Photoinduced single electron transfer initiated heterolytic carbon-selenium bond dissociation. Sequential one-pot selenenylation and deselenenylation reaction

Abstract

Recently we have reported in situ generation of electrophilic selenium (PhSe+) species via diphenyl diselenide radical cation (PhSeSePh)*+ formed by single electron transfer (SET) from PhSeSePh (1) to the excited singlet of 1,4-dicyanonaphthalene (DCN,2).* 1We report herein electron transfer (ET) from compounds possessing a carbon-selenium bond to 'DCN* leading to heterolytic C-Se bond dissociation via a radical cation intermediate with concurrent demonstration of a new, very mild, synthetically promising way of effecting deselenenylation reactions.Organoselenium compounds 5-8 (Scheme I) efficiently quench the fluorescence of 2 with a diffusion-controlled2 rate constant, ( ). Emission and absorption spectroscopic properties of mixtures of 5-8 and 2 fail to reveal ground or excited state complex formation in polar and nonpolar solvents. A SET mechanism for the fluorescence quenching of 2 by 5-8 is supported by the endoergic value for the free energy change (AGET) estimated by the Weller equation3 and the correlation plot of log AL^v s (£j/2(ox))4 of 5-8, which showed a linear relationship5 (Table I). This suggested the possibility of performing photosensitized SET initiated reaction from compounds 5-8. To test this concept, we irradiated6 78(>280 nm) a mixture of 5-8 (3 mM) with 2 (0.3 mM) in methanol, for which the details are given in Table I. Bibenzyl formation from compound 6 seems to occur by deselenenylation of PhCH2Se* (PhCH2Se* -PhCH2* + Se), which is evident from the observation of only a trace amount of bibenzyl (3-6%) compared to other products.7The above results can be rationalized with reference to Scheme I, which considers the intermediacy of an exciplex with partial charge-transfer character. A double reciprocal plot of quantum yield ( ^ ) vs 5-8 concentration ( ~ vs [Q]"1) resulted a straight line with an identical AfqETT (intercept/slope) as obtained from fluorescence measurements (Table I), which supports the above argument. Electron transfer between 5-8 and 2 results in generation of the solvent-separated ion pair (SSIP). The corresponding radical cation undergoes C-Se bond cleavage (58 kcal/mol),8 the carbonium ion escaping and the radical reacting in the cage. In the polar media R|+ is more stabilized than the radical R2Se* so that the former diffuses and the latter reacts with 7IICT Communication No. 2425.

Addition and cycloaddition reactions via photoinduced electron transfer

“…Pandey reported the 1,4-dicyanonaphthalene-sensitized cyclization of CH 2 = CH(CHz),OH (n = 3, 4) in the presence diphenyldiselenide [129]. This photoreaction is initiated by the addition of the PhSe • radical to the alkenes as shown in Scheme 43.…”

A Theoretical Investigation on the Reaction Mechanism of the C9H12+· Side‐chain Decomposition

“…Charge transfer from small ions to alkylbenzenes in the ion flow tube can generate alkylbenzene cations such as C 10 H 14 i ＋ 1 and C 8 H 10 i ＋ . 2,3 The thermal decomposition processes are important steps in plasma-chemical reaction mechanisms, but little experimental and theoretical [4][5][6][7][8][9][10][11][12] information exists on collisional energy transfer from molecular ions, which are highly excited. C 9 H 12 i ＋ 13 has been prepared by the charge transfer reaction C 9 H 12 ＋O 2 i ＋ →C 9 H 12 i ＋ ＋O 2 in a turbulent ion flow tube (TIFT), and its collisional stabilization and thermal dissociation were reported.…”

Studien zur oxidativen Funktionalisierung von Alkenen mittels Selen-pi-Säure-Katalyse

“…Ausgangspunkt für die Realisierung einer solchen Selen-Oxidase-Katalyse sollten Arbeiten von Pandey et al sein, die durch den Einsatz von Photoredoxkatalysatoren die generelle Nutzbarkeit von O 2 als terminaler Elektronenakzeptor in selenvermittelten Alkenfunktionalisierungen unter stöchiometrischen Bedingungen zeigen konnten. [191][192][193] Zu Beginn dieser Arbeit existierte jedoch keine Methodik, die den Einsatz von O 2 als Oxidationsmittel in Selen-π-Säure-katalysierten Umsetzungen ermöglicht. Zusätzlich waren die Bedingungen zur Generierung elektrophiler Selenspezies mittels Photoredoxchemie sehr harsch (z.B.…”

“…[257] Der Ausgangspunkt für die Entwicklung einer intermolekularen Selen-π-Säure-Katalyse mit exogenem Nukleophil und O 2 als terminales Oxidationsmittel waren Arbeiten von Pandey et al über die photochemische Selenofunktionalisierung nichtaktivierter Alkene. [191][192][193]258,259] Den Autoren gelang die Selenoetherifizierung verschiedener Olefine unter Verwendung von O 2 als terminales Oxidationsmittel. Als Redoxmediator verwendeten Pandey und Mitarbeiter 1,4-Dicyanonaphthalin (DCN), dessen photoangeregter Zustand (λ > 280 nm) als Einelektronenoxidationsmittel diente.…”

“…Als Redoxmediator verwendeten Pandey und Mitarbeiter 1,4-Dicyanonaphthalin (DCN), dessen photoangeregter Zustand (λ > 280 nm) als Einelektronenoxidationsmittel diente. Unter diesen Bedingungen können sowohl aus Diseleniden [191,258] als auch aus Alkylseleniden [192,259] elektrophile Selenspezies generiert werden, die zur Aktivierung einfacher Alkene genutzt werden können (Gleichung 3.6). Darüber hinaus konnten Pandey et al zeigen, dass eine einstufige Sequenz aus stöchiometrischer Selenofunktionalisierung und Deselenierung unter photooxidativen Bedingungen möglich ist.…”