Lewis Acids and Lewis Acid-Functionalized Ligands in Rhodium-Catalyzed Methyl Acetate Carbonylation

The application of Lewis acids and Lewis acid-functionalized ligands as activators for methyl acetate in the rhodium-catalyzed carbonylation of methyl acetate to acetic anhydride has been investigated. The reaction of methyl acetate with B(C6F5)3 results in the formation of the adduct [MeOAc·B(C6F5)3]. The combination of this adduct with [Rh(OAc)(CO)2]2 results in a transfer of the Lewis acid to the rhodium complex, rather than an anticipated oxidative addition reaction. In a second approach, novel Lewis acid-functionalized rhodium(I) complexes [Rh(CO)Cl(BPP)], [Rh(CO)2(BPP)]SbF6, and [Rh(MeCN)2(BPP)]SbF6 (BPP = PhB(C6H4PPh2)2) have been prepared. The lack of reactivity of [Rh(CO)2(BPP)]SbF6 toward MeOAc has shown that the rhodium–boron interaction is too strong for activation of methyl acetate, and no carbonylation activity was observed under the conditions used.