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)(OiPr)n(Br)3-n (n = 1−3, L = tBuNHCH2CH2[C{NtBu(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 d0 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.