Rhenium(IV) and rhenium(V) complexes with 3,5-dimethylpyrazole

Mono- and dinuclear Re-IV and Re-V complexes with 3,5-dimethylpyrazole (Me(2)pzH) were synthesized. The cis- [Re2O3Cl4(3,5- Me(2)pzH)(4)] complex (cis-1) was prepared by the reaction of NH4ReO4 with K[HB(Me(2)pz)(3)] in concentrated HCl or by refluxing of [ReCl3(MeCN)(PPh3)(2)] with Me(2)pzH in air. The bromide complex trans-[Re2O3Br4(3,5-Me(2)pzH)(4)] (trans-2) was synthesized by passing dry HBr through a solution of [Re2O3Br2(mu-3,5-Me(2)pz)(2)(3,5-Me(2)pzH)(2)] (4) in chloroform. The pyrazolate-bridged complex [Re2O3Cl2(mu-3,5-Me(2)pz)(2)(3,5-Me(2)pzH)(2)] (3) was prepared from (Et4N)(2)[ReOCl5] or Cs-2[ReOCl5] and Me(2)pzH. The corresponding bromide and iodide complexes [Re2O3X2(3,5-Me(2)pz)(2)(3,5-Me(2)pzH)(2)] center dot C6H6 (X = Br (4) or 1 (5)) were synthesized by the reactions of (NH4)(2)[ReBr6] or K-2[ReI6], respectively, with Me(2)pzH. The [ReO(OMe)(3.5-Me(2)pzH)(4)]Br-2, center dot 3,5-Me(2)pzH center dot 4H(2)O complex (6) was obtained as a by-product in the synthesis of complex 4. The reaction of [ReNCl2(PPh3)(2)] with Me(2)pzH was accompanied by hydrolytic denitration giving rise to the mixed-ligand complex [Re2O3Cl2(mu-3.5-Me(2)pz)(2)(3,5-Me(2)pzH)(PPh3)] (7). The reaction of (NH4)(2)[ReBr6] with a Me(2)pzH inelt gave the trans-[ReBr4(3,5-Me(2)pzH)(2)], center dot Me2CO Complex (8). The structures of complexes 2 and 4-8 were established by X-ray diffraction. All compounds were characterized by elemental analysis, electronic absorption spectroscopy, H-1 NMR and IR spectroscopy, mass spectrometry, and cyclic voltammetry.