From the literature, I propose to design a redox-active ligand, their transition metal complexes and then to determine the molecular, electronic structure, and applications of such complexes and finally to systematically investigate the redox-driven reactivity properties at the metal sites. During this work, organic as well as inorganic synthesis, separation, purification and characterization of organic/inorganic molecules will be done.
Ligands can be broadly classified as either innocent (those that do not take part in redox reactions) or non-innocent (those that can undergo redox reactions). This redox non-innocence of the ligands has made describing the electronic structure of such complexes challenging. As these redox active metal complexes play a crucial role in catalysis and multielectron reactivity so for the next upcoming years research will be based on its application of metal complexes with non-innocent ligands. One family of bidentate non-innocent ligands includes o–phenylene diamines, catechols, and o–aminophenols. These can exist in three different oxidation states that are depicted, starting from the fully reduced o–amidophenolate dianon, in Scheme.
Non-innocent (Redox-active) ligands, o-Catecholate, o-Phenylenediamine, o-Benzene dithiol, o-Aminophenol, o-Aminothiophenol, are the best studied ligands that are capable of redox-active upon metal complexation. The coordination chemistry of the metal-coordinated ligand radicals has been intensively studied in recent years due to its occurrence in the active site of many metalloenzymes. Extensive efforts have been made to provide valuable insight into the general aspects of the structure, physicochemical properties, and functions of phenoxyl radical complexes with a series of transition metal ions.
In an attempt to understand the spectroscopic properties, redox features, stability, and chemical reactivity of phenoxyl radical a series of complexes with the metal-radical interaction have been studied by Wieghardt et al., Tolman et al., Stack et al., Whittaker et al., Pierre et al., Itoh et al., and Yamauchi et al.
The fundamental challenge associated with this idea is how to effectively interface the redox-active moiety with the ligating moiety to best affect the ligand field. Furthermore, it is necessary to probe these new complexes to determine the extent of redox-activity from the ligand to the transition metal center. We intend to use synthetic chemistry, experimental characterization and will check the biological applications.
To achieve this goal the following objectives are proposed:
- Synthesizing the non-innocent ligands
- Synthesizing and characterization of transition-metal complexes
- Checking the applications
Research methodology to achieve the research objectives.
Synthesis of ligands. I propose to synthesize H2L1 Ligand. H2L1: Ligand H2L1 will be synthesized by using the procedure reported in the literature.1 In Ist step, pyridine-2-carboxilic acid is refluxed with SOCl2 and pyridine-2-carbonyl chloride will obtain.
In 2nd step, A solution of 2-Amino-4-tert-butylphenol (1.0 g, 4.9 mmol) in dry THF (40 mL) was taken in a 100 mL round bottom flask. To it pyridine carbonylchloride (0.694 g, 4.9 mmol) and triethyl-amine (0.50 g, 4.9 mmol) was added and the mixture was stirred for 24 h in N2 atmosphere. It was then filtered and the residue was washed with dichloromethane. The filtrate was concentrated under reduced pressure. A solid compound thus obtained was subjected to column chromatography [ethyl acetate and n-hexane (80:20), as mobile phase] over silica gel (100–200 mesh). After solvent removal the purified compound was obtained as white crystalline solid.
Synthesis of complexes. With ligand H2L1: Synthesis of complexes from ligand H2L1 will be done using the following reported procedures. The ligand H2L (0.100 g, 0.22 mmol) was dissolved in CH3OH (10 mL) and to it was added metal salt in portions. The color of the solution changed from something to dark brown. The mixture was stirred for 2 h. After removal of the solvent a solid was obtained, which was recrystallized from Methanol/Et2O affording shining crystals.
The ligand H2L (0.100 g, 0.22 mmol) was dissolved in N, N′-dimethylformamide (DMF) (8 mL) under N2 atm., and to it was added solid NaH (0.026 g, 0.44 mmol). The combination was stirred for 15 min resulting in a light brown solution. To this solution, solid metal complex (0.11 mmol) was added portionwise. The resulting deep brown solution was stirred for 2 h and filtered. The solvent of the solution was evaporated and 1 mL CH3CN was added and 20 ml diethyl ether was added to it and kept in deep freeze. After 12 hours, the ppt. formed was filtered and washed with ether. Solid obtained was dried under vacuum.
For Characterization NMR, Mass, IR, CHN, UV-Vis Spectroscopy, Electrochemistry, Spectroelectrochemistry, EPR (Electron paramagnetic resonance), Solution Magnetic moment, Mössbauer etc. will be done and will find new properties and applications of non-innocent ligands and their transition metal complexes.
