Linkage Isomerization Reactions Of Cobalt(iii) Complexes

A series of meta and para substituted 5-phenyl-tetrazole complexes of cobalt(III) have been synthesized from their corresponding nitrile complexes utilizing nucleophilic addition of the azide anion. The N1 bonded isomers have been found to spontaneously isomerize to the corresponding N2 bonded isomers. Both the products and the reactants, along with the synthetic precursor m-trifluoromethylbenzonitrilecobalt(III) perchlorate, have been completely characterized utilizing C,H&N analysis, IR, (\u271)H and (\u2713)C NMR and UV-VIS spectroscopy.The kinetics of linkage isomerization have been investigated for the pentaamminecobalt(III) complexes of N1-5-(R-C(,6)H(,4))-CN(,4) where R = p-CH(,3), H, p-C1, m-CF(,3) and p-NO(,2) as a function of both temperature and pH. An acid catalyzed pathway involving the protonated form of the complexes was found with a rate approximately fifty times that of the deprotonated complexes.The 5-(p-nitrophenyl)tetrazole complex showed significant spectral changes due to changes in ionic strength (maintained with NaClO(,4)). This has been ascribed to a shift in the K(,a). This phenomenon also occurred in the p-nitrophenylamide complex.A method was developed to permit the determination of the percentage of N2 bonded impurity present in N1 bonded samples. Samples were found to contain as little as 11% N2 bonded isomer.The kinetically determined acid dissociation constants for the N1 bonded complexes, K(,a)1\u27s, were found to correlate well with the Hammett sigma parameter, while the spectrophotometrically determined acid dissociation constants for the N2 bonded complexes, K(,a)2\u27s, were found to correlate with sigma minus. This was attributed to the inability of the N1 bonded isomers to achieve coplanarity between the phenyl ring and the tetrazolato ring. In N2-5-(p-nitrophenyl)tetrazole, the evidence indicates that a conjugated pathway exists not only between the two aromatic rings, but additionally includes the nitro group. This resonance pathway is suggested by a bathochromic shift in (lamda)(,max) in the ultraviolet spectrum and the Hammett correlation with sigma minus