Carbonylation of alkanes

Catalytic carbonylation of alkanes, RH, proved possible via CH activation catalyzed by RhCl(CO)(PMe3)2 under irradiation. In this reaction, the alkyl hydride intermediate undergoes CO insertion, followed by reductive elimination of the aldehyde, RCHO. 

The HF-SbFs system works well in the Gattermann-Koch formylatlon of arenes and the Koch carbonylation of alkanes [54]. For instance, biphenyl is diformylated in HF-SbFs-CO to afford 4,4 -diformylbiphenyl as a major isomer (Scheme 14.20). The carbonylation of alkanes with C5-C9 carbon atoms in the HF-SbFs-CO system affords mixtures of C3-C8 carboxylic acids after hydrolysis of the generated secondary carbenium ions [55]. Successive treatment of methylcyclopentane with CO in HF-SbF and with water produces cyclohexanecarboxylic acid as a major product (Scheme 14.21) [56]. It seems that a tertiary methylcyclopentyl cation readily isomerizes to the more stable cyclohexyl cation before being trapped by CO. Bicyclic a, -unsaturated ketones are functionahzed by HF-SbF or FSOsH-SbFs under a CO atmosphere to give saturated keto esters after methanolysis (Scheme 14.22) [57]. Alcohols with short carbon chains also react with CO in HF-SbFs to give the corresponding methyl esters [58]. y-Butyrolactones are carboxy-lated under the same conditions to afford 1,5-dicarboxyhc acids [59]. 

Early hydrocarboxylation-hydroesterification literature deals largely with Ni and Co as activating metals, but during the last three decades the noble group VIII metals, especially Pd, Pt, Rh and Ir, have been studied. Similarly, the use of pyridine promoted Co catalysts has been optimized. This section will not include references to metals of lesser or more specialized activity, such as Fe, Ru and Cu(I), nor strong acid catalysis, nor oxidative carbonylation of alkanes. 

Reaction of Ruthenium Carbonyls with Alkyl Radicals Boese and Goldman reported that in the presence of aryl ketones, d8 metal carbonyls such as Ru(CO)3(dmpe) mediate photocatalytic carbonylation of alkanes via a free radical mechanism.161 The activity was proposed to be initiated by the addition of an alkyl radical to the metal carbonyl and the formation of a metal-acyl radical intermediate. The transition states and the products of the reaction between alkyl radicals and ruthenium carbonyls were studied utilizing the B3LYP level of theory.162 The methyl addition to a carbonyl of Ru(CO)5 or Ru(CO)3(dmpe) was computed to be about 6 kcal/mol more exothermic than addition to free CO. 

Superacid DF-SbFs induces protium-deuterium exchange in isobutane [54b]. Strong acids (BF3, BFj-HjO, HF-BFj, CF3SO3H)catalyze carbonylation of alkanes including methane by carbon monoxide [54c], whereas sulfuric acid can induce carbonylation of iso- and cycloalkanes [54e,d]. In both cases, carboxylic acids are obtained. The elimination of molecular hydrogen from alkyl can occur (see a recent theoretical study of the Hz elimination from CzHs [54f]). 

In parallel with progress on the oxidation of alkanes to alcohols and alkyl halides have been reports on the oxidative carbonylations of alkanes and arenes to form carboxylic acids. Fujiwara showed that stoichiometric amounts of arylpalladium acetates formed from the reaction of Pd(OAc)j with arenes and that the resulting arylpalladium complex reacts with CO in acetic acid to form aromatic acids (Equation 18.22). When O, BuOOH, alkyl halides, or K SPj were added as oxidant, the reaction became catalytic in palladium, and benzoic acids were generated from benzene, CO, and the oxidant in the presence of palladium acetate (Equation 18.23). Tl-ie highest yields were obtained with KjSPg as oxidant. Sen has reported related oxidation reactions in acidic media. - ... 

Sulfated zirconia catalysts can also be used for carbonylation of alkanes. Between 1931 and 1944, it was found that small alkanes were carbonylated with CO in the presence of anhydrous aluminum chloride and that under CO pressure higher than 100 atm and elevated temperature, propane and butanes were converted in a mixture of ketones and carboxylic acids and esters in the presence of... 

Carbonylation of Alkanes. It has been reported that propane and isobutane undergo carbonylation on zeolite H-ZSM-5 in accordance with the following scheme (100) ... 

The CO insertion into nitrite-substituted alkoxy-palladium bonds to give a Pd(COORONO)2 species followed by reductive elimination of dinitrite-substituted oxalate ester was proposed as a mechanism in this Pd-catalyzed carbonylation of alkane dinitrite (Scheme ll).[ ],[vo]... 

Scheme 6.11 Carbonylation of alkanes with CO and O2 catalyzed by NHPI.

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