Insights into Single-Electron-Transfer Processes in Frustrated Lewis Pair Chemistry and Related Donor–Acceptor Systems in Main Group Chemistry

Abstract

The activation and utilization of substrates mediated by Frustrated Lewis Pairs (FLPs) was initially believed to occur solely via a two-electron, cooperative mechanism. More recently, the occurrence of a single-electron transfer (SET) from the Lewis base to the Lewis acid was observed, indicating that mechanisms that proceed via oneelectron-transfer processes are also feasible. As such, SET in FLP systems leads to the formation of radical ion pairs, which have recently been more frequently observed. In this review, we aim to discuss the seminal findings regarding the recently established insights into the SET processes in FLP chemistry as well as highlight examples of this radical formation process. In addition, applications of reported main group radicals will also be reviewed and discussed in the context of the understanding of SET processes in FLP systems.

Defect-Induced Synergetic Effect of Bi-Based Compounds for One-Pot Conversion of Organic Pollutants into CO via Coupling Photodegradation of Carbamazepine with Photoreduction of CO2

“…The free energy of five successive reaction steps including CO 2 adsorption, proton-coupled electron transfer to form the COOH* intermediate, dehydroxylation to produce CO*, hydrogenation of CO*, and CO desorption on the catalysts was calculated to explore the mechanism of CO 2 conversion in Figure a. The formation of COOH* was an endergonic reaction with high energy input which was the rate-limiting step in the CO 2 –CO process . Less reaction energy (0.86 eV) was required for BiOBr/BiVO 4 than BiOBr/BiVO 4 (Control) (a simple heterojunction with fewer O v , 2.29 eV) to realize the transformation of CO 2 * to COOH*.…”

“…The formation of COOH* was an endergonic reaction with high energy input which was the rate-limiting step in the CO 2 −CO process. 42 Less reaction energy (0.86 eV) was required for BiOBr/BiVO 4 than BiOBr/BiVO 4 (Control) (a simple heterojunction with fewer O v , 2.29 eV) to realize the transformation of CO 2 * to COOH*. The restraint of the hydrogenation of CO* was a critical step to selectively produce CO.…”

Light-Induced Polymeric Frustrated Radical Pairs as Building Blocks for Materials and Photocatalysts

“…As observed in EPR samples, mixing concentrated toluene solutions (67.6 mM of B/P moieties) of Poly-1 (10 mol % loading, M n,th = 33300) and Poly-3 (10 mol % loading, M n,th = 29800) led to a noticeable increase in viscosity (Supporting Information Figure S2). 31 P NMR spectra showed no change from pure Poly-1, indicating no substantive binding between the LA and LB moieties on the NMR timescale. Coordination of boron would also quench molecule fluorescence under long-range wavelength UV; this is also not observed.…”

“…That same year, Wang et al also reported single electron oxidation of a methylene-bridged triphenylamine by B­(C 6 F 5 ) 3 . In later studies, phosphine-coordinated boryl radicals were developed and characterized, including the observation of a Lewis basic radical cation (R 3 P•+) by Stephan et al − and the [B­(C 6 F 5 ) 3 ]•– radical anion by Slootweg et al (Scheme b). − Müller et al also spectroscopically observed the SET between B­(C 6 F 5 ) 3 and bespoke LBs (Scheme c,d). , This fundamental understanding has recently been extended to radical-assisted catalysis. − Besides these findings, Meijer et al also extended FRP into supramolecular chain structure by small molecular boranes and amines, with photoinduced SET between LA and LB observed (Scheme e). , Most recently, Lin et al reported the FRP-mediated regioselective C–H functionalization using the neutral [HMDS • /HPDS • / t BuO • ] [TEMPO • ] pair. , …”

“…The low loading of boron moieties in Poly-1 (5 mol %) prevented detection of peaks in the 11 B NMR spectrum, similar to other reports of polymeric LAs. 15,47 The presence of boron centers was instead confirmed using 31 ). 48 Taken together, these analyses confirm a single Lewis acidic boron environment in Poly-1 and thus a clean and quantitative reduction reaction.…”