1-((Dimethyl(3-((2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl)oxy)propyl)silyl)oxy)-3,5,7,9,11,13,15-heptakis((dimethylsilyl)oxy)-octasilsesquioxane

Abstract

The title compound was synthesized using Pt-catalyzed hydrosilylation of octasilane POSS and allyl 1H,1H-perfluorooctyl ether. The purity and structure were determined by NMR (¹H, ¹³C, ¹⁹F, ²⁹Si), and MALDI TOF-MS.

1. Introduction

Polyhedral oligomeric silsesquioxanes, commonly known as POSS, represent a class of hybrid organic–inorganic nanomaterials that have been studied in various scientific and engineering disciplines. At their core, POSS molecules are characterized by a unique cage-like nanometer-sized structure composed of a silicon–oxygen (Si-O) framework, typically with the general formula (RSiO_1.5)_n, where ‘R’ can be an organic functional group and ‘n’ denotes the number of silicon atoms in the cage (most commonly 8, 10, or 12) [1]. The dual nature of POSS allows it to possess the robust, high-temperature stability and chemical inertness characteristics of inorganic silicates, while also offering the versatility and processability associated with organic compounds through its peripheral ‘R’ groups [2]. These organic functionalities can be tailored to be reactive for incorporation into polymer matrices to impart specific physical properties.

The precise, nanoscale dimensions (typically 1–3 nm) and well-defined structure of POSS cages allow them to act as molecular building blocks, offering a unique opportunity to manipulate bulk properties of materials at the molecular level [3]. When incorporated into polymers, POSS can lead to significant enhancements in thermal stability, mechanical strength, oxidative resistance, reduced flammability, and surface durability, often with minimal loading levels. This makes POSS a highly promising additive for developing high-performance composites and advanced functional materials for applications ranging from aerospace and electronics to biomedicine and coatings [4]. Hybrid materials have shown to be potentially critical to space applications given their ability to protect against vacuum ultraviolet degradation and withstand atomic oxygen collisions [5]. As part of ongoing work for the development of heat transfer fluids, we have prepared a partially fluorinated POSS, specifically 1-((dimethyl(3-((2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooc-tyl)oxy)propyl)silyl)oxy)-3,5,7,9,11,13,15-heptakis((dimethylsilyl)oxy)-octasilsesquioxane (F-POSS), by Pt-catalyzed hydrosilylation of octakis(hydrodimethylsiloxy) octasilsequioxane (H-POSS) with allyl 1H,1H-perfluorooctyl ether (Scheme 1).

2. Results and Discussion

F-POSS was successfully isolated as a white solid in 57% yield using Pt-catalyzed (Karstedt’s catalyst, Pt divinylsiloxane complex in xylene) hydrosilylation of octasilane POSS (H-POSS) and allyl 1H,1H-perfluorooctyl ether (NMR spectrum can be found in the Supplementary Materials). The quantitative conversion to the product after 1 h was observed by ¹H NMR with the disappearance of the allyl ether signals at 5.86 ppm and 5.28 ppm and appearance of new signals at 0.13 ppm (6H) from the single substitution of the allyl group onto the -OSi(CH₃)₂-. The remaining unsubstituted -OSi(CH₃)₂H group remained at 0.23 ppm with a relative integration of 42H. The unsubstituted silylhydride (Si-H) from the POSS cage chemical shifts appeared at 4.72 ppm with a relative integration of 7H. These chemical shifts are also observed in the ¹³C NMR with signals at 0.02 ppm and −0.58 ppm representing the methyl groups on the unsubstituted (-OSi(CH₃)₂H) and substituted (OSi(CH₃)₂R’) dimethylsiloxane moieties, respectively. ¹⁹F NMR revealed the retention of the fluorine signals from the starting material with the fluoroalkyl (-CF₂-) signals as multiplets ranging from −119.5 ppm to −126.1 ppm and the terminal fluorine (-CF₃) signal at −80.7 ppm. ²⁹Si NMR showed the silicon substitution with peaks at 13.8, 0.9, and −108.2 ppm with a respective ratio of 1:7:8. MALDI-TOF confirmed the presence of the F-POSS m/z [M + Na]⁺ of 1481.62 m/z, along with residual H-POSS starting material as well as di-substituted F-POSS (two additions of allyl 1H,1H-perfluorooctyl ether) signals at 1039.40 m/z and 1921.61 m/z, respectively. However, based on ¹H and ²⁹Si NMR peak integration analysis, the desired singularly substituted F-POSS was observed in greater than 90% purity.

3. Materials and Methods

Chemicals and solvents were purchased through commercial suppliers and used as received as reagent-grade (>95% purity) unless specifically noted. Allyl 1H,1H-perfluorooctyl ether was purchased from SynQuest Labs (Alachua, FL, USA)and octasilane POSS from Hybrid Plastics. ¹H, ¹³C{¹H}, and ¹⁹F NMR spectra were recorded on a Jeol 500 MHz spectrometer. Chemical shifts were reported in parts per million (ppm), and the residual solvent peak was used as an internal reference: proton (chloroform δ 7.26), carbon (chloroform, C{D} triplet, δ 77.0 ppm), silicon (tetramethylsilane δ 0.00), and fluorine (fluoroform, CFCl₃ δ 0.00). Data are reported as follows: chemical shift, multiplicity (s = singlet, m = multiplet at mid-point), coupling constants (Hz), and integration. Matrix-assisted laser desorption/ionization (MALDI) spectra were recorded using a Bruker AutoFlex Speed MALDI time-of-flight mass spectrometer (TOF MS) (Billerica, MA, USA). The matrix used was 2,5-dihydroxybenzoic acid prepared in TA30 solvent (30:70 v/v acetonitrile: 0.1% TFA in water, ca. 20 mg/mL) [6]. This matrix solution was mixed with the DCM solutions (ca. 2 mg/mL) of the POSS derivative analyte in a 1:1 ratio. Mass spectra were measured in reflectron mode. The data was analyzed using FlexAnalysis 3.4 software (Bruker). Mass calibration was performed using external standard (red phosphorous).

1-((Dimethyl(3-((2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooc-tyl)oxy)propyl)silyl)oxy)-3,5,7,9,11,13,15-heptakis((dimethylsilyl)oxy)-octasilsesquioxane (F-POSS)

Allyl 1H,1H-perfluorooctyl ether (0.796 g, 1.807 mmol) and octasilane POSS (H-POSS) (1.673 g, 1.643 mmol) in toluene (2 mL) were combined at room temperature in a 20 mL screwcap vial equipped with a magnetic stir bar. Karstedt’s catalyst (5 μL, 3 wt% in xylene) was added and allowed to stir for 1 h. The reaction was monitored by ¹H NMR until reactant vinyl peaks (CH₂=CHCH₂R’) were no longer present. After the reaction, the liquid was loaded on a silica gel pad and eluted with 100% hexanes, concentrated using a rotary evaporator, and placed under high vacuum (5 mm Hg), affording the title compound as a white powder (1.360 g, 57%). ¹H NMR (CDCl₃, 500 MHz) δ 4.72 (m, 7H, Si-H), 3.91 (t, ¹J = 14 Hz, 2H), 3.55 (t, ¹J = 6.5 Hz, 2H), 1.66 (m, 2H), 0.58 (m, 2H), 0.23 (s, 42H), 0.13 (s, 6H); ¹³C{¹H} NMR (CDCl₃, 126 MHz) δ 75.7 (s), 68.0 (t, ¹J = 25 Hz), 23.1 (s), 13.4 (s), 0.02 (s), −0.58 (m); ¹⁹F NMR (CDCl₃, 471 MHz) δ −80.7 (m, 3F), −119.5 (m, 2F), −122.0 (overlapping m, 4F), −122.7 (m, 2F), −123.3 (m, 2F), −126.1 (m, 2F); ²⁹Si NMR (CDCl₃, 99.3MHz) δ 13.8 (s), 0.9 (s), −108.2 (s). MS (MALDI-TOF) m/z: [M + Na]⁺ Calcd for C₂₇H₆₃Si₁₆O₂₁F₁₅Na 1481.11; Found 1481.62.