Structural flexibility of titanocene diselenolene complexes: Combined structural and VT NMR investigations

A comparative investigation on five different Cp₂Ti(diselenolene) complexes, i.e. Cp₂Ti(Se₂C₂Z₂) (Z = -CO₂Me), Cp₂Ti[Se₂C₂Z(CF₃)], Cp₂Ti(bds) (bds = 1,2-benzene-diselenato), Cp₂Ti(dsit) (dsit = 1,3-dithiole-2-thione-4,5-diselenato) and Cp₂Ti(ddds) (ddds = 5,6-dihydro-1,4-dithiine-2,3-diselenato) is performed based on structural and variable-temperature NMR data. Preparation of Cp₂Ti[Se₂C₂Z(CF₃)] involves the reaction of Cp₂TiSe₅ with an excess of methyl-4,4,4-trifluorotetrolate while Cp₂Ti(bds) is obtained from the bds²⁻ diselenolate and Cp₂TiCl₂. Their X-ray crystal structures have been determined, showing that Cp₂Ti(bds) is not isostructural with the sulfur analog Cp₂Ti(bdt). Similarly the structures of Cp₂Ti(dsit) and Cp₂Ti(Se₂C₂Z₂) were also determined from single crystal X-ray diffraction. All complexes exhibit a strong folding of the metallacycle along the Se?Se hinge, ranking from 47.8° in Cp₂Ti(Se₂C₂Z₂) to 52.3° in Cp₂Ti(ddds). VT NMR investigations on Cp₂Ti[Se₂C₂Z(CF₃)] and Cp₂Ti(ddds), complementing earlier results on the other complexes, show that the largest activation energies and associated folding angles are observed with the most electron rich diselenolenes (ddds, bds), a behavior closely related to that observed earlier in dithiolene complexes.