An Ionic Liquid-Coordinated Palladium Complex:  A Highly Efficient and Recyclable Catalyst for the Heck Reaction

Abstract

[structure: see text] The monoquaternary product of 2,2'-biimidazole with iodobutane is an ionic liquid that acts as both the solvent and ligand for catalytic reactions. A new palladium complex was prepared by adding PdCl(2) to this ionic liquid to form a catalytic solution that is effective for Heck reactions with good recyclability.

Crystal structure of trans-dichloro-bis[(E)-2-(1-methoxy-imidazol-2-yl)-2-oxoacetaldehyde O-methyl oxime]palladium(II), PdCl2(C7H9N3O3)2

“…Similar trans-dichlorobis(imidazole)-Pd(II)( not counting benzimidazole) complexes have been reported previously [2][3][4][5][6][7][8][9][10][11][12][13]. However, complexes involving 1,2-disubstituted imidazole ligands seem to be rare [14][15][16][17]. The O1-C6 bond of the methoxy group is twisted out of the imidazole plane by 80°, and the oxygen atom O1 is also bent out of this plane showing adistance of 0.192 Åfrom the imidazole ring.…”

Synthesis of novel room temperature chiral ionic liquids: application as reaction media for the heck arylation of aza-endocyclic acrylates

“…Shreeve has described a series of achiral 2-imidazolyl or 2-pyridylimidazolium salt useful for the preparation of palladium complexes. 33 In line with this work we envisioned the synthesis of such compounds from a chiral primary amine by means of a one-pot multi-component reaction. Although application of this route to the preparation of chiral 2,2'-bisimidazole did not appear viable, 37 we succeeded in preparing a 2-pyrydylimidazole.…”

“…In order to drive the interaction between the ionic liquid and the catalytic species we opted for the use of chiral ionic entities bearing a N-heterocycle susceptible to coordination to the metal centre. Indeed, several studies by Shreeve and co-workers 33 have recently described catalytically active entities based on the complex between a palladium salt and an ionic liquid bearing a basic functionality. To the best of our knowledge, no examples of chiral derivative of that kind were reported so far.…”

“…The aqueous solution was washed with dichloromethane (3 × 80 mL) and concentrated to dryness under reduced pressure. The brown oil obtained was purified by flash column chromatography (dichloromethane/methanol, 9:1 to 1:1 + 3 drops of NH 4 OH/10 mL of eluent) to furnish the pyridinium chloride 31 ( 2-(1-(1-phenylethyl)-1H-imidazol-2-yl)pyridine (33) To a solution of (S)-a-methylbenzylamine (2.25 g, 18.6 mmol) and aqueous ammonia (2.0 mL, 37.2 mmol) in propan-1-ol (10.0 mL) at 0 °C was added dropwise a solution of glyoxal (2.34 mL, 20 mmol) and 2-pyridinecarboxaldehyde (1.9 mL, 20 mmol) in propan-1-ol (20 mL). After 1 h at 0 °C, the solution was heated to 80 °C and left stirring for 4 h. It was then cooled to room temperature and water was added.…”

A novel ionic liquid-supported Schiff base ligand applied in the Pd-catalyzed Suzuki–Miyaura coupling reaction

“…Thus, the development of phosphine-free recyclable catalysts is of great importance. [19][20][21][22] Most recently, much more attention has been focused on the synthesis of functionalized ionic liquids (FILs), via incorporation of additional functional groups such as amine, amide, nitrile, ether, alcohol, acid, urea or thiourea, etc. as a part of the cation and/or anion for task specific purposes.…”