Mechanistic behaviour of alkylcobaloximes and imino-oxime complexes related to vitamin B12

Abstract

The ligand substitution reactions of complexes of the type trans-[(R)Co(Chel)S](+/0) with L, where chel = (DO)(DOH)pn = 2,2'-(1,3-diaminopropanebis(2-methyl-3-butanone)oxime), R = CH(3), L = imidazole, pyrazole, 1,2,4-triazole and 1-methylimidazole, and S = water and MeOH, and chel = (Hdmg)(2) = bis(dimethylglyoximate), R = CH(2)Cl, CH(2)Br, and CH(2)I, L = thiourea and pyridine, and S = water, were studied in detail as a function of temperature and pressure. The reported activation parameters (DeltaH, DeltaS and DeltaV) support the operation of a dissociative interchange (I(d)) mechanism. Complexes of the type trans-[RCo(Hdmg)(2)L] (R = CH(2)Cl, CH(2)Br, and CH(2)I; L = H(2)O and Py) were fully optimized at the B3LYP/LANL2DZp level, and the structural data support the mechanistic assignment based on the reported activation parameters. For the reaction of trans-[(CH(3))(2)Co((DO)(DOH)pn)] with acid, the activation parameters (DeltaH, DeltaS and DeltaV) were found to be 37 +/- 1 kJ mol(-1), -86 +/- 3 J mol(-1) K(-1) and -18.9 +/- 0.7 cm(3) mol(-1), respectively, and support a protonation mechanism.

Trans influence of cyanide on the structural and electronic properties of a series of organocobaltIII(TIM) complexes

“…Nonetheless, both species typically bear a L-type ligand (L = neutral ligand; commonly a weak Lewis base) in the trans position relative to the R group, and substantial work on the influence of these ligands on the nature of the cobalt–carbon bond, and vice versa , has been performed. 9,10…”

“…ligands on the nature of the cobalt-carbon bond, and vice versa, has been performed. 9,10 On the other hand, significantly less attention has been devoted to vitamin B 12 model systems bearing X-type ligands (X = monoanionic ligand) in the analogous trans position. 11,12 A related family of Co III complexes is based on TIM (2,3,9,10tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene; type C in Scheme 1), where the Co III center is substantially more electron-deficient than those in types A and B due to TIM being neutral.…”

Vibrational spectra of zirconium chelate of 1, 2-naphthoquinone dioxime by DFT and HF

“…The specific action of the grouping towards nickel ions has been attributed to the anti isomers of the compounds. A major aim to study such compounds originated from the fact that these types of ligand showed biological importance [1][2][3][4][5][6][7]. Oximes and dioximes have often been used as chelating ligand in the field of coordination chemistry and their metal complexes have been of great interest for many years.…”

Synthesis, characterisation and antimicrobial activity of bivalent metal (Zn, Cd, Hg, Pb and Ag) chelates of 1, 2- naphthoquinone dioxime

“…The specific action of the grouping towards nickel ions has been attributed to the anti isomers of the compounds. A major aim to study such compounds originates from the fact that these types of ligands shows biological importance [4,10]. Oximes and dioximes have often been used as chelating ligands in the field of coordination chemistry and their metal complexes have been of great interest for many years.…”