Crystal structure of (±)-1-({[4-(allyloxy)phenyl]sulfanyl}methyl)-2-(diphenylthiophosphoryl)ferrocene

The title compound is a ferrocene derivative substituted in 1,2 positions by a diphenylthiophosphoroyl and a {[4-(allyloxy)phenyl]sulfanyl}methyl chain.

The title compound, [Fe(C 5 H 5 )(C 27 H 24 OPS 2 )], is built up from a ferrocene moiety substituted in the 1-and 2-positions by {[4-(allyloxy)phenyl]sulfan-yl}methyl and diphenylthiophosphoryl groups, respectively. The two S atoms lie on opposite sides of the cyclopentadienyl ring plane to which they are attached. In the crystal, C-HÁ Á ÁS hydrogen bonds link the molecules into a ribbon running parallel to the (110) plane. C-HÁ Á Á interactions link the ribbons to form a three-dimensional network.

Chemical context
Homogenous asymmetric catalysis by transition metals has received considerable attention over the last few decades and numerous chiral ligands and complexes allowing high efficiency reactions have been reported (Jacobsen et al., 1999;Bö rner, 2008). Amongst the various chiral ligands which have been synthesized, ferrocenyl phosphines have proven to be very efficient for numerous asymmetric reactions (Buergler et al., 2012;Gó mez Arrayá s et al., 2006;Toma et al., 2014). We have long been interested in the synthesis of chiral ferrocenyl ligands for asymmetric catalysis (Audin et al., 2010;Bayda et al., 2014;Wei et al., 2012;Loxq et al., 2014) and, in particular, we synthesized a series of chiral P,S-ferrocenyl ligands with planar chirality, which have been successfully used in different homogeneous asymmetric catalytic reactions, such as allylic substitution, methoxycarbonylation and hydrogenation (Kozinets et al., 2012;Diab et al., 2008). We recently started to explore the grafting of these ligands on solid support. This will allow us to work in heterogeneous conditions favoring both easy catalyst separation from products and recycling. Beside the expected catalyst activity reduction observed under heterogeneous conditions compared to homogeneous reaction, surface-catalyst interaction has proven to play an important, and still unclear, role on selectivity. A better understanding of these interactions would improve both grafting interest and probably industrial applications of such systems.
To reach this goal, we needed to developed new chiral P,Sferrocenyl ligands bearing an alkene moiety such as compound (3), allowing polymerization or functionalization for inorganic grafting of the ligand [such as compound (4)] (Fig. 1). Functionalized P,S ferrocenyl phosphine is prepared ISSN 2056-9890 in a three-step synthesis from 2-thiodiphenylphosphino(hydroxymethyl)ferrocene (1) (Fig. 1). This compound can be prepared in multigram quantities and isolated as a racemic mixture or in an enantiomerically pure form, opening direct access to chiral ligands (Mateus et al., 2006). Its functionalization can be performed in a one-pot process by successive addition of a strong acid (HBF 4 ), generating probably a ferrocenyl carbocation, and then the nucleophile thiol. Addition of a base allows to generate the phenolate which reacts with bromoallyl giving rise to compound (3). The phosphoryl group, protected from oxidation by sulfuration in order to carry out the former steps in air, can be recovered by refluxing in toluene with P(NMe 2 ) 3 .

Structural commentary
The molecular structure of compound (3) (see Scheme) is built up from a ferrocene moiety substituted by a diphenylthiophosphoryl and a {[4-(allyloxy)phenyl]sulfanyl}methyl chain (Fig. 2). As observed in other (diphenylthiophosphoryl)ferrocenes (Table 1), the S atom (S1) of the diphenylthiophosphoryl group is endo towards Fe with respect to the Cp ring with a distance to the ring of 1.263 (5) Å (a perpendicular distance of S1 to the Cp ring plane). This distance is the largest one observed within similar structures. The difference observed might be related to the occurrence of the C30-H30BÁ Á ÁS1(Àx, Ày, Àz) hydrogen bond. Atom S2 is exo, with a distance to the Cp ring of 1.763 (4) Å , which is in agreement with the values observed for related compounds. The much shorter distance, 0.457 Å , is related to the lowest angle (15.77 ) observed between the C2/C21/S2 plane and the Cp ring. In all other compounds, including the title one, the C2/ C21/S2 plane is roughly perpendicular to the Cp ring, with values ranging from 71.83 to 89.50 (Table 1).
The geometry of the ferrocenyl is identical to related compounds with the two Cp rings nearly parallel to each other with a dihedral angle of 3.94 (15) in the title compound, whereas the corresponding values range from 0.70 to 2.38 in the other compounds ( Table 1). The two Cp rings are roughly eclipsed, with a twist angle of 2.8 (2) . As observed in Table 1, the geometry of the C-PSPh 2 and C-CH 2 -S fragments are roughly identical within experimental error. In the diphenylthiophosphoryl group, the C1-P1 distances range from 1.788 (4) to 1.802 (3) Å , whereas the P1-S1 distances range from 1.956 (2) to 1.961 (1) Å . In the C-CH2-S fragment, the C2-C21 distances range from 1.488 (2) to 1.502 (11) Å , whereas the C21-S2 distances range from 1.811 (3) to 1.835 (2) Å .

Supramolecular features
The cohesion within the crystal is based on weak C-HÁ Á ÁS and C-HÁ Á Á interactions ( Table 2). The C-HÁ Á ÁS interactions build up a ribbon developing parallel to the (110) plane (Fig. 3). The C-HÁ Á Á interactions link the ribbons to form a three-dimensional network (Fig. 4).
Notes: ANG1 is the dihedral angle between the C2/C21/S2 plane and the Cp ring; S1-to-Cp1 and S2-to-Cp1 represent the perpendicular distance of the S atom to the substituted Cp ring plane; Cp1/Cp2 is the dihedral angle between the two Cp rings; C1-P1, P1-S1 and C2-C21 are the bond lengths.

Figure 2
Molecular view of the title compound, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented as small spheres of arbitrary radii.
2.5 equivalents) in acetone (20 ml) were mixed for 2 min. Then, allyl bromide (0.047 ml, 1 equivalent) was added to the mixture, which was heated under reflux overnight. After cooling to room temperature, the product was recovered by chromatography on silica with petroleum ether/ethyl acetate (90/10). After evaporation of the solvent, compound (3) (yield 266 mg, 85%) was isolated as a yellow-orange powder.