Metal-Free Synthesis of 1,3-Disiloxanediols and Aryl Siloxanols

Abstract

The first example of metal-free oxidative hydrolysis of hydrido-siloxanes is reported. Both base-catalyzed and organocatalytic hydrolysis methods are demonstrated to transform 1,3-dihydrido-disiloxanes into 1,3-disiloxanediols. The first example of a chemoselective silane hydrolysis is demonstrated.

Selective Electrochemical Hydrolysis of Hydrosilanes to Silanols via Anodically Generated Silyl Cations

“…With optimized experimental conditions in hand, we set out to evaluate the scope of the electrochemical hydrolysis of hydrosilanes.A ss ummarized in Scheme 2, aw ealth of triphenylsilane derivatives carrying different electronically and sterically varied phenyl substituents reacted well, affording the corresponding silanols 3-14 in 70-80 %y ields.A variety of substituents,including alkyl (3,4,12,14), methoxyl (5), silyl (6), fluoro (13), chloro (7), trifluoromethyl (8), phenyl (9), ester (10), and cyano (11)g roups,w ere welltolerated under the current reaction conditions.Remarkably, benzylic C À Hbonds otherwise susceptible to oxidation under previously reported NHPI-mediated electrochemical conditions remained intact (e.g., 3, 12 and 14), [13d] thus showing high chemoselectivity of our method. Apart from phenyl substituents,n aphthyl-substituted substrates also participated in the…”

Selective Electrochemical Hydrolysis of Hydrosilanes to Silanols via Anodically Generated Silyl Cations

“…With optimized experimental conditions in hand, we set out to evaluate the scope of the electrochemical hydrolysis of hydrosilanes.A ss ummarized in Scheme 2, aw ealth of triphenylsilane derivatives carrying different electronically and sterically varied phenyl substituents reacted well, affording the corresponding silanols 3-14 in 70-80 %y ields.A variety of substituents,including alkyl (3,4,12,14), methoxyl (5), silyl (6), fluoro (13), chloro (7), trifluoromethyl (8), phenyl (9), ester (10), and cyano (11)g roups,w ere welltolerated under the current reaction conditions.Remarkably, benzylic C À Hbonds otherwise susceptible to oxidation under previously reported NHPI-mediated electrochemical conditions remained intact (e.g., 3, 12 and 14), [13d] thus showing high chemoselectivity of our method. Apart from phenyl substituents,n aphthyl-substituted substrates also participated in the Tabelle 1: Optimization of reaction conditions.…”

“…Based on this concept, aseries of catalytic systems based on noble metal catalysts,such as Pd, [9a] Cu, [9b] Ru, [9c] Ir, [9d] Re, [9e] Ag, [9f,j] Pt, [9g] Au, [9h,i] and Rh, [9k] have been successfully established for the hydrolysis of hydrosilanes to silanols (Scheme 1a,b ottom). Despite these advances,most of these metal-catalyzed methods still resulted in the formation of disiloxane byproducts.Moreover,most of catalysts used in these procedures are expensive and commercially unavailable.B esides transition-metal catalysis, organocatalytic [10] and enzymatic [11] approaches have been explored for selective oxidation of hydrosilanes to silanols in the presence of H 2 O 2 or O 2 ,but the former method needs to be conducted in as trictly controlled buffer solution and the latter method suffers from limited substrate scope (Scheme 1b). Consequently,itwould be much more fascinating and yet challenging to develop ag eneral and practical protocol that allows for highly selective conversion of hydrosilanes to silanols without the use of an oble metal catalyst under mild and neutral reaction conditions.…”

Selective Enzymatic Oxidation of Silanes to Silanols

“…[1] Methods that start from functionalized precursors such as chlorosilanes [6] or use strong oxidants [7] in combination with hydrosilanes often result in disiloxane formation, lead to other side reactions, or generate waste products in substantial amounts. Direct catalytic hydrosilane oxidation is an attractive alternative, and several methods have been developed, most of which rely on precious metals; [8] base-metal catalysts [9] or metal-free transformations [10] are rare.…”

“…A limited number of methods use other oxidants like oxygen or hydrogen peroxide together with base metals [9d-g] or even metal-free, although very basic, conditions (Scheme 1, top, b). [10] Few reported selective syntheses of silanols employ environmentally friendly catalysts, proceed under mild reaction conditions, and avoid competing side reactions. [1] We hypothesized that a biocatalytic approach employing natures versatile oxidation catalysts could be a valuable complement to existing synthetic methods.…”