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New mono- and diethynylsiloxysilsesquioxanes – efficient procedures for their synthesis† Beata Dudziec,*a Monika Rzonsowska,a Bogdan Marciniec,b Dariusz Brząkalskia and Bartosz Woźniaka Ethynyl-substituted siloxysilsesquioxanes are promising building blocks for a wide range of substances based on a POSS/DDSQ core, especially for (oligo-)polymer syntheses and modifications (the formation

Received 27th June 2014, Accepted 6th July 2014 DOI: 10.1039/c4dt01950d www.rsc.org/dalton

of hybrid materials with interesting photophysical and mechanical properties). In this study, we report on a series of new mono- and diethynylsiloxysilsesquioxanes formed via an efficient and highly selective one-pot process from silsesquioxanes with reactive Si–OH groups based on sequential condensation, hydrolysis, chlorination and substitution reactions. All newly synthesized compounds were isolated and characterized by spectroscopic methods.

Introduction Polyhedral silsesquioxanes (POSS) of the general formula (RSiO3/2)n, containing a well-defined nanosized, three dimensional inorganic cubic core of Si–O–Si moieties, constitute a broad class of organic–inorganic hybrid compounds. The most important POSS materials are the cube-like T8 derivatives (RSiO3/2)8, which have found a wide range of technological applications and can be easily functionalized with one or eight reactive groups. These systems are of particular strong interest to scientists not only because of their construction, but also mainly because of their unique chemical and physical properties (solubility, non-flammability, oxidation resistance, and very good dielectric properties). Organo-functionalized silsesquioxanes have been proven to constitute an excellent new class of nanofillers and modifiers used for the preparation of nanostructured composites with a unique set of attributes.1 They are also widely used as silica-supported catalysts,1,2 dendrimers,3 in optoelectronics4 (e.g. OLEDs5) and as biocompatible materials or “scaffolds” for liquid crystals.6 The development of new and effective methods for POSS synthesis with various functional groups influences the number of their possible applications. This is particularly important in terms of reactive functional groups attached to a POSS core, e.g. vinyl, amino, epoxy, methacryloxy, and chloropropyl

a Department of Organometallic Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland. E-mail: [email protected]; Fax: (+48)61 8291508; Tel: (+48)61 8291366 b Faculty of Chemistry and Center for Advanced Technologies, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c4dt01950d

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groups.6c–g To these derivatives one should also add silsesquioxanes bearing very reactive ethynyl functionalities.7 Ethynyl- or alkynyl-substituted silsesquioxanes (title compounds) seem to be promising reagents for further modifications because of their interesting electronic properties. There are few examples of one –CC– triple bond in a functional chain of the POSS or DDSQ core. These are based on the introduction of one or two alkynyl- or ethynyl functionalities in stages, e.g. via subsequent catalytic reactions, i.e. metathesis and Sonogashira coupling8 or via hydrolytic condensation and consecutive alkynyl–imide or alkynyl–alkyl formation (used for rare examples of DDSQ functionalization with two alkynyl groups).9 There are some examples of compounds with eight alkynyl groups introduced into the POSS core.10 Yet, all these methods are based on functionalization with alkynyl- or ethynyl-substituted reagents, although Csp–Csp triple bond moieties are usually located at some distance (separated by an organic group, e.g. phenyl, alkyl, etc.) from the Si–O–Si core. Attempts at introducing the ethynyl group in the vicinity of the cubic core have been rare. There is a method based on the hydrolytic condensation of a POSS (tri-)silanol form with EtOSiMe2CCH, performed in toluene, followed by addition of p-toluenesulfonic acid.7 Yet, the above mentioned method entails certain difficulties, e.g. the necessity of p-toluenesulfonic acid addition means that it is of the utmost importance to control the pH value to avoid POSS structural degradation or rearrangements of other functional groups at POSS. There is growing interest in combining POSS/DDSQ units with organic moieties, e.g. via copper-catalyzed Huisgen 1,3-dipolar cycloaddition producing an imidazole ring that is a spacer between these two groups and also affects their physical properties.6c,11 The double-decker silsesquioxane methods of functionalization include hydrolytic condensation reactions, hydrosily-

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lation, etc.11e–j Because of the considerable importance of and even greater prospect for the functionalized, DDSQ-based compounds to become precursors for the synthesis of a wide range of materials (also oligo- and polymeric), this new diethynylderivative of silsesquioxane would be particularly interesting. In view of the unchanged reactivity of the spC–H bond at the silsesquioxane core, we expect that these alternative procedures for the synthesis of the title compounds would enhance the availability of a new variety of silsesquioxanes. Over the last few years, the scientific interest of the Prof. Marciniec team has turned to polyhedral oligosilsesquioxanes (POSS), and the T8 system in particular, as well as spherosilicates. The research conducted in this area has concerned, among other aspects, the improvement of procedures for the synthesis of functionalized mono- and octa-substituted silsesquioxanes and spherosilicates via, e.g., hydrolytic condensation and nucleophilic substitution.6e,f,12 This paper presents the synthesis of new, mono- and diethynylsiloxy-functionalized silsesquioxanes (also the double-decker type of silsesquioxane (DDSQ)) utilizing easy to handle and commercially available silanol precursors of silsesquioxanes (POSS and DDSQ).

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Synthesis of mono- and diethynylsiloxysilsesquioxanes in a one-pot reaction using TCCA Trisilanolisobutyl POSS (1,3,5,7,9,11,14-heptaisobutyltricyclo[7.3.3.15,11]heptasiloxane-endo-3,7,14-triol) (1A-1) was chosen as a model compound for monoethynylsiloxy POSS systems (6A) (Scheme 1). The diethynylsiloxy DDSQ system (6B) was synthesized according to the procedure proposed for (6A) (Scheme 2). 1A-1 was used as a starting material to be transformed in a sequence of two hydrolytic condensations and hydrolysis to hydrodimethylsiloxy(heptaisobutyl)silsesquioxane (4A-1), according to known procedures13 (Scheme 1). In the next step, the possibility of Cl-group substitution at the Si atom in 4A-1 was tested and, to this end, an attempt was made to transform the Si–H bond into Si–Cl. There are a few known chlorinating agents that could be used to perform the chlorination: Cl2, HCl, phosphorous trichloride, allyl chloride

Results and discussion A series of condensation reactions enabled us to obtain silsesquioxanes with reactive Si–H bond(s). We wanted to combine the properties of mild and effective chlorinating agents, i.e. TCCA (trichloroisocyanuric acid) for the Si–H to Si–Cl reaction, and obtain very reactive chlorosyloxy-substituted silsesquioxanes. Their subsequent reaction with ethynylmagnesium bromide enabled us to obtain mono- and diethynylsiloxy-substituted POSS in a one-pot reaction with high yields and selectivity in a short time. Since the above procedure involves five steps, one may have doubts about its overall efficiency. However, the yields of the title compounds are very good and the procedure exploits commercial reagents. In parallel, a more direct method was also worked out – involving three steps – to obtain the title silsesquioxanes, with high yields as well, via hydrolytic condensation of silanol (3A and 3B) precursors of POSS and DDSQ with ClSiMe2CCH. The title compounds may play an important role in the further synthesis of new organo-POSS and organo-DDSQ unsaturated derivatives, ligands and especially in materials science, i.e. (oligo-) polymer creation and modifications. The possibilities of introducing one or two ethynyl groups to POSS/DDSQ units were tested and the conclusion was that, mainly for steric reasons, it would be more possible to accomplish this idea via incorporating an ethynylsiloxy unit to the Si–O–Si core than the bare ethynyl group. Therefore, two paths of the reactions were performed, i.e. involving mono- and diethynylsiloxysilsesquioxanes (POSS – type A and DDSQ – type B).

13202 | Dalton Trans., 2014, 43, 13201–13207

Scheme 1 One-pot procedure for synthesis of monoethynylsiloxysilsesquioxane (POSS) (6A).

Scheme 2 One-pot procedure for the synthesis of diethynylsiloxysilsesquioxane (DDSQ) (6B).

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in the presence of activated charcoal on palladium, etc.14 However, there are major difficulties in their usage arising from one or more of the following: low yield, difficulty in handling the reagent, and tedious workup procedures to obtain a pure product. It was found that organic chloroimides, especially trichloroisocyanuric acid (TCCA) or 1,3,5-trichloro1,3,5-2,4,6-(1H,3H,5H)-trione, known since 1902, belong to this large group of compounds and would be the best chlorinating agent to transform silicon hydrides to the chloro derivatives. The reason for choosing this compound was to develop an efficient process involving a simple isolation procedure following the reaction which required only filtration to remove the insoluble by-product. Varaprath and co-workers proposed a very effective and selective protocol for the synthesis of chlorosilanes from silicon hydrides.15 This method has been shown to work perfectly even with sterically demanding trimethylsiloxy-substituted siloxanes with an Si–H bond, so it was decided that the method should be used for our purpose. In the tests, hydro-POSS and dihydro-DDSQ derivatives were necessary for effective chlorination reactions from Si–H to Si–Cl and this procedure using TCCA was proved to be very effective16 (Scheme 1). Hydrodimethylsiloxy-(heptaisobutyl)silsesquioxane (4A-1) was used to optimize the chlorination procedure using TCCA in a 10% excess for an Si–H group. The use of several solvents from two groups: aliphatic ethers, i.e. diethyl ether, THF, and chlorinated aliphatic hydrocarbons, i.e. dichloromethane, chloroform and 1,2-dichloroethane, was also explored. After several attempts, it was found that the reaction was most effective and selective when performed in dichloromethane or THF. When using DCM as the solvent, 4A-1 was added to a slurry of TCCA in CH2Cl2 and the reaction proceeded under reflux in 2–10 h. However, when THF was used, the reagents were added in reverse order. TCCA was added by means of a solid addition funnel to 4A-1 dissolved in THF cooled to −20 °C. The changed order of the addition of substances for the reactions in THF as well as the lower temperature (additional heating is not advisable) were necessary to prevent chlorination of THF by TCCA. The observations were similar to those presented by Varaprath and co-workers.15 Several tests were performed to optimize the reaction conditions and during the reaction path the intermediate products were isolated and the structure of chlorodimethylsiloxy (heptaisobutyl)silsesquioxane (5A-1) was confirmed on the basis of 29Si NMR analysis – a disappearing signal of the Si–H group (4A-1) at −2.99 ppm and the apparent signal of the Si–Cl group (5A-1) at −18.93 ppm. As the resulting product, i.e. chlorodimethylsiloxy(heptaisobutyl)silsesquioxane (5A-1), is reactive toward moisture with a tendency to condense, it is recommended to preserve dry and inert conditions. After isolation, which included filtration from unreacted TCCA and cyanuric acid and simple evaporation of the solvent, chlorosiloxy-POSS (5A-1) was then transformed via a known method with ethynylmagnesium bromide to ethynylsiloxy(heptaisobutyl)-silsesquioxanes (6A-1). The desired product 6A-1 was isolated according to standard procedures for post-Grignard mixtures that involved extraction of the desired ethynylsiloxy

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Paper Table 1 One-pot synthesis of ethynyl-substituted siloxysilsesquioxanes (6A) and (6B) – from silanol forms of POSS and DDSQ

Substrate (1A-1) R = i-Bu (1A-2) R = Et (1A-3) R = i-Oc (1A-4) R = c-C5H9 (1A-5) R = c-C6H11 (1A-6) R = Ph (1B-7) R = Ph

Reaction conditions a

b

Structure

Isolated yield [%]

(6A-1) (6A-2) (6A-3) (6A-4) (6A-5) (6A-6) (6B-7)

92 91 89 90 91 84 82

Condensation: SiCl4, THF, RT, 24 h – second condensation ClSiMe2H, THF, RT, 24 h; hydrolysis: THF–H2O, reflux, 12 h; TCCA chlorination: THF, 45 °C, 24 h; Grignard reaction: 0.5 M HCCMgBr in THF, 45 °C, 24 h. b Condensation: SiCl4 for POSS, MeSiCl3 for DDSQ, THF, RT, 24 h – second condensation for POSS-ClSiMe2H, THF, RT, 24 h; hydrolysis: THF–CHCl3, H2O, HCl, RT, 6–12 h; TCCA chlorination: THF, 45 °C, 24 h; Grignard reaction: 0.5 M HCCMgBr in THF, 45 °C, 48–72 h.

a

POSS followed by solvent evaporation. Column chromatography of a crude product afforded pure – over 92% yield – 6A-1 in the form of a powder. Given our optimized conditions, the scope of this one-pot reaction sequence using various trisilanol silsesquioxanes (1A) with different alkyl or phenyl groups attached to the seven silicon atoms in the corners of POSS (Table 1) was investigated. Since the synthetic procedures require the absence of by-products originating from unreacted trisilanol POSS (1A), all the condensation reactions were performed with 0.5–1% excess of chlorosilanes and with dry and deoxidized THF or CHCl3. Under these conditions, stoichiometric condensation processes and simple filtration from the resulting [Et3NH]+Cl− salt followed by evaporation of the solvent (and possible chlorosilane residues) was sufficient to obtain the desired product for the consecutive reaction. There was also no isolation step after the reaction with TCCA (the structure of the resulting chlorosiloxy-POSS derivative via 29Si NMR was controlled only for tests). Resulting chlorinated siloxysilsesquioxane (5A-1) was subjected to reaction with a 0.5 M THF solution of ethynylmagnesium bromide (24 h, 45 °C). The optimized amount of the ethynyl-Grignard reagent was a 2 molar excess for each Si–Cl bond. After post-Grignard silsesquioxane extraction and solvent evaporation, the crude product was purified via column chromatography (silica gel, eluent: n-hexane–diethyl ether for silsesquioxanes with alkyl substituents R = alkyl and n-hexane–CH2Cl2 for R = aryl) giving over 84% of the total yield.

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The protocol used for one-pot synthesis of ethynyl-siloxysilsesquioxanes (6A) was the same for alkyl substituents. However, to acquire 6A-6 with phenyl groups attached to silicon in seven corners of POSS in quantitative yield, it was required to perform the hydrolysis process using CHCl3 instead of THF.9a The other steps of the procedure were the same, except for the crude product purification. Because of the very poor solubility of 6A-6 in n-hexane, the eluent was n-hexane– CH2Cl2 3 : 7. All ethynylsiloxysilsesquioxanes (6A) obtained but one were white solids, and only for the R = iOc at the silicon corner (6A-3) was the final product a highly viscous, transparent oil (similar to the starting trisilanol (1A-3)). The proposed and optimized procedure for the synthesis of ethynyldimethylsiloxy(heptaisobutyl)silsesquioxanes (6A-1) with respective changes in R substituents as in the heptaphenyl derivative (6A-6) enabled us to subject the tetrasilanol form of double-decker silsesquioxanes (1B) to the same reaction sequence. The diethynylsiloxy DDSQ system (6B) was synthesized according to the procedure proposed for 6A-6 (Scheme 2). The structure of 6B-7 was confirmed by 29Si NMR spectroscopy and it was revealed that two geometrical isomers were obtained, i.e. trans-6B-7 and cis-6B-7. Signals at δ = −63.84, −79.16 and −79.44 ppm were assigned to the trans isomer, whereas signals at δ = −63.84, 79.16, −79.25, −79.64 ppm were assigned to the cis isomer. The 29Si NMR spectrum assignments of 6B-7 were consistent with the results of Ervithayasuporn and Kawakami11e–g and the cis-6B-7 was successfully separated by recrystallization in the THF– methanol solvent mixture. Synthesis of mono- and diethynylsiloxysilsesquioxanes via a condensation reaction using chloroethynyldimethylsilane The possibility of reducing the number of steps in the above procedure was also considered and it was checked whether it could be realized in 3 steps instead of 5. A common hydrolytic condensation procedure13 for the parallel reaction of monohydroxy POSS (3A) and dihydroxy DDSQ (3B) with chloro-ethynyldimethylsilane was tested. The main disadvantage of this method for the synthesis of (6A) and (6B) is that silane is not commercially available and is not that easy to handle because of the synthetic procedure and its low boiling point. ClMe2SiCCH can be prepared from diethynyltetramethyldisiloxane using HMPA, which has been described by S. Ichinohe and coworkers.17 Several tests of known condensation type reactions13c between mono- and dihydroxy-silsesquioxanes (POSS and DDSQ) and chloroethynyl-dimethylsilane were performed to obtain all of the expected ethynyl-substituted silsesquioxanes (POSS and DDSQ) (Scheme 3) that were isolated with high yields and their analytical data are identical to the ones obtained according to the first method.

Experimental General methods and chemicals All syntheses and manipulations were carried out under an argon atmosphere using standard Schlenk-line and vacuum

13204 | Dalton Trans., 2014, 43, 13201–13207

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Scheme 3 Procedure for the synthesis of mono- and diethynylsiloxysilsesquioxanes (POSS and DDSQ) via condensation with ClMe2SiCCH.

techniques. 1H, 13C, and 29Si NMR spectra were recorded at 298 K on Varian XL 300 MHz, Bruker Avance 400 MHz and 500 MHz spectrometers at r.t. using CDCl3 as a solvent. Chemical shifts are reported in ppm with reference to the residual solvent (CHCl3) peaks for 1H and 13C and to TMS for 29 Si. FT-IR spectra were recorded on a Bruker Tensor 27 Fourier transform spectrophotometer equipped with a SPECAC Golden Gate diamond ATR unit. In all cases, 16 scans at a resolution of 2 cm−1 were used to record the spectra. Elemental analyses were carried out on a Vario EL III instrument. MALDISynapt G2-S HDMS (Waters Inc.) mass spectrometer equipped with an electrospray ion source and Q-TOF type mass analyzer. The instrument was controlled and the recorded data were processed using the MassLynx V4.1 software package (Waters Inc. ). The trisilanol precursors of POSS (1) were obtained from Hybrid Plastics, other chemicals were purchased from Aldrich. The column chromatography was performed with silica gel 60 (70–230 mesh; Fluka). All solvents and liquid reagents were dried and distilled under an argon atmosphere prior to use. General procedure for the synthesis of ethynyl-substituted siloxysilsesquioxanes with an R-alkyl substituent (6A-1 as an example) in a one-pot reaction using TCCA A mixture consisting of 2.65 g (3.35 mmol) of 1,3,5,7,9,11,14heptaisobutyltricyclo [7.3.3.15,11] heptasiloxane-endo-3,7,14triol (1A-1) (dried under vacuum for 30 min prior to use), 1.17 g of triethylamine (11.72 mmol) and 100 mL of THF was placed under an Ar atmosphere in a Schlenk bomb flask fitted with a plug valve. The flask was placed in an ice bath and 569 mg (3.35 mmol) of SiCl4 was added to the mixture dropwise. The suspension was stirred for 24 h at room temperature and filtered on a glass frit (of triethylammonium chloride salt). The precipitate was washed with THF (3 × 5 mL) and solvent was evaporated. The residue left after evaporation was dissolved in a mixture of 100 mL of THF and 3.01 g (167 mmol) of H2O and heated at 65 °C for 18 h. After the reaction was complete (GC analysis), the THF was evaporated and the residue was extracted with n-hexane 3 × 15 mL. The

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organic phase was collected and dried with MgSO4. Evaporation gave the analytically pure product hydroxy(heptaisobutyl) silsesquioxane (3A-1) in the form of a white powder. The condensation procedure for the resulting 3A-1 was repeated with 364 mg (3.22 mmol) of chlorodimethylsilane and 666 mg (4.83 mmol) of Et3N in the same reaction and isolation conditions as for 1A-1. The hydrodimethylsiloxy(heptaisobutyl)silsesquioxane (4A-1) was obtained in the form of a white powder. A Schlenk bomb flask fitted with a plug valve and connected to a gas and vacuum line was charged under argon with 2.5 g (2.8 mmol) hydrodimethylsiloxy(hepta-isobutyl)silsesquioxane (4A-1) in 13 mL THF and was cooled down in an acetone/dry ice bath to −20 °C and 0.24 g (1.04 mmol) of trichloroisocyanuric acid (TCCA) was quickly added in one portion. The reaction was being mixed and kept to heat up to room temperature for 3 h. In order to remove unreacted TCCA and the resulting cyanuric acid precipitate, the mixture was filtered via cannula under an Ar atmosphere. The organic phase with chlorodimethylsiloxy(heptaisobutyl)silsesquioxane (5A-1) was added dropwise at the same time to 12.6 mL ethynylmagnesium bromide (0.5 M in THF) and placed in a two-necked, 50 mL flask equipped with a reflux condenser and connected to a gas and vacuum line. The reaction mixture was maintained at a temperature of 45 °C for 24 h. After completion of the reaction, unreacted ethynylmagnesium bromide was decomposed with 4 mL of i-PrOH and water and the product was extracted with CHCl3 (3 × 5 mL). The organic phase was collected and dried with MgSO4. Evaporation gave the crude product ethynylsiloxy (heptaisobutyl)silsesquioxane (6A-1) which was purified by column chromatography on silica gel, eluting with n-hexane– diethyl ether at a ratio of 11 : 1 (Rf = 0.75; I2). General procedure for the synthesis of ethynyl-substituted siloxysilsesquioxanes with an R-phenyl substituent (6A-6 as an example) in a one-pot reaction using TCCA The procedure for condensation of both the trisilanol precursor of heptaphenylsilsesquioxane (1A-6) and the tetrasilanol precursor of octaphenylsilsesquioxane (1B-7) is analogous to that described for 1A-1. The next step, i.e. the hydrolysis (consistent with literature9a) that is described below for synthesis of 6A-6, is different from that for alkyl derivatives. The crude condensation product, i.e. chloro(heptaphenyl)-silsesquioxane (2A-6) ( prepared from 2.65 g (2.84 mmol) (1,3,5,7,9,11,14heptaphenyltricyclo [7.3.3.15,11] heptasiloxane-endo-3,7,14-triol) (1A-6)), was dissolved in THF (1.5 mL) and chloroform (4 mL), water (4 mL) and diluted HCl (0.5 mL) over a 90 min period. The aqueous layer was separated and extracted twice with chloroform. The combined organic layers were extracted with water first, then with diluted HCl, water, saturated brine and then dried with MgSO4. After filtration, the solvent was removed under vacuum to obtain the product, i.e. hydroxy(heptaphenyl)silsesquioxane (3A-6), in the form of a white residue. The subsequent steps in the reaction procedures are analogous to those described for alkyl substituents (see the General procedure for the synthesis of ethynyl-substituted siloxysilsesquioxanes with an R-alkyl substituent (example for 6A-1)).

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The only difference is in the final purification of crude ethynylsiloxy(heptaisobutyl)silsesquioxane (6A-6) which was performed by column chromatography on silica gel, eluting with n-hexane–CH2Cl2 at a ratio of 7 : 3 (Rf = 0.73; UV). Experimental characterization data of isolated products 1-Ethynyldimethylsiloxy-3,5,7,9,11,13,15-hepta(isobutyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (6A-1). Yield: 2.85 g (92%); white solid; Rf = 0.75 (n-hexane–Et2O, 11 : 1; I2); IR (ATR) (cm−1): 3297, 2953–2870, 2042, 1464–1332, 1229–955, 836–684, 559; 1H NMR (400 MHz, CDCl3) δ( ppm) = 0.30 (s, 6H SiCH3), 0.60–0.64 (m, 14H CH2), 0.95–0.98 (m, 42H CH3), 1.83–1.93 (m, 7H CH), 2.38 (s, 1H, HCCSi); 13C NMR (100 MHz, CDCl3) δ( ppm) = 1.55 (SiMe3), 22.37, 22.79, 25.71, 88.45 (CC), 92.11 (CC); 29Si NMR (99 MHz, CDCl3) δ( ppm) = −16.05 (HCCSi), −66.89, −67.00, −67.86, −109.83. HRMS (FD): calcd for C32H70O13Si9Na: 937.2638; found: 937.2626. Anal. calcd for C32H70O13Si9 (%): C 41.97; H 7.71; found: C 41.87; H 7.73. 1-Ethynyldimethylsiloxy-3,5,7,9,11,13,15-hepta(ethyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (6A-2). Yield: 2.19 g (91%); white solid; Rf = 0.73 (n-hexane–Et2O, 11 : 1; I2); IR (ATR) (cm−1): 3288, 2964–2882, 2040, 1461–1414, 1253–1011, 836–692, 526; 1H NMR (400 MHz, CDCl3) δ( ppm) = 0.32 (s, 6H SiCH3), 0.61 (qu, J = 8 Hz, 14H, CH2), 0.99 (tr, J = 8 Hz, 42H CH3), 2.39 (s, 1H, HCCSi); 13C NMR (100.6 MHz, CDCl3) δ( ppm) = 1.45 (SiMe3), 3.97, 6.42, 88.26 (CC), 92.22 (CC); 29Si NMR (99 MHz, CDCl3) δ( ppm) = −15.58 (HCCSi), −65.01, −65.69, −65.73, −108.86. HRMS (FD): calcd for C18H42O13Si9Na: 741.0446; found: 741.0427. Anal. calcd for C18H42O13Si9 (%): C 30.06; H 5.89; found: C 29.95; H 5.91. 1-Ethynyldimethylsiloxy-3,5,7,9,11,13,15-hepta(isooctyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (6A-3). Yield: 3.89 (89%); pale yellowish oil. Rf = 0.76 (n-hexane–Et2O, 11 : 1; I2); IR (ATR) (cm−1): 3296, 2951–2869, 2042, 1467–1364, 1226, 1–92, 908, 844–683, 566; 1H NMR (400 MHz, CDCl3, 300 K) δ( ppm) = 0.3 (s, 6H SiCH3), 0.54–0.59, 0.74–0.78, 0.90, 1.00, 1.10–1.14, 1.30–1.34, 1.85 (m, i-Oc), 2.37 (s, 1H, HCCSi); 13C NMR (100 MHz, CDCl3) δ( ppm) = 1.61 (SiMe3), 23.38, 23.44, 24.96, 25.66, 30.13, 31.15, 38.13, 53.93, 88.42 (CC), 92.16 (CC); 29 Si NMR (99 MHz, CDCl3) δ( ppm) = −16.21 (HCCSi), −66.99, −67.19, −68.19, −110.00. HRMS (FD): calcd for C54H114O13Si9Na: 1245.6080; found: 1245.6068. Anal. calcd for C54H114O13Si9 (%): C 52.98; H 9.39; found: C 52.89; H 9.41. 1-Ethynyldimethylsiloxy-3,5,7,9,11,13,15-hepta(cyclopentyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (6A-4). Yield: 3.02 g (90%); white solid; Rf = 0.80 (n-hexane–Et2O, 11 : 1; I2); IR (ATR) (cm−1): 3293, 2948, 2865, 2041, 1450, 1253–949, 834–676, 513; 1H NMR (500 MHz, CDCl3) δ( ppm) = 0.31 (s, 6H SiCH3), 0.96–1.03, 1.46–1.60, 1.71–1.76 (m, c-C5H9), 2.38 (s, 1H, HCCSi); 13C NMR (125 MHz, CDCl3) δ( ppm) = 1.56 (SiMe3), 22.10, 22.17, 26.98, 27.28, 29.70, 88.47 (CC), 92.08 (CC); 29Si NMR (99 MHz, CDCl3) δ( ppm) = −15.90 (HCCSi), −65.87, −65.45, −65.87, −108.54. HRMS (FD): calcd for C39H70O13Si9Na: 1021.2638; found: 1021.2618. Anal. calcd for C39H70O13Si9 (%): C 46.85; H 7.06; found: C 46.84; H 7.07.

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These assignments are in good accord with those in the literature.7a 1-Ethynyldimethylsiloxy-3,5,7,9,11,13,15-hepta(cyclohexyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (6A-5). Yield: 3.34 g (91%); white solid; Rf = 0.81 (n-hexane–Et2O, 11 : 1; I2); IR (ATR) (cm−1): 3292, 2920, 2848, 2040, 1446, 1269–1011, 893–674, 507; 1H NMR (500 MHz, CDCl3) δ( ppm) = 0.33 (s, 6H SiCH3), 0.74–0.80, 1.20–1.28, 1.70–1.78 (m, c-C6H11), 2.39 (s, 1H, HCCSi); 13C NMR (125 MHz, CDCl3) δ( ppm) = 1.64 (SiMe3), 22.99, 23.09, 26.50, 26.83, 27.48, 88.57 (CC), 92.13 (CC); 29Si NMR (99 MHz, CDCl3) δ( ppm) = −16.14 (HCCSi), −67.83, −67.97, −68.66, −108.55. HRMS (FD): calcd for C46H84O13Si9Na: 1119.3733; found: 1119.3734. Anal. calcd for C46H84O13Si9 (%): C, 50.32; H, 7.71; found: C 50.16; H 7.73. 1-Ethynyldimethylsiloxy-3,5,7,9,11,13,15-hepta(phenyl)-pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (6A-6). Yield: 2.97 g (84%); white solid; Rf = 0.73 (n-hexane–CH2Cl2, 7 : 3; UV); IR (ATR) (cm−1): 3281, 3074–2965, 2038, 1595, 1430, 1260–997, 834–694, 558.; 1H NMR (500 MHz, CDCl3) δ( ppm) = 0.31 (s, 6H SiCH3), 2.27 (s, 1H, HCCSi), 6.88–7.73 (Ph); 13C NMR (125 MHz, CDCl3) δ( ppm) = 1.48 (SiMe3), 87.99 (CC), 92.75 (CC), 127.78–128.86, 130.08, 130.78, 134.18–134.29 (Ph); 29Si NMR (99 MHz, CDCl3) δ( ppm) = −14.62 (HCCSi), −78.03, 78.30, −78.33, −108.88. HRMS (FD): calcd for C46H42O13Si9Na: 1077.0446; found: 1077.0448. Anal. calcd for C46H42O13Si9 (%): C 52.34; H 4.01; found: C 52.19; H 4.02. Mixture of cis- and trans-di[9,19-ethynyldimethylsiloxymethyl]-1,3,5,7,11,13,15,17-octa(phenyl)pentacyclo-[11.7.1.13,11. 15,17.17,15]decasiloxane (6B-7). Yield: 3.71 g (82%); white solid; Rf = 0.68 (n-hexane–CH2Cl2, 6 : 4; UV); IR (ATR) (cm−1): 3277, 3074–2965.45, 2038, 1594, 1430, 1258, 1094–998, 835–694, 577; 1 H NMR (400 MHz, CDCl3) δ( ppm) = 0.24, 0.37 (s, 18H SiCH3), 2.18 (s, 2H, HCCSi), 7.21–7.66 (Ph); 13C NMR (100 MHz, CDCl3) δ( ppm) = −2.97; 1.05, 1.79 (SiMe3), 88.59 (CC), 92.44 (CC), 127.50–127.75, 130.41–131.77, 134.06–134.19 (Ph); 29 Si NMR (99 MHz, CDCl3) δ( ppm) = −17.19 (HCCSi), −63.84, −79.16, −79.25, −79.44, −79.64. HRMS (FD): calcd for C58H60O16Si12Na: 1371.1010; found: 1371.1007. Anal. calcd for C58H60O16Si12 (%): C 51.60; H 4.48; found: C 51.45; H 4.49.

Conclusions In summary, we have devised new versatile one-pot protocols for high yield preparation of new ethynylsiloxysilsesquioxanes bearing one or two ethynyl groups in a POSS/DDSQ molecule. Because of the potential importance of this new ethynyl functionalized DDSQ-based silsesquioxane, especially in view of its significant possible future application in the synthesis of a wide range of materials (also oligo- and polymeric), this compound could be particularly interesting. Two alternative ways for the synthesis of the title compounds were proposed. The first is a one-pot procedure involving five consecutive reactions without intermediate isolation, but with very good overall efficiency. According to the other protocol, the reaction is realized in three steps with very high isolating yields, but the

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main reagent, i.e. ClMe2SiCCH, is not commercially available. Both methods lead to mono- and diethynylsiloxy silsesquioxanes with good yields and are comparably effective. The products were isolated and characterized by spectroscopic methods (1H, 13C and 29Si NMR, FT-IR, HRMS). These alternative procedures for the synthesis of the title compounds will enhance the availability of a new variety of silsesquioxanes.

Acknowledgements The authors gratefully acknowledge support from the Ministry of Science and Higher Education (Poland), grant no. UMO-2012/05/D/ST5/03348 and from the European Regional Development Fund, Operational Programme Innovative Economy, 2007-2013, project no. UDA-POIG.01.03.01-30-173/ 09-02.

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Dalton Trans., 2014, 43, 13201–13207 | 13207

New mono- and diethynylsiloxysilsesquioxanes--efficient procedures for their synthesis.

Ethynyl-substituted siloxysilsesquioxanes are promising building blocks for a wide range of substances based on a POSS/DDSQ core, especially for (olig...
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