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.