Dendronized scorpionate complexes of molybdenum in low and high oxidation states

Abstract

Tridentate (L₃) and bidentate (L₂) poly(pyrazolyl)methane ligands (Gn-dend)OCH₂C(pz)₃ (1–4) and (Gn-dend)CH(3,5-Me₂pz)₂ (pz = pyrazol-1-yl) have been used to synthesize the molybdenum(0) complexes [Mo(CO)₃(L₃)] (G0–G3, 5–8), [Mo(CO)₄(L₂)] (G0–G1, 13–14), and [Mo(CO)₃(NCMe)(L₂)] (G0, 15), and the molybdenum(VI) complexes [MoCl₂O₂(L₂)] (9–12). The G0–G3 prefixes represent the generation of poly(aryl ether) dendrons in which the metal complexes are embedded. The molecular structures of compounds 13 and 15 have been determined by X-ray diffraction studies and the hydrodynamic radii of tricarbonyl complexes 5–8 calculated by diffusion-ordered NMR spectroscopy (DOSY). Molybdenum(VI) compounds 9–12 have also been evaluated as catalysts for olefin epoxidation, showing comparable but inferior performances than ligand-free MoCl₂O₂, probably because of the labile coordination of L₂.