Reaction of [Cp∗2W2O5] with mercaptocarboxylic acids: Addition rather than reduction. Isolation and characterization of Cp∗WO2(SCH2CH2COOH)

The reaction of Cp∗2W2O5 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 Cp∗WO2(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.

Contrary to Cp∗2Mo2O5, the tungsten analogue is not reduced by the thiol function in mercaptocarboxylic acid reagents, leading to equilibrated addition processes with release of water. The addition of the SH function yielding an alkylthiolato derivative is more favourable than addition of the COOH function yielding a carboxylato derivative.Figure optionsDownload as PowerPoint slideHighlights
► The mercapto function adds to Cp∗WVI more easily than the carboxylic acid function.
► Addition of mercapto function to Cp∗WVI rather than reduction.
► Equilibrated removal of water by thiolate on a WVI system.
► First structure of with a Cp∗O2S donor set for WVI.