The mononuclear square-planar Rh{κ2-X,N-(Xpy)}(η2-coe)(IPr) (X = O, NH, NMe, S) complexes have been synthesized from the dinuclear precursor [Rh(μ-Cl)(IPr)(η2-coe)]2 and the corresponding 2-heteroatom-pyridinate salts. The Rh-NHC-pyridinato derivatives are highly efficient catalysts for gem-specific alkyne dimerization. Particularly, the chelating N,O-pyridonato complex displays turnover frequency levels of up 17 000 h–1 at room temperature. Mechanistic investigations and density functional theory calculations suggest a pyridonato-based metal–ligand cooperative proton transfer as responsible for the enhancement of catalytic activity. The initial deprotonation of a Rh-π-alkyne complex by the oxo-functionality of a κ1-N-pyridonato moiety has been established to be the rate-limiting step, whereas the preferential protonation of the terminal position of a π-coordinated alkyne accounts for the exclusive observation of head-to-tail enynes. The catalytic cycle is closed by a very fast alkenyl–alkynyl reductive elimination.

Metal–Ligand Cooperative Proton Transfer as an Efficient Trigger for Rhodium-NHC-Pyridonato Catalyzed gem-Specific Alkyne Dimerization

Di Giuseppe, Andrea;
2021

Abstract

The mononuclear square-planar Rh{κ2-X,N-(Xpy)}(η2-coe)(IPr) (X = O, NH, NMe, S) complexes have been synthesized from the dinuclear precursor [Rh(μ-Cl)(IPr)(η2-coe)]2 and the corresponding 2-heteroatom-pyridinate salts. The Rh-NHC-pyridinato derivatives are highly efficient catalysts for gem-specific alkyne dimerization. Particularly, the chelating N,O-pyridonato complex displays turnover frequency levels of up 17 000 h–1 at room temperature. Mechanistic investigations and density functional theory calculations suggest a pyridonato-based metal–ligand cooperative proton transfer as responsible for the enhancement of catalytic activity. The initial deprotonation of a Rh-π-alkyne complex by the oxo-functionality of a κ1-N-pyridonato moiety has been established to be the rate-limiting step, whereas the preferential protonation of the terminal position of a π-coordinated alkyne accounts for the exclusive observation of head-to-tail enynes. The catalytic cycle is closed by a very fast alkenyl–alkynyl reductive elimination.
File in questo prodotto:
File Dimensione Formato  
26-Castarlenas-ACSCat-2021-7553.pdf

non disponibili

Tipologia: Documento in Versione Editoriale
Licenza: Creative commons
Dimensione 4.05 MB
Formato Adobe PDF
4.05 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11697/167444
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 4
  • ???jsp.display-item.citation.isi??? ND
social impact