Titanium(IV) Alkoxy-N-heterocyclic Carbenes: Structural Preferences of Alkoxide and Bromide Adducts

A series of titanium(IV) adducts of an amido-tethered N-heterocyclic carbene (NHC) of the form Ti(L)(O i Pr) n (Br) 3 - n ( n = 1−3, L = t BuNHCH 2 CH 2 [C{N t Bu(CHCH)N}]) have been synthesized and characterized. Structural characterization of the n = 2 complex shows marked bending of the two ligands cis (and perpendicular) to the plane of the NHC group in the direction of the carbene, suggestive of a pseudo-back-bonding interaction between adjacent ligands and the carbene p orbital, consistent with a bonding model recently proposed for d 0 metal-NHC complexes. However, inspection of a space-filling model and the calculation of bond order using DFT methods suggest that the bending is due to repulsions between lone pairs on the adjacent π-donor ligands in the complexes and not any specific interaction between the NHC and cis π-donor ligands.