82265-76-7Relevant academic research and scientific papers
Efficient and selective oxidation of tertiary benzylic C[sbnd]H bonds with O2 catalyzed by metalloporphyrins under mild and solvent-free conditions
Hu, Meng-Yun,Liu, Lei,Qi, Bei,She, Yuan-Bin,Shen, Hai-Min,Ye, Hong-Liang
, (2020/05/19)
The direct and efficient oxidation of tertiary benzylic C[sbnd]H bonds to alcohols with O2 was accomplished in the presence of metalloporphyrins as catalysts under solvent-free and additive-free conditions. Based on effective inhibition on the unselective autoxidation and deep oxidation, systematical investigation on the effects of porphyrin ligands and metal centers, and apparent kinetics study, the oxidation system employing porphyrin manganese(II) (T(2,3,6-triCl)PPMn) with bulkier substituents as catalyst, was regarded as the most promising and efficient one. For the typical substrate, the conversion of cumene could reach up to 57.6% with the selectivity of 70.5% toward alcohol, both of them being higher than the current documents under similar conditions. The superiority of T(2,3,6-triCl)PPMn was mainly attributed to its bulkier substituent groups preventing metalloporphyrins from oxidative degradation, its planar structure favoring the interaction between central metal with reactants, and the high efficiency of Mn(II) in the catalytic transformation of hydroperoxides to alcohols.
Studies on cobalt(II), nickel(II) and copper(II) derivatives of some new meso-aryl substituted octabromoporphyrins
George, Regimol G.,Padmanabhan
, p. 679 - 684 (2008/10/09)
A series of Co(II), Ni(II) and Cu(II) derivatives of a variety of porphyrins with tolyl (H2TxTP) and naphthyl (H2NxTP) moieties as meso-substituents are synthesised and characterised. H 2TxTP has the tolyl functions bonded to meso-carbons at the o-, m- or p-positions of the tolyl moieties while H2NxTP has naphthyl groups bonded through their α- or β-positions. Their octabromo derivatives (MTxOBP and MNxOBP) were also synthesised by electrophilic substitution at the β-pyrrole positions. Optical spectra showed that the Q bands remain almost unaltered for both tolyl and naphthyl derivatives of the nonbrominated porphyrins while the B bands of their naphthyl derivatives are seen to be more red-shifted than their tolyl analogues. Even though a similar trend based on the meso-substituents is observed among all MTxOBP and MNxOBP derivatives, a substantial red-shift is seen for all the bromoderivatives compared to their nonbrominated species MTxTP and MNxTP. The energy difference Δν? associated with this red-shift of the Soret band is seen to be in the range 1700-2050 cm-1 for Co(II) and Ni(II) derivatives, the naphthyl derivatives always having higher values. Energy level reordering due to electron-withdrawing Br-substituents, distortion bringing about nonplanarity in the π-framework resulting in HOMO-LUMO level changes and the mesomeric effect due to meso-aryl moieties can be considered to be the reasons for the observed spectral changes. The EPR spectra of the Cu(II) derivatives of bromoporphyrins have lower A∥Cu and A⊥Cu hyperfine values compared to their nonbrominated analogues, indicating enhanced delocalisation of electron spin to the octabromoporphyrinato moiety. An enhanced Cu-N σ-covalency is seen in the Cu(II)-bromoporphyrins, as evident from their lower α2 values.
