(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

Treatment of [(eta(5)-C5Me5)Ir(H2O)(3)](CF3SO3)(2) with adenine (AH) and 9- ethyladenine (9-EtA) affords the respective tetra- and trinuclear complexes [{(eta(5)-C5Me5)Ir(A)}(4)](CF3SO3)(4) (1) and [{(eta(5)-C5Me5)Ir(9-EtAH(-1 ))}(3)](CF3SO3)(3) (2), whose structures were established by X-ray analysis . The former compound exhibits a mu-1 kappa N-9:2 kappa(2)N(6),N-7 coordina tion mode for the bridging adeninate ligands, the latter a mu-1 kappa N-1:2 kappa(2)N(6),N-7 binding pattern, associated with a wide Ir-N7-C8 angle of 149 degrees and substantial respectively upfield (delta 7.65) and downfiel d (delta 8.82) shifts for the purine ring protons H2 and H8. Exclusive form ation of analogous diastereomeric trimers is likewise observed in the pH* r ange 3.5-9.0 for equimolar equilibrium systems of [(eta(5)-C5Me5)Ir(H2O)(3) ](2+) with 5'-AMP(2-) and 5'-ATP(4-). Reaction of this organometallic fragm ent with guanine (GH) and hypoxanthine (HxH) also provides tetramers [{(eta (5)-C5Me5)Ir(B)(H2O)}(4)](CF3SO3)(4) 3 (B = G) and 4 (B = Hx) in which, how ever, 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)-C6H6)Ru(Hx)(H2O)}(4)](CF3SO3)(4) (5) was c onfirmed by X-ray analysis. Two cyclic (presumably trimeric) oligomers with respectively mu-1 kappa N-9:2 kappa(2)O(6),N-7 and mu-1 kappa N-1:2 kappa( 2)N(7),O(H2O) binding patterns are present at an approximately 1:1 ratio in weakly acid equimolar equilibrium systems of [(eta(5)-C5Me5)Ir(H-2)(3)](2) with 5'-IMP2- and 5'-ITP4-. Phosphate coordination is absent for this fra gment in the presence of purine nucleoside 5'-triphosphates, in striking co ntrast to (eta(6)-(CH6)-H-6)Ru(II) and (eta(5)-C5Me5)Rh(III), whose pH-depe ndent reaction behaviour is reported for comparison purposes. (C) 2000 Else vier Science S.A. All rights reserved.