Aerobic oxidation of olefins

Textbook chemistry (297,298) teaches that palladium is the preferred catalyst for aerobic oxidation of olefins. When water is the solvent, nucleophilic water addition to coordinated olefins is the key step in the so-called Wacker cycle. Wacker oxidation occurs regiospecifically because a carbonyl group is formed at that carbon atom of the double bond where the nucleophile in a Markovnikov-like addition would enter. The Wacker reaction thus yields methylketones from primary alkenes ... 

In the present work zeoUte-encapsulated Fe-phthalocyanine (FePc) and Co- salophen (CoSp) catalysts, synthesized by different methods, were used as oxygen activating catalysts for the aerobic oxidation of olefins in a triple catalytic system. 

Several metal macrocycles, like iron phthalocyanine and cobalt salophen were tested in these palladium-catalyzed aerobic oxidation of olefins and dienes. These tnacrocycles were able to activate the molecular oxygen, but in the homogeneous system several problems have arised, such as poor solubility, self-degradation and the difficulty to reuse theses complexes. A... 

Groves, J. T. Quinn, R. Aerobic oxidation of olefins with ruthenium porphyrin catalysts. j. Am. Chem. Soc. 1985, 107, 5790-5792. 

Interestingly, dinuclear Pt systems have long been known to allow for catalytic aerobic oxidation of olefins leading to the corresponding olefin oxides and carbonyl compounds [38], Formation of epoxides, in particular, was thought to be a result of an intramolecular C(sp )-0 attack similar to the one in Fig. 13 where the oxygen atom of a p-hydroxoaUcyl intermediate attacks the metal(III)-bound carbon atom (Fig. 14). No studies of C-O reductive elimination have been performed for these systems. 

Some aerobic oxidation reactions progress effectively in SCCO2 without a catalyst. Aerobic oxidation of olefins (e.g. cw-cyclooctene and (/f)-(-F)-limonene) in the presence of aldehydes (e.g. 2-methyl-propionaldehyde) in SCCO2 (d = 0.75 g/mL) gave the corresponding epoxides without a catalyst. It is speculated that the stainless steel from autoclave walls triggered the formation of acylperoxy radicals from the aldehyde and oxygen, and the reaction proceeded via a non-catalytic radical... 

It is increasing interested in the utilization of heteropoly compounds as catalysts for the oxidation of various organic compounds. Recently, we have found that the mixed addenda heteropolyoxometallates such as (NH4)5H4PV0Mo0O4o 6H2O (PV0MO0) was efficient catalysts for the aerobic oxidation of olefinic compounds in the presence of isobutyraldehyde. We now present here the direct oxidation of amines and hydrocarbons with molecular oxygen by PV0MO0 catalyst. 

New Au C materials have been obtained using a nanocasting method, starting form preliminary functionalized silicas. Excellent dispersions were obtained, with Au particles partially embedded in carbon walls. This route is very promising for the preparation of catalysts for the aerobic oxidation of olefins in the liquid phase. 

The dihydroxylation of olefins with an osmium catalyst also utilizes chiral tertiary amine ligands to achieve high yields and enantioselectivity. Soon after Krief and coworkers reported on the coupled 02/PhSeCH2Ph oxidation [34], Bel-ler and coworkers discovered a direct 02-coupled catalytic aerobic oxidation of olefins was possible using a phosphate-buffered pH 10.4 solution (Scheme 5.21) [69]. Under increased pressure with air rather than O2, the catalyst remains active and a TOP of 40 h is possible. This system does not quite achieve as high an enantioselectivity as the AD-Mix methods [70]. 

However, all these systems suffer from high concentrations of chloride ion, so that substantial amounts of chlorinated by-products are formed. For these reasons there is a definite need for chloride- and copper-free systems for Wacker oxidations. One such system has been recently described, viz., the aerobic oxidation of terminal olefins in an aqueous biphasic system (no additional solvent)... 

A number of metal macrocycles were tested in the aerobic palladium-catalyzed oxidation of olefins and alcohols [3,4],... 

The group of Masui first attempted the direct epoxidation of olefins by using oxygen and NHPI with metalloporphyrins, but they obtained poor results [15]. Ishii and coworkers proposed two different methods. In the first protocol [16,17], the epoxidizing agent is obtained in situ by the aerobic oxidation of a suitable alcoholic (benzhydrol) compound in the presence of catalytic amounts of NHPI. The resulting oxidant, which is not able to promote the epoxidation by itself, is then activated in the presence of an olefin by catalytic amounts of hexafluoroacetone (HFA) (Scheme 6.1). 

TABLE 6.3 Epoxidation of olefins by aerobic oxidation of acetaldehyde, catalyzed by NHPI... 

Vapor-phase aerobic oxidations of lower olefins, e. g. propylene to acrolein or acrylic acid and isobutene to methacrolein or methacrylic acid, are well-established bulk chemical processes [1,2], They are usually performed over oxidic catalysts, such as bismuth molybdate or heteropoly compounds, although the scope of these allylic oxidations is limited to olefins that cannot form 1,3-dienes via oxidative dehydrogenation. Thus 1- and 2-butene are converted to butadiene, and methylbutenes to isoprene, and with higher olefins complex mixtures result from further oxidation. Hence, such methodologies are not relevant in the context of fine chemicals. 

Iron phthalocyanine encapsulated in zeolites was used as oxygen activating catalysts in the triple catalytic aerobic oxidation of hydroquinone to benzoquinone, in the allylic oxidation of olefins and in the selective oxidation of terminal olefins to ketones. The catalyst proved active in the above reactions. It is stable towards self-oxidation and can be recovered and reused. 

Macrocyclic metal complexes have recently attracted attention as possible oxygen activating catalysts in oxiciation reactions [2-5]. In one approach they are used as oxygen activating components in a triple catalytic system (Scheme 1) for oxidation of olefins [4,5] and alcohols [6]. This leads to very mild reactions reminiscent of aerobic processes occurring in living organisms. 

Khusnutdinova JR, Newman L, Zavalij PY et al (2008) Direct C(ip )-0 reductive elimination of olefin oxides from Pt" -oxetanes prepared by aerobic oxidation of Pt olefin derivatives (Olefin = cw-Cyclooctene, Norbomene). J Am Chem Soc 130 2174—2175... 

After screening several reductants in the aerobic epoxidation of olefins catalyzed by nickel(II) complexes, it was found that an aldehyde acts as an excellent reductant when treated under an atmospheric pressure of molecular oxygen at room temperature (Scheme 6). Similar reactions have been reported in the patents. Propylene was monooxygenated into propylene oxide with molecular oxygen in the coexistence of metal complexes and aldehyde such as acetaldehyde " or crotonaldehyde, but the conversion of olefin and the selectivity of epoxide were never reached satisfactory levels. Recently, praseodymium(III) acetate was also shown to be an effective catalyst for the aerobic epoxidation of olefins in the presence of aldehyde. ... 

Several efficient oxidation reactions with molecular oxygen were developed using transition-metal complexes coordinated by variuos ligands in combination with apprOTriate reductants. Recently, it was found that cyclic ketones such as 2-methylcyclohexanone and acetals of aldehyde such as propionaldehyde diethyl acetal were effectively employed in aerobic epoxidation of olefins catalyzed by cobalt(II) complexes. In the latter case, ethyl propionate and ethanol were just detected in nearly stoichiometric manner as coproducts (Scheme 12), therefore the reaction system is kept under neutral conditions during the epoxidation. 

Figure 7.13 Palladium-catalyzed aerobic oxidation of terminal olefins in water.

In 1984, Groves and Quinn reported the formation of a trans-dioxo-ruthenium(VI) porphyrin complex (5) by the reaction of Ru (TMP)CO with either mCPBA or iodosylbenzene [168]. 5 is stable even at room temperature as a diamagnetic compound, thus, NMR spectrum of 5 can be readily available to characterize the structure. The infrared spectrum of 5 showed a strong band at 821 cm" assigned to vru=0 [168]. The most interesting feature of 5 is aerobic epoxidation of olefins, i.e., in the presence of 5, olefins are oxidized by consuming O2 [169]. Further, they found Ru(II) porphyrins catalyzed the cis-trans isomerization of epoxides under mild conditions [170]. Che et al also prepared tr n.s-dioxo-Ru (OEP) complexes in the reaction of Ru (OEP)CO and... 

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