Izlaganje sa skupa

Structural and Solution Properties of Rhodoximes: the Rh Analogues of Cobaloximes, a Vitamin B₁₂ Model

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

Sažetak

Cobaloximes, LCo(DH)2 where L = neutral ligand, DH = monoanion of dimethylglyoxime and X = monoanionic ligand, have been widely studied in solution and in the solid state. Since then, they have been proposed as a model of the vitamin B12 system. These studies have furnished a foundation for understanding the mechanism of the Co-C bond cleavage in the vitamin B12 coenzyme. However, problems relating to the role played by the electronic and steric properties of the ligands around Co require further investigation. Therefore, the study has been extended to the pyRh(DH)2R complexes (rhodoximes). In fact, the ionic radius of Rh, larger than that of Co, should diminuish the steric interaction between the ligands. The NMR and kinetic results indicate that the transmission of the electronic effects from R to the trans neutral ligand in rhodoximes is similar to that observed in cobaloximes: the frans-influence and the irons-effect have the same trend as already found in the Co analogues. Structural data agree about a less hindered coordination around the metal centre than in the corresponding cobaloximes. Variation of the M-C distances with an increase in the bulk of axial ligand is significantly smoother in the Rh than in the Co complexes. Correspondingly, the irans-influence and -effect appear to be more enhanced in rhodoximes. Comparison between the behaviour of cobaloximes and rhodoximes is discussed on the basis of electronic and steric influences.

Ključne riječi

Hrčak ID:

136888

URI

https://hrcak.srce.hr/136888

Datum izdavanja:

1.8.1994.

Posjeta: 860 *