Comparative Reactivity of Zr– and Pd–Alkyl Complexes with Carbon Dioxide

Abstract

Structure/reactivity trends and DFT studies reveal mechanistic differences and parallels for the carboxylation of Zr and Pd alkyls. CO₂ reacts with Cp₂ZrMe­(C₆D₅Cl)⁺ >10⁴ faster than with Cp₂ZrMe₂, yielding monoacetate products in both cases. These reactions proceed by insertion mechanisms in which Zr- - -O interactions activate the CO₂. In contrast, CO₂ reacts readily with [(PO-ⁱPr)­PdMe₂]⁻ (PO-ⁱPr^– = 2-PⁱPr₂-4-Me-C₆H₃SO₃^–) to yield [(PO-ⁱPr)­PdMe­(OAc)]⁻ but not with (PO-ⁱPr)­PdMe­(L) species. Carboxylation of [(PO-ⁱPr)­PdMe₂]⁻ occurs by direct S_E2 attack of CO₂ at the Pd–Me_{<i>trans</i>‑to‑P} group, and the nucleophilicity of the Pd–Me group controls the reactivity. However, the S_E2 process is accelerated by a Li⁺- - -OCO interaction when Li⁺ is present