Rhodium(III) cationic methyl complexes containing dimethylformamide ligand, cis-[Rh(β-diket)(PPh3)2(CH3)(DMF)][BPh4] (β-diket = acetylacetonate or benzoylacetonate), in comparison with their acetonitrile analogs

• Complexes cis-[Rh(β-diket)(PPh3)2(CH3)(DMF)][BPh4] are synthesized.
• The cations have a slightly distorted octahedral geometry.
• Peculiar features of complexes in solid-state are unusual long Rh–O(DMF) bond.
• Complexes are fluxional at +20 °C though stereochemically rigid at −70 °C.

The rhodium(III) cationic methyl complexes, cis-[Rh(Acac)(PPh3)2(CH3)(DMF)][BPh4] (1) and cis-[Rh(BA)(PPh3)2(CH3)(DMF)][BPh4] (2) are formed upon reactions of cis-[Rh(β-diket)(PPh3)2(CH3)(MeCN)][BPh4] (β-diket = acetylacetonate, Acac, or benzoylacetonate, BA) with excess of dimethylformamide (DMF) in CH2Cl2 solution at ambient temperature. Complexes 1 and 2 were characterized by elemental analysis, 31P{1H} and 1H NMR spectra, and single crystal X-ray crystallography. The cations of 1 and 2 have slightly distorted octahedral geometry. The “equatorial” plane contains the β-diketonate and two PPh3 ligands; methyl and DMF ligands occupy the axial positions. Peculiar features of complexes 1 and 2 in solid state are: (i) unusually long Rh–O(DMF) bond and (ii) non-symmetrical orientation of the formyl C–H bond in relation to two oxygen atoms of the β-diketonate ligand. The signals from formyl protons in the 1H NMR spectra of 1 and 2 are shifted significantly upfield relatively to free DMF. The hydrogen bonding between formyl proton and one of the β-diketonate oxygen atoms is considered. In solutions, 1 and 2 show dynamic behavior at ambient temperature and keep their solid-state geometry at −70 °C.

The rhodium(III) cationic methyl complexes, cis-[Rh(β-diket)(PPh3)2(CH3)(DMF)][BPh4] (β-diket = Acac or BA), show dynamic behavior in solution at ambient temperature and keep their solid state geometry at −70 °C. Peculiar features of cations are unusual long Rh–O(DMF) bond and non-symmetrical orientation of the formyl C–H bond.Figure optionsDownload as PowerPoint slide