Molecular Hydrogen-Induced Carbon Chain Rearrangement in Cyclopentadienyl-Tethered Titanium(III) Permethyltitanocene Complexes
Abstract
Dihydrogen added at atmospheric pressure and ambient temperature to cyclopentadienyl-tethered titanium(III) permethyltitanocene complexes induced the rearrangement of their tether [-CH2-C(Me)=C(R)-Ti], moving the double bond to the lateral position [-CH2-C(=CHR)-CH2-Ti]. The methyl substituent on the β-carbon from the cyclopentadienyl ring is converted to methylene group binding the rearranged tether to titanium.
Subsequent hydrogenation of compounds with [-CH2-C(=CHR)-CH2-Ti] R = Ph or SiMe3 gave saturated rearranged products whereas compound with [-CH2-C(=CMeCMe=CHMe)-CH2-Ti] resisted. Computational studies elucidated the reaction mechanism and established the catalytical role of molecular hydrogen.
This type of isomerization can be conceived as a sigma-bond metathetic rearrangement leading to the formation of tethered complexes with decreased steric strain.