Paramagnetic Chromium(II) Complexes and Chromium(IV) Nitrides with Bulky Alkylcyclopentadienyl Ligands: Paramagnetic Chromium(II) Complexes and Chromium(IV) Nitrides with Bulky Alkylcyclopentadienyl Ligands

Easily available chromium(II) acetate was used for an entry into chromium chemistry: sodium tetraisopropylcyclopentadienide ((NaCp)-Cp-4), sodium 1,2,4-tri(tert-butyl)cyclopentadienide (NaCp"'), or lithium pentaisopropylcyclopentadienide ((LiCp)-Cp-5) convert the acetate to the acetate-bridged dimers [(CpCr)-Cp-4(mu-OOCCH3)](2) (1a), [Cp"'Cr(mu-OOCCH3)](2) (1b), or [(CpCr)-Cp-5(mu-OOCCH3)](2) (1c) in yields well above 70 %. These acetates could be converted into the halide-bridged dimers [(CpCr)-Cp-4(mu-Cl)](2) (2a), [(CpCr)-Cp-4(mu-Br)](2) (3a), [Cp"'Cr(mu-Br)](2) (3b), or [(CpCr)-Cp-5(mu-Br)](2) (3c), [(CpCr)-Cp-4(mu-I)](2) (4a), or [Cp"' Cr(mu-I)](2) (4b) with the corresponding trimethylsilyl halides in nearly quantitative yield. With bis(tri-methylsilyl)sulfate the acetate 1a gave crude bis(tetraisopropyl-cyclopentadienylchromium) sulfate (5a). From the bromide 3b and sodium bis(trimethylsilyl) amide the mononuclear chromium(II) silylamide [Cp"'CrN(SiMe3)(2)(THF)] (7b) was obtained as a tetrahydrofuran adduct. Upon reaction with sodium azide, the iodide 4a afforded the tetranuclear chromium(IV) nitride cubane [((CpCr)-Cp-4)(3)(mu(3)-N)(4)CrOH] (8a) after extraction with heptane containing traces of water. The analogous chromium nitride derivative [(Cp"'Cr)(3)(mu(3)-N)(4)CrBr] (9b) was obtained from the bromide 3b and sodium azide.