Gradual solid-state redox-isomerism in the lanthanide series.

Oxidation of [(ArBIG-bian)2-Yb2+(dme)] (1) (ArBIG-bian = 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene; dme = 1,2-dimethoxyethane) by 0.5 equivalent of Me2NC(S)S-S(S)CNMe2 in dme at ambient temperature affords a mixture of two products, [(ArBIG-bian)2-Yb3+{SC(S)NMe2}1-(dme)] and [(ArBIG-bian)1-Yb2+{SC(S)NMe2}1-(dme)], which represent two redox-isomers (2a and 2b, respectively). Their ratio in solution depends on the solvent as well as on the temperature. In the solid state, a decrease of temperature (350 → 100 K) caused an electron transfer from the Yb2+ ion to the ArBIG-bian radical-anion in isomer 2b to afford isomer 2a. Accordingly, the ratio of isomers 2a and 2b changes from 1 : 1 (350 K) to 3 : 1 (100 K). In contrast, in the dimer [(dme)(dpp-bian)1-Yb2+(µ-Cl)2Yb3+(dpp-bian)2-(dme)] (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene), which is the sole example of a lanthanide complex that reveals solid-state redox-isomerism (valence tautomerism) reported so far, the electron transfer from the Yb2+ ion to the dpp-bian radical-anion takes place at around 150 K and is completed within a temperature interval of ca. 7 K.

Low-coordinate Sm(II) and Yb(II) complexes derived from sterically-hindered 1,2-bis(imino)acenaphthene (ArBIG-bian).

Reduction of ArBIG-bian (1, 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene) with an excess of samarium in tetrahydrofuran (thf) and crystallization of the crude product from a thf/toluene mixture affords [(ArBIG-bian)Sm]·C7H8 (2a), which is free of the coordinating solvent. The use of 1,2-dimethoxyethane (dme) as the reaction medium resulted in the same product, [(ArBIG-bian)Sm]·C4H10O2 (2b), which differs from 2a only in the crystal lattice solvent. Reduction of 1 with an excess of ytterbium in dme gives compound [(ArBIG-bian)Yb(dme)]·2.5C7H8 (3), containing a coordinated dme molecule. All three products consist of dianionic ArBIG-bian ligands whose bulky 2,6-(Ph2CH)2-4-Me-C6H2 groups shield effectively the metal atoms. The newly prepared compounds 2a, 2b and 3 were characterized by 1H NMR and IR spectroscopy. The molecular structures of complexes 2a, 2b and 3 have been established by single crystal X-ray analysis. The intramolecular interactions were analysed on the basis of DFT calculations. The temperature dependence of the magnetic susceptibility of 2b and 3 in the region of 2-300 K was studied. The magnetic moments of complex 2b correspond to divalent samarium.

Alkali metal reduction of 1,3,2-diazaborol and 1,3,2-diazagermol derivatives based on 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene.

The reduction of [(dpp-bian)BBr] (1, dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with dilithium naphthalenide in Et2O gives [{(dpp-bian)BBr}Li2(Et2O)2]2 (3). The treatment of [(dpp-bian)BONa] (5) and [(dpp-bian)Ge:] (7) with sodium is accompanied by protonation of the acenaphthylene fragment and affords [{(H-dpp-bian)BONa(dme)2}Na(dme)3] (6) and [(H-dpp-bian)Ge:][Na(dme)3] (8), respectively. Compounds 3, 6 and 8 have been characterized by 1H NMR and IR spectroscopy. The molecular structures of 3, [(dpp-bian)BOK] (4) and 8 have been established by single crystal X-ray analysis.

Ca(ii), Yb(ii) and Tm(iii) complexes with tri- and tetra-anions of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene.

Reduction of [(dpp-bian)2-M2+(thf)4] (M = Ca, 1; Yb, 6; dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) by alkali metals results in heterometallic, [(dpp-bian)3-M2+K+(thf)2]2 (M = Ca, 2; Yb, 7), [(dpp-bian)4-Ca2+A2+(thf)4]2 (A = Na, 3; Li, 4; K, 5), [(dpp-bian)4-Yb2+K2+(thf)4]2 (8) and [(dpp-bian)24-Yb32+K2+(thf)8] (9). The reduction of [(dpp-bian)TmBr(thf)n] (in situ) affords [(dpp-bian)4-Tm3+Na+(thf)]2 (10).