Syntheses and Molecular Structures of New Calix[4]arene Molybdenum and Tungsten Complexes

Abstract

An unusual disproportionation reaction of the molybdenum(IV) and tungsten(IV) chlorides [MCl4L2] (M=Mo, L=Et2S, Et2O; M=W; L= Et2S) in the presence of p-tBu-calix[4]arene (Cax(OH)4) and triethylamine leads to d0 complexes [(CaxO4)[CaxO2(OH)2]M] (1) and d3 compounds (HNEt3)2[(CaxO4)2M2] (2). Complexes la (M = Mo), 1b (M = W), and the HCl adduct of 2a (M = Mo) have been structurally characterized. Compound 1a represents one of the few examples of a well-characterized molybdenum(VI) hexa-alkoxide complex of the type [Mo(OR)6]. Isolation and structural characterization of the side product [(CaxO4W)[kappa2(O)-kappa1(O)-CaxO3(OH)](CaxO4WCl)] (3) suggests the intermediacy of chloro-containing calix[4]arene complexes in these reaction mixtures. The reaction of 1a with HCI provides [CaxO4MoCl2] (4a), the first well-defined example of a mixed molybdenum(VI) alkoxide halide compound of the general formula [MoClx(OR)6-x].