A series of Pd-complexes containing nonsymmetrical bis(aryl-imino)acenaphthene (Ar-BIAN) ligands, characterized by substituents on the meta positions of the aryl rings, have been synthesized, characterized and applied in CO/vinyl arene copolymerization reactions. Crystal structures of two neutral Pd-complexes have been solved allowing comparison of the bonding properties of the ligand. Kinetic and mechanistic investigations on these complexes have been performed. The kinetic investigations indicate that in general ligands with electron-withdrawing substituents give more active, but less stable, catalytic systems, although steric effects also play a role. The good performance observed with nonsymmetrical ligands is at least in part due to a compromise between catalyst activity and lifetime, leading to a higher overall productivity with respect to catalysts based on their symmetrical counterparts. Additionally, careful analysis of the reaction profiles provided information on the catalyst deactivation pathway. The latter begins with the reduction of a Pd(II) Ar-BIAN complex to the corresponding Pd(0) species, a reaction that can be reverted by the action of benzoquinone. Then the ligand is lost, a process that appears to be facilitated by the contemporary coordination of an olefin or a CO molecule. The so formed Pd(0) complex immediately reacts with another molecule of the initial Pd(II) complex to give a Pd(I) dimeric species that irreversibly evolves to metallic palladium. Mechanistic investigations performed on the complex with a nonsymmetrical Ar-BIAN probe evidence that the detected intermediates are characterized by the Pd–C bond trans to the Pd–N bond of the aryl ring bearing electron-withdrawing substituents. In addition, the intermediate resulting from the insertion of 4-methylstyrene into the Pd–acyl bond is a five-member palladacycle and not the open-chain η3-allylic species observed for complexes with Ar-BIANs substituted in ortho position.

Catalyst activity or stability : the dilemma in Pd-catalyzed polyketone synthesis / F. Amoroso, E. Zangrando, C. Carfagna, C. Müller, D. Vogt, M. Hagar, F. Ragaini, B. Milani. - In: DALTON TRANSACTIONS. - ISSN 1477-9226. - 42:40(2013), pp. 14583-14602. [10.1039/c3dt51425k]

Catalyst activity or stability : the dilemma in Pd-catalyzed polyketone synthesis

M. Hagar;F. Ragaini
;
2013

Abstract

A series of Pd-complexes containing nonsymmetrical bis(aryl-imino)acenaphthene (Ar-BIAN) ligands, characterized by substituents on the meta positions of the aryl rings, have been synthesized, characterized and applied in CO/vinyl arene copolymerization reactions. Crystal structures of two neutral Pd-complexes have been solved allowing comparison of the bonding properties of the ligand. Kinetic and mechanistic investigations on these complexes have been performed. The kinetic investigations indicate that in general ligands with electron-withdrawing substituents give more active, but less stable, catalytic systems, although steric effects also play a role. The good performance observed with nonsymmetrical ligands is at least in part due to a compromise between catalyst activity and lifetime, leading to a higher overall productivity with respect to catalysts based on their symmetrical counterparts. Additionally, careful analysis of the reaction profiles provided information on the catalyst deactivation pathway. The latter begins with the reduction of a Pd(II) Ar-BIAN complex to the corresponding Pd(0) species, a reaction that can be reverted by the action of benzoquinone. Then the ligand is lost, a process that appears to be facilitated by the contemporary coordination of an olefin or a CO molecule. The so formed Pd(0) complex immediately reacts with another molecule of the initial Pd(II) complex to give a Pd(I) dimeric species that irreversibly evolves to metallic palladium. Mechanistic investigations performed on the complex with a nonsymmetrical Ar-BIAN probe evidence that the detected intermediates are characterized by the Pd–C bond trans to the Pd–N bond of the aryl ring bearing electron-withdrawing substituents. In addition, the intermediate resulting from the insertion of 4-methylstyrene into the Pd–acyl bond is a five-member palladacycle and not the open-chain η3-allylic species observed for complexes with Ar-BIANs substituted in ortho position.
palladium; polymerization; carbon monoxide; homogeneous catalysis; nitrogen ligands; olefins
Settore CHIM/03 - Chimica Generale e Inorganica
Settore CHIM/06 - Chimica Organica
2013
Article (author)
File in questo prodotto:
File Dimensione Formato  
Dalton_Revised.pdf

accesso aperto

Tipologia: Pre-print (manoscritto inviato all'editore)
Dimensione 858.92 kB
Formato Adobe PDF
858.92 kB Adobe PDF Visualizza/Apri
Dalton_SI_Revised.pdf

accesso aperto

Tipologia: Pre-print (manoscritto inviato all'editore)
Dimensione 976.73 kB
Formato Adobe PDF
976.73 kB Adobe PDF Visualizza/Apri
PdCopol2.pdf

accesso riservato

Descrizione: Articolo principale
Tipologia: Publisher's version/PDF
Dimensione 1.11 MB
Formato Adobe PDF
1.11 MB Adobe PDF   Visualizza/Apri   Richiedi una copia
Pubblicazioni consigliate

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: https://hdl.handle.net/2434/231011
Citazioni
  • ???jsp.display-item.citation.pmc??? 2
  • Scopus 34
  • ???jsp.display-item.citation.isi??? 33
social impact