Designing Dual Catalyst for Hydroamination:

We are currently working on assembling heterometals into a molecular catalytic system so that both metals can act catalytically for two different reactions. For example, we have recently shown that Ca and Zr metal centers can be assembled resulting a heterobimetallic catalyst which functions as dual catalyst in intramolecular hydroamination reactions of primary amino alkenes and secondary amino alkens. The Ca center cyclizes the primary aminoalkenes and the zirconium center cyclizes the secondary aminoalkenes.

 

 

 

 

 

 

 

Mukherjee et al.  Angew. Chem. Int. Ed. 2011, 50, 3968-3972 and RSC Adv., 2013, 3, 1255–1264.

 

Phenalenyl Non-Bonding Orbital for Organometallic Catalyst Design:

We are working on the development of molecular catalyst utilizing the nonbonding orbital of phenalenyl ligand system. Phenalenyl is a well-known odd alternant hydrocarbon with high symmetry (D_3h) which has the ability to form three redox species: cation, neutral radical, and anion. It has been demonstrated by Haddon and co-workers that the lowest unoccupied molecular orbital (LUMO) of spirobiphenalenyl boron derivatives posing cationic state of phenalenyl can readily accept one electron to become open shell molecular system leading to the development of the best known neutral organic conductor. The unpaired electron of neutral radicals serve as the charge carriers and orbital overlap between adjacent radicals generates the conduction pathway through the lattice in solid state. In this way a new genesis of multifunctional electronic and magnetic materials exhibiting simultaneous bi-stability in three physical channels: magnetic, electrical, and optical and earlier elusive resonating valence bond (RVB) ground  state in the solid state have been realized through open shell phenalenyl based molecular system.

We postulated that the vacant nonbonding orbital of cationic phenalenyl can not only be used in building of molecular conductors by electron acceptance but also it may have a great influence in catalytic reactions. The metal complexes of the phenalenyl based ligand systems are expected to behave as highly Lewis acidic. Very recently we have shown that the cationic state of phenalenyl based molecular system can be used for development of molecular catalyst for ring opening polymerization of cyclic esters  which works through electron acceptance into the LUMO of organoaluminum phenalenyl derivatives bearing the cationic state of phenalenyl moiety. In a recent study we demonstrated for the first time that the empty orbital of phenalenyl moiety can be used to tune the catalytic activity in ring opening polymerization reaction.

  

 

 

 

 

Sen et al. Chem. Eur. J. 2012, 18, 54-58.

Mukherjee et al. Chem. Eur. J. 2012, 18, 10530-10545

Sen et al. Dalton Trans. 2013, 42, 1893-1904.

 

 Spin Selective Organometallic Zinc Phenalenyl Complex:

Interaction between a ferromagnet and an organic molecule provides a complex study of interface chemistry and magnetism. However, the possibility to engineer these interface effects, by virtue of controlling the interface parameters such as molecular structure, morphology and electronic property of interface holds promise in realization of novel functional molecular spintronic devices. Magnetoresistance, defined as the change in resistance with applied magnetic field, in molecular devices such as vertical organic spin-valves and magnetic tunnel junctions involves two magnetic electrodes with spin diffusive or tunneling transport through the organic spacer layer. In a recent ongoing, we demonstrate a new interface phenomenon of a spin-filter effect using a single ferromagnet electrode and a phenalenyl derivative which may be considered as a mini fragment of a graphene sheet resulting in a large magnetoresistance of more than 20% close to room temperature. The existence of nonbonding orbital of the phenalenyl molecule leads to a open shell radical formation on interaction with the FM layer plays a key role in this interface phenomena. This findings including the possibility to use π-conjugated organic molecular systems as interface templates to selectively engineer the interface mechanisms will open up rich prospects for fundamental study and development of future molecular spintronic devices.

 

 

The first organometallic  molecular based memory device that works at near room temperature.

 
  (Raman et al., Nature, 2013, 493, 509-513)

 

 Abnormal N-Heterocyclic Carbene: Excellent Building Block to Design Catalyst:

Nearly two decades ago the isolation of heteroatom stabilized carbenes [normal N-heterocyclic carbenes (nNHCs)] by Arduengo has led to numerous breakthroughs in organometallic and organo-catalysis. In 2009, Bertrand and co-workers isolated a new class of carbene in which the carbene center is no longer located between the two nitrogen atoms but is generated between nitrogen and carbon atoms. This new class of carbenes is known as abnormal NHCs (aNHCs). We recently established the first use of aNHC, in organocatalytic ring opening polymerization of three different cyclic esters rac-lactide (rac-LA), ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) will be discussed.³The catalytic results unravel that 1 is efficient organocatalyst for ring opening polymerization at ambient temperature. This aNHC exhibited the fastest catalytic activity for ring opening polymerization of ε-caprolactone among any NHCs reported till date.

 

 

 

 

 

 

Sen et al. Chem. Commun. 2011, 47, 11972–11974.

Recently in another study, we accomplished the synthesis of halobridged palladium dimers containing abnormal NHC for Suzuki–Miyaura cross coupling of aryl chlorides. Palladium complexes bearing abnormal N-heterocyclic carbene were used as catalysts in Suzuki–Miyaura cross coupling of aryl chlorides at room temperature. The catalyst remained active for 10 successive catalytic runs and can activate 4-chlorotoluene at ambient temperature with 0.01 mol% catalyst loading resulting in a TON of 9500 within 6 h.

 

 

 

 

 

 

 

Sau et al.  Chem. Commun. 2012, 48, 555-557.

 

Supported Palladium Nanocatalyst as Recyclable Catalyst for C-C Coupling:

We are actively working on development of hetergenous palladium nanocatlyst for C-C coupling reactions which can be recycled. Recently we established a convenient method to develop palladium nanoparticles (PdNPs) embedded into a polymer matrix, PPS [PPS = poly(1,4-phenylene sulphide)] as well as with chemically modified single walled carbon nanotubes via the thermolysis of palladium acetate. These palladium nanoparticles (PdNPs-PPS) have been used as an efficient heterogeneous nanocatalytic system for copper free acyl Sonogashira reaction. A wide range of ynones was synthesized in high yields under mild reaction condition. The catalyst was recovered and recycled up to five times. Transmission electron microscopy (TEM) images revealed that the catalyst maintained nanospheric dimensions till four consecutive catalytic cycles. This simple protocol was further explored in one-pot multicomponent synthesis of 2,4-disubstituted pyrimidines and a tetrahydro-β-carboline derivative in improved yield.

 Santra et al.   Green Chem. 2011, 13, 3238-3247 and RSC Adv. 2012, 2, 7523–7533