Synthesis, Spectral Characterization and Crystal Structure of Chlororhodibalamin: A Synthesis Platform for Rhodium Analogues of Vitamin B12 and for Rh-Based Antivitamins B12

Chlororhodibalamin (ClRhbl), a rhodium analogue of vitamin B-12(cyanocobalamin), was prepared in 84% yield by metalation of the metal-free B(12)ligand hydrogenobalamin using the Rh-I-complex [Rh(CO)(2)Cl](2). ClRhbl was identified and characterized by UV/Vis, circular dichroism, high-resolution mass and heteronuclear NMR spectra. The Rh-III-corrin ClRhbl features the 'base-on' architecture of vitamin B-12. X-ray analysis of single crystals of ClRhbl have revealed its detailed 3D-geometry and close structural similarity to the Co-III-analogue chlorocobalamin (ClCbl). ClRhbl is a versatile starting material for the preparation of other rhodibalamins, among them the organometallic derivatives adenosylrhodibalamin and methylrhodibalamin, the Rh analogues of the important coenzyme and cofactor forms of B-12, adenosylcobalamin and methylcobalamin.