Photocatalytic Electron-Transfer Oxidation of Triphenylphosphine and Benzylamine with Molecular Oxygen via Formation of Radical Cations and Superoxide Ion

Abstract

Photooxygenation of triphenylphosphine (Ph3P) to triphenylphosphine oxide (Ph3P=O) with molecular oxygen (O2) occurs under photoirradiation of 9-mesityl-10-methylacridinium perchlorate ([Acr+–Mes]ClO4−) which acts as an efficient electron-transfer photocatalyst. Photooxidation of benzylamine (PhCH2NH2) with O2 also occurs efficiently under photoirradiation of Acr+–Mes to yield PhCH2N=CHPh and hydrogen peroxide (H2O2). Each photocatalytic reaction is initiated by intramolecular photoinduced electron transfer from the Mes moiety to the singlet excited state of the Acr+ moiety to produce the electron-transfer state (Acr•–Mes•+). The Mes•+ moiety oxidizes Ph3P and PhCH2NH2 to produce the radical cations (Ph3P•+ and PhCH2NH2•+, respectively), whereas the Acr• moiety reduces O2 to O2•−. The produced Ph3P•+ binds with O2•− as well as O2, leading to the oxygenated product (Ph3P=O). On the other hand, proton transfer from PhCH2NH2•+ to O2•− occurs, followed by hydrogen transfer, leading to the dehydrogenated dimer product, PhCH2N=CHPh. In each case, the radical intermediates were detected by laser flash photolysis and ESR measurements to clarify the photocatalytic mechanism.

Preparation, Characterization, and Oxygenase Activity of a Photocatalytic Artificial Enzyme

“…Photocatalytic oxygenation of sulfides [22] and phosphines [21] has been proposed to proceed via two distinct, often substrate dependent, mechanisms [19] that are initiated by photocatalysts via either (a) 1 O 2 formation or (b) electron abstraction from the organic substrate. This distinction is important for the prospect of engineering selective artificial enzymes since the substrate would more likely be located within the protein scaffold during the oxygenation process in the latter case (b).…”

Dynamics of Labeled Linear Polystyrenes in Semi‐Dilute Polystyrene Matrices in the Uncross‐Linked and Cross‐Linked States

“…[8] After forming an exciplex with an aminomethylsytrene group, thioxanthone abstracts an electron, and a proton is subsequently transferred to the diarylketone producing a ketyl and an aminomethyl radical. [9,10] The aminomethyl radicals are able to dimerize leading to N-benzylidene benzylamine derivatives acting as tetrafunctional cross-links.…”

New development of photoinduced electron-transfer catalytic systems

“…The Acr + -Mes also acts as an efficient photocatalyst for oxygenation of triphenylphosphine (Ph 3 P) to triphenylphosphine oxide (Ph 3 P=O) with molecular oxygen (O 2 ) [38]. Photooxidation of benzylamine (PhCH 2 NH 2 ) with O 2 also occurs efficiently under photoirradiation of Acr + -Mes to yield PhCH 2 N=CHPh and hydrogen peroxide (H 2 O 2 ) [38].…”

“…Photooxidation of benzylamine (PhCH 2 NH 2 ) with O 2 also occurs efficiently under photoirradiation of Acr + -Mes to yield PhCH 2 N=CHPh and hydrogen peroxide (H 2 O 2 ) [38]. Each photocatalytic reaction is initiated by intramolecular photoinduced ET from the Mes moiety to the singlet excited state of the Acr + moiety to produce the ET state (Acr • -Mes •+ ).…”