Oligomerization of Hydrosiloxanes in the Presence of Tris(pentafluorophenyl)borane

Abstract

Oligomerization reactions of 1,3-dihydro-1,1,3,3-tetramethyldisiloxane (HMMH) and of 1-hydro-1,1,3,3,3-pentamethyldisiloxane (HMM) catalyzed by tris(pentafluorophenyl)borane were studied. In the presence of this catalyst, HMMH is converted to a series of linear α,ω-dihydrooligodimethylsiloxanes of general formula HSiMe2(OSiMe2) n OSiHMe2 (HMD n MH) and dihydrodimethylsilane (Me2SiH2). In addition to these linear products, cyclic oligodimethylsiloxaneshexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasiloxane (D4)are also formed. The conversion of HMMH follows second-order kinetics to almost full substrate consumption. Trimer 1,5-dihydro-1,1,3,3,5,5-hexamethyltrisiloxane (HMDMH) and dihydrodimethylsilane are formed as primary products. Consecutive reactions of HMMH and the reactions between oligomeric products, i.e., higher oligomers, occur much more slowly. An exception is formation of D3 that is generated from linear tetramer 1,7-dihydrooctamethyltetrasiloxane (HMD2MH) in a fast consecutive reaction. The dismutation of HMM occurs much more slowly than that of HMMH and takes a more complex course. Permethyloligosiloxanes Me3Si(OSiMe2) n OSiMe3 (MD n M) are the dominant products. Oligomers of the homologous series, α-hydro-ω-methylsilyloligodimethylsiloxanes (HMD n M), are also formed, but they appear at lower concentrations than corresponding oligomers MD n M. The metathetic mechanism of this oligomerization, which includes transient formation of trisilyloxonium ion is discussed.

Siloxane‐Bond Formation Promoted by Lewis Acids: A Nonhydrolytic Sol–Gel Process and the Piers–Rubinsztajn Reaction

“…[43] 2013 [48] However, in NHSG, compounds with siloxane bonds (e.g., ClSiMe 2 OSiMe 3 ) are rarely used as precursors. Cleavage of siloxane bonds is also observed in the Piers-Rubinsztajn reaction even though they are unstrained Scheme 2.…”

Copolycondensation of Regular Functional Silane and Siloxane in Aqueous Emulsion Using B(C6F5)3 as a Catalyst

“…It has been reported in the literature that D 3 can be reopened by TPFPB, in the presence of Si-H functional silanes, in bulk or solution experiments. [22,23] Since the L 2 H is very rapidly consumed in this wet conditions, we suspect that only the TPFPB, or the Brönsted form of TPFPB with water, is able to open the strained cycle [23] and produce HO MDM OH which then further condense on themselves. [19] The generation of a complex between SiOH and TPFPB is known to extinct the natural fluorescence of TPFPB, [21] and produced ion-pairs because of preferred electrostatic interactions.…”

“…[18] It has been used in the polycondensation between all silicon-based molecules, namely SiH/ SiOH [19] or SiH/SiOAlk [20] reactions. The group of Chojnowski has been particularly active in unraveling the TPFPB activity, in wet systems, of different reactions involving silanes, i.e., condensation [21] and dismutation, [22] and more recently those concerning the ring opening of hexamethylcyclotrisiloxane. [23] One key feature of the TPFPB is its water tolerance; not only the molecule does not degrade in water into inactive hydroxides, but also some catalyst remains, in confined location (for instance at oil/water interface) partly active, while most of the catalyst is engaged into a water complexation thus promoting a Brönsted acidity.…”

A Highly Effective Route to Si−O−Si Moieties through O‐Silylation of Silanols and Polyhedral Oligomeric Silsesquioxane Silanols with Disilazanes

“…Classic methods are based on the condensation between various silicon compounds. [41][42][43][44][45][46][47][48][49][50] These protocols describe more-or less-sophisticateds olutions thatv ery often require expensive catalysts and harsh conditions. [39,40] Unfortunately, these reactions proceeda long with the evolution of various corrosiveb yproducts (e.g.,H Cl and HBr) or use toxic or sensitive materials.…”