Metal-free reduction of the greenhouse gas sulfur hexafluoride, formation of SF₅containing ion pairs and the application in fluorinations

Abstract

A protocol for the fast and selective two-electron reduction of the potent greenhouse gas sulfur hexafluoride (SF6) by organic electron donors at ambient temperature has been developed.

Photoredox Catalytic α‐Alkoxypentafluorosulfanylation of α‐Methyl‐ and α‐Phenylstyrene Using SF6

“…Nevertheless, we found a remarkably broad acceptance of various alcohols for the alkoxylation of 1 and 2 , and the obtained yields between 13 % and 53 % should be viewed in the context of the fact that compounds 10 – 28 were not previously synthetically accessible and bear a new and doubly functionalized structural motif. Additionally, our results show an orthogonal reactivity by the SF 5 ‐radical pathway, which allows the use a large excess (10.0 equiv) of alcohol without fully quenching of the reactive transient by deoxyfluorination . While the use of water as a nucleophile shut down the reaction, the use of tertiary alcohols favored the formation of alcohol 29 .…”

“…However, formation of the C−S bond still requires the use of extraordinarily toxic reagents, like S 2 F 10 , and the mixed‐sulfur halogenides SF 5 Cl and SF 5 Br. In contrast, reports on non‐toxic SF 6 in synthesis are rare although this would have strong environmental advantages . SF 6 is still indispensable as an insulating gas in technical applications, like high‐voltage gears, and as a protecting gas in the production of metals.…”

Photoredoxkatalytische α‐Alkoxypentafluorosulfanylierung von α‐Methyl‐ und α‐Phenylstyrol mithilfe von SF6

“…Zusätzlich zeigen unsere Resultate eine orthogonale Reaktivität durch den SF 5 ‐Radikalmechanismus, welche einen hohen Überschuss (10.0 Äquiv.) des Alkohols zulässt, ohne dass reaktive Intermediate durch Desoxyfluorierung abreagieren. Obwohl die Verwendung von Wasser als Nucleophil die Reaktion ausschaltet, wird die Bildung des entsprechenden Alkohols 29 durch die Verwendung des tertiären Ethinylcyclopentanols favorisiert.…”

“…Im Gegensatz dazu sind Berichte über das ungiftige SF 6 in der Synthese rar, obwohl es große Vorteile für die Umwelt brächte. [9][10][11][12][13][14][15] SF 6 ist als Isolierungsgas in technischen Anwendungen, wie der Hochchspannungstechnik, und als Schutzgas in der Metallproduktion noch unverzichtbar. SF 6 ist ein außerordentliches potentes Treibhausgas.…”

Nucleophilic Activation of Sulfur Hexafluoride: Metal‐Free, Selective Degradation by Phosphines

“…Ty pical technical methods include electrical or plasma discharge technologies,which suffer from the high energy consumption and yield especially toxic and corrosive decomposition products. [5] However,a sar esult of the extreme chemical inertness of SF 6 towards nucleophilic and electrophilic attack, [2c, 6] approaches for chemical activation at ambient conditions commonly require strong reducing agents such as elemental alkali metals, [7] organic reductants, [8] or photoredox conditions, [5a,9] all of which involve an initial single-electron transfer step to SF 6 .S uch an activation step has also been postulated in transition-metal-mediated transformations of SF 6 .I na ddition to stoichiometric reactions of SF 6 with transition-metal complexes, [10] ap articularly promising approach is the catalytic degradation of SF 6 at ab inuclear rhodium complex using stoichiometric amounts of phosphines and silanes as reducing agents. [5] However,a sar esult of the extreme chemical inertness of SF 6 towards nucleophilic and electrophilic attack, [2c, 6] approaches for chemical activation at ambient conditions commonly require strong reducing agents such as elemental alkali metals, [7] organic reductants, [8] or photoredox conditions, [5a,9] all of which involve an initial single-electron transfer step to SF 6 .S uch an activation step has also been postulated in transition-metal-mediated transformations of SF 6 .I na ddition to stoichiometric reactions of SF 6 with transition-metal complexes, [10] ap articularly promising approach is the catalytic degradation of SF 6 at ab inuclear rhodium complex using stoichiometric amounts of phosphines and silanes as reducing agents.…”