Crystal structure of pentacarbonyl(2,2-difluoropropanethioato-κS)manganese(I)

The synthesis and crystal structure of an unexpected CH3CF2C(O)SMn(CO)5 compound are described.

The title compound, [Mn{SC(O)CF 2 CH 3 }(CO) 5 ], has been isolated as a byproduct during the reaction of K[Mn(CO) 5 ] with CH 3 CF 2 COCl. It is built up from a difluoromethylpropanethioate bonded to an Mn(CO) 5 moiety through the S atom. The Mn atom has an almost perfect octahedral coordination sphere. It is one of the rare examples of compounds containing the (CO) 5 MnS-C fragment. In the crystal, the methyl group occupies a pocket surrounded by the O atoms of three carbonyl groups of the Mn(CO) 5 moiety; however, the HÁ Á ÁO distances are rather long. These interactions lead to the formation of layers lying parallel to (101), which enclose R 4 4 (15) and R 4 4 (16) ring motifs. The CF 2 group is disordered over two sets of sites with occupancies of 0.849 (3) and 0.151 (3).

Chemical context
Alkylpentacarbonylmanganese(I) complexes containing fluorinated alkyl groups, [MnR F (CO) 5 ], have been known since 1960 (Kaesz et al., 1960;Beck et al., 1961) but X-ray structures have been scarcely investigated until recently (Morales-Cerrada, Fliedel, Daran et al., 2019). Our interest in these compounds is related to a study of the homolytic Mn-C bond strength and how this is affected by the F substitution at the and positions of the alkyl chain . The compounds where R F stands for CH 2 CF 3 and CF 2 CH 3 may be considered as models for the role of [Mn(CO) 5 ] as a radical-trapping species in the polymerization of vinylidene fluoride, where the Mn-C bonds may be formed and cleaved reversibly. While the synthesis of the CH 2 CF 3 derivative could be accomplished as planned and the product could be obtained in a pure form and crystallized (Morales-Cerrada, Fliedel, Daran et al., 2019), the synthesis of the CF 2 CH 3 derivative led to the unexpected compound, [Mn{SC(O)CH 3 CF 2 }(CO) 5 ] (1), reported here. ISSN 2056-9890

Supramolecular features
In the crystal, the methyl group occupies a pocket surrounded by O atoms of three carbonyl groups, C11 O11, C12 O12 and C14 O14, forming a two-dimensional network that develops parallel to (101); see Table 2 Damerius et al., 1989) and -1,2-dithiooxalatobis(pentacarbonyl)manganese (TOXCMN; Weber & Mattes, 1979). The Mn-S, S-C, Mn-C bond distances and Mn-S-C bond angles are compared to those for compound (1) in Table 3. As in compound (1), the Mn-C bond trans to the S atom is significantly shorter than the four other Mn-C bonds.

Figure 2
A view of the crystal packing of compound (1). The C-HÁ Á ÁO interactions (Table 2) involving the major component of the disordered -CF 2 group, are shown as dashed lines.

Figure 1
A view of the molecular structure of compound (1), with the atom labelling. For clarity, only the major disordered component of the -CF 2 group is shown. Displacement ellipsoids are drawn at the 50% probability level.
attached to the C(S) atom, the Mn-S-C angle is nearly identical, 106.26 (6) and ca 105.64 , respectively (Table 3). In contrast, this angle is slightly larger for CECCES and for JEBNOT, ca 108.8 and 108.1 , respectively.

Synthesis and crystallization
The synthesis of the target compound, [Mn(CF 2 CH 3 )(CO) 5 ], requires transit through the corresponding acyl derivative, [Mn(COCF 2 CH 3 )(CO) 5 ], because direct alkylation of CH 3 CF 2 -X (X = Cl, Br) reagents by the powerful [Mn(CO) 5 ] À nucleophile suffers from the inverted polarity of the C-X bond, leading to [MnX(CO) 5 ] instead (Beck et al., 1961). The corresponding acylation using CH 3 CF 2 COCl as acylating agent was successful (Morales-Cerrada, Fliedel, Daran et al., 2019). However, the pure product could only be obtained when the 2,2-difluoropropanoyl chloride was synthesized by the action of oxalyl chloride on 2,2-difluoropropionic acid. In a first synthetic study, 2,2-difluoropropionic acid was chlorinated by the more common thionyl chloride reagent, SOCl 2 . When the resulting acyl chloride was used to acylate [Mn(CO) 5 ] À , the title compound crystallized as colourless single crystals. The sulfur atom must have been provided by the thionyl chloride remaining as a contaminant in the acyl chloride reagent. 2,2-Difluoropropanoyl chloride was freshly prepared as follows. To a 50 ml round flask equipped with a reflux condenser, was introduced 5.28 g of 2,2-difluoropropionic acid (47.97 mmol) and 10.05 g of thionyl chloride (84.48 mmol; previously purified by reflux in the presence of sulfur powder and then distilled) was added dropwise. The mixture was then heated up to 363 K over 2 h (reflux). The product was purified by distillation (b.p. 308-313 K), giving 4.85 g of a colourless liquid. The amount of thionyl chloride contaminant in the distilled product could not be estimated by NMR spectroscopy.
Synthesis of the title compound (1): To a Schlenk tube were introduced 390 mg (9.97 mmol) of metallic potassium and 358 mg (15.57 mmol) of metallic sodium under argon. They were crushed together to generate a liquid NaK alloy. A solution of dimanganese decacarbonyl (2.00 g, 5.13 mmol) in 30 ml of dry THF was added and the resulting mixture was stirred for 3 h at room temperature, leading to the formation of K + [Mn(CO) 5 ] À . The mixture was filtered through Celite to yield a greenish brown solution, rinsing the Celite with 10 ml of dry THF. Then, 2,2-trifluoropropanoyl chloride (1.31 g, 10.19 mmol), made as described above, was added dropwise at room temperature. The resulting solution was further stirred at room temperature for 3 h, followed by evaporation of the solvents under reduced pressure. The product was purified by column chromatography through a silica gel column, using npentane as the mobile phase. After elimination of a first yellow fraction corresponding to [Mn 2 (CO) 10 ], the mobile phase polarity was increased using a mixture of n-pentane and diethyl ether (2:1). An orange band was collected, followed by evaporation to dryness under reduced pressure to afford the product as an orange-brown liquid. The product was stored in the fridge (276-277 K), leading to the growth of thin colourless plate-like crystals of the title compound which were collected after two days.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. The methyl H atoms were fixed geometrically and treated as riding: C-H = 0.98 Å with U iso (H) = 1.5U eq (CH 3 ). The two fluorine atoms presented elongated ellipsoids, which could be related to disorder. To consider a realistic chemical disorder, we defined a model by rotation around the C1-C2 bond. Initially, the model could be refined isotropically to define the occupancy factors using a  Computer programs: APEX2 and SAINT (Bruker, 2014), SIR97 (Altomare et al., 1999), SHELXL2014 (Sheldrick, 2015), ORTEPIII (Burnett & Johnson, 1996), ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008). Table 3 Comparison of selected bond lengths (Å ) and bond angle ( ) in the title compound (1) and related compounds having an Mn(CO) 5 SC fragment. free variable. The result showed a major component with an occupancy factor of 85% and a minor one at 15%. As a result, it was impossible to freely refine the thermal ellipsoids for the disordered CF 2 group. The anisotropic refinement has been realized using severe EADP restraints for the C and F atoms.

Pentacarbonyl(2,2-difluoropropanethioato-κS)manganese(I)
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.