152135-89-2Relevant academic research and scientific papers
Formation of six-membered palladacycles from phenanthroline Pd(II) bisacetate precursors and phenylisocyanate Dedicated to Professor John A. Osborn.
Moulin, Solenne,Pellerin, Olivier,Toupet, Lo?c,Paul, Frédéric
, p. 521 - 525 (2014/06/09)
Phenylisocyanate reacts with palladium(II) bis-acetate phenanthroline complexes to give six-membered palladacycles in nearly quantitative yields. In this new reaction, the acetate ligands act as decarbonylating agents toward the isocyanate functionality by possibly forming the isolated palladacycles via an intramolecular rearrangement.
Palladium(0)-catalyzed trimerization of arylisocyanates into 1,3,5-triarylisocyanurates in the presence of diimines: A nonintuitive mechanism
Paul, Frederic,Moulin, Solenne,Piechaczyk, Olivier,Le Floch, Pascal,Osborn, John A.
, p. 7294 - 7304 (2008/02/06)
We show here that palladium(0) (dibenzylideneacetone) complexes bearing 1,10-phenanthroline constitute efficient catalysts for the cyclotrimerization of aromatic isocyanates. For the first time, the mechanism of this reaction has been investigated experimentally and theoretically with group 10 catalysts. This investigation provides a very consistent picture of the catalytic cycle. Notably, we establish that the reaction does not proceed by stepwise cycloadditions or ring insertions involving metallacyclic intermediates, as might have been anticipated. Rather, in our proposal, the initial steps of the mechanism resemble the chain-growth process operative during the anionic polymerization of isocyanates and feature charge-separated intermediates. These steps are then followed by ring closure on the metal center of the last intermediate formed to yield a seven-membered metallacycle that reductively eliminates the cyclotrimer and re-forms the active species. In addition, we conclusively show that the (known) palladacycles that could be isolated during the experimental investigations are not catalytic intermediates but result from catalyst deactivation. Thus, with Pd(0) diimine catalysts, the actual trimerization mechanism appears to be a blend between the two types of mechanisms proposed thus far for the oligomerization of heterocumulenes with very different catalysts. In conclusion, this work contributes to a better understanding of the reactivity of arylisocyanates in the vicinity of late group 10 metal centers in low oxidation state and sheds some light on the detrimental self-poisoning processes observed during the reductive carbonylation of nitroaromatic substrates catalyzed by related catalysts in non-nucleophilic media.
