(η 5-Pentamethylcyclopentadienyl)iridium(III) complexes of purine nucleobases and nucleotides: a comparison with (η 6-arene)ruthenium(II) and (η 5-pentamethylcyclopentadienyl)rhodium(III) species

Abstract

Treatment of [(η 5-C 5Me 5)Ir(H 2O) 3](CF 3SO 3) 2 with adenine (AH) and 9-ethyladenine (9-EtA) affords the respective tetra- and trinuclear complexes [{(η 5-C 5Me 5)Ir(A)} 4](CF 3SO 3) 4 ( 1) and [{(η 5-C 5Me 5)Ir(9-EtAH −1)} 3](CF 3SO 3) 3 ( 2), whose structures were established by X-ray analysis. The former compound exhibits a μ-1κ N 9:2κ 2 N 6, N 7 coordination mode for the bridging adeninate ligands, the latter a μ-1κ N 1:2κ 2 N 6, N 7 binding pattern, associated with a wide IrN7C8 angle of 149° and substantial respectively upfield ( δ 7.65) and downfield ( δ 8.82) shifts for the purine ring protons H2 and H8. Exclusive formation of analogous diastereomeric trimers is likewise observed in the pH* range 3.5–9.0 for equimolar equilibrium systems of [(η 5-C 5Me 5)Ir(H 2O) 3] 2+ with 5′-AMP 2− and 5′-ATP 4−. Reaction of this organometallic fragment with guanine (GH) and hypoxanthine (HxH) also provides tetramers [{(η 5-C 5Me 5)Ir(B)(H 2O)} 4](CF 3SO 3) 4 3 (B=G) and 4 (B=Hx) in which, however, O6 only participates in outer-sphere coordination through O6⋯H–O interactions to the water ligand. The μ- N 7, N 9 coordination mode in 3 and the analogous complex [{(η 6-C 6H 6)Ru(Hx)(H 2O)} 4](CF 3SO 3) 4 ( 5) was confirmed by X-ray analysis. Two cyclic (presumably trimeric) oligomers with respectively μ-1κ N 9:2κ 2 O 6, N 7 and μ-1κ N 1:2κ 2 N 7, O(H 2O) binding patterns are present at an approximately 1:1 ratio in weakly acid equimolar equilibrium systems of [(η 5-C 5Me 5)Ir(H 2O) 3] 2+ with 5′-IMP 2− and 5′-ITP 4−. Phosphate coordination is absent for this fragment in the presence of purine nucleoside 5′-triphosphates, in striking contrast to (η 6-C 6H 6)Ru(II) and (η 5-C 5Me 5)Rh(III), whose pH-dependent reaction behaviour is reported for comparison purposes.