title: Unprecedented Spectroscopic and Computational Evidence for Allenyl and Propargyl Titanocene(IV) Complexes: Electrophilic Quenching of Their Metallotropic Equilibrium.
abstract: The synthesis and structural characterization of allenyl titanocene(IV) [TiClCp2 (CH=C=CH2 )] 3 and propargyl titanocene(IV) [TiClCp2 (CH2 -C≡C-(CH2 )4 CH3 )] 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 4.1 Å for 3 and 9, respectively. Full (1) H, (13) C, Δ(1) H, and Δ(13) C NMR 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.
authors.affiliation: Department of Chemistry and Physics, ceiA3, Universidad de Almería, Carretera de Sacramento s/n, Almería, 04120, Spain.
authors.forename: Ana Belén
authors.initials: AB
authors.lastname: Ruiz-Muelle
authors.affiliation: Department of Chemistry and Physics, ceiA3, Universidad de Almería, Carretera de Sacramento s/n, Almería, 04120, Spain.
authors.forename: Pascual
authors.initials: P
authors.lastname: Oña-Burgos
authors.affiliation: Departament de Química, Universitat Autònoma de Barcelona, Edifici C.n, Barcelona, Cerdanyola del Vallès, 08193, Spain.|Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, 55455-0431, USA.
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Ortuño
authors.affiliation: Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, Campus Fuentenueva s/n, Granada, 18071, Spain.
authors.forename: J Enrique
authors.initials: JE
authors.lastname: Oltra
authors.affiliation: Department of Chemistry and Physics, ceiA3, Universidad de Almería, Carretera de Sacramento s/n, Almería, 04120, Spain.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Rodríguez-García
authors.affiliation: Department of Chemistry and Physics, ceiA3, Universidad de Almería, Carretera de Sacramento s/n, Almería, 04120, Spain. ifernan@ual.es.|BITAL, Research Centre for Agricultural and Food Biotechnology, Carretera de Sacramento s/n, Almería, Spain. ifernan@ual.es.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Fernández
keywords: DOSY; NMR spectroscopy; density functional calculations; metallotropic equilibrium; titanocenes