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South African Journal of Chemistry

versão On-line ISSN 1996-840X
versão impressa ISSN 0379-4350

S.Afr.j.chem. (Online) vol.65  Durban  2012

 

RESEARCH ARTICLE

 

Novel O^N^N pyrazolyl-imine and imidazolyl-imine pincer palladium complexes as Heck coupling catalysts

 

 

Sibulele BoltinaI; Margaret YankeyI; Ilia A. GuzeiII; Lara C. SpencerII; Stephen O. OjwachI, *; James DarkwaI, **

IDepartment of Chemistry, University of Johannesburg, Auckland Park Kingsway Campus, Auckland Park, 2006, South Africa
IIDepartment of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA

 

 


ABSTRACT

Five pyrazolyl and imidazolyl compounds, 2,4-di-tert-butyl-6-[2-pyrazol-1-yl-ethylimino-methyl]-phenol (L1), 2,4-di-tert-butyl-6-{[2-(3,5-dimethyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L2), 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L3), 4-tert-butyl-2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L4) and 2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L5) were synthesized by condensation of the appropriate 2-hydroxybenzaldehyde and the corresponding alkylamine. Reactions of L1-L5 with either [Pd(NCMe)2Cl2] or [Pd(COD)MeCl] led to in situ deprotonation of the phenolic-OH proton to afford the pincer palladium complexes [Pd(L1)Cl] (1), [Pd(L1)Me] (2), [Pd(L2)Cl] (3), [Pd(L3)Cl] (4), [Pd(L4)Cl] (5) and [Pd(L5)Cl] (6). The tridentate coordination modes of the ligands were confirmed by the solid state structures of 1, 2, 3 and 4.H2O: Complexes 1-6 catalyzed the Heck coupling reactions of iodobenzene and butylacrylate. In addition, complex 4 catalyzed the Heck coupling reaction of butyl acrylate and bromobenzene; giving conversions as high as 70 %.

Keywords: Pincer palladium complexes, pyrazolyl-imine, imidazolyl imine, aryl halides, Heck coupling catalysts


 

 

Full text available only in PDF format.

 

Acknowledgements

The authors would like to thank the National Research Foundation (NRF), South Africa, and University of Johannesburg for financial support.

 

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Received 18 January 2012
Revised 8 March 2012
Accepted 13 March 2012

 

 

* Present address: School of Chemistry, University of Kwa-Zulu Natal, Pietermariztburg.
** To whom correspondence should be addressed. E-mail: jdarkwa@uj.ac.za

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