Photocatalytic Arylation of P4 and PH3: Reaction Development Through Mechanistic Insight

• Published in: Angewandte Chemie 2021-11, Vol.133 (46), p.24855-24863
• Main Authors: Rothfelder, Robin, Streitferdt, Verena, Lennert, Ulrich, Cammarata, Jose, Scott, Daniel J., Zeitler, Kirsten, Gschwind, Ruth M., Wolf, Robert
• Format: Article
• Language: English
• Subjects: arylation; Catalysts; Chemistry; NMR; NMR spectroscopy; Nuclear magnetic resonance; phosphine; Phosphorus; Photocatalysis; photoredox catalysis; Reducing agents; Salts; white phosphorus
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202110619

Detailed 31P{1H} NMR spectroscopic investigations provide deeper insight into the complex, multi‐step mechanisms involved in the recently reported photocatalytic arylation of white phosphorus (P4). Specifically, these studies have identified a number of previously unrecognized side products, which arise from an unexpected non‐innocent behavior of the commonly employed terminal reductant Et3N. The different rate of formation of these products explains discrepancies in the performance of the two most effective catalysts, [Ir(dtbbpy)(ppy)2][PF6] (dtbbpy=4,4′‐di‐tert‐butyl‐2,2′‐bipyridine) and 3DPAFIPN. Inspired by the observation of PH3 as a minor intermediate, we have developed the first catalytic procedure for the arylation of this key industrial compound. Similar to P4 arylation, this method affords valuable triarylphosphines or tetraarylphosphonium salts depending on the steric profile of the aryl substituents. 31P{1H} NMR spectroscopic studies provide significant, new insights into the mechanism of the recently reported photocatalytic arylation of white phosphorus (P4). Through the first‐time observation of a series of reaction intermediates, these studies have also inspired the development of the first examples of direct, catalytic arylation of PH3, which is a key synthetic intermediate for industrial phosphorus chemistry.