Copper(II) arylhydrazone complexes as catalysts for CH activation in the Henry reaction in water

• Stereoselective CH functionalization in water.
• Water-soluble mono- and dinuclear copper(II) complexes.
• Sulfo-functionalized arylhydrazone of acetoacetanilide ligand.
• Copper(II) complexes effectively catalyze the Henry reaction.

Three new water-soluble copper(II) complexes [Cu(HL)(H2O){(CH3)2NCHO}] (1), [Cu(H2L)2(im)4]·CH3OH (2) and [Cu(HL)(CH3OH)]2(μ2-py) (3) were synthesized from copper(II) nitrate and sodium (Z)-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazinyl)benzene-sulfonate (NaH2L), in the absence (for 1) and presence of imidazole (im) (for 2) or pyrazine (py) (for 3), and fully characterized. The complexes 1–3 have been tested as stereoselective CH activating catalysts for the model nitroaldol (Henry) condensation of nitroethane with various aldehydes in water. 1 was the most active catalyst affording 64−87% yields with syn/anti diasteroselectivities up to 77:23.

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