Arylimido-Bridged Dinuclear Ti(μ-NAr) 2 Ti Scaffold for Alkyne Insertion into the ortho-C-H Bond of Arylimido Ligands.

Dinuclear titanium dialkyl complexes bridged by two μ-arylimido ligands, [CpTi(CH2 SiMe3 )(μ-NAr)]2 (Cp=cyclopentadienyl) activated an ortho-aryl C-H bond of an μ-arylimido ligand to form a four-membered titanacycle. The subsequent insertion reaction of 1-(trimethylsilyl)propyne into a metal-carbon bond of the four-membered titanacycle yielded the corresponding six-membered titanacycle. Further ortho-C-H bond activation of the other μ-arylimido ligand and an insertion reaction proceeded to give dinuclear titanium complexes with two six-membered titanacycles. An Eyring plot in the temperature range 130-150 °C revealed activation parameters for the alkenylation reaction, and deuterium-labeling experiments showed that the C-H bond activation step is the rate determining step. Relative Gibbs free energies of the starting complexes, reaction intermediates, and transition states were calculated by using DFT calculations.