The Deceptively Simple Thermolysis of Trivalent Permethyltitanocene Derivatives (η5-C5Me5)2TiR. Formation of a Tetramethylfulvene Titanium Compound (η6-C5Me4CH2)(η5-C5Me5)Ti and RH, Catalyzed by Permethyltitanocene Hydride, (η5-C5Me5)2TiH

摘要

The complexes Cp*2TiR (Cp* = η5-C5Me5; R = Me, Et, n-Pr, C2H3, CH2CMe3, Ph) undergo thermolysis to yield the fulvene complex Cp*FvTi (Fv = η6-C5Me4CH2) and RH. Kinetic measurements and deuterium labeling studies show that the decomposition is catalyzed by Cp*2TiH, which is formed either by β-hydrogen elimination from a titanium alkyl Cp*2TiCH2CH2R at low temperature or by hydrogenolysis of Cp*2TiR or Cp*FvTi, using dihydrogen eliminated from Cp*FvTi at elevated temperatures. Permethyltitanocene is not an intermediate. The rate of the catalyzed decomposition of Cp*2TiCH2CMe3 is linear in [Cp*2TiH]. For Cp*2TiMe it is proportional to [Cp*2TiH] and [Cp*2TiMe] and inversely proportional to the starting concentration of Cp*2TiMe. This is explained in a kinetic scheme, where H2, eliminated from Cp*2TiH to give Cp*FvTi, reacts with Cp*2TiR to regenerate Cp*2TiH and liberate RH. The model is supported by the reaction of (Cp*-d15)2TiD and Cp*2TiCH2CMe3 yielding Cp*2TiD and (Cp*FvTi-d29).