Cyclobutene Ring-Opening of Bicyclo[4.2.0]octa-1,6-dienes: Access to CF₃‑Substituted 5,6,7,8-Tetrahydro-1,7-naphthyridines

An efficient method for the synthesis of novel CF₃-substituted tetrahydro-1,7-naphthyridines including cyclic α-amino acid derivatives has been developed. The method is based on unusual cyclobutene ring-opening of bicyclo[4.2.0]­octa-1,6-dienes with pyrrolidine to afford the corresponding 1,5-diketones followed by their heterocyclization. A convenient <i>one-pot</i> procedure has been also elaborated starting from readily available trifluoromethylated 1,6-allenynes

Cyclobutene Ring-Opening of Bicyclo[4.2.0]octa-1,6-dienes: Access to CF₃‑Substituted 5,6,7,8-Tetrahydro-1,7-naphthyridines

An efficient method for the synthesis of novel CF₃-substituted tetrahydro-1,7-naphthyridines including cyclic α-amino acid derivatives has been developed. The method is based on unusual cyclobutene ring-opening of bicyclo[4.2.0]­octa-1,6-dienes with pyrrolidine to afford the corresponding 1,5-diketones followed by their heterocyclization. A convenient <i>one-pot</i> procedure has been also elaborated starting from readily available trifluoromethylated 1,6-allenynes

Coordination Chemistry of Mercury-Containing Anticrowns. Complexation of Perfluoro‑<i>o</i>,<i>o</i>′‑biphenylenemercury with <i>o</i>‑Xylene and Acetonitrile and the First X‑ray Diffraction Evidence for Its Trimeric Structure

The paper reports the first X-ray diffraction data evidencing the cyclic trimeric structure of the earlier synthesized octafluoro-<i>o</i>,<i>o</i>′-biphenylenemercury (<b>8</b>), being of considerable interest as a potential anticrown. The conclusion on the trimeric (<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₃ structure of this mercuracycle is based on an X-ray structural analysis of its <i>o</i>-xylene and acetonitrile complexes {[(<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₃]­(<i>o</i>-Me₂C₆H₄)₂} (<b>9</b>) and {[(<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₃]­(MeCN)₃} (<b>10</b>), which were obtained from <b>8</b> in an analytically pure state and fully characterized. Complex <b>9</b> contains two <i>o</i>-xylene species per one molecule of <b>8</b> and forms in the crystal infinite chains consisting of alternating mercuramacrocycle units and bridging <i>o</i>-xylene ligands. One more <i>o</i>-xylene molecule in each macrocyclic fragment of the chain serves as a terminal ligand. Both bridging and terminal molecules of <i>o</i>-xylene are coordinated in all cases with only one Hg site of the corresponding mercuracycle. The back transformation of complex <b>9</b> into <b>8</b> and <i>o</i>-xylene occurs on its heating in a vacuum at 100–120 °C for 2 h. In contrast to <b>9</b>, complex <b>10</b>, containing three acetonitrile ligands per one molecule of <b>8</b>, has a discrete structure in the crystal. In this complex, two of three acetonitrile species are bonded to one and the same Hg center of <b>8</b>, whereas the third MeCN species is coordinated with the other Hg atom of the mercuramacrocycle

Coordination Chemistry of Anticrowns. Synthesis and Structures of Double-Decker Sandwich Complexes of the Three-Mercury Anticrown (<i>o</i>‑C₆F₄Hg)₃ with Halide Anions Containing and Not Containing Coordinated Dibromomethane Molecules

The interaction of the three-mercury anticrown (<i>o</i>-C₆F₄Hg)₃ (<b>1</b>) with [PPh₄]­[BF₄] in methanol at room temperature leads to fluoride anion transfer from BF₄^– to <b>1</b> with the formation of a fluoride complex, [PPh₄]­{[(<i>o</i>-C₆F₄Hg)₃]₂F}, having a double-decker sandwich structure. The fluoride ion in this unique adduct is disposed between the mutually parallel planes of the central nine-membered rings of the anticrown units and cooperatively coordinated by all six Hg sites. The iodide anion also forms a double-decker sandwich in the interaction with <b>1</b>, but this sandwich, [PPh₄]­{[(<i>o</i>-C₆F₄Hg)₃]₂I}, has a wedge-shaped geometry. The reaction of <b>1</b> with [^<i>n</i>Bu₄N]Cl in dibromomethane at −15 °C affords a complex, [^<i>n</i>Bu₄N]­{[(<i>o</i>-C₆F₄Hg)₃]₂Cl­(CH₂Br₂)₂}, containing one chloride anion and two coordinated CH₂Br₂ species per two molecules of <b>1</b>. A similar bromide complex of <b>1</b>, containing two coordinated CH₂Br₂ moieties, has also been synthesized and structurally characterized. Both compounds represent wedge-shaped double-decker sandwiches wherein the halide anion is simultaneously bonded to all Hg centers of the anticrown molecules. The dibromomethane species in the isolated adducts are also arranged in the space between the mercuramacrocycles. One of these species is coordinated by each of its bromine atoms to a single Hg site of the adjacent macrocycle while the other interacts by only one bromine atom with a Hg center of the neighboring molecule of <b>1</b>

Coordination Chemistry of Anticrowns. Synthesis and Structures of Double-Decker Sandwich Complexes of the Three-Mercury Anticrown (<i>o</i>‑C₆F₄Hg)₃ with Halide Anions Containing and Not Containing Coordinated Dibromomethane Molecules

The interaction of the three-mercury anticrown (<i>o</i>-C₆F₄Hg)₃ (<b>1</b>) with [PPh₄]­[BF₄] in methanol at room temperature leads to fluoride anion transfer from BF₄^– to <b>1</b> with the formation of a fluoride complex, [PPh₄]­{[(<i>o</i>-C₆F₄Hg)₃]₂F}, having a double-decker sandwich structure. The fluoride ion in this unique adduct is disposed between the mutually parallel planes of the central nine-membered rings of the anticrown units and cooperatively coordinated by all six Hg sites. The iodide anion also forms a double-decker sandwich in the interaction with <b>1</b>, but this sandwich, [PPh₄]­{[(<i>o</i>-C₆F₄Hg)₃]₂I}, has a wedge-shaped geometry. The reaction of <b>1</b> with [^<i>n</i>Bu₄N]Cl in dibromomethane at −15 °C affords a complex, [^<i>n</i>Bu₄N]­{[(<i>o</i>-C₆F₄Hg)₃]₂Cl­(CH₂Br₂)₂}, containing one chloride anion and two coordinated CH₂Br₂ species per two molecules of <b>1</b>. A similar bromide complex of <b>1</b>, containing two coordinated CH₂Br₂ moieties, has also been synthesized and structurally characterized. Both compounds represent wedge-shaped double-decker sandwiches wherein the halide anion is simultaneously bonded to all Hg centers of the anticrown molecules. The dibromomethane species in the isolated adducts are also arranged in the space between the mercuramacrocycles. One of these species is coordinated by each of its bromine atoms to a single Hg site of the adjacent macrocycle while the other interacts by only one bromine atom with a Hg center of the neighboring molecule of <b>1</b>

Indenyl Rhodium Complexes with Arene Ligands: Synthesis and Application for Reductive Amination

An efficient protocol for synthesis of indenyl rhodium complexes with arene ligands has been developed. The hexafluoroantimonate salts [(η⁵-indenyl)­Rh­(arene)]­(SbF₆)₂ (arene = benzene (<b>2a</b>), <i>o</i>-xylene (<b>2b</b>), mesitylene (<b>2c</b>), durene (<b>2d</b>), hexamethylbenzene (<b>2e</b>), and [2.2]­paracyclophane (<b>2g</b>)) were obtained by iodide abstraction from [(η⁵-indenyl)­RhI₂]_<i>n</i> (<b>1</b>) with AgSbF₆ in the presence of benzene and its derivatives. The procedure is also suitable for the synthesis of the dirhodium arene complex [(μ-η:η′-1,3-dimesitylpropane)­{Rh­(η⁵-indenyl)}₂]­(SbF₆)₄ (<b>3</b>) starting from 1,3-dimesitylpropane. The structures of [<b>2e</b>]­(SbF₆)₂, [<b>2g</b>]­(SbF₆)₂, and [<b>3</b>]­(SbF₆)₄ were determined by X-ray diffraction. The last species has a sterically unfavorable conformation, in which the bridgehead carbon atoms of the indenyl ligand are arranged close to the propane linker between two mesitylene moieties. Experimental and DFT calculation data revealed that the benzene ligand in <b>2a</b> is more labile than that in the related cyclopentadienyl complexes [(C₅R₅)­Rh­(C₆H₆)]²⁺. Complex <b>2c</b> effectively catalyzes the reductive amination reaction between aldehydes and primary (or secondary) amines in the presence of carbon monoxide, giving the corresponding secondary and tertiary amines in very high yields (80–99%). This protocol is the most active in water

Indenyl Rhodium Complexes with Arene Ligands: Synthesis and Application for Reductive Amination

An efficient protocol for synthesis of indenyl rhodium complexes with arene ligands has been developed. The hexafluoroantimonate salts [(η⁵-indenyl)­Rh­(arene)]­(SbF₆)₂ (arene = benzene (<b>2a</b>), <i>o</i>-xylene (<b>2b</b>), mesitylene (<b>2c</b>), durene (<b>2d</b>), hexamethylbenzene (<b>2e</b>), and [2.2]­paracyclophane (<b>2g</b>)) were obtained by iodide abstraction from [(η⁵-indenyl)­RhI₂]_<i>n</i> (<b>1</b>) with AgSbF₆ in the presence of benzene and its derivatives. The procedure is also suitable for the synthesis of the dirhodium arene complex [(μ-η:η′-1,3-dimesitylpropane)­{Rh­(η⁵-indenyl)}₂]­(SbF₆)₄ (<b>3</b>) starting from 1,3-dimesitylpropane. The structures of [<b>2e</b>]­(SbF₆)₂, [<b>2g</b>]­(SbF₆)₂, and [<b>3</b>]­(SbF₆)₄ were determined by X-ray diffraction. The last species has a sterically unfavorable conformation, in which the bridgehead carbon atoms of the indenyl ligand are arranged close to the propane linker between two mesitylene moieties. Experimental and DFT calculation data revealed that the benzene ligand in <b>2a</b> is more labile than that in the related cyclopentadienyl complexes [(C₅R₅)­Rh­(C₆H₆)]²⁺. Complex <b>2c</b> effectively catalyzes the reductive amination reaction between aldehydes and primary (or secondary) amines in the presence of carbon monoxide, giving the corresponding secondary and tertiary amines in very high yields (80–99%). This protocol is the most active in water

Coordination Chemistry of Anticrowns. Isolation of the Chloride Complex of the Four-Mercury Anticrown {[(<i>o</i>,<i>o</i>′‑C₆F₄C₆F₄Hg)₄]Cl}⁻ from the Reaction of <i>o</i>,<i>o</i>′‑Dilithiooctafluorobiphenyl with HgCl₂ and Its Transformations to the Free Anticrown and the Complexes with <i>o</i>‑Xylene, Acetonitrile, and Acetone

The paper reports that the interaction of <i>o</i>,<i>o</i>′-dilithiooctafluorobiphenyl with HgCl₂ in ether results in the formation of the lithium chloride complex Li­{[(<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₄]­Cl} (<b>11</b>) of the four-mercury anticrown (<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₄ (<b>12</b>) along with the earlier isolated and characterized three-mercury anticrown (<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₃ (<b>2</b>). The complex was identified by the reaction with 12-crown-4 and determination of the structure of the [Li­(12-crown-4)₂]­{[(<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₄]­Cl} (<b>13</b>) formed. According to an X-ray analysis, the chloride anion in <b>13</b> is simultaneously coordinated with all four Hg centers of the anticrown, forming with them a pyramidal Hg₄Cl fragment. The reaction of <b>11</b> (in the form of an acetonitrile solvate, <b>11</b>·<i>n</i>MeCN) with boiling water leads to removal of LiCl from <b>11</b> and to the formation of free anticrown <b>12</b>, the subsequent recrystallization of which from <i>o</i>-xylene affords the <i>o</i>-xylene complex {[(<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₄]­(<i>o</i>-Me₂C₆H₄)₂} (<b>14</b>). The obtained <b>14</b> forms in the crystal infinite chains consisting of alternating anticrown units and bridging <i>o</i>-xylene moieties. Another <i>o</i>-xylene molecule in each macrocyclic fragment of the chain plays the role of a terminal ligand. In both cases, the <i>o</i>-xylene ligands in <b>14</b> are bonded to only one Hg center of the corresponding mercuramacrocycle. The back-conversion of complex <b>14</b> into <b>12</b> and <i>o</i>-xylene proceeds in the course of its thermal decomposition under vacuum at 100–120 °C. The reaction of <b>12</b> with acetonitrile yields the nitrile complex {[(<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₄]­(MeCN)₂} (<b>15</b>), which also forms infinite polymeric chains in the crystal. In each monomeric unit of the chain, the corresponding bridging nitrile is bonded to only one mercury atom of the anticrown moiety, whereas the other nitrile ligand is coordinated with two Hg sites. The synthesis and structure of the complex {[(<i>o</i>,<i>o</i>′-C₆F₄C₆F₄Hg)₄]­(Me₂CO)₂(H₂O)} (<b>16</b>), containing two acetone and one water ligand per molecule of <b>12</b>, are also reported. Each acetone molecule in <b>16</b> interacts with only one Hg atom of <b>12</b>, while the water molecule is coordinated with two mercury centers and, in addition, forms H-bonds with the oxygen atoms of the acetone species

Highly Cytotoxic Palladium(II) Pincer Complexes Based on Picolinylamides Functionalized with Amino Acids Bearing Ancillary <i>S</i>‑Donor Groups

The reactions of picolinyl and 4-chloropicolinyl chlorides with methyl esters of <i>S</i>-methyl-l-cysteine, l- and d-methionine, and l-histidine afforded a series of functionalized carboxamides, which readily formed pincer-type complexes upon interaction with PdCl₂(NCPh)₂ in solution under mild conditions. The direct cyclopalladation of the ligands derived was also accomplished in the solid phase, in particular, mechanochemically, although it was complicated by the partial deactivation of the starting amides. The resulting complexes with 5,5- and 5,6-membered fused metallocycles were fully characterized by IR and NMR spectroscopy, including variable-temperature and 2D-NMR studies. In the case of some cysteine- and methionine-based derivatives, the realization of κ³-<i>N,N,S-</i>coordination was supported by X-ray diffraction. The cytotoxic effects of these complexes were examined on HCT116, MCF7, and PC3 human cancer cell lines as well as HEK293 as a representative of normal cells. The comparative studies allowed us to determine that the presence of the sulfide ancillary donor group is crucial for cytotoxic activity of this type of Pd­(II) complexes. The main structure–activity relationships and the most promising palladocycles were outlined. The additional studies by gel electrophoresis revealed that 4-chloropicolinyl derivatives, despite the nature of an amino acid, can bind with DNA and inhibit topoisomerase I activity

Polyphenylenepyridyl Dendrons with Functional Periphery and Focal Points: Syntheses and Applications

For the first time we report syntheses of a family of functional polyphenylenepyridyl dendrons with different generations and structures such as focal groups, periphery, and a combination of phenylene and pyridyl moieties in the dendron interior using a Diels–Alder approach and a divergent method. The dendron structure and composition were confirmed using NMR spectroscopy, MALDI-TOF mass spectrometry, FTIR, and elemental analysis. As a proof of concept that these dendrons can be successfully used for the development of nanocomposites, synthesis of iron oxide nanoparticles was carried out in the presence of thermally stable dendrons as capping molecules followed by formation of Pd NPs in the dendron shells. This resulted in magnetically recoverable catalysts exhibiting exceptional performance in selective hydrogenation of dimethylethynylcarbinol (DMEC) to dimethylvinylcarbinol (DMVC)