Archetypal phosphine/borane frustrated Lewis pairs (FLPs) are famed for their ability to activate small molecules. The mechanism is generally believed to involve two‐electron processes. However, the detection of radical intermediates indicates that single‐electron transfer (SET) generating frustrated radical pairs could also play an important role. These highly reactive radical species typically have significantly higher energy than the FLP, which prompted this investigation into their formation. Herein, we provide evidence that the classical phosphine/borane combinations PMes
3
/B(C
6
F
5
)
3
and P
t
Bu
3
/B(C
6
F
5
)
3
both form an electron donor–acceptor (charge‐transfer) complex that undergoes visible‐light‐induced SET to form the corresponding highly reactive radical‐ion pairs. Subsequently, we show that by tuning the properties of the Lewis acid/base pair, the energy required for SET can be reduced to become thermally accessible.
Frustrated Lewis pairs (FLPs) are well knownf or their ability to activate small molecules.R ecent reports of radical formation within such systems indicate single-electron transfer (SET) could play an important role in their chemistry. Herein, we investigate radical formation upon reacting FLP systems with dihydrogen, triphenyltin hydride,o rt etrachloro-1,4-benzoquinone (TCQ) both experimentally and computationally to determine the nature of the single-electron transfer (SET) events;that is,being direct SET to B(C 6 F 5) 3 or not. The reactions of H 2 and Ph 3 SnH with archetypal P/B FLP systems do not proceed via ar adical mechanism. In contrast, reaction with TCQ proceeds via SET,w hichi so nly feasible by Lewis acid coordination to the substrate.Furthermore,SET from the Lewis base to the Lewis acid-substrate adduct may be prevalent in other reported examples of radical FLP chemistry, which provides important design principles for radical maingroup chemistry.
Frustrated Lewis pairs (FLPs) are well knownf or their ability to activate small molecules.R ecent reports of radical formation within such systems indicate single-electron transfer (SET) could play an important role in their chemistry. Herein, we investigate radical formation upon reacting FLP systems with dihydrogen, triphenyltin hydride,o rt etrachloro-1,4-benzoquinone (TCQ) both experimentally and computationally to determine the nature of the single-electron transfer (SET) events;that is,being direct SET to B(C 6 F 5) 3 or not. The reactions of H 2 and Ph 3 SnH with archetypal P/B FLP systems do not proceed via ar adical mechanism. In contrast, reaction with TCQ proceeds via SET,w hichi so nly feasible by Lewis acid coordination to the substrate.Furthermore,SET from the Lewis base to the Lewis acid-substrate adduct may be prevalent in other reported examples of radical FLP chemistry, which provides important design principles for radical maingroup chemistry.
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