Dendronized scorpionate complexes of molybdenum in low and high oxidation states

Tridentate (L-3) and bidentate (L-2) poly( pyrazolyl) methane ligands (Gn-dend)OCH2C(pz)(3)(1-4) and (Gn-dend)CH(3,5-Me(2)pz)(2)(pz = pyrazol-1-yl) have been used to synthesize the molybdenum(0) complexes [Mo(CO)(3)(L-3)] (G0-G3, 5-8), [Mo(CO)(4)(L-2)] (G0-G1, 13-14), and [Mo(CO)(3)(NCMe)(L-2)] (G0, 15), and the molybdenum(VI) complexes [MoCl2O2(L-2)] (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 L-2.