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

Abstract

A comparative investigation on five different Cp 2Ti(diselenolene) complexes, i.e. Cp 2Ti(Se 2C 2Z 2) (Z = –CO 2Me), Cp 2Ti[Se 2C 2Z(CF 3)], Cp 2Ti(bds) (bds = 1,2-benzene-diselenato), Cp 2Ti(dsit) (dsit = 1,3-dithiole-2-thione-4,5-diselenato) and Cp 2Ti(ddds) (ddds = 5,6-dihydro-1,4-dithiine-2,3-diselenato) is performed based on structural and variable-temperature NMR data. Preparation of Cp 2Ti[Se 2C 2Z(CF 3)] involves the reaction of Cp 2TiSe 5 with an excess of methyl-4,4,4-trifluorotetrolate while Cp 2Ti(bds) is obtained from the bds 2− diselenolate and Cp 2TiCl 2. Their X-ray crystal structures have been determined, showing that Cp 2Ti(bds) is not isostructural with the sulfur analog Cp 2Ti(bdt). Similarly the structures of Cp 2Ti(dsit) and Cp 2Ti(Se 2C 2Z 2) 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 Cp 2Ti(Se 2C 2Z 2) to 52.3° in Cp 2Ti(ddds). VT NMR investigations on Cp 2Ti[Se 2C 2Z(CF 3)] and Cp 2Ti(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.