Sustainable carbon-carbon bond formation catalyzed by new oxamate-containing palladium(II) complexes in ionic liquids

New and versatile bis(oxamato)palladate(II) complexes of formula (n-Bu4N)2[Pd(2-Mepma)2]$4H2O (1a)and (n-Bu4N)2[Pd(4-Mepma)2]$2H2O$MeCN (1b) (n-Bu4Nþ ¼ tetra-n-buthylammonium, 2-Mepma ¼ N-2-methylphenyloxamate and 4-Mepma ¼ N-4-methylphenyloxamate) have been synthesized andcharacterized by spectroscopic methods and single crystal X-ray diffraction. Each palladium(II) ion in 1a and 1b is four-coordinate with two oxygen and two nitrogen atoms from two fully deprotonated oxamate ligands building a centrosymmetric square planar surrounding. Their catalytic role has been investigated for both Heck and Suzuki coupling reactions using a series of aryl iodide/bromide derivatives in tetra-n-butylammonium bromide (n-Bu4NBr) as ionic liquid, i.e. molten salt. These precatalystsappear as highly efficient, easily recovered and reused at least eight times without any drasticloss of their exceptional reactivity or leaching from the ionic liquid medium.

New and versatile bis(oxamato)palladate(II) complexes of formula (n-Bu4N)2[Pd(2-Mepma)2].4H2O (1a) and (n-Bu4N)2[Pd(4-Mepma)2]$2H2O$MeCN (1b) (n-Bu4N+ = tetra-n-buthylammonium, 2-Mepma = N-2-methylphenyloxamate and 4-Mepma = N-4 methylphenyloxamate) have been synthesized andcharacterized by spectroscopic methods and single crystal X-ray diffraction. Each palladium(II) ion in 1a and 1b is four-coordinate with two oxygen and two nitrogen atoms from two fully deprotonated oxamateligands building a centrosymmetric square planar surrounding. Their catalytic role has been investigated for both Heck and Suzuki coupling reactions using a series of aryl iodide/bromide derivatives in tetra-n-butylammonium bromide (n-Bu4NBr) as ionic liquid, i.e. molten salt. These precatalysts appear as highly efficient, easily recovered and reused at least eight times without any drasticloss of their exceptional reactivity or leaching from the ionic liquid medium.