Reactivity Consequences of Steric Reduction in Cyclopentadienyl Chromium β-Diketiminate Complexes

A series of Cr(III) half-sandwich β-diketiminate complexes, CpCr[(ArNCMe)2CH]X, X = I (2), CH3 (3), or Cl (4), were prepared. Compared to previously communicated complexes with Ar = 2,6-iPr2C6H3 (Dpp, a), Cr(III) complexes with less sterically demanding ligands such as Ar = 2,6-Me2C6H3 (Xyl, b), 2,4,6-Me3C6H2 (Mes, c), or 2,6-Et2C6H3 (Dep, d) were more readily synthesized via salt metathesis reactions. Iodide compounds 2b−d were prepared by oxidation of the corresponding Cr(II) species CpCr[(ArNCMe)2CH] 1b−d with half an equivalent of iodine. The Cr(III) chloride complexes CpCr[(ArNCMe)2CH]Cl 4c−d were prepared in a two-step, one-pot reaction from anhydrous CrCl3. The reaction of MeMgI with either the Cr(III) chloride or iodide precursors yielded the Cr(III) methyl complexes CpCr[(ArNCMe)2CH](CH3) 4b−d. All of the paramagnetic Cr(III) complexes were characterized by UV−visible spectroscopy and elemental analysis, and the structures of 2b, 2c, 3b, 3c, 3d, 4c, and 4d were determined by X-ray crystallography. Reaction of CpCr[(ArNCMe)2CH] with iodomethane generates the Cr(III) iodide and Cr(III) methyl complexes. The rate of this single-electron oxidative addition reaction was shown to remain relatively invariant upon changing the β-diketiminate N-aryl substituent.