Radical Reactivity of the Biradical [⋅P(μ‐NTer)2P⋅] and Isolation of a Persistent Phosphorus‐Cantered Monoradical [⋅P(μ‐NTer)2P‐Et]. Issue 36 (19th May 2022)

• Record Type: Journal Article
• Authors: Rosenboom, Jan; Chojetzki, Lukas; Suhrbier, Tim; Rabeah, Jabor; Villinger, Alexander; Wustrack, Ronald; Bresien, Jonas; Schulz, Axel
• Is Part Of: Chemistry. Volume 28:Issue 36(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-05-19
• Subjects: biradicals -- molecular chemistry -- persistent radicals -- phosphorus chemistry -- radical chemistry; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202200624
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The activation of C−Br bonds in various bromoalkanes by the biradical [⋅P(μ‐NTer)2 P⋅] (1 ) (Ter=2, 6‐bis‐(2, 4, 6‐trimethylphenyl)‐phenyl) is reported, yielding trans ‐addition products of the type [Br−P(μ‐NTer)2 P−R] (2 ), so‐called 1, 3‐substituted cyclo ‐1, 3‐diphospha‐2, 4‐diazanes. This addition reaction, which represents a new easy approach to asymmetrically substituted cyclo ‐1, 3‐diphospha‐2, 4‐diazanes, was investigated mechanistically by different spectroscopic methods (NMR, EPR, IR, Raman); the results suggested a stepwise radical reaction mechanism, as evidenced by the in‐situ detection of the phosphorus‐centered monoradical [⋅P(μ‐NTer)2 P‐R].< To provide further evidence for the radical mechanism, [⋅P(μ‐NTer)2 P‐Et] (3Et ⋅) was synthesized directly by reduction of the bromoethane addition product [Br‐P(μ‐NTer)2 P‐Et] (2 a ) with magnesium, resulting in the formation of the persistent phosphorus‐centered monoradical [⋅P(μ‐NTer)2 P‐Et], which could be isolated and fully characterized, including single‐crystal X‐ray diffraction. Comparison of the EPR spectrum of the radical intermediate in the addition reaction with that of the synthesized new [⋅P(μ‐NTer)2 P‐Et] radical clearly proves the existence of radicals over the course of the reaction of biradical [⋅P(μ‐NTer)2 P⋅] (1 ) with bromoethane. Extensive DFT and coupled cluster calculations corroborate the experimental data for a radical mechanism in the reaction of biradical [⋅P(μ‐NTer)2 P⋅] with EtBr. In the field of hetero‐cyclobutane‐1, 3‐diyls, the demonstration of a stepwise radical reaction represents a new aspect and closes the gap between P‐centered biradicals and P‐centered monoradicals in terms of radical reactivity. Abstract : Revealing a radical route : The radical reactivity of the biradical [⋅P(μ‐NTer)2 Ṗ] has been investigated. It was possible to synthesize the persistent phosphorus‐centered monoradical [⋅P(μ‐NTer)2 P−Et] and identify it as a radical intermediate during the addition of bromoethane to [⋅P(μ‐NTer)2 Ṗ]. A possible stepwise mechanism of this reaction was formulated and is supported by both detailed quantum chemical calculations and experimental results.