Phosphoraneiminato cluster of iron. The crystal structures of [FeCl(NPEt3)](4), [Fe(C equivalent to C-SiMe3)(NPEt3)](4), and [Fe3Cl4{NP(NMe2)(3)}3]

The reaction of iron dichloride with the silylated phosphaneimine Me3SiNPEt 3 in the presence of potassium fluoride at 165 degrees C leads to the phosp horaneiminato complex [FeCl(NPEt3)](4) (1). Compound 1 forms black, moistur e and oxygen sensitive crystals. According to the crystal structure analysi s 1 has a heterocubane structure, in which the iron and the nitrogen atoms of the NPEt3- groups occupy the corners of a distorted cube and form Fe-N-F e bond angles of 83.1 degrees and N-Fe-N angles of 96.5 degrees. This resul ts in significantly short Fe...Fe contacts of 272.9 pm. The results of magn etic susceptibility measurements in the range of temperatures from 1.8 to 2 93 K and the Fe-57-Mossbauer spectra in the range of temperatures from 2 to 300 K are reported. Compound 1 reacts with the lithiated acetylenes LiC drop C-CMe3 and LiC dro p C-SiMe3 in n-hexane to form the iron-organic derivatives [Fe(C drop C-R)( NPEt3)](4) [R=CMe3 (2a), R=SiMe3 (2b)] keeping the heterocubane structure. Compounds 2a and 2b form crystals which are very reactive and also black. A ccording to the crystal structure analysis 2b has a Fe4N4 heterocubane stru cture which is less distorted than that in 1 with bond angles Fe-N-Fe of 85 .5 degrees and N-Fe-N of 94.2 degrees. This leads to the longer Fe Fe conta cts of 281.4 pm. With the dimethylamido derivative Me3SiNP(NMe2)(3) iron dichloride reacts u nder conditions similar to those in the synthesis of 1 to form the dark gre en mixed-valenced Fe-II/ Fe-III cluster [Fe3Cl4{NP(NMe2)(3)}(3)] (3) Accord ing to the crystal structure analysis the three iron atoms in 3 are connect ed via one mu(3)-N atom of a NP(NMe2)(3)(-) ligand, via two mu-N atoms of t he two remaining phosphoraneiminato ligands, and via one mu-Cl atom to form an incomplete heterocubane skeleton.