Synthesis, spectroscopic characterization and catalytic activity of cis‐dioxidomolybdenum (VI) complexes with chiral tetradentate Schiff bases

Abstract

New chiral mononuclear cis‐dioxidomolybdenum (VI) complexes, MoO2L1–MoO2L10, with tetradentate Schiff bases derived from various substituted salicylaldehydes and 1S,2S‐(+)‐2‐amino‐1‐(4‐nitrophenyl)‐1,3‐propanediol were synthesized. All complexes were characterized by elemental analysis, circular dichroism, electronic and IR spectroscopy. 1H NMR and also two‐dimensional (COSY, NOESY and gHSQC) NMR measurements made for MoO2L1–MoO2L10 complexes show that Schiff bases are coordinated to the MoO22+ cation, creating facial (fac) and meridional (mer) types of geometrical isomers. Moreover, catalytic activity studies were also performed for all complexes in asymmetric sulfoxidation of thioanisole and epoxidation of styrene, cyclohexene and two monoterpenes, i.e. S(−)‐limonene and (−)‐α‐pinene, using aqueous 30% H2O2 or tert‐butyl hydroperoxide as the oxygen source.

Catalytic activity of a new dioxidomolybdenum(vi) complex with a bipodal N2O-donor ligand in sulfur compound oxidation

“…In the last few decades, molybdenum has been employed in the synthesis of new bioinspired complexes coordinated by different ligands with biological importance like amino acids and carbohydrates. 1 These new molybdenum(VI) complexes have been evaluated for their catalytic activity for reactions with industrial and biological significance like oxidation of alcohols, oxidative halogenations of organic substrates, 2 as well as extensively applied in oxygen atom transfer (OAT) processes, such as epoxidation reactions [3][4][5][6][7][8][9] and sulfide oxidations. [10][11][12][13][14][15] Industrially, molybdenum-based materials and complexes are widely applied in plenty of oxidation reactions, hydrocarbon dehydrogenations, polymerization reactions and alkene metatheses.…”

“…1 These new molybdenum(VI) complexes have been evaluated for their catalytic activity for reactions with industrial and biological significance like oxidation of alcohols, oxidative halogenations of organic substrates, 2 as well as extensively applied in oxygen atom transfer (OAT) processes, such as epoxidation reactions [3][4][5][6][7][8][9] and sulfide oxidations. [10][11][12][13][14][15] Industrially, molybdenum-based materials and complexes are widely applied in plenty of oxidation reactions, hydrocarbon dehydrogenations, polymerization reactions and alkene metatheses. 16,17 Moreover, an increase in recent studies involving molybdenum complexes applied in the oxidative desulfurization (ODS) process is observed.…”

“…In the last few years, compounds containing molybdenum, mainly complexes coordinated by Schiff bases (ONO-donor ligands) and its derivatives have emerged as catalysts for sulfoxidation reactions, showing great selectivity as a catalyst. 13,[23][24][25] Molybdenum peroxocomplexes represent the most used molybdenum-based complexes in oxidation reactions reported in the literature. 14,26,27 These peroxocomplexes are formed in situ in presence of peroxides such as t-butylhydroperoxide (TBHP), hydrogen peroxide and urea hydroperoxide.…”

“…22,28,29 In this context, sulfide oxidation takes place with good results to produce sulfoxides and sulfone. 6,13,16,30 In general, these molybdenum(VI) complexes contain the dioxidomolybdenum(VI) unit and are N,O,S-coordinated by Schiff base (imine) ligands. This group of ligands stabilizes diverse metal ions in different oxidation states and influences their performance as catalysts in a plenty of chemical transformations.…”

“…In the last few years, compounds containing molybdenum, mainly complexes coordinated by Schiff bases (ONO-donor ligands) and its derivatives have emerged as catalysts for sulfoxidation reactions, showing great selectivity as a catalyst. 13,23–25…”