Metal-Purine Interactions: Homo- And Heterodinuclear Platinum(II) and/or Palladium(II) Complexes of 8-Thiotheophylline. Crystal Structures of [Pt(μ-TT)(dppm)]2·2DMSO and [(dppm)Pt(μ-TT)2Pd(dppm)]·7H2O

Article abstract of DOI:10.1021/ic961288p

The reaction of cis-[MCl₂(dppm)] (M = Pt(II) and Pd(II); dppm = bis(diphenylphosphino)methane) with H₂TT and NaOH (H₂TT = 8-thiotheophylline) yields neutral mononuclear [M(HTT-S(8))₂(dppm)] complexes. Homodinuclear [M(μ-TT-N(7),S(8))(dppm)]₂ (M = Pt(II) and Pd(II)) are prepared either by the reaction of [M(HTT)₂(dppm)] with cis-[MCl₂(dppm)] and NaOH or by the direct reaction of cis-[MCl₂(dppm)] with Na₂TT, prepared in situ from H₂TT and NaOH. The crystal structure of the Pt derivative is reported: [Pt(μ-TT)(dppm)]₂·-2DMSO (3) crystallizes in the triclinic space group P1 with a = 12.949(3) A?, b = 13.009(3) A?, c = 22.980(5) A?, α = 96.89(3)°, β= 103.53(3)°, γ = 106.43(3)°, Z = 2, and R₁ = 0.045. Heterodinuclear [(dppm)Pt(μ-TT)₂-Pd(L-L)] complexes are obtained by reaction of [Pt(HTT)₂(dppm)] with [PdCl₂(L-L)] in basic medium (L-L = dppm and 2,2′-bipyridine). The crystal structure of [(dppm)Pt(μ-TT)₂Pd(dppm)]·7H₂O (5) is reported. The complex crystallizes in the orthorhombic space group P2₁2₁2₁] with a = 16.560(5) A?, b = 17.063(5) A?, c = 24.428(5) A?, Z = 4, and R₁ = 0.042. The structures of 3 and 5 are almost identical, by which 5 can be seen as an isomorphic substitution of one of the Pt(II) ions of 3 by a Pd(II) ion. The structures consist of dinuclear units having a pseudo-2-fold axis perpendicular to that defined by the metal atoms. The two metal atoms are bibridged by two μ-TT-N(7),S(8) ligands, in a head to tail arrangement. The square-planar coordination of the metal atoms is completed by a chelate dppm ligand. The steric repulsions between the bulky dppm ligands must be the main factor precluding metal-metal interaction in these compounds.