Cobalt complexes reactions with aromatic hydrocarbons

They noted that in dimethoxyethane or in iso-octane (path a), the major product was dicarbonylcyclopentadienylcobalt (2) which must arise as a result of a retro Diels-Alder reaction of the norbornadiene (which would lead to the formation of acetylene and cyclopentadiene). When the solvent was changed to an aromatic hydrocarbon such as benzene or toluene (path b), the major cobalt-containing product was shown to be a complex derived from Co4(CO)i2, with three CO ligands on an apical cobalt being replaced by a molecule of the aromatic solvent (3). The group noted that they were also obtaining hydrocarbon and ketonic products derived from norbornadiene, acetylene and carbon monoxide .1,2... 

Cobalt.—Aromatic hydrocarbon hydrogenations with a discrete metal complex have now been achieved for the first time. Thus hydrogenation of benzene to cyclohexane proceeds slowly at 25 °C and < 760 mmHg pressure in the presence of [Co( y -C3HB)- P(OMe)3)3]. Alkylbenzenes are converted into alkylcyclohexanes, anisole into methoxycyclohexane, and ethylbenzoate into ethyl cyclohexenylcarboxylate. The suggested mechanism of reaction is summarized in Scheme 14. ... 

Hydrogen sulphide reacts reversibly with many unsaturated or aromatic hydrocarbons, in the presence of mixed oxide catalysts, to produce thiophens these may be polycyclic, according to the complexity of the starting hydrocarbon. This reaction, which is believed to be the source of many of the sulphur compounds found in crude oil, has been studied in particular by Klemm and his co-workers, who have now published their detailed results. A typical example is the formation of the isomeric benzonaphthothiophens (15) and (16) from the reaction of 2-phenylnaphthalene (14) with hydrogen sulphide over a sulphided cobaltous oxide-molybdic oxide-alumina catalyst at 450—630 in a flow system. 

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