Crystal structure of bis[(R,R)-1,2-(binaphthylphosphonito)ethane]dichloridoiron(II) dichloromethane disolvate

In the title compound, the FeII ion lies on a crystallographic twofold rotation axis and is coordinated by four P atoms from two (R,R)-1,2-bis(binaphthylphosphonito)ethane (BPE) ligands and two Cl ligands in a distorted cis-FeCl2P4 octahedral coordination geometry. Weak C—H⋯O and C—H⋯π interactions occur in the crystal.

As an extension of these studies, we now describe the synthesis and crystal structure of the iron(II) complex FeCl 2 (BPE) 2 , which crystallized as a dichloromethane solvate.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The Fe II ion lies on a crystallographic twofold rotation axis and is coordinated by four P atoms from two BPE ligands and two Cl ligands in a distorted cis-FeCl 2 P 4 octahedral coordination geometry. The largest distortion from ideal coordination geometry is the P2-Fe-P2 i angle of 108.49 (7) (see Table 1 for symmetry codes). The distortion is based on steric grounds involving the bulky binaphthylphosphonito ligands. The Fe-P distances are the same within experimental error. The P atoms are bonded to two O atoms, one C atom and coordinated to the Fe II ion in distorted tetrahedral geometries. The dihedral angles between the naphthalene rings in the BPE ligands (C1-C10/C11-20 and C21-C30/C31-C40) are the same, with values of 54.5 (2) . A weak intramolecular C-HÁ Á ÁO hydrogen bond is observed ( Table 2). The asymmetric unit contains one CH 2 Cl 2 solvent molecule, which is disordered over two sets of sites with refined occupancies in the ratio 0.700 (6):0.300 (6).

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.41, November, 2019;Groom et al., 2016) showed surprisingly that the title complex is the first iron(II) dichloride crystal structure with bidentate phosphorus donors with P-O-bonded substituents. There are 36 structures of related iron diphosphine complexes FeCl 2 (P 2 ) 2 (P 2 = a diphosphine) with P-C bonds reported. The majority, 33 complexes, crystallize with the chloride ions trans to each other, while there are three examples where the chloride ions are cis, as in the title complex. The complex trans-FeCl 2 (1,2bis(diphenylphosphino)ethylene) 2 , for example, crystallizes with the chloride ions trans (Cecconi et al., 1981). An example with cis chloride ions is the complex cis-FeCl 2 (1,2-di-

Figure 2
Part of the crystal structure of the title compound showing the formation of [100] chains linked by weak C-HÁ Á ÁO hydrogen bonds shown as blue lines. The disordered dichloromethane solvent molecules are not shown.

Figure 1
The molecular structure of the title compound with 30% probability ellipsoids. Unlabeled atoms are related by the symmetry operator (y, x, Àz + 1) and for the sake of clarity the disordered solvent molecule is not shown.
phospholanoethane) 2 (Field et al., 1998). In the trans complexes, the Fe-Cl distances range from 2.21 to 2.38 Å with 22 structures having a distance of 2.34-2.37 Å . This compares with the distances of 2.3422 (11) and 2.3423 (11) Å in the title complex.

Synthesis and crystallization
The ligand was synthesized according to a literature procedure using (R)-BINOL (Steinmetz et al., 1999). The iron complex was synthesized as follows: in a nitrogen-filled glovebox, FeCl 2 Á1.5THF (6.0 mg, 0.030 mmol, 1 equivalent) was combined with (R,R)-BPE (50 mg, 0.08 mmol, 3 equivalents) in 10 ml THF and stirred in a 20 ml dram vial for 24 h. The THF was vacuumed off to yield a brown powder: 31 P{ 1 H} NMR (202 MHz, C 6 D 6 ): 257.72 ppm, singlet. To purify, the powder was dissolved in a minimum of DCM, precipitated out with addition of diethyl ether, and filtered over a glass frit. The precipitate collected on the frit was redissolved in DCM, and re-purified by the same procedure twice more. To obtain crystals, a concentrated DCM solution of the purified complex was left in a closed 20 ml dram vial in a nitrogen-filled glovebox for approximately one week at least, depending on the exact concentration. The crystals were orange coloured. Attempts to convert this complex into a hydride complex were unsuccessful.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms were included in calculated positions with C-H = 0.95 and 0.99 Å for aromatic and methylene C atoms, respectively, and were included in a riding-model approximation with U iso (H) = 1.2U eq (C).
The major component of the disordered CH 2 Cl 2 solvent molecule was refined without restraints while the minor component was restrained to have similar geometry and anisotropic displacement parameters to the major component using the SAME and SADI instructions in SHELXL (Sheldrick, 2015b).

Funding information
RHM thanks NSERC Canada for a Discovery Grant.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.