Reactions of Modified Intermolecular Frustrated P/B Lewis Pairs with Dihydrogen, Ethene, and Carbon Dioxide

In this contribution, we discuss the reactivity of different phosphanes (XPhos (1a), ^tBuXPhos (1b), and Mes₂PEt (1c)) and tris­(pentafluorophenyl)­borane (and in one case, EtB­(C₆F₅)₂) against small molecules. 1a/B­(C₆F₅)₃, 1b/B­(C₆F₅)₃, and 1c/B­(C₆F₅)₃ split dihydrogen heterolytically to yield the phosphonium borate salts 2a, 2b, and 2c, respectively. Control experiments with D₂ gave the respective deuterated phosphonium borates 2a-D₂, 2b-D₂, and 2c-D₂. The FLP systems 1b/B­(C₆F₅)₃ and 1c/B­(C₆F₅)₃ underwent 1,2-addition reactions with ethene, resulting in the generation of the ethylene-bridged phosphonium borates 3b and 3c. As well, the Lewis pair EtB­(C₆F₅)₂ and Mes₂PEt reacted with ethene to yield the corresponding 1,2-addition product 3d. At low temperature, the FLP systems 1a/B­(C₆F₅)₃ and 1c/B­(C₆F₅)₃ coordinated carbon dioxide (4a, 4c). The new compounds 2a, 2b, 3b, 3c, 3d, 4a, and 4c were characterized by X-ray crystal structure analyses.