Formation, Operation and Deactivation of Cr Catalysts in Ethylene Tetramerization Directly Assessed by Operando EPR and XAS

Operando EPR under elevated ethylene pressure supported by in situ XAS was for the first time applied to discriminate between active and deactivating Cr species in ethylene tetramerization. Starting from Cr(III) in the Cr(acac)(3) precursor, a (PNP)Cr(II)-(CH3)(2) complex is most likely formed upon adding PNP and MMAO, which is regarded as the active species that converts ethylene to 1-octene by passing a reversible redox cycle, while reduction to Cr(I) leads to deactivation.</p