Synthesis, spectroscopic and crystal structure studies of N-{3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-(ethylsulfanyl)-1H-pyrazol-5-yl}-2,2,2-trifluoroacetamide

The synthesis, crystal structure, and some spectroscopic details for the phenylpyrazole-based insecticide N-{3-cyano-1-[2,6-dichloro-4- (trifluoromethyl)phenyl]-4-(ethylsulfanyl)-1H-pyrazol-5-yl}-2,2,2- trifluoroacetamide (C15H8N4Cl2F6OS) are presented.


Chemical context
The title compound is a phenylpyrazole-based insecticide. It is related to ethiprole, an insecticide used to kill or remove insects from crops and grains during storage (Arthur, 2002). Phenylpyrazole insecticides render an insect's central nervous system toxic by blocking the body's glutamate-gated chloride channel. Ethiprole itself is a non-systemic insecticide that is effective against a wide range of chewing and sucking insects (Wu, 1998) and is an active ingredient used in many insecticides for crop-protection products. Fipronil (see, for example, Park et al., 2017) and fipronil sulfone belong to the same class of compounds. The design, synthesis, and insecticidal activity of novel phenylpyrazoles containing a 2,2,2-trichloro-1-alkoxyethyl moiety have been published by Zhao et al. (2010).
The starting material for the title compound, 5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-ethylsulfanyl-1Hpyrazole-3-carbonitrile, is also an important intermediate in the preparation of ethiprole. In view of the importance of phenylpyrazoles, especially in the context of their use in insecticides, this paper reports the synthesis, crystal structure, and spectroscopic studies of the phenylpyrazole derivative, C 15 H 8 N 4 Cl 2 F 6 OS (I).

Structural commentary
The molecular structure of I (Fig. 1), consists of a pyrazole ring with four chemically diverse substituents. A 2,6-dichloro-4trifluoromethylphenyl group is attached to atom N1 of the pyrazole ring. A 2,2,2-trifluoroacetamide group is attached to the adjacent carbon of the pyrazole, with ethylsulfanyl and cyano substituents attached sequentially at the next two carbon atoms of the pyrazole. The pyrazole and phenyl rings are essentially perpendicular, forming a dihedral angle of 89.80 (5) . The mean plane of the amide group (r.m.s. deviation = 0.0079 Å ) forms a dihedral angle of 74.33 (6) with the pyrazole ring, while the dihedral angle between the plane of the ethylsulfanyl substituent and the pyrazole is 81.31 (8) . There are no unusual bond lengths, bond angles, or torsion angles in the structure, and no noteworthy intramolecular interactions.

Supramolecular features
There is only one strong intermolecular hydrogen bond in I, namely N3-H3NÁ Á ÁO1 i (symmetry codes as per Table 1), between c-glide related acetamide groups (Table 1), which propagates to form chains that extend parallel to the a-axis (Fig. 2). The default HTAB command in SHELXL (Sheldrick, 2015b) also flags three C-HÁ Á ÁF close contacts (Table 1). Two of these, C11-H11Á Á ÁF5 iii and C13-H13Á Á ÁF6 iv , are oriented so as to associate 2 1 -screw-related molecules into chains,   An ellipsoid plot (50% probability) of I. Table 1 Hydrogen bonds and other short contacts (Å , ) in I.
which again extend parallel to the a-axis (Fig. 3). There are no stacking interactions, but inversion-related molecules have their Cl1 atoms mutually located directly over the benzene rings of their inversion-related counterparts [Cl1Á Á ÁCg(C9-C14) v = 3.4967 (6) Å , where Cg represents the ring centroid], as shown in Table 1 and Fig. 4. These combine to produce pleated sheets that extend in the ac plane ( Fig. 5), which then stack along the b-axis direction. Atom-atom contact coverages derived from a Hirshfeld-surface analysis using CrystalExplorer (Spackman et al., 2021) are given in Table 2.

Database survey
All other atom-atom contact coverages are $0.0%

Figure 4
Pairs of inversion-related molecules in I showing mutual contacts between Cl and the benzene rings (dotted lines).

Figure 3
A partial packing plot of I showing zigzag chains along the a-axis direction resulting from weak C-HÁ Á ÁF contacts (thin dashed lines).

Figure 5
A partial packing plot of I showing pleated sheets that extend in the ac plane. Diagram generated using Mercury (Macrae et al., 2020). Table 3 Some structures similar to I deposited in the CSD.
All entries have 2,6-dichloro-4-(trifluoromethyl)phenyl and cyano groups attached at the equivalent of N1 and C3 of I, respectively. Substituents R 0 and R represent groups attached at the equivalent of C1 and C2 in I, respectively.  Hainzl & Casida (1996) search on this fragment with any nitrogen-bound substituent at the equivalent of C1 (i.e., the carbon adjacent to the substituted nitrogen) gave 76 hits, and a subsequent search with 2,6-dichloro-4-(trifluoromethyl)phenyl attached at N1 of the pyrazole ring gave 60 hits. Further addition of any sulfurbound substituent at the equivalent of C2 gave nine hits, only eight of which are unique. Two of these structures, FOCCUW (Tang, Zhong, Li et al., 2005) and TOLFUY  are dimers. The remaining six, along with three other similar structures, are listed in Table 3.
The title compound was characterized by IR and 1 H NMR spectroscopies, as follows: FT-IR ( in cm

Refinement
Crystal data, data collection, and structure refinement details are summarized in Table 4. All H atoms were found in difference-Fourier maps. Carbon-bound hydrogens were subsequently included in the refinement using riding models, with constrained distances set to 0.98 Å (RCH 3 ), 0.99 Å (R 2 CH 2 ) and 0.95 Å (R 2 CH). The nitrogen-bound hydrogenatom coordinates were refined freely. U iso (H) parameters were set to values of either 1.2U eq or 1.5U eq (RCH 3 only) of the attached atom.

Figure 6
The overall reaction scheme for the synthesis of I.

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.