Encapsulating ruthenium and osmium with tris(2-aminoethyl)amine based tripodal ligands

The reaction of a series of tripodal ligands, H3L1,2 and L3–6, with [M(PPh3)2Cl2] (M = Ru, Os) affords a family of coordination cage compounds of the type [MIIIL1,2] (1–4) or [MIIL3–6](BPh4)2 (5–12). The Schiff base ligands (H3L1, L3, L5) have been synthesized by condensation of tris(2-aminoethyl)amine with salicylaldehyde, pyridine-2-aldehyde and 1-methyl-2-imidazolecarboxaldehyde. These ligands were further reduced and subsequently methylated to form the new ligands (H3L2, L4, L6). Single crystal X-ray diffraction studies of 1 and 2 show that the tripodal ligand wraps around the metal center as a hexadentate ligand to form a cage. All the synthesized compounds have been thoroughly characterized by ESI-MS, FT-IR, UV–Vis and NMR spectroscopic methods. To the best of our knowledge, this is the first ever report of osmium complexes with tris(2-aminoethyl)amine based tripodal ligands. DFT calculations were performed to obtain geometry optimized structures of all the other complexes (3–12).

Synthesis and characterization of ruthenium and osmium complexes of twelve tripodal Schiff base ligands have been described. The tripodal ligands wrap around the metal center as hexadentate ligand. Ligands (H3L1, L3, L5) were synthesized by condensation of Tris(2-aminoethyl)amine with salicylaldehyde, pyridine-2-aldehyde and 1-methyl-2-imidazolecarboxaldehyde and (H3L2, L4, L6) subsequent reduction followed by N-methylation.Figure optionsDownload as PowerPoint slideHighlights
► Ruthenium and osmium complexes of tripodal ligands.
► Crystal structure determination of two of the complexes.
► DFT study of the complexes to understand the electronic spectra and to get geometry optimized structures.