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Solid State and Solution Properties of Vitamin B₁₂ Models

Lucio Randaccio ; Dipartimento di Scienze Chimiche, Universita di Trieste, 34127 Trieste, Italy

Sažetak

Octahedral organometallic derivatives of cobalt(III) dimethylglyoximates, LCO(DH)2R, where L = neutral ligand, R = alkyl group, DH = monoanion of dimethylglyoxime, the so called alkylcobaloximes, and other organocobalt (III) complexes with macrocyclic equatorial ligands, have been extensively studied for their ability to mimic the behaviour of the more complex system of vitamin B12, the well known cobalamins. Hence, their study has produced an incredible amount of data both in solution and in solid state, which have allowed us to establish empirical relationships between structure and solution properties of these models. Up to date, results relative to the model and comparison, when possible, with cobalamins support the idea that the homo- lytic cleavage of the Co-C bond in the B12 coenzyme is due to a »trigger« mechanism, originated by steric interactions. However, the weakening of this bond may be »helped« by electronic influences due to the lengthening of the ligand trans to the carbon atom bonded to Co.
Analysis of the chemical properties of a large number of derivatives with different alkyl groups shows approximately linear relationships between bond lengths, kinetic, and spectroscopic NMR data. For R = CH2Y group the above properties can be rationalized on the basis of the 01 and OR constants used in organic chemistry for each Y residue. An alternative interpretation is more general, since it can be applied to any alkyl group. It is based on the finding that, when the alkyl group is changed, both Co-L axial distances and kinetics properties vary linearly with an electronic parameter (EP) derived from NMR data for each R group.

Ključne riječi

Hrčak ID:

137292

URI

https://hrcak.srce.hr/137292

Datum izdavanja:

31.12.1991.

Posjeta: 849 *