Splitting a C–O bond in dialkylethers with bis(1,2,4-tri-tert-butylcyclopentadienyl)cerium hydride does not occur by a σ-bond metathesis pathway: a combined experimental and DFT computational study

International audience; The addition of diethylether to [1,2,4(Me3C)3C5H2]2CeH, abbreviated Cp′2CeH, gives Cp′2CeOEt and ethane. Similarly, di-n-propyl- or di-n-butylether gives Cp′2Ce(O-n-Pr) and propane or Cp′2Ce(O-n-Bu) and butane, respectively. Using Cp′2CeD, the propane and butane contain deuterium predominantly in their methyl groups. Mechanisms, formulated on the basis of DFT computational studies, show that the reactions begin by an α- or β-CH activation with comparable activation barriers, but only the β-CH activation intermediate evolves into the alkoxide product and an olefin. The olefin then inserts into the Ce–H bond forming the alkyl derivative, Cp′2CeR, which eliminates alkane. The α-CH activation intermediate is in equilibrium with the starting reagents, Cp′2CeH and the ether, which accounts for the deuterium label in the methyl groups of the alkane. The one-step σ-bond metathesis mechanism has a much higher activation barrier than either of the two-step mechanisms.