Cationic methyl complexes of rhodium(III): synthesis, structure, and some reactions

Abstract

Cationic methyl complex of rhodium(III), trans-[Rh(Acac)(PPh 3) 2(CH 3)(CH 3CN)][BPh 4] ( 1) is prepared by interaction of trans-[Rh(Acac)(PPh 3) 2(CH 3)I] with AgBPh 4 in acetonitrile. Cationic methyl complexes of rhodium(III), cis-[Rh(Acac)(PPh 3) 2 (CH 3)(CH 3CN)][BPh 4] ( 2) and cis-[Rh(BA)(PPh 3) 2(CH 3)(CH 3CN)][BPh 4] ( 3) (Acac, BA are acetylacetonate and benzoylacetonate, respectively), are obtained by CH 3I oxidative addition to rhodium(I) complexes [Rh(Acac)(PPh 3) 2] and [Rh(BA)(PPh 3) 2] in acetonitrile in the presence of NaBPh 4. Complexes 2 and 3 react readily with NH 3 at room temperature to form cis-[Rh(Acac)(PPh 3) 2(CH 3)(NH 3)][BPh 4] ( 4) and cis-[Rh(BA)(PPh 3) 2(CH 3)(NH 3)][BPh 4] ( 5), respectively. Complexes 1– 5 were characterized by elemental analysis, 1H and 31P{ 1H} NMR spectra. Complexes 1, 2, 3 and 4 were characterized by X-ray diffraction analysis. Complexes 2 and 3 in solutions (CH 2Cl 2, CHCl 3) are presented as mixtures of cis-(PPh 3) 2 isomers involved into a fluxional process. Complex 2 on heating in acetonitrile is converted into trans-isomer 1. In parallel with that isomerization, reductive elimination of methyl group with formation of [CH 3PPh 3][BPh 4] takes place. Replacement of CH 3CN in complexes 1 and 2 by anion I − yields in both cases the neutral complex trans-[Rh(Acac)(PPh 3) 2(CH 3)I]. Strong trans influence of CH 3 ligand manifests itself in the elongation (in solid) and labilization (in solution) of rhodium–acetonitrile nitrogen bond.