Three platinum complexes of water-soluble, bidentate phosphine lig
ands have beenprepared
and characterized. The complexes, PtCl
2(P-P) (P-P = (
m-NaSO
3C
6H
4)
2PCH
2CH
2P(
m-C
6H
4SO
3Na)
2, DPPETS, (
m-NaSO
3C
6H
4)
2PCH
2CH
2CH
2P(
m-C
6H
4SO
3Na)
2, DPPPTS, (
m-NaSO
3C
6H
4)
2PCH
2CH
2CH
2CH
2P(
m-C
6H
4SO
3Na)
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 theintermediate
1-allenyl complexes. For PtCl
2(DPPBTS) the
1-allenyl complex Pt(C(Et)CCH
2)(X)(DPPBTS), where X is either OH
-, OH
2, or Cl
-, is formed. However for PtCl
2(DPPPTS)
and PtCl
2(DPPETS) the extent of formation of the coordinated complex is much less. Thestability of the coordinated Pt(
1-allenyl)(X)(P-P) complexes shows a significant effect onchelate ring size, with DPPBTS > DPPPTS > DPPETS being the order of decreasing stability.Catalytic hydrations of 4-pentyn-1-ol with PtCl
2(P-P) show a major effect of chelate ringsize in the opposite direction, DPPETS > DPPPTS > DPPBTS. For 3-pentyn-1-ol catalytichydration 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 bythe alcohol according to Baldwin's rules,
and rearrangement to 5-hydroxypentan-2-one.