Synthesis,Structural Characterization,Photophysics, and Broadband Nonlinear Absorption of a Platinum(II) Complex with the 6‐(7‐Benzothiazol‐2′‐yl‐9,9‐diethyl‐9 H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl Ligand

A platinum complex with the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl ligand ( 1 ) was synthesized and the crystal structure was determined. UV/Vis absorption, emission, and transient difference absorption of 1 were systematically investigated. DFT calculations were carried out on 1 to characterize the electronic ground state and aid in the understanding of the nature of low‐lying excited electronic states. Complex 1 exhibits intense structured ¹π–π* absorption at λ_abs<440 nm, and a broad, moderate ¹M LCT/¹LLCT transition at 440–520 nm in CH₂Cl₂ solution. A structured ³π–π*/³M LCT emission at about 590 nm was observed at room temperature and at 77 K. Complex 1 exhibits both singlet and triplet excited‐state absorption from 450 nm to 750 nm, which are tentatively attributed to the ¹π–π* and ³π–π* excited states of the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridine ligand, respectively. Z‐scan experiments were conducted by using ns and ps pulses at 532 nm, and ps pulses at a variety of visible and near‐IR wavelengths. The experimental data were fitted by a five‐level model by using the excited‐state parameters obtained from the photophysical study to deduce the effective singlet and triplet excited‐state absorption cross sections in the visible spectral region and the effective two‐photon absorption cross sections in the near‐IR region. Our results demonstrate that 1 possesses large ratios of excited‐state absorption cross sections relative to that of the ground‐state in the visible spectral region; this results in a remarkable degree of reverse saturable absorption from 1 in CH₂Cl₂ solution illuminated by ns laser pulses at 532 nm. The two‐photon absorption cross sections in the near‐IR region for 1 are among the largest values reported for platinum complexes. Therefore, 1 is an excellent, broadband, nonlinear absorbing material that exhibits strong reverse saturable absorption in the visible spectral region and large two‐photon‐assisted excited‐state absorption in the near‐IR region.     

A density functional study of 1,1,5‐tris(4‐dimethylaminophenyl)‐3‐methyl‐divinylene

The optimized molecular structural parameters and UV‐vis, IR and Raman spectra of a dye molecule with an open formula of 1,1,5‐Tris(4‐dimethylaminophenyl)‐3‐methyl‐divinylene are determined by means of density functional theory (DFT) calculations using B3LYP/6‐31G** formalism. Neutral and cationically charged molecules are used for DFT computations. C? C, C?C, and N? C bond distances of dimethylaminophenyl groups of the dye molecule are in reasonable agreement with the experimental and theoretical C? C, C?C, and N? C bond lengths of the group reported in the literature. Because Vis‐NIR region is near UV‐Vis region in the electromagnetic spectra, calculated maximum wavelengths of UV‐vis spectra are close to those of the experimental VIS‐NIR spectra reported. C?C stretching frequencies calculated for dimethylaminophenyl, alkene, and benzene ring groups are also in good agreement with experimentally reported values. All calculated frequencies fall within 2.2% of the experimental frequency region. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

1‐Carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium chloride 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate monohydrate: a crystal stabilized by imidazolium zwitterions

The title compound, C₆H₉N₂O₂⁺·Cl⁻·C₆H₈N₂O₂·H₂O, contains one 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate inner salt molecule, one 1‐carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium cation, one chloride ion and one water molecule. In the extended structure, chloride anions and water molecules are linked via O—H...Cl hydrogen bonds, forming an infinite one‐dimensional chain. The chloride anions are also linked by two weak C—H...Cl interactions to neighbouring methylene groups and imidazole rings. Two imidazolium moieties form a homoconjugated cation through a strong and asymmetric O—H...O hydrogen bond of 2.472 (2) Å. The IR spectrum shows a continuous D‐type absorption in the region below 1300 cm⁻¹ and is different to that of 1‐carboxymethyl‐3‐methylimidazolium chloride [Xuan, Wang & Xue (2012). Spectrochim. Acta Part A, 96 , 436–443].     

Ferromagnetic Interactions in a 1D Alternating Linear Chain of π‐Stacked 1,3‐Diphenyl‐7‐(thien‐2‐yl)‐1,4‐dihydro‐1,2,4‐benzotriazin‐4‐yl Radicals

X‐ray studies show that 1,3‐diphenyl‐7‐(thien‐2‐yl)‐1,4‐dihydro‐1,2,4‐benzotriazin‐4‐yl ( 6 ) adopts a distorted, slipped π‐stacked structure of centrosymmetric dimers with alternate short and long interplanar distances (3.48 and 3.52 Å). Cyclic voltammograms of 7‐(thien‐2‐yl)benzotriazin‐4‐yl 6 show two fully reversible waves that correspond to the ?1/0 and 0/+1 processes. EPR and DFT studies on radical 6 indicate that the spin density is mainly delocalized over the triazinyl fragment. Magnetic susceptibility measurements show that radical 6 obeys Curie–Weiss behavior in the 5–300 K region with C=0.378 emu K mol^?1 and θ=+4.72 K, which is consistent with ferromagnetic interactions between S=1/2 radicals. Fitting the magnetic susceptibility revealed the behavior is consistent with an alternating ferromagnetic chain (g=2.0071, J₁=+7.12 cm^?1, J₂=+1.28 cm^?1).     

Aggregation behavior of poly(γ‐benzyl‐L‐glutamate)‐b‐polyisoprene‐b‐poly(γ‐benzyl‐L‐glutamate) rod‐coil‐rod triblock copolymer in N,N‐dimethylformamide

Solution property of poly(γ‐benzyl‐L ‐glutamate)‐b‐polyisoprene‐b‐poly(γ‐benzyl‐L ‐glutamate) (GIG copolymer) was studied by using dynamic light scattering and static light scattering for N,N‐dimethylformamide (DMF) solution and DMF/toluene mixed solutions. GIG copolymer proved to aggregate in DMF and under DMF‐rich condition, that is, high‐polar region. The aggregate decreased in size, and completely disappeared under toluene‐rich condition, that is, low‐polar region. The correlation between solubility parameter and aggregate size of GIG copolymer in the DMF/toluene solution systems quantitatively demonstrated how strongly polarity caused by hydrogen bond made an impact on the aggregation behavior. Because the main driving force to the aggregation under DMF‐rich condition originates with polyisoprene (PIP) blocks, the aggregate in DMF is considered to be a core‐shell micelle consisting of flexible PIP core surrounded by rigid poly(γ‐benzyl‐L ‐glutamate) (PBLG) shell. The values of dimensionless parameter ρ, defined as the ratio of radius of gyration 〈S²〉^1/2 to hydrodynamic radius R_H, revealed that a single chain of GIG copolymer had the form of rigid rod with flexibility, that is, once‐broken rod, caused by the incorporation of a flexible PIP chain between two rigid PBLG rods in the DMF/toluene solution system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1740–1748, 2010     

Synthesis and photophysical properties of novel amphiphilic ruthenium (II) complexes containing 4,4′‐dialkylaminomethyl‐2,2′‐bipyridyl ligands

The synthesis of a number of new 2,2′‐bipyridine ligands functionalized with bulky amino side groups is reported. Three homoleptic polypyridyl ruthenium (II) complexes, [Ru(L)₃]²⁺ 2(PF₆^?), where L is 4,4′‐dioctylaminomethyl‐2,2′‐bipyridine (Ru4a), 4,4′‐didodecylaminomethyl‐2,2′‐bipyridine (Ru4b) and 4,4′‐dioctadodecylaminomethyl‐2,2′‐bipyridine (Ru4c), have been synthesized. These compounds were characterized and their photophysical properties examined. The electronic spectra of three complexes show pyridyl π → π* transitions in the UV region and metal‐to‐ligand charge transfer bands in the visible region. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydrogen‐bonded network in biphenyl‐4,4′‐diphosphonic acid

The crystal structure of the title compound, C₁₂H₁₂O₆P₂, displays two different regions alternating along the a axis: a hydrogen‐bonded region encompassing the end‐positioned phosphonic acid groups and a hydrophobic region formed by the aromatic spacers. The asymmetric unit contains only half of the biphenyl‐4,4′‐diphosphonic acid (4,4′‐bpdp) molecule, which is symmetric with an inversion centre imposed at the mid‐point between the two aromatic rings. The periodic organization of the molecules is controlled by two strong O—H...O interactions between the phosphonic acid sites. Weak C—H...π interactions are established in the aromatic regions.     

NIR‐Absorbing Donor–Acceptor Based 1,1,4,4‐Tetracyanobuta‐1,3‐Diene (TCBD)‐ and Cyclohexa‐2,5‐Diene‐1,4‐Ylidene‐Expanded TCBD‐Substituted Ferrocenyl Phenothiazines

A series of unsymmetrical (D‐A‐D₁, D₁‐π‐D‐A‐D₁, and D₁‐A₁‐D‐A₂‐D₁; A=acceptor, D=donor) and symmetrical (D₁‐A‐D‐A‐D₁) phenothiazines ( 4 b , 4 c , 4 c′ , 5 b , 5 c , 5 d , 5 d′ , 5 e , 5 e′ , 5 f , and 5 f′ ) were designed and synthesized by a [2+2] cycloaddition–electrocyclic ring‐opening reaction of ferrocenyl‐substituted phenothiazines with tetracyanoethylene (TCNE) and 7,7,8,8‐tetracyanoquinodimethane (TCNQ). The photophysical, electrochemical, and computational studies show a strong charge‐transfer (CT) interaction in the phenothiazine derivatives that can be tuned by varying the number of TCNE/TCNQ acceptors. Phenothiazines 4 b , 4 c , 4 c′ , 5 b , 5 c , 5 d , 5 d′ , 5 e , 5 e′ , 5 f and 5 f′ show redshifted absorption in the λ =400 to 900 nm region, as a result of a low HOMO–LUMO gap, which is supported by TD‐DFT calculations. The electrochemical study exhibits reduction waves at low potential due to strong 1,1,4,4‐tetracyanobuta‐1,3‐diene (TCBD) and cyclohexa‐2,5‐diene‐1,4‐ylidene‐expanded TCBD acceptors. The incorporation of cyclohexa‐2,5‐diene‐1,4‐ylidene‐expanded TCBD stabilized the LUMO energy level to a greater extent than TCBD.     

The Synthesis of 2‐(Chromon‐2/3‐yl)‐3‐(5‐thione‐4‐hydro‐1,3,4‐thiadiazol‐2‐yl)‐4‐oxo‐thiazolidine

2‐Formylchromones and 3‐formylchromones as the first materials singly reacted with 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole to give the corresponding Schiff bases, which on cyclocondensation with mercapto‐acetic acid in 1,4‐dioxane yielded target compounds named 4‐oxo‐thiazolidines. The structures of all the synthetic compounds were confirmed by elemental analysis and IR, ¹H NMR, LC‐MS (ESI) spectral data.     

Synthesis and antibacterial activity of 2‐alkylcarbamato/trichloromethyl/chloroethoxy/aryloxy‐1,2,3,4‐tetrahydro‐1,3,2‐benzodiazaphosphorine 2‐oxides

Several 2‐trichloromethyl/2‐chloro‐ethoxy/2‐aryloxy‐1,2,3,4‐tetrahydro‐1,3,2‐benzodiaza‐phosphorine 2‐oxides ( 4a–d ), and 2‐alkyl/alkenyl/alkynylcarbamato 2‐oxides ( 7a‐f ) have been synthesized from reactions of equimolar quantities of 2‐aminobenzylamine ( 2 ) with various aryl or alkyl phosphorodichloridates ( 3b–d ), trichloromethylphosphonic dichloride ( 3a ) and dichlorophosphinyl carbamates ( 6a–f ) at 40–50°C in dry toluene in the presence of triethylamine. IR, ¹H, ¹³C, ³¹P NMR and mass spectral analyses were collected and analyzed and supported all structures. The title compounds were screened for antibacterial activity against Bacillus subtilis and Escherichia coli. Several of the agents exhibited significant activity in the assays. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:323–328, 2000     

Synthesis,characterization, and large two‐photon absorption cross‐sections of solid red‐emitting 1,4‐diketo‐3,6‐diphenylpyrrolo [3,4‐c]pyrrole/3,6‐carbazole/terfluorene copolymers

The synthesis, one‐ and two‐photon absorption (TPA) and emission properties of three novel 1,4‐diketo‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole (DPP)/3,6‐carbazole (Cz)/terfluorene (TF) copolymers are reported. The molar ratios of DPP versus TF are 15:85 ( TCP15 ), 25:75 ( TCP25 ), and 50:50 ( TCP50 ) under Cz:(TF + DPP) = 1. Two distinguished one‐photon absorption and emission bands observed in solutions imply that the electronic states of Cz–DPP–Cz and Cz–TF–Cz are not well mixed and the energy transfer from TF segments to DPP units is incomplete. However, in film states, all three copolymers are monochromatic red emitting with the peak wavelengths at 617, 621, and 631 nm for TCP15 , TCP25 , and TCP50 , respectively, indicating that the interchain interactions also have played an important role in the energy transfer. In two‐photon measurement, the copolymer solutions still exhibit two distinguished emission bands but the relative intensities at short‐wavelength region are obviously decreased, implying that Cz–TF–Cz segment is high one‐photon active but low TPA active, whereas Cz–DPP–Cz unit is low one‐photon active but high TPA active. All the copolymers show large δ over the range of measured wavelengths and the δ values of TCP15 , TCP25 , and TCP50 increase with DPP contents and are up to 530, 770, and 850 GM per repeating unit, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and antimicrobial activity of novel 2‐alkyl/arylcarbamato‐6‐(1,1‐dimethylethyl)‐3‐cyclohexyl‐3,4‐dihydro‐2H‐1,3,2‐benzoxazaphosphorine‐2‐oxides

Novel 2‐alkyl/arylcarbamato‐6‐(1,1‐dimethylethyl)‐3‐cyclohexyl‐3,4‐dihydro‐2H‐1,3,2‐benzoxaza‐phosphorine‐2‐oxides ( IV ) have been synthesized from reactions of 2‐cyclohexylaminomethyl‐4‐t‐butylphenol I [8c] with various dichlorophosphinyl carbamates ( III ) [8a‐b] in dry toluene in the presence of triethylamine at 40‐50 °C. All the title compounds ( IVa‐j ) at reflux temperature are degraded to 2‐amino‐6‐(1,1‐dimethylethyl)‐3‐cyclohexyl‐3,4‐dihydro‐2H‐1,3,2‐benzoxazaphosphorine‐2‐oxide ( IVk ) exclusively. The structures are determined by ir, nmr and mass spectral studies. They were screened for antifungal activity against Penicillium notatum, Aspergillus niger and Helminthosporium sps, and antibacterial activity on Escherchia coli, Staphylococcus aureus and Pseudomonas aeruginosa. A few of them possess significant activity.     

The layered compound poly[μ2‐4,4′‐bipyridyl‐di‐μ2‐chlorido‐mercury(II)]

The title compound, [HgCl₂(C₁₀H₈N₂)]_n, features two‐dimensional [HgCl₂(4,4′‐bipy)]_n neutral networks (4,4′‐bipy is 4,4′‐bipyridine), based on an octahedral Hg atom coordinated by four μ₂‐Cl atoms and two μ₂‐4,4′‐bipy ligands in trans positions, yielding a HgCl₄N₂ octahedron. The structure has mmm symmetry about the Hg atoms, with most of the atoms on at least one mirror plane, but the unsubstituted C atoms of the 4,4′‐bipy rings are disordered across a mirror plane. Photoluminescent investigations reveal that the title compound displays a strong emission in the green region, which probably originates from a ligand‐to‐ligand charge‐transfer transition.     

Hydrogen‐bonded networks in 1‐(4‐methoxyphenyl)‐2,2‐dimethylpropan‐1‐ol

The asymmetric unit of the title compound, C₁₂H₁₈O₂, contains two independent molecules. They differ only slightly in conformation but form completely different intermolecular hydrogen‐bonded arrays. One molecule exhibits disorder in the hydroxy group region, but this does not influence the formation of hydrogen bonds. The bulky tert‐butyl group on one side of the carbinol C atom and the benzene ring on the other side promote the formation of discrete dimeric motifs via hydrogen‐bridged hydroxy groups. Dimers are further joined by strong hydroxy–methoxy O—H...O bonds to form chains with dangling alcohol groups. Weaker intermolecular C—H...O interactions mediate the formation of a two‐dimensional network.     

Highly stable electrochromic polyamides based on N,N‐bis(4‐aminophenyl)‐N′,N′‐bis(4‐tert‐butylphenyl)‐1,4‐phenylenediamine

A new triphenylamine‐containing aromatic diamine monomer, N,N‐bis(4‐aminophenyl)‐N′,N′‐bis(4‐tert‐butylphenyl)‐1,4‐phenylenediamine, was synthesized by an established synthetic procedure from readily available reagents. A novel family of electroactive polyamides with di‐tert‐butyl‐substituted N,N,N′,N′‐tetraphenyl‐1,4‐phenylenediamine units were prepared via the phosphorylation polyamidation reactions of the newly synthesized diamine monomer with various aromatic or aliphatic dicarboxylic acids. All the polymers were amorphous with good solubility in many organic solvents, such as N‐methyl‐2‐pyrrolidinone (NMP) and N,N‐dimethylacetamide, and could be solution‐cast into tough and flexible polymer films. The polyamides derived from aromatic dicarboxylic acids had useful levels of thermal stability, with glass‐transition temperatures of 269–296 °C, 10% weight‐loss temperatures in excess of 544 °C, and char yields at 800 °C in nitrogen higher than 62%. The dilute solutions of these polyamides in NMP exhibited strong absorption bands centered at 316–342 nm and photoluminescence maxima around 362–465 nm in the violet‐blue region. The polyamides derived from aliphatic dicarboxylic acids were optically transparent in the visible region and fluoresced with a higher quantum yield compared with those derived from aromatic dicarboxylic acids. The hole‐transporting and electrochromic properties were examined by electrochemical and spectro‐electrochemical methods. Cyclic voltammograms of the polyamide films cast onto an indium‐tin oxide‐coated glass substrate exhibited two reversible oxidation redox couples at 0.57–0.60 V and 0.95–0.98 V versus Ag/AgCl in acetonitrile solution. The polyamide films revealed excellent elcterochemical and electrochromic stability, with a color change from a colorless or pale yellowish neutral form to green and blue oxidized forms at applied potentials ranging from 0.0 to 1.2 V. These anodically coloring polymeric materials showed interesting electrochromic properties, such as high coloration efficiency (CE = 216 cm²/C for the green coloring) and high contrast ratio of optical transmittance change (ΔT%) up to 64% at 424 nm and 59% at 983 nm for the green coloration, and 90% at 778 nm for the blue coloration. The electroactivity of the polymer remains intact even after cycling 500 times between its neutral and fully oxidized states. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2330–2343, 2009     

Low‐bandgap donor–acceptor copolymers with 4,6‐bis(3′‐(2‐ethylhexyl)thien‐2′‐yl)thieno[3,4‐c][1,2,5]thiadiazole: synthesis,optical, electrochemical,and photovoltaic properties

Two new low‐bandgap alternating copolymers (CEHTF and CEHTP) consisting of 4,6‐bis(3′‐(2‐ethylhexyl)thien‐2′‐yl)thieno[3,4‐c][1,2,5] thiadiazole and 9,9‐bis(2‐ethylhexyl)fluorene or 2,5‐bis(isopentyloxy)benzene were synthesized by Suzuki coupling reaction of corresponding comonomers. Their optical, electrochemical, and photovoltaic (PV) properties were studied and are reported. Both the copolymers exhibited long‐wavelength absorption covering the whole visible spectral region, which is in CEHTP thin films extended up to near infrared region, ambipolar redox properties, and electrochromism. High‐electron affinities and low‐optical bandgap values, 1.37 and 1.15 eV, were determined for CEHTF and CEHTP, respectively. PV devices with bulk heterojunction made of blends of copolymers and fullerene derivative [6,6]‐phenyl‐C⁶¹‐butyric acid methyl ester ([60]PCBM) were prepared and characterized. Effects of intramolecular charge transfer strength and side‐chain nature and length on photophysical properties are discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Single‐Stranded DNA: Replacement of Canonical by Base‐Modified Nucleosides in the Minihairpin 5′‐d(GCGAAGC)‐3′ and Constructs with the Aptamer 5′‐d(GGTTGGTGTGGTTGG)‐3′

The minihairpin 5′‐d(GCGAAGC)‐3′ ( 1 ) was modified either in the loop region, in the base‐paired stem, or at the 5′‐terminus by incorporation of base‐modified nucleosides. The thermal melting was correlated to the structural changes induced by the various donor‐acceptor properties of the nucleosides. Overhanging nonpaired nucleosides at the 5′‐terminus stabilized the hairpin, while a reverse of the dG³?dA⁵ sheared base pair to dA³?dG⁵ severely affected the stability. The combination of the minihairpin 5′‐d(GCGAAGC)‐3′ ( 1 ) and the thrombin‐binding aptamer 5′‐d(GGTTGGTGTGGTTGG)‐3′ ( 2 (= 46 )) resulted in the new construct 5′‐d(GGTTGGGCGAAGC GGTTGG)‐3′ ( 43 ) arising by replacement of the 5′‐d(TGT)‐3′ loop of 2 by the minihairpin. The fused oligonucleotide 43 exhibits a two‐phase thermal transition indicating the presence of the two unaltered moieties. According to slight changes of the T_m values of the construct 43 as compared to the separate units 1 and 2 , cooperative distorsions are discussed.     

Synthesis of novel N‐alkyl/aryl‐N′‐(4‐arylthiazol‐2‐yl)‐N″‐xylosyl guanidines

The reaction of 2,3,4‐tri‐O‐acetyl‐β‐D‐xylopyranosyl isothiocyanate ( 1 ) and 2‐amino‐4‐arylthiazoles ( 2 ) gave xylosylthioureas 3 . These thiourea derivatives reacted with alkyl/aryl amine in the presence of HgCl₂ to give a new series of N‐alkyl/aryl‐N″‐(4‐arylthiazol‐2‐yl)‐N″‐xylosyl guanidines 4 . Some of the synthesized guanidines were screened for their biological activity. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:688–694, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20379     

2‐(2‐Pyridyl­imino)‐2H‐1,2,4‐thia­diazo­lo­[2,3‐a]­pyridine

The title compound, C₁₁H₈N₄S, is found to have a symmetrical resonance structure in which both pyridyl‐N atoms interact with the S atom forming hemi‐bonds. This also results in the formation of a delocalized di­imine region and disturbance of the aromaticity in the pyridyl rings.     

A QM/MM study on the reaction pathway leading to 2‐Aceto‐2‐hydroxybutyrate in the catalytic cycle of AHAS

The reaction between the intermediate 2‐hydroxyethyl‐thiamin diphosphate (HEThDP^?) and 2‐ketobutyrate, in the third step of the catalytic cycle of acetodydroxy acid synthase, is addressed from a theoretical point of view by means of hybrid quantum/molecular mechanical calculations. The QM region includes one molecule of 2‐ketobutyrate, the HEThDP^? intermediate, and the residues Arg 380 y Glu 139; whereas the MM region includes the rest of the protein. The study includes potential energy surface scans to identify and characterize critical points on it, transition state search and activation barrier calculations. The results show that the reaction occurs via a two‐step mechanism corresponding to the carboligation and proton transfer in the first stage; and the product release in the second step. © 2014 Wiley Periodicals, Inc.