Reactions of alkenes (ethylene, propene, and 1-hexene) with water in the presence of cis-Pt(Cl)2(TPPTS)2 (TPPTS = P(m-C6H4SO3Na)3) produces stoichiometrically the Wacker
oxidation product (acetaldehyde, acetone, and 2-hexanone, respectively) and trans-Pt(Cl)(H)(TPPTS)2. The presence of the phosphine ligands provides stability to the hydride complex
such that decomposition to the metal is prevented. For C2H4 the final product is trans-Pt(Cl)(C2H5)(TPPTS)2. These reactions are fully consistent with the PdCl4
2- oxidation of alkenes.
At higher temperatures, however, C2H4 is catalytically oxidized to CH3CHO in a mechanism
that appears to be different. At 95 °C, 90 turnovers are observed.
Reactions of alkenols with cis-Pt(Cl)2(TPPTS)2 (TPPTS = P(m-C6H4SO3Na)3) in water result in [Pt(η3-allyl)(TPPTS)2]+ as the exclusive platinum product with 1 equiv of oxidized alkenol. The η3-allyl is
not fluxional in water, and the syn and anti isomers can be distinguished at room temperature. For 3-buten-1-ol and 4-penten-1-ol, in addition to the η3-allyl complex and oxidation of the alkene, catalytic
isomerization of the alkene is observed. No reaction occurs for cis-Pt(Cl)2(P(p-tolyl)3)2, cis-Pt(Cl)(THF)(P(p-tolyl)3)2
+, or cis-Pt(THF)2(P(p-tolyl)3)2
2+ with the alkenols in THF, indicating the importance of
H2O. Excess Cl- inhibits the reaction. The oxidation product is selectively deuterated. These observations
are combined into a proposed mechanism.
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