Square-planar nickel(II) and copper(II) complexes containing 14- and 15-membered tetraaza macrocyclic ligands

Abstract

The synthesis of nickel(I1) and copper(I1) complexes with uninegative and neutral macrocyclic ligands derived from acetylacetone and various linear tetramines has been studied in order to determine the scope of the cyclization reaction and to study the effect of ring size on the acidity of the coordinated neutral ligands. Both nickel(I1) and copper(I1) complexes containing 14-membered rings have been prepared in both forms I and 11; whereas, complexes with a 15-membered ring have been isolated only for nickel(I1) and only in form 11. No copper(I1) complexes with 15-membered rings nor nickel(I1) or copper(I1) complexes with 16-membered rings have been prepared by these techniques. The pKa of Ni([ 141 dieneN,)-(PF,), is 6.45 while that of Cu([ 141 dieneN,)I, is 9.3. These values are of the same order of magnitude as those obtained for the related M([ 131 dieneN,)X, systems and it is concluded that the addition of an extra methylene group opposite the diimine ring does not change the steric environment of the proton which is ionized. No pKa data could be obtained for Ni([ 151 dieneN,)(PF,), in aqueous solution which indicates a marked decrease in ligand acidity in the 15-membered macrocycle. This has been explained in terms of steric crowding due to the positioning of three six-membered chelate rings adjacent to one another, which may prohibit formation of the basic uninegative form of the ligand.(1)

Photochemical dehalogenation mediated by macrocyclic nickel(II) complexes

“…The complexes 1a [6], 1b [11], 1c [12], 1d [13], 2a [14], 2b [15], 2c [16], 2d [17], 3a [18], 3b [19], 3c [20], 3d [21], 4a [22], 4b [23], 4c [24], and 4d [25] were prepared according to the previously reported methods. Biotech-grade acetonitrile stored under argon was used, applying syringe techniques.…”

Reactions of copper(II) and nickel(II) .beta.-keto imine complexes. 3

“…The ligands and their copper(II) and nickel(II) complexes were prepared by published procedures9 and purified as previously described.3 All reactions were run in oven-dried glassware in essentially 142-145 20 Diamagnetic Red crystals 0 baen == the Schiff base condensation product of 2,4-pentanedione and 1,2-diaminoethane; bapn the Schiff base condensation product of 2,4-pentanedione and 1,2-diaminopropane; A = p-toluenesulfonyl isocyanate; B = diethyl azodicarboxylate; C = dimethyl acetylenedicarboxylate. 6 See text for clarification of structure. the same fashion.…”

“…Since these reactions may be regarded as electrophilic substitution reactions,4 the marked decrease in the reactivity of Ni(baen) relative to Cu(baen) could be due to the much greater acidity of the methine protons of Ni(baen) as has been found for similar compounds. 5,6 If this tenet is correct, then electrophilic reactions with Ni(baen) should occur with more reactive electrophiles, e.g., those which bear strong electron-withdrawing substituents. As part of a continuing research program in this area, the reactions of the electron-deficient electrophiles, p-toluenesulfonyl isocyanate (tosNCO, A), diethyl azodicarboxylate (B), and dimethyl acetylenedicarboxylate (C), with Ni(baen) and Cu(baen) have been investigated.…”

Application of N,N′-ethylenebis(acetylacetoneiminato) Nickel (II) and Copper (II) Schiff Base Complexes as Acid–Base Sensing Materials and Indicators in Volumetric Titrations : Qualitative, Spectroscopic and Titrimetric Analyses

“…The reversible equilibrium position for the acid-base behaviour is dependent on the stability of intermediates, electronic properties of the metal ion and the acidity of the protons at the d carbon of the ligand, L. It has been reported that the relative acidity of the protons at the d carbon of related macrocyclic ligands depends markedly on the nature of the metal ion bonded to it, and is 1000 times less for Cu(II) complexes than for Ni(II) complexes [19]. Therefore, the intermediate, 8 formed may be more inert for [Ni(L)] than that for [Cu(L)] so that the regeneration of original complex may be more difficult for [Ni(L)] than that for [CuL].…”