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

Abstract

The synthesis and characterization of several complexes of the composition [{M(terpy)} n (L)](ClO 4) 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)(H 2O)] 2+ with 1-methylimidazole leads to [M(terpy)(1-methylimidazole)](ClO 4) 2 ( 1: M = Pt; 2: M = Pd). The analogous reaction of [Pt(terpy)(H 2O)] 2+ with 1-methyltetrazole leads to the organometallic compound [Pt(terpy)(1-methyltetrazolate)]ClO 4 ( 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)](ClO 4) 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 ( I), 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⋯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.