Cyclohexene epoxidation by the mono-oxygenase model (tetraphenylporphyrinato)manganese(III) acetate-sodium hypochlorite

Abstract

SummaryOxidation of cyclohexene by (tetraphenylporphyrinato)m anganese(III) acetate (Mn(TPP)OAc) and sodium hypochlorite as oxidant has been studied in a two-phase w ater-dichlorom ethane system in the presence of a phase transfer reagent. A kinetic study with this system reveals the following features: (1 ) the main product of the reaction (yield > 80%) is 1 ,2-epoxycyclohexane; (2 ) in the presence of excess oxidant the reaction is zero order in cyclohexene; (3) the reaction order in Mn(III) concentration decreases from 1 to -0 with increasing concentration of this catalyst; (4) the reaction order in hypochlorite decreases from 1 to 0 with increasing concentration of this reagent; (5) pyridine and substituted pyridines enhance the reaction rate. A H am m ett treatm ent of the rate data for various substituted pyridines gives a p-value of -1.00; (6 ) anchoring of Mn(TPP)OAc onto poly(vinylpyridine) or a polym er of an isocyanide, (R-N = C < Jn, increases the reaction rate by a factor of 1.5 -6.0.Based on these findings and on evidence from the literature, a m ech anism for the epoxidation of cyclohexene is proposed. The key intermediate is an oxo-manganese(V) complex, which is formed from Mn(III) and hypo chlorite in a pyridine-catalyzed step. The Mn(V) species may react in 2 ways: either with substrate to give epoxide or with Mn(III) to form a i±-oxomanganese(IV) dimer. The latter route is suppressed when the catalyst is anchored to the polymeric support.

Rhodium Porphyrin Bound to a Merrifield Resin as Heterogeneous Catalyst for the Cyclopropanation Reaction of Olefins

“…From the data of the elemental analysis obtained for the catalyst 4 , we estimate the content of the rhodium porphyrin to be around 1 mmolar per gram of solid, a value very close to those obtained for other porphyrin functionalized solids [21,22,23,24]. The binding of the catalyst 3 to the solid through the ethereal function allows to separate the functionalized resin from the bulk of the reaction by vacuum filtration and reuse it.…”

Enzyme‐Like Selectivity on Metalloporphyrin‐Catalyzed Oxidation by a Linear Homopolymer

“…In the low concentration range the presence of the polymer coil may be able to isolate the catalytic centers apart to prevent oxidative self‐destruction and formation of inactive μ‐oxo dimer. This site‐isolating effect was reported before only for rigid polymeric supports with covalently bounded Mn porphyrin …”

“…The attempt to use CH 2 Cl 2 /CH 3 CN 7/3 as in the case of PS resulted in precipitation of the polymer when H 2 O 2 was added. Interestingly, association of a manganese porphyrin to P4VP enhanced cyclohexene epoxidation rate, however in a rather different system . In this case, Razenberg and coworkers covalently bound the metalloporphyrin via meso aryl groups to pyridyl moieties of poly(4‐vinylpyridine‐ co ‐styrene), with 10 % styrene, and used NaOCl as oxygen donor agent in CH 2 Cl 2 /H 2 O biphasic medium.…”

“…Few works describe the effect of linear polymers on catalytic performance of metalloporphyrins in aqueous solution . Water‐soluble meso ‐tetrakis( N ‐methylpyridyl)‐porphyrinatoiron(III) was reported to interact electrostaticaly with poly(sodium acrylate) and poly(sodium 4‐styrenesulfonate) and also covalently bonding to anionic functional groups .…”

Catalytic Oxidation of Olefins

“…A. S. J. Razenberg [10] introduced that oxidation of cyclohexene by (tetraphenylporphyrinato) manganese (III) acetate (Mn(TPP)OAc) and sodium hypochlorite as oxidant had been studied in a two-phase water-dichloromethane system in the presence of a phase transfer reagent. A kinetic study with this system reveals the following features: (1) the main product of the reaction (yield 80%) is 1, 2-epoxycyclohexane; (2) in the presence of excess oxidant the reaction is zero order in cyclohexene; (3) the reaction order in Mn (III) concentration decreases from 1 to 0 with increasing concentration of this catalyst; (4) the reaction order in hypochlorite decreases from 1 to 0 with increasing concentration of this reagent; (5) pyridine and substituted pyridines enhance the reaction rate.…”