Tetramethyl(perfluoroalkyl)cyclopentadienyl rhodium(III) complexes containing phosphorus and nitrogen monodentate donors. Crystal structure of [(eta(5)-C5Me4C4F9)Rh(PPr3i)Cl-2]
Abstract
Cleavage of a double l-halo bridge in complexes [(C5Me4CnF2n+1)RhX2]2 (n = 4, 6; X = Cl, Br) with two-electron monodentate Pdonors 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 1/2ðg5-C5Me4C4F9ÞRhðPPri 3ÞCl2 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 DG = 14.8 +- 0.1 kcal mol1 at 27 C and DG = 14.9 +- 0.1 kcal mol1 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.