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 2 O)] 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 2 O)] 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- N 3 ( I ), 1-methyl-1,2,4-triazole- N 4 ( II ), 1-methyltetrazole- N 3 ( III ), or 3-methylpyridine- N 1 ( 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.