Europium(II) Ynolate Complex: Synthesis, Bonding, and Reactivity
Qingqing Wen1, Ruyi Li2, Xiaojuan Liu1
1Spin-X Institute, School of Chemistry and Chemical Engineering, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510641, China.
Abstract:
Anionic ketenes [RCCO]- exhibit two resonance forms: ketenyl anions and ynolate anions. While ketenyl complexes have been isolated and characterized, crystalline ynolate complexes remain elusive. Herein, we report the first lanthanide ynolate complex, namely, the europium ynolate complex. A σ-bond metathesis reaction of Me3Si(H)CN2 with a europium(II) hydrido or alkyl complex yields a europium(II) nitrilimine, which reacts with CO to provide a europium(II) ynolate complex. Single-crystal X-ray diffraction and DFT calculations confirm the dominance of the ynolate resonance form, showing two orthogonal π orbitals between the C-C unit and a significant negative charge (-0.83) on the oxygen atom. Reactivity studies demonstrate C-centered trapping products with trimethylsilyl trifluoromethanesulfonate, benzophenone, isothiocyanate, and carbodiimide. Mechanistic DFT analysis of the carbodiimide reaction reveals a gradual shift from ynolate to ketenyl anion, enhancing reactivity for [2 + 2] cyclization.
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