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

摘要

Treatmet of [(#eta#~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 [{(#eta#~5-C_5Me_5)Ir(A)}_4] (1) and [{(#eta#~5-C_5Me_5)Ir(9-EtAH_(-1))}_3](CF_3SO_3)_3 (2), whose structues were established by X-ray analysis. The former compound exhibits a #mu#-1kN~9:2k~2N~6,N~7 coordination mode for the bridging adeninate ligands, the latter a #mu#-1kN~1:2k~2N~6,N~7 binding pattern, associated with a wide Ir-N7-C8 angle of 149deg and substantial respectively upfield (#delta# 7.65) and downfield (#delta# 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 [(#eta#~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 [{(#eta#~5-C_5Me)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 #mu#-N~7,N~9 coordination mode in 3 and the analogous complex [{(#eta#~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 #mu#-1kN~9:2k~2O~6, N~7 and #mu#-1kN~1:2k~2N~7, O(H_2O) binding patterns are present at an approximately 1:1 ratio in weakly acid equimolar equilibrium systems of [(#eta#~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 (#eta#~6-C_6H_6)Ru(II) and (#eta#~5-C_5Me_5)Rh(III), whose pH-dependent reaction behaviour is reported for comparison purposes.