Research
Phosphinidene chemistry
Phosphinidenes are the phosphorus analogs of carbenes and nitrenes, having the general structure R-P (where the phosphorus atom is in +1 oxidation state and have two active lone pairs). Phosphinidenes have shown their potential as very strong sigma donor ligands like N-heterocyclic carbenes (NHCs). Phosphinidenes are also capable of binding two metal centers simultaneously because of their two available lone pairs of electrons. However, unlike NHCs, the use of phosphinidene as a ligand in transition metal chemistry is very limited. We are interested in using phosphinidene as a ligand to stabilize unusual metal complexes and utilize them as catalysts in various organic transformations. We are also interested in studying the magnetic properties of lanthanide-phosphinidene hybrid materials.
J. Am. Chem. Soc. 2018, 140, 151-154.
Stabilization of p-block element radicals
Radical chemistry has long been of interest both from academic and industrial point of views. Among the most widely used radical chemistry in industrial processes is the manufacturing of low-density polyethylene. While metal-based radical systems involving coordination complexes have been far more amenable for isolation and characterization, similar examples involving carbon and other main-group elements, while known, are still rare. Surprisingly, however, nature stabilizes molecular oxygen in its biradical form quite readily. Considering the instability of the radicals, typical methods for stabilizing main-group element based radicals mainly involve delocalization of the unpaired electron on the overall molecular scaffold to achieve thermodynamic stability and/or by employing sterically encumbered groups around the main-group element. In the case of latter, the radicals are stabilized kinetically and are prevented from reacting with other species. Bertrand et al. in 2005 reported that cyclic (alkyl)(amino)carbenes (cAACs) which have a nitrogen and a carbon attached to the carbene center have the better sigma-donor ability as well as better pi-electron accepting properties than conventional NHCs. The empty p-orbital of cAACs can indeed engage in pi-back bonding interactions and delocalize the electron density and, at the same time stabilize an electron-deficient center by sigma-donation. This dual nature of the cAACs is becoming extremely promising for the isolation of main-group radicals. Our group is exploring the utility of carbene ligands for the isolation of main-group radicals.
Polymeric materials based on main group elements
The past two decades have witnessed tremendous progress in the synthesis of polymers that contain main-group elements (other than carbon) in their main-chain. These polymeric materials are highly attractive for their potential applications in diverse areas such as ceramics, rubber technologies, lubricants, medicines, flame retardants, cosmetics, etc. The unique properties of these polymers arise from the dramatic differences in bonding and chemical reactivity of the elements present in the main-chain. We are interested in the synthesis of polymeric materials, where main-group elements (other than carbon) constitute the backbone structure, or at least a significant part, and give rise to unique properties.
Angew. Chem. Int. Ed. 2019, 58, 5846-5870.
Main-group compounds in redox-cycling catalysis and small molecules activation
During the last two decades, significant progress has been made in the activation of various small molecules by main‐group compounds. A variety of stoichiometric and catalytic processes have been formulated using the p‐block elements. In this regard, compounds containing low‐valent main‐group elements with a frontier orbitals of relatively small energy gaps or compounds forming frustrated Lewis pair (FLP) became quite successful. Despite these promising stoichiometric and catalytic transformations, redox‐cycling catalysts based on main‐group elements remain extremely rare. Recently, it has been observed that pincer type ligands supported geometry constrained main‐group compounds are capable of acting as redox catalysts similar to those of the transition metals. Our group is working on the catalytic activity of pincer ligand supported compounds of group 15 elements (P, Sb, Bi).