Interaction of Pt(II) and Pd(II) complexes of terpyridine with 1-methylazoles:: A combined experimental and density functional study

The synthesis and characterization of several complexes of the composition [{M(terpy)}(n)(L)](ClO4)(m) (M = Pt, Pd; L = 1-methylimidazole, 1-methyltetrazole, 1-methyltetrazolate; terpy = 2,2':6',2"-terpyridine; n = 1, 2; m = 1, 2, 3) is reported and their applicability in terms of a metal-mediated base pair investigated. Reaction of [M(terpy)(H2O)](2+) with 1-methylimidazole leads to [M(terpy)(1-methylimidazole)](ClO4)(2) (1:M = Pt; 2: M = Pd). The analogous reaction of [Pt(terpy)(H2O)](2+) with 1-methyltetrazole leads to the organometallic compound [Pt(terpy)(1-methyltetrazolate)]ClO4 (3) in which the aromatic tetrazole proton has been substituted by the platinum moiety. For both platinum(II) and palladium(II), doubly metalated complexes [{M(terpy)}(2)(1-methyltetrazolate)](ClO4)(3) (4: M = Pt; 5: M = Pd) can also be obtained depending on the reaction conditions. In the latter two compounds, the [M(terpy)](2+) moieties are coordinated via C5 and N4. X-ray crystal structures of 1, 2, and 3 are reported. In addition, DFT calculations have been carried out to determine the energy difference between fully planar [Pd(mterpy)(L)](2+) complexes Ip-IVp (mterpy = 4'-methyl-2,2':6',2"-terpyridine; L = 1-methylimidazole-N3 (1), 1-methyl-1,2,4-triazole-N4 (II), 1-methyltetrazole-N3 (III), or 3-methylpyridine-N1 (IV)) and the respective geometry-optimized structures Io-IVo. Whereas this energy difference is larger than 70 kJ mol(-1) for compounds I, II, and IV, it amounts to only 0.8 kJ mol(-1) for the tetrazole-containing complex III, which is stabilized by two intramolecular C-H center dot center dot center dot N hydrogen bonds. Of all complexes under investigation, only the terpyridine-metal ion-tetrazole system with N3-coordinated tetrazole appears to be suited for an application in terms of a metal-mediated base pair in a metal-modified oligonucleotide. (c) 2006 Elsevier B.V. All rights reserved.