Cationic Olefin Research Articles

Unusual solidification and phosphate binding to benzimidazole cations in the presence of water

Reaction of bis(benzimidazolonium)alkane cations with phosphate ions in aqueous medium leads to the formation of solid masses with a water content as high as 99%. Optical microscopy shows this to arise from formation of a network of fibrous crystals. A crystal structure determination suggests this to arise from the coincidence of the directions of hydrogen bonding interactions between phosphate anions and stacking interactions between benzimidazole cations. Potentiometric titrations show that phosphate binds to benzimidazole cations in 50% aqueous alcohol solution at pH 7. It is argued that this is a reflection of the importance of matching the pKa values of hydrogen bond donors and acceptors. In the case of favourable matching, hydrogen bond donors can successfully compete for anions with water.

Activation of ketones by electrophilic metal complexes: Synthesis of some ketonyl platinum(II) complexes and X-ray crystal structure of [PtCl{CH2C(O)CH3}(1,10-phenanthroline)]·1/2Y (Y = H2O or CH2Cl2)

Cationic olefin complexes of platinum(II), [PtCl(η2-olefin)(N–N)]+, when the chelate ligand is an aromatic di-imine smoothly react with α-methyl ketones (CH3C(O)R) in acidic conditions to quantitatively form the ketonyl species [PtCl{CH2C(O)R}(N–N)] with elimination of the olefin and of a proton. In contrast, when N–N is an aliphatic diamine the reaction does not occur. The obtained ketonyl complexes (N–N=1,10-phenanthroline, R=CH3, 1, or CH2CH3, 1′; N–N=2,2′-bipyridyl, R=CH3, 2, or CH2CH3, 2′) have been fully characterized via elemental analysis, ESI-MS, and 1H NMR. Crystals of 1, grown from un-dried acetone or dichloromethane, were yellow and dark orange, respectively; both contained a molecule of solvent (water in the yellow form) per two molecules of complex. The dark orange crystals are luminescent at room temperature and, upon heating (above 384K), they lose the solvent molecule and change into an amorphous yellow powder. In both crystals the molecules form stacked columnar arrays. In the yellow form the column axis is tilted from the normal to the phenanthroline planes by 27.38°; the interplanar distances are alternately 3.434 and 3.488Å, while the Pt···Pt distances are 4.4787(7) and 6.4132(8)Å, respectively. In the dark orange form the column axis is nearly perpendicular to the planes of the complexes; the interplanar distances are alternatively ∼3.40 and 3.52Å, while the Pt···Pt distances are 3.4022(2) and 7.6533(2)Å, respectively.

1,ω-Bis(pyridinium)alkane Cation as Templates for the Self-Assembly of the Mo(W)/S/Cu Polymeric Clusters

Self-assembly of a series of effective cation-templates with [Mo(W)/Cu/S]-based clusters was studied. Permanent templated products {(bppp)[MoOS3Cu3I3(4,4′-bipy)1.5]}n (1), {(bpbt)[MoOS3Cu3I3(4,4′-bipy)1.5]}n (2), {(bppp)[WOS3Cu3I3(4,4′-bipy)1.5]}n (3), and {(bpbt)[WOS3Cu3Br3(4,4′-bipy)1.5]}n (4) show 1D anionic zigzag pattern (bppp = 1,3-bis(pyridinium) propane, bpbt = 1,4-bis(pyridinium) butane). Compounds 1–4 have been characterized by single-crystal X-ray diffraction, elemental analysis, IR, UV–vis and thermogravimetric Analysis. The results may provide fascinating insights into template effects on the construction of the cluster-based coordination polymers and that coordination modes of compounds 3 and 4 have not been found in the reported one-dimensional zigzag coordination polymers.

Product and mechanistic analysis of the reactivity of a C6-pyrimidine radical in RNA.

Nucleobase radicals are the major reactive intermediates produced when hydroxyl radical reacts with nucleic acids. 5,6-Dihydrouridin-6-yl radical (1) was independently generated from a ketone precursor via Norrish Type I photocleavage in a dinucleotide, single-stranded, and double-stranded RNA. This radical is a model of the major hydroxyl radical adduct of uridine. Tandem lesions resulting from addition of the peroxyl radical derived from 1 to the 5'-adjacent nucleotide are observed by ESI-MS. Radical 1 produces direct strand breaks at the 5'-adjacent nucleotide and at the initial site of generation. The preference for cleavage at these two positions depends upon the secondary structure of the RNA and whether O(2) is present or not. Varying the identity of the 5'-adjacent nucleotide has little effect on strand scission. In general, strand scission is significantly more efficient under anaerobic conditions than when O(2) is present. Strand scission is more than twice as efficient in double-stranded RNA than in a single-stranded oligonucleotide under anaerobic conditions. Internucleotidyl strand scission occurs via β-fragmentation following C2'-hydrogen atom abstraction by 1. The subsequently formed olefin cation radical ultimately yields products containing 3'-phosphate or 3'-deoxy-2'-ketouridine termini. These end groups are proposed to result from competing deprotonation pathways. The dependence of strand scission efficiency from 1 on secondary structure under anaerobic conditions suggests that this reactivity may be useful for extracting additional RNA structural information from hydroxyl radical reactions.

Formation of novel Olefin–Copper(I) coordination compound dependent on conformation of Olefin ligand

Solvothermal treatments of (E)-1,3-diallyl-2-styryl-3 H -benzo[d]imidazol-1-ium bromide olefin ligand 1 and CuX (X═Br, 2 and X═Cl, 3) in the presence of methanol as solvent at 75 °C for 1 week offer organic–inorganic hybrid compound 2 and olefin–copper(I) compound 3. The conformation of olefin cation ligand affects the coordination of allyl group. Two allyl groups existing at different sides of benzoimidazole plane successfully coordinate to copper(I) centers to form olefin–copper(I) coordination compound 3, which shows two-dimensional structure of (4,4) network with [Cu6Cl4Br4]2− cluster nods. The dielectric measurement results show there is no dielectric anomaly observed within the temperature range of 120 K to 300 K for compound 3.

Geometric Effects in Olefinic Cation−π Interactions with Alkali Metals: A Computational Study

Although cation-π interactions commonly involve aromatic or heteroaromatic rings as the source of π-electrons, isolated and nonconjugated olefins are equally effective donors of π-electron density. Previous comparisons of these π-electron sources have indicated that the net energy of the binding interactions is not a simple additive function of the number of π-bonds involved. For instance, the enthalpy of binding (ΔH°) of Li(+), Na(+), or K(+) cations to two ethylene molecules or to one benzene molecule is approximately the same, despite the 4:6 ratio of π-electrons involved. This present density functional theory study indicates that geometric factors can partially account for the proportionally greater interaction energies of olefins, but whether they are symmetrically placed around the cation or grouped on one hemisphere has little effect on the binding energy. Instead, flexible ligands that permit olefinic π-electrons to be oriented more favorably toward the metal than those in rigid aromatic rings can be correlated with greater bonding. For Li(+) complexes, this appears to be an appreciable factor, although it is less significant with Na(+) and K(+) complexes. For all three cations, stronger polarization interactions with olefins compared to arenes contribute to the strength of cation-π interactions involving olefinic π-bonds.

Deprotonation versus Nucleophilic Substitution in Some Platinum(II) Coordinated Olefins Containing an Electron Withdrawing Group

Two new cationic olefin complexes of platinum(II) with electron-withdrawing substituents on the allylic carbon, [PtCl(η2-CH2═CHCH2X)(tmeda)]+ (X = −C(O)OCH3 (1a), −OC(O)CH3 (1b)) have been synthesized and their reactivity toward nucleophiles investigated. The reaction of 1a with various nucleophiles, including water, causes allylic deprotonation and formation of the η3-allyl complex [Pt{η3-CH2CHCHC(O)OCH3}(tmeda)]+ (4a). In nonaqueous media it was possible to identify also a transient alkenyl species, [PtCl{η1-CH═CHCH2C(O)OCH3}(tmeda)] (2a), formed by loss of a vinylic proton. In contrast, the reaction of 1b with nucleophiles does not lead to deprotonation but to substitution of the acetate group followed by addition to the olefinic double bond. The latter can be intramolecular, as in the case of acetylacetonate, leading to [PtCl{η1-CH2CHCH2C[C(O)CH3]═C(CH3)O}(tmeda)] (5b) or requires a second molecule of nucleophile, as in the case of secondary amines, leading to the Markovnikov and anti-Markovnikov addi...

西沢麦夫博士を偲んで：人との出会い，研究テーマとの巡り会い

Dr. Mugio Nishizawa, Professor of Tokushima Bunri University, passed away on May 1, 2010. After his Japan Pharmaceutical Society Award receiving party on April 17, he appeared to be slightly recovered from the spread of cancer metastasis that was in the terminal stage. However, he became seriously ill and died leaving his last words, “Thank you for meeting with people and research projects”. He made significant contributions to natural products chemistry as well as synthetic organic chemistry represented by his cationic olefin cyclization, mercuric triflate-catalyzed organic synthesis, and the development of the immuno-activating TDCM for anti-cancer agent. Furthermore, he left many nice memories of his charming personality. In this issue, a brief review of Dr. Nishizawa’s chemistry and career is presented.

Coupling of cationic olefin complexes of platinum(II) with potential ambident nucleophiles

Cationic complexes [PtCl(η 2 -CH 2 CHR)(tmeda)] + (R = H, 1a , or Me, 1b ) have shown a different reactivity towards aromatic nucleophiles: 1a couples both with the heteroatom and a ring carbon, while, in the same experimental conditions, 1b undergoes only deprotonation. The reactivity of [PtCl(η 2 -CH 2 CHR)(tmeda)] + (R = H, 1a , or Me, 1b ; tmeda = N,N,N ′ ,N ′-tetramethyl-1,2-diaminoethane) towards some ambident nucleophiles like anilines and phenolate anion has been tested. The reaction of 1a with N -methylaniline gives immediately N -addition to the coordinated ethene ( 3a ), but, in the presence of an inorganic carbonate, a partial rearrangement, with the para carbon of the phenyl ring taking the place of nitrogen, is observed ( 4a and 5a ). Reaction with a tertiary aromatic amine, such as N,N -dimethylaniline, leads exclusively to the C -coupled species. The phenolate anion acts initially as an oxygen donor, however the resulting species ( 6a ), in contact with free phenol, rearranges to C -bonded species ( 7a ). For free phenol/ 6a ratios ⩾ 5 the rearranged product has an isomeric ortho / para ratio of ≈3. For lower free phenol/ 6a ratios (⩽ 1) oligomeric complexes, in which two or three platinum ethanide moieties are bound to the same phenol ring, are also formed. In the case of 1b , the above described reactivity has to compete with the base-induced deprotonation of propene, leading to formation of the allyl-bridged platinum dimer [{PtCl(tmeda)}(μ-η 1 :η 3 -CHCHCH 2 ){Pt(tmeda)}] + . The X-ray crystal structure of 1b has also been determined; the structural parameters are very similar to those previously reported for 1a . DFT calculations have shown a similar activation of the two complexes towards nucleophilic addition at the coordinated olefin, although in 1b the electrophilic character of the olefin is masked by the Brønsted acidity of the propene methyl protons.

Ion Pairing in Cationic Olefin−Gold(I) Complexes

The relative anion-cation orientation in [(PPh(3))Au(4-Me-styrene)]BF(4) (1BF(4)) and [(NHC)Au(4-Me-styrene)]BF(4) [2BF(4); NHC = 1,3-bis(di-iso-propylphenyl)-imidazol-2-ylidene] has been investigated by combining (19)F,(1)H-HOESY NMR spectroscopy and Density Functional Theory (DFT) calculations incorporating solvent and relativistic effects. It has been found that BF(4)(-) locates on the side of 4-Me-styrene, close to the olefin region that is opposite to the 4-Me-Ph moiety in 1BF(4). In 2BF(4), the counterion approaches the cation from the side of the NHC ligand and is mainly located close to the imidazole ring. In both cases, the counterion resides far away from the gold site, the latter carrying only a small fraction of the positive charge. This indicates that the preferential position of the counterion is tunable through the choice of the ancillary ligand, and this opens the way to greater control over the properties and activity of these catalysts.

A Systematic Design and Facile Construct of Metal Pseudohalide Frameworks Directed By 1,ω-Bis(pyridinium)alkane Cations

Cation-templated self-assembly of 1,ω-bis(pyridinium)alkanes (ω = 1−6) with cuprous thiocyanate was studied, and six sparse polymeric thiocyanate frameworks were obtained and characterized by X-ray crystallography: {(bpm)[Cu(NCS)4]}n (1), {(bpe)[Cu2(NCS)4]}n (2), {(bppp)[Cu(NCS)3]}n (3), {(bpbt)[Cu(NCS)4]}n (4), {(bppt)[Cu2(NCS)4]}n (5), and {(bph) [Cu2(NCS)4]}n (6) (bpm = 1,1′-bis(pyridinium)methylene, bpe = 1,2-bis(pyridinium)ethane, bppp = 1,3-bis(pyridinium)propane, bpbt = 1,4-bis(pyridinium)butane, bppt = 1,5-bis(pyridinium)pentane, bph = 1,6-bis(pyridinium) hexane). The structures consist of 0−3-dimensional frameworks with the bispyridinium cations trapped within host network cavities. Compound 1 has a 3D porous (6,3)/(6,4) joint topology structure, compounds 2 and 5 have two-dimensional polypseudorotaxane interlocked structures, compound 3 has a dimeric structure, compound 4 has a two-dimensional honeycomb structure, and compound 6 exhibits an interesting 1D hanging ladder-shaped complementary chain structure. The third-order NLO effect of 3 was studied by Z-scan techniques. The dimer exhibits self-focusing optical nonlinearities, and the effective third-order NLO refractive index (n2) value is 3.03 × 10−11 esu.

Selective Cationic Cyclizations with α-Pyrones as Terminators

The process of the cationic olefin cyclization of 3-sub­stituted 4-hydroxy-2H-pyran-2-ones 3 that may produce both trans- and cis-pyrano[4,3-b]chromen-1-ones (4) and trans- and cis-pyrano[2,3-b]chromen-4-ones (5) can be efficiently controlled by properly choosing reagents and reaction conditions. The highly ­selective formation of trans-4 can be achieved with Et2AlCl as a Lewis acid. Preferred formation of cis-4 is observed with PTSA ­under microwave conditions at high temperatures. PTSA and low temperatures produce cis-5 in excess.

Stereoselectivity in a Chiral Ruthenium Ethylene Hydride Complex: Evidence of an Agostic Intermediate

Treatment of Ru(η6:η1-Me2NC6H4C6H4PCy2)Cl2 with MeLi resulted in the formation of Ru(η6:η1-Me2NC6H4C6H4PCy2)Me2, which reacted with Ph3CPF6 to form the cationic olefin hydride complex [Ru(η6:η1-Me2NC6H4C6H4PCy2)(H2CCH2)(H)]PF6. The new complexes were characterized by spectroscopy and by X-ray crystallographic analysis. The diastereomeric olefin hydride complexes were observed to exhibit two fluxional processes: a facile olefin rotation and another process that results in the exchange of the hydride and olefin protons. As the rate of diastereomer interconversion is much slower than that of olefin insertion, our studies suggest that the latter exchange takes place through an agostic species which undergoes dynamic methyl rotation.

Synthesis and characterisation of aluminophosphate-based zeotype materials prepared with α,ω-bis(N-methylpyrrolidinium)alkane cations as structure-directing agents

New routes to the preparation of two families of small pore microporous solids are described. Flexible diquaternary alkyl ammonium cations (C4H8)CH3N+(CH2)nN+CH3(C2H8), n = 3–5, have been found to act as structure directing agents in the synthesis of aluminophosphate-based materials of the ABC-6 group. The templates exhibit considerable selectivity in crystallising phases of the ERI or AFX-type (MeAPO-17 or MeAPO-56, respectively) from a wide variety of metalloaluminophosphate gels (Me = Mg2+, Co2+ or Si4+). For example, from gels containing Mg/P = 0–0.25, 1,4-bis(N-methylpyrrolidinium)butane cations gave MgAPO-17, and 1,5-bis(N-methylpyrrolidinium)pentane cations gave MgAPO-56. Notably, materials could be prepared with levels of metal-substitution tailored to a high degree and distributed non-randomly within the framework. As-prepared solids have been characterised by powder XRD, multinuclear solid state NMR, FT-IR, SEM, and thermal and elemental analysis.

Cationic olefin Pd(II) complexes bearing α-iminoketone N,O-ligands: synthesis, intramolecular and interionic characterization and reactivity with olefins and alkynes

Complexes [Pd(η 1, η 2-5-OMe–C 8H 12)(N,O)]BF 4 (N,O=2,6-( i-Pr) 2(C 6H 3)NC(Ph)–C(Ph)O, 1; 2,6-( i-Pr) 2(C 6H 3)NC(Me)–C(Ph)O, 2; 2-benzoylpyridine, 3) were synthesized by the reactions of [Pd(η 1,η 2-5-OMe–C 8H 12)Cl] 2 with the suitable N,O-ligand. They were tested as catalysts for olefin or alkyne polymerizations. During such reactions 1– 3 quantitatively transformed into their η 1,η 2-1-OMe–C 8H 12 isomers ( 1a– 3a). The same isomerization occurred in methylene chloride, even in the absence of olefins or alkynes, with a much slower rate. All complexes were fully characterized in solution by multinuclear and multidimensional low temperature NMR spectroscopy. The solid state structures of complexes 1 and 1a were investigated by X-ray single crystal studies. 19F, 1H-HOESY NMR experiments carried out in methylene chloride-d 2 at 217 K indicated that the anion prefers to locate on the side of N,O-ligand shifted toward the O-arm in 1– 1a and 2– 2a while it approaches the N-arm in 3 and 3a compounds.

A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

A large class of stereochemcial and related interactions in organic chemistry are repulsive and others are attractive, but the relative orientation of two methyl groups and the amount of energy required to twist one relative to the other (the hindered rotation energy barriers), or the alignment of such a group with respect to a conjugated ring to which it is attached (widely attributed to a mechanism called “hyperconjugation”) are estimated to be small in compared with the total energy of the molecule. We used theories of both isotropic and anisotropic proton hyperfine interactions in the π-electron systems developed in the early sixties. They are approximated by the magnetic dipole nteractions between each proton and an electron spin magnetization that is distributed in 2s and 2p Slater atomic orbitals center on carbon atoms. We have extended these theories to the non-planar olefinic cation radicals, which are very important in biochemistry as well as in petroleum catalysis. A three dimensional electron spin density equation has been developed in this paper to handle some Jahn-Teller vibronic molecules. The new electron spin density equation related the observed proton hyperfine splittings to the non-planar structures of the open-chain alkene cation radicals generated by radiolysis and various chemical oxidation methods. The spin densities and the conformational calculations based on valence bond theory and symmetry principles are compared with some more elaborated molecular orbital calculations in the literature. The localized valence bond approaches are better in accord with our experimental results. The anomalous line-width effect of the four methyl groups observed in the 2,3-dimethyl-2-butene cation radicals also confirmed the positive sign of the electron-proton hyperfine constant of hyper-conjugation mechanism. A methyl substituent attached to a conjugated molecule often behaves as if it formed part of the region of conjugation; the charge appears to flow from the methyl group into the π electron system and it may also give rise to an appreciable dipole moment. Methylation also gives rise to an appreciable dipole moment, and the resultant red shift of electronic absorption bands is of some importance in the design of dye molecules.

New Cationic Olefin Cyclization—Pinacol Reactions. Ring‐Expanding Cyclopentane Annulations that Directly Install Useful Functionality in the Cyclopentane Ring.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and odor of optically active trans-2,2,6-trimethylcyclohexyl methyl ketones and their related compounds

The synthesis characterized by cationic olefin cyclizations accomplished using ketone enol esters and odor of novel (1 R,6 S)- and (1 S,6 R)-2,2,6-trimethylcyclohexyl methyl ketones ( 5 ) are described. The stereoselective syntheses of ( E)-(1 R,6 S)- and ( E)-(1 S,6 R)-1-(2,2,6-trimethylcyclohexyl)-2-buten-1-one ( 6 ) and (1 R,6 S)-ethyl 2,2,6-trimethylcyclohexylcarboxylate ( 7 ), useful raw materials for flavor and fragrance, starting from the (1 R,6 S)- and (1 S,6 R)- 5 are also described.

New cationic olefin cyclization-pinacol reactions. Ring-expanding cyclopentane annulations that directly install useful functionality in the cyclopentane ring.

Two new tandem cationic olefin cyclization-pinacol reactions that provide cyclopentane-fused cycloalkanone products are described. Treatment of cis-1-[2-alkenyl-2-(triethylsiloxy)cycloalkyl]but-3-en-2-ol derivatives 21-24 with triflic anhydride at -78 degrees C affords cycloalkanones 31-34 in 54-90% yields with diastereoselectivities of typically >20:1. In this unusual transformation, the starting cycloalkanone is ring-expanded and fused to a 2-alkenylcyclopentane fragment. Reaction of cis-(2-siloxy-2-alkenylcycloalkyl)pyrrolidin-1-ylethanones 15-17 with triflic anhydride and 2,6-di-tert-butyl-4-methylpyridine (DTBMP) at -20 to +65 degrees C followed by hydrolysis of the intermediate iminium salts 64 with aqueous KHCO(3) affords cycloalkanediones 46-48 in moderate yield and high diastereoselectivity (>20:1). These are the first examples of ring-expanding cyclopentane annulations that directly introduce a carbon side chain or carbonyl functionality at the cyclopentane C2 position. The high diastereoselectivities observed in these reactions are believed to arise from reaction through highly organized cyclic transition states.

Structural Characterization of a Cationic Zirconocene Olefin Polymerization Catalyst with its Methylated Boralumoxane Counterion Netherlands Institute for Catalysis Research (NIOK) publication RUG 02-04-01.

Structural Characterization of a Cationic Zirconocene Olefin Polymerization Catalyst with its Methylated Boralumoxane Counterion Netherlands Institute for Catalysis Research (NIOK) publication RUG 02-04-01.