Reductive Elimination of Anhydrides from Anionic Iodo Acetyl Carboxylato Rhodium Complexes

Abstract

AbstractThe first part of this study is devoted to the search for improved and highly efficient synthetic procedures for the preparation of rhodium carbonyl precursors, and the second part to the production of acetyl derivatives. Microwave heating of a methanol solution of RhCl3·xH2O for 10 min under 5–10 bar CO produces the complex [H]+[RhCl2(CO)2]–, which is quantitatively converted into the dimeric complex [Rh2(μ‐Cl)2(CO)4] (1) by rapid solvent evaporation under a stream of CO. The treatment of1with NaI or AgOAc under a CO atmosphere gives [Rh2(μ‐I)2(CO)4] (2) and [Rh2(μ‐OAc)2(CO)4] (3), respectively. The complexcis‐[PPN][RhI2(CO)2] (4) is prepared in high yield by the reaction of RhI3withN,N‐dimethylformamide (DMF) at 160 °C under CO followed by metathesis of the [NH2Me2]+cation with [bis(triphenylphosphoranylidene)ammonium]chloride ([PPN]Cl). The analoguecis‐[PPN][Rh(OAc)2(CO)2] (5) is obtained by reaction of4with AgOAc. Complex4reacts with neat CH3I to afford quantitatively the dimeric rhodium(III) complex [PPN]2[Rh2(μ‐I)2I4(COMe)2(CO)2] (7). The cleavage of the iodo bridging ligands in7occurs readily with CO, pyridine or 1,2‐dimethylimidazole to give [PPN][RhI3(COMe)(CO)2] (8), [PPN][RhI3(COMe)(CO)(Py)] (9) and [PPN][RhI3(COMe)(CO)(1,2‐MeIm)] (10), respectively, whereas the reactions with the chelating 2‐acetylpyridine and methyl‐2‐picolinate ligands give the neutral [Rh(COMe)I2(CO)(κ2‐2‐acetylpyridine)] (11) and [Rh(COMe)I2(CO)(κ2‐methyl‐2‐picolinate)] (12) complexes, respectively. The X‐ray crystal structures of4,7(centrosymmetric isomer),8,11and12have been solved. The reductive elimination from7and8in the presence of various carboxylato sources to provide acid anhydrides is described.