cis-Dichlorido(1,3-dimesitylimidazolidin-2-ylidene)(2-formylbenzylidene-κ2 C,O)ruthenium diethyl ether solvate

The title compound, [RuCl2(C8H6O)(C21H26N2)]·C4H10O, contains a catalytically active ruthenium carbene complex of the ‘second-generation Grubbs/Hoveyda’ type with Ru in a square-pyramidal coordination, the apex of which is formed by the benzylidene carbene atom with Ru=C 1.827 (2) Å. The complex shows the uncommon cis, rather than the usual trans, arrangement of the two chloride ligands, with Ru—Cl bond lengths of 2.3548 (6) and 2.3600 (6) Å, and a Cl—Ru—Cl angle of 89.76 (2)°. This cis configuration is desirable for certain applications of ring-opening metathesis polymerization (ROMP) of strained cyclic olefins. The crystalline solid is a diethyl ether solvate, which is built up from a porous framework of Ru complexes held together by π–π stacking and C—H⋯Cl and C—H⋯O interactions. The disordered diethyl ether solvent molecules are contained in two independent infinite channels, which extend parallel to the c axis at x,y = 0,0 and x,y = , and have solvent-accessible void volumes of 695 and 464 Å3 per unit cell.

The title compound, [RuCl 2 (C 8 H 6 O)(C 21 H 26 N 2 )]ÁC 4 H 10 O, contains a catalytically active ruthenium carbene complex of the 'second-generation Grubbs/Hoveyda' type with Ru in a square-pyramidal coordination, the apex of which is formed by the benzylidene carbene atom with Ru C 1.827 (2) Å . The complex shows the uncommon cis, rather than the usual trans, arrangement of the two chloride ligands, with Ru-Cl bond lengths of 2.3548 (6) and 2.3600 (6) Å , and a Cl-Ru-Cl angle of 89.76 (2) . This cis configuration is desirable for certain applications of ring-opening metathesis polymerization (ROMP) of strained cyclic olefins. The crystalline solid is a diethyl ether solvate, which is built up from a porous framework of Ru complexes held together bystacking and C-HÁ Á ÁCl and C-HÁ Á ÁO interactions. The disordered diethyl ether solvent molecules are contained in two independent infinite channels, which extend parallel to the c axis at x,y = 0,0 and x,y = 1 2 , 1 2 and have solvent-accessible void volumes of 695 and 464 Å 3 per unit cell.

Comment
The ruthenium complex RuCl 2 (C 8 H 6 O)(C 21 H 26 N 2 ), which is the main constituent of the title compound, (I), was prepared by a carbene exchange reaction of (H 2 IMes)(pyridine) 2 (Cl) 2 RuCHPh (1eq.; H 2 IMes = 1,3-bismesityl-4,5-dihydroimidazol-2-ylidene) with 2-vinylbenzaldehyde (2 eq.) in CH 2 Cl 2 at room temperature (Slugovc et al., 2004). In sharp contrast to most of the ruthenium carbene complexes bearing two halides and neutral donor co-ligands (phosphines or N-heterocyclic carbenes), which exhibit a trans stereochemistry of the two halide ligands, the ruthenium complex of the title compound bears them in a cis-disposition of a square pyramidal coordination about Ru, the apex of which is formed by the benzylidene carbon C41 with a characteristically short Ru-C bond of 1.827 (2) Å whereas the bond to the N-heterocyclic carbene carbon C11 is longer by 0.077 Å ( Fig. 1 and Table 1). It has been shown, that cis-isomer is thermodynamically favoured over its trans-dichlorido counterpart (Slugovc et al., 2004). Ruthenium carbene complexes bearing a cis-dichlorido arrangement are particularly interesting, because they exhibit distinctly lower initiation rates in ring opening metathesis polymerization (ROMP) of strained cyclic olefins when compared to their trans-dichlorido counterparts (Gstrein et al., 2007). This feature is used to design latent ROMP initiators and catalysts for e.g. ring closing metathesis at elevated temperatures (Szadkowska & Grela, 2008;Burtscher et al., 2006;Vougioukalakis & Grubbs, 2010).
A view of the Ru complex in the title compound is presented in Fig. 1. Bond lengths and angles about Ru (Table 1) are in good agreement with the bis-dichloromethane solvate of the same complex, RuCl 2 (C 8 H 6 O)(C 21 H 26 N 2 ).2CH 2 Cl 2 , which crystallizes in a moclinic lattice, space group P2 1 /c, a = 12.1933 (6), b = 15.4520 (7), c = 19.3799 (9) Å, β = 108.181 (1)°, (Slugovc et al., 2004). Both complexes, in (I) and in the dichloromethane solvate, show similar conformations and are stabilized by significant intramolecular π-π stacking interactions between the 2-formylbenzylidene and the adjacent mesityl moiety with the shortest intramolecular π-π contacts of C41···C21 = 3.00 Å, C42···C22 = 3.40 Å, and C43···C24 = 3.45 Å in (I) and 2.99, 3.42, and 3.43 Å in the dichloromethane solvate. Moreover, both complexes show intramolecular C-H···O,Cl interactions, e.g. in (I) between C37 and Cl1 and and C29 and Cl1 ( Fig. 1 and Table   2). In contrast to the dichloromethane solvate, where the Ru complexes do not show any intermolecular π-π-stacking but are held together mainly by C-H···π and C-H···Cl intercations, intermolecular π-π-stacking is an important factor in the crystal structure of (I). Fig. 2 demonstrates that the structure of (I) contains columnar stacks of molecules extending along the c-axis and showing intermolecular π-π-stacking between the formylbenzylidene and one of the two mesityl groups [corresponding π-π-contacts are C44···C33(x,1 -y,-1/2 + z) = 3.59 Å and C43···C32(x,1 -y,-1/2 + z) = 3.81 Å]. Further π-π-stacking interactions arise from the mutual indentation of these stacks [corresponding π-π-contacts are C22···C24(y,x,1/2 -z) = 3.82 Å, C23···C23(y,x,1/2 -z) = 3.64 Å and C24···C22(y,x,1/2 -z) = 3.82 Å]. Finally, the Ru-complexes are also held together by a larger number of weak intermolecular C-H···Cl,O interactions ( Table 2). The result of all these interactions between the Ru complexes in (I) is a framework-like structure of tetragonal symmetry containing continuous channels which extend along the c-axis and contain the diethyl ether solvent molecules. As shown in Fig. 3, there are two different kinds of continuous channels in the this framework, both coinciding with the two crystallographically different sets of 4 axes of the supplementary materials sup-2 lattice. The larger channel in this framework is centered at x,y = 0,0 and has a minimal net-diameter in the (001)-projection of 5.6 Å and a solvent-accessible volume per unit cell of 695 Å 3 (program PLATON; Spek, 2009). The smaller channel is centered at x,y = 1/2,1/2, has in the projection a minimal net-diameter of 4.2 Å and a solvent-accessible volume per unit cell of 464 Å 3 . As described in the experimental section, the diethyl ether solvent molecules inside these channels are disordered with about 5 molecules per unit cell in the large and about 3 molecules per unit cell in the small channel.

Experimental
The title compound was synthesized as described by Slugovc et al. (2004). It was then dissolved in a small amount of CHCl 3 and crystallized at room temperature by the vapour diffusion method using diethyl ether as the anti-solvent. Small green prismatic crystals were obtained, which remained stable at room temperature under oil for at least one hour. They were accompanied by some larger green crystals of different morphology, which after removal from the mother liquor crumbled by solvent loss within minutes and were probably a CHCl 3 containing solvate.

Refinement
All H atoms were placed in calculated positions and thereafter treated as riding. A torsional parameter was refined for each methyl group. U iso (H) = 1.2U eq (C non-methyl ) and U iso (H) = 1.5U eq (C methyl ) were used. The diethyl ether solvent molecules, which reside in two different infinite channels extending about the 4 axes parallel to the c-axis were disordered.
The presence of CHCl 3 was ruled out because solvent Fourier peaks did not exceed 2.   Fig. 1. The structure of (I) with displacement ellipsoids for the non-hydrogen atoms drawn at the 50% probability level.