Synthesis, characterization, and electronic structure of diimine complexes of chromium

We have prepared and structurally characterized several complexes of chromium coordinated by diimine (or 1,4-diazadiene) ligands, that is, Ar-N = C(R)-(R)C = N - Ar (L-R(Ar)) (where Ar = 2,6-diisopropylphenyl ('' iPr '') or 2,6-dimethylphenyl ('' Me '') and R = H or Me). The reaction of CO2 with L-H(iPr) gave dinuclear [(L-H(iPr))Cr](2)(mu-Cl)(3)(Cl)(THF) when isolated from Et2O; in THF solution, however, the product exists as mononuclear (L-H(iPr))CrCl2(THF)(2). Two isostructural derivatives, (L-Me(Me))CrCl2(THF)(2) and (L-H(Me))CrCl2(THF)(2), have also been prepared. Furthermore, the bis-ligand complex, (L-H(iPr))(2)Cr, has been prepared along with its reduction product, Li(THF)(4)[(L-H(iPr))(2)Cr]. We have also synthesized the tetracarbonyl complex, (L-H(iPr))Cr(CO)(4), by addition of L-H(iPr) to Cr(CO)(4)(NCCH3)(2). The structure and variable temperature magnetic susceptibility of the previously reported Cr halide dimer, [(L-H(iPr))Cr(mu-Cl)](2), is also discussed in detail. All of the diimine complexes have been characterized structurally, spectroscopically, and magnetically, and their electronic structures are discussed with the aid of density-functional theory calculations.