Three Generations of Cobalt Porphyrins as Catalysts in the Oxidation of Cycloalkanes

Abstract

Three generations of cobalt porphyrins were synthesized, physicochemically characterized by FTIR and UV/Vis spectroscopy as well as cyclic voltammetry and applied as catalysts in the oxidation of cycloalkanes with atmospheric molecular oxygen under mild conditions. All examined catalysts were active in the tested reaction, and their catalytic activity varied with the nature and number of substituents on the porphyrin ring. Introduction of electron‐withdrawing or electron‐donating substituents at the porphyrin rings increases the activity of metalloporphyrin complexes. It was found, for the first time, that generation II cobalt porphyrins show higher activity in cycloalkane oxidation than cobalt porphyrins of generation III. The lower catalytic activity of generation III cobalt porphyrins can be attributed to the saddle‐shaped deformation of the porphyrin macrocycle. DFT modeling of Co porphyrins and their interactions with molecular oxygen provided explanations for the observed effects. On the basis of prior reports and the obtained results, a reaction mechanism is proposed and discussed.

Oxygen Adsorption and Activation on Cobalt Center in Modified Keggin Anion-DFT Calculations

“…These issues will be the subject of a separate publication (in preparation), where cobalt complexes will be compared with other transition metal complexes. From the literature and our unpublished calculations, it follows that some ligands, especially those containing nitrogen moieties, favor the exchange with the O 2 molecule [49,50]. Our unpublished calculations of HPA complexes show that, e.g., water and acetonitrile are not exchanged with the O 2 molecule, but are exchanged with OOH or H 2 O 2 .…”

Tailoring Electronic Properties of Porphyrin Manganese on Boron Nitride for Enhancing Aerobic Oxidative Desulfurization at Room Temperature

“…It was suggested that the UV–vis spectrum is the fingerprint of the structure of TPPMnCl. The Soret band is formed by the strong electron transition in the TPPMnCl from the ground state to the second excited state, and the Q band is formed by the weak electron transition from the ground state to the first excited state . The positions of the Soret and Q bands of the TPPMnCl immobilized on the catalysts were collected and listed (Table ).…”

“…Based on the literature, , the aldehyde could be catalytically oxidized by oxygen on transition metals, generating peroxyacid, which is known as one kind of ROS. , On the other hand, the metalloporphyrin can also be modified to accommodate a variety of catalytic systems. It is suggested that the electronic structure of the metal atom in metalloporphyrin plays an essential role in the catalytic oxygenation reaction . Moreover, the metalloporphyrin has received much attention in the ODS research.…”

CO2 to CO Electroreduction, Electrocatalytic H2 Evolution, and Catalytic Degradation of Organic Dyes Using a Co(II) meso-Tetraarylporphyrin

“…Cobalt porphyrins provide a rich electrochemistry consisting of both metal- (Co(I)/Co(II)/Co(III) and porphyrin-centred redox processes. By variation of the substituents on the phenyl core of the porphyrin ligands, these processes can cover a huge range of potentials [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Moreover, there are one or two axial positions available for binding small molecules [ 10 , 11 , 12 , 26 , 27 , 28 , 29 ].…”

“…Recently, Zn(II) [ 12 , 15 , 71 , 72 ] and Co(II) porphyrins [ 10 , 11 , 26 , 73 ] have been used as catalysts in the degradation of organic dyes with H 2 O 2 . In view of the first oxidation potential of Co(TPP) complexes lying in the range of 0.1 to 0.75 V vs. SCE [ 10 , 11 , 13 , 16 , 17 , 22 , 24 , 25 , 26 , 61 , 62 ], their high reactivity in radical-based organic transformations [ 14 , 58 , 59 , 60 ] is not unexpected and a very recent study on a (5,10,15,20-tetrakis(2,5-dimethoxyphenyl)porphyrinato)cobalt(II) has revealed some mechanistic details in such decomposition reactions using H 2 O 2 [ 73 ].…”