Cyclohexane transition metal catalysis

Oxidation catalysts are either metals that chemisorb oxygen readily, such as platinum or silver, or transition metal oxides that are able to give and take oxygen by reason of their having several possible oxidation states. Ethylene oxide is formed with silver, ammonia is oxidized with platinum, and silver or copper in the form of metal screens catalyze the oxidation of methanol to formaldehyde. Cobalt catalysis is used in the following oxidations butane to acetic acid and to butyl-hydroperoxide, cyclohexane to cyclohexylperoxide, acetaldehyde to acetic acid and toluene to benzoic acid. PdCh-CuCb is used for many liquid-phase oxidations and V9O5 combinations for many vapor-phase oxidations. 

Liquid phase oxidation of hydrocarbons by molecular oxygen forms the basis for a wide variety of petrochemical processes,3 "16 including the manufacture of phenol and acetone from cumene, adipic acid from cyclohexane, terephthalic acid from p-xylene, acetaldehyde and vinyl acetate from ethylene, propylene oxide from propylene, and many others. The majority of these processes employ catalysis by transition metal complexes to attain maximum selectivity and efficiency. 

The conversion of cyclohexanes to aromatics is a classical dehydrogenation reaction which will readily take place on many transition metals and metal oxides. On chromia-alumina Herington and Eideal (S) have demonstrated the occurrence of cyclo-olefin intermediate products. Weisz and Swegler 25) have demonstrated the effect on benzene yield of allowing early diffusional escape of cyclo-olefin from the porous catalyst particle. Prater et al. 26) have developed evidence that cyclohexene occurs as a quasi-intermediate in aromatization catalysis over platinum catalyst also, although at a smaller concentration, because of a larger ratio of effective rate constants fe/Zci in the scheme... 

However, a totally different catalysis is observed when the protons are not neutralized, so that transition metal clusters and Bronsted sites co-exist in the same catalyst. For such bifimctional catalysts, for instance Pd/HNaY or Pd/HY, ring opening is a minor side reaction, but ring-enlargement becomes the major reaction pathway, with benzene and cyclohexane as the predominant reaction products [28. 29]. Apparently, a carbenium ion has been formed from MCP, it is isomerized via the fused cyclopropane ring to the cyclohexylcarbocation, as depicted in scheme 9 ... 

Tosylimino)iodobenzene (PhINTs) is a relatively newer tool for catalysis compared to iodosylbenzene, being first reported in 1975 [69]. Nevertheless, applications of this reagent in transition metal-catalyzed reactions have become an important class of reactions in their own right. In 1982, it was discovered that manganese or iron porphyrins could catalyze the insertion of the NTs from PhINTs into a CH bond of cyclohexane (3) [70] ... 

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