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

Abstract

a b s t r a c tThe reaction of Cp * 2 W 2 O 5 with HS(CH 2 ) n COOH (n ¼ 1, 2) in MeOH or in CH 2 Cl 2 solutions at room temperature proceeds in slightly different ways depending on the value of n. For n ¼ 2, it selectively yields compound Cp * WO 2 (SCH 2 CH 2 CO 2 H), 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 Na 2 SO 4 in CH 2 Cl 2 , 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 ¼ 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 1 H NMR spectrum suggests a different, asymmetric structure.

Speciation of [Cp*2M2O5] in Polar and Donor Solvents

“…Related known reactivity patterns in support of this behavior are the cycloaddition reactions observed for [Cp*WO 3 ] − , but not for [Cp*MoO 3 ] − , with the ketene PhCHCO and the alkyne MeO 2 CC≡CCO 2 Me,10b leading to isolated products having a coordination sphere of type [Cp*WO 2 X 2 ] − and therefore isoelectronic with that of [{Cp*WO 2 (μ‐OMe)} 2 ]. Another example is the addition of thioglycolic acid to [Cp* 2 W 2 O 5 ] to yield [Cp*WO(OH)(SCH 2 COO‐κ 2 S , O )],12 whereas no adduct is generated from [Cp* 2 Mo 2 O 5 ]. The nature of this product has been further investigated by computational methods, which are strongly in favor of a mononuclear formulation (see later).…”

“…The addition of small amounts of D 2 O (spectra in the upper figure) induces a downfield shift for both resonances and a dramatic intensity redistribution with an increase of A and a decrease of B. Related known reactivity patterns in support of this behavior are the cycloaddition reactions observed for [Cp*WO 3 ] À , but not for [Cp*MoO 3 ] À , with the ketene PhCH=C=O and the alkyne MeO 2 CC CCO 2 Me, [10b] leading to isolated products having a coordination sphere of type [Cp*WO 2 X 2 ] À and therefore isoelectronic with that of [12] whereas no adduct is generated from [Cp* 2 Mo 2 O 5 ]. Increasing the amount of water further shifts all resonances downfield, with C increasing in intensity.…”