Design of cationic mixed phosphine/N-Heterocyclic carbene palladium(II) pi-Allyl complexes as monoligated phosphine Pd(0) precatalysts: synthesis, structural studies, catalysis, and reactivity

Normand, Adrien T., Stasch, Andreas ORCID: https://orcid.org/0000-0002-7407-8287, Ooi, Liling and Cavell, Kingsley John 2008. Design of cationic mixed phosphine/N-Heterocyclic carbene palladium(II) pi-Allyl complexes as monoligated phosphine Pd(0) precatalysts: synthesis, structural studies, catalysis, and reactivity. Organometallics 27 (24) , pp. 6507-6520. 10.1021/om8008052

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Abstract

Compounds of general formula [Pd(L)(NHC)(L′)]BF4 (where L = allyl or crotyl, NHC = tetramethylimidazolin-2-ylidene (tmiy) or 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene (dipdmiy), and L′ = tertiary phosphine) have been prepared from the parent [Pd(L)Cl(NHC)(L′)] complexes and fully characterized. A perpendicular orientation of the NHC is observed in the solid state (X-ray) and in solution (NOESY). The crystal structures of these complexes reveal the double-bond character of the allyl trans to the phosphine ligand; for example, [Pd(η3-C3H5)(tmiy)(PPh3)]BF4 (4d) displays C−C distances of 1.198 Å (trans to P) and 1.374 Å (trans to the NHC). The NHC-Pd-allyl precatalysts are thought to generate monoligated phosphine-Pd(0) active species by reductive elimination of 2-allylimidazolium following η3−η1 isomerization of the allyl group. This was observed in the case of [Pd(η3-C3H5)(tmiy)(PCy3)]BF4 (4b), which successfully catalyzed the coupling of imidazolium salts with ethylene. The intriguing reactivity of 4b with PhI, yielding 2-phenylimidazolium selectively, is also reported.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Chemistry Cardiff Catalysis Institute (CCI)
Subjects:	Q Science > QD Chemistry
Publisher:	American Chemical Society
ISSN:	0276-7333
Last Modified:	17 Oct 2022 09:53
URI:	https://orca.cardiff.ac.uk/id/eprint/6084

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