Complexes of cis-dioxomolybdenum(VI) with unsymmetrical tripodal NO3-donor ligands: Synthesis, characterization and catalytic applications

• Complexes of cis-{MoO2}2+ with unsymmetrical tripodal NO3-donor ligands were synthesized.
• The solid state structures of all the complexes were determined by X-ray crystallography.
• Spectroscopic and electron transfer characteristics of the complexes were scrutinized.
• The catalytic activities of the complexes in some organic oxidation reactions were assessed.

A series of cis-dioxomolybdenum(VI) complexes of general formula cis-[MoO2(HLn)] (1–4) have been synthesized in 80–85% yields by reacting equimolar amounts of [MoO2(acac)2] (acac− = acetylacetonate) with 2,2′-(2-hydroxy-3,5-R1,R2-benzylazanediyl)diethanols (H3Ln, n = 1–4) in methanol. Characterization of the complexes has been performed by elemental analysis, spectroscopic (IR, UV–Vis, 1H and 13C NMR) and electrochemical measurements. The molecular structures of all four complexes have been determined by single-crystal X-ray diffraction studies. In each of these analogous complexes, the metal centre is in a distorted octahedral NO5 coordination sphere assembled by the single edge shared 5,5,6-membered chelate rings forming NO3-donor (HLn)2− and two cis oriented oxo groups. Crystal structures of the complexes reveal formation of discrete centrosymmetric dimeric species via a pair of reciprocal intermolecular O–H⋯O hydrogen bonding interactions. Spectroscopic data of all the complexes are consistent with their molecular structures. In the cyclic voltammograms, the redox-active complexes display a quasi-reversible to irreversible metal centred reduction with the cathodic peak potential in the range −0.92 to −1.12 V (versus Ag/AgCl). All the complexes have been evaluated for their catalytic activities in oxidative bromination reactions of styrene and salicylaldehyde and in benzoin oxidation reaction.

Four new complexes of cis-{MoO2}2+ with tripodal NO3-donor 2,2′-(2-hydroxy-3,5-R1,R2-benzylazanediyl)diethanols (H3Ln) are reported. Molecular structures of the diamagnetic and redox active complexes of general formula cis-[MoO2(HLn)] are established by spectroscopic and X-ray crystallographic measurements. The catalytic activities of all the complexes in some organic oxidation reactions are described.Figure optionsDownload as PowerPoint slide