Density Functional Theory Calculations of Ti−TEMPO Complexes: Influence of Ancillary Ligation on the Strength of the Ti−O Bond

Abstract

A series of mono(cyclopentadienyl)titanium TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) complexes were investigated by density functional theory (DFT) calculations to study the influence of the ligands on the Ti−O bond energies. Mono-Cp complexes with pendant amino groups were found to possess significantly weaker Ti−O bonds than those lacking pendant donor ligands. On the basis of DFT predictions, a novel mono-Cp pendant dimethylamino complex, CpNTiCl2(TEMPO) (12; CpN = C5H4CH2CH2N(CH3)2), was identified as a mono-Cp titanium TEMPO complex with a weak Ti−O bond (25 kcal/mol). The calculated bond energy of this complex is comparable to that of Cp2TiCl(TEMPO) (3; 17 kcal/mol). Thermolysis of 12 in the presence of CCl4 at 100 °C resulted in the formation of CpNTiCl3, consistent with the predicted low Ti−O bond energy.