(η5-Pentamethylcyclopentadienyl)(η6-toluene)ruthenium(II) hexafluoridophosphate

In the title complex, [Ru(C7H8)(C10H15)]PF6, the cation lies on a mirror plane and the anion lies on an inversion center. The distance between the Ru atom and the centroid of the benzene ring is 1.706 (5) Å and the distance between the Ru atom and the cyclopentadienyl ring is 1.811 (5) Å. The crystal structure is stabilized by weak C—H⋯F hydrogen bonds. The H atoms of the methyl groups which lie on the mirror plane are disordered over two sites with equal occupancies.

In the title complex, [Ru(C 7 H 8 )(C 10 H 15 )]PF 6 , the cation lies on a mirror plane and the anion lies on an inversion center. The distance between the Ru atom and the centroid of the benzene ring is 1.706 (5) Å and the distance between the Ru atom and the cyclopentadienyl ring is 1.811 (5) Å . The crystal structure is stabilized by weak C-HÁ Á ÁF hydrogen bonds. The H atoms of the methyl groups which lie on the mirror plane are disordered over two sites with equal occupancies.

Comment
The heterolytic splitting of dihydrogen across a transition metal-amido bond provides an important metal-hydride and a protic amine group for the efficient catalytic homogenous hydrogenation of polar bonds to produce valuable alcohols and amines (Clapham et al., 2004). We are interested in the use of chelating primary amine and N-heterocyclic carbene ligands (C-NH 2 ) that resemble those of the phosphine-amine analogues. Thus, the transmetalation reaction of 1.5 equiv of RuCp*(cod)Cl (cod = 1,5-cyclooctadiene) and [Ni(C-NH 2 ) 2 ] (PF 6 ) 2 in acetonitrile, and subsequent workup in tetrahydrofuran and excess pyridine afforded the active catalyst, [RuCp*(C-NH 2 )(py)]PF 6 ( Fig. 2), for the hydrogenation of polar bonds in basic solution (O et al., 2010). The use of 2 equiv. of RuCp*(cod)Cl and 1 equiv of [Ni(C-NH 2 ) 2 ] (PF 6 ) 2 , with subsequent workup in tetrahydrofuran, toluene and pyridine mixtures, however, afforded selective crystallization of small amounts of title molecule, [Cp*Ru(η 6 -toluene)]PF 6 , as a side product. We report here the crystal structure of the title molecule. The synthesis of such compounds have been reported elsewhere (Fagan et al., 1989;Schmid et al., 2003;Loughrey et al., 2008). The spectroscopic data for the reaction mixture containing the title molecule matches those reported in the literature (Arliguie et al., 1988;Loughrey et al., 2008).
The molecular structure of the title complex is shown in Fig. 1. The title sandwich complex consists of a coordinated planar arene ring and a pentamethylcyclopentadienyl ring in η 6 -and η 5 -hapticities, respectively. The bond distances are in reasonable agreement for analogous complexes with, for example, coordinated hexamethylbenzene and anisole in η 6hapticities (Fagan et al., 1989(Fagan et al., , 1990He et al., 1991;Nolan et al., 1993). The distance between the Ru atom and the centroid of the benzene ring is 1.706 (5) Å and the distance between the Ru atom and the cyclopentadienyl ring is 1.811 (5) Å. The angle formed with the centroids of the coordinated rings and the Ru II ion is 179.49 (15)°. The crystal structure is stabilized by weak C-H···F hydrogen bonds.
Dry acetonitrile (8 ml) was added to the reaction mixture, and it was refluxed under an argon atmosphere for 3 h. The deep green solution was evaporated under reduced pressure, and the residue was extracted with oxygen-free tetrahydrofuran (4 ml) and toluene (1 ml), and filtered through a pad of Celite under a nitrogen atmosphere. To the yellow-brown solution was added pyridine (11 mg, 15 fold excess), and the orange coloured solution was evaporated under reduced pressure. The solid residue was extracted with tetrahydrofuran (3 ml) and dichloromethane (1 ml). Addition of diethyl ether (8 ml) to this solution afforded an orange precipitate, which gave the crude products of [RuCp*(C-NH 2 )py]PF 6 and about 17% of the title salt, [Cp*Ru(η 6 -toluene)]PF 6 , as determined by 1 H NMR spectroscopy of the bulk solid. This was filtered and dried in vacuum to yield an orange powder. Suitable crystals for an X-ray diffraction study were obtained by slow diffusion of diethyl ether into a saturated solution of the mixture in acetone under a nitrogen atmosphere to afford colourless blocks.
supplementary materials sup-2 Refinement Hydrogen atoms were placed in calculated positions with C-H distances ranging from 0.95 to 1.00 Å and included in the refinement in a riding-model approximation with U iso (H) = 1.2U eq (C) or U iso (H) = 1.5U eq (C) for methyl H atoms. Fig. 1. The molecular structure of the title compound showing 30% probability ellipsoids. Atoms labeled with suffixes 'a' and 'b' are related by the symmetry codes (-x, -y + 1, -z + 1) and (x, -y + 1/2, z) respectively.