Ruthenium and osmium complexes of novel carbohydrate derived salen ligands: Synthesis, characterization and in situ ligand reduction

Synthesis and characterization of two ruthenium(II) and osmium(II) complexes (1 and 2) having carbohydrate derived salen ligand and in situ ligand reduction are reported. The1,2-O-isopropylidene-3,5-diazido-3,5-dideoxy-α-d-xylopyranoside (L1) was reduced by catalytic hydrogenation using continuous flow hydrogen reactor in the presence of salicylaldehyde to form the corresponding bis-imino derivative H2L2. The ligand H2L2 has been transformed to H2L3 upon reduction of one of the imine bonds in consequence to the oxidation of the leaving PPh3 group to POPh3. Systematic spectroscopic characterization, 1H and 13C NMR, mass spectrometry, electronic spectra reveals the composition of the complexes. X-ray crystal structures of both the complexes are reported. Detailed electrochemical studies reveal the redox behaviour of the complexes and DFT calculations help to get the idea about the intense lowest-energy absorption for these two complexes.