Oxidation unactivated C—H bonds

Why do we want to catalyze a reaction Usually the goal is to make the rate fast enough for the reaction to be performed in a timely and practical manner. For example, C-H bonds in the presence of oxygen alone take an impossibly long time to be converted to alcohols, so a catalyst is needed if we are to efficiently oxidize unactivated C-H bonds. 

As stoich. [Ru(0)((N 0)p7CH3CN it oxidised primary alcohols to aldehydes, secondary alcohols to ketones, alkenes to aldehydes, tetrahydrofuran to y-butyrolactone. Styrene, cis- and tran -stilbenes gave benzaldehyde and adamantane gave 1-adamantol exclusively, while cyclohexanol gave cyclohexanone, suggesting that the complex is an effective oxidant for unactivated C-H bonds [636]. Immobilisation of the catalyst within Nation films on a basal plane pyrohtic graphite electrode was achieved, but the... 

Oxidation Catalyzed by Metalloporphyrins. Much attention has been devoted to the metal-catalyzed oxidation of unactivated C—H bonds in the homogeneous phase. The aim of these studies is to elucidate the molecular mechanism of enzyme-catalyzed oxygen atom transfer reactions. Additionally, such studies may eventually allow the development of simple catalytic systems useful in functionalization of organic compounds, especially in the oxidation of hydrocarbons. These methods should display high efficiency and specificity under mild conditions characteristic of enzymatic oxidations. 

The a-keto acid-dependent enzymes [206-208] catalyze a diverse array of reactions (Figure 26) involving functionalization of an unactivated C—H bond concomitant with the oxidative decarboxylation of a keto acid. For the hydroxylation... 

The chemical reactivity most associated with dioxiranes is the electrophilic transfer of oxygen to electron-rich substrates (e.g., epoxidation, N-oxidation) as well as oxygen insertion reactions into unactivated C-H bonds. The reactivity-selectivity relationships among these types of reactions has been examined in depth by Curci. The reaction kinetics are dependent upon a variety of factors, including electron-donor power of the substrate, electrophilicity of the dioxirane, and steric influences (95PAC811]. 

Fig-i Mechanism for Ru04-mediated oxidation of unactivated C-H bonds... 

The early functional models for this oxidation chemistry were rather simple Udenfriend used iron(II), EDTA, ascorbic acid (as the reducing agent) and O2 to hydroxylate arenes, while Hamilton showed that the same system hydroxylates unactivated C—H bonds (e.g. androsten-3-ol-17-one is converted to androsten-3,7-diol-17-one). Mimoun developed the use of an iron(II)/PhNHNHPh/ H1CO2H/O2 system which is also active for alkane hydroxylation. Curiously, other metals [copperfll), manganese(II), vanadium(II), cobalt(II)] are also active. In the hydroxylation of arenes, an arene oxide is believed to be the intermediate in P-450 dependent systems, because a 1,2-shift of a proton in the arene, the NIH shift is often observed. Neither the Udenfriend nor Mimoun models show such a shift, however. 

Oxidation of Unactivated C—H Bonds QaC + CjHn -------------- CI3CH + CeHn ... 

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