Trifluoroacetylacetonate rhodium(III) methyl complexes, cis-[Rh(TFA)(PPh3)2(CH3)(L)][BPh4] and cis-[Rh(TFA)(PPh3)2(CH3)(I)] (L = CH3CN, NH3, pyridine), in comparison with their acetylacetonate analogs

The oxidative addition of CH3I to planar rhodium(I) complex [Rh(TFA)(PPh3)2] in acetonitrile (TFA is trifluoroacetylacetonate) leads to the formation of cationic, cis-[Rh(TFA)(PPh3)2(CH3)(CH3CN)][BPh4] (1), or neutral, cis-[Rh(TFA)(PPh3)2(CH3)(I)] (4), rhodium(III) methyl complexes depending on the reaction conditions. 1 reacts readily with NH3 and pyridine to form cationic complexes, cis-[Rh(TFA)(PPh3)2(CH3)(NH3)][BPh4] (2) and cis-[Rh(TFA)(PPh3)2(CH3)(Py)][BPh4] (3), respectively. Acetylacetonate methyl complex of rhodium(III), cis-[Rh(Acac)(PPh3)2(CH3)(I)] (5), was obtained by the action of NaI on cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] in acetone at −15 °C. Complexes 1–5 were characterized by elemental analysis, 31P{1H}, 1H and 19F NMR. For complexes 2, 3, 4 conductivity data in acetone solutions are reported. The crystal structures of 2 and 3 were determined. NMR parameters of 1–5 and related complexes are discussed from the viewpoint of their isomerism.

In solutions, cis isomers of cationic complexes cis-[Rh(β-diket)(PPh3)2(CH3)(CH3CN)][BPh4] (β-diket is acetylacetonate or trifluofoacetylacetonate) coexist in dynamic exchange. At low temperature, exchange slows down and the structure of predominant isomer depends on the electronegativity of substituents in the β-diket ligand.Figure optionsDownload as PowerPoint slideHighlights
► Reaction of [RhI(TFA)(PPh3)2] with CH3I yields cis isomers of RhIII methyl complexes.
► Cationic and neutral complexes, cis-[Rh(TFA)(PPh3)2(CH3)(L)], were isolated.
► Methyl ligand in the predominant isomers is placed trans to CF3 substituent.