Carbon Monoxide Activation via O-Bound CO Using Decamethylscandocinium–Hydridoborate Ion Pairs

Abstract

Ion pairs [Cp*₂Sc]⁺[HB(p-C₆F₄R)₃]⁻ (R = F, 1-F; R = H, 1-H) were prepared and shown to be unreactive toward D₂ and α-olefins, leading to the conclusion that no back-transfer of hydride from boron to scandium occurs. Nevertheless, reaction with CO is observed to yield two products, both ion pairs of the [Cp*₂Sc]⁺ cation with formylborate (2-R) and borataepoxide (3-R) counteranions. DFT calculations show that these products arise from the carbonyl adduct of the [Cp*₂Sc]⁺ in which the CO is bonded to scandium through the oxygen atom, not the carbon atom. The formylborate 2-R is formed in a two-step process initiated by an abstraction of the hydride by the carbon end of an O-bound CO, which forms an η²-formyl intermediate that adds, in a second step, the borane at the carbon. The borataepoxide 3-R is suggested to result from an isomerization of 2-R. This unprecedented reaction represents a new way to activate CO via a reaction channel emanating from the ephemeral isocarbonyl isomer of the CO adduct.