Studies in Coordination Chemistry

Abstract

Several new 14-membered tetradentate macrocyclic ligands and their metal complexes were synthesized. The macrocycles, 5,6,12,13 - Tetramethyl - 1,4,8,11 - tetra-azacyclotetradeca - 4,11 - diene dihydroperchlorate; Me4 [14]diene.2HC104 (A) and 5,12 - Diethyl - 1,4,8,11 - tetra-azacyclotetradeca - 4,11 - diene dihydroperchlorate; Et2[14]diene.2HC104 (B) were prepared by the reaction of 1,2 - diaminoethane monohydroperchlorate with methylisopropenyl ketone (MIK) and ethyl vinyl ketone (EVK) respectively.

[Diagram (A)] [Diagram (B)]

Both reactions appeared to be stereospecific giving the transoid-isomers (A) and (B) rather than the cisoid-isomers of the macrocycles. Metal ion complexes of Me4 [14]diene.2HC104 (A) of the general formulation [M(Me4[14]diene)](C104)2 (M = Cu2+, Ni2+, Zn2+ and Hg2+) were prepared and the studies extended to the isolation of [CIII (Me4[14]diene )X2]n+ (where X = Cl ¯, Br ¯, N02 ¯, SCN ¯ , N3 ¯ , CH3CO2 ¯, NH3) complexes. The structures of all compounds were confirmed by elemental analyses and by spectroscopic investigations. The spectroscopic properties of the complexes are consistent with a square planar geometry for the metal (II) perchlorate salts (M=Cu(II) and Ni(II)) and a trans-arrangement of the unidentate ligands in the octahedral cobalt(III) derivatives [Co(Me4[14]diene)X2]n+. Reduction of the 5,12 - Dimethyl - 1,4,8,11 - tetra-azacyclotetradeca - 4,11 - diene dihydroperchlorate with Ni/Al alloy gave two isomeric amines i.e C - meso – 5,12 - imethyl - 1,4.8,11 - tetra-azacyclotetradecane (Isomer (a)) (LA) and C - rac - 5,12 - dimethyl - 1,4,8,11 – tetra-azacyclotetradecane (Isomer (b)) (LB).

[Diagram (LA)] [Diagram (L¬B)]

The preparation and properties of some Ni(ll),Cu(ll),Zn(ll),Mn(ll),Rh(IIl) and Co(lll) complexes of (LA) and (LB) are reported. Methylation of the secondary nitrogen protons in several macrocyclic amine ligands yielded the corresponding N-tetramethyl derivatives. The second section of the investigation dealt with the reactivity of octahedral complexes of cobalt(lll) of the type cis-[Co(en)2 (RNH2)Br]Br2 (where R=H, CH3,C2H5,n-C3H7,n-C5H11,n-C6H13, aminoacetaldehyde dimethylacetal, cyclopropylamine, 3-amino-1-propanol, 6-amino-1-hexanol). All of these complexes were assigned cis-configurations on the basis of their spectral characteristics. The base hydrolysis kinetics for bromide release were studied spectrophotometrically at 25.0°C and 1=0.10M. Loss of coordinated halide results in the formation of hydroxo product i.e. cis - [Co(en)2 (RNH2 )0H]2+ with retention of configuration. Some features of the base hydrolysis kinetics of amino acids and dipeptide esters coordinated to cobalt(lll) were also studied. [Co(dien)(aa)X]n+ (X = Cl, N02; aa = glycinate anion, glycylglycine ethyl ester, glycinamide) complexes were prepared. The rate constant kOH for peptide bond hydrolysis normally falls within the range 0.67 - 0.88 M-1s-1 at 25.0° and 1 = 0.10m. Base hydrolysis of the complexed peptide is ca 2 X 104 times faster than for the uncomplexed peptide. The kinetics of base hydrolysis of chloro - and nitro substituents in these complexes were also studied. Very rapid chloride hydrolysis occurs if the dien ligand adopts a mer - configuration and the reactions are 102 – 104 times faster than for analogous complexes where the dien ligand adopts a fac - configuration.