Enhanced Catalytic Activity and Unexpected Products from the Oxidation of Cyclohexene by Organic Nanoparticles of 5,10,15,20‐Tetrakis‐(2,3,4,5,6‐pentafluorophenyl)porphyrinatoiron(III) in Water by Using O₂

Abstract

The catalytic oxidation of alkenes by most iron porphyrins using a variety of oxygen sources, but generally not dioxygen, yields the epoxide with minor quantities of other products. The turnover numbers for these catalysts are modest, ranging from a few hundred to a few thousand depending on the porphyrin structure, axial ligands, and other reaction conditions. Halogenation of substituents increases the activity of the metalloporphyrin catalyst and/or makes it more robust to oxidative degradation. Oxidation of cyclohexene by 5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl) (tppf 20 )] with a diameter of 10 nm, formed by host-guest solvent methods, catalytically oxidize cyclohexene with O 2 to yield only 2-cyclohexene-1-one and 2-cyclohexene-1-ol with approximately 10-fold greater turnover numbers compared to the non-aggregated metalloporphyrin in acetonitrile/methanol. These ONPs facilitate a greener reaction because the reaction solvent is 89% water and O 2 is the oxidant in place of synthetic oxygen sources. This reactivity is unexpected because the metalloporphyrins are in close proximity and oxidative degradation of the catalyst should be enhanced, thus causing a significant decrease in catalytic turnovers. The allylic products suggest a different oxidative mechanism compared to that of the solvated metalloporphyrins. These results illustrate the unique properties of some ONPs relative to the component molecules or those attached to supports.

Nanoaggregates of Mn(III)tetraperfluorophenylporphyrin: a greener approach for allylic oxidation of olefins

“…The aggregation of the metalloporphyrins in the nanoscaled particles were also confirmed by the broadening of the Soret and Q-bands as discussed previously [36,37]. For ONP of Mn(III)TPPF 20 the Soret band gets broadened and red shifted by 20 nm and appears at 483 nm.…”

“…ONP of porphyrin and metalloporphyrins are promising components for advance materials because of their remarkable photochemical and catalytic properties, stability, and ease of preparation [35][36][37]. ONP can be considered as self-organized systems and are governed by non-covalent interactions such as Van der Waals forces, H-bonding, and electrostatic interactions that depend on the structure of the porphyrin, the central metal ion, nature of the axial ligand, solvent, and the method of preparing the nanoparticles.…”

“…In the present work the porphyrins are dissolved in THF and water serves as the guest solvent. The size and structure of porphyrinic nanoparticles formed depends on: (a) the nature and magnitude of intermolecular forces between the various components, e.g., the porphyrin, host and guest solvents, and the PEG stabilizer; (b) the ratio of the host to guest solvent, (c) the type of mixing, and (d) the nature of peripheral substituents on the porphyrin core [37]. These ONP are stable for weeks when placed in refrigerator at 4 °C.…”

“…ONP of catalytically active metalloporphyrins are Recently, we reported that 10 nm diameter ONP of 5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)porphyrinato iron(III), Fe(III)TPPF 20 , have enhanced catalytic activity for allylic oxidations of cyclohexene to yield the αβ-unsaturated ketone and alcohol. These are greener catalysts since the reaction solvent is mostly water and they activate O 2 [37]. Conversely, the epoxide is the only product from the solvated metalloporphyrin in organic solvent, and synthetic oxygen sources such as H 2 O 2 are required.…”

Synthesis, crystal structure of two new Zn(II), Cu(II) porphyrins and their catalytic activities to ethylbenzene oxidation

“…Noncovalent interactions have a great influence on controlling structures and properties of supramolecules [24,25]. For example, noncovalent interaction supramolecules constructed from porphyrins exhibit interesting optical, electronic and catalytic properties [26][27][28][29][30][31]. So constructing porphyrin supermolecule is a promising strategy to improve stability of porphyrin catalyst without forming inactive dimers.…”