Bonding along a linear B...N...B triad

The Journal of Organic Chemistry
Peter D LivantThomas R Webb

Abstract

The synthesis of tris(2,6-dihydroxyphenyl)amine diborate, 4, is reported. This compound contains a linear B...N...B array for which a symmetrical three-center two-electron (3c-2e) bond is possible. The X-ray crystal structure of 4 shows that 3c-2e bonding is, in fact, absent. Rather, the B-N-B array of 4 is unsymmetrical, having a 2c-2e B-N dative bond with the remaining boron pyramidalized outward and bonded to the oxygen of THF, i.e., 4 x THF. In THF solution, 4 displays temperature-dependent 13C NMR spectra from which a DeltaG++ of 11.6 kcal/mol at 262 K may be calculated. The dynamic process observed in solution corresponds to a bond-switching equilibrium in which the B-N bond oscillates between the two borons ("bell clapper"). Ab initio calculations indicate that the most likely pathway for the bond switch does not involve a 3c-2e B...N...B bond, but rather occurs by nucleophilic attack of THF on the datively bonded boron to generate 4 x (THF)2, lacking any B-N interactions, followed by loss of one THF. The B-N-B system of 4 sans the perturbing effect of solvent was also investigated computationally. The form of 4 containing a 3c-2e bond is found to be a transition state in the solvent-free bond-switch reaction of 4, lying...Continue Reading

Citations

Feb 14, 2006·Organic Letters·Makoto YasudaAkio Baba
Sep 29, 2015·Journal of Materials Chemistry. B, Materials for Biology and Medicine·Conghui YuanLizong Dai
Feb 27, 2009·Journal of the American Chemical Society·Leonie Anna MückGernot Frenking
Apr 22, 2020·Chemical Science·Chenting YanMasayoshi Nakano
Oct 14, 2017·Journal of the American Chemical Society·Haipeng WeiZebing Zeng
May 28, 2011·The Journal of Physical Chemistry. a·Richard D Harcourt
Jun 16, 2006·Organic Letters·Thomas K WoodMasood Parvez

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