481695-52-7Relevant academic research and scientific papers
C-H bond activation processes in cationic and neutral titanium benzyl compounds with cyclopentadienyl-arene ligands
Deckers, Patrick J.W.,Hessen, Bart
, p. 5564 - 5575 (2008/10/08)
Titanium tribenzyl complexes with cyclopentadienyl-arene ligands, (η5-C5H4CMe2Ar)Ti-(CH2 Ph)3 (Ar = 3,5-Me2C6H3 (1), Ph (2)), were synthesized. Reaction of 1 with either B(C6F5)3 or [Ph3C][B(C6F5)4] affords the cation [(η,5:η-C5H4CMe2-3,5-Me 2C6H3)Ti(η-CH2Ph)2]- (3), in which the pendant arene group and the benzyl ligands show fluxional behavior. Reaction of 2 with B(C6F5)3 leads to rapid ortho cyclometalation of the pendant arene to give the contact ion pair [(η5:η1-C5H4CMe2C 6H4)Ti(η1-CH2Ph)][η6 -PhCH2B(C6F5)3] (4) and toluene. Reaction of 2 with [Ph3C][B(C6F5)4] also leads to ligand ortho metalation, giving [(η5:η1-C5H4CMe2C 6H4)-Ti(η2-CH2Ph)] [B(C6F5)4] (5) with a η2-benzyl group. Thermolysis of compounds 1 and 2 (50 °C, 50 h) results in the ortho-cyclometalated dibenzyl species (η5:η1-C5H4CMe2Ar ′)Ti-(CH2Ph)2 (Ar′ = 3,5-Me2C6H2 (6), C6H4 (7)) and toluene. The thermolysis of 1 follows first-order kinetics (k ≈ 10-5 s-1 at 333 K) with ΔH? = 24 ± 2 kcal mol1 and ΔS? = -5 ± 5 cal mol-1 K-1. For the thermolysis of the related titanium trialkyl (η5-C5H4CMe2Ph)Ti-(CH2 SiMe3)3 (9), activation parameters of ΔH? = 21 ±2 kcal mol-1 and ΔS? = -18 ± 4 cal mol-1 K1 were found. Deuterium labeling studies with (η5-C5H4CMe2C6D5 )Ti(CH2Ph)3 (2-d5) show that thermolysis of the neutral compound involves initial formation of an alkylidene intermediate, followed by o-CH addition to the Ti=C bond. In the corresponding cationic species, ortho cyclometalation proceeds via direct σ-bond metathesis.
