First Examples of Dinickel Complexes Containing the N<sub>3</sub>Ni(μ<sub>2</sub>-SR)<sub>3</sub>NiN<sub>3</sub> Core. Synthesis and Crystal Structures of [L<sub>2</sub>Ni<sub>2</sub>][BPh<sub>4</sub>]<sub>2</sub> and [L<sub>3</sub>Ni<sub>2</sub>][BPh<sub>4</sub>]<sub>2</sub> (L = 2,6-Di(aminomethyl)-4-<i>tert</i>-butyl-thiophenolate)

1998-07-07T00:00:00Z (GMT) by Berthold Kersting Dieter Siebert
A coordinatively unsaturated dinuclear Ni<sup>II</sup> complex of the tridentate ligand 2,6-di(aminomethyl)-4-<i>tert</i>-butyl-thiophenol (HL) has been synthesized and investigated in the context of ligand binding and oxidation state changes. The starting complex [L<sub>2</sub>Ni<sub>2</sub>][BPh<sub>4</sub>]<sub>2</sub> (<b>1</b>) is readily prepared from NaL, NiCl<sub>2</sub>·6H<sub>2</sub>O, and NaBPh<sub>4</sub> in methanol. Compound <b>1</b>·CH<sub>3</sub>CN·CH<sub>3</sub>OH crystallizes from an acetonitrile/methanol mixed-solvent system in monoclinic space group <i>P</i>2<sub>1</sub>/<i>n</i> with <i>a</i> = 21.940(4) Å, <i>b</i> = 13.901(3) Å, <i>c</i> = 23.918(5) Å, β = 110.00(3)°, and <i>Z</i> = 4. The structure consists of dinuclear [L<sub>2</sub>Ni<sub>2</sub>]<sup>2+</sup> cations with two distorted planar <i>cis</i>-N<sub>2</sub>S<sub>2</sub>Ni coordination units joined by the thiophenolate sulfur atoms. The molecule has idealized <i>C</i><sub>2</sub><i><sub>v</sub></i> symmetry. Complex <b>1</b> readily adds another 1 equiv of HL to afford the pale green complex [L<sub>3</sub>Ni<sub>2</sub>]Cl (<b>2</b>). The dinuclear structure and its formulation as a 3:2 complex (six-coordinate Ni ions) is derived from UV spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction of its oxidation product, [L<sub>3</sub>Ni<sub>2</sub>]<sup>2+</sup>. The dication was prepared by chemical oxidation of <b>2</b> with iodine in DMF and isolated as the dark brown BPh<sub>4</sub><sup>-</sup> salt, [L<sub>3</sub>Ni<sub>2</sub>][BPh<sub>4</sub>]<sub>2</sub>·CH<sub>3</sub>OH (<b>3</b>), which crystallizes in monoclinic space group <i>P</i>2<sub>1</sub>/<i>c</i> with <i>a</i> = 23.678(5) Å, <i>b</i> = 20.090(4) Å, <i>c</i> = 16.797(3) Å, β = 106.16(3)°, and <i>Z</i> = 4. Complex <b>3</b> is the first structurally characterized example that features a bioctahedral N<sub>3</sub>Ni(μ<sub>2</sub>-SR)<sub>3</sub>NiN<sub>3</sub> core. Distortions from <i>D</i><sub>3</sub><i><sub>h</sub></i> symmetry suggest that <b>3</b> is a trapped-valence Ni<sup>II</sup>Ni<sup>III</sup> compound. The Ni−S and Ni−N bond lengths vary from 2.2975(9) to 2.4486(12) Å and from 2.027(3) to 2.120(3) Å, respectively. On the CV time scale complex <b>2</b> undergoes two reversible electron-transfer reactions at <i>E</i><sub>1/2</sub> = −0.02 and +0.44 V vs SCE, affording <b>3</b> and the transient dark green trication [L<sub>3</sub>Ni<sub>2</sub>]<sup>3+</sup> (τ<sub>1/2</sub> ≈ 15 min at 295 K), respectively. While <b>2</b> is EPR silent, the EPR spectrum of a powdered sample of <b>3</b> reveals <i>g</i><sub>⊥</sub> = 4.0 and <i>g</i><sub>∥</sub> = 2.09 at 77 K, consistent with an <i>S</i> = <sup>3</sup>/<sub>2</sub> spin state of the mixed-valent Ni<sup>II</sup>Ni<sup>III</sup> complex.