Benzoic acid derivatives, role

The synthesis of tctrahydropyranols from the reaction between an aldehyde and a homoallylic alcohol with catalytic amounts of Ce(OTf)3 immobilised in [C4Ciim][PF6] affords the desired product in moderate yield after 12 hours at room temperature, see Scheme 9.18.[64] Addition of one equivalent of benzoic acid as co-catalyst was found to increase the isolated yield, but its role is not yet clear. A beneficial effect of performing the reaction in the ionic liquid is that, contrary to the reaction in chloroform, no ether derivatives were observed. 

More remarkably, structurally well-characterized Phen-containing transition metal complexes have been prepared and further applied in challenging organic transformations. Thus, cationic palladium complexes of t)fpe Pd(phen)2X2 (where X = CF3SO3, PFs, BF4) are very stable and found fairly active in combination with either benzoic acids or phosphorus acids as cocatalysts in the conversion of nitroarenes to the corresponding carbamate derivatives. Extensive studies have evidenced the key role of the nature of counteranion X of such Phen-based catalysts in the reaction outcome and even metaUacycles of type A have been isolated and identified as active intermediates in the reductive carbonyla-tion of nitrobenzene (eq l). ... 

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