A smart palladium catalyst in ionic liquid for tandem processes.

New catalytic systems based on in situ and preformed palladium nanoparticles in ionic liquids (characterised by TEM) starting from palladium acetate or dipalladiumtris(dibenzylideneacetone) have been applied in the synthesis of 4-phenylbutan-2-one (II), a model compound for the preparation of fragrances. Imidazolium-based ionic liquid containing a methyl hydrogenophosphonate anion leads to an efficient Pd-catalyzed tandem coupling/reduction process, taking advantage of the multi-role of this solvent (nanoparticles stabiliser, base, hydrogen transfer agent). The influence of the mono-phosphine ligands (1-3) on the catalyst has been evaluated, showing that the ligand-free palladium system turns into the most appropriate for the formation of II using Pd(OAc)(2) as precursor. Fine-tuning conditions involved in this multi-parameter process have led us to propose a plausible mechanism based on the hydrogen transfer coming from the methyl hydrogenophosphonate anion.

Unexpected activation of carbon-bromide bond promoted by palladium nanoparticles in Suzuki C-C couplings.

Dihydroanthracene derivatives (1-6) containing imide (1-3) and amine (4-6) functions have been used for the stabilization of palladium nanoparticles, starting from Pd(0) and Pd(ii) organometallic precursors. Well-dispersed nanoparticles of mean size in the range ca. 1.9 to 3.6 nm could be obtained using Pd(0) precursors (PdLc and PdLd, where L = 1-6 and c and d mean the organometallic precursor involved, [Pd(2)(dba)(3)] and [Pd(ma)(nbd)] respectively). With the aim to evaluate the behaviour of homogeneous species and nanoparticles used as catalytic precursors, palladium complex coordinated to the diamine 6, [Pd(OAc)(2)(κ(2)-N,N-6)], was prepared, reporting for the first time the X-ray diffraction structure of a metallic complex containing a ligand with a 9,10-dihydroanthracene backbone. Palladium systems were evaluated in Suzuki C-C coupling reactions and relevant differences were observed comparing the reactivity of the homogeneous systems in relation to that obtained using palladium nanoparticles as starting catalyst in relation to the activation of the C-Br bonds for deactivated substrates.

Sugar-based diphosphoroamidite as a promising new class of ligands in Pd-catalyzed asymmetric allylic alkylation reactions.

We have designed a new family of readily available modular diphosphoroamidite ligands from d-xylose for Pd-catalyzed asymmetric allylic alkylation reactions. This constitutes the first example of diphosphoroamidite ligands applied to this process. Good-to-excellent activities (TOFs up to 850 mol substratex(mol Pdxh)-1) and enantioselectivities (ee's up to 95%) have been obtained for several substrates with different electronic and steric properties. The results indicate that catalytic performance is highly affected by the substituents and the axial chirality of the biaryl moieties of the ligand. We also discuss the synthesis and characterization of the Pd-pi-allyl intermediates to get more insight into the origin of enantioselectivity using these catalytic systems.

First chiral phosphoroamidite-phosphite ligands for highly enantioselective and versatile Pd-catalyzed asymmetric allylic substitution reactions.

[reaction: see text] A series of phosphite-phosphoroamidite ligands, derived from readily available d-xylose, has been successfully applied for the first time in the Pd-catalyzed allylic substitution of several substrates with different steric and electronic properties, with high enantioselectivities (ee's up to 98) and activities in standard conditions.