Research Projects

Selective oxidation of alkane and alkene moieties is a major challenge for synthetic chemists. Metalloenzymes routinely perform selective oxidative transformations and scientists have taken inspiration from them to develop such catalysts. In enzymes, the protein scaffold defines both the primary and second coordination sphere of metal centers, influencing key aspects of catalytic activity and substrate selectivity. The mechanisms of O2 activation and the site selectivity in oxidation reactions are governed by protein residues in second coordination sphere. Till date the first coordination sphere in the oxidation ability of transition metal (TM) complexes has been amply studied, however, implementation of second coordination sphere elements in well-defined homogenous catalysts is still in its infancy. The structural and chemical diversity offered by peptides provides a chemically versatile tool to combine with TM complexes to provide a functional second coordination sphere. Peptides have been combined with TM complexes to improve their catalytic properties. The combination of peptides and metal catalysts has been used in several asymmetric transformations such as hydrosilylation, cyclopropanation, allylic alkylation, conjugate additions to enones, and addition of cyanides to aldehydes (Strecker reaction). Peptides are also potentially valuable components for designing oxidation catalysts because they are robust against oxidation. The use of peptides as organocatalysts in epoxidation reactions is well established, making Julia-Colonna epoxidation a notable example. On the contrary, very less examples of usage of metallopeptides as catalysts in oxidation reactions, particularly in C-H and C=C oxidation, have been reported to date. Remarkably, in recent studies, the peptide-transition metal supramolecular weak interactions have exhibited superior selectivities in their oxidation reactions compared to catalysts based on non-peptidic coordination complexes. However, the direct engagement of peptides in the secondary coordination sphere of transition metal complexes undergoing C-H or C=C oxidation has not been reported to date. This proposal aims to combine the advantages of peptides with the high catalytic activity of bioinspired oxidation catalysts to develop selective transition metal oxidation catalysts towards C-H and C=C bonds. In this aspect, peptide chains will be tied up with reported biomimetic systems, metalated with Fe and Co and treated with peroxides (H2O2, cumene hydroperoxide, t-butyl hydroperoxide). These metal-oxygen systems will be tested for C-H and C=C bond oxidations towards various hydrocarbons. To gain insights into the nature of transient species in the transformation reaction, the metal-oxygen intermediates will be trapped, wherever possible and characterized by different spectroscopic methods (initially by ESI-MS, UV-Vis and if required Mössbauer, EPR, Resonance Raman will be used).