Evidence for Intramolecular C-H Bond Activation and the Formation of a "Tucked-In" Complex of Hexamethylbenzene at a Tantalum(III) Center

Article abstract of DOI:10.1021/ja00188a033

The reactions of the d² tantalum complex (η⁶-C6Me6)Ta(OR)2Cl (1, OR=2,6-diisopropylphenoxide) with 3,3-dimethyl-1-butyne and 3-chloropropene provide the η¹-pentamethylbenzyl compounds (E)-(η¹-C6Me5CH2)Ta(CH=CH-(CMe3))(OR)2Cl (3) and (η¹-C6Me5CH2)Ta(CH2CH2CH2Cl)(OR)2Cl (5), respectively.Both complexes are proposed to have arisen through the intermediacy of an unprecedented d⁰ "tucked-in" hexamethylbenzene compound, viz. (η⁶,η¹-C6Me5CH2)Ta(H)(OR)2Cl (4).The intramolecular metalation of a methyl C-H bond in 1 and the existence of a hydride intermediate are also inferred from various deuterium labeling and kinetics studies.The metalated hexamethylbenzene can be functionalized selectively as demonstrated in the iodination of 3 to form C6(CH3)5CH2I and (E)-CHI=CH(CMe3).