Paramagnetic Bis(1,4-di-tert-butyl-1,4-diazabutadiene) Adducts of Lithium, Magnesium, and Zinc

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Abstract

Treatments of activated magnesium and zinc, M*, in THF and of sonified bulk lithium in hexane with 1,4-dizerz-butyl-1,4-diazabutadiene (Bu'2DAB) afford [M(Bu‘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 ( = Li (3) (gav = 2.0034 in hexane, <z(14NX2) = 4.66 X 10™4 cm™1, a(‘HX2) = 4.90 X 10-4 cm-1, a(7Li) = 1.36X KHcm™* 1)). Reaction of M*/MH2 with Bul2DAB 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(Bul2DAB)2]+[M(Bu'2DAB)2]™ (gav (1) = 2.0068, ú(14NX2) = 4.66 X 10-4 cm™1, a('HX2) = 6.23 X 10™4 cm™1,gav (2) = 2.0077, e(14NX2) = 4.66 X KH cm™1, a('HX2) = 6.23 X 10™4 cm™1). At low temperature a dipole-dipole-coupled spectrum is observed, affording a distance of 4.75 Á between the electrons each centered on a Bu‘2DAB ligand. In the solid state 1 and 2 have mm crystallographic\nsymmetry, 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 , X = 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) A3 45, 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) A3, Z = 4, R = 0.036; 3,\nmonoclinic, space group P2\\/c, a = 11.671(7) A, b = 10.598(1) A, c = 20.026(1) A, ß = 104.60(3)°, V = 2397(2) A3, Z = 4, R = 0.056.

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