Dataset Information

Magnesium Boryl Reactivity with 9-BBN and Ph₃ B: Rational B-B' Bond Formation and Diborane Isomerization.

ABSTRACT: Reactions of a magnesium-based pinacolatoboryl nucleophile with the electrophilic organoboranes, 9-BBN and Ph₃ B, provide facile B-B' single bond formation. Although the Ph₃ B derivative is thermally stable, when heated, the unsymmetrical diborane(5) anion derived from 9-BBN is found to isomerize to two regioisomeric species via a proposed mechanism involving dehydroboration of the borabicyclo[3.3.1]nonane and syn-diboration of the resultant alkenyl carbocycle.

SUBMITTER: Pecharman AF

PROVIDER: S-EPMC5767756 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Publications

Magnesium Boryl Reactivity with 9-BBN and Ph3 B: Rational B-B' Bond Formation and Diborane Isomerization.

Pécharman Anne-Frédérique AF Hill Michael S MS McMullin Claire L CL Mahon Mary F MF

Angewandte Chemie (International ed. in English) 20171127 51

Reactions of a magnesium-based pinacolatoboryl nucleophile with the electrophilic organoboranes, 9-BBN and Ph3 B, provide facile B-B' single bond formation. Although the Ph3 B derivative is thermally stable, when heated, the unsymmetrical diborane(5) anion derived from 9-BBN is found to isomerize to two regioisomeric species via a proposed mechanism involving dehydroboration of the borabicyclo[3.3.1]nonane and syn-diboration of the resultant alkenyl carbocycle. ...[more]

PMID: 29115736

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Project description:Reactions of the β-diketiminato magnesium diboranate derivative, [(BDI)Mg{pinB(n-Bu)Bpin}] (BDI = HC{(Me)CNDipp}2; Dipp = 2,6-i-Pr2C6H3), with N,N'-dialkyl and N,N'-diaryl carbodiimides provided the corresponding C-borylated magnesium borylamidinates. This reactivity occurs with the displacement of n-BuBpin and with the apparent addition of a nucleophilic {Bpin} anion to the electrophilic unsaturated carbodiimide carbon centres. In contrast, while analogous reactions of [(BDI)Mg{pinB(n-Bu)Bpin}] with N-alkyl or N-aryl aldimines and ketimines also resulted in facile displacement of n-BuBpin, they provided the organomagnesium products of {Bpin} addition to the imine nitrogen atom rather than the more electrophilic trigonal imine carbon. Computational assessment by density functional theory (DFT) indicated that, although the energetic differences are marginal, the organomagnesium products may be considered as the kinetic outcome of these reactions with respect to the generation of alternative amidomagnesium regioisomers. This latter deduction was borne out by the thermally-induced conversion of two such organomagnesium species to their C-borylated amidomagnesium isomers, both of which occur with negligible entropies of activation indicative of purely intramolecular processes. Detailed analysis by DFT of the reaction of [(BDI)Mg{pinB(n-Bu)Bpin}] with PhN[double bond, length as m-dash]CHPh indicated that B-N bond formation is initiated by attack of the imine nitrogen at the three-coordinate boron atom of the diboranate anion rather than the more crowded magnesium centre. Consistent with an effectively spontaneous reaction, the resultant cleavage of the B-B bond of the diboranate unit is accomplished via the traversal of two very modest barriers of only 8.3 and 6.7 kcal mol-1. This analysis was also supportive of a subsequent intramolecular B-N to B-C isomerisation process. Of greater general significance, however, the addition of the {Bpin}- anion to the reducible aldimine is best rationalised as a consequence of the electrophilic character of this three-coordinate boron centre rather than any intrinsic nucleophilicity associated with the B-B bond of the [pinBB(n-Bu)pin]- anion.

Dataset Information

Magnesium Boryl Reactivity with 9-BBN and Ph₃ B: Rational B-B' Bond Formation and Diborane Isomerization.

Publications

Magnesium Boryl Reactivity with 9-BBN and Ph<sub>3</sub> B: Rational B-B' Bond Formation and Diborane Isomerization.

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