Insight into the Selective Room-Temperature Platinum(II) Catalytic Hydration of Alkynes in Water

• Published in: Organometallics 2002-06, Vol.21 (12), p.2481-2490
• Main Authors: Lucey, Derrick W, Atwood, Jim D
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om020011w

Three platinum complexes of water-soluble, bidentate phosphine ligands have been prepared and characterized. The complexes, PtCl2(P−P) (P−P = (m-NaSO3C6H4)2PCH2CH2P(m-C6H4SO3Na)2, DPPETS, (m-NaSO3C6H4)2PCH2CH2CH2P(m-C6H4SO3Na)2, DPPPTS, (m-NaSO3C6H4)2PCH2CH2CH2CH2P(m-C6H4SO3Na)2, DPPBTS), catalyze the hydration of 3-pentyn-1-ol and 4-pentyn-1-ol. 2-Pentyn-1-ol is slowly polymerized, allowing characterization of the intermediate η1-allenyl complexes. For PtCl2(DPPBTS) the η1-allenyl complex Pt(C(Et)CCH2)(X)(DPPBTS), where X is either OH-, OH2, or Cl-, is formed. However for PtCl2(DPPPTS) and PtCl2(DPPETS) the extent of formation of the coordinated complex is much less. The stability of the coordinated Pt(η1-allenyl)(X)(P−P) complexes shows a significant effect on chelate ring size, with DPPBTS > DPPPTS > DPPETS being the order of decreasing stability. Catalytic hydrations of 4-pentyn-1-ol with PtCl2(P−P) show a major effect of chelate ring size in the opposite direction, DPPETS > DPPPTS > DPPBTS. For 3-pentyn-1-ol catalytic hydration is less affected by the chelate ring size. The effect of excess Cl- is also examined. A mechanism is proposed for the catalytic hydration involving coordination, cyclic attack by the alcohol according to Baldwin's rules, and rearrangement to 5-hydroxypentan-2-one.