Tetra-functional double-decker silsesquioxanes as anchors for reactive functional groups and potential synthons for hybrid materials

Article abstract of DOI:10.1039/c7cc03958a

A series of double-decker silsesquioxane derivatives with four reactive functional groups were designed, efficiently synthesized, and characterized. These novel inorganic-organic hybrids show highly attractive features for applications as building blocks

Full text of DOI:10.1039/c7cc03958a

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Tetra-functional double-decker silsesquioxanes as
anchors for reactive functional groups and
potential synthons for hybrid materials†
Cite this:DOI: 10.1039/c7cc03958a
Received 22nd May 2017,
Accepted 29th August 2017
a
a
a
a
a
K. Mituła, J. Duszczak, D. Brz a˛ kalski, B. Dudziec, * M. Kubicki and
ab
B. Marciniec
DOI: 10.1039/c7cc03958a
rsc.li/chemcomm
A series of double-decker silsesquioxane derivatives with four and the chemistry of these compounds is considerably depen-
reactive functional groups were designed, efficiently synthesized, dent on the type and number of functional groups (Scheme 1).
and characterized. These novel inorganic–organic hybrids show
Research on molecular and macromolecular organosilicon
highly attractive features for applications as building blocks with DDSQ-based systems is developing in two directions. Molecular
Si–O–Si rigid cores (good thermal properties) with four reactive derivatives based on DDSQ are interesting from a purely
moieties, which can be functionalized in further processes.
cognitive point of view, related to syntheses of compounds
with interesting physicochemical properties. In contrast, they
The development of novel materials with specially designed can be precursors and reagents in the synthesis of oligo- and
1
1
and tailored chemical, mechanical, or physical properties has polymeric networks. The number of examples of D T -closed
2
8
become increasingly important to meet the various requirements architectures has increased recently. Not only have hydrolytic
and expectations of applications in many fields of science and condensation reactions been applied to their syntheses, but
everyday life. Polyhedral oligomeric silsesquioxanes are a broad catalytic reactions of di-functional DDSQ-based compounds
family of compounds known for a large variety of structures. with reactive FG vertex groups have also been used in their
1
2–14
15–18
Their structures may vary from random, ladder, open, and syntheses. Ervithayasuporn et al.,
incompletely condensed species to closed and well-defined group have made significant contributions to the studies on
cages. The POSS general formula is [RSiO1 (where R = H, geometric cis- and trans-DDSQ-2Si isomers whose formation
Lee et al.,
and our
]
.5 n
alkyl, aryl, etc. and n = 4, 6, 8, 10. . .). Their main components are is related to the different spatial arrangements of the FG and
1
9–22
cubic T cages consisting of rigid, crystalline silica-like cores with R substituents on the DDSQ core.
A skillful selection of
8
eight covalently bonded R groups (either the same or different solvents based on the differences in the solubilities of the
1–3
functional groups (FGs)). Another type of silsesquioxane struc- isomers, e.g., THF/hexane, enables their efficient separation
ture is a double-decker silsesquioxane (DDSQ – M and D ), via fractional crystallization. The main idea behind the intro-
whose efficient synthesis was reported by Yoshida et al. just duction of two FGs into the DDSQ core was the potential to use
4 8
T
2 8
T
4
–10
over a decade ago.
The structure of DDSQ differs from those these new systems as precursors for the synthesis of macro-
of symmetric, cubic T systems. It consists of two ‘‘decks’’ of molecular compounds with DDSQ as a linker or a fragment
8
cyclosiloxane rings stacked on top of one another with four incorporated into the copolymer chain. The consecutive processes
inert phenyl groups at the silicon atoms of each ring. The rings
are joined by oxygen bridges. DDSQ compounds may take an
6
,7
9,10
open M
4
T
8
(DDSQ-2OSi)
2 8
or closed D T (DDSQ-4OSi)
framework with either four or two reactive groups, respectively,
a
Faculty of Chemistry, Adam Mickiewicz University in Poznan, Umultowska 89B,
6
1-614 Poznan, Poland. E-mail: beata.dudziec@gmail.com
b
Centre for Advanced Technologies, Adam Mickiewicz University in Poznan,
Umultowska 89C, 61-614 Poznan, Poland
†
Electronic supplementary information (ESI) available: Experimental proce-
dures, analytical data of isolated compounds and CIF data for 1-Me, 2-Me, and
-Me (pdf). CCDC 1503391, 967454 and 1544710. For ESI and crystallographic
4
data in CIF or other electronic format see DOI: 10.1039/c7cc03958a
Scheme 1 Double-decker silsesquioxane derivatives – possible structures.
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leading to co-polymeric materials are based on organic/ product formation, the respective silane should be used in
organometallic-type transformations with FGs at the Si vertex 1.05 equiv. per Si–OH moiety. THF was chosen as the best solvent
(
DDSQ) and organic, di-functional co-monomers, e.g., dehydro- because of the solubility of DDSQ-4OH; NEt was chosen as the
3
coupling polycondensation, nucleophilic substitution, hydro- base and HCl the scavenger. We tested a few types of bases,
1
1,20,21,23–28
silylation, metathesis, and silylative coupling.
As a e.g., K CO and N(iPr) Et, but NEt was the most efficient. The
2 3 2 3
result, an interesting group of compounds has been designed reaction time depended on the reagent concentrations in THF and
2
9
and prepared over the last few years. They have been found to was monitored using Si NMR for the disappearance of
exhibit interesting mechanical and optical properties, offer low Si–OH resonance lines, usually up to 24 h (see Fig. S4 in ESI†).
dielectric constants, and above all, high thermal stability. In The crude reaction mixture was purified by filtration from the
contrast, the number of scientific reports on the synthesis of [HNEt
tetra-functional double-decker-based molecular compounds performed to afford 1-Me, 1-Ph, and 2-Ph or column chromato-
DDSQ-4Si) is still limited. A few reports on tetra(N-ethylcarbazole) graphy was performed for 3-Me, 5-Me-hex, and 5-Me-dec with
DDSQ derivatives applied in OLED (organic light-emitting high yields of 68–95%. The solubility of 2-Me and 4-Me in MeOH
3
]Cl salt. Then, either recrystallization in MeOH was
(
2
9
diode) devices or ethylene glycol-based DDSQ compounds was observed to be significantly higher than that of the other
with interesting proton conductivity properties have been pub- compounds (which might be explained by the different polarities
3
0,31
lished thus far.
DDSQ-4OH) has been used as a ligand scaffold for a Zr complex
or as a co-monomer in the formation of macromolecular DDSQ
Further, the tetrasilanol form of DDSQ of these molecules, possibly due to the changed electronic effects
32
(
of the vinyl and ethynyl groups).
This process not only allowed a thorough purification of
these compounds but also made it possible to obtain crystals
3
3
systems with titanium(IV) atoms as the nodes.
Herein, we present an efficient synthesis of tetra-functional for single crystal XRD studies. The condensation of 5-Me was
DDSQ compounds with a few FGs, i.e. Si–H, Si–alkene and ineffective, probably because of the steric hindrance of chloro(1-
Si–CRCH that are particularly interesting, e.g., for the syntheses decenyl)- and chloro(1-hexenyl)dimethylsilane and resulted in
2
9
of polymers or their modification or as new types of cores for incomplete Si–OH consumption ( Si NMR analysis). This was
specific types of dendritic systems, i.e., playing the role of the core also reflected by the relatively low yield of 3-Me. Consequently,
for dendrons arising at four independent branches. Their struc- we decided to explore another reaction pathway to obtain the
tures were analyzed using a variety of spectroscopic methods desired product 5-Me.
(
also XRD for 1-Me, 2-Me, and 4-Me). Further, the thermal
properties of these compounds were measured and compared as a substrate in hydrosilylation, using commercially available
with those of known DDSQ-based derivatives. Pt–Karstedt’s catalyst [Pt (dvs) ] and a corresponding diene,
The tetrahydro-functional DDSQ derivative 1-Me served
2
3
The synthetic importance of tetra-functional DDSQ-based i.e., 1,5-hexadiene and 1,9-decadiene. A particular amount of
À4
compounds as building blocks for hybrid materials of both catalyst was used to ensure the proportion of 10 mole of Pt per
molecular and macromolecular architectures may be even greater mole of the Si–H group. The reaction was monitored by following
À1
than that of di-functional DDSQ. This opens a route for the design the disappearance of the bands at uꢀ = 2100 and 903 cm
,
and synthesis of novel types of inorganic–organic DDSQ-based originating from the stretching and bending vibrations of the
systems. The type of FG attached to the core plays a decisive role Si–H group (Fig. S5 in ESI†). The reaction conditions enabled
in planning the reaction strategy.
499% Si–H conversion and selective formation of the b-product
The fundamental process that leads to tetra-functional (Scheme 2). The crude products were purified from the catalyst
double-decker silsesquioxanes is the hydrolytic condensation using column chromatography with a DCM : hexane (3 : 2) eluent,
of the commercially available tetrasilanol (DDSQ-4OH) with and its evaporation yielded analytically pure compounds with very
1
1,23
dichloro (or dialkoxy) functionalized silanes.
The syntheses high isolation yields of 93–94%. All the products were character-
2
9
of 1–5 were performed as per Scheme 2. The condensation ized using spectroscopic methods. The results of the Si NMR
reactions were optimized enabling the highest conversions of analysis are presented in Table 1.
DDSQ-4OH. This process involves the verification of the reagent
The location of the resonance lines of the Si atoms derived
stoichiometry, reaction times, and amounts of solvent. For effective from the rigid Si–O–Si core ( ) was not affected much by the
presence of FGs, but the chemical shifts of the four Si atoms
from external Si–O– groups ( ) were changed decisively (because
of the differences in the electronic effects of the substituents at
the M type Si). The Ph groups’ vicinity to the Si–O– groups ( ) in
2
9
1
-Ph and 2-Ph affects the location of the Si NMR chemical
signals of Si atoms ( ) predominantly (the resonance lines
are shifted to À45.5 ppm for 1-Ph and to À20.3 ppm for 2-Ph)
when compared with the shifts observed for their Me deriva-
tives. For 3-Me, 5-Me-hex, and 5-Me-dec, the resonance lines of
the M-type Si atoms are shifted toward positive ppm values
(lower field) because of the presence of the Me– group and
Scheme 2 Reaction pathway for the synthesis of tetra-functional DDSQ
derivatives.
additional –CH – (Csp ) moieties of alkenyl groups.
3
2
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29
Table 1
Si NMR data of 1–5
29
Prod. abbrev.
Si NMR resonance lines [ppm] in CDCl
3
1
1
2
2
3
4
5
5
-Me
-Ph
-Me
-Ph
-Me
-Me
-Me-hex
-Me-dec
À3.9 ( ), À75.8 ( ), À79.0 ( )
À45.4 ( ), À78.1 ( ), À79.4 ( )
À0.8 ( ), À75.9 ( ), À78.9 ( )
À20.3 ( ), À76.2 ( ), À77.7 ( )
7.9 ( ), À75.8 ( ), À78.7 ( )
À16.5 ( ), À75.8 ( ), À78.6 ( )
10.9 ( ), À76.2 ( ), À78.8 ( )
11.0 ( ), À76.1 ( ), À78.7 ( )
Fig. 3 Perspective view of the molecule 4-Me. Ellipsoids are drawn at the
35% probability level.
Type of Si atom: M
3
(–Si–O–) and T (–Si(O–) )
Fig. 4 Comparison of the shapes of molecules (left) 1-Me (red) and 2-Me
green), and (right) 2-Me and 4-Me (blue).
(
1
.614(8) Å in 1-Me) differ slightly from those of the SiOC3
grouping in which these bonds are significantly longer
1.644 and 1.639 Å). The Si–O–Si bond angles are considerably
Fig. 1 Perspective view of the molecule 1-Me. Ellipsoids are drawn at the
0% probability level.
(
5
more flexible and have values ranging from 1351 to 1551. In the
crystal structures, the van der Waals forces organize molecules
We succeeded in obtaining crystal structures of three of the into three-dimensional networks (Fig. S1–S3 in ESI†).
synthesized compounds, i.e., 1-Me, 2-Me, and 4-Me. The per-
Subsequently, all obtained samples 1–5 were subjected
spective views of the molecules are presented in Fig. 1–3. The to thermogravimetric studies. The analysis of the obtained
molecule 1-Me is C -symmetrical, as it lies at the inversion thermograms led to the conclusion that all the compounds
i
5
%
center in the space group P1%. Even though 2-Me is not exactly show relatively high thermal resistance T
(all over 350 1C in
d
symmetrical, the overall shapes and disposition of the substi-
tuents in both molecules are quite similar (Fig. 4). The geome-
N
N
2
and 290 1C in air) with a residue at 1000 1C of up to 58% in
and 45% in air (Table 2). TGAs of compounds 1–5 (Fig. S6
2
trical features are quite typical; one can infer that the Si–O bond and S7 in ESI†) show general information about the thermal
lengths of SiO
C (mean values of 1.618(7) Å in 2-Me and stability of these systems. Here, the final residues’ mass values
at 1000 1C (within the range of 22% to 58% in N and air
3
2
respectively) may not reflect the mass loss caused by the
process other than decomposition (i.e., sublimation, volatiliza-
2
tion or evaporation). It is hard to make a direct correlation
between the thermal stability and structure/composition with-
out additional analysis to account for the mass loss by these
other processes. However, the theoretical yields of SiO in air
2
were calculated within the range of 38% for 2-Ph and 5-Me-hex
to 55% for 1-Me, respectively. The lower residue values may be
2
attributed to possible sample sublimation. In general, the presence
of a Me or Ph substituent at the M-type Si–O– moiety may be
5
%
10%
d
reflected by the difference in the T
d
and T
temperatures (higher
for Ph derivatives in N and air) (Table 2). DDSQ-4OSi-FGs are
2
characterized by different 5% and 10% mass loss temperatures
compared to the analogous DDSQ-4OSi-based systems, which
Fig. 2 Perspective view of the molecule 2-Me. Ellipsoids are drawn at the
5% probability level.
3
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Table 2 Thermal properties of DDSQ-4OSi-FG (1–5) (measured in N
ChemComm
2
and air) Notes and references
Residue at
1000 1C (%)
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)
10% (in air) (N
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(In air)
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1
1
2
2
3
4
5
5
-Me
-Ph
-Me
-Ph
-Me
-Me
351
390
400
423
362
373
331
344
361
377
297
347
400
361
373
428
429
456
397
440
427
457
358
399
379
412
378
377
433
425
37
24
37
31
34
58
31
31
30
22
37
37
45
43
22
30
4
5
-Me-hex 404
-Me-dec 426
6
7
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2
9,30
may be attributed to the differences in the FGs.
of 4-Me, the final residue was at 58%.
In the case
8
9
The presence of –CCH moieties may suggest their possibility to
undergo an intermolecular thermal coupling reaction to yield a
co- or polymeric material. A similar observation was reported by 10 H. Oikawa, M. Yamahiro, K. Ohguma, N. Ootake, K. Watanabe,
K. Ohno, Y. Tsujii and T. Fukuda, US7375170 B2, 2008.
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34
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1
1
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4
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Financial support from the National Science Centre (Poland)
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The authors have no conflicts of interest to declare for this
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4
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