Synthesis and characterization of cobalamines with anionic and neutral phosphorous donor ligands

In dimethyl formamide as solvent aquacobalamine reacts with the triorganyl phosphites 3-7 to give the corresponding (diorganylphosphito-P)cobalamines, their new β-axial ligands [P(O)(OR)₂]^- (3a-7a) being formed by partial hydrolysis. In methanol, however, additional methanolysis normally leads to (dimethylphosphito-P)cobalamine with the axial ligand [P(O)-(OMe)₂]^- (2a). Exceptions are P(OCH₂CH₂NMe₂)₃ (4) giving a complex with the only partially methanolized chiral ligand [P(O)(OCH₂CH₂NMe₂)- (OMe)]^- (4b), too, and the bicyclic phosphite 5 which is also coordinated in the unchanged, nonhydrolyzed form. All complexes are characterized by elementary analysis, electrophoresis, UVVis and ¹H, ³¹P NMR spectra. The chirality of the cobalamine moiety causes diatropism of the two organyl groups in the prochiral ligands [P(O)(OR)₂]^- which is well seen in the NMR spectra of the complexes with the methyl and phenyl derivatives 2a and 6a, whereas the spectra with ligands 3a and (in part) 4a are not resolved well enough to distinguish the two forms. With the chiral ligand 4b two diastereomers are obtained in different yields; this asymmetric induction is indicated by the intensities of the respective signals in the NMR spectra.