Synthesis and Characterisation of trans- and cis-[Co(en)2(py)X]n+ (X=Cl, OH, OH2) and Optical Resolution of the cis Complexes
The synthesis of the putative trans-[Co(en)2(py)Cl]2+ complex, isolated as various salts, is reported. New or revised procedures are given for precursor complexes, some of which were known previously, and 2D NMR studies which permit the unambiguous assignment of the NH resonances for all the trans ions. NMR characterisation of a synthetic precursor, the double salt trans-[(NO2)(en)2Co(OH)…H…(OH)Co(en)2(NO2)]3+, which entails the symmetric bridging H3O2− ion in the solid state (X-ray structure), provides evidence of a kinetic role for the H3O2− bridge which must persist at low levels in solution. Reliable NMR techniques for assigning the NH protons are discussed. The synthesis and a reliable optical resolution of the well known cis-[Co(en)2(py)Cl]2+ complex are also reported, along with the syntheses of trans-, rac-cis and Λ-cis-[Co(en)2(py)OH2]3+ derivatives, all isolated for the first time. ORD and CD data are reported for all the resolved ions, and absolute configurations have been determined through chemical correlations.
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