Kinetically and Thermodynamically Controlled Formation of Homo- and Heterobinuclear Platinum(II) and Palladium(II) Complexes Supported by Bidentate Triazolopyrimidine Ligands.

Abstract

The formation of the mononuclear Pt(II) compound cis-[Pt(NH(3))(2)(Hmtpo-N(3))(2)](NO(3))(2).2H(2)O (1) (Hmtpo = 4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine) upon reaction of Hmtpo with cisplatin is reported. Subsequent reactions of 1 with Pd(II) electrophiles of the type [Pd(am)(2)(H(2)O)(2)](NO(3))(2) ((am)(2) = en, bpy) in neutral aqueous media afford heterobinuclear complexes of formula [(NH(3))(2)Pt(&mgr;-mtpo-N(3),N(4))(2)Pd(am)(2)](NO(3))(2), where (am)(2) = bpy (2) and en (3). On the other hand, reaction of 1 with the platinum electrophile [Pt(bpy)(H(2)O)(2)](2+) yields the binuclear compound [(mtpo-N(3))(NH(3))(2)Pt(&mgr;-mtpo-N(3),N(4))Pt(bpy)(OH)](NO(3)).6H(2)O (4). The compounds have been structurally characterized by 1-D and 2-D (1)H NMR spectroscopy and X-ray crystallography (1, 2, and 4). Compound 1 crystallizes in the triclinic space group P&onemacr; with unit cell dimensions a = 7.859(1) Å, b = 11.811(2), c = 12.986(2) Å, alpha = 73.69(1) degrees, beta = 84.53(1) degrees, gamma = 85.80(1) degrees, and Z = 2. Compound 2 crystallizes in the monoclinic space group P2(1)/c with unit cell dimensions a = 13.752(1) Å, b = 12.5658(8) Å, c = 19.215(1) Å, beta = 118.08(1) degrees, and Z = 4. Compound 4 crystallizes in the triclinic space group P&onemacr; with unit cell dimensions a = 10.282(2) Å, b = 14.133(3) Å, c = 14.794(3) Å, alpha = 110.63(3) degrees, beta = 97.83(3) degrees, gamma = 108.48(3) degrees, and Z = 2. The structure of 1 consists of mononuclear cis-[Pt(NH(3))(2)(Hmtpo-N(3))(2)](2+) cations, in which the Hmtpo ligands are coordinated through N(3) in a monodentate fashion. In compound 2, two mtpo moieties bridge the metal centers through N(3) and N(4), giving rise to a Pt-Pd separation of 3.083(1) Å. On the other hand, only one bridging mtpo moiety is present in 4, which accounts for a lengthening in the M-M separation to 3.337(1) Å. The environment around the metal centers consists of four nitrogens, except for one Pt nucleus in compound 4, which presents a rare example of a terminal OH group. The (1)H NMR studies show clearly that these structures are retained in solution. Finally, a bidentate bridging mode through N(1)/N(3) is postulated for the species generated in solution by the reaction of 1 with the electrophile [Pt(NH(3))(2)(H(2)O)(2)](2+), which may lead to tetranuclear or polymeric species.