Evidence of Al^IIRadical Addition to Benzene

Abstract

Electrophilic AlIII species have long dominated the aluminum reactivity towards arenes. Recently, nucleophilic low‐valent AlI aluminyl anions have showcased oxidative additions towards arenes C−C and/or C−H bonds. Herein, we communicate compelling evidence of an AlII radical addition reaction to the benzene ring. The electron reduction of a ligand stabilized precursor with KC8 in benzene furnishes a double addition to the benzene ring instead of a C−H bond activation, producing the corresponding cyclohexa‐1,3(orl,4)‐dienes as Birch‐type reduction product. X‐ray crystallographic analysis, EPR spectroscopy, and DFT results suggest this reactivity proceeds through a stable AlII radical intermediate, whose stability is a consequence of a rigid scaffold in combination with strong steric protection.

Dearomatization of C6 Aromatic Hydrocarbons by Main Group Complexes

“…Subsequent coupling with an aromatic ring (toluene or p ‐xylene) leads to the generation of a radical 128 a – b , followed by the reaction with another molecule of 127 , which provides the final product 129 a – b . Similar benzene activation was reported by the Andrada group upon the reduction of iodoalane in benzene very recently [74] …”

“…[72] Andrada group upon the reduction of iodoalane in benzene very recently. [74] Additionally, Yamashita and co-workers reported a benzene activation by an AlÀ Sc complex (Scheme 18c). [75] Treatment of the AlÀ Sc complex 130 with benzene in the presence of alkyl bromide (Ph 2 CHBr) resulted in the formation of a 1,4-dialuminated cyclohexadiene 131 together with a concomitant formation of the alkyl-alkyl coupled product 132.…”

Visible‐Light Activation of Diorganyl Bis(pyridylimino) Isoindolide Aluminum(III) Complexes and Their Organometallic Radical Reactivity

“…[7] The vivid field of Main Group redox chemistry in general, [7,8] and subvalent aluminum chemistry in particular, clearly reflects the interest in approaching aluminum redox cycles in the future. [9,[10][11][12][13] This is likewise illustrated by modern photo- [14] or electrochemical approaches. [15] One hotly debated reaction type in transition metal chemistry is the homolytic generation of radicals by ligandto-metal (LMCT) or ligand-to-ligand charge transfer (LLCT), [16] to achieve, for instance, CÀ H activation reactions or radical-polar crossover reactivity (Scheme 1a).…”

“…[42] We could not reproduce the coupling strength by calculations, because the exact structure of the photoproduct is unknown, making simulation challenging as recently discussed for aluminum radicals. [12] The simulation shown in Figure 4 (red line) is the best obtained fit and consists of the computed species 1-AlMe * and a species with two couplings to nitrogen (Figure 4, Sim species 2, for details see Section 8 of Supporting Information). Our findings support the occurrence of single-electron processes and BPI radicals as transient species.…”

Aktivierung von Diorganyl‐bis(pyridylimino)isoindolid‐Aluminiumkomplexen mit sichtbarem Licht und deren organometallische Radikalreaktivität

“…Dies erschwert die Simulation enorm, wie es auch erst kürzlich für Aluminiumradikale diskutiert wurde. [12] Die in Abbildung 4 (rote Linie) gezeigte Simulation stellt die beste erhaltene Anpassung dar und setzt sich aus der berechneten Spezies 1-AlMe * und einer Spezies mit großer Kopplung zu zwei Stickstoffatomen zusammen (Abbildung 4, Sim Spezies 2, Details siehe Abschnitt 8 in den Hintergrundinformationen). Unse-re Beobachtungen unterstützen aber zweifelsfrei das Auftreten von Einelektronenprozessen und BPI-Radikalen als transiente Spezies.…”