Syntheses of N^O-donor palladium(II) complexes and applications as recyclable catalysts in biphasic methoxycarbonylation of alkenes

Abstract

Treatments of 2-(((2-methoxyethyl)imino)methyl)phenol (L1H), 2-((2-hydroxyethylimino) methyl) phenol (L2H), and 3,5-di-tert-butyl-2-(((2-methoxyethyl)imino)methyl)phenol (L3H) with Pd(OAc)2 afforded the corresponding Pd(II) complexes [Pd(L1)2] (Pd1), [Pd(L2)2] (Pd2) and [Pd(L3)2] (Pd3) in good yields. Similarly, reactions of the hydrophilic ligands sodium 4-hydroxy-3-(((2-methoxyethyl)imino)methyl)benzenesulfonate (L4H), sodium 4-hydroxy-3-(((2-methoxyethyl)imino)methyl)benzenesulfonate (L5H) and sodium 3-(((2-(dimethylamino)ethyl)imino)methyl)-4-hydroxybenzenesulfonate (L6H) with Pd(OAc)2 gave the respective Pd(II) complexes [Pd(L4)2] (Pd4), [Pd(L5)2] (Pd5) and [Pd(L6)2] (Pd6) in moderate yields. Molecular structures of compounds Pd1 and Pd3 confirmed the N^O bis(chelated) four-coordinate species. The palladium complexes (Pd1-Pd6) afforded active catalysts in the methoxycarbonylation of olefins, to give maximum yields of 90% with regioselectivity of up to 78% in favor of linear esters. The water-soluble catalysts (Pd4-Pd6) could be reused four times under biphasic media with minimum effects on catalytic performance.