Abhishek Dutta Chowdhury

An iron catalyzed regioselective oxidation of terminal alkenes to aldehydes

Fe(BF(4))(2)·6H(2)O with pyridine-2,6-dicarboxylic acid and PhIO can efficiently catalyze the regioselective oxidation of terminal alkene derivatives to aldehydes under mild and benign reaction conditions.

Towards a Practical Development of Light‐Driven Acceptorless Alkane Dehydrogenation

The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter-chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom-efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans-[Rh(PMe3)2(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C4) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.

Electronic structure and catalytic aspects of [Ru(tpm)(bqdi)(Cl/H2O)]n, tpm = tris(1-pyrazolyl)methane and bqdi = o-benzoquinonediimine

The diamagnetic complexes [Ru(tpm)(bqdi)(Cl)]ClO(4) ([1]ClO(4)) (tpm = tris(1-pyrazolyl)methane, bqdi = o-benzoquinonediimine) and [Ru(tpm)(bqdi)(H(2)O)](ClO(4))(2) ([2](ClO(4))(2)) have been synthesized. The valence state-sensitive bond distances of coordinated bqdi [C-N: 1.311(5)/1.322(5) Å in [1]ClO(4); 1.316(7)/1.314(7) Å in molecule A and 1.315(6)/1.299(7) Å in molecule B of [2](ClO(4))(2)] imply its fully oxidised quinonediimine (bqdi(0)) character. DFT calculations of 1(+) confirm the {Ru(II)-bqdi(0)} versus the antiferromagnetically coupled {Ru(III)-bqdi˙(-)} alternative. The (1)H NMR spectra of [1]ClO(4) in different solvents show variations in chemical shift positions of the NH (bqdi) and CH (tpm) proton resonances due to their different degrees of acidity in different solvents. In CH(3)CN/0.1 mol dm(-3) Et(4)NClO(4), [1]ClO(4) undergoes one reversible Ru(II)⇌ Ru(III) oxidation and two reductions, the reversible first electron uptake being bqdi based (bqdi(0)/bqdi˙(-)). The electrogenerated paramagnetic species {Ru(III)-bqdi(0)}(1(2+)) and {Ru(II)-Q˙(-)}(1) exhibit Ru(III)-type (1(2+): = 2.211/Δg = 0.580) and radical-type (1: g = 1.988) EPR signals, respectively, as is confirmed by calculated spin densities (Ru: 0.767 in 1(2+), bqdi: 0.857 in 1). The aqua complex [2](ClO(4))(2) exhibits two one-electron oxidations at pH = 7, suggesting the formation of {Ru(IV)[double bond, length as m-dash]O} species. The electronic spectral features of 1(n) (n = charge associated with the different redox states of the chloro complex: 2+, 1+, 0) in CH(3)CN and of 2(2+) in H(2)O have been interpreted based on the TD-DFT calculations. The application potential of the aqua complex 2(2+) as a pre-catalyst towards the epoxidation of olefins has been explored in the presence of the sacrificial oxidant PhI(OAc)(2) in CH(2)Cl(2) at 298 K, showing the desired selectivity with a wide variety of alkenes. DFT calculations based on styrene as the model substrate predict that the epoxidation reaction proceeds through a concerted transition state pathway.

Towards the Efficient Development of Homogeneous Catalytic Transformation to γ‐Valerolactone from Biomass‐Derived Platform Chemicals

Recent efforts focused on the production of selected chemicals from biomass as an effective approach to replace fossil feedstocks. Among them, transformation of the biogenic platform molecule levulinic acid to γ‐valerolactone has been an extensively studied reaction. Although this transformation can be achieved by heterogeneous catalysis, there exists also a strong interest for effective homogeneous catalysis that can operate selectively under milder and sustainable conditions. Herein, we report the utilization of various triphos‐analogue ligands that in the presence of Ru(acac)3 (acac=acetylacetonate) lead to highly efficient γ‐valerolactone production (yield up to 95 %). Excellent catalyst turnover numbers (up to 75 855) and turnover frequencies (up to 1382 h−1) were accomplished.

Four-Center Oxidation State Combinations and Near-Infrared Absorption in [Ru(pap)(Q)2]n (Q=3,5-Di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, pap=2-Phenylazopyridine)

The complex series [Ru(pap)(Q)2](n) ([1](n)-[4](n); n = +2, +1, 0, -1, -2) contains four redox non-innocent entities: one ruthenium ion, 2-phenylazopyridine (pap), and two o-iminoquinone moieties, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine (aryl = C6H5 (1(+)); m-(Cl)2C6H3 (2(+)); m-(OCH3)2C6H3 (3(+)); m-(tBu)2C6H3 (4(+))). A crystal structure determination of the representative compound, [1]ClO4, established the crystallization of the ctt-isomeric form, that is, cis and trans with respect to the mutual orientations of O and N donors of two Q ligands, and the coordinating azo N atom trans to the O donor of Q. The sensitive C-O (average: 1.299(3) Å), C-N (average: 1.346(4) Å) and intra-ring C-C (meta; average: 1.373(4) Å) bond lengths of the coordinated iminoquinone moieties in corroboration with the N-N length (1.292(3) Å) of pap in 1(+) establish [Ru(III)(pap(0))(Q(·-))2 ](+) as the most appropriate electronic structural form. The coupling of three spins from one low-spin ruthenium(III) (t2g(5)) and two Q(·-) radicals in 1(+)-4(+) gives a ground state with one unpaired electron on Q(·-), as evident from g = 1.995 radical-type EPR signals for 1(+)-4(+). Accordingly, the DFT-calculated Mulliken spin densities of 1(+) (1.152 for two Q, Ru: -0.179, pap: 0.031) confirm Q-based spin. Complex ions 1(+)-4(+) exhibit two near-IR absorption bands at about λ = 2000 and 920 nm in addition to intense multiple transitions covering the visible to UV regions; compounds [1]ClO4-[4]ClO4 undergo one oxidation and three separate reduction processes within ±2.0 V versus SCE. The crystal structure of the neutral (one-electron reduced) state (2) was determined to show metal-based reduction and an EPR signal at g = 1.996. The electronic transitions of the complexes 1(n)-4(n) (n = +2, +1, 0, -1, -2) in the UV, visible, and NIR regions, as determined by using spectroelectrochemistry, have been analyzed by TD-DFT calculations and reveal significant low-energy absorbance (λmax >1000 nm) for cations, anions, and neutral forms. The experimental studies in combination with DFT calculations suggest the dominant valence configurations of 1(n)-4(n) in the accessible redox states to be [Ru(III)(pap(0))(Q(·-))(Q(0))](2+) (1(2+)-4(2+))→[Ru(III)(pap(0))(Q(·-))2](+) (1(+)-4(+))→[Ru(II)(pap(0))(Q(·-))2] (1-4)→[Ru(II)(pap(·-))(Q(·-))2](-) (1(-)-4(-))→[Ru(III)(pap(·-))(Q(2-))2](2-) (1(2-)-4(2-)).

Photocatalytic Acceptorless Alkane Dehydrogenation: Scope, Mechanism, and Conquering Deactivation with Carbon Dioxide

Alkane dehydrogenation is of special interest for basic science but also offers interesting opportunities for industry. The existing dehydrogenation methodologies make use of heterogeneous catalysts, which suffer from harsh reaction conditions and a lack of selectivity, whereas homogeneous methodologies rely mostly on unsolicited waste generation from hydrogen acceptors. Conversely, acceptorless photochemical alkane dehydrogenation in the presence of trans-Rh(PMe3 )2 (CO)Cl can be regarded as a more benign and atom efficient alternative. However, this methodology suffers from catalyst deactivation over time. Herein, we provide a detailed investigation of the trans-Rh(PMe3 )2 (CO)Cl-photocatalyzed alkane dehydrogenation using spectroscopic and theoretical investigations. These studies inspired us to utilize CO2 to prevent catalyst deactivation, which leads eventually to improved catalyst turnover numbers in the dehydrogenation of alkanes that include liquid organic hydrogen carriers.

Efficient Iron-Catalyzed Acetal Formation from Styrene Derivatives

Acetals have immense industrial significance as diesel additives and polymeric materials and as flavoring agent in beverages, cosmetics, and foods. Acetalization is the most useful synthetic technique in any targeted organic synthesis to protect the aldehyde and ketone groups of various multifunctional organic molecules. Acetals constitute a versatile class of organic synthons and intermediates, as they can easily be converted into other useful functional groups. 3] Moreover, acetals are the common functional group in natural products such as ( )xylomollin, anthogorgiene D, allamcin, incargutine B, and so on. The enzyme glycosyltransferase catalyzes the formation of acetals from hemiacetals during the formation of glycosidic bonds in cellulose. Furthermore, the influential role of acetals in biological activities has recently been demonstrated.

Influence of nitrosyl coordination on the binding mode of quinaldate in selective ruthenium frameworks. Electronic structure and reactivity aspects

The nitrosyl complexes, [RuII(trpy)(L)(NO+)Cl]BF4, [1]BF4, and [RuII(trpy)(L)(NO+)](BF4)2, [2](BF4)2, (trpy = 2,2′:6′,2′′-terpyridine, L− = deprotonated form of unsymmetrical quinaldic acid) have been synthesized. Single crystal X-ray structures of [1]BF4 and [2](BF4)2 reveal that in the former L− binds to the ruthenium ion selectively in a monodentate fashion through the O− donor whereas the usual bidentate mode of L− (O−, N donors) has been retained in [2](BF4)2 with the same meridional configuration of trpy being seen in both. The Ru–NO group in [1]BF4 or [2](BF4)2, exhibits almost linear (sp-hybridized form of NO+) geometry. The difference in bonding mode of the unsymmetrical quinaldate in [1]BF4 and [2](BF4)2 has been reflected in their corresponding ν(NO)/ν(CO) frequencies as well as in their NO based two-step reduction processes, {RuII–NO+} → {RuII–NO•} and {RuII–NO•}→{RuII–NO−}. The close to bent geometry (sp2-hybridized form of NO•) of the one-electron reduced 1 or [2]+ is been reflected in their DFT optimized structures. The spin density plot of the reduced species reveals that NO is the primary spin-bearing center with slight delocalization onto the metal ion which has been reflected in its radical EPR spectrum. [1]+ and [2]2+ undergo facile photorelease of NO with significantly different kNO (s−1) and t1/2 (s) values which eventually lead to the concomitant formation of the corresponding solvent species. The photoreleased NO• can be trapped as an Mb–NO adduct. The reduced species 1 selectively reacts with the molecular oxygen (O2) at pH ∼ 1 to yield the corresponding nitro species, [RuII(trpy)(L)(NO2)Cl]−.

Visualizing pore architecture and molecular transport boundaries in catalyst bodies with fluorescent nanoprobes

AbstractThe performances of porous materials are closely related to the accessibility and interconnectivity of their porous domains. Visualizing pore architecture and its role on functionality—for example, mass transport—has been a challenge so far, and traditional bulk and often non-visual pore measurements have to suffice in most cases. Here, we present an integrated, facile fluorescence microscopy approach to visualize the pore accessibility and interconnectivity of industrial-grade catalyst bodies, and link it unequivocally with their catalytic performance. Fluorescent nanoprobes of various sizes were imaged and correlated with the molecular transport of fluorescent molecules formed during a separate catalytic reaction. A direct visual relationship between the pore architecture—which depends on the pore sizes and interconnectivity of the material selected—and molecular transport was established. This approach can be applied to other porous materials, and the insight gained may prove useful in the design of more efficient heterogeneous catalysts.The accessibility of materials’ porous domains is typically explored through bulk, and often non-visual, measurements. Now, an integrated fluorescence microscopy approach has established a direct visual relationship between pore architecture (which depends on pore sizes and interconnectivity), molecular transport, and in turn catalytic performance in industrial-grade catalyst particles.

Is a naked platinum nanocatalyst better than the analogous supported catalysts

The performance of naked nanocatalyst 1, derived from Chini cluster ([Pt15(CO)30]2−), has been evaluated with special reference to the analogous catalysts 2 and 3 which were derived from the same [Pt15(CO)30]2− but supported by MCM-41 and the water soluble polymer PDADMAC, respectively.