{μ-2-[4-(Benzothiazol-2-yl)benzyl]-2-azapropane-1,3-dithiolato-1:2κ4 S,S′:S,S′}bis[tricarbonyliron(I)]

The title compound, [Fe2(C16H14N2S3)(CO)6], was prepared as the biomimetic model for the active site of iron-only hydrogenase. The structure is similar to the diiron subsite of the iron-only hydrogenase active site, and contains a diiron-azadithiolate moiety in which a boat six-membered ring is fused with a chair six-membered ring. The substituted benzyl group attached to the bridging N atom resides in an equatorial position. The sum of the C—N—C angles around this N atom [331.9 (12)°] indicates sp 3 hybridization.

The structure of title compound is similar to the active site of iron-only hydrogenases, with a butterfly architectonic Fe 2 S 2 core and the usual distorted square-pyramidal geometry around the iron centre. The length of Fe-Fe bond [2.5013 (12) Å] is somewhat shorter than those in the structures of natural enzymes (ca 2.6 Å) (Peters et al., 1998, Nicolet et al., 1999. The N-substituted azadithiolate ligand is η 2 :η 2 -coordinated to the Fe(CO) 3 moieties to form two fused six-member rings. Ring Fe1-S1-C7-N1-C8-S2 has a chair conformation, while ring Fe2-S1-C7-N1-C8-S2 has a boat conformation. The substituted benzyl ring attached to N1 atom resides in an equatorial position and the nitrogen lone electron pair is in an axial position. As a result, the C1-Fe1-Fe2 angle [147.16 (11)°] and the C6-Fe2-Fe1 angle [148.57 (11)°] are almost equal. The sum of C-N-C angles around N1 atom is 331.9 (12)°, roughly consistent with an sp 3 -hybridization of N1 atom.
Selected bond distances and angles are summarized in Table 1, and the molecular structure of the title compound is shown in Fig.1.
The reaction mixture was stirred for 1 h at 195 K, and allowed to warm up to room temperature. The solvent was removed in vacuo and the resulting red solid was purified by column chromatography (silica, 20% dichlorometnane in hexane as eluent). The title compound was obtained in 72% yield (1.77 g). Recrystallization in the CH 2 Cl 2 /hexane solution afforded crystals suitable for X-ray study.

Refinement
The H atoms attached to C were placed in geometrically calculated positions (C-H = 0.93-0.97 Å) and refined as riding, with U iso (H) = 1.2U eq (C).

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at 30% probability level.

{µ-2-[4-(Benzothiazol-2-yl)benzyl]-2-azapropane-1,3-dithiolato-1:2κ 4 S,S′:S,S′}bis[tricarbonyliron(I)]
Crystal data 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 > σ(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.