An Efficient Method for the Synthesis of Symmetrical Disiloxanes from Alkoxysilanes Using Meerwein's Reagent

Abstract

We report here a new and efficient route to symmetrical disiloxanes from their corresponding alkoxysilanes using Meerwein's reagent as mediator and potassium carbonate as additive under mild reaction conditions in acetonitrile. Our methodology is very simple, economic, and high yielding. We have also proposed a reaction mechanism with the plausible silyloxonium intermediates.Siloxanes with Si-O-Si backbone are ubiquitous in nature. They have a broad range of potential applications, including health care products, dry-cleaning process, 1a and adhesives. 1b Liquid crystalline siloxane oligomers were investigated for their mesogenic properties. 2 Water repellent siloxanes act as antiperspirants. 3 A polyorganosiloxane 4a emulsion 4b is used for the preparation of cosmetic products. 4c Particularly, disiloxanes act as an important class of compounds with versatile applications. They are used in microelectronic device and sensor fabrication 5 and as liquid crystal display element. 6 Anion recognition phenomenon was observed by Kondo and Unno in the presence of disiloxane-1,3-diol. 7 Gunji and co-workers used 1,3-diphenyldisiloxane as a building block of silsesquioxanes. 8 Narumi and Miyano reported the use of disiloxane to prepare bridged calix[4]arenes. 9 Napier used disiloxanes as cross-coupling partner in Hiyama-type coupling reaction with aryl halides. 10 Marciniec efficiently used divinyl-substituted silanes and disiloxanes in cross-metathesis in the presence of Grubbs catalyst. 11 The general strategy to efficiently generate disiloxanes is via hydrosilanes. Hydrolytic oxidation of hydrosilanes in the presence of cationic oxorhenium catalyst provides disiloxanes. 12 Matsuo and Kawaguchi observed the formation of disiloxane from CO 2 and hydrosilanes using zirconium-borane complexes. 13 Chojnowski et al. used tris(pentafluorophenyl)borane as Lewis acid catalyst to produce disiloxanes via coupling reaction of hydrosilanes with alkoxysilanes. 14 Lewis acids were further utilized as catalyst in the synthesis of symmetrical disiloxanes via aerobic oxidation of hydrosilanes. 15 Schubert recently reported the use of transition-metal catalyst to generate disiloxanes from hydridosilanes. 16 In our recent report, we discovered a novel sol-gel polycondensation of tetraethoxysilane (TEOS) to silica using Meerwein's reagent (MR) 17 in acetonitrile (MeCN) solvent. 18 We extended our work on MR and successfully achieved various fluorosilanes from alkoxysilanes via nucleophilic fluorination to the silicon centre (S N 2-Si) in excellent yields (Scheme 1). 19 Here, in this work we suppressed the effect of fluoride ion by using K 2 CO 3 as an additive and demonstrated the synthesis of various symmetrical disiloxanes from their corresponding monoalkoxysilanes (Scheme 1). We further propose the possible reaction mechanism of alkoxysilanes condensation. To our knowledge this is the first report of MR-assisted alkoxysilanes condensation to corresponding symmetrical disiloxanes proceeding via silyloxonium intermediate. Scheme 1 MR-Medi...

Catalytic Synthesis of Oligosiloxanes Mediated by an Air Stable Catalyst, (C6F5)3B(OH2)

“…1c is a solid so the catalytic reactions were enabled by the addition of minimum amount of dry toluene (∼1 mL). The disiloxane products formed (3a-3c) from this synthetic route were isolated and confirmed by several characterization techniques in conjunction ( Supplementary Figures 1-28) (Jorapur and Shimada, 2012). Generally, the complete conversion to disiloxane is much slower in the absence of H 2 O and no reaction can be observed in the absence of the catalyst ( Table 1).…”

“…3a (Sridhar et al, 2009;Jorapur and Shimada, 2012) 1 H NMR (400 MHz CDCl 3 ): δ 0.95-0.91 (t, CH 3 , 6H), δ 0.55-0.49 (q, CH 2 , 4H). 13 C{ 1 H} NMR (100.6 MHz, CDCl 3 ): δ 6.7 (s, CH 2 ), δ 6.4 (s, CH 3 ).…”

“…GC-MS: cal'd: 246.1835 m/z; observed 246.1900 m/z. 3b (Jorapur and Shimada, 2012;Sawama et al, 2016) 1 H NMR (400 MHz CDCl 3 ): δ 7.57-7.36 (m, Ph, 10H), δ 0.35 (s, CH 3 , 12H…”