The Competition between Allene and Butadiene in the Carbon−Hydrogen Bond Activation Initiated by a Tungsten Allyl Complex: A DFT Study

Abstract

Mechanisms for H-transfer from 1,1-dimethylallyl (DMA) to neopentyl (CH2t-Bu) in the complex Cp*W(NO)(CH2t-Bu)(η3-DMA) are examined by B3LYP-DFT calculations. Either the mid-H or the methyl H on the DMA can transfer to the W-bound neopentyl to generate neopentane (2,2-dimethylpropane) and Cp*W(NO)(η2-1,1-dimethylallene) or Cp*W(NO)(η2-2-methylbuta-1,3-diene) intermediates, respectively. The open coordination site created by the neopentane loss is the site of the subsequent C−H bond activation of alkanes and arenes. The similarities in the overall enthalpic barriers for these mechanisms, 23−24 kcal/mol, explain the observed deuterium distribution (65% on the mid-carbon and 35% on the methyls of the DMA) when benzene-d6 reacts as substrate.