White phosphorus (P4) is the common precursor to a plethora of organophosphorus compounds with numerous industrial uses. Unfortunately, the current state-of-the-art for the synthesis of all these compounds relies on inefficient and wasteful multi-step procedures that produce substantial quantities of unwanted byproducts, while also requiring the use of very hazardous and difficult to handle reagents such as Cl2 or PH3. Far superior would be methods that directly transform P4 into desirable monophosphorus compounds in a catalytic fashion, but such methods have remained poorly developed even after decades of research in the field. This lecture will describe our recent efforts to design new P4 activation and functionalization protocols (Figure 1). Building on current advances in organic photoredox catalysis, we have developed a photocatalytic P4 arylation procedure. By using an iridium-based photocatalyst ([Ir]PF6) or, alternatively, an organic photosensitizer (3DPAFIPN), iodoarenes and triethylamine, this method converts P4 into valuable triarylphosphines and tetraarylphosphonium salts in a single step (Figure 1A). Pursuing an alternative approach, we have found that hydrostannylation of P4 with tri-n-butyltin hydride allows for the facile and effective preparation of various industrially relevant monophosphorus species in a single step from P4 (Figure 1B). The organtin reagent can be effectively recycled and even used catalytically. Current investigations focus on further extensions of this methodology which could render the method even more efficient and practical, including the use of other tin hydride reagents and replacing the organtin compound entirely. The results of mechanistic studies and their implications for reaction development will also be discussed.

Metal-mediated methods for the functionalization of white phosphorus

ACS Spring 2022

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