Computational Study of the Isomerization Reactions of Borirane

Abstract

Borirane is isoelectronic to the cyclopropyl cation, but is stable toward electrocyclic ring opening to 2-bora-propa-1,3-diyl A, the boron analogue of the allyl cation. A computational investigation using density functional theory (B3LYP) in combination with highly correlated electronic structure theory methods of the coupled-cluster [CCSD­(T)] and multireference configuration interaction (MRCI) type in conjunction with basis sets of up to quadruple-ζ quality reveal that formation of A is endothermic by roughly 15 kcal mol–1 and that A collapses almost without barrier (0.2 kcal mol–1) to borirane. The vinylborane isomer B is more stable than borirane and its formation is associated with a barrier of 36–38 kcal mol–1. Methyl methylideneborane E, only slightly less stable than B, can only be accessed by pathways involving barriers of at least 60 kcal mol–1.

On the 3D → 2D Isomerization of Hexaborane(12)

“…This barrier increases to 270 kJ•mol −1 if we consider the energy difference of TS 2 with respect to R. Similar energy barriers can be found in organoboron chemistry, such as in the isomerization of borirane BC 2 H 5 -a triangular cyclic structure isoelectronic with the cyclopropyl cation [33]-to methyl methylideneborane, as shown in Equation ( 1) below. In this isomerization the computed energy barrier is 250 kJ•mol −1 , computed with highly correlated methods [33], and involves a C-C bond breaking and a hydrogen shift from B-H to one CH 2 group in borirane.…”

Threshold photoelectron spectroscopy of trimethylborane and its pyrolysis products

“…It is thus unlikely to be observed under our experimental conditions. 38 Even though Imam et al propose the exclusive production of CH 3 BCH 2 1 via a concerted CH 4 loss, 8 a different mechanism might exist leading to different isomers. Furthermore, at high temperatures, rearrangements to other isomers may be possible.…”

Ring-Opening Reactions of NHC-Boriranes with In Situ Generated HCl: Synthesis of a New Class of NHC-Boralactones

“…Boriranes (boracyclopropanes) are rare, and therefore little is known about their chemistry . Borirane itself is isoelectronic with the cyclopropyl cation (Figure a).…”

“…Borirane itself is isoelectronic with the cyclopropyl cation (Figure a). The archetypical transformation of this cation is disrotatory ring opening to the allyl cation, but experimental studies by Denmark (on 1,2,3-triphenylborirane) and calculations by Bettinger (on borirane) show that boriranes do not undergo this reaction.…”