Crystal structure of [1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene]dichlorido{2-[1-(dimethylamino)ethyl]benzylidene}ruthenium including an unknown solvate

The compound [RuCl2(C21H26N2)(C11H15N)] is an example of a new generation of N,N-dialkyl metallocomplex ruthenium catalysts with an N→Ru coordination bond in a six-membered chelate ring.


Chemical context
Since the 1980s metathesis has become an important industrial process, but applications of the first-generation catalysts to targets bearing various functional groups were often precluded by the dramatic increase of their catalytic activity (Delaude & Noels, 2005;Astruc, 2005). Hence, in recent years a large number of new catalysts have been proposed, developed and implemented in organic chemistry processes. These new catalysts may be used in the presence of various functional groups, moisture traces, in a wide range of solvents under different temperatures and for many metathesis reactions including CM (cross metathesis), ROM (ring-opening metathesis), RCM (ring-closing metathesis), ROMP (ringopening metathesis polymerization), ADMET (acyclic diene metathesis polymerization) and others (Dragutan et al., 2005;Grubbs et al., 2015;Hoveyda & Zhugralin, 2007). Currently, the most widely used catalysts are ruthenium-based heterocyclic carbene-coordinated metallocomplexes, containing, as rule, a five-membered ruthenium-containing ring with an O!Ru coordination bond (the Hoveyda-Grubbs catalysts of the second generation) (Ogba et al., 2018;Samojłowicz & Grela, 2009;Vougioukalakis & Grubbs, 2010). ISSN 2056-9890 Currently, there is only scarce information about the synthesis and application in the metathesis reactions of the nitrogen-containing Grubbs catalysts, where the oxygen atom is substituted by an N atom in a five-membered ring. The known compounds of that type have promising catalytic properties and are already used in the industry. For example, there is patent information that describes applications of such a type of catalysts in ring-opening metathesis polymerization reactions (Zheng-Yun, 2017;Xia, 2017;Zheng-Yun, 2011;Polyanskii et al., 2015;Ivin & Mol, 1997).
The purpose of this study is to elaborate the synthesis of new generation of N,N-dialkyl metallocomplex ruthenium catalysts, resulting in establishment of connection between the nature of the functional groups born by the nitrogen atom and the catalytic activity and stability of these catalysts in various metathesis reactions as well as in the determination of the effect of substituents on the structures of the obtained products.

Figure 2
A view of the coordination geometry about the Ru atom, which lies between square-based pyramidal and trigonal-bipyramidal.

Figure 1
The molecular structure of the title complex with displacement ellipsoids for the non-hydrogen atoms drawn at the 50% probability level.
H distances of 0.93-0.97 Å , and with U iso (H) = 1.2 or 1.5U eq (C). The measurements of the 202, 002), 111, 402, 110, 312), 221, 200 and 1135 reflections were affected by shielding by the beam stop and were therefore excluded from the refinement. A region of electron density, most probably disordered solvent molecules, occupying voids of ca 1096 Å 3 for an electron count of 419, was removed with the SQUEEZE procedure in PLATON (Spek, 2015) following unsuccessful attempts to model it as a plausible solvent molecule. The stated formula mass, density, etc. do not include the disordered solvent.