Intramolecular hydrophosphination/cyclization of phosphinoalkenes and phosphinoalkynes catalyzed by organolanthanides: Scope, selectivity, and mechanism

M. R. Douglass, C. L. Stern, T. J. Marks

Research output: Contribution to journalArticlepeer-review

187 Citations (Scopus)

Abstract

Organolanthanide complexes of the general type Cp′2LnE(TMS)2 (Cp′ = η/5-Me5C5; Ln = La, Sm, Y, Lu; E = CH, N; TMS = SiMe3) serve as effective precatalysts for the rapid intramolecular hydrophosphination/cyclization of the phosphinoalkenes and phosphinoalkynes RHP(CH2)nCH=CH2 (R = Ph, H; n = 3, 4) and H2P(CH2)nC≡C-Ph (n = 3, 4) to afford the corresponding heterocycles CH3CH(CH2)nPR and Ph(H)C=C(CH2)nPH, respectively. Kinetic and mechanistic data for these processes exhibit parallels to, as well as distinct differences from, organolanthanide-mediated intramolecular hydroamination/cyclizations. The turnover-limiting step of the present catalytic cycle is insertion of the carbon-carbon unsaturation into the Ln-P bond, followed by rapid protonolysis of the resulting Ln-C linkage. The rate law is first-order in [catalyst] and zero-order in [substrate] over approximately one half-life, with inhibition by heterocyclic product intruding at higher conversions. The catalyst resting state is likely a lanthanocene phosphine-phosphido complex, and dimeric [Cp′2YP(H)Ph]2 was isolated and cystallographically characterized. Lanthanide identity and ancillary ligand structure effects on rate and selectivity vary with substrate unsaturation: larger metal ions and more open ligand systems lead to higher turnover frequencies for phosphinoalkynes, and intermediate-sized metal ions with Cp′2 ligands lead to maximum turnover frequencies for phosphinoalkenes. Diastereoselectivity patterns also vary with substrate, lanthanide ion, and ancillary ligands. Similarities and differences in hydrophosphination vis-à-vis analogous organolanthanide-mediated hydroamination are enumerated.

Original languageEnglish
Pages (from-to)10221-10238
Number of pages18
JournalJournal of the American Chemical Society
Volume123
Issue number42
DOIs
Publication statusPublished - Oct 24 2001

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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