Ruthenium(II) carbonyl compounds with the 4′-chloro-2,2′:6′,2′′-terpyridine ligand

The RuII atoms in the crystal structures of two new potential catalyst precursors, [Ru(Tpy-Cl)(CO)2Cl][Ru(CO)3Cl3] and [Ru(Tpy-Cl)(CO)2Cl2] (Tpy-Cl = 4′-chloro 2,2′:6′,2′′-terpyridine-κ3 N), exhibit distorted octahedral coordination spheres.


Chemical context
Ruthenium-carbonyl compounds with polypyridine ligands are known to be active catalysts for several catalytic processes including the reduction of carbon dioxide (Collomb-Dunand-Sauthier et al., 1994;Chardon-Noblat et al., 2002;Kuramochi et al., 2015), water-gas shift reaction (Luukkanen et al., 1999) and hydroformylation (Alvila et al., 1994). Many of these systems are metallopolymers obtained by reducing mononuclear precursors either chemically or electrochemically. The 2,2 0 -bipyridine ligand or its derivatives are the most commonly used ligand systems in these catalysts. It is also reported that possible substituents on polypyridine rings can have a strong impact on the catalytic behaviour of the compounds (Chardon-Noblat et al., 2001), which could offer a route to tailor the catalytic activity. Compounds with terpyridine and its derivatives as ligands together with carbonyl ligands are less commonly used (Deacon et al., 1984;Gibson et al., 1997;Ziessel et al., 2004), although it has also been shown that these types of compounds can be used to obtain active catalysts. Terpyridines are able to act as strong tridentate ligands because of the arrangement of the pyridine nitrogen atoms. However, bidentate coordination is also known (Deacon et al., 1984;Kooijman et al., 2007;Amoroso et al., 2010).

Structural commentary
Compound (I) is a salt and crystallizes in the monoclinic space group P2 1 /c with four formula units in the unit cell. The coordination sphere of the Ru II atom in the cation is a slightly distorted octahedron. The equatorial positions are occupied by three pyridine N atoms from the Tpy-Cl ligand and by one carbonyl ligand; axial positions are occupied by one chloride and one carbonyl ligand. The charge on the Ru II atom is balanced by an octahedrally shaped fac-[Ru(CO) 3 Cl 3 ] À anion ( Fig. 1). As expected, in the cation the Ru1-N5 bond to the central pyridine ring of the tpy-Cl ligand [2.019 (2) Å ] is the shortest of the Ru-N bonds (Gibson et al., 1997;Ziessel et al., 2004). The Ru1-N1 [2.097 (2) Å ] and Ru1-N15 [2.093 (2) Å ] bonds involving the outer pyridine rings are lengthened to relieve strain and to retain a typical terpyridine bite angle of about 79 . Similar structures can be found in other ruthenium(II) complexes containing terpyridine ligands (Gibson et al., 1997). The Ru1-C2 bond of the equatorial carbonyl group [1.918 (3) Å ] is longer than the Ru1-C1 bond [1.893 (3) Å ] of the axial carbonyl group, indicating a slightly stronger trans-influence caused by the pyridine N atom. The Ru1-Cl1 distance [2.4279 (7) Å ] is in the range of typical Ru-Cl bond lengths (Deacon et al., 1984;Ziessel et al., 2004). The corresponding Ru-Cl bond lengths in the [Ru(CO) 3 Cl 3 ] À counter-anion [2.4129 (7)-2.4212 (7) Å ] also fall into the typical range of Ru-Cl bonds (Table 1).
The Tpy-Cl ligand in compound (I) is non-planar, despite coordination of all its three N atoms [dihedral angles between the mean planes of the central pyridine ring and the adjacent pyridine rings are 5.70 (8) and 13.28 (7) ]. In compound (II), the ring with the non-coordinating N atom is inclined considerably relative to the coordination plane of the two pyridine rings [dihedral angle 57.71 (9) ].

Supramolecular features
The packing of molecules (I) and (II) are dominated by van der Waals interactions; packing plots are displayed in Fig. 3 Table 1 Selected bond lengths (Å ) for (I).

Figure 2
The molecular structure of compound (II). Displacement ellipsoids are drawn at the 50% probability level.

Figure 1
The molecular structures of the cation and anion in compound (I). Displacement ellipsoids are drawn at the 50% probability level.
(I) and Fig. 4 for (II). Only weak hydrogen bonds andcontacts can be found in these structures. In both (I) and (II), some non-conventional hydrogen bonds between the aromatic C-H hydrogen atoms and chlorido ligands of neighboring molecules do exist. The shortest contacts are summarized in Tables 3 and 4. In addition to these hydrogen bonds, the aromatic rings in structure (I) are involved in weak face-toface --interactions with considerable offsets. The shortest intermolecular C-C distances range from 3.23 to 3.50 Å . In (II), an edge-to-face contact exists between C3-H3 and C16 of the neighboring molecule. The distance between H3 and C16 is 2.89 Å and the angle C3-H3Á Á ÁC16 amounts to 134 .
All interactions considered, three-dimensional network structures are obtained both for (I) and (II).

Synthesis and crystallization
The title compounds were synthesized using a literature procedure (Homanen et al., 1996) and both compounds were obtained in a single pot reaction. A solution of [Ru(CO) 3 Cl 2 ] 2 (25.6 mg, 0.05 mmol) in 3 ml of THF was refluxed for 1 h under argon gas. After the reaction time, 26.7 mg (0.1 mmol) of tpy-Cl in 3 ml of THF was added to the above reaction mixture. The resulting mixture was refluxed for another 2 h in air with continuous stirring. During the reaction, the pale yellow solution turned to a reddish solution with a colourless precipitate. The precipitate was collected through centrifugation and the filtrate was evaporated for crystallization. Compound (I) was obtained as a major product originating from the precipitate and compound (II) was collected as a minor product from the filtrate. High-quality crystals of the salt (I) for single-crystal X-ray diffraction were obtained from research communications Figure 4 The crystal packing of (II) in a view along the b axis. Table 3 Hydrogen-bond geometry (Å , ) for (I). Symmetry codes: (i) Àx; Ày þ 1; Àz; (ii) Àx; y þ 1 2 ; Àz þ 1 2 ; (iii) x; y À 1; z. Table 4 Hydrogen-bond geometry (Å , ) for (II).

Figure 3
The crystal packing of (I) in a view along the b axis.
DMSO solution and those of complex (II) were obtained as brown-coloured crystals from the filtrate.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 5. All H atoms were positioned in calculated positions and constrained to ride on their parent atoms, with C-H = 0.95 Å and U iso = 1.2U eq (C). The maximum electron density in complex (I) is located at 0.67 Å from atom C8 and in complex (II) at 1.28 Å from atom N2, respectively. The minimum density in complex (I) is located at 0.77 Å from atom Ru1 and in complex (II) at 0.87 Å from atom Ru1, respectively.

tricarbonyltrichloridoruthenate(II)]
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.