Tetramethyl(perfluoroalkyl)cyclopentadienyl rhodium(III) complexes containing phosphorus and nitrogen monodentate donors. Crystal structure of [(η5-C5Me4C4F9)Rh(PPr3i)Cl2]

Cleavage of a double μ-halo bridge in complexes [(C5Me4CnF2n+1)RhX2]2 (n = 4, 6; X = Cl, Br) with two-electron monodentate P-donors like phosphines or phosphites or monodenate N-donors like pyridine-derived heterocyclic amines gave mononuclear Rh(III) complexes of piano-stool type [(C5Me4CnF2n+1)RhX2L] (L = two-electron donor). Crystal structure of [(η5-C5Me4C4F9)Rh(PPr3i)Cl2] was determined by X-ray diffraction. The compound had a pseudo-tetrahedral ligand arrangement around the Rh atom. The perfluoroalkyl chain was averted from the phosphine ligand but not completely; after projection to the ring plane the P– (ring centroid) –CF2 angle was around 166°. In contrast to their Cp∗ analogs, the pyridine complexes were stable in solution at room temperature. Free rotation of triarylphosphine ligands around Rh–P bond and 2-substituted pyridine ligands around Rh–N bond was hindered, giving the values of ΔG‡ = 14.8 ± 0.1 kcal mol−1 at 27 °C and ΔG‡ = 14.9 ± 0.1 kcal mol−1 at 52 °C for tri(m-tolyl)phosphine and quinoline complexes, respectively, as followed from the analysis of variable temperature NMR spectra. In the 2-methylpyridine complex, the hindered rotation was accompanied by a reversible decoordination of the ligand at higher temperatures.

Rh(III) piano-stool type complexes [(C5Me4CnF2n+1)RhX2L] (n = 4, 6; X = Cl, Br; L = two-electron donor) were prepared, crystal structure of [(η5-C5Me4C4F9)Rh(PPr3i)Cl2] was determined by X-ray. Hindered rotation of triarylphosphine and 2-substituted pyridine ligands around Rh–L bond was observed and analyzed with the help of variable temperature NMR.Figure optionsDownload as PowerPoint slide