Dinesh De

A Porous Cu(II)-MOF with Proline Embellished Cavity:Cooperative Catalysis for the Baylis-Hillman Reaction

l-Proline has been covalently attached in a rigid linear ligand, H4L, having an isophthalate moiety at each terminal to form the chiral ligand, H4LPRO. This linker has been used for the construction of a porous MOF, LCuPRO. The free l-proline moiety in the cavity of the framework in the presence of imidazole as a cocatalyst functions synergistically to catalyze the Baylis-Hillman reaction between α,β-unsaturated carbonyl compounds and aromatic aldehydes. High porosity of the framework is proven by the nitrogen adsorption isotherm.

Guest dependent reversible single-crystal to single-crystal structural transformation in a flexible Gd(III)-coordination polymer

The ligand 2,6,2′,6′-tetranitro-biphenyl-4,4′-dicarboxylic acid (H2L) reacts solvothermally with [Gd(NO3)3]·6H2O to produce a flexible and porous metal–organic framework, {[Gd2(L)3(DMF)4]·(4DMF)·(3H2O)}n (1) (DMF = N,N′-dimethylformamide). An X-ray crystallographic study reveals that compound 1 contains a 3D framework structure with two different 1D channels (A and B) that are occupied by solvent DMF and water molecules. Crystals of 1 when kept in a dichloromethane solution of 4-chlorobenzaldedhyde (4-ClPhCHO) afford the daughter product {[Gd2(L)3(DMF)4]·(4-ClPhCHO)·(4DMF)}n (1a), via single-crystal to single-crystal (SC–SC) transformation, where lattice water molecules of channel B are replaced by guest aldehyde molecules. Likewise, exposure of 4-fluorobenzaldehyde (4-FPhCHO) and 4-methylbenzaldehyde (4-MePhCHO) vapors to fresh crystals of 1 afforded two isostructural daughter frameworks, {[Gd(L)1.5(DMF)(H2O)3]·(4-FPhCHO)·(DMF)·(3H2O)}n (1b) and {[Gd(L)1.5(DMF)(H2O)3]·(4-MePhCHO)·(2DMF)·(H2O)}n (1c), respectively. Here, the guest aldehyde molecules occupy both the channels of the framework. Interestingly, the latter transformations exhibit a drastic rearrangement of the framework channels followed by several ‘carboxylate-shift’ processes, and concomitant movement of the water molecules from the cavity to the metal center. Importantly, all the host–guest complexes revert back to the as-synthesized crystal when kept in fresh DMF, rendering the mother framework a flexible and dynamic container for the aromatic aldehydes. All these transformations transpire through an SC–SC fashion under ambient conditions, pointing to the high flexibility of the framework and “guest-responsive fitting” of the channels. All the compounds are characterized by X-ray crystallography, thermogravimetry, elemental analysis, powder X-ray diffraction measurements and infrared spectroscopy.

Enantioselective Aldol Reactions in Water by a Proline-Derived Cryptand and Fixation of CO2 by Its Exocyclic Co(II) Complex

The secondary amine donors present in the bridges of a laterally nonsymmetric oxa-aza cryptand have been derivatized with l-proline to obtain the chiral cryptand L. The cryptand L efficiently catalyzed aldol reactions in water with up to 75% ee. On reacting with Co(II) perchlorate in the presence of KSCN, L readily formed the trinuclear complex {[Co3(L)2(NCS)6]·(15CH3CN)(5acetone)(6H2O)} (1). The complex 1 in combination with the cocatalyst tetrabutylammonium bromide (TBAB) formed an efficient catalytic system in the synthesis of cyclic carbonates from CO2 and epoxides at room temperature and atmospheric pressure.

A Multifunctional Metal–Organic Framework for Oxidative C–O Coupling Involving Direct C–H Activation and Synthesis of Quinolines

A robust paddle-wheel Cu(II)-based metal-organic framework (MOF) 1, having dual functionalities, namely, Lewis acid and basic sites, has been explored as a heterogeneous catalyst. This MOF, because of its large void volume (10298 Å3, 67.6%), large surface area (1480 m2/g), and high thermal stability, encouraged us to see its applicability in two catalytic reactions, namely, oxidative C-O coupling (cross-dehydrogentaive coupling reaction) involving direct C-H activation and Friedländer reaction under solvent free and ambient conditions. This study demonstrates the green aspect of MOFs in coupling reactions because of the simplified recovery, shorter reaction time, minimum waste, and smooth activation of the C-H bond, which is very challenging in synthetic chemistry.