107681-81-2Relevant articles and documents
Intramolecular C-H bond activation of benzyl ligands by metalated cyclopentadienyl derivatives of permethylhafnocene. Molecular structure of (η5-C5Me5) (η5,η1-C5Me4CH 2)HfCH2C6H5 and the mechanism of rearrangement to its ...
Ray Bulls,Schaefer, William P.,Serfas, Michael,Bercaw, John E.
, p. 1219 - 1226 (2008/10/08)
Full title: Intramolecular C-H bond activation of benzyl ligands by metalated cyclopentadienyl derivatives of permethylhafnocene. Molecular structure of (η5-C5Me5) (η5,η1-C5Me4CH 2)HfCH2C6H5 and the mechanism of rearrangement to its hafnabenzocyclobutene tautomer (η5-C5Me5)2HfCH 2-o-C6H4. Thermal decomposition of Cp*2Hf(CH2C6H5)2 (Cp* = η5-C5Me5) in benzene-d6 cleanly affords toluene and hafnabenzocyclobutene Cp*2HfCH2-o-C6H4. Deuterium labeling of the benzyl ligands indicates that decomposition of Cp*2Hf(CY2C6H5)2 (Y = H, D) proceeds primarily by α-H abstraction to form a permethylhafnocene benzylidene intermediate [Cp*2Hf=CHC6H5], which rapidly rearranges to the metalated cyclopentadienyl or tucked-in benzyl complex Cp*(η5,η1-C5Me4CH 2)HfCH2C6H5. The observed product arises from rearrangement of Cp*(η5,η1-C5Me4CH 2)HfCH2C6H5 to its tautomer Cp*2HfCH2-o-C6H4. A series of meta-substituted benzyl derivatives of the proposed metalated cyclopentadienyl intermediates, Cp*-(η5,η1-C5Me 4CH2)HfCH2C6H4X (X = H, CH3, CF3, NMe2), has therefore been prepared. The kinetics of their conversion to Cp*2HfCH2-o-C6H3X have been examined in order to probe the nature of the transition state for aryl C-H bond activation that occurs in the final steps of the rearrangement. The rates are found to be insensitive to the nature of X, suggesting that the benzyl π system is not attacked by the electrophilic hafnium center along the reaction coordinate for C-H bond activation. The structure of Cp*(η5,η1-C5Me4CH 2)HfCH2C6H5, as determined by single-crystal X-ray diffraction techniques, indicates that the complex is best described as a Hf(IV) derivative containing an η5,η1-C5Me4CH2 ligand rather than a Hf(II) η6-fulvene adduct. Cp*(η5,η1-C5Me4CH 2)HfCH2C6H5 crystallizes in the triclinic space group P1 (a = 9.084 (2) A?, b = 10.492 (2) A?, c = 12.328 (1) A?; α = 95.81 (1)°, β = 96.60 (1)°, γ = 91.15 (2)°; Z = 2). Least-squares refinement led to a value for R of 0.048 (I > 3σI) and a goodness-of-fit of 4.37 for 4029 independent reflections.
