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.

Graphical abstractBased on structural and variable-temperature NMR data, a comparative investigation of five different Cp2Ti(diselenolene) complexes shows the evolution of the static and dynamic properties associated with the folding of the TiSe2C2 metallacycle along the Se⋯Se hinge. Larger folding angles and ΔGc‡ activation energies for the folding process are associated with the most electron rich diselenolenes (bds, ddds), when compared with those bearing electron-withdrawing CO2Me or CF3 substituents.Figure optionsDownload full-size imageDownload as PowerPoint slide