Pyrazolato metal complexes: Synthesis, characterization and X-ray crystal structures of rhenium(I) derivatives

The mononuclear complexes [Re(CO)3(HpZ)2Br] (1) and [Re(CO)3(Hdmpz)2Br] (2) were obtained by treating [Re(CO)5Br] with pyrazole (Hpz) or 3,5-dimethylpyrazole (Hdmpz). Complex 1 reacted with triethylamine affording a mixture of the ionic dinuclear derivative (Et3NH)[Re2-(CO)6(Pz)2Br] (3) and of the mononuclear species [Re(CO)3-(Hpz)2(pz)] (4). Complex 4 was obtained in a pure form by carrying out the reaction in the presence of excess free pyrazole. Treatment of 4 with pyridine afforded the [Re(CO)3(Py)(Hpz)(pz)] species (6). The analogues of 4 and 6 with Hdmpz, i.e. [Re(CO)3(Hdmpz)2(dnipz)] (7) and [Re(CO)3(py)(Hdmpz)(dmpz)] (8) were also synthesized. All species were characterized in solution by 1H-NMR spectroscopy, while the crystal structures of complexes 1, 3, 4 and 6 were determined by single-crystal X-ray diffraction analysis. The [(CO)3Re(μ-pz)2(μ-Br)Re(CO)3]- anion represents the first structurally characterized species containing rhenium(I) atoms bridged by μ-pyrazolate ligands.