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Dicyanopyrazine photoredox catalysts: Correlation of efficiency with photophysics and electronic structure

Rok: 2024

Druh publikace: článek v odborném periodiku

Název zdroje: Journal of Catalysis

Název nakladatele: Elsevier Science Inc.

Místo vydání: New York

Strana od-do: 115348

Tituly:

Jazyk	Název	Abstrakt	Klíčová slova
cze	Dikyanpyrazinové fotoredoxní katalyzátory: korelace účinnosti s fotofyzikou a elektronovou strukturou	Katalytická účinnost tří strukturně příbuzných dikyanopyrazinových katalyzátorů byla sledována ve třech fotoredoxních transformacích: deuterace aldehydů, cross-couplingu jodovaných (hetero)aromatických substrátů, a abstrakce alfa-vodíku z aminů následovaná anelací na pyrrolochinolin. Významný rozdíl v katalytické aktivitě fotokatalyzátorů byl pozorován s využitím elektrochemických, spektroskopických a kvantově-chemických metod.	Dikyanpyrazin; Fotoredoxní katalýza; Deuterace; Cross-coupling
eng	Dicyanopyrazine photoredox catalysts: Correlation of efficiency with photophysics and electronic structure	Catalytic performance of three structurally-related dicyanopyrazine catalysts has been investigated in three photoredox transformations including deuteration of aldehydes, cross-coupling of iodo-substituted (hetero)aromatic substrates, and alpha-hydrogen abstraction from amines followed by annulation to pyrroloquinoline. Significantly different catalytic activity of the photocatalysts has been explained with the aid of electrochemical, spectroscopic, and quantum-chemical methods. Electrochemical measurements pointed to reversible oneelectron reduction of the photocatalysts affording the corresponding radical anion, and, therefore, dicyanopyrazines are principally well-suited for reductive quenching cycle. Triplet excited state turned out to be a major excited species employed in photoinduced electron transfer. The measured excited state reduction potentials (Ered* = +1.88/+1.43 V) classify the (5-methoxy)thiophene-substituted dicyanopyrazines among the organic photocatalysts with high oxidation power, which is in contrast to N,N-dimethylanilino-substituted photocatalysts. Whereas 5-methoxythiophene photocatalyst forms triplet excited state almost independently on the solvent polarity, transient absorption spectroscopy evidenced the triplet state of N,N-dimethylanilino derivative only in nonpolar media. Moreover, its subsequent reduction to the corresponding radical anion is chemically cumbersome, which contrast to facile one-electron reduction of both cyano groups of photocatalyst bearing weak 5-methoxythiophene donors. The doublet excited radical anion of the latter proved to be very powerful but short-lived reductant with Eox* = -2.84 V. Its reduction power has been demonstrated in a cross-coupling reaction involving consecutive photoinduced electron transfer to preassociated iodo(hetero)arenes. Hence, bis(5methoxythiophen-2-yl)-2,3-dicyanopyrazine can be utilized in photoredox catalysis either as powerful oxidant or reductant.	Dicyanopyrazine; Photoredox catalysis; Deuteration; Cross-coupling; Transient absorption spectra

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