Synthesis and structural studies of mixed-ligand rhenium(V) complexes anchored by tridentate pyrazole-based ligands

Abstract

The novel oxorhenium dichlorides mer-[ReO(L1)Cl 2] ( 1) and fac-[ReO(L2)Cl 2] ( 2) (L1 = 2-[2-(pyrazol-1-yl)ethyliminomethyl]phenolate; L2 = 2-[2-(pyrazol-1-yl)ethylaminomethyl]phenolate) were synthesized by reacting [NBu 4][ReOCl 4] with L1H and L2H, respectively. X-ray structural analysis of 1 and 2 has shown that L1 and L2 act as (N,N,O)-tridentate chelators coordinating to the Re(V) centre in a meridional and in a facial fashion, respectively. The reactivity of 2 towards potential bidentate/dianionic substrates is strongly dependent on the donor atom set, being observed that the presence of sulphur favours the displacement of the ancillary ligand (L2). By contrast, complex 2 reacted with (O,O)-bidentate substrates (1,2-ethanediol and oxalic acid) providing the mixed-ligand complexes fac-[ReO(L2)(OCH 2CH 2O)] ( 3) and fac-[ReO(L2)(C 2O 4)] ( 4). Complexes 3 and 4 are air and water-stable and have been characterized by the common spectroscopic techniques (IR, 1H and 13C NMR) and by X-ray diffraction analysis.