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-ditert-butyl-1,4-diazabutadiene (BuDAB) afford [M(BuDAB)] 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 = 2.0034 in hexane, a(N×2) = 4.66 × 10cm, a(H×2) = 4.90 × 10 cm, a(Li) = 1.36 × 10cm)). Reaction of M*/MH with BuDAB in THF also gives 1 and 2, as do the reactions of MgCl and ZnCl with 3, and the reaction of 1 with ZnCl affords 2. The room-temperature EPR spectrum of 2 displays two signals attributed to cation/anion ligand-centered radicals, [M(BuDAB)][M(BuDAB)] (g (1) = 2.0068,(N×2) = 4.66 ×10 cm, a(H×2) = 6.23 × 10 cm,g(2) = 2.0077, a(N×2) = 4.66 × 10 cm, a(H×2) = 6.23 X 10 cm). At low temperature a dipole-dipole-coupled spectrum is observed, affording a distance of 4.75 A between the electrons each centered on a BuDAB 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) A, (1), 1.999(4), 2.013(4) A, (2), N-M-N = 82.1(3), 82.4(3)° (1), 84.8(2), 84.7(2)° (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 A (N-Li-N = 88.3(3)°), and a neutral bidentate ligand, Li-N(mean) = 2.141 A (N-Li-N = 79.5(2)°). Crystal data (Mo K, λ= 0.710 69 A): 1, orthorhombic, space group Ibmm, a = 12.063(1) A, b = 14.266(2) A, c = 14.252(3) A, V = 2452.8(7) A, Z = 4, R = 0.051; 2, orthorhombic, space group Ccmm, a = 12.388(3) A, b = 14.225(3) A, c = 13.705(1) A, V = 2415.2(8) A, Z = 4, R = 0.036; 3, monoclinic, space group P2/c, a = 11.671(7) A, b = 10.598(1) A, c = 20.026(1) A, β = 104.60(3)°, V = 2397(2) A, Z = 4, R = 0.056.