1H and 13C NRM and infrared spectral studies on mixed ligand complexes of the type cis-[Co(en)2(Im)Cl]Cl2

A number of mixed ligand complexes of the type [Co(en)₂(Im)Cl]Cl₂ (Im = imidazole or a substituted imidazole) have been synthesized by reaction of trans-[Co(en₂Cl₂]Cl with the imidazole ligands. Electrical conductivity measurements support the ionic (1:2) formulation of the compounds, the electronic spectra is in agreement with an octahedral stereochemistry, and the IR and NMR (¹H and ¹³C) spectra strongly favour the cis configuration for the isolated complexes, [Co(en)₂(Im)Cl]Cl₂.Trans-[Co(en)₂Cl₂]Cl reacts with KNCS to form cis-[Co(en)₂(NCS)₂Cl, the crystal structure of which is briefly reported. This lends additional support in favour of the probable cis configuration of the above complexes.     

Indium-mediated regio- and diastereoselective reduction of norbornyl alpha-diketones

A novel, efficient, and regio- as well as diastereoselective conversion of non-enolizable bicyclic alpha-diketones into synthetically useful acyloins mediated by indium metal is described. The reduction is highly diastereoselective, leading exclusively to endo-acyloins (endo-hydroxyl groups) in excellent yields, and tolerates a variety of sensitive substituents, such as acetate, ester, and bridgehead halogens. The regioselectivity in the reductions of monosubstituted alpha-diketones varied from 70:30 to 100:0 for the two possible isomeric alcohols. The methodology is extended to the synthesis of highly functionalized cyclopentane carboxaldehydes, potential building blocks in organic syntheses, by cleavage of the acyloins by treating them with Pb(OAc)4 in MeOH/PhH. Allylindium additions to carboxaldehydes 22 have been found to be highly diastereoselective.     

Kinetics of aquation and base hydrolysis ofcis-(carboxylato) (ethylamine)bis(ethylenediamine)cobalt(III) ions

Summary The aquation ofcis-[Co(en)₂(NH₂Et)O₂CR]²⁺ [R=H or Me] is strongly acid-catalysed and the rate and activation parameters for this process are reported. No significant rate difference is observed in the spontaneous aquation path for the complexes. The acetato complex undergoes acid catalysed aquation at a rate comparable to the of the corresponding formato complex, in contrast with the relative basicities of the coordinated formate and acetate. This result is interpreted in terms of relative solvation effects of the initial and transition states of both complexes.The base hydrolysis of both complexes obeys overall second order kinetics in the 0.05[OH^–]_T 0.35 mol dm^–3 range (I=0.5 mol dm^–3). The formato complex reacts five times faster than its acetato analogue under comparable conditions, which is fully consistent with the dissociative mode of activation of the amido conjugate base involving Co–O bond heterolysis. A substantially large positive value for the activation entropy supports SN₁CB mechanism for base hydrolysis.     

Kinetics and mechanism of base hydrolysis oftrans-bis(Hmalonato)bis(ethylenediamine)cobalt(III) ion

Summary The kinetics of the first step of base hydrolysis oftrans-bis(Hmalonato)bis(ethylenediamine)cobalt(III) [malH^–=HO₂CCH₂CO ₂ ^– ] has been investigated in the 15–35° C range, I=0.3 mol dm^–3 (NaClO₄) and [OH^–]=0.015–0.29 mol dm^–3. The rate law is given by –d In[complex]_T/dt=k₁[OH^–] and at 30° C, k₁=8.5×10^–3 dm³ mol^–1s^–1, H=117.0±7.0 kJ mol^–1 and S=99.0±24.0 JK^–1mol^–1. The activation parameters data are consistent with the SN₁ cb mechanism.     

Effect of solvent on reactions of coordination complexes. Part 12: Kinetics and mechanism of chloride substitution reactions ofcis-(chloro)(2-aminoethanol)bis(ethylenediamine) cobalt(III) andcis-(chloro)(1-aminopropan-2-ol)-bis(ethylenediamine) cobalt(III) ions in acidic and basic ethylene glycol-water media

Summary The loss of chloride ion from the title complexes resulted in the predominant formation of the chelated amino-alcohol productscis-[Co(en)₂(NH₂CH₂CH(X)O/H)]^2+/3+ (X=H or Me). The kinetics of chloride release were investigated in aqueous ethylene glycol (EG) media (0 to 80% by wt of EG) at 40°–65°C in acidic media and at 20°–35°C in basic media. The rate constants decreased linearly with increasing mol fraction of the cosolvent. The plots of log kversus D _s ^–1 (S_s=bulk dielectric constant, k=first order or second order rate constants) were essentially linear with negative slopes for the reactions in an acidic medium, and tended to be curved for the base catalysed reactions. The activation enthalpies and entropiesversus X_EG (X_EG=mol fraction of EG) plots indicated extrema which might be associated with the effects of the solvent structural changes on these thermodynamic parameters. The observed solvent isotope effect at 50°C, [HClO₄]=0.010 mol dm^–3 for Cl^– release was lower than the value for the aquation ofcis-[Co(en)₂(alkylamine)Cl]²⁺ complexes reported in the literature. This is consistent with the lack of direct solvent molecule participation in the actual act of substitution at the cobalt(III) centre, as expected for a true intramolecular reaction.Part-11: A. C. Dash and J. Pradhan,Ind. J. Chem.,29A, 167 (1990).     

Electrochemical studies of azido(imidazole) cobaloxime complexes

Summary Cyclic voltammetric studies of a series of azido(imidazole) cobaloxime complexes in acetonitrile with tetraethylammonium perchlorate as the supporting electrolyte reveal the presence of the central cobalt atom in these complexes in the +III state. In addition to reductions to cobalt(II), cobalt(I) and cobalt(0) species, evidence for oxidation to cobalt(IV) also was noted.     

Liquid-liquid extraction of uranium(VI) by Cyanex 301/alamine 308 and their mixtures with TBP/DDSO

Quantitative extraction of uranium(VI) is observed from 0.2M HCl by 5% (v/v) Cyanex 301. The extraction decreases with increasing acid concentration. Mixtures of Cyanex 301 with tri-n-butyl phosphate (TBP), didecyl sulfoxide (DDSO) and Alamine 308 result in significant synergism in the extraction process, where a species of the type UO₂R₂. L is proposed to be extracted [RH=Cyanex 301 and L=TBP, DDSO or Alamine 308]. Significant extraction of uranium(VI) by 5% (v/v) Alamine 308 is observed at and above 2M HCl, which increases with further increase in acidity attaining a maximum at 6M, after which a slight decrease in extration is observed. Mixtures of Alamine 308 with TBP or DDSO result in a synergism, where a species of the type (R ₃ NH)₂ UO₂Cl₄. Lis extracted. [R ₃ N=Alamine 308, L=TBP or DDSO]. Mixtures of Alamine 308 and Cyanex 301 at 2M HCl result in a profound antagonism in the extraction of uranium(VI).     

Kinetics and mechanism of complex formation between beryllium(II) and the 3-nitrosalicylatopentaamminecobalt(III) ion

Summary The kinetics of formation and dissociation of the binuclear complex of Be²⁺ with 3-nitrosalicylatopentaamminecobalt(III) have been investigated in the 20–40 and 25–40 °C ranges (I = 0.3 mol dm ^–3), respectively. At 25 °C the rate and activation parameters for the formation of the binuclear species are: k _f = 26.9 × 10² dm³mol^–1s^–1, H = 104 ± 7kJ mol^–1 S = 91 ± 22JK^–1mor^–1.The rate constant, activation enthalpy and activation entropy for the acid-catalysed dissociation of the binuclear species are: 1.25 ± 0.08dm³mol ^–1 at 25 °C, 53 ± 3kJ mol^–1 and - 67 ± 9 J K ^–1 mol^–1, respectively. The formation of the binuclear species is chelation controlled while the dechelation is acid catalysed.     

Thorium(IV) complexes with tetradentate Schiff base ligands

Summary Some thorium(IV) complexes were synthesized with the tetradentate Schiff base ligands (N₂O₂ donor set) obtained by the condensation of ethylenediamine with salicylaldehyde (H₂salen) or acetylacetone (H₂ acacen). In all cases the neutral Schiff bases and not their anions are coordinated to the central thorium(IV) atom. The complexes have the general formula: ThL₂Xa (L = H₂ salen; X = Cl, Br, 1, NCS and L = lie acacen; X = Cl, 1, NCS, ClO₄) or ThLX₄ (L = H₂ salen; X = NO₃, ClO₄ and L = H₂ acacen; X = Br, NO₃). The stoichiometry and coordination number of the complexes was determined on the basis of elemental analysis, conductivity measurements, i.r. spectra and t.g.a./d.t.a. data. The coordination number of the complexes is either 12 or 8 for the bisor monocomplexes respectively.     

Liquid-liquid extraction of molybdenum(VI) and uranium(VI) by LIX 622

The order of extraction of Mo(VI) from 1M acid solutions by 5% (v/v) LIX 622 (HL) in benzene is HCl>HNO₃>HClO₄>H₂SO₄, and extraction decreases with increasing concentration of HCl and H₂SO₄, and increases slightly with increasing concentration of HNO₃ and HClO₄. The extracted species is shown to be MoO₂L₂ as established by IR data of organic extracts and the extracted species in the solid form. Extraction is almost quantitative at and above 10% LIX 622, and is found to be independent of [Mo(VI)] in the range of 10^–4 to 10^–3 M. The diluents CCl₄, CHCl₃ and C₆H₆ are found to be superior to solvents of high dielectric constant for extraction of Mo(VI). Extraction of uranium(VI) by 10% (v/v) LIX 622 in benzene was found to increase with increasing equilibrium pH (3.0 to 6.0), and becomes quantitative at pH 5.9. Tributyl phosphate acts as a modifier up to 2% (v/v). Thorium(IV) is almost not extracted by LIX 622 or its mixture. Separation of Mo(VI) and U(VI) is feasible.