The visible-light-induced photocatalytic strategy has been well-known by ruthenium and iridium polypyridyl complexes. However, since ruthenium and iridium are expensive and rare metals, there is a long-standing interest in replacing them with cheap and abundant metals. Recent development of research on photoactive complex and photoredox reaction reported using first-low transition metals such as Co, Cu, Ni. However, iron complex based photoredox reactions have been rarely reported. Iron complex, such as [Fe(bpy)3]2+ , has been difficult to utilize due to their short excited-state lifetime (~50 fs), and several studies have been investigated to design iron complexes having long excited-state lifetime through ligand modification. Wärnmark group reported FeIII hexa N-heterocyclic carbene complex, [Fe(btz)3]3+, with 100 ps LMCT lifetime and its absorption maximum is in 528 nm, 558 nm (green light region). This complex present high excited-state reduction potentials (E 0(3+*/2+) = +1.5 V vs Fc+/0) which have the ability to act as a one-electron oxidant of styrenes. Here, we designed radical cation Diels-Alder reaction between two electron rich, styrenes and 1,3-butadienes, upon irradiation with green light, and [Fe(btz)3]3+ complex was found to be an efficient catalyst for radical cation Diels-Alder reaction to afford cyclohexene derivatives.

Iron(III) N-heterocyclic carbene complex: Green-light-driven photocatalytic radical cation Diels-Alder reaction

ACS Fall 2020 Virtual Meeting

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