Organometallics
Organometallics
5 years ago

Intermetallic Cooperation in C–H Activation Involving Transient Titanium-Alkylidene Species: A Synthetic and Mechanistic Study

Intermetallic Cooperation in C–H Activation Involving Transient Titanium-Alkylidene Species: A Synthetic and Mechanistic Study
Miguel Mena, Cristina Santamaría, Juan I. González-Pérez, Diego García-López, María Gómez-Pantoja, Jorge J. Carbó, Avelino Martín
Remote carbon–hydrogen activation on titanium dinuclear complexes [{Ti(η5-C5Me5)R2}2(μ-O)] [R = CH2SiMe3 2, CH2CMe3 3, and CH2Ph 5) have been examined both synthetically and theoretically. While the thermal treatment of the oxoderivative [{Ti(η5-C5Me5)(CH2SiMe3)2}2(μ-O)] (2) led to a series of metallacycle complexes (2a–c) by sequential carbon–hydrogen activation processes, [{Ti(η5-C5Me5)(CH2CMe3)2}2(μ-O)] (3) gave rise to the formation of the metallacycle tuck-over species [Ti2(η5-C5Me5)(μ-η5-C5Me4CH2-κC)(CH2CMe3)(μ-CH2CMe2CH2)(μ-O)] (4), as result of hydrogen abstraction from a η5-C5Me5 ligand. However, the thermolysis of the tetrabenzyl complex [{Ti(η5-C5Me5)(CH2Ph)2}2(μ-O)] (5) yielded the derivative [Ti2(η5-C5Me5)(μ-η5-C5Me4CH2-κC)(CH2Ph)3(μ-O)] (6) that only exhibits tuck-over η5-C5Me5 metalation. DFT calculations show that the mechanism involves a first α-hydrogen abstraction to generate a transient titanium alkylidene, which enables it to activate β- and γ-C(sp3)-H bonds on the adjacent titanium center. The calculations also establish a reactivity order for the different type of γ-H abstractions, trimethylsilyl > neopentyl ≌ benzyl, allowing us to explain the observed selectivity.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00416

DOI: 10.1021/acs.organomet.7b00416

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