Electronic Effects of Icosahedral Carboranes. Retentive Solvolysis of (1,2-Dicarba-closo-dodecaboran-1-yl)benzyl p-Toluenesulfonates

Some aspects of the chemical behavior of icosahedral carboranes

“…38 The strong electron withdrawing effect of the 1 o car boranyl group is responsible for high acidity of C car boxy , C hydroxy , and C mercaptocarboranes. [39][40][41] The high acidity of 1 hydroxy o carborane was con firmed 42 by measurements of pK a during titration of a 50% ethanolic solution of this compound with aqueous NaOH.…”

Electronic effects of icosahedral carboranes: mechanistic alteration in solvolysis of α-(o-carboranyl)benzyl tosylates by electronic effect of substituents

“…2 In our kinetic investigations, we found that the order of the rates of acetolysis of a-(o-, m-and p-carboranyl)benzyl tosylates (1a, 2a and 3) 3 was consistent with the electron-withdrawing effects of the icosahedral carboranes. 4 However, the hydrolysis of 1a, bearing what is thought to be the most electron-withdrawing group among the carboranes, was significantly accelerated compared with those of 2a and 3. 4 Furthermore, in the hydrolysis of (+)-1a, the reaction afforded the retentive product, with an enantiomeric purity of 71%, whereas the products formed from (+)-2a and (+)-3 were racemic.…”

“…4 However, the hydrolysis of 1a, bearing what is thought to be the most electron-withdrawing group among the carboranes, was significantly accelerated compared with those of 2a and 3. 4 Furthermore, in the hydrolysis of (+)-1a, the reaction afforded the retentive product, with an enantiomeric purity of 71%, whereas the products formed from (+)-2a and (+)-3 were racemic. 4 We suggested a mechanism involving interaction between the oxygen atom of the nucleophile and the 3-position boron atom in the o-carborane cage to explain the characteristic reaction of 1a.…”

“…4 Furthermore, in the hydrolysis of (+)-1a, the reaction afforded the retentive product, with an enantiomeric purity of 71%, whereas the products formed from (+)-2a and (+)-3 were racemic. 4 We suggested a mechanism involving interaction between the oxygen atom of the nucleophile and the 3-position boron atom in the o-carborane cage to explain the characteristic reaction of 1a. Recently, we have reported the results of the solvolysis of a-(o-, m-and p-carboranyl)benzyl tosylates substituted at the second carbon atom with a phenyl group bearing a range of substituents (4, 5 and 6).…”

“…4 Optically active a-(carboranyl)benzyl tosylates were prepared from the corresponding alcohols, which were obtained by optical resolution of the racemic alcohols (1c, 1h, 1j and 1k) as (−)-camphonic acid esters, followed by alkaline hydrolysis. 4 The optical purity of the optically active a-(carboranyl)benzyl derivatives was determined by 1 tron-releasing to electron-withdrawing (1a-h), both in 70% and 90% dioxane-d 8 -D 2 O.…”