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 PtBu3 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-CH2CH2C=CH were studied as a geminal Lewis acid reference. Most of the products were characterized by X-ray diffraction.
Liu, Y. L., Kehr, G., Daniliuc, C. G., & Erker, G. (2017). Geminal bis-borane formation by borane Lewis acid induced cyclopropyl rearrangement and its frustrated Lewis pair reaction with carbon dioxide. Chemical Science, 8(2), 1097–1104. https://doi.org/10.1039/c6sc03468c