Crystal structure of acetonitrile[η6-1-methyl-4-(1-methylethyl)benzene][1-(pyrimidin-2-yl)-3H-indol-1-ium-2-yl-κ2 N,C]ruthenium(II) bis(hexafluoridoantimonate)

Cyclometalated Ru complexes play a major role in catalytic transformation. The Ru cation is coordinated by a pyrimidyl-3H-indole ligand, as well as a para-cymene ligand and one acetonitrile molecule.


Chemical context
Cyclometalated ruthenium compounds are well known catalytic intermediates in the C-H activation of various substrates (Arockiam et al., 2012;Li et al., 2012;Ferrer Flegeau et al., 2011). In a recent study on oxidative Rucatalysed heteroarene C-H arylation (Wang et al., 2015;Ackermann & Lygin, 2011), we demonstrated that [{RuCl 2 (pcymene)} 2 ] in the presence of AgSbF 6 selectively ruthenates the C2-H bond of N-pyrimidine-substituted pyrroles and indoles (Sollert et al., 2015). We concluded that in our catalytic system, the resulting ruthenacyclic species likely act as precursors rather than on-cycle intermediates. In the course of our studies we observed the unusual formation of the title complex, which shows protonation at the C3 position. The title compound and related cyclometalated ruthenium complexes are shown schematically in Fig. 1.

Supramolecular features
The packing allows no direct interaction of equivalent ruthenium complexes. The crystal packing shows a complex pattern in which two crystallographically independent SbF 6 À counter-ions occupy a void formed by symmetry-equivalent metal complexes. C-H hydrogen bonds of the pyrimidylindole and para-cymene ligands with the SbF 6 À ions mainly account for the observed packing pattern (Table 1).

Database survey
This structure is related to chloro( 6 -para-cymene)[ 2 -N,C-1-(pyrimidin-2-yl)-1H-indole]ruthenium (Sollert et al., 2015), in which the double bond is at C2 C3. The Ru1-C2 and Ru1cymene distances, however, are almost unaltered. This is consistent with the development of a positive charge at N1 to effect the C3 protonation rather than at the Ru II atom. The C2 atom in the title compound is therefore formally an anionic ligand, and not a carbene carbon. A similar cyclometalated pyrrolinyl complex (2) Buil et al., 2015;Fig. 1) was obtained through HBF 4 -mediated rearrangement of N-allylic substituents. The Ru-C distances of 2.077 (4) Å (Buil et al., 2003) are comparable to the Ru1-C2 distance of the title compound. The Ru-catalysed rearrangement of a 1,7-eneyne afforded the C2-cyclometalated 3H-indole (3) (Chiang et al., 2010;Fig. 1). Structural parameters of this cyclopentadienylcoordinated ruthenium complex are in good agreement with the title compound.

Synthesis and crystallization
A pre-dried Young's tube was charged with chlorido( 6 -paracymene)[ 2 -N,C-1-(pyrimidin-2-yl)-1H-indole]ruthenium (50 mg, 1.0 equiv., 0.11 mmol) and AgSbF 6 (76 mg, 2.0 equiv., 0.22 mmol). The tube was evacuated and backfilled with argon three times. The tube was equipped with a rubber septum and anhydrous MeCN (2 mL) was added via a syringe. The septum was removed, the tube sealed and wrapped in aluminium foil to protect the reaction mixture from light. The mixture was left stirring at room temperature for 18 h, after which the resulting precipitate was filtered off rapidly under air and the filtrate transferred immediately into a pre-dried roundbottom flask under argon. The solvent was evaporated under reduced pressure and a green solid was obtained. The solid was dissolved in d 8 -THF and transferred into a NMR tube under argon. The title compound was obtained as green crystals upon slow evaporation of the solvent. The title compound (I) and related cyclometalated ruthenium complexes (II) (Sollert et al., 2015) and (III) (Chiang et al., 2010). Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x; Ày þ 1 2 ; z þ 1 2 ; (ii) Àx þ 2; y À 1 2 ; Àz þ 3 2 ; (iii) Àx þ 3 2 ; y þ 1 2 ; z.

Figure 2
ORTEP representation of the molecular components of the title compound, showing 50% probability displacement ellipsoids.

Refinement
Crystal data, data collection and refinement details are summarized in Table 2. All H atoms on carbon were placed at calculated positions [C-H = 0.95 (aromatic), 0.98 (methyl), 0.99 (methylene) and 1.00 (methine) Å ] using a riding model with U iso (H) = 1.2U eq (C) or 1.5U eq (C methyl ). The Ru-C bonds were ignored in the ideal placement of the aromatic H atoms.

Special details
Experimental. X-ray crystallographic data for I were collected from a single-crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker smart diffractometer equipped with an APEX II CCD Detector, a graphite monochromator. The crystal-to-detector distance was 5.0 cm, and the data collection was carried out in 512 x 512 pixel mode. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq