[1,2-Bis(diphenylphosphanyl)ethane-2κ2 P,P′]tetracarbonyl-1κ3 C,2κC-(μ-2-cyclopentyl-2-azapropane-1,3-dithiolato-1:2κ4 S,S′:S,S′)diiron(II)(Fe—Fe)

In the title compound, [Fe2(C7H13NS2)(C26H24P2)(CO)4], the Fe2S2 core exhibits a butterfly-like shape, with two S atoms bridging the Fe–Fe dumbbell. Each of the two Fe atoms exhibits a distorted octahedral environment. One Fe atom is additionally bonded to three carbonyl C atoms, whereas the other Fe atom is additionally bonded to one carbonyl C atom and two P atoms of the chelating dppe [dppe = 1,2-bis(diphenylphosphanyl)ethane] ligand. Non-classical intramolecular C—H⋯S hydrogen-bonding interactions are present in the structure. The packing of adjacent molecules along [100] is accomplished mainly through van der Waals forces.

In the title compound, [Fe 2 (C 7 H 13 NS 2 )(C 26 H 24 P 2 )(CO) 4 ], the Fe 2 S 2 core exhibits a butterfly-like shape, with two S atoms bridging the Fe-Fe dumbbell. Each of the two Fe atoms exhibits a distorted octahedral environment. One Fe atom is additionally bonded to three carbonyl C atoms, whereas the other Fe atom is additionally bonded to one carbonyl C atom and two P atoms of the chelating dppe [dppe = 1,2bis(diphenylphosphanyl)ethane] ligand. Non-classical intramolecular C-HÁ Á ÁS hydrogen-bonding interactions are present in the structure. The packing of adjacent molecules along [100] is accomplished mainly through van der Waals forces.

Comment
Hydrogenases are capable of efficiently catalysing the oxidation of molecular hydrogen or its production from protons and electrons (Darensbourg et al., 2000;Lawrence et al., 2001). The well-known active sites of intensively studied Fe-Fe hydrogenases include Fe 2 S 2 clusters and a cuboidal Fe 4 S 4 unit, with the former playing an important role in the catalytic process.
The title compound is a mimic of the Fe 2 S 2 cluster. As shown in Fig. 1, the two Fe atoms are linked through an Fe-Fe single bond and further bridged by two S atoms. Thus a butterfly arrangement is formed, with the dihedral angle between the two Fe 2 S planes being 73.28 (8)° and the average Fe-S bond length 2.285 Å. Each Fe atom exhibits a distorted octahedral environment. Atom Fe1 is bonded to three carbonyl C atoms, whereas atom Fe2 is bonded to one carbonyl C atom and two P atoms of the chelating dppe [dppe = 1,2-bis(diphenylphosphanyl)ethane] ligand. Notably, the P atoms of dppe have substituted two carbonyl C atoms at Fe2, with one P atom in apical position and the other in basal position. Because the Fe-Fe dumbbell is asymetrically substituted, there is an obvious difference among Fe-C bond lengths (Table 1; average value 1.79 Å). The Fe2-P2 bond is 0.04 Å longer than the Fe2-P1 bond due to steric effects, and the average Fe-P bond length is 2.25 Å. The P-Fe-P angle [88.10 (7)°] is much smaller than the mean C-Fe-C bond angle [97 (5)°], because of the rigidity of the dppe ligand. Non-classical intramolecular C-H···S hydrogen bonding interactions (Table 2) are present in the structure.
The packing diagram is shown in Fig. 2. The packing of adjacent molecules along [100] is accomplished mainly through van der Waals forces.

Experimental
The synthesis of the title compound was carried out under an dry, purified, oxygen-free nitrogen atmosphere using standard Schlenk techniques. Solvents, such as THF and hexane, were dried according to standard methods. Commercially available products, like paraformaldehyde, [Fe(CO) 5 ], LiBEt 3 H, F 3 CCOOH, dppe and C 5 H 9 NH 2 were of reagent grade and used as received. The starting material [Fe 2 (SH) 2 (CO) 6 ] was prepared as documented. The title compound was prepared by a condensation of Fe 2 (SH) 2 (CO) 6 with formaldehyde in the presence of cyclopentyamie (Li & Rauchfuss, 2002), followed by substitution of carbonyls by dppe (1,2-bis(diphenylphosphanyl)ethane).
[Fe 2 S 2 (CO) 6 ] (1 mmol, 0.344 g) was dissolved in dry THF (40 ml) under a nitrogen atmosphere and then cooled to 195 K with acetone and liquid nitrogen. After the solution was stirred for 30 minutes, LiBEt 3 H (2 mmol) was added dropwise very slowly. At the midpoint of the addition, the color of the reaction mixture turned from red to dark green; for the rest of addition it remained green. After another 30 minutes, F 3 CCOOH (2 mmol, 0.149 ml) was added. The new mixture was stirred for an additional hour. The cool solution was added to a mixture of paraformaldehyde (40 mmol, 1.2 g) and C 5 H 9 NH 2 (1 mmol) in THF which had been stirred for 10 h and cooled to 273 K. The last mixture was stirred for 24 h and the majority of the solvent was evaporated under vacuum. The remaining residual was filtered through silica gel. A red fraction was collected by elution with hexane. 1 mmol (excess) dppe was added to the red fraction, and the solution gradually became purple, after which the solution was stirred for another 3 h. Recrystallization of the crude purple product from freshly distilled pentane in a refridgerator at 253 K for several days produced crystals in moderate yield (~60%) suitable for X-ray crystallography.

Refinement
Hydrogen atoms were placed at idealized positions and allowed to ride on their parent atoms, with CH 2 and CH 3 bonds set equal to 0.97 and 0.96 Å, respectively. For all H atoms, U iso (H) = 1.2U eq (C). The highest residual peak was located at 0.06 Å from Fe2. Reflections 111, 110, 011, 011, and 101 were affected by the beam stop and were omitted from the refinement. Fig. 1. The molecular structure of the title compound, with atom labels and 20% probability displacement ellipsoids for all non-H atoms.

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.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.