. This indicates
that cyclohexyl hydroperoxide is not formed in the course of the oxidation (for this simple method,
´
1
see [48–51]). The yield of oxygenates was 24% and TON = 64, TOF = 256 h
.
The oxidation of n-octane (0.12 M) with m-CPBA (0.13 M) in the presence of compound
1
´ ˝
10 M) and co-catalyst HNO (0.05 M) at 60 C during 3 h gave rise to the formation of
3
4
(5
ˆ
a mixture of 2-, 3-, and 4-octanones (0.009, 0.009, and 0.008 M, respectively; yield 22%; TON = 52,
´
1
TOF = 208 h ). The oxidation of methylcyclohexane under similar conditions gave predominantly
isomeric ketones (products P2 P4; M) and tert-alcohol P5 (M; Figures 5 and 6). Concentrations (M) of
–
the isomers were the following: P2 (0.0034), P3 (0.0036), P4 (0.0013), P5 (0.012), P6 (0.0003), P7 (0.0008),
P8 (0.0004), P9 (0.0002), P10 (0.0009), and P11 (0.0004); yield was 9% (TON = 47). It can be clearly
seen that the ratio of isomeric alcohols in the case of this catalytic system (a, b) is different from that

Molecules 2016, 21, 665
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obtained earlier for other catalysts (c–f). Indeed, concentrations of isomers P8 and P9 is noticeably
low in comparison with amounts of both P6 P7 and P10 P11. This effect has not been found for other
catalysts (c–f) and is apparently due to sterical hindrance around catalytic centers in . Like in the
cyclohexane oxidation, chromatograms of oxygenates obtained from methylcyclohexane (Figure 6a,b)
,
,
1
before and after reduction with PPh are very similar and this indicates that alkyl hydroperoxides are
3
also not formed in this experiment.
Table 1. Oxidation of cyclohexane with m-CPBA catalyzed by complex 1 1.
Entry
Time (min)
Reduction with PPh3
Cyclohexanone (M)
Cyclohexanol (M)
˝
at 20 C
1
2
3
4
120
300
no
yes
no
0.007
0.005
0.009
0.008
0.007
0.006
0.006
0.007
yes
˝
at 50 C
5
6
7
7
no
yes
no
yes
yes
no
yes
no
yes
yes
no
0.008
0.007
0.009
0.02
0.017
0.022
0.023
0.0003
0.0027
0.00007
0.022
0.022
0.0007
0.002
0.023
0.023
0.001
15
2
8
9
0.009
3
0.0002
0.0005
0.00004
0.009
4
1
1
0
1
4
1
2
30
60
1
3
0.009
3
1
1
4
5
0.0007
0.0005
0.009
0.009
0.001
4
1
6
no
1
7
yes
yes
´4
3
1
8
1
Conditions. Concentrations [1]
total volume of the reaction solution was 5 mL; For this entry, TON = 64, TOF = 256 h
used instead of catalyst 1; An experiment in the absence of any Ni compound.
0
= 5
ˆ
10 M, [cyclohexane]
0
= 0.46 M, [m-CPBA]
0
= 0.13 M. Solvent MeCN,
2
´1
3
3 2
; Salt Ni(NO ) was
4
HO
H
H
H
H
H
Me
CHO
Me
Me
Me
Me
O
+
+
+
+
+
O
O P4
Methylcyclohexane
Cyclohexanecarboxaldehyde
-Methylcyclohexanone
P1
P2
P3
3-Methylcyclohexanone
4-Methylcyclohexanone
P5
1-Methylcyclohexanol
2
H
H
H
H
H
H
H
Me
Me
Me
Me
Me
Me
CH OH
2
OH
OH
+
+
+
+
+
+
OH
HO
OH
P6
trans-2-Methylcyclohexanol
cis-2-Methylcyclohexanol
P7
P8
P9
P10
P11OH
P12
Cyclohexylmethanol
cis-4-Methylcyclohexanol
trans-3-Methylcyclohexanol cis-3-Methylcyclohexanol
trans-4-Methylcyclohexanol
Figure 5. Products formed in the methylcyclohexane oxidation.

Molecules 2016, 21, 665
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Figure 6. Chromatograms (fragments) of products formed in the methylcyclohexane oxidation by
various systems: complex /m-CPBA ( , this work); [O Cu {N(CH CH O) } (BOH) ][BF ] /TBHP
(CuO) (NaO ) ]/TBHP ( , [19]); [(PhSiO
1
a,
b
Ă
4
2
2
3 4
4
4 2
(
(
c
, [52]); [(PhSiO1
)
d
)
(CuO) (NaO ) ]/H O (
e, [19]);
.5 12
4
0.5 4
1.5 10
2
0.5 2
2
2
6
η -p-cym)Os(py)Cl /py/H O (f, [53]).
2
2
2
The oxidation of cis-1,2-dimethylcyclohexane with m-CPBA in MeCN catalyzed complex
1
proceeds non-stereoselectively: the ratio of formed tertiary trans and cis alcohols t/c was 0.88 before
reduction with PPh and 0.93 after the reduction (yield was 12% based on cis-1,2-DMCH; TON = 34).
3
In the blank experiment (without complex
was 5%).
1) the t/c ratio was 0.77 after reduction with PPh (yield
3
3
. Materials and Methods
3
.1. Synthesis of Compound 1
Compound PhSi(OEt) and solvents were purchased from Acros Organics (Moscow, Russia) and
3
were used as received.
Compound PhSi(OEt) (3 g, 12.48 mmol), water (0.45 g, 24.96 mmol) and NaOH (0.5 g, 12.50 mmol)
3
in 20 mL of methanol were placed into a flask, equipped with a magnetic stirrer and condenser.
After total dissolution of NaOH, the solution was heated to reflux for 1.5 h. Afterwards solution
was cooled down to room temperature and mixed with 85 mL of dioxane. Then Ni(NH ) Cl (1.4 g,
3
6
2
6.04 mmol) was added at once. Mixture was brought to reflux along with simultaneous distillation
of the solution to remove methanol from reaction mixture. When 18 mL of distillate was collected,
mixture was heated to reflux for additional 4 h and then left stirring at room temperature overnight.
Then reaction mixture was filtered into an evaporation flask containing benzonitrile (8 mL). The flask
was equipped with a septum and needle to allow solvents to evaporate under a slow current of
nitrogen. Immediately after yellow-colored crystals began to form, the flask was transferred to the
fridge and stored there until the crystal fraction growth (two weeks) ceased, as visually determined.

Molecules 2016, 21, 665
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A few selected single crystals were used for the X-ray study (for details, see below). Yield: 0.41 g, 20%;
elemental analysis calcd (%) for [(PhSiO1.5)12(NiO) (NaCl)]: Ni 17.12, Si 16.39, C 42.04, H 2.94, N 0;
6
found (in a vacuum-dried sample): Ni 17.01, Si 16.30, C 42.64, H 3.07, N traces.
3
.2. X-ray Diffraction Study
X-ray diffraction studies were carried out on Bruker APEX DUO diffractometer (Madison, WI,
USA). The structure was solved by direct method and refined in anisotropic approximation against
F2. The positions of hydrogen atoms were calculated from geometrical point of view and refined in
isotropic approximation (the C-H and O-H distances and displacement parameters of hydrogen atoms
are constrained). All calculations were carried out with SHELX (Gottingen, Germany) [54,55] and
OLEX2 software (Durham, UK) [56]. The experimental parameters and crystal data are summarized
in Table 2.
Table 2. Crystal data and experimental parameters of the product.
Brutto Formula
C138H178ClN NaNi O Si
2
6
52 12
Formula weight
3437.54
120
T, K
Space group
Z
P2 /n
1
2
a, Å
b, Å
16.1899 (12)
18.2778 (14)
27.093 (2)
101.513 (2)
7855.9 (10)
1.456
c, Å
˝
β,
3
V, Å
-
3
dcalc, g℘cm
-
1
µ, cm
F(000)
9
3600
50
˝
2
θmax,
Reflections collected
Independent reflections
Reflections with I > 2σ(I)
Parameters
100,379
23,101
11,161
942
R1 [for refl. with I > 2σ(I)]
wR2
0.0823
0.2050
GOF
1.006
2.600/´2.575
-
3
Residual electron density, e
¨
Å (
ρmin/ρmax
)
3
.3. Catalytic Oxidation of Alkanes and 1-Phenylethanol
Typically, the catalyst and the co-catalyst (nitric or trifluoroacetic acid) were introduced into
the reaction mixture in the form of stock solutions in acetonitrile. The reactions of alcohols and
hydrocarbons were carried out in air in thermostated Pyrex cylindrical vessels with vigorous stirring
and using MeCN as solvent. The substrate (alcohol or hydrocarbon) was then added and the reaction
started when the oxidant was introduced in one portion (CAUTION: the combination of air or
molecular oxygen and peroxides with organic compounds at elevated temperatures may be explosive!).
1
The reactions with 1-phenylethanol were analyzed by H-NMR method (solutions in acetone-d ;
6
“Bruker AMX-400” instrument, 400 MHz, Billerica, MA, USA). Areas of methyl group signals were
measured to quantify oxygenates formed in oxidations of 1-phenylethanol. As stated previously, the
samples obtained in the alkane oxidation were typically analyzed twice (before and after their treatment
with PPh ) by GC. This method (an excess of solid triphenylphosphine is added to the samples
3
1
0–15 min before the GC analysis) was proposed by one of us earlier [48–51]. Samples of the reaction
mixture were analyzed by GC (Agilent 6890, Santa Clara, California, United States, N was carrier gas,
2
FID) and GC-MS (Shimadzu QP-2010 Plus, Nishinokyo-Kuwabara-cho, Nakagyo-ku, Kyoto 604-8511,
Japan; He was carrier gas); in both instruments the column was BP-20 (SGE; polyethyleneglycol

Molecules 2016, 21, 665
9 of 12
´
30 m
ˆ
250
µ
m
ˆ
0.25
µ
m). Assignment of peaks was made by comparison with chromatograms of
authentic samples and by GC-MS.
4
. Conclusions
Synthesized in this work complex (PhSiO1,5)12(NiO) (NaCl)(C H O ) (PhCN) (H O) represents
6
4
8
2 13
2
2
2
very rare case of polyhedral complexation of metallasilsesquioxane with benzonitrile. The complex
exhibited catalytic activity in oxidation of alcohols with tert-butylhydroperoxide and alkanes with
meta-chloroperoxybenzoic acid.
Supplementary Materials: Supplementary materials can be accessed at: http://www.mdpi.com/
1
420-3049/21/5/665/s1. CCDC 1471551 contains the supplementary crystallographic data for complex 1.
These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments: The authors gratefully acknowledge support of the Russian Foundation for Basic Research
(
projects 14-03-00713, 16-03-00206, 16-03-00254) and the “Science without Borders Program, Brazil–Russia”, CAPES
grant A017-2013). D.M. is grateful to CNPq (grants 311585/2013-2, 472130/2012-9).
(
Author Contributions: A.N.B., M.M.L., E.S.S. and G.B.S. conceived and designed experiments on synthesis and
catalytic application of compound , A.I.Y. made synthesis of , L.S.S. and D.M. performed experiments on
1
1
oxidations and analysis of products, A.A.K., A.V.V. and M.A.E. carried out X-ray experiments, their analysis
and topological analysis. A.N.B. and G.B.S. wrote the paper. Authors disclosed no actual or potential conflict of
interest, and have approved the article.
Conflicts of Interest: The authors declare no conflict of interest.
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