The methyl zirconocene complex Cp*₂Zr(Me)OMes reacts with H₃C–B(C₆F₅)₂ and CO to give the respective acetyl(methyl)borate Zr complex. Cp*₂Zr(H)OMes reacts with H₃C–B(C₆F₅)₂ and CO to give the respective acetyl(hydrido)borate Zr product, admixed with a minor amount of the formyl(methyl)borate Zr complex isomer. Prolonged exposure to CO under close to ambient conditions results in the uptake of another CO equivalent to yield the corresponding borata-β-lactone zirconocene product.