Exploring Hydrophosphination Mediated by Molybdenum Phosphenium Complexes

Date

2023-04-27

Authors

Muir, Vanessa

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Abstract

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. 

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Keywords

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

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