Dicarbonyl(hexamethylene-1,3,5,7-tetramine-κN 1)(η5-pentamethylcyclopentadienyl)iron(II) tetrafluoridoborate

In the title compound, [Fe(C10H15)(C6H12N4)(CO)2]BF4, the arrangement around the FeII atom corresponds to a three-legged piano stool. The pentamethylcyclopentadienyl (Cp*) ligand occupies three coordination sites, while two CO ligands and one N atom of the hexamethylenetetramine ligand occupy the remaining coordination sites, completing a pseudo-octahedral geometry. Both the complex cation and the BF4 − anion reside on crystallographic mirror planes. The Fe—N bond length is 2.069 (2) and the Fe—Cp*(centroid) distance is 1.7452 (3) Å.

In the title compound, [Fe(C 10 H 15 )(C 6 H 12 N 4 )(CO) 2 ]BF 4 , the arrangement around the Fe II atom corresponds to a threelegged piano stool. The pentamethylcyclopentadienyl (Cp*) ligand occupies three coordination sites, while two CO ligands and one N atom of the hexamethylenetetramine ligand occupy the remaining coordination sites, completing a pseudooctahedral geometry. Both the complex cation and the BF 4 À anion reside on crystallographic mirror planes. The Fe-N bond length is 2.069 (2) and the Fe-Cp*(centroid) distance is 1.7452 (3) Å .
The title compound was obtained as part of our ongoing investigation of the reactions of substitutionally unsaturated metal complexes with nitrogen donor ligands (M'thiruaine et al., 2012a; M'thiruaine et al., 2012b). The synthesis and characterization data was previously reported by us, but its crystal structure is not known. To the best of our knowledge the structure of the title compound is the first of the hexamethylenetetramine complex containing the Cp*(CO) 2 Fe moiety to be reported. It exhibits a typical three legged piano stool structure with Fe II coordinated by hexamethylenetetramine through the nitrogen atom, in which the coordination geometry around Fe can be described as distorted octahedral with three sites occupied by the η 5 -pentamethylcyclopentadienyl ligand, while the two CO ligands and hexamethylenetetramine occupy the remaining three sites to complete the octahedron (Fig 1). Its structure is similar to those of the anionic 1,3,5-triaza-7-phosphaadamantane (PTA) complexes [CpFe(CN) 2 (PTA)] -, [CpFe(CN) 2 (PTAH)] - (Darensbourg et al., 2003) and that of neutral [CpW(CO) 2 (PTA)H] (Shafiq et al., 2000).
Both the iron complex and the BF 4anion crystallize on mirror planes at b= 0.25 and b=0.75 in the crystal structure of the title compound. In the case of the iron complex, the mirror plane goes through the iron atom and bisects the pentadienyl ligand and tertraamine equally, with the carbonyl atoms being located on either side of the mirror plane. In the case of the BF 4anion, the boron atom and two of the flourine atoms (F2 and F3) are located on the mirror plane, while the remaining flourine atoms are located at either side of the mirror. Consequently, the asymmetric unit of the title compound contains half a monocationic molecule and half a counter-anion. From a molecular structure point of view, the Fe-N bond was found to have a length of 2.069 (2) Å, which is slightly shorter than the 2.0817 (17)

Refinement
Non-hydrogen atoms were first refined isotropically followed by anisotropic refinement by full matrix least-square calculations on F 2 using SHEXTL. Hydrogen atoms were first located in the difference map then positioned geometrically and allowed to ride on their respective parent atoms.

Figure 1
The molecular structure of the title complex with the atom labeling scheme. Ellipsoids are drawn at 50% probability level. 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.

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