[Pd0(N,N-chelate)(olefin)] complexes containing nitrogen chelates derived from carbohydrates and their use in mild hydrogenation of olefins in water †

New nitrogen chelates of formula 6-R-C5H3NCHNR′-2 and R′NCHCHNR′ (R = H or Me; R′ = 2,3,4,6-tetra-O-acetyl-β-D-glucopyranose residue) were prepared. The nitrogen donor atom is directly linked to a chiral carbon, i.e. the C1 atom of the sugar ring. The ability of the ligands to induce enantioselective co-ordination of prochiral olefins was assessed by preparing palladium(0) complexes of formula [Pd(N,N-chelate)(olefin)]. Hydrophilic complexes obtained by deprotection of the hydroxy groups of the sugar residue were used for hydrogenating alkenes in water. The course of the reaction is strongly influenced by pH, and homogeneous hydrogenation of the double bond takes place only under basic conditions.