Functionalization of octaspherosilicate (HSiMe2O)8Si8O12 with buta-1,3-diynes by hydrosilylation

Hydrosilylation with octaspherosilicate (HSiMe2O)8Si8O12 (1) has provided hundreds of molecular and macromolecular systems so far, making this method the most popular in the synthesis of siloxane-based, nanometric, cubic, and reactive building blocks. However, there are no reports on its selective reaction with 1,3-diynes, which allows for the formation of new products with unique properties. Therefore, herein we present an efficient protocol for monohydrosilylation of symmetrically and non-symmetrically 1,4-disubstituted buta-1,3-diynes with 1. The compounds obtained bear double and triple bonds and other functionalities (e.g., Br, F, OH, SiR3), making them highly desirable, giant building blocks in organic synthesis and material chemistry. These compounds were fully characterized by 1H, 13C, 29Si, 1D NOE, 1H–13C HSQC NMR, FT–IR, and MALDI TOF MS, EA, UV–Vis, and TGA analysis. The TGA proved their high thermal stability up to 427 ℃ (Td10%) for compound 3j.


Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS)
MALDI-TOF mass spectra were recorded on a UltrafleXtreme mass spectrometer (Bruker Daltonics), equipped with a SmartBeam II laser (355 nm) in 500-4000 m/z range. 2,5-Dihydroxybenzoic acid (DHB, Bruker Daltonics, Bremen, Germany) served as a matrix and was prepared in TA30 solvent (30:70 v/v acetonitrile: 0.1% TFA in water) at a concentration of 20 mg/mL. Studied samples were dissolved in dichloromethane (2 mg/mL) and then mixed in a ratio 1:1 v/v with matrix solution. Matrix/sample mixtures (1 µL) were spotted onto the MALDI target and dried in air. Mass spectra were measured in reflection mode. The data were analyzed using the software provided with the Ultraflex instrument -FlexAnalysis (version 3.4). Mass calibration (cubic calibration based on five to seven points) was performed using external standards (Peptide Calibration Standard).

FT-IR analysis
Fourier Transform-Infrared (FT-IR) spectra were recorded on a Bruker Tensor 27 Fourier transform spectrophotometer equipped with a SPECAC Golden Gate, diamond ATR unit, with ensuring a resolution of 2cm −1 .

In situ FT-IR analysis
In situ FT-IR measurements were performed on a Mettler-Toledo ReactIR 15 spectrometer equipped with 9.5 mm AgX DiComp (diamond) probe and a liquid nitrogen-cooled MCT detector. The spectra were taken with the resolution of 4 cm -1 collecting scans for each spectrum at 15 s intervals for 8 h and 2 minutes for the rest of reaction time. The reaction progress in the studied systems of parent compounds and catalysts was quantified by observing the rate of changes occurring with time in the area of the band at 904 cm -1 originating from stretching vibrations of Si-H bond. A detailed description of the equipment used is available on the manufacturer's website 1 . Figure S2. Hydrosilylation of buta-1,3-diynes with octaspherosilicate 1 monitored by in situ FT-IR spectroscopy.

Thermogravimetric analysis (TGA)
Thermogravimetric Analyses (TGA) were performed using a Netzsch TG 209 Libra thermal gravimetric analyzer. The measurements were conducted under nitrogen (flow of 20 mL/min), from 29 ℃ to 995 °C at the heating rate of 10 °C/min. The temperature of initial degradation (T5%) was taken as the onset temperature at which 5 wt% of mass loss occurs.

Elemental analyses
Elemental analyses were performed using a Vario EL III instrument.

UV-vis analysis
UV-vis spectra were recorded on a Jasco V-750 UV-visible spectrophotometer.

Synthesis of (bromoethynyl)tri(isopropyl)silane
The title compound was prepared according to the literature with some modification 2 : To a solution of tri(isopropyl)silylacetylene (10 mmol) in acetone (100 mL), N-bromosuccinimide (12 mmol) and silver nitrate (1 mmol) were successively added. The reaction mixture was stirred without light access at room temperature over 18 h before adding water (100 mL). The resulting mixture was extracted with hexanes (3 x 100 mL) and the combined organic layers were washed with brine (100 mL), dried over MgSO4, filtered through a pad of silica and concentrated to give a colorless liquid. Caution: (bromoethynyl)tri(isopropyl)silane is strong lachrymator. The isolation should be performed under the hood.

Synthesis of symmetrical 1,3-diynes (2b-c)
Symmetrical 1,3-diynes were prepared according to the following procedure: The CuCl (0.1 mmol) was placed in a round bottom bulb equipped with a condenser and magnetic stirring bar. Subsequently, toluene (10 mL), piperidine (0.15 mmol), and alkyne (5 mmol) were placed in the reaction vessel. The reaction was performed at 80 °C for 18 hours with a constant gentle flow of compressed air delivered from the top of the condenser. Afterwards, the reaction mixture was cooled and all volatiles were removed under vacuum. The crude residue was dissolved in hexanes (with a small amount of dichloromethane if necessary) and purified. The synthesis of 2a was performed in a Rotaflo®-type Schlenk vessel due to the low boiling point of the initial alkyne.

Synthesis of unsymmetrical 1,3-diynes (2e-m)
The unsymmetrical 1,3-diynes were prepared according to the literature with some modifications 3 : CuCl was dissolved in a 2:3 mixture by volume of n-BuNH2:H2O (5 mL/mmol alkyne) and the solution was cooled to 0 °C in an ice bath. Hydroxylamine hydrochloride was slowly added until trace amounts of copper(II) were reduced and the color of the solution changed from blue to colorless. The alkyne bromide and alkyne were dissolved in dichloromethane (5 mL/mmol alkyne), cooled down to 0 °C, and this solution was added to the reaction flask at once. The biphasic mixture was vigorously stirred overnight under an argon atmosphere. Subsequently, the organic layer was removed and washed with portions of saturated aq. NH4Cl until these portions no longer took on a blue color. The organic layer was dried (MgSO4) and concentrated by rotary evaporation. The crude residue was dissolved in hexanes and purified.