Alkylation of Pentaborane-9 Catalyzed by Lewis Acids

B-Methyl derivatives of the closo-carborane 2,4-C2B5H7

“…Methyl Substituent Contributions to the 11B Chemical Shifts II values for each of the contributions are given which are determined by averaging as many comparison chemical shifts as possible. The calculated values from eq [1][2][3] are given in parentheses in Table I and it can be seen that the predictive value is as good as previously observed in another cage system.14 '16 . Significant effects observed in the 'H NMR spectra are as follows: (a) an antipodal upfield shift of 0.15 ppm for H (7) is observed upon B(l) methyl substitution (compare 1,5,6-(CH3)3C2B5H4 with 5,6-(CH3)2C2B5H5); (b) apex Me-B chemical shift values are 1.0-1.3 ppm to higher field than equatorial Me-B shifts, which is in reasonable agreement with predicted chemical shift differences based on ring-current considerations17 in the C2BsH7 cage; (c) upfield shifts are ca.…”

“…This complex increases the coordination number of the skeletal atom undergoing substitution, and after subsequent loss of H+ to form the alkyl derivative, the substituted atom reverts back to the original coordination number. The "belt" atoms (positions [2][3][4][5][6] of the pentagonal bipyramid of QB5H7 would not increase to as high a coordination number upon formation of the complex as would the two apical atoms (positions 1 and 7) and would thus be favored if coordination numbers were the only important factor involved.…”

Chromium(V) oxidations of organic compounds

“…Therefore, the mechanism of disproportionation can be represented by eq 4 and 5. The values of the second-order rate constants (Table II) depend 2Cr(y) t£t Cr(VI) + Cr(IV) (4) Cr(V) + Cr(IV) -Cr(VI) + Cr(III)…”

Chemistry of Pentaborane(9). A Review

“…It was shown in the 1960s that reaction of olefins with B 5 H 9 yielded 2-substituted alkyl derivatives 36 , and Friedel-Crafts catalyzed attack of B 5 H 9 by alkenes and alkyl halides led to 1-substituted derivatives 37 rane derivatives were apparently unobtainable by the latter route because of the low Friedel-Crafts reactivity of the aryl halides.…”