Dendronized scorpionate complexes of molybdenum in low and high oxidation states

Tridentate (L(3)) and bidentate (L(2)) poly(pyrazolyl)methane ligands (Gn-dend)OCH(2)C(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 MoCl(2)O(2)(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 MoCl(2)O(2), probably because of the labile coordination of L(2).