Preparation of rhenium hydride complexes with pyrazole and pyrazolato ligands

Hydride-pyrazolato ReH(Rpz)(HRpz)(NO)(PPh3)2 complexes (R = H (1), 5-Me (2)) were prepared by allowing the ReH2(NO)(PPh3)3 derivative to react with pyrazole (HRpz) in refluxing toluene. The complexes were characterised spectroscopically (IR and NMR data) and by the X-ray crystal structure determination of the ReH(5-Mepz)(H-5-Mepz)(NO)(PPh3)2 derivative. An intramolecular hydrogen bond N–H⋯N between the pyrazolato and the pyrazole ligands was established both in the solid state and in solution. Protonation reaction with Brønsted acid of compound 1 was studied and led to the unstable bis(pyrazole) [ReH(Hpz)2(NO)(PPh3)2]+ cation. Acetylide-pyrazolato Re(CCAr)(Rpz)(HRpz)(NO)(PPh3)2 (3, 4) complexes (Ar = Ph, p-tolyl; R = H, 5-Me) were also prepared by reacting hydride ReH(Rpz)(HRpz)(NO)(PPh3)2 species with terminal alkynes HCCAr in refluxing 1,2-dichloroethane.

Graphical abstractThe synthesis of rhenium hydride ReH(Rpz)(HRpz)(NO)(PPh3)2 complexes containing both pyrazole and pyrazolato as supporting ligands is described. An intramolecular hydrogen bond N–H⋯N between the pyrazolato and the pyrazole ligands is present both in the solid state and in solution. Acetylide pyrazolato Re(CCAr)(Rpz)(HRpz) (NO)(PPh3)2 complexes were also prepared by reacting the ReH(Rpz)(HRpz)(NO)(PPh3)2 hydrides with terminal alkynes.Figure optionsDownload full-size imageDownload as PowerPoint slide