Syntheses and molecular structures of new calix[4]arene molybdenum and tungsten complexes

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 d(o) complexes [(CaxO(4))(CaxO(2)(OH)(2)}M] (1) and d(3) compounds (HNEt3)(2)[(CaxO(4))(2)M-2] (2). Complexes 1a (M = Mo), 1b (M = W), and the HCl adduct of 2a (M = Mo) have been structurally characterized. Compound la 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 [(CaxO(4)W){kappa (2)(O)-kappa (1)(O)-CaxO(3)(OH)}- (CaxO(4)WCl)] (3) suggests the intermediacy of chloro-containing calix[4]arene complexes in these reaction mixtures. The reaction of 1a with HCl provides [CaxO(4)MoCl(2)] (4a), the first well-defined example of a mixed molybdenum(vl) alkoxide halide compound of the general formula [MoCl2(OR)(6-v)].