Mian Hr Mahmood

Crystal structure, magnetic and catalytic oxidation properties of manganese(III) tetrakis(ethoxycarbonyl)porphyrin

A new meso-tetraalkyl porphyrin manganese complex, 5,10,15,20-tetrakis(ethoxycarbonyl)porphyrinatomanganese (MnIIITECPCl), had been prepared and characterized by X-ray structure determination. MnIIITECPCl exists as a coordinated dimer in its crystal structure with a weak antiferromagnetic coupling between two Mn(III) ions. The catalytic oxidation of styrene by MnIIITECPCl was carried out in acetonitrile. MnIIITECPCl was found to be recyclable with a high conversion efficiency when using TBHP as an oxidant and the major product was benzaldehyde. MnIIITECPCl was also reusable by using an PhIO oxidant, but the major products turned out to be phenyl acetaldehyde and styrene epoxide.

Second order nonlinear optical properties of corroles: experimental and theoretical investigations

The first hyperpolarizabilities, βHRS, of corrole derivatives have been measured by using Hyper–Rayleigh Scattering technique. The results showed that βHRS of corroles could be greatly enhanced by modifying its periphery with donor–acceptor groups. Maximum value reaches 354 × 10-30 esu at an incident wavelength of 1500 nm. βHRS of investigated corroles were also calculated with the Zerners intermediate neglect of differential overlap/configuration interaction/sum-over-states method. The calculated and experimental results are in good agreement and conclude that βHRS arises mainly from the charge transfer along molecules non-symmetrical axis and strong coupling between two different excited states of the Soret band.

DNA/HSA interaction and nuclease activity of an iron(III) amphiphilic sulfonated corrole

The DNA binding of amphiphilic iron(III) 2,17-bis(sulfonato)-5,10,15-tris(pentafluorophenyl)corrole complex (Fe-SC) was studied using spectroscopic methods and viscosity measurements. Its nuclease-like activity was examined by using pBR322 DNA as a target. The interaction of Fe-SC with human serum albumin (HSA) in vitro was also examined using multispectroscopic techniques. Experimental results revealed that Fe-SC binds to ct-DNA via an outside binding mode with a binding constant of 1.25 × 10(4) M(-1). This iron corrole also displays good activity during oxidative DNA cleavage by hydrogen peroxide or tert-butyl hydroperoxide oxidants, and high-valent (oxo)iron(V,VI) corrole intermediates may play an important role in DNA cleavage. Fe-SC exhibits much stronger binding affinity to site II than site I of HSA, indicating a selective binding tendency to HSA site II. The HSA conformational change induced by Fe-SC was confirmed by UV/Vis and CD spectroscopy.

Solvent effects on the catalytic activity of manganese(III) corroles

Four Mn(III) corroles that differ in their electronic environments based on meso-substitution by pentafluorophenyl and phenyl groups were synthesized and characterized by spectroscopic techniques. Utilization of these Mn(III) corroles for styrene oxidation using iodosylbenzene (PhIO) as oxygen source in toluene, dichloromethane (DCM), DMF, DMAc, THF and DMSO revealed a remarkable effect of solvent on the catalytic activity. Furthermore, the transformation of Mn(III) corroles into their corresponding Mn(V)-oxo corroles, and subsequent treatment with styrene also indicated that more electron-deficient Mn(V)-oxo corroles exhibit higher reactivity in toluene and DCM, while less electron-deficient Mn(V)-oxo corroles exhibit higher reactivity in DMF and DMAc. A significant difference in the observed rates of reaction suggest that the catalytic oxidation of styrene by manganese corroles may proceed through different pathways, and is strongly solvent-dependent.

Reactivity of (oxo)manganese(V) corroles in one-electron redox state: insights from conceptual DFT and transition state calculations

The electronic and structural features of (oxo)manganese(V) corroles (Mn(V)-oxo(cor)) in different oxidation states and their oxygen atom transfer (OAT) reactivity towards dimethyl sulfide (DMS) have been investigated by density functional theory (DFT) calculations. Three Mn(V)-oxo corroles with different β-substituents (Br(1), H(2), CH3(3)) were choosen as model complexes. The results revealed that Mn(V)-oxo corrole bearing electron-withdrawing substituent (Br) is more reactive than those having electron-donating substituents. Moreover, the conceptual DFT descriptor ω for Mn(V)-oxo corrole in one-electron oxidized state is always larger than the neutral or one-electron reduced state. These calculations for the transition state involved in OAT reaction also indicated that the radical cation formed after one-electron oxidation, Mn(V)-oxo(cor+•), is the most reactive specie, while the neutral [Mn(V)-oxo(cor)] in the triplet states are more reactive than those in the singlet states.

Oxygen atom transfer reactions from sterically encumbered brominated (oxo)manganese(V) corroles to styrene

Seven A3- and trans-A2B manganese(III) corroles (1–7-Mn) differing widely in their electronic and steric features were synthesized and transformed to their corresponding β-brominated manganese(III) corroles derivatives (1a–7a-Mn). Their corresponding (oxo)manganese(V) corroles 1–7-Mn(oxo) and 1a–7a-Mn(oxo) were further prepapred by treating with iodosylbenzene (PhIO). The reactivity for the oxygen atom transfer from 1–7-Mn(oxo) to styrene followed the order of 1-Mn(oxo) > 2-Mn(oxo) > 7-Mn(oxo) > 4-Mn(oxo) > 3-Mn(oxo) > 6-Mn(oxo) ≈5-Mn(oxo). The same pattern was observed for their β-brominated analogs 1a–7a-Mn(oxo), albeit their reactivity was remarkably higher. The steric protection of MnV ≡O moiety by ortho–ortho′-dibromophenyl substituents was found to enhance the stability of (oxo)manganese(V) corroles significantly.

Unexpected Synthesis of a Bulky Bis-Pocket A3B-Type Meso-Cyano Porphyrin

A one-pot synthesis of bulky bis-pocket A3B-type meso-cyano porphyrin, 5-cyano-10,15,20-tris(2,4,6-triphenylphenyl)porphyrin, has been accomplished via trifluoroacetic acid (TFA) catalyzed condensation of pyrrole and 2,4,6-triphenylbenzaldehyde in an acceptable yield of about 4%. DDQ served as oxidant and the cyanating agent.

Spontaneous resolution of chiral bis-sulfoxides with asymmetric atropisomerism

Restricted rotation of the ortho sulfinyl groups directs the trans ortho-substituted bis-sulfoxide (3) to adopt right-handed (P) or left-handed (M) conformation and thus produces symmetric atropisomeric (R,R)-3/(S,S)-3 and asymmetric atropisomeric enantiomers (R,S)-3, respectively. (R,S)-3 exhibits spontaneous resolution and crystallizes as a conglomerate (P,R,S)-3/(M,R,S)-3 with a homochiral supramolecular helix (P/M-helix) conformation.