Ancillary Ligand Control of the Regiochemistry of Coupling of 3,3-Dimethyl-1-butyne at Titanium Metal Centers
摘要:
The ambient-temperature sodium amalgam (2 Na per Ti) reduction of hydrocarbon solutions of [Cp(ArO)TiCl2] (ArO = 2,3,5,6-tetraphenylphenoxide) (1) in the presence of 3,3-dimethyl-1-butyne yields the 2,5-di(tert-butyl)titanacyclopentadiene compound [Cp(ArO)Ti(C4H2Bu2t -2,5)] (2). An X-ray diffraction study of 2 confirms the regiochemistry and shows carbon-carbon distances of 1.343(3) and 1.492(3) Angstrom for the double and single bonds, respectively. In contrast the analogous reaction of either [Cp2TiCl2] or [(ArO)(2)TiCl2] in the presence of 3,3-dimethyl-1-butyne yields the corresponding 2,4-di(tert-butyl)titanacyclopentadiene compounds. When 2 is heated at 100 degreesC for a few days in C6D6 solution, isomerization to the more stable 2,4-di(tertbutyl) regioisomer 3 is observed by NMR. An attempt is made to rationalize the regiochemistry of the kinetically formed titanacyclopentadiene in terms of steric factors within the intermediate bis(alkyne) complex.
Ancillary Ligand Control of the Regiochemistry of Coupling of 3,3-Dimethyl-1-butyne at Titanium Metal Centers
摘要:
The ambient-temperature sodium amalgam (2 Na per Ti) reduction of hydrocarbon solutions of [Cp(ArO)TiCl2] (ArO = 2,3,5,6-tetraphenylphenoxide) (1) in the presence of 3,3-dimethyl-1-butyne yields the 2,5-di(tert-butyl)titanacyclopentadiene compound [Cp(ArO)Ti(C4H2Bu2t -2,5)] (2). An X-ray diffraction study of 2 confirms the regiochemistry and shows carbon-carbon distances of 1.343(3) and 1.492(3) Angstrom for the double and single bonds, respectively. In contrast the analogous reaction of either [Cp2TiCl2] or [(ArO)(2)TiCl2] in the presence of 3,3-dimethyl-1-butyne yields the corresponding 2,4-di(tert-butyl)titanacyclopentadiene compounds. When 2 is heated at 100 degreesC for a few days in C6D6 solution, isomerization to the more stable 2,4-di(tertbutyl) regioisomer 3 is observed by NMR. An attempt is made to rationalize the regiochemistry of the kinetically formed titanacyclopentadiene in terms of steric factors within the intermediate bis(alkyne) complex.