OH insertion

Despite the considerable progress made in the few years in which anodic insertion/extraction films have been known, neither film compositions, film properties, nor electrochemical reactions are sufficientiy well characterized. There have been disagreements, as indicated for h-IrO and h-NiO in Table 2, as to whether is being extracted or OH inserted during coloration. The general problem is best illustrated by the important example of Pmssian blue. Early work (47—50) resulted in two different sets of equations for electrochromic reduction ... 

Reactions of the hydrido(hydroxo) complex 2 with several substrates were examined (Scheme 6-14) [6]. The reactions are fairly complicated and several different types of reachons are observed depending on the substrate. Methyl acrylate and small Lewis bases such as CO, P(OMe)3, BuNC coordinate to the five-coordinated complex 2 affording the corresponding six-coordinate complexes. In reactions with the unsaturated bonds in dimethylacetylenedicarboxylate, carbon dioxide, phenylisocyanate indications for the addition across the O-H bond but not across the Os-OH bond were obtained. In reactions with olefins such as methyl vinyl ketone or allyl alcohol, elimination of a water molecule was observed to afford a hydrido metalla-cyclic compound or a hydrido (ethyl) complex. No OH insertion product was obtained. 

A number of minima corresponding to oxonium ylides and H-bonded structures were found on the potential-energy surface for reaction of singlet carbenes with water and alcohols." Laser flash photolysis revealed that the rates of reaction between cyclopentadienylidene or fluorenylidene and alcohols increased with alcohol acidity and had linear Bronsted plots with slopes of 0.061 and 0.082, respectively.100 These results point to protonation with a very early transition state or to concerted OH insertion. For tetrachlorocyclopentadienylidene, the results showed that ylide formation (100) is predominant. 

MCI reactions of alkynyliodonium salts with enolates derived from active methylene compounds containing two acidic CH bonds follow a divergent course that leads to furans, presumably via carbenic insertion into enolic OH bonds (equation 122)28. In the reaction of acetylacetonate ion with the l-decynyl(phenyl)iodonium ion, CH insertion is competitive with OH insertion (equation 123)28. 

Ethoxy-methoxy-phenyl- E14a/1, 582 [R-C(OR) = N-NH-S02-R + R-OH] E19b, 1653 (Carben — OH-Insertion)... 

Ethoxy-propyloxy-phenyl-E19b, 1653 (Carben-OH-Insertion)... 

To synthesize ethanol more effectively from CO2, the Cu-Zn-Al-K mixed oxide catalyst was combined with the Fe-based catalyst. An F-T type Fe-Cu-Al-K mixed oxide catalyst, which has been developed already in our laboratory [1], converted CO2 to both ethanol and hydrocarbons, while the Cu-based catalyst converted CO2 to CO and methanol with high selectivity. Through the combination of these two catalysts, the three functions were harmonized C-C bond growth, partial reduction of CO2 to CO, and OH insertion to the products. Furthermore, combination catalyst of Fe- and Cu-based ones was modified with both Pd and Ga to maintain the desirable reduced state of the metal oxides during the reaction. As the result, the space-time yield of ethanol was enhanced to 476 g/l-h at SV=20,000 h ... 

Performances of each catalyst is shown in Figure 1. The ethanol synthesis catalyst (Fe-based catalyst. Cat. 1) have both functions of F-T synthesis and alcohol synthesis. The main products were hydrocarbons, ethanol and methanol. With the increase of CO in reaction gas, the yield of ethanol increased[l]. The Cu-based catalyst (Cat. 2) converted CO2 to CO with selectivity more than 70% at a temperature range from 270 to 370°C, and other products were methanol and a slight amount of methane. Ethanol and C2 hydrocarbons were not produced. In order to harmonize the three functions, C-C bond growth, partial reduction of CO2 to CO, and OH insertion to products, the mixed ratio of Fe-based catalyst to Cu-based catalyst was coordinated at the range from Cu/Fe =... 

Photolysis of (o-allyloxy)phenyldiazomethanes 277 in methanol was found to give OH insertion products 278 along with cyclopropane derivative 279. Product distributions are strongly affected by triplet sensitization in contrast to those of analogous intermolecular reactions (91JA3925). 

Excess diazomethane has been used to convert phenols to methyl ethers in the presence or absence of acids . Employment of transition metal derivatives, typically Rh2(OAc)4 and recently CHsReOs , allows one to react functionalized diazo compounds in an intramolecular or intermolecular 0-aUtylation (equation 13). The stability of diazo compounds derived from active methylene compounds toward OH insertion was compared... 

Optimized Geometries (A) and Energies (kcal/mol) for the Singlet NiH(OH) Insertion... 

Substrate probes have aided mechanistic understanding of the key C— H activation step in the MMOH reaction cycle. Chiral alkanes and radical-clock substrate probes " " were used to discriminate between radical recoil/rebound and nonsynchronous concerted insertion pathways. A short lifetime (< 150 fs) estimated for the putative radical species derived from cyclopropane-based radical-clock substrates favors the latter process,whereas partial racemization of chiral ethane substrate is consistent with the former scenario. A unifying model was proposed, in which both recoil/rebound and concerted reaction channels are available for a bound radical intermediate and the partitioning between each trajectory is dependent on the substrate. Formation of carboca-tion-derived products from certain probes implicates yet another route involving a formal OH+ insertion.Participation of multiple species capable of oxygen transfer is an emerging mechanistic view in both heme and nonheme systems, as exemplified by the studies of cP450s and their synthetic models.Scheme 3 depicts various density functional theory (DFT) models of MMOHq and their computed reaction pathways, which are reviewed in detail elsewhere. 

In studies on superacid-catalyzed oxyfunctionalization of methane it has been found that hydrogen peroxide in superacidic media gives methyl alcohol with very high (> 95%) selectivity . Electrophilic OH insertion by protonated hydrogen peroxide in the C—H... 

The use of ylides as carbene precursors constitutes a novel original approach to control or extend carbenic reactions. The thiophenium ylide XXVIII prepared by catalytic decomposition of methyl diazomalonate in the presence of dichloro-2,5-thiophene has been successfully applied as a carbene equivalent or precursor to the cyclopropanation of olefins, the OH insertion and the C-H insertion reaction in activated arenes [112, 113] the catalyst being rhodium(II) acetate or copper(II) acetylaceto-nate. 

In my laboratory, we have used a Teflon covered YSI-5331 platinum/silver electrode with a half-saturated KCl solution as electrolyte (Yellow Springs Instrument Co., Yellow Springs, OH) inserted into a 1.8 mL incubation chamber (Gilson Medical Electronics, Inc., Middleton, WI) in such a way that it is possible to complete a measurement in less than five minutes. Under these conditions, it is possible to make rapid, multiple determinations under the same experimental conditions, thereby enhancing reproducibility of the data. 

This original and promising pathway has been successfully applied to typical carbene reactions (cyclopropanation of olefins, OH insertion, C—H insertion into activated arenes) [109,110]. 

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