A systematic study on the activation of simple polyethers by MoCl5 and WCl6

Abstract

MoCl₅, 1a, and WCl₆, 1b, activate 1,3-dioxolane at room temperature in chlorinated solvents: the compound [MoOCl₃{OC(H)OCH₂CH₂Cl}]₂, 2, has been isolated from MoCl₅/dioxolane. The mixed oxo-chloro species WOCl₄, 1c, reacts with 1,3-dioxolane, selectively giving the coordination adduct WOCl₄(κ¹-C₃H₆O₂), 3. Dimethoxymethane, CH₂(OMe)₂, undergoes activation including C–H bond cleavage when reacted with 1a to give the molybdenum complexes [MoOCl₃{OC(H)OMe}]₂, 4, and Mo₂Cl₅(OMe)₅, 5. The reactions of 1b with CH₂(OR)₂ (R = Me, Et) proceed via O-abstraction with formation of the oxo-derivatives WOCl₄[O(R)CH₂Cl] (R = Me, 6a; R = Et, 6b) in admixture with equimolar amounts of RCl. The reactions of 1a,b with CMe₂(OMe)₂ lead to mesityl oxide, MeC(O)CHC(Me)₂. A series of simple diethers of general formula ROCH₂(CHR′)OR′′ are activated by 1a,b in CDCl₃, usually via cleavage of C–O bonds at high temperature. The complex WCl₅(OCH₂CH₂OMe), 7, has been detected in solution as an intermediate species in the course of the degradation of 1,2-dimethoxyethane (dme) by 1b. The activation of CH(OMe)₃ by 1 is limited to C–O bonds and selectively gives methyl chloride and methylformate, which has been found coordinated in WOCl₄[OC(H)OMe], 8. The organic fragments produced in the reactions have been detected by GC-MS and NMR analyses, upon hydrolysis of the reaction mixtures. Compounds 2 and 5, which have had their molecular structures ascertained by X-ray diffraction, represent rare examples of crystallographically-characterized dinuclear Mo(V) species containing both halides and oxygen ligands.