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

Mono- and dinuclear ReIV and ReV complexes with 3,5-dimethylpyrazole (Me2pzH) were synthesized. The cis-[Re2O3Cl4(3,5-Me2pzH)4] complex (cis-1) was prepared by the reaction of NH4ReO4 with K[HB(Me2pz)3] in concentrated HCl or by refluxing of [ReCl3(MeCN)(PPh3)2] with Me2pzH in air. The bromide complex trans-[Re2O3Br4(3,5-Me2pzH)4] (trans-2) was synthesized by passing dry HBr through a solution of [Re2O3Br2(μ-3,5-Me2pz)2(3,5-Me2pzH)2] (4) in chloroform. The pyrazolate-bridged complex [Re2O3Cl2(μ-3,5-Me2pz)2(3,5-Me2pzH)2] (3) was prepared from (Et4N)2[ReOCl5] or Cs2[ReOCl5] and Me2pzH. The corresponding bromide and iodide complexes [Re2O3X2(3,5-Me2pz)2(3,5-Me2pzH)2] ·C6H6 (X = Br (4) or I (5)) were synthesized by the reactions of (NH4)2[ReBr6] or K2[ReI6], respectively, with Me2pzH. The [ReO(OMe)(3,5-Me2pzH)4]Br2·3,5-Me2pzH·4H2O complex (6) was obtained as a by-product in the synthesis of complex 4. The reaction of [ReNCl2(PPh3)2] with Me2pzH was accompanied by hydrolytic denitration giving rise to the mixed-ligand complex [Re2O3Cl2(μ-3,5-Me2pz)2(3,5-Me2pzH)(PPh3)] (7). The reaction of (NH4)2[ReBr6] with a Me2pzH melt gave the trans-[ReBr4(3,5-Me2pzH)2]·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, 1H NMR and IR spectroscopy, mass spectrometry, and cyclic voltammetry