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

The chromium(II) tricarbonyl methyl complex [Cp ''' Cr(CO)(3)CH3] (1, Cp ''' = eta(5)-C(5)H(2)tBu(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)(COCH3)] in solution via reversible, slightly endothermic methyl migration from chromium to a carbonyl ligand with Delta 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(mu-Cl)](2) (2), which was crystallized as the blue-green chromium(III) half sandwich complex [Cp ''' CrCl2(THF)] (3) in the presence of tetrahydrofuran vapor. Attempted sublimation of the known chromium(II) iodo complex [(CpCr)-Cp-4(mu-I)](2) resulted in a redox reaction with formation of the chromium(III) iodo dimer [(CpCrI)-Cp-4(mu-I)](2), whose tri(tert-butyl)cyclopentadienyl derivative [Cp ''' CrI(mu-I)](2) (4) could also be prepared by oxidation of [Cp ''' Cr(mu-I)](2) with iodine. The chromium(III) bis(2,6-diisopropylphenolate) complex [(CpCr)-Cp-4(OC(6)H(3)iPr(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)iPr(2)-2,6)(2)] (6). The chromium(II) starting compound [Cp ''' Cr(mu-Br)](2) afforded the phenolate-bridged chromium(II) dimer [Cp ''' Cr(mu-OC6H5)](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)tBu(2)-2,6)(THF)] (8).