Terminal titanium-ligand multiple bonds. Cleavages of C=O and C=S double bonds with Ti imido complexes

Treatment of ^t-BuN=TiCl₂Py₃ with 2 equiv lithium ketiminate compound, Li[OCMeCHCMeN(Ar)] (where Ar = 2,6- diisopropylphenyl), in toluene at room temperature gave ^t-BuN= Ti[OCMeCHCMeN(Ar)]₂ (1) in high yield. The reaction of 1 with phenyl isocyanate at room-temperature resulted in imido ligand exchange producing PhN=Ti[OCMeCHCMeN(Ar)]₂ (2). Compound 1 decomposed at 90 °C to form a terminal titanium oxo compound O=Ti[OCMeCHCMeN(Ar)]₂ (3) and ^t-BuNHCMeCHCMeNAr (4). Also, the compound 3 could be obtained by reacting 1 with CO₂ under mild condition. Similarly, while 1 reacts with an excess of carbon disulfide, a novel terminal titanium sulfido compound S=Ti[OCMeCHCMeN(Ar)]₂ (5) was formed via a C=S bond breaking reaction. A novel titanium isocyanate compound Ti[OCMeCHCMeN(Ar)] ₂(NCO)(OEt) (6) was formed on heating 1 with 1 equiv of urethane, H₂NCOOEt. Compounds 1-6 have been characterized by ¹H and ¹³C NMR spectroscopies. The molecular structures of 1, 3, 5, and 6 were determined by single-crystal X-ray diffraction. A theoretical calculation predicted that the cleavage of the C-S double bonds for carbon disulfide with the Ti=N bond of compound 1 was estimated at ca. 21.8 kcal·-mol ^-1 exothermic.