Tetramethyl(perfluoroalkyl)cyclopentadienyl rhodium(III) complexes containing phosphorus and nitrogen monodentate donors. Crystal structure of [(η(5)-C5Me4C4F9)Rh(PPr(i)3)Cl-2]
Abstract
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-eletron donor). In contrast to their Cp* analogs, the pyridine complexes were stable in solution at room temperature.
Crystal structure of [(η5-C5Me4C4F9)Rh(PPr(i)3)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 degrees. 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 Delta G double dagger = 14.8 +/- 0.1 kcal mol(-1) at 27 degrees C and Delta G double dagger = 14.9 +/- 0.1 kcal mol(-1) at 52 degrees 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.