Nickel‐Catalyzed Cross‐Coupling of Redox‐Active Esters with Boronic Acids

A transformation analogous in simplicity and functional group tolerance to the venerable Suzuki cross‐coupling between alkyl‐carboxylic acids and boronic acids is described. This Ni‐catalyzed reaction relies upon the activation of alkyl carboxylic acids as their redox‐active ester derivatives, specifically N‐hydroxy‐tetrachlorophthalimide (TCNHPI), and proceeds in a practical and scalable fashion. The inexpensive nature of the reaction components (NiCl₂?6 H₂O—$9.5 mol^?1, Et₃N) coupled to the virtually unlimited commercial catalog of available starting materials bodes well for its rapid adoption.     

Stabilization of High‐Valence Ruthenium with Silicotungstate Ligands: Preparation,Structural Characterization,and Redox Studies of Ruthenium(III)‐Substituted α‐Keggin‐Type Silicotungstates with Pyridine Ligands, [SiW11O39RuIII(Py)]5−

Ruthenium(III)‐substituted α‐Keggin‐type silicotungstates with pyridine‐based ligands, [SiW₁₁O₃₉Ru^III(Py)]^5?, (Py: pyridine ( 1 ), 4‐pyridine‐carboxylic acid ( 2 ), 4,4′‐bipyridine ( 3 ), 4‐pyridine‐acetamide ( 4 ), and 4‐pyridine‐methanol ( 5 )) were prepared by reacting [SiW₁₁O₃₉Ru^III(H₂O)]^5? with the pyridine derivatives in water at 80 °C and then isolated as their hydrated cesium salts. These compounds were characterized using cyclic voltammetry (CV), UV/Vis, IR, and ¹H NMR spectroscopy, elemental analysis, titration, and X‐ray absorption near‐edge structure (XANES) analysis (Ru K‐edge and L₃‐edge). Single‐crystal X‐ray analysis of compounds 2 , 3 , and 4 revealed that Ru^III was incorporated in the α‐Keggin framework and was coordinated by pyridine derivatives through a Ru? N bond. In the solid state, compounds 2 and 3 formed a dimer through π? π interaction of the pyridine moieties, whereas they existed as monomers in solution. CV indicated that the incorporated Ru^III–Py was reversibly oxidized into the Ru^IV–Py derivative and reduced into the Ru^II–Py derivative.     

8‐Amidoquinoline, 8‐(Trialkylsilylamido)quinoline, 2‐Pyridylmethylamide,and (2‐Pyridylmethyl)(trialkylsilyl)amide Complexes of Gallium

Lithium 8‐amidoquinoline ( 1 ) and lithium 8‐(trialkylsilylamido)quinoline [SiMe₂tBu ( 2 ), SiiPr₃ ( 3 )] react with dimethylgallium chloride to the metathesis products dimethylgallium 8‐amidoquinoline ( 4 ) as well as dimethylgallium 8‐(trialkylsilylamido)quinoline [SiMe₂tBu ( 5 ), SiiPr₃ ( 6 )]. The gallium atoms are in distorted tetrahedral environments. During the synthesis of 5 , orange dimethylgallium 2‐butyl‐8‐(tert‐butyldimethylsilylamido)quinoline ( 7 ) was found as by‐product. The metathesis reactions of Me₂GaCl with LiN(R)CH₂Py (Py = 2‐pyridyl) yield the corresponding 2‐pyridylmethylamides Me₂Ga‐N(H)CH₂Py ( 8 ), Me₂Ga‐N(SiMe₂tBu)CH₂Py ( 9 ) and Me₂Ga‐N(SiiPr₃)CH₂Py ( 10 ). In these complexes the gallium atoms show a distorted tetrahedral coordination sphere. However, derivative 8 crystallizes dimeric with bridging amido units whereas in 9 and 10 the 2‐pyridylmethylamido moieties act as bidentate ligands leading to monomeric molecules.     

Design of two series of 1:1 cocrystals involving 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine and carboxylic acids

Two series of a total of ten cocrystals involving 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine with various carboxylic acids have been prepared and characterized by single‐crystal X‐ray diffraction. The pyrimidine unit used for the cocrystals offers two ring N atoms (positions N1 and N3) as proton‐accepting sites. Depending upon the site of protonation, two types of cations are possible [Rajam et al. (2017). Acta Cryst. C 73 , 862–868]. In a parallel arrangement, two series of cocrystals are possible depending upon the hydrogen bonding of the carboxyl group with position N1 or N3. In one series of cocrystals, i.e. 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–3‐bromothiophene‐2‐carboxylic acid (1/1), 1 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–5‐chlorothiophene‐2‐carboxylic acid (1/1), 2 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–2,4‐dichlorobenzoic acid (1/1), 3 , and 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–2‐aminobenzoic acid (1/1), 4 , the carboxyl hydroxy group (–OH) is hydrogen bonded to position N1 (O—H…N1) of the corresponding pyrimidine unit (single point supramolecular synthon). The inversion‐related stacked pyrimidines are doubly bridged by the carboxyl groups via N—H…O and O—H…N hydrogen bonds to form a large cage‐like tetrameric unit with an R₄²(20) graph‐set ring motif. These tetrameric units are further connected via base pairing through a pair of N—H…N hydrogen bonds, generating R₂²(8) motifs (supramolecular homosynthon). In the other series of cocrystals, i.e. 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–5‐methylthiophene‐2‐carboxylic acid (1/1), 5 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–benzoic acid (1/1), 6 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–2‐methylbenzoic acid (1/1), 7 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–3‐methylbenzoic acid (1/1), 8 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–4‐methylbenzoic acid (1/1), 9 , and 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–4‐aminobenzoic acid (1/1), 10 , the carboxyl group interacts with position N3 and the adjacent 4‐amino group of the corresponding pyrimidine ring via O—H…N and N—H…O hydrogen bonds to generate the robust R₂²(8) supramolecular heterosynthon. These heterosynthons are further connected by N—H…N hydrogen‐bond interactions in a linear fashion to form a chain‐like arrangement. In cocrystal 1 , a Br…Br halogen bond is present, in cocrystals 2 and 3 , Cl…Cl halogen bonds are present, and in cocrystals 5 , 6 and 7 , Cl…O halogen bonds are present. In all of the ten cocrystals, π–π stacking interactions are observed.     

Influence of Isotope Substitution on Lattice and Spin‐Peierls‐Type Transition Features in One‐Dimensional Nickel Bis‐dithiolene Spin Systems

Four new 1D spin‐Peierls‐type compounds, [D₅]1‐(4′‐R‐benzyl)pyridinium bis(maleonitriledithiolato)nickelate ([D₅]R‐Py; R=F, I, CH₃, and NO₂), were synthesized and characterized structurally and magnetically. These 1D compounds are isostructural with the corresponding non‐deuterated compounds, 1‐(4′‐R‐benzyl)pyridinium bis(maleonitriledithiolato)nickelate (R‐Py; R=F, I, CH₃, and NO₂). Compounds [D₅]R‐Py and R‐Py (R=F, I, CH₃, and NO₂) crystallize in the monoclinic space group P2₁/c with uniform stacks of anions and cations in the high‐temperature phase and triclinic space group P$\bar 1$ with dimerized stacks of anions and cations in the low‐temperature phase. Similar to the non‐deuterated R‐Py compounds, a spin‐Peierls‐type transition occurs at a critical temperature for each [D₅]R‐Py compound; the magnetic character of the 1D S=1/2 ferromagnetic chain for [D₅]F‐Py and the 1D S=1/2 Heisenberg antiferromagnetic chain for others appear above the transition temperature. Spin‐gap magnetic behavior was observed for all of these compounds below the transition temperature. In comparison to the corresponding R‐Py compound, the cell volume is almost unchanged for [D₅]F‐Py and shows slight expansion for [D₅]R‐Py (R=I, CH₃, and NO₂) as well as an increase in the spin‐Peierls‐type transition temperature for all of these 1D compounds in the order of F>I≈CH₃≈NO₂. The large isotopic effect of nonmagnetic countercations on the spin‐Peierls‐type transition critical temperature, T_C, can be attributed to the change in ω₀ with isotope substitution.     

Carboxylation Reactions with Carbon Dioxide Using N‐Heterocyclic Carbene‐Copper Catalysts

The development of versatile catalyst systems and new transformations for the utilization of carbon dioxide (CO₂) is of great interest and significance. This Personal Account reviews our studies on the exploration of the reactions of CO₂ with various substrates by the use of N‐heterocyclic carbene (NHC)‐copper catalysts. The carboxylation of organoboron compounds gave access to a wide range of carboxylic acids with excellent functional group tolerance. The C?H bond carboxylation with CO₂ emerged as a straightforward protocol for the preparation of a series of aromatic carboxylic esters and butenoates from simple substrates. The hydrosilylation of CO₂ with hydrosilanes provided an efficient method for the synthesis of silyl formate on gram scale. The hydrogenative or alkylative carboxylation of alkynes, ynamides and allenamides yielded useful α,β‐unsaturated carboxylic acids and α,β‐dehydro amino acid esters. The boracarboxylation of alkynes or aldehydes afforded the novel lithium cyclic boralactone or boracarbonate products, respectively. The NHC‐copper catalysts generally featured excellent functional group compatibility, broad substrate scope, high efficiency, and high regio‐ and stereoselectivity. The unique electronic and steric properties of the NHC‐copper units also enabled the isolation and structural characterization of some key intermediates for better understanding of the catalytic reaction mechanisms.     

New trans/cis tetrahydroisoquinolines. 2. trans‐ and cis‐3‐(1‐methyl‐1h‐pyrrol‐2‐yl)‐1‐(2H)‐oxo‐2‐phenethyl‐1,2,3,4‐tetrahydroisoquino‐lin‐4‐carboxylic acids and subsequent transformations

Stereochemical course of the reaction of homophthalic anhydride and N‐(1‐methyl‐1H‐pyrrol‐2‐yl‐methylidene)‐phenethylamine was studied. Mixtures of the expected trans‐ and cis‐1,2,3,4‐tetrahydroiso‐quinoline‐4‐carboxylic acids trans‐ 4 and cis‐ 4 were obtained along with by‐products 5 and 6 . The ratios of all products and the diastereomers, obtained under different reaction conditions, were established by pmr. THF as a solvent and ultrasonic treatment are applied for the first time in the reaction of this type. The reaction was made diastereoselective towards any isomer. The carboxylic group of trans‐ 4 was transformed in four steps into various cyclic amino‐methyl groups yielding numerous new tetrahydroisoquinolinones trans‐ 10a‐i incorporating a given fragment of pharmacological interest. Reduction of 10a‐i was studied.     

Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N‐(2‐Pyridylethyl)‐N′‐(2,6‐diisopropylphenyl)pivalamidine

N‐(2,6‐Diisopropylphenyl)‐N′‐(2‐pyridylethyl)pivalamidine (Dipp‐N=C(tBu)‐N(H)‐C₂H₄‐Py) ( 1 ), reacts with metalation reagents of lithium, magnesium, calcium, and strontium to give the corresponding pivalamidinates [(tmeda)Li{Dipp‐N=C(tBu)‐N‐C₂H₄‐Py}] ( 6 ), [Mg{Dipp‐N=C(tBu)‐N‐C₂H₄‐Py}₂] ( 3 ), and heteroleptic [{(Me₃Si)₂N}Ae{Dipp‐N=C(tBu)‐N‐C₂H₄‐Py}], with Ae being Ca ( 2 a ) and Sr ( 2 b ). In contrast to this straightforward deprotonation of the amidine units, the reaction of 1 with the bis(trimethylsilyl)amides of sodium or potassium unexpectedly leads to a β‐metalation and an immediate deamidation reaction yielding [(thf)₂Na{Dipp‐N=C(tBu)‐N(H)}] ( 4 a ) or [(thf)₂K{Dipp‐N=C(tBu)‐N(H)}] ( 4 b ), respectively, as well as 2‐vinylpyridine in both cases. The lithium derivative shows a similar reaction behavior to the alkaline earth metal congeners, underlining the diagonal relationship in the periodic table. Protonation of 4 a or the metathesis reaction of 4 b with CaI₂ in tetrahydrofuran yields N‐(2,6‐diisopropylphenyl)pivalamidine (Dipp‐N=C(tBu)‐NH₂) ( 5 ), or [(thf)₄Ca{Dipp‐N=C(tBu)‐N(H)}₂] ( 7 ), respectively. The reaction of AN(SiMe₃)₂ (A=Na, K) with less bulky formamidine Dipp‐N=C(H)‐N(H)‐C₂H₄‐Py ( 8 ) leads to deprotonation of the amidine functionality, and [(thf)Na{Dipp‐N=C(H)‐N‐C₂H₄‐Py}]₂ ( 9 a ) or [(thf)K{Dipp‐N=C(H)‐N‐C₂H₄‐Py}]₂ ( 9 b ), respectively, are isolated as dinuclear complexes. From these experiments it is obvious, that β‐metalation/deamidation of N‐(2‐pyridylethyl)amidines requires bases with soft metal ions and also steric pressure. The isomeric forms of all compounds are verified by single‐crystal X‐ray structure analysis and are maintained in solution.     

四个对苯酚四唑硫酮金属(II)配合物的合成和晶体结构

四唑酸(–CN4H)与羧酸(–COOH)具有相似的酸性。对苯酚四唑硫酮(H2L)可以作为单齿(–S或–N)或双齿(–N, N或–N, S)配体与金属离子配位形成配位化合物。合成了4个以H2L为配体的金属(II)配合物：Co(HL)2(Py)2(H2O)2 (1), [Mn(HL)2(H2O)4]·2H2O (2), Mn(HL)2(Phen)2 (3), and [Zn(HL)2(Phen)2]·0.5H2O·1.5CH3OH (4),并用X−射线单晶衍射法测定了晶体结构。晶体结构分析表明,在这些配合物中所有的中心金属原子均呈现六配位的八面体构型。在配合物1和2中,HL–配体以氧原子与中心金属原子配位,而在配合物3和4中HL–配体则以硫原子与中心金属原子配位。     

Cationic palladium complex‐catalyzed carbonylation of 2,3‐dien‐1‐ols to 1,3‐diene‐2‐carboxylic acids and esters under mild conditions

A cationic palladium complex, [Pd(PPh₃)₂(MeCN)₂](BF₄)₂, catalyzed the carbonylation of 2,3‐dien‐1‐ols under mild conditions. The dienols bearing two or more alkyl substituents on the diene part afforded 1,3‐diene‐2‐carboxylic acids successfully in tetrahydrofuran (THF), while those possessing one or no alkyl substituent gave polymers of the products exclusively. The former afforded the corresponding methyl esters in good yields when the reactions were carried out in methanol, while the latter afforded mainly the Diels–Alder reaction products of the resulting esters. An alkylidene group‐substituted π‐allylpalladium species has been presumed to be an intermediate. Copyright © 2000 John Wiley & Sons, Ltd.     

SO2F2‐Mediated One‐Pot Synthesis of Aryl Carboxylic Acids and Esters from Phenols through a Pd‐Catalyzed Insertion of Carbon Monoxide

A one‐pot Pd‐catalyzed carbonylation of phenols into their corresponding aryl carboxylic acids and esters through the insertion of carbon monoxide has been developed. This procedure offers a direct synthesis of aryl carboxylic acids and esters from inexpensive and abundant starting materials (phenols, SO₂F₂ and CO) under mild conditions. This method tolerates a broad range of functional groups and is also applicable for the modification of complicated natural products.     

Thermal isomerization of ruthenium hydride compounds containing asymmetric bidentate pyrrole‐imine ligands

A series of ruthenium hydride compounds containing substituted bidentate pyrrole‐imine ligands were synthesized and characterized. Reacting RuHCl(CO)(PPh₃)₃ with one equivalent of [C₄H₃NH(2‐CH=NR)] in ethanol in the presence of KOH gave compounds {RuH(CO)(PPh₃)₂[C₄H₃N(2‐CH=NR)]} where trans‐Py‐Ru‐H 1, R = CH₂CH₂C₆H₉; cis‐Py‐Ru‐H 2, R = Ph‐2‐Me; and cis‐Py‐Ru‐H 3, R = C₆H₁₁. Heating trans‐Py‐Ru‐H 1 in toluene at 70°C for 12 hr resulted a thermal conversion of the trans‐Py‐Ru‐H 1 into its cis form, {RuH(CO)(PPh₃)₂[C₄H₃N(2‐CH=NCH₂CH₂C₆H₉)]} (cis‐Py‐Ru‐H 1) in very high yield. The ¹H NMR spectra of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 2, cis‐Py‐Ru‐H 3, and cis‐Py‐Ru‐H 1 all show a typical triplet at ca. δ–11 for the hydride. The trans and cis form indicate the relative positions of pyrrole ring and hydride. The geometries of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 1, and cis‐Py‐Ru‐H 3 are relatively similar showing typical octahedral geometries with two PPh₃ fragments arranged in trans positions.     

Report on an Unusual Cascade Reaction between Azulenes and 2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone (=4,5‐Dichloro‐3,6‐dioxocyclohexa‐1,4‐diene‐1,2‐dicarbonitrile; DDQ)

The oxidation of 1‐(3,8‐dimethylazulen‐1‐yl)alkan‐1‐ones 1 with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (=4,5‐dichloro‐3,6‐dioxocyclohexa‐1,4‐diene‐1,2‐dicarbonitrile; DDQ) in acetone/H₂O mixtures at room temperature does not only lead to the corresponding azulene‐1‐carboxaldehydes 2 but also, in small amounts, to three further products (Tables 1 and 2). The structures of the additional products 3 – 5 were solved spectroscopically, and that of 3a also by an X‐ray crystal‐structure analysis (Fig. 1). It is demonstrated that the bis(azulenylmethyl)‐substituted DDQ derivatives 5 yield on methanolysis or hydrolysis precursors, which in a cascade of reactions rearrange under loss of HCl into the pentacyclic compounds 3 (Schemes 4 and 7). The found 1,1′‐[carbonylbis(8‐methylazulene‐3,1‐diyl)]bis[ethanones] 4 are the result of further oxidation of the azulene‐1‐carboxaldehydes 2 to the corresponding azulene‐1‐carboxylic acids (Schemes 9 and 10).     

CC Coupling of N‐Heterocycles at the fac‐Re(CO)3 Fragment: Synthesis of Pyridylimidazole and Bipyridine Ligands

A new family of cationic rhenium tricarbonyl complexes with either two N‐alkylimidazole (N‐RIm) and one pyridine (Py) ligand, or two pyridine and one N‐RIm ligand, [Re(CO)₃(N‐RIm)_(3?x)(Py)_x]⁺, has been prepared. The reaction of these complexes with a strong base, followed by an oxidant, selectively afforded 2,2’‐pyridylimidazole complexes as the result of intramolecular dehydrogenative C?C coupling reactions. For tris(pyridine) complexes [Re(CO)₃(Py)₃]⁺ the reaction pattern upon a deprotonation/oxidation sequence is maintained, which allows the generation of complexes with 2,2’‐bipyridine ligands. In the particular combination of two different types of pyridine ligand in the cationic fac‐Re(CO)₃ complexes only the cross‐coupling products with asymmetric 2,2’‐bipyridine ligands were obtained; the homocoupling products were not observed.     

Nitro‐substituted iron(II) tridentate bis(imino)pyridine complexes as high‐temperature catalysts for the production of α‐olefins

A new series of nitro‐substituted bis(imino)pyridine ligands {2,6‐bis[1‐(2‐methyl‐4‐nitrophenylimino)ethyl]pyridine, 2,6‐bis[1‐(4‐nitrophenylimino)ethyl]pyridine, (1‐{6‐[1‐(4‐nitro‐phenylimino)‐ethyl]‐pyridin‐2‐yl}‐ethylidene)‐(2,4,6‐trimethyl‐phenyl)‐amine, and 2,6‐bis[1‐(2‐methyl‐3‐nitrophenylimino)ethyl]pyridine} and their corresponding Fe(II) complexes [{p‐NO₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐ Me? p‐NO₂}FeCl₂ ( 10 ), L₂FeCl₂ ( 11 ), {m‐NO₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? m‐NO₂}FeCl₂ ( 12 ), and {p‐NO₂? Ph? N?C(Me)? Py? C(Me)?N? Mes}FeCl₂ ( 14 )] were synthesized. According to X‐ray analysis, there were shortenings of the axial Fe? N bond lengths (up to 0.014 Å) in para‐nitro‐substituted complex 10 and (up to 0.015 Å) in meta‐nitro‐substituted complex 12 versus the Fe(II) complex without nitro groups [{o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me}FeCl₂ ( 1 )]. Complexes 10 , 12 , and 14 afforded very active catalysts for the production of α‐olefins and were more temperature‐stable and had longer lifetimes than parent non‐nitro‐substituted Fe(II) complex 1 . The reaction between FeCl₂ and a sterically less hindered ligand [p‐NO₂? Ph? N?C(Me)? Py? C(Me)?N? Ph? p‐NO₂] resulted in the formation of octahedral complex 11 . A para‐dialkylamino‐substituted bis(imino)pyridine ligand [p‐NEt₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt₂] and the corresponding Fe(II) complex [{p‐NEt₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt₂}FeCl₂ ( 16 )] were synthesized to evaluate the effect of enhanced electron donation of the ligand on the catalytic performance. According to X‐ray analysis, there was a shortening (up to 0.043 Å) of the axial Fe? N bond lengths in para‐diethylamino‐substituted complex 16 in comparison with parent Fe(II) complex 1 . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2615–2635, 2006     

Effect of Heavy‐Atom (Br) at the Phenyl Rings of Schiff‐Base Ligands on the NIR Luminescence of their Bimetallic Zn‐Nd Complexes

Two heterobimetallic Zn‐Nd phenylene‐bridged Schiff‐base ligands complexes [ZnNd L¹ (Py)(NO₃)₃] ( 1 ) and [Zn L² Nd(Py)(NO₃)₃]·MeCN ( 2 ) (Py = pyridine, H₂L¹ = N,N′‐bis‐ (3‐methoxy‐salicylidene)phenylene‐1,2‐diamine, H₂L² = N,N′‐bis‐5‐bromo‐3‐methoxy‐salicylidene)phenylene‐1,2‐diamine) were obtained. Both 1 and 2 were structurally characterized by X‐ray crystallography, and their near‐infrared (NIR) luminescent properties were determined. For the two complexes, the occupation of pyridine at the axial position of 3d Zn²⁺ ions could effectively prevent luminescent quenching arising from OH‐, NH‐ or CH oscillators of the solvates around the 4f Nd³⁺ ions, and the heavy‐atom (Br) effect of the Schiff‐base ligands on their NIR luminescent properties is also discussed.     

Synthesis of a Pyridine–Zinc‐Based Porous Organic Polymer for the Co‐catalyst‐Free Cycloaddition of Epoxides

The synthesis of solid catalysts for the co‐catalyst‐free cycloaddition of CO₂ has attracted much attention. Herein, we report a hierarchical porous organic polymer, Py‐Zn@MA, that is able to catalyze the cycloaddition reaction of epoxides and CO₂ without using any additives or co‐catalyst to afford turnover frequency (TOF) values as high as 250 and 97 h⁻¹ at 130 °C by using pure and diluted CO₂ (simulating flue gas), respectively. These results are superior to those obtained from previously reported heterogeneous co‐catalyst‐free systems. The high activity of Py‐Zn@MA is mainly attributed to its bifunctional nature with ZnBr₂ and pyridine activating the epoxide in a cooperative way. Notably, Py‐Zn@MA can be easily prepared on a large scale without using any catalyst and the chemicals are cost effective. Moreover, Py‐Zn@MA shows good substrate universality for the cycloaddition reactions of epoxides. Our designed porous organic polymer Py‐Zn@MA material has the potential to serve as an efficient catalyst for the direct conversion of flue gas with epoxides into value‐added cyclic carbonates.     

Synthesis of Isoindolo[2,1‐a]quinazoline‐5,11‐dione Derivatives via the Reductive One‐Pot Reaction of N‐Substituted 2‐Nitrobenzamides and 2‐Formylbenzoic Acids

Various isoindolo[2,1‐a]quinazoline‐5,11‐dione derivatives 3 were synthesized in good yields by means of the reductive reaction of N‐substituted 2‐nitrobenzamides 1 and 2‐formylbenzoic acids 2 in the presence of SnCl₂?2 H₂O under reflux in EtOH (Scheme, Table). The procedure needed two steps, the reduction of the nitro group of the 2‐nitrobenzamide and ring closure by nucleophilic addition of the NH₂ group to both the formyl and carboxylic acid C?O groups.     

Nickel‐Catalyzed Mizoroki–Heck‐ versus Michael‐Type Addition of Organoboronic Acids to α,β‐Unsaturated Alkenes through Fine‐Tuning of Ligands

Various arylboronic acids reacted with activated alkenes in the presence of [Ni(dppe)Br₂], ZnCl₂, and H₂O in CH₃CN at 80 °C to give the corresponding Mizoroki–Heck‐type addition products in good to excellent yields. Furthermore, 1 equivalent of the hydrogenation product of the activated alkene was also produced. By tuning the ligands of the nickel complexes and the reaction conditions, Michael‐type addition was achieved in a very selective manner. Thus, various p‐ and o‐substituted arylboronic acids or alkenylboronic acid reacted smoothly with activated alkenes in CH₃CN at 80 °C for 12 h catalyzed by Ni(acac)₂, P(o‐anisyl)₃, and K₂CO₃ to give the corresponding Michael‐type addition products in excellent yields. However, for m‐substituted arylboronic acids, the yields of Michael‐type addition products are very low. The cause of this unusual meta‐substitution effect is not clear. By altering the solvent or phosphine ligand, the product yields for m‐substituted arylboronic acids were greatly improved. In contrast to previous results in the literature, the present catalytic reactions required water for Mizoroki–Heck‐type products and dry reaction conditions for Michael‐type addition products. Possible mechanistic pathways for both addition reactions are proposed.     

Effect of Bulkiness on Reversible Substitution Reaction at MnII Center with Concomitant Movement of the Lattice DMF: Observation through Single‐Crystal to Single‐Crystal Fashion

The porous coordination polymer ({[Mn(L)H₂O](H₂O)_1.5(dmf)}_n, 1 ) (DMF=N,N‐dimethylformamide) exhibits variety of substitution reactions along with movement of lattice DMF molecule depending upon bulkiness of the external guest molecules. If pyridine or 4‐picoline is used as a guest, both lattice and coordinated solvent molecules are simultaneously substituted (complexes 6 and 7 , respectively). If a bulky guest like aniline is used, a partial substitution at the metal centers and full substitution at the channels takes place (complex 8 ). If the guest is 2‐picoline (by varying the position of bulky methyl group with respect to donor N atom), one Mn^II center is substituted by 2‐picoline, whereas the remaining center is substituted by a DMF molecule that migrates from the channel to the metal center (complex 9 ). Here, the lattice solvent molecules are substituted by 2‐picoline molecules. For the case of other bulky guests like benzonitrile or 2,6‐lutidine, both the metal centers are substituted by two DMF molecules, again migrating from the channel, and the lattice solvent molecules are substituted by these guest molecules (complex 10 and 11 , respectively). A preferential substitution of pyridine over benzonitrile (complex 12 ) at the metal centers is observed only when the molar ratio of PhCN:Py is 95:5 or less. For the case of an aliphatic dimethylaminoacetonitrile guest, the metal centers remain unsubstituted (complex 13 ); rather substitutions of the lattice solvents by the guest molecules take place. All these phenomena are observed through single crystal to single crystal (SC–SC) phenomena.