Crystallographic and theoretical studies of (η5-C5Me5)Ru(2,4-dimethyl-η5-pentadienyl) and [(η5-C5Me5)Rh(2,4-dimethyl-η5-pentadienyl)][BF4]

The determination of the solid state structure of Cp*Ru(2,4-dimethyl-η5-pentadienyl) (1), where Cp* = pentamethylcyclopentadienyl, fills the gap in the series of previously established structures of closely related compounds. Compound 1 does not exhibit the ideal CS symmetry and its conformation is intermediate between the CS-synperiplanar eclipsed and CS-antiperiplanar arrangements of the ligands. Density functional theory studies indicate that the CS-synperiplanar eclipsed, CS-antiperiplanar, and intermediate conformations of 1 and Cp*Rh(2,4-dimethyl-η5-pentadienyl)+ (2) do not differ by more than a few tenths of 1 kcal/mol. The geometrical features of cation 2 are similar to those of 1, and in both complexes the pentadienyl ligands are not planar. The metal–carbon distances to the Cp* ligands in 1 and 2 are comparable, while the metal–carbon distances to the pentadienyl moiety are somewhat shorter in the Ru complex. A study of the conformational flexibility of the Cp* ligand in 5610 organometallic complexes showed that it usually shields the central metal by 36.2(10)%, provided the metal–centroid(Cp*) distances are normalized to 2.28 Å. The corresponding values in 1 and 2 are 37.2% and 37.4%, respectively.