Synthesis, structure, spectral properties and theoretical studies of two half-sandwich titanium-complexes with adamantoxy ligands

Two novel half-sandwich Ti complexes, both incorporating two adamantoxy (OAd) ligands coordinated to their central atoms were synthesized. The complexes were characterized by 1H, 13C, 19F NMR, EI-MS and IR spectroscopy and by single-crystal X-ray diffraction. In both complexes, the coordination environment is pseudo-tetrahedral and is assembled of two O-coordinated adamantoxy and one η5-coordinated permethylcyclopentadienyl ligand. The fourth ligand in complex 1 is a methyl group coordinated through a regular σ-bond, whereas in complex 2 the same coordination site is occupied by the methyl group of the balancing (C6F5)3BMeˉ anion. DFT computations complemented with NBO analyses of 2 have unveiled, that in addition to the electrostatic interactions occurring between the half-sandwich titanocene moiety and the anionic ligand, delocalization of one methyl CH bond into the available acceptor orbital on the central atom takes place. AIM analyses of 2 have revealed the presence of a Bond Critical Point between the metal atom and the anionic methyl group. These results prove foundation for the description of 2 as a zwitterionic complex coupled with a concurrent Ti⋯CH agostic interaction in its molecule. The comparison of 2 with its analogous complex equipped with two Ot-Bu ligands instead of both OAd has suggested only a minor change in the extent of the agostic interaction, despite significant geometric differences between the two complexes.