Rhodium complexes possessing the unidentate anion of 2,4-pentanedione as a ligand; X-ray crystal structure of carbonyl(2,4-pentanedionato-O)bis(tri-isopropylphosphine)rhodium(I)

Abstract

Rhodium complexes having the unidentate anion of 2,4-pentanedione as a ligand have been synthesized by the reaction of [Rh(acac)(CO)₂][Hacac = acetylacetone (2,4-pentanedione)] with highly basic tertiary phosphines. The X-ray crystallographic analysis revealed that the co-ordination chemistry about the Rh atom is square planar with two phosphine ligands in trans positions. The unidentate 2,4-pentanedionate ligand has a trans configuration with respect to the CC bond. Proton n.m.r. studies indicated a singlet resonance for the methine of the pentanedione anion, which is widely accepted as a proof of the cis configuration. In the i.r. spectra absorptions characteristic of the unidentate pentanedionate were observed in the 1 500–1 620 cm^–1 region, but the ketonic absorptions were unusually low for αβ-unsaturated carbonyls.