Ramesh Bembi

Copper(II), copper(III) and nickel(II) complexes of the macrocyclic diamide ligands 1,4,7,10-tetra-azacyclododecane-2,3-dione, 1,4,7,11-tetra-azacyclotridecane-2,3-dione, 1,4,8,11-tetra-azacyclotetradecane-2,3-dione and electrochemical studies on the copper and nickel complexes of 1,4,8,11-tetra-azacyclotetradecane-5,7-dione

Abstract The syntheses of three new macrocyclic diamide ligands, 1,4,7,10-tetra-azacyclododecane-2,3-dione (L A ), 1,4,7,11-tetra-azacyclotridecane-2,3-dione (L B ) and 1,4,8,11-tetra-azacyclotetradecane-2,3-dione (L C ) are described. A number of copper(II) and nickel(II) complexes of these ligands have been characterised in the solid state. The complexes are non-electrolytes in aqueous solution due to ionisation of two amide protons to give neutral complexes [M(L2H)]. The yellow planar nickel(II) complex of L B , [Ni(L B 2H)] exists in equilibrium with the blue octahedral species [Ni(L B 2H)(H 2 O) 2 ]. For the octahedral ⇌ planar equilibrium, K = 0.51 at 25 °C, and the corresponding thermodynamic parameters are ΔH° = 4.23 kcal mol −1 and ΔS° 298 = +12.8 cal K −1 mol −1 . The copper(II) complexes of L A , L B and L C are oxidised in aqueous solution by hydrogen peroxide to give the corresponding copper(III) complexes. The copper(III) complexes are brownish-yellow in colour with d–d bands at ca. 350 nm. Cyclic voltammetry on the copper(II)/copper(III) and nickel(II)/nickel(III) redox systems with 1,4,8,11-tetraazacyclotetradecane-5,7-dione (L D ) indicate completely reversibility of the copper(II)/copper(III) couple in N,N-dimethylsulphoxide solution (E 1 2 = +0.43 V versus Ag/AgCl at 25 °C). The nickel(II)/nickel(III) couple is irreversible in aqueous solution.

Characterization of Diastereoisomeric [Ni(Me8[14]ane)]2+ Cations

The isomeric Me8[l4]anes, designated by LA, LB and LC, on reaction with nickel(II) acetate tetrahydrate and subsequent addition of LiClO4·3HO yield yellow or orange-yellow square planar [NiL](ClO4)2 diastereoisomers. It has been possible to isolate two N-chiral diastereoisomers for each ligand and these give distinct infrared and 1H NMR spectra. The structures of these isomers have been assigned mainly on the basis of their 1H NMR spectra. One structure, namely [NiLBα ](ClO4)2, has been confirmed by x-ray crystallography.

Preparation and characterisation of some new 12- and 14-membered dibenzotetraaza macrocyclic complexes of iron(III)

The iron(III) macrocyclic complexes of some 12- and 14-membered dibenzo tetraaza macrocycles have been synthesised by the template process using o-phenylenediamine and the appropriate diketone. This affords a method to prepare these complexes with different ring substituents and varying degrees of unsaturation. All complexes were characterised by elemental analysis, molar conductance, magnetic susceptibility, visible and infrared spectra. They are all high spin and six coordinate. These macrocycles tend to attain a ‘saddle shape’ which favours a cis-geometry. This is supported by the infrared and Mossbauer spectra.

The Kinetics of the acid-catalysed dissociation of the macrocyclic complexes [Ni(trans-Me6[18]dieneN4)]2+ [Cu(trans-Me6[18]dieneN4]2+ and [Cu(cis-Me6[18]dieneN4)]2+ and the kinetics of the base-catalysed dissociation of the copper(II) complexes

Abstract The acid-catalysed dissociation of the copper(II) and nickel(II) complexes of trans-Me6[18]dieneN4 (2,4,4,11,13,13-hexamethyltetra-azacyclo-octadeca-1,10-diene) and the copper(II) complex of cis-Me6[18]dieneN4 (2,4,4,11,11,13-hexamethyltetra-azacyclo-octadeca-1,13-diene) have been studied kinetically. For the complexes of trans-Me6[18]dieneN4, the observed rate constant at constant hydrogen ion concentration (kobs) is given by the expression (i), where ko represents the solvolytic dissociation path way The acid catalysed reactions of the trans-diene complexes involve a rapid pre-equilibrium protonation step, followed by a slow loss of the metal ion from the protonated complex. Activation parameters for the k and ko pathways have been determined. The acid-catalysed dissociation of the copper(II) complex of the cis-diene, which is known to have pseudo-tetrahedral stereochemistry, is very much faster than that of the trans-diene which is essentially planar. This reaction shows no solvolytic pathway, but both general and specific acid catalysed pathways. Thus in the presence of acetic acid (HA) the rate expression at constant pH is given by The kinetics of dissociation of the two copper(II) complexes in basic solution have also been studied in detail. For 1 X 10−2 to 5 X 10−2 M hydroxide, the reactions show a second order dependence on the hydroxide ion concentration and the dissociation can be represented by the equations. At high base concentrations the reactions show a first order dependence on [OH−] (as all CuL2+ is converted to CuLOH+). Values of K and k have been determined. The equilibrium CuL2+ + N−3 ⇌ [CuLN3]+ has also been studied for the trans diene, the equilibrium constant is 7.3 M−1 compared with 0.27 M−1 for the reaction with hydroxide ion at 25 °C.

Synthetic and kinetic studies on copper(II), nickel(II) and cobalt(III) complexes of 1,4,7,11,14-penta-azacycloheptadecane([17]aneN5)

The preparation of the pentadentate macrocyclic ligand L (= II, 4,7,11,14-penta-azacycloheptadecane) is described. The complexes [CuL](ClO4)2, [NiL(H2O)](ClO4)2, [CoClL](ClO4)2, [CoL(CO3)]ClO4, [Co([15]aneN5)CO3]ClO4, [CoL(DMF)](ClO4)3, [CoL(OOCH)](ClO4)2 and [CoL(OH2)](ClO4)2 have been prepared and characterised. The copper(II) complex appears to be square pyramidal on the basis of its dd spectrum and the nickel(II) complex is octahedral. The copper and nickel complexes dissociate in acidic solution and the reactions have been studied kinetically. For the copper(II) derivative, rate = kH[Complex][H+]2 with kH = 1.2 X 103 M−2 s−1 at 25 °C and I = 0.1 M (NaClO4) (ΔH‡ = 29.8 kJ mol−1 and ΔS298‡ = −86 JK−1 mol−1). Dissociation rates of the copper complexes increase in the order[15]aneN5 < [16]aneN5 < [17]aneN5. For the dissociation of the nickel(II) complex, rate = kH[Complex][H+] with kH = 0.23 M−1 s−1 at 25°C (Δ‡ = 44.0 kJ mol−1, ΔS298‡ = −109 JK−1mol−1). Mechanisms for these reactions are considered. The nickel(II) complex is oxidised to nickel(III) in acetonitrile solvent in a pseudo-reversible process (Esol12 = +1.11 V with reference to S.C.E.). Mercury(II) catalysed aquation of [CoClL]2+ has been studied (kHg = 1.4 X 10−2 M−1 s−1 at 25°C). Potentiometric titration of the aqua-complex gives pKa = 6.2 for the aqua ⇌ hydroxo equilibrium. The hydroxo complex [CoL(OH)]2+ reacts rapidly with CO2 to give the monodentate carbonato complex [CoL(CO3)]+. Decarboxylation of the carbonato complex occurs in acidic solution and the reaction has been studied kinetically, k = 0.43 s−1 at 25°C (ΔH‡ = 48.4 kJ mol−1; ΔS298‡ = −90 JK−1 mol−1). Similar studies on [Co([15]aneN5)CO3]+ are also reported. The base hydrolysis of the monodentate formato complex [CoL(OOCH)]2+ has also been investigated (kOH = 3.0 x 104 M−1 s−1 at 25°C, ΔH‡ = 41.1 kJ mol−1; ΔS298‡ = −20 JK−1 mol−1).

SYNTHESIS AND CHARACTERIZATION OF COPPER(II) AND NICKEL(II) COMPLEXES WITH 1,5,8,12-TETRAAZACYCLOHEPTADECANE AND 1,5,8,12-TETRAAZACYCLOOCTADECANE

Abstract Copper(II) and nickel(II) complexes with 1,5,8,12-tetraazacycloheptadecane and 1,5,8,12-tetraazacyclo-octadecane have been synthesised. These complexes contain 8- and 9-membered chelate rings. The visible spectra of the copper(II) complexes show that the 5,6,5 chelate ring sequence is the most favourable geometry for coordination. The nickel(II) complex of 1,5,8,12-tetraazacycloheptadecane is square planar, but can be converted into corresponding octahedral complexes. The geometrical features of this macrocyclic ligand show that the 4-coordinate nickel(II) species is favoured over the 6-coordinate one.

Synthesis and characterisation of cobalt(II), cobalt(III) and rhodium(III) complexes of N, N', N", N"-tetra(2-cyanoethyl) cyclam (TCEC) and N, N', N", N'-tetra(3-aminopropyl) cyclam (TAPC)

SummaryComplexes of cobalt(II), cobalt(III) and rhodium(III) with TCEC and TAPC have been synthesised. TCEC with cobalt(II) gave [Co(TCEC)Br]Br and [Co(TCEC)Cl]Cl, five coordinate high spin square pyramid complexes, but the corresponding cobalt(III) complex could not be characterised. Rhodium(III) gave a six coordinate [Rh(TCEC)Cl2]Cl complex, in which the two coordinated chlorides have acis-geometry and the four pendant arms lie on one side of the N4 plane with none of the —C≡N groups coordinated TAPC on the other hand gives the cobalt(III) complex, [Co(TAPC)Br]Br2, in which one of the amino groups of the four pendant arms is coordinated to cobalt. Rhodium(III) with TAPC gave [Rh(TAPC)Cl]Cl2 in which one axial site is occupied by the amino group of one of the pendant arms and the other by Cl−.

Acid dissociation kinetics of the copper(II) Ccomplex of 1,5,8,12-tetra-azacyclo-octadecane ([18]aneN4) and the nickel(II) complex of 1,5,8,12-tetra-azacycloheptadecane ([17]aneN4)

SummaryThe kinetics of the dissociation of [Cu([18]aneN49)]2+ and [Ni([17]aneN48)]2+ in acidic solution have been studied in detail. The dissociation of [Cu([18]aneN48)]2+ displays saturation kinetics beyond 0.4 mol dm−3 HC1O4 with values of kobs becoming independent of [HClO4]. The kinetic behaviour can be rationalised in terms of the scheme,

The preparation and reactivity of bidentate phosphato complexes of cobalt(III). Cis-[Co(cyclen)PO4], cis-[Co(en)2PO4] and the p-(nitrophenylphosphato)bisethylenediaminecobalt(III) cation

\begin{gathered} CuL^{2 + } + H^ + \mathop \rightleftharpoons \limits^K CuLH^{3 + } \hfill \\ CuLH^{3 + } \mathop \to \limits^k Cu^{2 + } + protonated ligand \hfill \\ \end{gathered}