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), (t)BuXPhos (1b), and Mes(2)PEt (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 D-2 gave the respective deuterated phosphonium borates 2a-D-2, 2b-D-2, and 2c-D-2. 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 Mes(2)PEt 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.