A systematic study on the activation of simple polyethers by MoCl5 and WCl6.
MoCl(5), 1a, and WCl(6), 1b, activate 1,3-dioxolane at room temperature in chlorinated solvents: the compound [MoOCl(3){O=C(H)OCH(2)CH(2)Cl}](2), 2, has been isolated from MoCl(5)/dioxolane. The mixed oxo-chloro species WOCl(4), 1c, reacts with 1,3-dioxolane, selectively giving the coordination adduct WOCl(4)(kappa(1)-C(3)H(6)O(2)), 3. Dimethoxymethane, CH(2)(OMe)(2), undergoes activation including C-H bond cleavage when reacted with 1a to give the molybdenum complexes [MoOCl(3){O=C(H)OMe}](2), 4, and Mo(2)Cl(5)(OMe)(5), 5. The reactions of 1b with CH(2)(OR)(2) (R = Me, Et) proceed via O-abstraction with formation of the oxo-derivatives WOCl(4)[O(R)CH(2)Cl] (R = Me, 6a; R = Et, 6b) in admixture with equimolar amounts of RCl. The reactions of 1a,b with CMe(2)(OMe)(2) lead to mesityl oxide, MeC(O)CH=C(Me)(2). A series of simple diethers of general formula ROCH(2)(CHR')OR'' are activated by 1a,b in CDCl(3), usually via cleavage of C-O bonds at high temperature. The complex WCl(5)(OCH(2)CH(2)OMe), 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 WOCl(4)[O=C(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.
Dolci
Sara
S
Università di Pisa, Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, I-56126, Pisa, Italy.
Marchetti
Fabio
F
Pampaloni
Guido
G
Zacchini
Stefano
S