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

作者：Belen Ruiz Muelle Ana; Ona Burgos Pascual; Ortuno Manuel A; Oltra J Enrique; Rodriguez Garcia Ignacio; Fernandez Ignacio^*

来源：Chemistry - A European Journal, 2016, 22(7): 2427-2439.

DOI：10.1002/chem.201504281

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

The synthesis and structural characterization of allenyl titanocene(IV) [TiClCp2(CH=C=CH2)] 3 and propargyl titanocene(IV) [TiClCp2(CH2-CC-(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 angstrom for 3 and 9, respectively. Full H-1, C-13, H-1, and (CNMR)-C-13 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.

• 出版日期2016-2-12