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

The mononuclear complexes [Re(CO)(3)(Hpz)(2)Br] (1) and [Re(CO)(3)(Hdmpz)(2)Br] (2) were obtained by treating [Re(CO)(5)Br] with pyrazole (Hpz) or 3,5-dimethylpyrazole (Hdmpz). Complex 1 reacted with triethylamine affording a mixture of the ionic dinuclear derivative (Et3NH)[Re-2(CO)(6)(pz)(2)Br] (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)(dmpz)] (7) and [Re(CO)(3)(py) (Hdmpz)(dmpz)] (8) were also synthesized. All species were characterized in solution by H-1-NMR spectroscopy, while the crystal structures of complexes 1, 3, 4 and 6 were determined by single-crystal X-ray diffraction analysis. The [(CO)(3)Re(mu-pz)(2)(mu-Br)Re(CO)3](-) anion represents the first structurally characterized species containing rhenium(I) atoms bridged by mu-pyrazolate ligands.