Synthesis and crystal structure of [(Sp )-(2-phenylferrocenyl)methyl]trimethylammonium iodide dichloromethane monosolvate

The packing of the title disubstituted ferrocene derivative is stabilized by weak C—H⋯X (X = I, Cl), C—H⋯π(Cp) and C—Cl⋯π(phenyl) interactions, building a three-dimensional network. The cation has planar chirality with S p(Fc) absolute configuration. The structure of the title compound is compared with related disubstituted (trimethylammonio)methyl ferrocenes.

As a follow-up to our research on the chemistry of disubstituted ferrocene derivatives, the synthesis and the structure of the title compound, [Fe(C 5 H 5 )(C 15 H 19 N)]IÁCH 2 Cl 2 , is described. The cation molecule is built up from a ferrocene disubstituted by a trimethylammonium methyl group and a phenyl ring. The asymmetric unit contains the iodide to equilibrate the charge and a disordered dichloromethane solvate. The disordered model results from a roughly statistical exchange (0.6/0.4) between one Cl and one H. The packing of the structure is stabilized by weak C-HÁ Á ÁX (X = I, Cl), C-HÁ Á Á(Cp) and C-ClÁ Á Á(phenyl) interactions, building a three-dimensional network. The cation has planar chirality with S p (Fc) absolute configuration. The structure of the title compound is compared with related disubstituted (trimethylammonio)methyl ferrocenes.

Chemical context
Asymmetric catalysis by transition metals has received considerable attention over the last few decades and numerous chiral ligands and complexes allowing high activity and enantioselectivity have been reported (Jacobsen et al., 1999;Bö rner, 2008). For this purpose, catalysts need a chiral ligand presenting at least a chiral center, a chiral axis or a planar chirality. Amongst the various chiral ligands that have been synthesized, ferrocenyl phosphines have proven to be particularly efficient for numerous asymmetric reactions (Buergler et al., 2012;Gó mez Arrayá s et al., 2006;Toma et al., 2014) Over the last few years, our team has developed the synthesis of various chiral ferrocenyl ligands for asymmetric catalysis Labande et al., 2007;Bayda et al., 2014;Daran et al., 2010;Wei et al., 2012Wei et al., , 2014Loxq et al., 2014). We mainly focused on a series of chiral bidentate PX ferrocenyl ligands (X = OR, SR, NHC) bearing planar chirality, which have been successfully used in different homogeneous asymmetric catalytic reactions: allylic substitution, methoxycarbonylation, hydrogenation (Kozinets et al., 2012;Le Roux et al., 2007;Diab et al., 2008;Routaboul et al., 2005). All of these ligands present a planar chiral 1,2-disubstituted ferrocenyl group with coordination sites on both substituents. More recently, we wanted to extend the application of planar chiral 1,2-disubstituted ferrocenyl groups to the synthesis of ligands with only one substituent bearing a coordination site for fine tuning of existing ligands. To this aim, we needed an enantiomerically pure planar chiral building block bearing a good leaving group in order to introduce a planar chiral substituent on nucleophilic atoms. In this context, we report here the twostep synthesis of the title [(S p )-(2-phenylferrocenyl)methyl]trimethylammonium iodide salt.
The latter is synthesized in two steps, the first consists in the enantioselective synthesis of (S p )-A following the procedure developed by S.-L. You and co-workers (Gao et al., 2013), the second step is a quaternization of the tertiary amine to the ammonium salt by reaction with an excess of iodo methane. (Ferrocenylmethyl) ammoniums have been used successfully as electrophiles because of the stabilization of carbocations in an position of ferrocene derivatives and because of the presence of a good leaving group: trimethylamine. Nucleophilic[EM2] substitution (Lin et al., 2020) on the methylene carbon atom in the position of the ferrocene moiety in compound B, [(Sp)-(2-phenylferrocenyl)methyl]trimethylammonium iodide, should then be favoured and should provide an efficient access to a wide range of various enantiomerically pure ferrocene derivatives of type C including View of the asymmetric unit of the title compound with the atomlabelling scheme. Ellipsoids are drawn at the 30% probability level and the H atoms are represented as small circles of arbitrary radii. C-HÁ Á ÁX (X = I, Cl) interactions are represented as dashed lines.

Structural commentary
The molecular structure is based on a ferrocene moiety in which one of the Cp rings is disubstituted in the 1,2 position by a tri-methylammonium-methyl and a phenyl substituent. The molecule has a positive charge, which is counterbalanced by an iodide (Fig. 2). Moreover, there is one disordered dichloromethane solvate molecule per asymmetric unit. The disordered model results from the exchange between one Cl and one H in the ratio 0.6/0.4 (Fig. 3). This disorder might be induced by the occurence of weak C-ClÁ Á ÁI intramolecular and C-HÁ Á ÁCl intermolecular interactions. There are weak intramolecular C-HÁ Á ÁI interactions within the asymmetric unit.
As a result of the presence of the two substituents on the Cp ring, the cation molecule has planar chirality and its absolute structure is S p , which is confirmed by the refinement of the Flack parameter (Parsons et al., 2013). The phenyl ring is twisted with respect to the Cp ring by 48.74 (17) and the C1-C11-N1 unit is roughly perpendicular to the Cp ring to which it is attached, making a dihedral angle of 89.7 (2) .

Supramolecular features
The crystal packing is governed by the occurrence of weak C-HÁ Á ÁX (X = Cl, I), C-HÁ Á Á and C-ClÁ Á Á interactions ( Table 1). The iodine atom is engaged in many weak C-HÁ Á ÁI interactions involving some of the H atoms of the methyl groups, one H atom of the methylene group and the nondisordered H atoms of the dichloromethane solvate. These interactions build up a ribbon developing parallel to the b axis ( Fig. 4). Then the Cl2 atom of the chloroform solvate interacts with the C12-H12C methyl group, thus building a link between the strips, resulting in a layer parallel to the (101) plane ( Fig. 4). Moreover, there are two weak C-HÁ Á Á interactions involving atom H13B of the C13 methyl group with the centroid of the Cp ring (C6-C10; Ct2) and atom C23 of the phenyl group with the centroid of the substituted Cp ring (C1-C5; Ct1). Finally, there is also a C-ClÁ Á Á interaction involving the Cl1 atom of the solvate [C30-Cl1Á Á ÁCt3 (C21-C26), 1.757 (8), 3.4096 (2) and 4.7694 (3) Å , 132.13 (1) ]. All these interactions build up a three-dimensional network.

Database survey
A search in the Cambridge Structural Database (version 5.36; Groom et al., 2016) using a fragment containing a ferrocenyl disubsituted by a trimethylamoniummethyl and at least a C atom gave six hits that could be compared with the title compound. A comparison of C1-C11, C11-N1 distances and dihedral angles between the Cp ring and the C1-C11-N1 plane is shown in Partial packing view showing the C-HÁ Á ÁX (X = I, Cl) intermolecular interactions resulting in the formation of ribbons parallel to the b axis and C-HÁ Á ÁCl interactions linking the ribbons to form a layer parallel to (101) plane. The dichloromethane solvate builds the link between the layers. Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
ORTEP view of the disordered CH 2 Cl 2 solvent molecule. Ellipsoids are drawn at the 20% probability level. H atoms are represented as small circles of arbitrary radii. N(CH 3 ) 3 group is always above the Cp ring to which it is attached. The dihedral angles between the Cp and the C-C-N plane range from 69.8 to 89.7 for the title compound.

Synthesis and crystallization
Synthesis of ( To a solution of phenylboronic acid (110 mg, 1 mmol) in DMA (8 mL
The occurrence of three large residual densities around the C atom of the solvate with distances around 1.76 Å initially suggested the presence of a chloroform solvate molecule. However, if one of the Cl atoms (Cl1) could be refined   (Malezieux et al., 1994); LIFXAZ (Malezieux et al., 1994); PIJLEB (Butler et al., 2002); VIKZIA (Butler et al., 2002); XEKQIN (Deck et al., 2000). correctly with full occupancy, the two others display large and elongated ellipsoids. Refining their occupancy factors using the restraints available in SHELXL gave a ratio of 0.6/0.4. So the disordered model is based on an exchange between one H and one Cl (Fig. 3). The model has been refined using the PART instruction to model two CH 2 Cl 2 models. The nondisordered atoms C30, H30 and Cl1 were split with occupancy factor 0.5 and introduced in the two models (C30A, C30B, H30A, H30B, Cl1A, Cl1B). Their coordinates and thermal parameters were constrained to be identical using the EXYZ and EADP commands available in SHELXL. This disordered model is not perfect, as suggested by a large residual electron density in the vicinity of the atom H30B. Data collection: APEX2 (Bruker, 2015); cell refinement: SAINT (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: ORTEPIII (Burnett & Johnson, 1996), ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2020); software used to prepare material for publication: SHELXL2018 (Sheldrick, 2015b). 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.