Theoretical Study of N2 Coordination to Titanocene(III) Monochloride in Ionic Liquid

A N-2 coordination to titanocene monochloride, [Cp2TiCl], in an ionic liquid (IL), 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate (Pyr(4)FAP), was detected by frozen solution EPR spectroscopy, although such a formation was not detected in toluene and THF. To understand the effect of IL toward the N-2 coordination to [Cp2TiCl], density functional theory (DFT) calculations were carried out applying dielectric permittivity (epsilon) of solvents (toluene and IL) for the following six model structures; dimeric [(Cp2TiCl)(2)] in the singlet (1) and triplet states (2), monomeric [Cp2TiCl] (3), [Cp2TiCl(N-2)] (4), and [Cp2TiCl(N-2)](double dagger) in the transition state (4-TS). The DFT calculations have revealed that the model complexes, such as 1 and 2, with a small e value are stabilized by solvents with a small value. To consider the effect of FAP anion toward titanocene complexes, we further performed the calculations for 3, 4 and 4-TS complexes interacting with FAP anion, 3'-FAP, 4'-FAP and 4'-FAP-TS, using empirical corrections (GD3BJ). Although the core structures of titanocenes in 3'-FAP and 4'-FAP are similar to those without FAP anion, F atoms in FAP anion show weak interaction toward H atoms on Cp rings. These findings suggest that the N-2 coordination to [Cp2TiCl] in IL could have been induced by interaction of the metal complex with a polar domain in Pyr(4)FAP.