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

Dinuclear titanium dialkyl complexes bridged by two mu-arylimido ligands, [CpTi(CH2SiMe3)(mu-NAr)](2) (Cp = cyclo-pentadienyl) activated an ortho-aryl C-H bond of an mu-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 m-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 degrees 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.