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

Abstract

Easily available chromium(II) acetate was used for an entry into chromium chemistry: sodium tetraisopropylcyclopentadienide (Na4Cp), sodium 1,2,4‐tri(tert‐butyl)cyclopentadienide (NaCp′′′), or lithium pentaisopropylcyclopentadienide (Li5Cp) convert the acetate to the acetate‐bridged dimers [4CpCr(µ‐OOCCH3)]2 (1a), [Cp′′′Cr(µ‐OOCCH3)]2 (1b), or [5CpCr(µ‐OOCCH3)]2 (1c) in yields well above 70 %. These acetates could be converted into the halide‐bridged dimers [4CpCr(µ‐Cl)]2 (2a), [4CpCr(µ‐Br)]2 (3a), [Cp′′′Cr(µ‐Br)]2 (3b), or [5CpCr(µ‐Br)]2 (3c), [4CpCr(µ‐I)]2 (4a), or [Cp′′′Cr(µ‐I)]2 (4b) with the corresponding trimethylsilyl halides in nearly quantitative yield. With bis(trimethylsilyl)sulfate the acetate 1a gave crude bis(tetraisopropylcyclopentadienylchromium)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 [(4CpCr)3(µ3‐N)4CrOH] (8a) after extraction with heptane containing traces of water. The analogous chromium nitride derivative [(Cp′′′Cr)3(µ3‐N)4CrBr] (9b) was obtained from the bromide 3b and sodium azide.