Bonding to titanium

The recent synthesis of a crystalline compound containing Ti bonded to cyclopentadienyl and a substituted dienyl fragment prompted the question of whether Ti-C contacts that were found to be shorter than other such bonded contacts in the same molecule should be considered as short nonbonded contacts or "nonclassical metal-to-saturated-carbon atom interactions", fitting the description of agostic interactions. This question has a unique answer within the framework of the quantum theory of atoms in molecules (QTAIM). QTAIM uses the measurable electron density to assign a molecular structure and the physics of an open system to determine the nature of the bonded interactions. All of the classical bonding descriptors, when recast in terms of the topologies of the electron density and the pair density, are faithfully recovered when QTAIM is applied to the hydrocarbon framework of the Ti complex, thereby justifying its application to the analysis of the Ti-C interactions. No bond paths are found to link the Ti to the carbons exhibiting the "short contacts", and the topology of the density gives no indication of an incipient change in structure that would result in their formation.