On the Reactivity of Silylboranes toward Lewis Bases: Heterolytic B–Si Cleavage vs. Adduct Formation. Issue 15 (5th April 2013)

• Record Type: Journal Article
• Authors: Kleeberg, Christian; Borner, Corinna
• Is Part Of: European journal of inorganic chemistry. Issue 15(2013)
• Page Start: 2799
• Page End: 2806
• Publication Date: 2013-04-05
• Subjects: Silicon -- Boranes -- Lewis bases -- Heterocycles -- Carbenes -- B–Si activation; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201300119
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract: Silylboranes are important reagents in a variety of catalytic silylation and silaboration reactions. While transition‐metal‐catalyzed reactions are well established, organo‐/Lewis base‐catalyzed reactions of silylboranes have only recently emerged. For both catalytic processes the reactivity of silylboranes toward Lewis bases is of relevance. While for organo‐catalyzed reactions Lewis base activation of the silylborane has been proposed, transition‐metal‐ and especially copper‐catalyzed reactions also frequently require the presence of Lewis basic alkali metal alkoxides. In the present study we explore the reaction of K(18‐crown‐6) tert ‐butoxide and the NHC 1, 3‐diisopropyl‐4, 5‐dimethyl‐imidazol‐2‐ylidene as exemplary Lewis bases with the two silylboranes pinB‐SiMe2 Ph and pinB‐SiPh3 (pin = OCMe2 CMe2 O). The reaction with K(18‐crown‐6) tert ‐butoxide results in activation of the boron–silicon bond. The isolated product of this activation is either the potassium silyl complex [K(18‐crown‐6)SiPh3 ] or [K(18‐crown‐6)(thf)2 ][pinB(SiMe2 Ph)2 ], the formal Lewis acid/base adduct of [K(18‐crown‐6)SiMe2 Ph] with pinB‐SiMe2 Ph. Both complexes react essentially as sources of nucleophilic silyl moieties in reactions with exemplary electrophiles. In contrast, usage of the carbene leads to the formation of isolable Lewis acid/base adducts of the type (NHC)pinB‐SiR3, which do not react as sources of nucleophilic silyl moieties. The identification and characterization of these species appears of relevance for the mechanistic understanding and further development of Lewis base/organo‐ as well as transition‐metal‐catalyzed silyl transfer reactions. Abstract : The reaction of a Lewis base with a silylborane is central to a series of Lewis base‐mediated reactions of silylboranes. For [K(18‐C‐6)O t Bu] and an NHC the reaction products were isolated and characterized. Either the activation of a B–Si bond or the formation of Lewis acid/base adducts is observed. The reactivity of the reaction products toward selected electrophiles is studied.