Unprecedented Spectroscopic and Computational Evidence for Allenyl and Propargyl Titanocene(IV) Complexes: Electrophilic Quenching of Their Metallotropic Equilibrium

Ana Belén Ruiz-Muelle, Pascual Oña-Burgos, Manuel A. Ortuño, J. Enrique Oltra, Ignacio Rodríguez-García, Ignacio Fernández

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

The synthesis and structural characterization of allenyl titanocene(IV) [TiClCp2(CH=C=CH2)] 3 and propargyl titanocene(IV) [TiClCp2(CH2-C≡C-(CH2)4CH3)] 9 have been described for the first time. Advanced NMR methods including diffusion NMR methods (diffusion pulsed field gradient stimulated spin echo (PFG-STE) and DOSY) have been applied and established that these organometallics are monomers in THF solution with hydrodynamic radii (from the Stokes-Einstein equation) of 3.5 and 4.1Å for 3 and 9, respectively. Full 1H, 13C, Δ1H, and Δ13CNMR data are given, and through the analysis of the Ramsey equation, the first electronic insights into these derivatives are provided. In solution, they are involved in their respective metallotropic allenyl-propargyl equilibria that, after quenching experiments with aromatic and aliphatic aldehydes, ketones, and protonating agents, always give the propargyl products P (when carbonyls are employed), or allenyl products A (when a proton source is added) as the major isomers. In all the cases assayed, the ratio of products suggests that the metallotropic equilibrium should be faster than the reactions of 3 and 9 with electrophiles. Indeed, DFT calculations predict lower Gibbs energy barriers for the metallotropic equilibrium, thus confirming dynamic kinetic resolution.

Original languageEnglish (US)
Pages (from-to)2427-2439
Number of pages13
JournalChemistry - A European Journal
Volume22
Issue number7
DOIs
StatePublished - Feb 12 2016

Keywords

  • density functional calculations
  • DOSY
  • metallotropic equilibrium
  • NMR spectroscopy
  • titanocenes

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't

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