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)
Catalytic reduction of the diimine linkages of 11,13-dimethyl-1,4,7,10-tetraazacyclotrideca-11,13-dienenickel(II) hexafluorophosphate, [Ni( [ 13 ] dieneNa)] (PF6)2, and 12,14-dimethyl-1,4,8,11 -tetraazacyclotetradeca-12,14-dienenickel(II) hexafluorophosphate, [Ni( [ 14]dieneN4) ] (PFe) 2, in aqueous solution over Raney nickel yields Ni(II) complexes containing the fully reduced, dimethyl-substituted macrocyclic ligands. Conversion of the PFe™ salts to NO3™ derivatives has been accomplished by column chromatography. Compounds with a variety of other anions have been prepared by metathetical reactions on solutions of the NO3" complexes. Ten new complexes have been characterized on the basis of elemental analyses, conductivity and magnetic susceptibility measurements, and infrared and electronic spectral studies. [Ni([13]aneN4)]X2 and [Ni([ 14]aneN4)]X2 where X™ = PFe™ and L contain singlet ground-state Ni(II) and the planar forms of both macrocyclic ligands. Axial coordination occurs when X™ = Cl™, Br™, and NO3™ and complexes of formulation [Ni([14]aneN4)X2] have been characterized as high spin tetragonal. Two complexes, [NÍ2([13]aneN4)20x](PF6)2 and [Ni2([14]aneN4)20x](PF6)2, are dimers which contain oxalato bridging groups. These two compounds, along with monomeric [Ni([14]aneN4)(SCN)2],exhibit pseudooctahedral Ni(II) spectral characteristics and must contain folded forms of the macrocyclic ligands. Analysis of electronic spectral data for the tetragonal complexes gives a Dq*y of 1470 cm™1 for the dimethyl-substituted 14-membered ligand. This value is nearly the same as that reported for cyclam which leads us to conclude that substitution of two methyl groups on the cyclam ring has negligible steric and electronic effects.
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