Single electron transfer promoted photoaddition reactions of α-trimethylsilyl substituted secondary N-alkylamines with fullerene C₆₀

Abstract

Single electron transfer (SET) promoted photoaddition reactions of secondary N-α-trimethylsilyl-N-alkylamines to C were explored to gain a deeper understanding of the mechanistic pathways followed and to expand the library of novel types of organofullerenes that can be generated using this approach. The results show that photoreactions of 10% EtOH-toluene solutions containing C and N-α-trimethylsilyl-N-alkylamines produce either aminomethyl-1,2-dihydrofullerenes or symmetric fulleropyrrolidines as major products depending on the nature of alkyl substituents. In contrast, photoreactions of 10% EtOH-ODCB solutions of these amines with C mainly lead to the formation of symmetric fulleropyrrolidines. Based on the analysis of product distributions and the results of earlier studies, two feasible mechanistic pathways are proposed for these processes. One route is initiated by SET from the amine substrates to the triplet-excited state of C to form the corresponding aminium radicals and C anion radicals. EtOH-promoted desilylation of the aminium radicals then takes place to produce aminomethyl radicals which can either add to C or couple with the C radical anions to form respective radicals or anion precursors of aminomethyl-1,2-dihydrofullerene products. The competing pathway leading to the generation of symmetric fulleropyrrolidines also involves the formation of aminomethyl radicals by using the sequential SET-desilylation process. In this route, the aminomethyl radicals are oxidized by SET to C to form iminium ions, which are then transformed to azomethine ylides by a pathway involving a second molecule of the secondary amine. Dipolar cycloaddition of the azomethine ylides to C forms the symmetric fulleropyrrolidine cycloadducts. Importantly, the observation that symmetric fulleropyrrolidines are the sole products formed in photoreactions between N-α-trimethylsilyl-N-alkylamines and C in 10% EtOH-ODCB has synthetic significance.

Subphthalocyanine capsules: molecular reactors for photoredox transformations of fullerenes

“…Classically, reactions of C 60 under high energy UV light irradiation with tertiary amines involve single electron transfer (SET) from the amines to the photoexcited C 60 , leading to radicals that enable addition reactions to form different fullerene derivatives. 34–40 We have selected diphenyl(trimethylsilylmethyl)amine 40 as a radical precursor to demonstrate the abilities of capsule 2 as a molecular photoreactor to accomplish addition reactions over fullerenes under benign green light illumination through SubPc-triggered SET processes. Importantly, to the best of our knowledge, this is the first time that a porphyrinoid cage works as a container for photocatalyzed fullerene derivatization.…”

Photochemical Approach for the Preparation of N-Alkyl/Aryl Substituted Fulleropyrrolidines: Photoaddition Reactions of Silyl Group Containing α-Aminonitriles with Fullerene C60

“…For the photochemical reactions, a variety of α-aminonitriles bearing both (trimethylsilyl)­methyl and alkyl groups at a nitrogen atom were initially synthesized by well-established base-promoted cyanomethylation of respective secondary N -(trimethylsilyl)­methyl substituted amines with bromoacetonitrile (BrCH 2 CN). These synthetic sequences gave rise to production of the target α-aminonitriles possessing both silyl and cyano groups successfully in modest to high yields (64–91%) (Scheme ).…”

“…Individual acetonitrile solutions (100 mL) containing secondary N -alkyl amines 7a – 7k (5 mmol), K 2 CO 3 (10 mmol), and 2-bromoacetonitrile (5.5 mmol) were stirred for 12 h at room temperature. Then, the reaction solutions were concentrated in vacuo to give residues that were partitioned between water and CH 2 Cl 2 .…”

Silyl Tether-Assisted Photooxygenation of Electron-Deficient Enaminoesters: Direct Access to Oxamate Formation

“…Inspired by the above results and our recent study on the single electron transfer (SET)-promoted photoaddition reaction of α-silylamines, , we envisioned that visible light-induced photooxygenation reactions of highly electron-deficient enaminoesters using a metal-free organic photosensitizer, which can serve as an efficient 1 O 2 -generating photosensitizer, might generate dioxetane intermediates, which would undergo a cycloreversion process to form oxamate analogues. To verify this synthetic protocol, we prepared several types of di(carboxymethyl) group-containing enaminoesters and carried out photochemical reactions of them in the presence of methylene blue (MB).…”