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 (Na 4 Cp), sodium 1,2,4‐tri(tert‐butyl)cyclopentadienide (NaCp′′′), or lithium pentaisopropylcyclopentadienide (Li 5 Cp) convert the acetate to the acetate‐bridged dimers [ 4 CpCr(µ‐OOCCH 3 )] 2 ( 1a ), [Cp′′′Cr(µ‐OOCCH 3 )] 2 ( 1b ), or [ 5 CpCr(µ‐OOCCH 3 )] 2 ( 1c ) in yields well above 70 %. These acetates could be converted into the halide‐bridged dimers [ 4 CpCr(µ‐Cl)] 2 ( 2a ), [ 4 CpCr(µ‐Br)] 2 ( 3a ), [Cp′′′Cr(µ‐Br)] 2 ( 3b ), or [ 5 CpCr(µ‐Br)] 2 ( 3c ), [ 4 CpCr(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(SiMe 3 ) 2 (THF)] ( 7b ) was obtained as a tetrahydrofuran adduct. Upon reaction with sodium azide, the iodide 4a afforded the tetranuclear chromium(IV) nitride cubane [( 4 CpCr) 3 (µ 3 ‐N) 4 CrOH] ( 8a ) after extraction with heptane containing traces of water. The analogous chromium nitride derivative [(Cp′′′Cr) 3 (µ 3 ‐N) 4 CrBr] ( 9b ) was obtained from the bromide 3b and sodium azide.