PARAMAGNETIC BIS(1,4-DI-TERT-BUTYL-1,4-DIAZABUTADIENE) ADDUCTS OF LITHIUM, MAGNESIUM, AND ZINC

Treatments of activated magnesium and zinc, M*, in THF and of sonified bulk lithium in hexane with 1,4-di-tert-butyl-1,4-diazabutadiene (Bu(t)2DAB) afford [M(Bu(t)2DAB)2] as triplet, ligand-centered biradicals in the solid state and at low temperature in solution (M = Mg (1) (previously studied using EPR), Zn (2)) or a ligand-centered radical (M = Li (3) (g(av) = 2.0034 in hexane, a(N-14 X 2) = 4.66 X 10(-4) cm-1, a(H-1 X 2) = 4.90 X 10(-4) cm-1, a(Li-7) = 1.36 X 10(-4) cm-1)). Reaction of M*/MH2 with Bu(t)2DAB in THF also gives 1 and 2, as do the reactions of MgCl2 and ZnCl2 with 3, and the reaction of 1 with ZnCl2 affords 2. The room-temperature EPR spectrum of 2 displays two signals attributed to cation/anion ligand-centered radicals, [M(Bu(t)2DAB)2]+[M(Bu(t)2DAB)2]-(g(av)(1) = 2.0068, a(N-14 X 2) = 4.66 X 10(-4) cm-1, a(H-1 X 2) = 6.23 X 10(-4) cm-1, g(av) (2) = 2.0077, a(N-14 X 2) = 4.66 X 10(-4) cm-1, a(H-1 X 2) = 6.23 X 10(-4) cm-1). At low temperature a dipole-dipole-coupled spectrum is observed, affording a distance of 4.75 A between the electrons each centered on a Bu(t)2DAB ligand. In the solid state 1 and 2 have mm crystallographic symmetry, with mainly angular distortions from regular tetrahedral geometry at the metal centers, M-N = 2.070(7), 2.067(7) angstrom, (1), 1.999(4), 2.013(4) angstrom, (2), N-M-N = 82.1(3), 82.4(3)degrees (1), 84.8(2), 84.7(2)degrees (2), whereas 3 has angular and bond distance tetrahedral distortions, in accordance with the metal center being bound by a radical anion bidentate ligand, Li-N(mean) = 1.995 angstrom (N-Li-N = 88.3(3)degrees), and a neutral bidentate ligand, Li-N(mean) = 2.141 angstrom (N-Li-N = 79.5(2)degrees). Crystal data (Mo Kalpha, lambda = 0.710 69 angstrom): 1, orthorhombic, space group Ibmm, a = 12.063(1) angstrom, b = 14.266(2) angstrom, c = 14.252(3) angstrom, V = 2452.8(7) angstrom3, Z = 4, R = 0.051; 2, orthorhombic, space group Ccmm, a = 12.388(3) angstrom, b = 14.225(3) angstrom, c = 13.705(1) angstrom, V = 2415.2(8) angstrom3, Z = 4, R = 0.036; 3, monoclinic, space group P2(1)/c, a = 11.671(7) angstrom, b = 10.598(1) angstrom, c = 20.026(1) angstrom, 104.60(3)degrees, V = 2397(2) angstrom3, Z = 4, R = 0.056.