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

Abstract

Detailed 31 P{ 1 H} NMR spectroscopic investigations provided eeper insight into the complex, multi-step mechanisms involved in the recently reported photocatalytic arylation of white phosphorus (P 4 ). Specifically,t hese studies have identified anumber of previously unrecognized side products, which arise from an unexpected non-innocent behavior of the commonly employed terminal reductant Et 3 N. The different rate of formation of these products explains discrepancies in the performance of the two most effective catalysts, [Ir(dtbbpy)(ppy) 2 ][PF 6 ]( dtbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) and 3DPAFIPN.I nspired by the observation of PH 3 as am inor intermediate,w eh ave developed the first catalytic procedure for the arylation of this key industrial compound. Similar to P 4 arylation, this method affords valuable triarylphosphines or tetraarylphosphonium salts depending on the steric profile of the aryl substituents.

Light-Induced Access to Carbazole-1,3-dicarbonitrile: A Thermally Activated Delayed Fluorescent (TADF) Photocatalyst for Cobalt-Mediated Allylations

“…During the photophysical investigations of photoredox reactions involving 3DPAFIPN (1) by irradiation with visible light in the absence of any quencher, we observed the formation of another product, which was isolated and fully characterized. By careful 1 H and 13 C NMR analysis, and application of several two-dimensional NMR techniques (see the Supporting Information for details), we were able to assign the structure of 2 to the newly formed compound. First, we checked if the starting material contained any impurity that could drive the photochemical transformation.…”

“…Then, inhibitor-free dry THF (10 mL) was added, and the reaction mixture was irradiated with a blue Kessil lamp (456 nm) ∼15 cm from the light source, under vigorous stirring for 48 h. After that, the solvent was removed under reduced pressure. The crude solid was purified by flash column chromatography (SiO 2 , DCM) to afford product 2 as a bright yellow solid in 78% (44 mg, 0.07 mmol): 1 H NMR (400 MHz, CDCl 3 ) δ 7.69 (d, J = 8.0 Hz, 1H), 7.57 (m, 3H), 7.49 (m, 2H), 7.36 (t, J = 7.5 Hz, 1H), 7.30−7.15 (m, 16H overlapped with the residual peak of the solvent), 7.12−7.04 (m, 3H), 7.04−6.96 (m, 8H); 13 Standard Procedure for Photoredox Cobalt-Catalyzed Allylation of Aldehydes. All of the reactions were performed on a 0.2 mmol scale of aldehyde, or in duplicate on a 0.1 mmol scale.…”

“…The title compound was isolated by flash column chromatography (100% DCM) as a mixture of syn and anti diasteroisomers. Spectroscopic data were according to the literature: 47 1 H NMR (400 MHz, CDCl 3 , 25 °C) mixture of diastereoisomers δ 5.86−5.76 (m, 1H), 5.14−5.08 (m, 3H), 3.76−3.70 (m, 1H), 2.28− 2.22 (m, 1H), 2.16−2.04 (m, 1H), 2.04−1.87 (m, 2H), 1.66 (s, 3H), 1.69−1.55 (m, 3H), 1.58 (s, 3H), 1.51−1.05 (m, 2H), 0.90 (dd, J = 6.4, 6.4 Hz, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 , 25 °C) mixture of diastereoisomers δ 135.1, 135.0, 131.4, 124.9, 118.3, 118.2, 68.9, 68. 5, 44.5, 44.4, 42.9, 42.3, 38.0, 36.9, 29.5, 29.1, 25.9, 25.6, 25.6, 20.4, 19.3, 17.8.…”

“…7 Specifically, 2,4,6-tris(diphenylamino)-5fluoroisophthalonitrile (3DPAFIPN) has been used in recent years for a number of visible-light-fueled synthetic protocols, for instance, in intramolecular cyclizations 8,9 and C−C, 10,11 N−C, 12 and P−C bond formation. 13 3DPAFIPN is reported to be stable under the reaction conditions used for photocatalysis, 14,15 as determined in experiments by some of us in the photoredox allylation of aldehydes by using either titanium 16,17 or nickel 18 in its low oxidation state. The photostability of 3DPAFIPN in those applications was demonstrated by its recovery at the end of the reaction, making its reuse possible.…”

Taming PH3: State of the Art and Future Directions in Synthesis

“…PH 3 generated by decomposition of Zn 3 P 2 has been detailed more recently by Ball 74 and Wolf. 75 Ball has elegantly demonstrated the application of in situ generated PH 3 for the synthesis of tert-alkyl phosphonium triflates, where the byproduct of the reaction is TMSOAc. Due to the high levels of substitution these products cannot be formed using a hydrophosphination route, while the conventional route to secondary alkyl phosphines, R 2 PH, would employ PCl 3 and organomagnesium or organolithium reagent, followed by reduction of the remaining P−Cl bond with a hydride reagent.…”