Triggering the Generation of an Iron(IV)-Oxo Compound and Its Reactivity toward Sulfides by Ru^II Photocatalysis

Abstract

The preparation of [FeIV(O)(MePy2tacn)]2+ (2, MePy2tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane) by reaction of [FeII(MePy2tacn)(solvent)]2+ (1) and PhIO in CH3CN and its full characterization are described. This compound can also be prepared photochemically from its iron(II) precursor by irradiation at 447 nm in the presence of catalytic amounts of [RuII(bpy)3]2+ as photosensitizer and a sacrificial electron acceptor (Na2S2O8). Remarkably, the rate of the reaction of the photochemically prepared compound 2 toward sulfides increases 150-fold under irradiation, and 2 is partially regenerated after the sulfide has been consumed; hence, the process can be repeated several times. The origin of this rate enhancement has been established by studying the reaction of chemically generated compound 2 with sulfides under different conditions, which demonstrated that both light and [RuII(bpy)3]2+ are necessary for the observed increase in the reaction rate. A combination of nanosecond time-resolved absorption spectroscopy with laser pulse excitation and other mechanistic studies has led to the conclusion that an electron transfer mechanism is the most plausible explanation for the observed rate enhancement. According to this mechanism, the in-situ-generated [RuIII(bpy)3]3+ oxidizes the sulfide to form the corresponding radical cation, which is eventually oxidized by 2 to the corresponding sulfoxide.

Photocatalytic oxidation of alkenes and alcohols in water by a manganese(v) nitrido complex

“…18 Active non-heme Fe=O species have also been generated by photochemical means. 19,20 Recently, we reported that the square pyramidal manganese(V) nitrido complex (PPh 4 ) 2 [Mn(N)(CN) 4 ] (1) can efficiently catalyse the oxidation of alkenes, alcohols and alkanes by H 2 O 2 with excellent yields (> 95%). 21,22 Experimental and computational studies suggest that the active oxidant is a manganese(VII) nitrido oxo species that is generated by O-atom transfer from H 2 O 2 to 1 (equation 1).…”

Metal‐ and Additive‐Free Oxidation of Sulfides into Sulfoxides by Fullerene‐Modified Carbon Nitride with Visible‐Light Illumination

“…[7][8][9][10][11] However,t hese methodss uffer from several drawbacks, such as low selectivity,t he high input of energy, and the release of highly toxic waste. [16] Nevertheless, these photocatalytic systemsr equirea large excess of sacrificial electron acceptors, such as [Co(NH 3 ) 5 Cl]Cl 2 and Na 2 S 2 O 8 .F rom the viewpoint of green and sustainable chemistry,O 2 is the most attractive oxidantb ecause it is an environmentally friendly and readily available oxidant, with harmless water as the only byproduct generated in the reaction. Photocatalytic transformations, which utilize sunlight as an abundant and readilya vailables ource of energy for driving chemical reactions, have been considered to be an important pathway towards as ustainable future.…”

Photocatalytic Oxygenation Reactions Using Water and Dioxygen

“…Cl] 2 + electron acceptor (one-electrono xidant) can be replaced by at wo-electrono xidant such as Na 2 S 2 O 4 in photocatalytic oxygenation of thioanisole by Na 2 S 2 O 4 with [Fe II (MePy 2 tacn)] 2 + (MePy 2 tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane) as an oxygenation catalyst and [Ru II (bpy) 3 ] 2 + as ap hotoredox catalyst [63]. An iron(IV)-oxo complex ([Fe IV (O)(MePy 2 tacn)] 2 + )w as produced by the ET oxidation of [Fe II (MePy 2 tacn)] 2 + with H 2 Ob yt wo equivalents of [Ru III (bpy) 3 ] 3 + ,w hich were generated by ET from [Ru II (bpy) + to SO 4 C À [63]. Then, thioanisole was oxygenated by [Fe IV (O)(MePy 2 tacn)] 2 + to yield the sulfoxide, in which the oxygen atom comes from H 2 O [63].…”

“…An iron(IV)-oxo complex ([Fe IV (O)(MePy 2 tacn)] 2 + )w as produced by the ET oxidation of [Fe II (MePy 2 tacn)] 2 + with H 2 Ob yt wo equivalents of [Ru III (bpy) 3 ] 3 + ,w hich were generated by ET from [Ru II (bpy) + to SO 4 C À [63]. Then, thioanisole was oxygenated by [Fe IV (O)(MePy 2 tacn)] 2 + to yield the sulfoxide, in which the oxygen atom comes from H 2 O [63]. 3.…”