Geminal bis-borane formation by borane Lewis acid induced cyclopropyl rearrangement and its frustrated Lewis pair reaction with carbon dioxide

Abstract

Cyclopropylacetylene reacts with two molar equivalents of Piers' borane [HB(C₆F₅)₂] under mild conditions by an addition/rearrangement sequence with cyclopropyl ring opening to give a mixture of two α-B(C₆F₅)₂ substituted tetrahydroboroles. This compound forms an active frustrated Lewis pair with P^tBu₃ that heterolytically splits dihydrogen and adds carbon dioxide as a geminal chelate bis-boryl component. The respective reactions of the two-fold HB(C₆F₅)₂ addition to Ph-CH₂CH₂CCH were studied as a geminal Lewis acid reference. Most of the products were characterized by X-ray diffraction.