NewIr Birch O-PC™
Benzoperylene photocatalysts (Birch O-PCTM) are some of the strongest visible light reductants in existence, enabling even challenging Birch reductions under benchtop conditions.1 Here are the ranges of photo and electrochemical properties for benzoperylene PC derivatives:
|Excited state redox potential (two hν)||Eo(1PC/2PC●-*) = < -3.0 V vs. SCE|
|Ground state reduction potential||E1/2(1PC/2PC●-) = -1.1 V to -1.3 V vs. SCE|
|Excited state energy (first hν)||E(singlet) = 1.9 to 2.3 eV|
|λmax,abs||489 – 535 nm (local max 1); 415 – 450 nm (local max 2)|
|εmax,abs||6,700 – 9,500 M-1cm-1 (local max 1);
23,000 – 34,000 M-1cm-1 (local max 2)
In a conventional Birch reduction reaction, solvated electrons are generated by dissolving alkali metals in liquid ammonia to reduce benzenes to 1,4-cyclohexadienes. Due to these harsh reaction conditions, Birch reductions are largely discouraged at process scale and limited to lab scale synthesis. Using photocatalysis, benzoperylene PCs now enable Birch reductions under mild benchtop conditions with solvated electrons generated via photoexcitation. This mild photocatalytic method alleviates the prior process scale concerns and makes Birch reductions a practical solution for industrial usage.
Mechanistic studies suggest two photons are involved in generating a solvated electron.1 Benzoperylene PCs have been shown spectroscopically to first complex with a hydroxide anion to form [PC-OH–]. This species is proposed to undergo photoinduced electron transfer to produce a radical anion 2PC●-. Notably, 2PC●- is a persistent and stable radical that can absorb the second photon to generate 2PC●-*, which is proposed to ionize as a solvated electron responsible for Birch reduction reactivity. Work is currently underway to reduce reaction times, improve yields and increase substrate scope.