Synthesis and structural characterization of diene- and carbonyl-rhodium(I) complexes containing bridging adeninate ligands

Article abstract of DOI:10.1016/0022-328X(91)83070-K

Diene- and dicarbonyl-rhodium(I) complexes <(diene)Rh(μ-BH_-1)>2 (diene = cod, nbd) and <(CO)2Rh(μ-BH_-1)>2 have been prepared by the reaction of <(diene)Rh(acac)> or <(CO)2Rh(acac)> with the adenine derivatives: adenine (AdH), N⁶-methyladenine (6MadH) and N⁶,N⁶-dimethyladenine (DmadH).These dimeric complexes exhibit N3, N9 coordination of the bridging adeninate ligands as demonstrated by an X-ray structural study of <(CO)Rh(μ-Dmad)(PPh3)>2 3c, prepared by substitution of a carbonyl ligand in <(CO)2Rh(μ-Dmad)>2 3b by PPh3.In contrast, a tetrameric structure was observed for <(CO)2Rh(μ-3madH_-1)>4 4 (3mad = 3-methyladenine), in which the 3madH_-1 anions are coordinated at N6 and N7.When N7 coordination is unfavourable and N9 unavailable, which is the case for 8-aza-9-methyladenine (Maad), N1, N6 binding may be observed, as established by an X-ray structural study of <(cod)Rh(μ-MaadH_-1)>2 5.However, in order to achieve this coordination mode it is necesssary for the substituted exocyclic amino groups (N6) to twist by an average angle of 31.2 deg out of the base plane.