Square Planar Nickel(II) Complexes with Halogenated o‐Diiminobenzosemiquinonato Ligation: Synthesis, Characterization, and Redox Property

Abstract

AbstractSeven square planar bis(o‐diiminobenzosemiquinonato)nickel(II) complexes, [Ni(o‐C6H4(NH)(NAr))2] (Ar=Mes, 1; p‐F‐C6H4, 2; p‐Cl‐C6H4, 3), [Ni(o‐4,5‐F2‐C6H2(NH)(NPh))2] (4), and [Ni(o‐4,5‐Cl2‐C6H2(NH)(NAr))2] (Ar=Ph, 5; 2,6‐F2‐C6H3, 6; 2,6‐Cl2‐C6H3, 7), have been synthesized and characterized by 1H NMR, 13C NMR, 19F NMR, IR, UV‐Vis‐NIR, elemental analyses, HRMS, as well as single‐crystal X‐ray diffraction studies (1 and 7). The cyclic voltammograms of these complexes exhibit two reversible redox processes of [NiL2]0/1− and [NiL2]1−/2−, and one irreversible process of [NiL2]0/2+. Substituent effects on the redox properties of these complexes, in addition with those of the known complexes [Ni(o‐C6H4(NH)(NPh))2] (8) and [Ni(o‐3,5‐But2‐C6H2(NH)2)2] (9), are identified by comparing the half‐wave potentials of the reduction waves, as 1≈9<8≈2<3<4<5<7<6, reflecting the ease of reduction of [NiL2] parallels the electron‐donating and ‐withdrawing ability of the substituent group. Reduction of 1 with one or two equivalents of sodium metal in THF has led to the isolation of [Na(THF)3][1] and [Na(THF)3]2[1]. The structure data of these two complexes revealed by low‐temperature X‐ray crystallography suggest their corresponding electronic structures of [NiII(1L·1−)(1L2−)]1− and [NiII(1L2−)2]2−, which are in line with those of [9]n (n=1−, 2−) suggested by spectroelectrochemical study.