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Title: Preparative, kinetic and mechanistic aspects of cobalt(III) amine complexes containing carboxylate, aminoacid-derived and peptide ligands
Author: Ford, Peter D.
ISNI:       0000 0001 3474 2510
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1981
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This thesis describes some ligand substitution and peptide formation reactions in the coordination sphere of cobalt(III). The influence of various factors on rates of base hydrolysis of chloropentaminecobalt(III) complexes has been investigated. In the series of complexes trans-[Co(en)[2]Cl(RC0[2][-])][+] (en = 1,2-diaminoethane R = -H, -CH[2]CH[3], -C(CH[3])[3]) rates of base hydrolysis to cis- and trans-[Co(en)[2]OH(RCO[2][-])][+] decrease 12-fold along the series, while the cis/trans product ratio depends very much on the size of R. In the aminosulphonate complexes cis-[Co(en)[2]Cl(NH[2]{CH[2]}nSO[3][-])][+] (n = 1,2) base hydrolysis rates depend sensitively on n and the SO[3][-] group in the aminomethylsulphonate complex (n = 1) causes a 200-fold enhancement in reactivity. A comparison with base hydrolysis of a series of corresponding aminocarboxylic acid complexes is made. In the complexes cis-[Co(en)[2]Cl(RNH[2])][2+] (R = C[6]H[5]-, p-CH[3]C[3]H[4]-, m-CH[3]C[6]H[4]) rates of base hydrolysis are enhanced 10[4] fold in the presence of 1.0 M mercury(II) at 50°C. The role of cobalt(III) in promoting various reactions has also been investigated. The complex cis-[Co(en)[2]Cl(NH[2]CH[2]CH0)][2+] has been prepared and intramolecular imine formation between the carbonyl centre and an amine ligand investigated. The reaction is stereospecific and in the product [Co(en)Cl(NH[2]{CH[2]}[2]N=CHCH[2]NH[2])CI][2+] the tridentate imine ligand adopts a facial arrangement in the coordination octahedron. A new, high yield and stereospecific method for peptide synthesis in the coordination sphere of cobalt(III) has been developed using the reaction between cis-beta-[Co(trien)Cl[2]]Cl (trien = triethylenetetramine) and various aminoacid esters. A number of symmetrical and unsymmetrical dipeptide ester complexes have been prepared. Reduction of suspensions of these complexes in acidified methanol with H2S provides a facile method for isolating the free dipeptide ester ligands. These have been used to prepare tripeptide ester complexes and in two cases the method has been applied to the synthesis of tetrapeptide esters from the constituent aminoacid esters.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemistry, general