Cobalt in a Bis-β-diketiminate Environment

Abstract

The reaction of Co(2)(mesityl)(4) with acetonitrile leads to the formation of a planar, low spin, bis-β-diketiminate cobalt(II) complex, (1-mesitylbutane-1,3-diimine)(2)Co (1). EPR spectroscopy, magnetic studies, and DFT calculations reveal the Co(II) ion to reside in a tetragonal ligand field with a (2)B(2)(d(yz))(1) ground state electronic configuration. Oxidation of 1 with ferrocenium hexafluorophosphate furnishes (1-mesitylbutane-1,3-diimine)(2)Co(THF)(2)PF(6) (2). The absence of significant changes in the metal-ligand bond metrics of the X-ray crystal structures of 1 and 2 supports ligand participation in the oxidation event. Moreover, no significant changes in C-C or C-N bond lengths are observed by X-ray crystallography upon oxidation of a β-diketiminate ligand, in contrast to typical redox noninnocent ligand platforms.

A Tetradentate β‐Diiminato Ligand Containing Phenolate Substituents: Flexivalent Coordination to MnIII, CoIII, NiII, and CuII

“…The αHOMO of the copper complex, shown in Figure 12, primarily has electron density on the ligand. In contrast to the electronic structure of an NacNac ligand, whose HOMO is a non-bonding π-orbital that has two nodes at the imine carbon atoms, [15][16][17] the present structure shows substantial localization of the αHOMO on the imine bond N2-C12. The results suggest that the oxidation of the complex occurs at the ligand rather than at the Cu center and that the oxidation gives rise to a ligand-based radical species.…”

“…16 The solution was heated at reflux for 2 h, during which the reddish solid of the product precipitated.…”

“…[1][2][3][4] The resulting complexes display interesting structural features, which may give the compounds important catalytic activity, for example, in the polymerization of lactide, [5,6] isoprene, [7] ethylene, [8][9][10] and propylene, [11] the copolymerization of epoxide and CO 2 , [12] and also in the oxidation of alkanes [13] and cyclohexene. [15][16][17][18] The structures and thus the functions of β-diiminato-metal complexes can be highly tuned by the steric and electronic effects of the substituents at the nitrogen and carbon atoms of the backbone. [15][16][17][18] The structures and thus the functions of β-diiminato-metal complexes can be highly tuned by the steric and electronic effects of the substituents at the nitrogen and carbon atoms of the backbone.…”

Noninnocent β‐Diiminate Ligands: Redox Activity of a Bis(alkylimidazole)methane Ligand in Cobalt and Zinc Complexes

“…Accordingly, attention was centered on the redox properties and reactivity of the coordinated metal center, whereas the redox non‐innocent properties of these ligands have been less explored . To our knowledge, three literature reports detail on the one electron oxidation of a coordinated anionic NacNac − ligand in [M II (NacNac) 2 ]‐type complexes to form [M II (NacNac)(NacNac . )] + (M=Co, Ni and Zn).…”

On the non-innocence of “Nacnacs”: ligand-based reactivity in β-diketiminate supported coordination compounds

“…These cationic species are therefore best described as containing an open-shell BDI • π-radical ligand whereby the ligand spin is delocalized over the two ligands with electron density located at the BDI γ-carbon in the SOMO (Scheme 3). [40][41][42] On the basis of these observations, such phenomena might be underestimated and it is possible that the exact nature of some BDI metal species has previously been misidentified. 40 This is in contrast with the well-studied α-diimine redox-active ligands, featuring an even number of atoms in the ligand backbone, and showing significant correlation between the intraligand metrical parameters and oxidation states.…”