Gopal S. Mishra

Scorpionate complexes of vanadium(III or IV) as catalyst precursors for solvent-free cyclohexane oxidation with dioxygen*

The V-scorpionate vanadium complexes [VCl3{HC(pz)3}] (pz = pyrazolyl) and [VCl3{SO3C(pz)3}] catalyze cyclohexane oxidation with dioxygen, to cyclohexanol (the main product) and cyclohexanone, under solvent-free conditions. [VCl3{HC(pz)3}] provides the best activity (13 % conversion into the ketone and alcohol, with high selectivity, at the O2 pressure of 15 atm, at 140 ºC, 18 h reaction time). The reaction is further promoted (to 15 % conversion) by pyrazinecarboxylic acid (PCA). The use of C- or O-radical traps supports the involvement of a free-radical reaction mechanism. Several reaction parameters have been varied in a systematic study, directed toward optimization of the process.

Polymer encapsulated scorpionate Eu3+ complexes as novel hybrid materials for high performance luminescence applications

N,N,N-Tri(1-pyrazolyl)methane europium complexes, [Eu{HC(pz)3}(H2O)6]Cl3, encapsulated with polymethyl methacrylate (PMMA) gel, polyvinyl acetate (PVA) gel or hexagonal mesoporous silica–PVA (HMS–PVA), have been synthesized, by using a sol–gel technique, as hybrid materials. The geometric structure of the new Eu complex has been confirmed by single crystal X-ray analysis. The hybrid Eu–PVA sample has performed the most effective unit mass luminescence emission with a longer lifetime 444 μs, higher quantum efficiency, greater thermal stability and better exposure durability in comparison to the other Eu–PMMA (379 μs) and Eu–HMS–PVA (55 μs) samples. The characterization results support that these hybrid polymers have made a proper network structure with the Eu3+ complex and act as antennae for the transfer of energy to the central Eu3+ ions, and could be use for enhanced OLED light.

Immobilized Pd complexes over MCM-41 as supported catalysts for effective reformation of hydrocarbons

The ethylthio alkane ligands i.e. di(ethylthio)ethane, I, and di(ethylthio)propane, II, have been used for the synthesis of Pd(II) complexes. These complexes were covalently anchored to the modified MCM-41 matrix as supported hybrid catalysts (MCM-41/I as Pd–I and MCM-41/II as Pd–II). Remarkable catalytic effects were observed when these supported catalysts act in n-hexane and n-heptane reformation reactions in the presence of H2. Catalyst Pd–I provided the high TONs of 2325 with 91% selectivity for n-hexane and high TONs of 2145 with 88% selectivity for n-heptane under optimized and relatively mild conditions. A carbenium-based mechanism has been included to explain the product formation. TGA analysis indicates that these catalysts were thermally stable up to the reaction temperature and recyclable for further utilization.