Reaction of [Cp12W2O5] with mercaptocarboxylic acids: Addition rather than reduction. Isolation and characterization of Cp1WO2(SCH2CH2COOH)

The reaction of Cp¹₂W₂O₅ with HS(CH₂)_nCOOH (n = 1, 2) in MeOH or in CH₂Cl₂ solutions at room temperature proceeds in slightly different ways depending on the value of n. For n = 2, it selectively yields compound Cp¹WO₂(SCH₂CH₂CO₂H), which has been isolated and characterized by elemental analysis, NMR and single crystal X-ray diffraction. The reaction is equilibrated, being shifted to the product by absorption of water by anhydrous Na₂SO₄ in CH₂Cl₂, and to the reactants by addition of water. Contrary to the Mo analogue, no products resulting from metal reduction are obtained. The corresponding reaction for n = 1 occurs similarly at low substrate/W ratios (<0.5), but proceeds further to several uncharacterized products for greater substrate amounts. The primary product could not be isolated, but its ¹H NMR spectrum suggests a different, asymmetric structure.