Substituent and Noncovalent Interaction Effects in the Reactivity of Purine Derivatives with Tetracarboxylato-dirhodium(II) Units. Rationalization of a Rare Binding Mode via N3

Reactions between [Rh₂(CH₃COO)₄] with 2,6-diaminopurine (HDap) or 6-chloro-2-aminopurine (HClap) and [Rh₂((CH₃)₃CCOO)₄] with HClap produce, three new dirhodium­(II) carboxylate complexes of the general form, [Rh₂(RCOO)₄(Purine)₂] (R= CH₃, (CH₃)₃C). Single crystal X-ray diffraction studies confirm that in all cases the purine coordinates to the axial position of the dirhodium­(II)­tetracarboxylate unit. However, while the complex obtained with HDap features the typical purine binding mode via N(7), complexes containing HClap show unusual N3 coordination. This is an extremely rare instance of an unrestricted purine binding via N3. Some rationalization of these data is offered based on a series of DFT calculations.