Synthesis and Hydrosilylation of Vinyl-Substituted Open-Cage Silsesquioxanes with Phenylsilanes: Regioselective Synthesis of Trifunctional Silsesquioxanes

Trifunctional Silsesquioxanes

Article

Synthesis and Hydrosilylation of Vinyl-Substituted Open-Cage

Silsesquioxanes with Phenylsilanes: Regioselective Synthesis of

Magdalena Grzelak,* Rafa ł Januszewski, and Bogdan Marciniec

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c00947

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sı Supporting Information

ABSTRACT: Herein, we report an eﬃcient synthesis and

functionalization of trifunctional open-cage-type silsesquioxanes.

The method proposed has been successfully applied for the

synthesis of a library of incompletely condensed silsesquioxanes

with vinyldiorganosilyl functional groups, which allows further

modiﬁcation. Detailed studies of hydrosilylation of sterically

diﬀerent open-cage vinylsilsesquioxanes with a wide spectrum of

phenylsilanes catalyzed by platinum and rhodium compounds are

also reported. The inﬂuence of the reaction parameters, types of

reagents, and catalysts employed on the eﬃciency of the process

was examined. Optimization of the process based on the above

results permitted the design of a very attractive method for the

synthesis of multifunctionalized silsesquioxanes with excellent

yields and regioselectivity. Moreover, the results allowed the choice of the most eﬃcient catalyst whose application led to the

selective formation of substituted open-cage silsesquioxanes. These new compounds have been fully characterized and studied in

terms of their thermal properties.

13−18

1,2

INTRODUCTION

coupling,

and many others ). Among all of the above-

■

mentioned methods, hydrosilylation of oleﬁns (the addition of

Si−H bonds to unsaturated systems, e.g., CC bonds, resulting

in the formation of a C−Si bond) is one of the fundamental

processes used in industry and laboratory. This transformation is

most often catalyzed by platinum compounds, although

rhodium, nickel, and other transition-metal complexes are also

Silsesquioxanes make up a group of organosilicon macro-

molecular cage compounds diﬀering in the number and manner

of combination of T units [the basic building blocks consist of

one silicon atom covalently linked to three oxygen atoms

(Figure 1 )]. The research area focused on silsesquioxanes is one

19,20

used.

In scientiﬁc literature, the most widely described group is that

of completely condensed silsesquioxanes, but an interesting

alternative to cubic POSS cages may be incompletely condensed

open-cage silsesquioxanes (IC-POSSs; Figure 1), which, thanks

to their unique structure, may exhibit diﬀerent physicochemical

21,22

properties and diﬀerent reactivity.

Most literature reports

about incompletely condensed silsesquioxanes focus on the use

of POSS trisilanols as precursors for the synthesis of completely

Figure 1. Structural diﬀerences between exemplary (a) open-cage-type

and (b) completely condensed silsesquioxanes.

−3,23

condensed derivatives

and metallasilsesquioxanes com-

plexes as molecular models for silica-grafted catalytic cen-

1,22,24

ters.

Liu et al. investigated the hydrogen-bonded

of the most dynamically developing in the chemistry of silicon

compounds. Polyhedral oligomeric silsesquioxanes (POSSs) are

characterized by structural diversity and the possibility of

attachment of a variety of functional groups that signiﬁcantly

Received: March 30, 2020

−4

change their reactivity and solubility. These properties can be

easily modiﬁed by the introduction of various substituents by

using a wide spectrum of catalytic and noncatalytic chemical

−9

10−16

reactions (e.g., Heck coupling,

metathesis,

silylative

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Scheme 1. Scope of Work

Scheme 2. Synthesis of Open-Cage Silsesquioxanes with Three Vinyldiorganosilyl Groups

interaction in POSS silanols and the possibility of their usage as

mers, carbazole-functionalized structures, and composite

anion receptors to form host−guest complexes. The scientiﬁc

reports about trifunctional IC-POSSs are scarce. There are only

a few examples of the synthesis and use of its vinylfunctional

derivatives, which, because of the presence of several functional

groups protruding from the cage, can be as multifunctional

precursors and nanoﬁllers of many materials used, e.g., in

electronics and hybrid materials. Lorenz et al. have provided the

ﬁrst example of complete functionalization of the POSS

trisilanol (with cyclohexyl groups in the corners) with

chlorodimethylvinylsilane, leading to the formation of a product

ﬁlms of poly(methyl methacrylate) matrixes with IC-POSS

1,42

ﬁllers.

It should be emphasized that the above-mentioned studies

concerning hydrosilylation of trivinyl-substituted open-cage

silsesquioxanes have not been devoted to optimization of the

hydrosilylation process. Some of the above-mentioned literature

reports only concerned the preparation of functional silsesquiox-

anes without their further modiﬁcation. Therefore, this study

was undertaken to comprehensively investigate hydrosilylation

of trivinylsilyl-substituted open-cage silsesquioxanes with

phenylsilanes (Scheme 1). The inﬂuence of the types of IC-

POSSs and silane structures as well as the nature of the catalyst

and reaction conditions on the eﬀectiveness and selectivity of

the hydrosilylation process was examined. The reactions were

monitored with H, C, and Si NMR and in situ Fourier

transform infrared (FT-IR) spectroscopies. As follows from the

perusal of relevant literature, it seems that no detailed

comparison of the activity of various silanes and open-cage

vinylsilsesquioxanes in the hydrosilylation reaction has been

performed until now. To date, no one has ever compared a

spectrum of catalysts in the hydrosilylation of trivinyl functional

open-cage silsesquioxanes. Moreover, in our study for the ﬁrst

time, real-time FT-IR spectroscopy was applied to the

monitoring of hydrosilylation of trifunctional IC-POSSs,

which provided detailed data about the kinetics of hydro-

silylation of these compounds and the inﬂuence of substrates

structures on the course of the reaction. Additionally, the

structure-dependent thermal properties of a series of IC-POSSs

and their selected derivatives are presented.

with three functional groups. In 2010, Miyasaka et al.

demonstrated that this compound can be functionalized by

hydrosilylation, and it is used for the synthesis of branched

polysiloxanes. We have recently focused on open-cage POSSs,

but in this work, the substrate scope was limited only to

chlorodimethylvinylsilane and chlorodimethylvinylgermane

with various kinds of commercially available POSS silanols.

Our recent work has been aimed at the synthesis of a library of

IC-POSSs with three types of vinyldiorganosilyl groups and their

further catalytic functionalization. Recently, Hreczycho’s group

has reported the Sc(OTf)₃, Bi(OTf)₃, and also Naﬁon -

catalyzed formation of Si−O−Si bonds, which has been

successfully used in the functionalization of POSS silanols, and

methods were expanded to the introduction of boron and

germanium functionalities to silsesquioxanes. Laine’s group

has presented another approach to the functionalization of such

structures by blocking hydroxyl groups in trisilanolphenyl POSS,

followed by modiﬁcation of inert phenyl groups, resulting in the

synthesis of stilbene−silesquioxanes. Other examples of using

trivinyl-substituted open-cage silsesquioxanes are based on the

substitution of one functional group with POSS or silane,

followed by the formation of cyclic compounds and

RESULTS AND DISCUSSION

■

Synthesis of Incompletely Condensed Silsesquiox-

anes. The ﬁrst and fundamental part of the study was the

preparation of incompletely condensed silsesquioxanes with

diﬀerent steric hindrances protruding from the POSS core’s

5,36

polymers.

There are also reports on the application of

trifunctional silsesquioxanes with Si−H groups in ﬁlm-forming

materials, amphiphilic molecules, hyperbranched poly-

Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Figure 2. Examples of the FT-IR spectrum of the reaction mixture of 4 synthesis compared with that of trisilanolisobutyl POSS.

Table 1. Condensation of POSS Silanols with Chlorosilanes

Reaction conditions: [POSS silanol]:[chlorosilane]:[Et N] = 1:3.1:6; THF; 0−25 °C. The progress of the reaction was followed by FT-IR

spectroscopy.

moieties. For this purpose, the IC-POSS architectures (1−9)

were synthesized by the hydrolytic condensation of commer-

cially available POSS trisilanols with chlorodimethylvinyl-,

chloromethylphenylvinyl-, and chlorodiphenylvinylsilanes, ac-

cording to Scheme 2.

In the process of reaction optimization, the eﬀects of the

amount of silane, triethylamine, and solvent used in con-

densation were determined. Because the eﬃciency and time of

condensation reaction also strongly depend on the concen-

tration of the reagents, we decided to use tetrahydrofuran

cool the reaction mixture in an ice bath during the addition of

chlorosilane. A small excess of chlorosilane was used to fully

convert POSS silanol (molar ratio [POSS trisilanol]:[chlor-

osilane] = 1:3.1). Then, the cooling bath was left to warm to

room temperature. The progress of the condensation reactions

was monitored by FT-IR spectroscopy as the disappearance of

the signals assigned to the stretching vibrations of the −OH

groups present in the silanol substrates and the simultaneous

appearance of characteristic absorption bands at 1593 cm⁻

attributed to CC bonds from vinyl groups in the formed

product (Figure 2).

(

THF) as a reaction medium because silsesquioxane silanols are

highly soluble in it. To avoid side-reactions, it was necessary to

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Scheme 3. Hydrosilylation of Incompletely Condensed Trivinyl-Substituted Silesquioxanes with Phenylsilanes in the Presence of

Platinum and Rhodium Catalysts

Table 2. Hydrosilylation of Selected IC-POSSs with Dimethylphenylsilane in the Presence of Platinum and Rhodium Catalysts

C1 = PtO , C2 = PtCl , C3 = H PtCl , C4 = [Rh(COD)Cl] , and C5 = Pt (dvs) . Reaction conditions: [IC-POSS]:[silane a]:[platinum or

−

−3

−2 c

rhodium] = 1:3:(3 × 10 ) /(3 × 10 ) /(3 × 10 ) ;T = 95 °C; toluene; m_P_O_S_S/V_t_o_l= 100 mg/mL; reaction time 48 h (C1 and C2) and 24 h

(C3−C5).

Finally, the crude product was isolated from the reaction

was evaporated. All products 1−9 were obtained with good

yields of 87−93%.

mixture and puriﬁed. After the reactions, the mixtures were

ﬁltered oﬀ by a glass ﬁlter type G4 with silica gel and Celite, and

then the column was ﬂushed by ethyl acetate to rewash all

products. HCl formed during the reaction was bound to

During the course of the reactions, it was noted that the time

needed for complete conversion of POSS trisilanol increases

with increasing steric hindrance of the chlorosilane used, in the

order from chlorodimethylvinyl- to chlorophenylmethylvinyl- to

chlorodiphenylvinylsilane. The same eﬀect was also observed for

the derivatives containing Ph and C H inert groups. The

triethylamine, and the side product Et NHCl (hardly soluble in

the reaction mixture) was retained on the column. The excess of

the solvent was evaporated, and the product was dried under

vacuum. In the cases of 3, 6, and 9 (silsesquioxanes with C H

reaction times were 2.5−8 h for 1−6 and 6−12 h for 7−9 (data

are compiled in Table 1). It should be added that the iBu and

C H silanols react faster than the Ph silanol in the presented

inert groups in the framework), the solution after ﬁltration was

evaporated, the product was extracted with dichloromethane/

water, then the organic phase was dried over anhydrous

magnesium sulfate for 24 h and ﬁltered oﬀ, and the solvent

reaction. The reason for the longer times of condensation of

POSS silanols with chlorodiphenylvinylsilane might be a greater

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Table 3. Hydrosilylation of Selected IC-POSS with Triphenylsilane in the Presence of Platinum and Rhodium Catalysts

C1 = PtO , C2 = PtCl , C3 = H PtCl , C4 = [Rh(COD)Cl] , and C5 = Pt (dvs) . Reaction conditions: [IC-POSS]:[silane b]:[platinum or

−

−3

−2 c

rhodium] = 1:3:(3 × 10 ) /(3 × 10 ) /(3 × 10 ) ];T = 95 °C; toluene; m_P_O_S_S/V_t_o_l= 100 mg/mL; reaction time 48 h (C1 and C2) and 24 h

(C3−C5).

steric hindrance caused by the phenyl groups in chlorosilane and

changes in the electronic eﬀects of the inert groups attached to

the silsesquioxane core.

the hydrosilylation reaction to selectively bond chromophores

(in the form of phenylsilanes) to derivatives 1−9, which have

three vinyl functional groups protruding from the silsesquioxane

cage, thus enabling their further modiﬁcation and making them

molecular scaﬀolds for the bonding of chromophores.

Screening of Catalysts. At the beginning of this study,

three IC-POSS derivatives with the same inert iBu group and

three diﬀerent types of open moieties (dimethylvinylsilyl, 1;

phenylmethylvinylsilyl, 4; diphenylvinylsilyl, 7) and two silanes,

namely, dimethylphenylsilane (a) and triphenylsilane (b), with

signiﬁcantly diﬀerent steric properties were selected as our

model systems for catalyst screening (Scheme 3). Optimization

of the reaction conditions was carried out using diﬀerent

The diﬀerences in the properties and structures of the

obtained open-cage silsesquioxanes are also manifested in the

Si NMR spectra as changes in the resonance lines assigned to

silicon atoms. For derivatives 3 and 9, containing in their

structures inert 2,4,4-trimethylpentyl (C H ) groups, we

observed the multiplicity of the signals in the Si NMR spectra

probably caused by the interaction and rotation of these

compounds. For all compounds, the chemical shifts of the three

silicon atoms from the functional groups Si−CHCH were

changed because of the diﬀerences in the electronic eﬀects of the

substituents at silicon atoms. The resonance lines were shifted

toward lower chemical shift values from alkyl to aryl substituents

and with the increasing number of phenyl substituents. On the

other hand, chemical shifts of the silicon atoms derived from the

Si−O−Si core were just slightly changed. A similar eﬀect has

been reported for tetrakis(methylsilylated) double-decker

octaphenylsilsesquioxane and tris(methylsilylated) heptaphe-

loadings of selected catalysts [PtO

, PtCl , H PtCl , [Rh-

2 2 6

(COD)Cl] , and Karstedt’s catalyst Pt (dvs) ] known for high

19,20

catalytic activity in the hydrosilylation of oleﬁns.

The

conversion of all reagents and the formation of products were

determined by H, C, and Si NMR spectroscopy. The results

of the experiments are presented in Tables 2 and 3.

In all experiments, the conversion of substrates was very high

and amounted to over 96%. Moreover, hydrosilylation of 1, 4,

and 7 with dimethylphenylsilane a resulted in the exclusive

formation of β-isomeric products (1a, 4a, and 7a) with a

selectivity of over 99% in the presence of platinum catalysts.

Some test reactions with the bis(1,5-cyclooctadiene)dirhodium-

(I) dichloride complex led to the formation of α and β (main)

products and dehydrogenative coupling products (entry 14 in

Table 2 and entry 9 in Table 3). However, hydrosilylation of

selected silsesquioxanes with triphenylsilane b brought about

nylsilsesquioxane.

Synthesis of Functionalized Open-Cage Silsesquiox-

anes. Having these sterically and electronically diﬀerent vinyl

IC-POSSs, we decided to functionalize them via the hydro-

silylation reaction. Moreover, the employment of real-time FT-

IR spectroscopy allowed us to examine the inﬂuence of the

structural diversity of POSS compounds as well as applied

hydrosilanes on the reactivity of the investigated derivatives in

the trifunctional POSS derivatives functionalization. We chose

Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Figure 3. Kinetic plots for hydrosilylation of silsesquioxanes 1−4, and 7 with dimethylphenylsilane (a), in the presence of Karstedt’s catalyst, measured

by in situ FT-IR (the formation of products 1a−4a and 7a). Reaction conditions: toluene; 95 °C; m /V = 100 mg/mL; Pt (dvs) catalyst; [POSS]:

POSS

tol

−

[

silane]:[platinum] = 1:3:(3 × 10 ).

the predominant formation of β products (1b, 4b, and 7b over

4%) and a greater number of dehydrogenative coupling

required for total hydrosilylation of CC bonds in the reactions

between phenyldimethylsilane and POSS derivatives (1−3)

reached 397, 1197, and 897 min, respectively. So, for the POSSs

with alkyl inert groups, the reaction was faster than that for the

aromatic (phenyl) group, although, at the beginning of the

process, the reaction of 2 was faster than that of 3. However,

eventually more time was needed to complete the addition of

Si−H to CC bonds. Additionally, the smaller the alkyl

substituent, the shorter the reaction (time < time ). The

reason for such a reactivity could be the diﬀerent electronic

eﬀects and steric hindrances of the alkyl and aryl groups. In the

case of IC-POSSs with the same iBu inert cage groups and

diﬀerent moieties protruding from the cage dimethylvinylsilyl

(1), phenylmethylvinylsilyl (4), and diphenylvinylsilyl (7), the

reaction time increased with increasing steric hindrance of the

functional groups. The reaction time was 397 min for 1, 867 min

for 4, and 2522 min for 7, and diﬀerences in the reactivity and

reaction times were quite signiﬁcant.

products and α products. The conducted experiments showed

that the rhodium catalyst was the least selective in hydro-

silylation of IC-POSS with phenylsilanes. All catalysts showed

less selectivity in the reactions with the more sterically crowded

−

silane b. Although in the initial tests with 10 mol of C1−C4

−

and 10 mol of C5 of metal loading per 1 mol of Si−H group we

obtained products with similar conversion of the reagents and

selectivity, we decided to reduce the catalyst loadings. It turned

out that C5 proved to be in all cases the most selective catalyst

with the lowest metal loading (10⁻mol of platinum per Si−H

group). On the basis of the preliminary results, we decided to use

Karstedt’s catalyst, as the most eﬃcient hydrosilylation

promoter, in our further study.

iBu

octyl

In Situ FT-IR Experiments. On the basis of earlier results,

we decided to perform several additional experiments using in

situ FT-IR spectroscopy to more precisely explore the eﬀect of

the silsesquioxane structure on the reaction time. The applied

methodology allowed precise monitoring of the experiments by

measurement of the reaction trends and proﬁles in real time,

providing highly speciﬁc information, e.g., about the kinetics,

reaction initiation, and conversion of the reagents in the course

of the reaction. For this purpose, we chose simple

dimethylphenylsilane (a) and two groups of silsesquioxanes:

the ﬁrst of 1−3 with the same dimethylvinylsilyl opening moiety

and diﬀerent inert groups in the POSS cage and the second of 1,

Figure 4 shows 2D and 3D illustrations of the disappearance

of the characteristic Si−H signal in the course of an exemplary

hydrosilylation reaction of 7 with dimethylphenylsilane, which

leads to complete conversion of the substrates, selective

functionalization of all functional groups, and formation of 7a.

Hydrosilylation of Open-Cage Silsesquioxanes with

Phenylsilanes. The positive results achieved in the catalytic

tests of hydrosilylation of selected IC-POSSs with silanes a and b

prompted us to extend the range of POSSs and silanes. We

decided to extend the described method to functionalization of

all obtained IC-POSSs (1−9). Our choice of silanes was based

on the tests with silanes with diﬀerent steric hindrances (Tables

2 and 3). Therefore, we decided to perform the next experiments

with silanes containing a dimethylsilylhydride moiety. In the

earlier selected reaction conditions, new trisubstituted deriva-

tives were obtained in the stoichiometric reaction of IC-POSSs

(1−9) with phenylsilanes (Scheme 4). The molar ratio was as

follows: [IC-POSS]:[silane a/b/c/d]:[platinum] = 1:3:(3 ×

4, and 7 with the same inert group and diﬀerent types of

vinyldiorganosilyl moieties. In these experiments, 1 equiv of

silsesquioxane (1−4 or 7), 3 equiv of dimethylphenylsilane, and

mL of toluene were added to a glass reactor equipped with an

in situ FT-IR probe and placed in an oil bath at 95 °C, and then

−

mol of platinum (per each Si−H group) of Karstedt’s

catalyst was added. The progress of hydrosilylation of selected

silsesquioxanes with PhSiMe H in the presence of Karstedt’s

complex was possible to control by monitoring of the high

−

−4

absorption bands assigned to Si−H units (v = 822 cm ), which

10 ). For 1−6, we conducted the reaction for 24 h, and for 7−9,

decreased over time. All results are shown in Figure 3.

the reaction was for 48 h. Using silane e in the stoichiometric

reactions with silsesquioxanes, various types of cross-linked

structures were obtained, which is related to the presence of two

The rate of hydrosilylation of the CC bond was found to

strongly depend on the silsesquioxane structure. The time

Inorg. Chem. XXXX, XXX, XXX−XXX

Article

compared with the disiloxanes, which could be explained by the

steric properties of the POSS molecules.

A deﬁnite advantage of 1d, 2d, 3d, 1e, and 2e is the presence

of three bromine atoms and three Si−H groups, which may

allow further functionalization of these compounds and their

5,46

application, for example, in hybrid materials

blocks for organic optoelectronic materials.

and building

7−51

Figure 5 shows an exemplary starting mixture and the

postreaction mixture of 1e formation. Progress of the reaction

was followed by attenuated-total-reﬂectance FT-IR. Because of

−

overlap of the substrate signals at about 900 cm , the progress

of the reaction was monitored by observing decreasing signals

−

assigned to Si−H groups at 2119 cm , and additionally, as the

−

reaction progresses, a band around 800 cm started to appear.

The reaction was completed after 24 h because changes in the

conversion of Si−H were no longer observed. After the

reactions, the mixtures were ﬁltered oﬀ by a glass ﬁlter type

G4 with silica gel and Celite. The solvent was evaporated, and

the products were dried under vacuum.

Figure 4. (a) 2D and (b) 3D illustrations of the Si−H bond

disappearance recorded in real time during hydrosilylation of 7 with

dimethylphenylsilane (the formation of 7a) in the presence of

Karstedt’s catalyst.

THERMAL PROPERTIES

■

Compounds 1−9 exhibit the so-called open-cage structure.

Besides various substituents at the protruding groups (which

aﬀect steric hindrance), these structures have three types of inert

groups surrounding the POSS core (iBu, Ph, and C H ). All

reactive Si−H groups in the 1,4-bis(dimethylsilyl)benzene

molecule. However, by changing the molar ratio and using a

little excess of silane, we obtained compounds 1e and 2e at the

presented types of structural modiﬁcations aﬀected not only the

syntheses of the compounds but also their physical properties

such as the physical state, solubility, and thermal properties.

Thermogravimetric analysis (TGA) revealed that both types of

substituents (inert groups in the POSS framework and opening

moieties) aﬀected the thermal properties of the open-cage-type

silsesquioxanes and their derivatives. The inﬂuence of the

structural diversity on the thermal properties of the samples

studied was evaluated for IC-POSSs 1−9 and their selected

−

molar ratio [IC-POSS]:[silane e]:[platinum] = 1:3.1:(3 × 10 )

by selective functionalization of only one functional group in

silane. We assume that, at the initial stage of reaction,

monosubstitution of 1,4-bis(dimethylsilyl)benzene is observed.

However, when conversion of the substrates is very high, the

remaining vinyl groups may react with the dimethylsilyl units

incorporated with the POSS molecules, which leads to the cross-

linked structure. In order to avoid hydrosilylation of both

dimethylsilyl groups in 1,4-bis(dimethylsilyl)benzene, the

equilibrium of the reaction must be shifted toward the formation

of monosubstituted products; therefore, for selective mono-

functionalization, a slight excess of silane e was required. A

similar eﬀect was observed, e.g., for functionalization of 1,1,3,3,-

10%

derivatives on the basis of the 5% (T

) and 10% (T

) mass

loss temperatures and the amount of residue at 1000 °C (all

results are shown in Table 4).

Considering the inﬂuence of the inert group, the highest

thermal stability was found for the compounds with Ph groups

(2, 5, and 8). Additionally, the presence of functional groups

with greater steric hindrance increases the thermal stability of

the derivatives (1 < 4 < 7), which is related to the generally

greater stability of the phenyl compounds compared to the alkyl

tetramethyldisiloxane with vinylsilanes; however, for function-

alization of POSS compounds with 1,4-bis(dimethylsilyl)-

benzene, a signiﬁcantly lower excess of silane e had to be used

52,53

structures.

However, for compounds with the alkyl inert

Scheme 4. Hydrosilylation of IC-POSSs (1−9) with Phenylsilanes (a−e) in the Presence of Karstedt’s Catalyst

Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Figure 5. FT-IR spectra of (a) starting mixture 1 + 3.1 equiv of silane e and (b) postreaction mixture/formation of 1e.

Table 4. Thermal Properties of IC-POSSs 1−9

substituents iBu and C H , only for the dimethylvinylsilyl

8 17

group, compound 3 (C H ) is more stable than 1 with the

mass loss temperature

smaller iBu inert group. When the functional groups are

phenylmethylvinylsilyl (4−6) or diphenylvinylsilyl (7−9), the

thermal stability increases in the order 6 < 4 < 5 and 9 < 7 < 8.

The observed impact of the type of functional group on the

thermal stability of silesquioxanes may be caused by the changed

distance between these groups and the wider opening of the

silsesquioxane structure, making it more ﬂexible. Furthermore, it

should be strongly emphasized that the residue observed at 1000

[°C]

entry

product

T_d⁵^%

T_d¹⁰^%

residue at 1000 °C [%]

269

440

335

372

427

364

388

464

269

295

310

334

332

340

499

359

434

488

385

427

520

320

328

339

344

387

364

C was the highest for the trisilanolphenyl POSS-derived

products, which is consistent with the literature data.

Figures 6 and 7 show the TGA curves obtained for selected

functionalized structures. We compared the inﬂuence of the

modiﬁer (substituted silane) and diﬀerent inert groups in the

compounds with the same modiﬁer on their thermal properties.

Analysis of the obtained results showed that functionalization of

IC-POSSs with phenylsilanes strongly inﬂuenced the thermal

properties of the resulting products (1a−1c); the T_dvalues

signiﬁcantly increased compared to those of the unmodiﬁed

Figure 6. TGA curves obtained for selected compounds: 1 and 1a−1c (inﬂuence of the modiﬁer on the thermal properties).

Inorg. Chem. XXXX, XXX, XXX−XXX

The Supporting Information is available free of charge at

Article

Figure 7. TGA curves obtained for selected compounds: 1a, 4a, and 7a (inﬂuence of the inert group on the thermal properties).

silsesquioxanes. A similar eﬀect of the thermal behavior of IC-

silicon substituents in the functional group) and phenylsilanes

(e.g., their arrangement, structure, etc.) and their physicochem-

ical properties allowing the design of macromolecules with

desirable properties.

We believe that the compounds based on open-cage

silsesquioxanes can undoubtedly become very useful reagents

for the synthesis of building blocks and scaﬀolds for hybrid

materials, which, because of the unique structure and greater

ﬂexibility of the core, can compete with completely condensed

silsesquioxanes.

POSSs after the incorporation of aryl groups into the

silsesquioxane core was observed by the Naka group.

However, for 4a and 7a, the T_d⁵parameter was decreased for

the modiﬁed structures probably because of diﬀerences in the

steric hindrance of the silyl groups in the open corner of

silsesquioxanes, which aﬀected the arrangement of the aromatic

units and interaction between them. For derivatives 1a, 4a, and

a modiﬁed with the same dimethylphenylsilane but containing

diﬀerent inert groups, we observed increasing thermal stability in

the order from iBu to C H and Ph. On the other hand, after the

initial degradation, the decomposition of 7a progressed much

faster compared with that of 4a, which clearly indicates higher

resistance of the phenyl derivative than the alkyl one to

thermooxidative decomposition.

ASSOCIATED CONTENT

sı Supporting Information

https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00947.

■

General procedures for the synthesis of IC-POSSs (1−9)

and for hydrosilylation of IC-POSSs with phenylsilanes,

NMR and MALTI-TOF data and spectra of compounds

synthesized in this paper, and TGA curves obtained for

selected compounds 1−9 (PDF )

CONCLUSION

■

In summary, we synthesized a library of trifunctional open-cage

silsesquioxanes diﬀering in the structure of the inert groups and

opening moiety. Having these sterically and electronically

diﬀerent vinyl IC-POSSs, we modiﬁed them with a series of

silanes of diﬀerent structures, functionalities, and steric

hindrances in hydrosilylation reactions. Diﬀerent homogeneous

and heterogeneous catalytic systems were examined to

determine their impact on the eﬀectiveness and selectivity of

hydrosilylation evaluated by monitoring of the processes with

AUTHOR INFORMATION

Corresponding Author

■

Magdalena Grzelak − Faculty of Chemistry and Center for

Advanced Technology, Adam Mickiewicz University in Poznan,

H, C, and Si NMR and in situ FT-IR spectroscopy.

61-614 Poznan, Poland; orcid.org/0000-0003-2807-5840;

Email: magdalena.grzelak@amu.edu.pl

The most interesting outcome of our study is the ﬁrst example

of a fully speciﬁed synthetic protocol allowing modiﬁcation of

trivinylsubstituted open-cage silsesquioxanes with silanes to be

obtained via a hydrosilylation reaction. The applied method-

ology of synthesis does not require the use of complicated

isolation of the ﬁnal products. The hydrosilylation reactions

catalyzed by Karstedt’s catalyst proceeded in a highly

regioselective manner to give exclusively anti-Markovnikov

products.

Additionally, we studied the structure-dependent thermal

properties of a series of IC-POSSs and their selected derivatives.

Full characterization of the products enabled us to identify the

relationship between the structures of the silsesquioxanes

studied (e.g., the types of inert groups in the framework and

Authors

Rafał Januszewski − Faculty of Chemistry and Center for

Advanced Technology, Adam Mickiewicz University in Poznan,

1-614 Poznan, Poland; orcid.org/0000-0002-5562-6647

Bogdan Marciniec − Faculty of Chemistry and Center for

Advanced Technology, Adam Mickiewicz University in Poznan,

1-614 Poznan, Poland

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.0c00947

Notes

The authors declare no competing ﬁnancial interest.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

(21) Quadrelli, E. A.; Basset, J. M. On Silsesquioxanes ’ Accuracy as

Article

Silsesquioxanes Obtained via Silylative Coupling Reaction. Organo-

metallics 2020, 39, 74−79.

ACKNOWLEDGMENTS

■

The authors are thankful for ﬁnancial support from the National

Science Centre (Poland) under Project Preludium, UMO-

017/25/N/ST5/00404. M.G. was the recipient of an Adam

Mickiewicz University Foundation scholarship in the academic

(

19) Marciniec, B. Comprehensive Handbook on Hydrosililation;

Pergamon Press, 1992.

(20) Marciniec, B.; Maciejewski, H.; Pietraszuk, C.; Pawluc, P.

Hydrosilylation: A Comprehensive Review on Recent Advances; Springer,

year 2018−2019.

2009.

Molecular Models for Silica-Grafted Complexes in Heterogeneous

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