Diastereomeric separations and crystal structures of rhodium(III) and iridium(III) complexes containing adenosine and related nucleosides

Six C3 cyclic trinuclear complexes [{M(Cp*)(L)}3]3+(M = RhIII and IrIII; Cp*=5–C5Me5) containing adenosine nucleosides [L: adenosine (Hado), 2-deoxyadenosine (Hdeoado) and 5-acetyl-2,3-isopropylideneadenosine (Haipado)] were prepared and characterized by UV/Vis and circular dichroism (CD) spectra, NMR spectroscopy, electrospray ionization mass spectroscopy and X-ray crystal structure analysis. The isolations of one and/or two diastereomers were successfully carried out for the four systems by second-order asymmetric transformation and/or fractional crystallization. Interestingly, a striking kinetic difference was found between the present RhIII– and IrIII–ado systems. The crystal structure of CCC-[{Rh(Cp*)(ado)}3](CF3SO3)3·2.5H2O· CH3OH revealed that the ado ligand adopts a µ-1N1:22N6,N7 bridging mode and the three purine rings forming a triangle dome-like cavity can include one methanol molecule into its cavity. The absolute configurations were assigned to these complexes based on the crystal structural result and CD spectral arguments. The RhIII–Nmethyl adenosine (HNMeado) system exceptionally gave a di-µ-hydroxy anti-dinuclear structure because of the weak coordination ability of the N(6) donor.