Chromium(III) and Chromium(II) Phenolate Complexes with Bulky Alkylcyclopentadienyl Ligands

The chromium(II) tricarbonyl methyl complex [Cp′′′Cr(CO) 3 CH 3 ] ( 1 , Cp′′′ = η 5 ‐C 5 H 2 t Bu 3 ‐1,2,4) was obtained from chromium hexacarbonyl, NaCp′′′, and methyl iodide. 1 was found to establish an equilibrium with the dicarbonyl acetyl isomer [Cp′′′Cr(CO) 2 (COCH 3 )] in solution via reversible, slightly endothermic methyl migration from chromium to a carbonyl ligand with Δ H ca. 3.6 kJ/mol and E a ca. 49.5 kJ/mol. Phosphorus pentachloride oxidized 1 to the green, dinuclear tetrachloro complex [Cp′′′CrCl(µ‐Cl)] 2 ( 2 ), which was crystallized as the blue‐green chromium(III) half sandwich complex [Cp′′′CrCl 2 (THF)] ( 3 ) in the presence of tetrahydrofuran vapor. Attempted sublimation of the known chromium(II) iodo complex [ 4 CpCr(µ‐I)] 2 resulted in a redox reaction with formation of the chromium(III) iodo dimer [ 4 CpCrI(µ‐I)] 2 , whose tri( tert ‐butyl)cyclopentadienyl derivative [Cp′′′CrI(µ‐I)] 2 ( 4 ) could also be prepared by oxidation of [Cp′′′Cr(µ‐I)] 2 with iodine. The chromium(III) bis(2,6‐diisopropylphenolate) complex [ 4 CpCr(OC 6 H 3 i Pr 2 ‐2,6) 2 ] ( 5 ) was obtained from chromium trichloride in a one pot reaction with sodium tetraisopropylcyclopentadienide, followed by sodium 2,6‐diisopropylphenolate. The chromium(III) starting compound 2 reacted with 2,6‐diisopropylphenolate to the Cp′′′ derivative [Cp′′′Cr(OC 6 H 3 i Pr 2 ‐2,6) 2 ] ( 6 ). The chromium(II) starting compound [Cp′′′Cr(µ‐Br)] 2 afforded the phenolate‐bridged chromium(II) dimer [Cp′′′Cr(µ‐OC 6 H 5 )] 2 ( 7 ) upon treatment with sodium phenolate, while the product of the analogous reaction with 2,6‐di( tert ‐butyl)phenolate was the mononuclear tetrahydrofuran adduct [Cp′′′Cr(OC 6 H 3 t Bu 2 ‐2,6)(THF)] ( 8 ).