Magnesium and calcium complexes with two diimine radical-anion ligands. Molecular structure of the Ca complex with 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene

Abstract

Four and five coordinate magnesium and calcium complexes containing two di imine radical anion ligands with compositions (dpp BIAN) 2 Mg (1), (dpp BIAN) 2 Ca (2), (dtb BIAN) 2 Mg (3), and (dtb BIAN) 2 Ca(THF) (4) (dpp BIAN is 1,2 bis[(2,6 diiso propylphenyl)imino]acenaphthene and dtb BIAN is 1,2 bis[(2,5 di tert butylphenyl)imi no]acenaphthene) were synthesized. At 120 К, the ESR spectra of complexes 1-4 in a toluene matrix show signals characteristic of biradical derivatives. The molecular structure of com pound 2 was established by X ray diffraction analysis. At 293 К, the magnetic moments of compounds 1, 2, 3, and 4 are 2.55, 2.57, 2.76, and 2.79 µ B , respectively, which are indicative of the presence of two unpaired electrons localized on the ligands.In recent years, diimines, including conformationally rigid 1,2 bis[(2,6 diisopropylphenyl)imino]acenaphthene (dpp BIAN), have been widely used as chelating ligands in transition metal chemistry. 1 Complexes of Ni, Rh, Pt, Pd, Cu, and other metals with this ligand are among the most efficient olefin polymerization catalysts. 2-6 How ever, until recently main group metal complexes with such ligands remained unknown. In 2003, we prepared first complexes of main group metals (Na, Li, Mg, and Ca) with various reduced forms of the BIAN ligand. 7 We found that alkali metals successively reduce dpp BIAN to mono di, tri , and tetraanions, 7,8 whereas exclusively the com plexes with the dpp BIAN dianion, (dpp BIAN) 2-M 2+ L n (M = Mg, Ca; L = THF, C 5 H 5 N), are formed in quanti tative yields in the reactions with Mg or Ca in THF. 9 X ray diffraction studies demonstrated that monomeric complexes, in which the metal atoms are chelated by the dpp BIAN dianion, are formed in all cases. The number of solvent molecules coordinated to the central atom in creases with increasing ionic radius of the metal atom. For example, the magnesium complex crystallizes with three coordinated solvent molecules from a THF solu tion, whereas the calcium complex crystallizes with four solvent molecules. Recently, we have synthesized two new acenaphthenediimine ligands, viz., 1,2 bis[(2,5 di tert butylphenyl)imino]acenaphthene (dtb BIAN) and 1,2 bis[(2 biphenyl)imino]acenaphthene (bph BIAN), and prepared magnesium and calcium complexes with these ligands. 10 Recent studies demonstrated that the (dpp BIAN)Mg(THF) 3 complex, which is readily gener ated in situ, is highly reactive toward various organic com pounds. 11-13 Some reactions of this complex are accom panied by reduction of organic compounds and oxidation of the coordinated dpp BIAN dianion to the radical an ion to give paramagnetic complexes. The latter were iso lated in the crystalline state and characterized by ESR spectroscopy and X ray diffraction analysis. 11-13As part of our continuing studies of Group II metal complexes with acenaphthene 1,2 diimine radical anion ligands, we made an effort to prepare complexes with two paramagnetic radical anion ligands. In the present study, we synthesized homoleptic magnesium and cal cium comp...

Molecular and Electronic Structures of Homoleptic Nickel and Cobalt Complexes with Non‐Innocent Bulky Diimine Ligands Derived from Fluorinated 1,4‐Diaza‐1,3‐butadiene (DAD) and Bis(arylimino)acenaphthene (BIAN)

“…Consequently, local symmetry is missing completely in 3. In contrast, complexes 1, 2, and all structurally characterized [Ni(DAD) 2 ] complexes with diverse sterically demanding N-substituents, [8,9] as well as [Ca(dip-BIAN) 2 ] with bulky N-dip groups [17] all form distorted tetrahedra with pseudo C 2 /D 2 symmetry. The distorted tetrahedral geometry of 3 can be ascribed to intermolecular arene-arene interactions observed in the crystal structure.…”

“…The observed dihedral angles along with deviation of N-C(phenyl) bonds from the diimine planes can be readily ascribed to intramolecular interactions between sterically demanding substituted phenyl rings. The only structurally characterized complex of the type [M(BIAN) 2 ] was reported very recently by Fedushkin et al [17] The crystal structure of paramagnetic [Ca II (dip-BIAN) 2 ] reveals a dihedral angle of 28°between the diimine moieties and does not show any π stacking between the diimine moieties in the crystal lattice.…”

“…Very recently, Fedushkin et al [17] reported the first homoleptic complexes of the type [M II (BIAN) 2 ] (M = Mg, Ca). The molecular structure of [Ca II (dip-BIAN) 2 ] (dip -2,6-diisopropylphenyl) was established and monoanionic nature of both ligands along with conventional oxidation state for calcium were established.…”

Solvent‐free alkali and alkaline earth metal complexes of di‐imine ligands

“…At first sight, the lack of the C N bond alternations within the di-imine moiety upsets the above hypothesis about the relationship between the nonequivalence of nitrogen atoms in the dianionic dpp-BIAN ligand and blue color of its metal complexes. However, detailed inspection of the X-ray diffraction data reveal that there is no default plane of symmetry bisecting the NLi-N angles in both Li-metallocycle because the interaction of CH 3 The calcium complex 3 is related to structurally characterized solvent-free complex (dpp-BIAN) 2 Ca, which consists of two radical-anionic dpp-BIAN ligands [9]. The synthesis and ESR characterization of its magnesium analog (dpp-BIAN) 2 Mg (4) has also been reported [9], but its molecular structure was not determined until recently.…”

“…However, detailed inspection of the X-ray diffraction data reveal that there is no default plane of symmetry bisecting the NLi-N angles in both Li-metallocycle because the interaction of CH 3 The calcium complex 3 is related to structurally characterized solvent-free complex (dpp-BIAN) 2 Ca, which consists of two radical-anionic dpp-BIAN ligands [9]. The synthesis and ESR characterization of its magnesium analog (dpp-BIAN) 2 Mg (4) has also been reported [9], but its molecular structure was not determined until recently. We were interested in the determination of the molecular structure of 4 because it is a solvent-free dpp-BIAN magnesium complex, and owing to the differences in Mg 2+ and Ca 2+ ionic radii, it may form a different structure due to the steric crowding imposed by bulky dpp-BIAN ligands.…”