A Radical Mechanism for Frustrated Lewis Pair Reactivity

Abstract

The frustrated Lewis pairs (FLPs) derived from tBu 3 P and E(C 6 F 5 ) 3 (E = B, Al) react with pO 2 C 6 Cl 4 and Ph 3 SnH to give [tBu 3 POC 6 Cl 4 OE(C 6 F 5 ) 3 ] (E = B 1, Al 2), [tBu 3 PSnPh 3 ][HB(C 6 F 5 ) 3 ] 3, and [tBu 3 PSnPh 3 ][(m-H)(Al(C 6 F 5 ) 3 ) 2 ] 4. These products form via the accepted two-electron process involving a transient ''encounter complex.'' In contrast, the corresponding reactions of Mes 3 P and E(C 6 F 5 ) 3 (E = B, Al) with pO 2 C 6 Cl 4 give [(Mes 3 POC 6 Cl 4 OE(C 6 F 5 ) 3 ] (E = B 8, Al 9); however, the identification of the intermediates [Mes 3 P$] 2 [(C 6 F 5 ) 3 EOC 6 Cl 4 OE(C 6 F 5 ) 3 ] (E = B 5, Al 6) supports a mechanism that proceeds via a single-electron transfer process. This is further supported by the reactions of Mes 3 P and E(C 6 F 5 ) 3 (E = B, Al) with Ph 3 SnH, which yielded [Mes 3 PH] [HB(C 6 F 5 ) 3 ] 10 and [Mes 3 PH][(m-H)(Al(C 6 F 5 ) 3 ) 2 ] 11, respectively, with the concurrent formation of Ph 3 SnSnPh 3 .

Reactions of an Aluminium/Phosphorus Frustrated Lewis Pair (FLP) with α,β‐Unsaturated Carbonyl Compounds: FLPs as Efficient Two‐Electron Reductants with the Formation of Enolates, a cis‐Enediolate, and an Allene

“…The interaction of the reduced benzil molecule to the functional groups of the FLP forces the stereospecific formation of a cis ‐enediol . Only recently, a radical mechanism with a biradical intermediate and unpaired electrons at P and B has been proposed for reactions of a bimolecular B/P FLP . In contrast, the Al and P atoms in 1 are bridged by an sp 2 ‐C atom, and the most stable biradical was calculated for a model compound (see the Supporting Information) to result from opening of the C−C π‐bond.…”

Isolable Anionic, Neutral and Cationic Radicals from Reactions ofN,N′‐Dimesityldiamidocarbene and Lewis Acids

“…Erker and co‐workers showed that FLPs could capture NO to generate radical species which are effective in radical polymerizations . However in 2016, we demonstrated that a one‐electron transfer between Mes 3 P and B(C 6 F 5 ) 3 generated a “frustrated radical pair” (FRP) which homolytically cleaved Sn−H bonds . This stood in sharp contrast to the corresponding reaction of t Bu 3 P and B(C 6 F 5 ) 3 where heterolytic Sn‐H cleavage was seen.…”

Hydrogen splitting by pyramidalized 13–15 donor–acceptor cryptands: A computational study

“…Energy decomposition analysis of the transition states (TSs) of heterolytic hydrogen splitting by Heshmat and Privalov and Skara et al reveal that both electrostatic and covalent interactions are important. Recently, it was shown that in some cases, radical mechanism, which involves a single‐ET process from LB to LA, is also operational . Radicals derived from LA/base pairs were the topic of the recent review .…”