Epoxidation Of Styrene Derivatives Research Articles

Chemogenetic engineering of nitrobindin toward an artificial epoxygenase

Chemogenetic engineering turned the heme protein nitrobindin into an artificial epoxygenase: MnPPIX was introduced and subsequent protein engineering increased the activity in the epoxidation of styrene derivatives by overall 7-fold.

Multicore Artificial Metalloenzymes Derived from Acylated Proteins as Catalysts for the Enantioselective Dihydroxylation and Epoxidation of Styrene Derivatives.

Artificial metalloenzymes (AME's) are an interesting class of selective catalysts, where the chiral environment of proteins is used as chiral ligand for a catalytic metal. Commonly, the active site of an enzyme is modified with a catalytically active metal. Here we present an approach, where the commercial proteins lysozyme (LYS) and bovine serum albumin (BSA) can be converted into highly active and enantioselective AME's. This is achieved by acylation of the proteins primary amino groups, which affords the metal salts in the core of the protein. A series of differently acylated LYS and BSA were reacted with K2 OsO2 (OH)4 , RuCl3 , and Ti(OMe)4 , respectively, and the conjugates were tested for their catalytic activity in dihydroxylation and epoxidation of styrene and its derivatives. The best suited system for dihydroxylation is fully acetylated LYS conjugated with K2 OsO2 (OH)4 , which converts styrene to 1,2-phenylethanediol with an enantioselectivity of 95 % ee (S). BSA fully acylated with hexanoic acid and conjugated with three moles RuCl3 per mole protein shows the highest ee values for the conversion of styrene to the respective epoxide with enenatioselectivities of over 80 % ee (R), a TON of more than 2500 and a yield of up to 78 % within 24 h at 40 °C. LYS has two favored selective binding sites for the metal catalyst and BSA has even three. The AME's with titanate in the active center invert the enantioselectivity of styrene epoxidation.

Mononuclear Nonheme High-Spin (S=2) versus Intermediate-Spin (S=1) Iron(IV)-Oxo Complexes in Oxidation Reactions.

Mononuclear nonheme high-spin (S=2) iron(IV)-oxo species have been identified as the key intermediates responsible for the C-H bond activation of organic substrates in nonheme iron enzymatic reactions. Herein we report that the C-H bond activation of hydrocarbons by a synthetic mononuclear nonheme high-spin (S=2) iron(IV)-oxo complex occurs through an oxygen non-rebound mechanism, as previously demonstrated in the C-H bond activation by nonheme intermediate (S=1) iron(IV)-oxo complexes. We also report that C-H bond activation is preferred over C=C epoxidation in the oxidation of cyclohexene by the nonheme high-spin (HS) and intermediate-spin (IS) iron(IV)-oxo complexes, whereas the C=C double bond epoxidation becomes a preferred pathway in the oxidation of deuterated cyclohexene by the nonheme HS and IS iron(IV)-oxo complexes. In the epoxidation of styrene derivatives, the HS and IS iron(IV) oxo complexes are found to have similar electrophilic characters.

Mononuclear Nonheme High‐Spin (S=2) versus Intermediate‐Spin (S=1) Iron(IV)–Oxo Complexes in Oxidation Reactions

AbstractMononuclear nonheme high‐spin (S=2) iron(IV)–oxo species have been identified as the key intermediates responsible for the C−H bond activation of organic substrates in nonheme iron enzymatic reactions. Herein we report that the C−H bond activation of hydrocarbons by a synthetic mononuclear nonheme high‐spin (S=2) iron(IV)–oxo complex occurs through an oxygen non‐rebound mechanism, as previously demonstrated in the C−H bond activation by nonheme intermediate (S=1) iron(IV)–oxo complexes. We also report that C−H bond activation is preferred over C=C epoxidation in the oxidation of cyclohexene by the nonheme high‐spin (HS) and intermediate‐spin (IS) iron(IV)–oxo complexes, whereas the C=C double bond epoxidation becomes a preferred pathway in the oxidation of deuterated cyclohexene by the nonheme HS and IS iron(IV)–oxo complexes. In the epoxidation of styrene derivatives, the HS and IS iron(IV) oxo complexes are found to have similar electrophilic characters.

ChemInform Abstract: Lewis Acid Coupled Electron Transfer of Metal—Oxygen Intermediates

AbstractReview: 102 refs.

Lewis Acid Coupled Electron Transfer of Metal-Oxygen Intermediates.

Redox-inactive metal ions and Brønsted acids that function as Lewis acids play pivotal roles in modulating the redox reactivity of metal-oxygen intermediates, such as metal-oxo and metal-peroxo complexes. The mechanisms of the oxidative CH bond cleavage of toluene derivatives, sulfoxidation of thioanisole derivatives, and epoxidation of styrene derivatives by mononuclear nonheme iron(IV)-oxo complexes in the presence of triflic acid (HOTf) and Sc(OTf)3 have been unified as rate-determining electron transfer coupled with binding of Lewis acids (HOTf and Sc(OTf)3 ) by iron(III)-oxo complexes. All logarithms of the observed second-order rate constants of Lewis acid-promoted oxidative CH bond cleavage, sulfoxidation, and epoxidation reactions of iron(IV)-oxo complexes exhibit remarkably unified correlations with the driving forces of proton-coupled electron transfer (PCET) and metal ion-coupled electron transfer (MCET) in light of the Marcus theory of electron transfer when the differences in the formation constants of precursor complexes were taken into account. The binding of HOTf and Sc(OTf)3 to the metal-oxo moiety has been confirmed for Mn(IV) -oxo complexes. The enhancement of the electron-transfer reactivity of metal-oxo complexes by binding of Lewis acids increases with increasing the Lewis acidity of redox-inactive metal ions. Metal ions can also bind to mononuclear nonheme iron(III)-peroxo complexes, resulting in acceleration of the electron-transfer reduction but deceleration of the electron-transfer oxidation. Such a control on the reactivity of metal-oxygen intermediates by binding of Lewis acids provides valuable insight into the role of Ca(2+) in the oxidation of water to dioxygen by the oxygen-evolving complex in photosystem II.

Secondary deuterium isotope effects on olefin epoxidation by cytochrome P-450

Secondary deuterium isotope effects have been determined for the epoxidation of p-phenylstyrene (1a) and p-methylstyrene (1b) by cytochrome P-450 of rat liver microsomes. With both substrates there is an inverse isotope effect of 7 per cent/deuterium (i.e. k H k D = 0.93 ) at C α of the olefin, but no isotope effect is observed at C β. The epoxidation of (1a) by m-chloroperbenzoic acid has previously been shown to be accompanied by an inverse secondary isotope effect of 9 if per cent/deuterium at C β, with no detectable isotope effect at C α. Thus in both the enzymatic (P-450) and non-enzymatic (peracid) epoxidation of styrene derivatives, the oxygen atom is transferred to the vinyl group in an asymmetric non-concerted fashion. However, the fact that the isotope effects for these two systems are reversed, together with previous comparisons of substituent effects on the two reactions, suggests that there is little mechanistic similarity between cytochrome P-450 enzymes and organic peracids as chemical models for these enzymes.