134818-46-5

Upstream product

• 134818-43-2 meso-(tetrakis(2,6-dibromophenyl)porphinato)chromium(III)chloride 
• 3240-34-4 [bis(acetoxy)iodo]benzene 

Relevant academic research and scientific papers

Evaluation of the selectivity of the epoxidation of cis- versus trans-alkenes by oxo[meso-tetrakis(2,6-dibromophenyl)porphinato]chromium(V). Dynamics, products, and van der Waals energies

Studies of the reaction of oxo[meso-tetrakis(2,6-dibromophenyl)porphinato]chromium(V) [(Br8TPP)CrV(O)(X)] with a number of trans-alkenes have been carried out with the objective of clarifying the nature of the reported stereoselectivity of the epoxidation of cis-alkenes as compared to trans-alkenes. The alkenes employed were trans-p,p′-dimethoxystilbene, trans-stilbene, trans-β-methylstyrene, trans-p,p′-dicyanostilbene, trans-2-pentene, trans-5-decene, trans-2-hexenyl acetate, (E)-1,2-bis(trans-2,trans-3-diphenylcyclopropyl)ethene, and also (Z)-1,2-bis(trans-2,trans-3-diphenylcyclopropyl)ethene. The influence of electronic and steric factors in determining the second-order rate constants (k1) for the reactions of trans-alkenes with (Br8TPP)CrV(O)(X) were separated by use of the linear free-energy relationship of log k1 and the one-electron oxidation potentials (E1/2) established by the reaction of a series of cis-alkenes with (Br8TPP)CrV(O)(X). Quantification of the steric factors established that there is no appreciable steric retardation of the second-order rate constants for reaction of trans-p,p′-dimethoxystilbene, trans-β-methylstyrene, trans-2-pentene, trans-5-decene, and trans-2-hexenyl acetate with (Br8TPP)CrV(O)(X). Steric hindrance is quite marked with trans-stilbene, trans-p,p′-dicyanostilbene, and (E)-1,2-bis-(trons-2,trans-3-diphenylcyclopropyl)ethene. In comparison with trans-stilbene, the lack of a kinetic steric effect with trans-p,p′-dimethoxystilbene requires a change of mechanism. The standard free energy (ΔGo) for one-electron oxidation of trans-p,p′-dimethoxystilbene [(Br8TPP)CrV(O)(X) + >C=C8TPP)CrIV(O)(X) + >C+C?o values for trans-stilbene and cis-stilbene by 0.46 and 0.59 V, respectively. Thus, trans-p,p′-dimethoxystilbene but not trans-stilbene can undergo facile le- oxidation by (Br8TPP)CrV(O)(X). This can be shown to be allowed by comparison of ΔGo and ΔGa values. One-electron transfer can take place at significantly longer distances than can covalent bond formation. Computer docking experiments have defined the stereochemistry associated with the closest approach of minimal van der Waals repulsive forces in the reaction of trans- and cis-stilbene. For trans-stilbene the closest approach is at a distance of 3.88 A? from directly above the CrV(O) while for cis-stilbene lowest energy closest approach is at 2.81 A? with the C=C bond: (i) lined parallel to opposite meso carbons; and (ii) above the CrV(O) oxygen with an offset (α) from the perpendicular CrV-O bond of α = 24°. Product yields are in accord with assigned steric effects and the nature of the products and mode of formation are discussed.

Is a Linear Relationship between the Free Energies of Activation and One-Electron Oxidation Potential Evidence for One-Electron Transfer Being Rate Determining? Intermediates in the Epoxidation of Alkenes by Cytochrome P-450 Models. 4. Epoxidation of a Series of Alkenes by Oxo(meso-te...

The mechanism of reaction of (porphyrin)CrV(O)(X) with alkenes has been investigated by combining the electrochemical determinations of redox potentials with the tools of kinetics and product identification.Studies include the following: (i) the dynamics of the reaction of oxo(meso-tetrakis(2,6-dibromophenyl)porphinato)chromium(V) ((Br8TPP)CrV(O)(X) with 16 alkenes (1,4-diphenyl-1,3-butadiene, 4-methoxystyrene, 1,1-diphenylethylene, 4-methylstyrene, 2,3-dimethyl-2-butene, cis-stilbene, styrene, 4-acetoxystyrene, cyclohexene, norbornene, cis-cyclooctene, 4-cyanostyrene, cis-2-pentene, cyclopentene, 1-hexene, 1-octene); (ii) the dynamics of the reaction of norbornene with five (porphyrin)CrV(O)(X) species (oxo(meso-tetraphenylporphinato)chromium(V), oxo(meso-tetrakis(2,4,6-trimethylphenyl)porphinato)chromium(V), oxo(meso-tetrakis(2,6-dichlorophenyl)porphinato)chromium(V), oxo(meso-tetrakis(2,6-difluorophenyl)porphinato)chromium(V), and oxo(meso-tetrakis(2,6-dibromophenyl)porphinato)chromium(V)).Alkenes were selected on the basis of their 1e oxidation potential so as to cover the widest range of E1/2 possible (1.14-2.80 V (SCE)), and the 1e oxidation potentials for the (porphyrin)CrV(O)(X) varied from 0.790 to 0.975 V (SCE).Standard solutions of (porphyrin)CrV(O)(X) were obtained by controlled-potential bulk electrolysis of the corresponding (porphyrin)CrIV(O) and used in the kinetic (CH2Cl2 solvent, 30 deg C) and product studies.The time course for the change in concentration of (Br8TPP)CrV(O)(X), (Br8TPP)CrIV(O), and (Br8TPP)CrIII(X) was simulated for the reaction of (Br8TPP)CrV(O)(X) with selected alkenes possessing "low, medium, and high" oxidation potentials.The time dependence of V(O)(X)>, IV(O)>, and III(X)> as well as the could be accurately fit to a scheme involving the following: (i) bimolecular reaction of alkene with (Br8TPP)CrV(O)(X) to provide alkene oxidation product + (Br8TPP)CrIII(X); (ii) reversible comproportionation of (Br8TPP)CrV(O)(X) + (Br8TPP)CrIII(X) to provide (Br8TPP)CrIV(O) + (Br8TPP)CrIV(X)2; (iii) a spontaneous reversion (due to oxidation of solvent or solutes) of (Br8TPP)CrV(O)(X) to (Br8TPP)CrIV(O).The remainder of the alkene oxidations were followed by the more simplistic procedure of following disappearance of (Br8TPP)CrV(O)(X).The second-order rate constants (k1) determined by either method were found to be in agreement.For about half the alkenes studied, the standard free energies for 1e oxidation by (Br8TPP)CrV(O)(X), to provide alkene-derived ? cation radicals (calculated from the potentials for 1e reduction of (Br8TPP)CrV(O)(X) and 1e oxidation of the alkenes to ? cation radicals), exceed the free energies of activation for epoxidation of alkenes by (Br8TPP)CrV(O)(X).A unified mechanism ...