Exploring Hydrophosphination Mediated by Molybdenum Phosphenium Complexes




Muir, Vanessa

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Metal-catalyzed hydrophosphination (HP) has seen huge growth over the last two decades. Almost all catalysts rely on intermediates containing phosphido ligands (PR2⁻). The nucleophilicity of these ligands has resulted in an HP unsaturated substrate scope mostly limited to electron-deficient alkenes and alkynes. We propose a catalyst system that relies on intermediates containing electrophilic phosphenium ligands (PR2⁺). This should allow P-C bond formation using simple and electron-rich alkenes and alkynes, thus widening the HP unsaturated substrate scope. We have prepared a series of molybdenum-phosphenium complexes that participate in a stoichiometric HP reaction, which is a very exciting proof of concept for phosphenium-mediated HP. To test the reactivity of these complexes, fourteen unsaturated substrates ranging in electron-richness and steric bulk have been selected and assessed by me. Under catalytic conditions (i.e., presence of excess alkene and phosphine), substrate phosphine formed an adduct with the Mo-bound phosphenium ligand, resulting in the deactivation of the catalyst. To address these issues, I investigated the behaviour of these adducts by adding substrate phosphine to the monophosphine and bisphosphine phosphenium complexes. The results suggest catalysis is a challenge, as the P-P adducts are extremely robust. Further investigation was completed to probe the strength and possible reversibility of this adduct formation, and to confirm the species forming in these reactions. 



hydrophosphination, molybdenum phosphenium, molybdenum, electron-rich unsaturated substrates, electrophilic, lewis acid, phosphines, phosphenium