Inorganic Chemistry, Vol.41, No.20, 5276-5285, 2002
New chloro, mu-oxo, and alkyl derivatives of dioxomolybdenum(VI) and -tungsten(VI) complexes chelated with N2O tridentate ligands: Synthesis and catalytic activities toward olefin epoxidation
syA new series of cis-dioxomolybdenum(VI) complexes MoO2(L-n)CI (n = 1-5) were prepared by the reaction of MoO2CI2(DME) (DME = 1,2-dimethoxyethane) with 2-N-(2-pyridylmethyl)aminophenol (HL1) or its N-alkyl derivatives (HLn) (n = 2-5) in the presence of triethylamine. The new mu-oxo dimolybdenum compounds [MoO2(L-n)](2)O (n = 1, 4, 5, 7) were also prepared by treating the corresponding ligand HLn with MoO2(acac)(2) (acac = acetylacetonate) in warm methanolic solutions or (NH4)(6)[Mo7O24].4H(2)O in the presence of dilute HCl. Treatment of MoO2(L-1)Cl or [MoO2(L-1)](2)O with the Grignard reagent Me3SiCH2MgCl gave the alkyl compound MoO2(L-1)(CH2SiMe3), which represents the first example of dioxomolybdenum(VI) alkyl complex supported by a N2O-type ancillary ligand. The analogous chloro, and mu-oxo tungsten derivatives WO2(L-n)CI (n = 6, 7) and [WO2(L-n)](2)O (n = 1, 4, 6, 7) were prepared by the reaction of WO2CI2(DME) with HLn in the presence of triethylamine. Similar to their molybdenum analogues, the tungsten alkyl complexes WO2(L-n) (R) (n = 6, 7; R = Me, Et, CH2SiMe3, (C6H4Bu)-Bu-t-4) were synthesized by treating WO2(L-n)CI or [WO2(L-n)2O (n = 6, 7) with the appropriate Grignard reagents. The catalytic properties of selected dioxo-Mo(VI) and -W(VI) chloro and mu-oxo complexes toward epoxidation of styrene by tert-butyl hydroperoxide (TBHP) were also investigated.