Molybdenum‐ and Tungsten‐Based Coordination Polymers as Catalysts for an Efficient and Rapid Synthesis of Hexahydro‐5‐oxoquinoline‐3‐carboxylates and 1,4‐Dihydropyridine‐3,5‐dicarboxylates

Hexahydro‐5‐oxoquinoline‐3‐carboxylates and 1,4‐dihydropyridine‐3,5‐dicarboxylates were synthesized efficiently and rapidly (2 min) in the presence of molybdenum‐ and tungsten‐based coordination polymers [M(Bu₃Sn)₂O₄)]_n (M=Mo or W) as catalysts (Schemes 1 and 2; Tables 2 and 3). The products were formed at room temperature in excellent yields (90–98%). The catalysts worked under heterogeneous conditions and were recyclable. The earlier reports for the application of these polymers to conduct organic synthesis are limited. The present method explores a new and useful application of these catalysts.     

B‐MWW Zeolite: The Case Against Single‐Site Catalysis

Boron‐containing materials have recently been identified as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins. It has previously been demonstrated by several spectroscopic characterization techniques that the surface of these boron‐containing ODH catalysts oxidize and hydrolyze under reaction conditions, forming an amorphous B₂(OH)_xO_(3?x/2) (x=0–6) layer. Yet, the precise nature of the active site(s) remains elusive. In this Communication, we provide a detailed characterization of zeolite MCM‐22 isomorphously substituted with boron (B‐MWW). Using ¹¹B solid‐state NMR spectroscopy, we show that the majority of boron species in B‐MWW exist as isolated BO₃ units, fully incorporated into the zeolite framework. However, this material shows no catalytic activity for ODH of propane to propene. The catalytic inactivity of B‐MWW for ODH of propane falsifies the hypothesis that site‐isolated BO₃ units are the active site in boron‐based catalysts. This observation is at odds with other traditionally studied catalysts like vanadium‐based catalysts and provides an important piece of the mechanistic puzzle.     

Asymmetric 1,3‐Dipolar Cycloadditions of 2‐Diazocyclohexane‐1,3‐diones and Alkyl Diazopyruvates

The 1,3‐dipolar cycloaddition reactions of 2‐diazocyclohexane‐1,3‐dione ( 7a ; Table 1) and of alkyl diazopyruvates ( 11a – e ; Table 3) to 2,3‐dihydrofuran and other enol ethers have been investigated in the presence of chiral transition metal catalysts. With Rh^II catalysts, the cycloadditions were not enantioselective, but those catalyzed by [Ru^IICl₂( 1a )] and [Ru^IICl₂( 1b )] proceeded with enantioselectivities of up to 58% and 74% ee, respectively, when diazopyruvates 11 were used as substrates. The phenyliodonium ylide 7c yielded the adduct 8a in lower yield and poorer selectivity than the corresponding diazo precursor 7a (Table 2) upon decomposition with [Ru(pybox)] catalysts. This suggests that ylide decomposition by Ru^II catalysts, contrary to that of the corresponding diazo precursors, does not lead to Ru‐carbene complexes as reactive intermediates. Our method represents the first reproducible, enantioselective 1,3‐cycloaddition of these types of substrates.     

Ring‐opening metathesis polymerization of cis‐cyanocyclooct‐4‐ene: Search for active catalysts,variation of monomer to catalyst ratios and monomer concentrations

The ring‐opening metathesis polymerization (ROMP) of cis‐cyanocyclooct‐4‐ene initiated by ruthenium‐based catalysts of the first, second, and third generation was studied. For the polymerization with the second generation Grubbs catalyst [RuCl₂(?CHPh)(H₂IMes)(PCy₃)] (H₂IMes = N,N′‐bis(mesityl)‐4,5‐dihydroimidazol‐2‐ylidene), the critical monomer concentration at which polymerization occurs was determined, and variation of monomer to catalyst ratios was performed. For this catalyst, ROMP of cis‐cyanocyclooct‐4‐ene did not show the features of a living polymerization as M_n did not linearly increase with increasing monomer conversion. As a consequence of slow initiation rates and intramolecular polymer degradation, molar masses passed through a maximum during the course of the polymerization. With third generation ruthenium catalysts (which contain 3‐bromo or 2‐methylpyridine ligands), polymerization proceeded rapidly, and degradation reactions could not be observed. Contrary to ruthenium‐based catalysts of the second and third generation, a catalyst of the first generation was not able to polymerize cis‐cyanocyclooct‐4‐ene. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Polymer‐ and Silica‐Supported Iron BPMEN‐Inspired Catalysts for CH Bond Functionalization Reactions

Direct catalytic C? H bond functionalization is a key challenge in synthetic chemistry, with many popular C? H activation methodologies involving precious‐metal catalysts. In recent years, iron catalysts have emerged as a possible alternative to the more common precious‐metal catalysts, owing to its high abundance, low cost, and low toxicity. However, iron catalysts are plagued by two key factors: the ligand cost and the low turnover numbers (TONs) typically achieved. In this work, two approaches are presented to functionalize the popular N¹,N²‐dimethyl‐N¹,N²‐bis(pyridin‐2‐ylmethyl)ethane‐1,2‐diamine (BPMEN) ligand, so that it can be supported on porous silica or polymer resin supports. Four new catalysts are prepared and evaluated in an array of catalytic C? H functionalization reactions by using cyclohexane, cyclohexene, cyclooctane, adamantane, benzyl alcohol, and cumene with aqueous hydrogen peroxide. Catalyst recovery and recycling is demonstrated by using supported catalysts, which allows for a modest increase in the TON achieved with these catalysts.     

Chiral Calcium–BINOL Phosphate Catalyzed Diastereo‐ and Enantioselective Synthesis of syn‐1,2‐Disubstituted 1,2‐Diamines: Scope and Mechanistic Studies

A highly enantioselective, chiral, Lewis acid calcium–bis(phosphate) complex, Ca[ 3 a ]_n, which catalyzes the electrophilic amination of enamides with azodicarboxylate derivatives 2 to provide versatile chiral 1,2‐hydrazinoimines 4 is disclosed. The reaction gives an easy entry to optically active syn‐1,2‐disubstituted 1,2‐diamines 6 in high yields with excellent enantioselectivities, after a one‐pot reduction of the intermediate 1,2‐hydrazinoimines 4 . The geometry and nature of the N‐substituent of the enamide affect dramatically both the reactivity and the enantioselectivity. Although the calcium–bis(phosphate) complex was a uniquely effective catalyst, the exact nature of the active catalytic species remains unclear. NMR spectroscopy and MS analysis of the various calcium complexes Ca[ 3 ]_n reveals that the catalysts exist in various oligomer forms. The present mechanistic study, which includes nonlinear effects and kinetic measurements, constitutes a first step in understanding these calcium–bis(phosphate) complex catalysts. DFT calculations were carried out to explore the mechanism and the origin of the enantioselectivity with the Ca[ 3 ]_n catalysts.     

Synthesis of multifunctional polymer containing Ni‐Pd NPs via thiol‐ene reaction for one‐pot cascade reactions

Recently, acid–base bifunctional catalysts have been considered due to their abilities, such as the simultaneous activation of electrophilic and nucleophilic species and their high importance in organic syntheses. However, the synthesis of acid–base catalysts is problematic due to the neutralization of acidic and basic groups. This work reports a facial approach to solve this problem via the synthesis of a novel bifunctional polymer using inexpensive materials and easy methods. In this way, at the first step, heterogeneous poly (styrene sulfonic acid‐n‐vinylimidazole) containing pentaerythritol tetra‐(3‐mercaptopropionate) (PETMP) and trimethylolpropane trimethacrylate (TMPTMA) cross‐linkers were synthesized in the pores of a mesoporous silica structure using click reaction as a novel bifunctional acid–base catalyst. After that, Ni‐Pd nanoparticles supported on poly (styrenesulfonic acid‐n‐vinylimidazole)/KIT‐6 as a novel trifunctional heterogeneous acid–base‐metal catalyst was prepared. The prepared catalysts were characterized by various techniques like FT‐IR, TGA, ICP‐AES, DRS‐UV, TEM, FE‐SEM, EDS‐Mapping, and XRD. The synthesized catalysts were efficiently used as bifunctional/trifunctional catalysts for one‐pot, deacetalization‐Knoevenagel condensation and one‐pot, three‐step and a sequential reaction containing deacetalization‐Knoevenagel condensation‐reduction reaction. It is important to note that the synthesized catalyst showing high chemo‐selectivity for the reduction of nitro group, alkenyl double bond and ester group in the presence of nitrile. Moreover, it was found that the different nanoparticles including Ni, Pd, and alloyed Ni‐Pd showing different chemo‐selectivity and catalytic activity in the reaction.     

Neodymium‐based catalysts bearing phosphate ligands for ring‐opening polymerization of ɛ‐caprolactone

Neodymium‐based catalysts coordinated with phosphate ligands (NdCl₃·3L), where L = triethyl phosphate (TEP) or tris(2‐ethylhexyl) phosphate (TEHP), were synthesized. The ring‐opening polymerizations (ROP) of ɛ‐caprolactone (ɛ‐CL) with these catalysts in the presence of benzyl alcohol initiator were performed, yielding polymers with well‐defined molecular weights and relatively narrow polydispersity index (PDI = 1.22–1.65). In situ NMR analysis of the reaction between NdCl₃·3TEP and benzyl alcohol indicated that ROP proceeds through a coordination‐insertion mechanism. The end groups of the resultant polymers were determined using MALDI‐ToF mass spectrometry and NMR spectroscopy. The quasi‐living nature of this catalytic system was demonstrated by kinetic studies and the successful synthesis of the block copolymer poly(ɛ‐caprolactone)‐block‐poly(l ‐lactide) by sequential monomer addition. Kinetic studies revealed that the catalyst with the bulkier TEHP ligand increased the rate of ROP of ɛ‐CL as compared to the TEP ligand. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1289–1296     

Ordered mesoporous SBA‐15 functionalized with yttrium(III) and cerium(III) complexes: Towards active heterogeneous catalysts for oxidation of sulfides and preparation of 5‐substituted 1H‐tetrazoles

Mesoporous SBA‐15 was synthesized and modified with 3‐chloropropyltrimethoxysilane and then used in immobilization of creatinine groups, which were employed to introduce Y³⁺ and Ce³⁺ to give rise to two novel yttrium and cerium catalysts: SBA‐15@Creatinine@M (M = Y and Ce). The structures of the SBA‐15@Creatinine@M catalysts were determined using various techniques. These catalysts offered outstanding catalytic performances in the oxidation of sulfides to sulfoxides and in the preparation of 5‐substituted 1H‐tetrazoles. An important characteristic of the SBA‐15@Creatinine@M catalysts is that they are very stable without a considerable decrease in their catalytic performance lasting seven cycles.     

Transition‐Metal‐Free Deconstructive Lactamization of Piperidines

One of the major challenges in organic synthesis is the activation or deconstructive functionalization of unreactive C(sp³)–C(sp³) bonds, which requires using transition or precious metal catalysts. We present here an alternative: the deconstructive lactamization of piperidines without using transition metal catalysts. To this end, we use 3‐alkoxyamino‐2‐piperidones, which were prepared from piperidines through a dual C(sp³)–H oxidation, as transitory intermediates. Experimental and theoretical studies confirm that this unprecedented lactamization occurs in a tandem manner involving an oxidative deamination of 3‐alkoxyamino‐2‐piperidones to 3‐keto‐2‐piperidones, followed by a regioselective Baeyer–Villiger oxidation to give N‐carboxyanhydride intermediates, which finally undergo a spontaneous and concerted decarboxylative intramolecular translactamization.     

SBA‐15‐supported N‐coordinate ruthenium(II) materials bearing sulfonamide‐type ligands: Effect of ligand backbones on catalytic transfer hydrogenation of ketones and aldehydes

[RuLCl(p ‐cymene)] (L = N ‐arylsulfonylphenylenediamine) complexes ( 2 _{a – d} ) were synthesized from the reaction between [Ru(p ‐cymene)Cl₂]₂ and ligand. Additionally, SBA‐15–[RuLCl(p ‐cymene)] derived catalysts ( 3 _{a – d} ) were successfully immobilized onto mesoporous silica (SBA‐15) by an easily accessible approach. The structural elucidations of 2 _{a – d} and 3 _{a – d} were carried out with various methods such as ¹H NMR, ¹³C NMR and infrared spectroscopies, elemental analysis, thermogravimetric/differential thermal analysis, nitrogen adsorption–desorption and scanning electron microscopy/energy‐dispersive X‐ray analysis. The Ru(II) complexes and materials were found to be highly active and selective catalysts for the transfer hydrogenation (TH) reaction of aldehydes and ketones. The influence of various 1,2‐phenylenediamines on the reactivity of the catalysts (complexes or materials) was studied and the catalysts ( 2 _d and 3 _d ) with a 4,5‐dichlorophenylenediamine substituent showed the best activity (the maximum turnover frequencies are 2916 and 2154 h⁻¹ for TH of 4‐fluoroacetophenone, and 6000 and 4956 h⁻¹ for TH of 4‐chlorobenzaldehyde).     

Whole‐Cell‐Catalyzed Multiple Regio‐ and Stereoselective Functionalizations in Cascade Reactions Enabled by Directed Evolution

Biocatalytic cascade reactions using isolated stereoselective enzymes or whole cells in one‐pot processes lead to value‐added chiral products in a single workup. The concept has been restricted mainly to starting materials and intermediate products that are accepted by the respective wild‐type enzymes. In the present study, we exploited directed evolution as a means to create E. coli whole cells for regio‐ and stereoselective cascade sequences that are not possible using man‐made catalysts. The approach is illustrated using P450‐BM3 in combination with appropriate alcohol dehydrogenases as catalysts in either two‐, three‐, or four‐step cascade reactions starting from cyclohexane, cyclohexanol, or cyclohexanone, respectively, leading to either (R,R)‐, (S,S)‐, or meso‐cyclohexane‐1,2‐diol. The one‐pot conversion of cyclohexane into (R)‐ or (S)‐2‐hydroxycyclohexanone in the absence of ADH is also described.     

Dehydration of Castor Oil over NaHSO4/MCM‐41 Catalyst Modified by n‐Dodecyltriethoxysilane

n‐Dodecyltriethoxysilane (DTEOS) modified NaHSO₄/MCM‐41 catalysts (silanized catalysts) were synthesized by different impregnation sequences and evaluated in the liquid‐phase dehydration of castor oil. The samples were evaluated by X‐ray diffraction, nitrogen adsorption‐desorption, SEM, TEM, FT‐IR spectroscopy, XPS, ²⁹Si MAS NMR spectroscopy, contact angle measurements, NH₃‐TPD, and pyridine‐FT‐IR spectroscopy. The analyses demonstrated that silanization enhanced the hydrophobicity of the catalysts, and the impregnation sequence of silanized catalysts had a significant effect on the NaHSO₄ dispersion, surface area, acid distribution, and hydrophobicity of the silanized catalysts. The catalytic activity of the silanized catalysts was much higher than that of NaHSO₄/MCM‐41. Among the silanized catalysts, the catalyst prepared by simultaneous impregnation with DTEOS and NaHSO₄ showed the highest iodine value of 141.8 [g(I₂) per 100 g] and lowest hydroxyl value of 11.3 [mg(KOH) · g^–1].     

Enzyme‐catalyzed ring‐opening polymerization of 3(S)‐isopropylmorpholine‐2,5‐dione

The enzymatic ring‐opening polymerization of a 6‐membered cyclic depsipeptide, 3(S)‐isopropylmorpholine‐2,5‐dione in the bulk, was investigated by using lipases as catalysts at 100 and 130°C. Unchanged monomer was recovered in the absence of the enzyme or using an inactivated enzyme, indicating that the present polymerization proceeds through enzymatic catalysis. Poly(3‐isopropylmorpholine‐2,5‐dione) has a carboxylic acid group at one end and a hydroxy group at the other end.     

Enantioselective Allylic Amination of Morita‐Baylis‐Hillman Acetates Catalyzed by Chiral Thiourea‐Phosphine

The enantioselective allylic amination of Morita‐Baylis‐Hillman acetates catalyzed by chiral cyclohexane‐based thiourea‐phosphine catalysts was investigated. In the presence of 20 mol% rosin‐derived thiourea‐phosphine 3j , the chiral amines were obtained in up to 88% yield and up to 85% ee.     

Isosteviol‐amino Acid Conjugates as Highly Efficient Organocatalysts for the Asymmetric One‐pot Three‐component Mannich Reactions

Isosteviol‐amino acid conjugates were synthesized and used as chiral catalysts for the asymmetric three‐component Mannich reaction with hydroxyacetone as donor molecule. Good yields (up to 98%) and excellent stereoselectivities (up to 97:3 dr and 99% ee) were achieved in a short reaction time. In addition, syn‐ or anti‐configurations of α‐hydroxy‐β‐amino carbonyl compounds were obtained as main products with different chiral catalysts.     

Schiff base‐functionalized boehmite nanoparticle‐supported molybdenum and vanadium complexes: efficient catalysts for the epoxidation of alkenes

Boehmite nanoparticles, with high surface area and high degree of surface hydroxyl groups, were prepared via hydrothermal‐assisted sol–gel processing of aluminium 2‐butoxide. The produced powder was covalently functionalized with 3‐(trimethoxysilyl)propylamine, and then, in order to support vanadium oxosulfate and molybdenum hexacarbonyl complexes, all the terminal amine groups were changed to Schiff bases by refluxing with salicylaldehyde. These catalysts were applied in the epoxidation of cis‐cyclooctene and other olefins with tert‐BuOOH in CCl₄. The catalytic procedures for both catalysts were optimized for various parameters such as solvent and oxidant. Recycling experiments revealed that these heterogeneous nano‐catalysts could be repeatedly applied for the epoxidation of alkenes. Copyright © 2015 John Wiley & Sons, Ltd.     

Enantioselective Heterogeneous Epoxidation and Hetero‐Diels‐Alder Reaction with Mn‐ and Cr‐salen Complexes Immobilized on Silica Gel by Radical Grafting

Vinyl‐substituted chiral salens (salen=bis(salicylidene)ethylidenediamine) are used for attachment to Me₃Si‐hydrophobized silica gel (controlled‐pore glass, CPG), carrying covalently bound mercaptopropyl ‘substituents', by AIBN‐mediated radical addition of SH groups to styryl C=C bonds (Scheme 1, Table 1, and Figs. 1 and 2). The immobilized Mn‐ and Cr‐salen complexes, thus accessible, have been employed in enantioselective epoxidations (Scheme 2, Tables 2 and 3, and Fig. 3) and hetero‐Diels‐Alder additions of aldehydes to Danishefsky's diene (Scheme 3, Tables 4 and 5, and Figs. 4 and 5), with an emphasis on multiple use of the immobilized catalysts. The enantioselectivities (es) of the two reactions were very similar to those reported for homogeneous conditions. After five to seven runs, all the CPG‐bound Mn‐salen complexes performed somewhat less well (70 instead of 75% es with styrene; Fig. 3). The Cr complex, which was shown to give rise to a linear relationship between the enantiomeric purities of ligand and product under homogeneous conditions (Fig. 4), exhibited the opposite behavior: after five runs, the enantioselecitivity of the hetero‐Diels‐Alder reaction had risen (from an average of 76 to ca. 83%) to remain constant for another five runs (Fig. 5). We have established for both catalysts that no reaction takes place in the supernatant solution (no leaching of catalytically active Mn or Cr species from the CPG into solution; heterogeneity test; Tables 3 and 5). The results described are yet another demonstration for the successful ‘conversion' of homogeneous to heterogeneous catalysts by immobilization on hydrophobic CPG, with multiple application of the same catalyst batch.     

Polymer‐supported half‐titanocene catalysts for the syndiospecific polymerization of styrene

Monocyclopendienyltitanium trichloride (CpTiCl₃) was supported on polymer carriers with different hydroxyl contents, and the supported catalysts were used for styrene polymerization. The supported catalysts exhibited high activity even at low Al/Ti ratios and increased the molecular weight of the products, indicating that polymer carriers could stabilize the active sites. The polymers prepared with unsupported and supported catalysts were extracted with boiling n‐butanone and characterized by carbon nuclear magnetic resonance (¹³C NMR) and differential scanning calorimetry. The polymers obtained by supported catalysts had a high fraction of boiling n‐butanone‐insoluble part and high melting temperatures, but ¹³C NMR results showed that syndiotacticity decreased compared with that of polymers prepared with an unsupported catalyst. ESR study on the supported catalysts confirmed that the active sites supported on the carrier dropped into the solution and formed active sites the same as those in the unsupported system when they reacted with methylaluminoxane. ¹³C NMR analysis showed that the polymerization mechanism of the supported active sites was an active‐site controlled mechanism instead of a chain‐end controlled mechanism of the unsupported active sites. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 127–135, 2000     

Microwave‐Assisted Expedite Synthesis of 2‐Phenylimidazo[1,2‐a]pyridylquinoxalin‐2(1H)‐ones

An efficient methodology has been developed for the synthesis of quinoxalin‐2(1H)‐one derivatives of 2‐phenylimidazo[1,2‐a]pyridines by microwave‐irradiated Hinsberg heterocyclization between 2‐phenylimidazo[1,2‐a]pyridine‐3‐glyoxalates and o‐phenylenediamine using either montmorillonite K‐10 or Yb(OTf)₃ as catalysts. Montmorillonite K‐10 was proven to be an efficient catalyst for the heterocyclization reaction between sterically hindered glyoxalate and o‐phenylenediamine only under microwave conditions. The use of Yb(OTf)₃/tetrahydrofuran was also found to be an effective catalyst for the above chemical transformation among a series of Lewis acids screened under microwave conditions; however, comparatively lesser yields were obtained as compared with the use of montmorillonite K‐10.