Pyridine Bond Research Articles

De- and Rearomatisation of Pyridine in Silylene Chemistry.

Traditional methods relying on metal-ligand cooperation for activating pyridine bonds in de- and rearomatisation are being challenged by the abundant metal-free element species as alternatives. Here, we investigated the de/re-aromatisation of pyridine facilitated by pyridylamino-functionalised silylene reactions with ketones and ketene. The reactivity outcome is highly dependent on the substituents on the ketones. By carefully tuning the steric demand of the ketone, each intermediate of the reaction sequence could be isolated. At room temperature, benzophenone and acetophenone substrates led to dearomatisation of the pyridine moiety, with the case of acetophenone showing an intermediate silaoxirane preceding dearomatisation. However, when subjected to acetone or diphenylketene, only silaoxiranes were formed without dearomatisation of the pyridine moiety. Notably, only benzophenone-derived dearomatised species demonstrated rearomatisation upon heating. Furthermore, the reduced steric bulk of the ketene facilitated further ring expansion with another equivalent of the substrate, forming sila-1,3-dioxolanes. Both steric hindrance and aromatic groups collectively influence the dearomatisation of pyridine in pyridylaminosilylene reactions.

High performance and stable perovskite solar cells modified with 8-hydroxyquinoline lead

The quality of the perovskite active layer is the critical factor that affects the photovoltaic performance of perovskite solar cells (PSCs). In this paper, the 8-hydroxyquinoline lead (Pbq2) containing pyridine bonds, C–O bonds, and quinoline ring groups was introduced into the MAPbI3 perovskite layer to improve the performances and stabilities of PSCs. The doped Pbq2 could adjust the growth of perovskite crystals by coordinating interactions between the above functional groups in Pbq2 with Pb2+, MA+, and I− in perovskite together. And as a result, high-quality and dense perovskite films with larger grain sizes were obtained. At the same time, large molecule-sized Pbq2 chelated at the grain boundary of perovskite, which passivated the defects and suppressed non-radiative recombination of photo carriers and ion migration at grain boundaries. Therefore, the interface energy barrier between the perovskite layer and the electron transfer layer (ETL) was reduced by the Pbq2 doping, which accelerated the separation and transportation of carriers at the ETL/perovskite layer interface. Finally, Pbq2-modified PSCs achieved a power conversion efficiency (PCE) of 20.82% with an open circuit voltage (Voc) of 1.144 V and a fill factor (FF) of 77.4% compared to a PCE of 17.87% for the reference sample. Furthermore, Pbq2-modified PSCs showed better light stability and moisture resistance in air conditions.

Bond-Dissociation Energies to Probe Pyridine Electronic Effects on Organogold(III) Complexes: From Methodological Developments to Application in π-Backdonation Investigation and Catalysis.

In this work, we report on the synthesis of several organogold(III) complexes based on 4,4'-diterbutylbiphenyl (C^C) and 2,6-bis(4-terbutylphenyl)pyridine (C^N^C) ligands and bond with variously substituted pyridine ligands (pyrR). Altogether, 33 complexes have been prepared and studied with mass spectrometry using higher-energy collision dissociation (HCD) in an Orbitrap mass spectrometer. A complete methodology including the kinetic modeling of the dissociation process based on the Rice-Ramsperger-Kassel-Marcus (RRKM) statistical method is proposed to obtain critical energies E0 of the pyrR loss for all complexes. The capacity of these E0 values to describe the pyridine ligand effect is further explored, at the same time as more classical descriptors such as 1H pyridinic NMR shift variation upon coordination and Au-NpyrR bond length measured by X-ray diffraction. An extensive theoretical work, including density functional theory (DFT) and domain-based local pair natural orbital coupled-cluster theory (DLPNO-CCSD(T)) methods, is also carried out to provide bond-dissociation energies, which are compared to experimental results. Results show that dissociation energy outperforms other descriptors, in particular to describe ligand effects over a large electronic effect range as seen by confronting the results to the pyrR pKa values. Further insights into the Au-NpyrR bond are obtained through an energy decomposition analysis (EDA) study, which confirms the isolobal character of Au+ with H+. Finally, the correlation between the lability of the pyridine ligands toward the catalytic efficiency of the complexes could be demonstrated in an intramolecular hydroarylation reaction of alkyne. The results were rationalized considering both pre-catalyst activation and catalyst reactivity. This study establishes the possibility of correlating dissociation energy, which is a gas-phase descriptor, with condensed-phase parameters such as catalysis efficiency. It therefore holds great potential for inorganic and organometallic chemistry by opening a convenient and easy way to evaluate the electronic influence of a ligand toward a metallic center.

C–H and H–H Bond Activation by a Cationic Germylyne Complex

Reactivities of a cationic germylyne complex [Cp*(CO)2W≡Ge(IPr)](BAr4F) (1) [IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene] toward several unsaturated organic substrates and dihydrogen were investigated. Complex 1 underwent activation of the formyl C–H bond of benzaldehyde and the ortho C–H bond of pyridine to afford base-stabilized germylene complexes, indicating that coordination of the heteroatom (O/N) of the substrates to the Lewis acidic Ge center facilitates the C–H bond activation on W. The reactions with alkenes resulted in the terminal C–H bond cleavage on Ge by coordination of the C═C double bond to W, giving η3-germaallyl complexes. The reactions with terminal alkynes, on the contrary, proceeded through no C–H bond cleavage to produce metallacyclopropenylgermylenes, which have an unprecedented bonding situation with a lone pair on Ge. Complex 1 also reacted with dihydrogen at room temperature to afford a dihydrido(dihydrogermyl) complex finally through a hydrido(hydrogermylene) complex. Characterization of these products including X-ray crystal diffraction study (XRD) and possible reaction mechanisms based on cooperative action at the W–Ge unsaturated bond platform are described.

Tracking the pyrolysis process from 2D Mn2n polymer to high-rate anode materials for lithium ion batteries

By manipulating the pyrolysis of multidimensional precursors, excellent energy storage materials can be obtained. On the molecular level, however, the pyrolysis tracking and evolution of two-dimensional (2D) precursors require additional study. Here, we designed a 2D layered Mn-based polymer (Mn2n, [Mn2L2(CH3OH)2]n, L = 3-ethoxylsalicylate iso-nicotinyl hydrazone) bridged with L as a precursor, and obtained a 2D porous nanosheet N-doped carbon skeleton embedded with Mn2+O (Mn2+O/NC) through controlled pyrolysis under an inert atmosphere. The pyridine nitrogen coordination of isoniazid is astonishingly essential for the formation of 2D layered Mn2n polymers. The formation of Mn-N(pyridine) bonds serves as a bridge between the basic units of Mn2. Thermogravimetric mass spectrometry (TG-MS) could track the pyrolysis process and provide a potential evolutionary from a 2D Mn2n precursor to a 2D porous nanosheet Mn2+O/NC structure. The specific capacity of Mn2+O/NC-800 electrode reaches up to 614.1 mAh g−1 after 600 cycles at 200 mA g−1 current density when the pyrolysis product is used as the anode material of lithium ion battery. Dynamic analysis indicates that the 2D porous nanosheet structure of Mn2+O/NC has a high pseudocapacitance contribution and charge transfer efficiency, which effectively improves the performance of lithium ion batteries. This work will provide a useful guidance for the design of new electrode materials.

Quantitative Assessment of Ligand Substituent Effects on σ- and π-Contributions to Fe-N Bonds in Spin Crossover FeII Complexes.

The effect of para‐substituent X on the electronic structure of sixteen tridentate 4‐X‐(2,6‐di(pyrazol‐1‐yl))‐pyridine (bppX ) ligands and the corresponding solution spin crossover [FeII(bppX )2]2+ complexes is analysed further, to supply quantitative insights into the effect of X on the σ‐donor and π‐acceptor character of the Fe‐NA (pyridine) bonds. EDA‐NOCV on the sixteen LS complexes revealed that neither ΔE orb,σ+π (R2=0.48) nor ΔE orb,π (R2=0.31) correlated with the experimental solution T1/2 values (which are expected to reflect the ligand field imposed on the iron centre), but that ΔE orb,σ correlates well (R2=0.82) and implies that as X changes from EDG→EWG (Electron Donating to Withdrawing Group), the ligand becomes a better σ‐donor. This counter‐intuitive result was further probed by Mulliken analysis of the NA atomic orbitals: NA (px ) involved in the Fe−N σ‐bond vs. the perpendicular NA (pz ) employed in the ligand aromatic π‐system. As X changes EDG→EWG, the electron population on NA (pz ) decreases, making it a better π‐acceptor, whilst that in NA (px ) increases, making it a better σ‐bond donor; both increase ligand field, and T1/2 as observed. In 2016, Halcrow, Deeth and co‐workers proposed an intuitively reasonable explanation of the effect of the para‐X substituents on theT1/2 values in this family of complexes, consistent with the calculated MO energy levels, that M→L π‐backdonation dominates in these M−L bonds. Here the quantitative EDA‐NOCV analysis of the M−L bond contributions provides a more complete, coherent and detailed picture of the relative impact of M−L σ‐versus π‐bonding in determining the observed T1/2, refining the earlier interpretation and revealing the importance of the σ‐bonding. Furthermore, our results are in perfect agreement with the ΔE(HS‐LS) vs. σp +(X) correlation reported in their work.

Synthesis of Finite Molecular Nanotubes by Connecting Axially Functionalized Macrocycles

Synthesis of Finite Molecular Nanotubes by Connecting Axially Functionalized Macrocycles

Mimicking Elementary Reactions of Manganese Lipoxygenase Using Mn-hydroxo and Mn-alkylperoxo Complexes.

Manganese lipoxygenase (MnLOX) is an enzyme that converts polyunsaturated fatty acids to alkyl hydroperoxides. In proposed mechanisms for this enzyme, the transfer of a hydrogen atom from a substrate C-H bond to an active-site MnIII-hydroxo center initiates substrate oxidation. In some proposed mechanisms, the active-site MnIII-hydroxo complex is regenerated by the reaction of a MnIII-alkylperoxo intermediate with water by a ligand substitution reaction. In a recent study, we described a pair of MnIII-hydroxo and MnIII-alkylperoxo complexes supported by the same amide-containing pentadentate ligand (6Medpaq). In this present work, we describe the reaction of the MnIII-hydroxo unit in C-H and O-H bond oxidation processes, thus mimicking one of the elementary reactions of the MnLOX enzyme. An analysis of kinetic data shows that the MnIII-hydroxo complex [MnIII(OH)(6Medpaq)]+ oxidizes TEMPOH (2,2′-6,6′-tetramethylpiperidine-1-ol) faster than the majority of previously reported MnIII-hydroxo complexes. Using a combination of cyclic voltammetry and electronic structure computations, we demonstrate that the weak MnIII-N(pyridine) bonds lead to a higher MnIII/II reduction potential, increasing the driving force for substrate oxidation reactions and accounting for the faster reaction rate. In addition, we demonstrate that the MnIII-alkylperoxo complex [MnIII(OOtBu)(6Medpaq)]+ reacts with water to obtain the corresponding MnIII-hydroxo species, thus mimicking the ligand substitution step proposed for MnLOX.

Efficacious Alkaline Copper Corrosion Inhibition by a Mixed Ligand Copper(II) Complex of 2,2′‐Bipyridine and Glycine: Electrochemical and Theoretical Studies

AbstractA mixed ligand copper(II) complex, namely, [Cu(BPy)(Gly)Cl]⋅2H2O (CuC) (BPy=2,2′‐bipyridine and Gly=glycine), was synthesized and characterized. The synthesized CuC complex was tested as inhibitor to effectively mitigate the corrosion of copper in alkaline solutions using the linear sweep voltammetry (LSV) and linear polarization resistance (LPR) techniques. For the sake of comparison, such two D.C. electrochemical techniques were also applied to the Cu/OH− interface in the presence of the two studied free ligands, namely, BPy and Gly. The results showed that the three studied compounds acted as mixed‐type inhibitors, with CuC being the most efficacious one. The adsorption of the inhibitor is confirmed from X‐ray photoelectron spectroscopy (XPS) profiles by the appearance of organic chlorine as well as pyridine and amine nitrogen bonds. Based on XPS data, it was presumed that the corrosion inhibitor stimulates the formation of Cu2CO3(OH)2 species at the electrode surface since, in the case of a corroded reference sample (in absence of inhibitors), its proportion is trivial. The reactivity of the isolated inhibitors was analyzed by computing several quantum chemical parameters based on the density functional theory (DFT). A good correlation was found between these parameters and the anticorrosive performance. Additionally, Monte Carlo simulation studies were applied to find the best configurational space of ligands and their complex on the Cu(111) surface.

Activation of the Ir-N(pyridine) Bond in Half-Sandwich Tethered Iridium(III) Complexes.

We present four new organometallic half-sandwich iridium(III) complexes of formula [Ir(η5:κ1-C5Me4CH2py)(N,N)](PF6)2, bearing a N,N-chelating ligand [ethylenediamine (en), 1; 1,3-diaminopropane (dap), 2; 2,2'-bipyridine (bipy), 3; 1,10-phenanthroline (phen), 4]; and a derivatized cyclopentadienyl ligand, C5Me4CH2C5H4N, which forms an additional five-membered chelate. The latter is hemilabile, and the Ir-N(py) bond can be reversibly cleaved by various stimuli. The four complexes are unreactive toward hydrolysis at pH 7. Interestingly, 1 and 2 react with hydrochloric acid and formate, and speciation between closed and open tether complexes can be followed by 1H NMR spectroscopy. Complex 1 binds to nucleobase guanine (9-ethylguanine, 9-EtG), yet interaction to calf-thymus DNA was not observed. New X-ray structures of closed tether complexes 1-4 and open tether complexes [Ir(η5-C5Me4CH2pyH)(en)Cl](PF6)2 (1·HCl) and [Ir(η5-C5Me4CH2py)(en)H]PF6 (1·hyd) have been determined. Hydride capture is efficient for 1 and 2. The kinetics of Ir-H bond formation and hydride transfer in a model organic molecule have been investigated, revealing a strong dependence on the temperature. Coincubation of complex 1 with nontoxic concentrations of sodium formate decreases the IC50 value in MCF7 breast cancer cells, indicating the possibility of intracellular activation of the Ir-N(py) tether bond to generate cytotoxic activity via iridium-mediated transfer hydrogenation.

UV activation of the pi bond in pyridine for efficient pyridine degradation and mineralization by UV/H2O2 treatment

Pyridine and organics containing pyridine rings are widely used but persist in the environment and cause toxic pollution. Due to the attraction of the nitrogen atoms to the electrons in the pi bond, the pyridine ring is difficult to oxidize by oxidant. Here, we propose that ultraviolet (UV) irradiation activates the electrons in the pi bond and enables combination with the hydroxyl radical (OH) originating from hydrogen peroxide (H2O2) to eliminate pyridine quickly and mineralize the byproducts. The removal rates of pyridine and total organic carbon (TOC) were compared in different treatments: UV irradiation, UV/H2O2 treatment and Fenton oxidation with different initial pyridine concentrations, pH values and H2O2 concentrations. The UV/H2O2 treatment yielded a higher pyridine removal rate and greater mineralization than the other treatments. The removal rate of pyridine was highest in neutral aqueous solution and H2O2 concentration of 10 mM. At an initial H2O2 concentration of 10 mM, more than 90% of the pyridine was degraded in 10 min, and approximately 70% of the TOC was removed in 60 min. The absorption of UV light at 254 nm by the pi bond of pyridine can accelerate the damage to the stable pyridine structure, especially in the presence of OH. This study provides a promising alternative for the removal and mineralization of pyridine ring-containing materials.

Construction of efficient “on-off-on” fluorescence aptasensor for ultrasensitive detection of prostate specific antigen via covalent energy transfer between g-C3N4 quantum dots and palladium triangular plates

Development of ultra-sensitive and high specific aptasensors is important for early diagnosis of prostate cancer. Herein, ultrasensitive detection of prostate specific antigen (PSA) aptasensor was realized based on the “on-off-on” model via fluorescence (FL) covalent energy transfer between g-C3N4 quantum dot (g-CNQDs) and palladium triangular plates (Pd TPs). Specifically, the Pd TPs were primarily linked with PSA aptamer (PA) as the reporter probe, followed by attaching them onto the g-CNQDs surfaces, causing the highly enlarged FL quenching rate (ca. 75%). After the introduction of PSA, the FL intensities recovered again because of the distinctively stronger affinity of PA to PSA than that of g-CNQDs. The bond of pyridine N with Pd was identified as efficient energy transfer pathway through the X-ray photoelectron spectroscopy (XPS) and FL measurements. The surface plasmon resonance (SPR) experiments certified the remarkably different affinity of PA towards g-CNQDs and PSA. The as-constructed FL aptasensor can accurately quantify PSA with wide linear range of 10 pg mL−1-50 ng mL−1 and ultra-low limit of detection (LOD, 4.2 pg mL−1), indicating the promising applications in clinical assay and biological detection.

Surface characterization of poly-2-vinylpyridine—A polymer for area selective deposition techniques

Thin films of OH terminated poly-2-vinylpyridine (P2VP), a polymer with potential for infiltration mediated thin film deposition, area selective deposition (ASD), and small feature size development via block copolymer (BCP) self-assembly, have been studied with hard x-ray photoelectron spectroscopy. From the N 1s and C 1s core level spectra, accurate values for the binding energy positions of the species present in the films were obtained, providing clear evidence for signals associated with pyridine bonds. The aromatic ring on the P2VP side chain is clearly identified in the studied core levels. These observations allow for a complete understanding of the chemical environment of the polymer and provide evidence of the potential reactions that can occur with metal diffusion into P2VP. Transmission electron microscopy, attenuated total reflection infrared spectroscopy, and atomic force microscopy measurements reveal high quality films, and this work provides a reference base for this functional material in terms of its utility for ASD, BCP, and subsequent atomic layer deposition based polymer infiltration processes.

Applicability of NBO and AIM Topology Analyses to Chemical Bonding in Some Diacetylplatinum(II) Complexes

The geometrical structures of six square-planar diacetylplatinum(II) complexes ([Pt(Ac)2L], L = hydrazine-type ligand) were calculated using six (B3LYP, CAM-B3LYP, B3PW91, M06, M06HF and PBE) DFT methods and one post-Hartree–Fock (MP2) method combined with 6-31G(d,p) basis sets for nonmetal atoms and LANL2DZ for Pt. Using percent relative errors, M06HF and MP2 are best for predicting Pt–N bond distances, but worst for Pt–C bond distances, whereas B3PW91 is best. Pt–N(pyridine) bonds have higher electron density at the bond critical points than Pt–N(hydrazone) bonds, and the former are more covalent than the latter. Further, Pt–C bonds trans to hydrazone moieties are more covalent than Pt–C bonds trans to Pt–N(pyridine) bonds. Pt–C bonds are mainly due to Pt→Ac back donation rather than Ac→Pt donation; σ-bonding is less important in this case, consistent with the high π-acidity and strong trans effect of acetyl groups. In contrast, Pt→N back donation is negligible and Pt–N bonds are mainly due to N→Pt σ-donation, which stabilizes trans Pt–C bonds.

Neutron diffraction study of quasi-1D Ising ferromagnet [Co(NCS)2(pyridine)2

The quasi-one-dimensional [Co(NCS)2(pyridine)2]n coordination polymer built of ferromagnetic chains of Co(II) ions linked by (NCS)2 anions is known as an Ising ferromagnet that magnetically orders at TC = 3.9 K. We performed a neutron diffraction study and show that the magnetic structure is collinear ferromagnetic, static, and without any glassy component. The magnitude of the ordered magnetic moment of Co(II) is 3.65(15) μB, which points to a relatively large contribution of the orbital moment. The direction of the moment is close to the direction of the Co–N(pyridine) bond, which confirms literature ab initio calculations. We show that dipolar interactions are mainly responsible for the magnetic interchain coupling.

Reactivity of highly Lewis acidic diborane(4) towards pyridine and isocyanide: formation of boraalkene-pyridine complex and ortho-functionalized pyridine derivatives.

The reaction of pinB-BMes2 (pin = pinacolato, Mes = 2,4,6-Me3C6H2) with Xyl-NC (Xyl = 2,6-Me2C6H3) and pyridine results in the formation of a pyridine-coordinated boraalkene that exhibits an intense color caused by an intramolecular charge-transfer interaction. In the presence of an excess of pyridine, the ortho C-H bond of pyridine was selectively functionalized to afford a quinoid compound or an isocyanide-coupled product. Based on the concentration effect, the reaction stoichiometry, and previously reported DFT calculations, a reaction mechanism that involves several rearrangement reactions was proposed. Using the present method, substituted pyridines and N-heterocycles afforded the corresponding functionalized derivatives. A subsequent hydrolysis of one of the resulting products furnished an aminomethylated pyridine derivative in two steps from parent pyridine.

1,2-CH Bond Activation of Pyridine across a Transient Titanium Alkylidene Radical and Re-Formation of the Ti═CHtBu Moiety

Reduction of the titanium alkylidene [(PNP)Ti═CHtBu(OTf)] (PNP– = N[2-PiPr2-4-methylphenyl]2–) with KC8 in the presence of pyridine results in formation of the transient titanium(III) alkylidene radical [(PNP)Ti═CHtBu)] (A) or the adduct [(PNP)Ti═CHtBu)(NC5H5)] (B), which activates the C–H bond of pyridine to form the titanium(III) pyridyl alkyl complex [(PNP)Ti(CH2tBu)(η2-NC5H4)] (1) in 64% yield as brown microcrystals. Low-temperature X-band EPR spectroscopy and single-crystal X-ray diffraction studies confirm the identity of 1 as a d1 metal-centric radical with superhyperfine coupling to one nitrogen atom and having a side-on pyridyl moiety, which results in formation of the two isomeric forms 1a,b. Oxidation of 1 with [FeCp*2][OTf] cleanly promotes α-hydrogen abstraction to re-form [(PNP)Ti═CHtBu(OTf)] with concurrent elimination of pyridine and FeCp*2. Re-formation of the alkylidene moiety most likely stems from an intermediate such as [(PNP)Ti(CH2tBu)(η2-NC5H4)(OTf)] (C).

Diastereoselective Cyclization of 1,5‐Dienes with the C−H Bond of Pyridine Catalyzed by a Cationic Mono(phosphinoamide) Alkyl Scandium Complex

AbstractThe carbocyclization of non‐conjugated dienes mediated by organometallics is an important reaction for the synthesis of a variety of carbocyclic derivatives, but the direct annulation of dienes with an inert C−H bond of a substrate has remained unexplored to date. We herein report a series of novel rare‐earth dialkyl complexes bearing a phosphinoamide anion and demonstrate that the combination of a mono(phosphinoamido)‐ligated scandium dialkyl complex with B(C6F5)3 results in an excellent catalyst for the cis‐selective cyclization of 1,5‐dienes with the ortho‐C(sp2)−H bond of pyridines to afford a new family of pyridyl‐functionalized 1,3‐disubstituted cyclopentane derivatives containing monocyclic, bicyclic, spirocyclic, and heterocyclic skeletons in moderate to excellent yields with high diastereoselectivities (cis/trans up to 99:1).

A luminescent bis(pyridyl)-substituted benzimidazole platinum(II) complex exhibiting an intermolecular anagostic interaction.

The photophysical properties of transition metal complexes of the 5,6-dimethyl-2-(pyridin-2-yl)-1-(pyridin-2-ylmethyl)-1H-benzimidazole ligand are of interest. Dichlorido[5,6-dimethyl-2-(pyridin-2-yl)-1-(pyridin-2-ylmethyl)-1H-benzimidazole-κ2N2,N3]platinum(II), [PtCl2(C20H18N4)], is luminescent in the solid state at room temperature. The compound displays a distorted square-planar coordination geometry. The Pt-N(imidazole) bond length is shorter than the Pt-N(pyridine) bond length. The extended structure reveals that symmetry-related molecules display weak C-H...N, C-H...Cl, and C-H...Pt hydrogen-bonding interactions that are clearly discernable in the Hirshfeld surface and fingerprint plots. The intermolecular C-H...Pt and C-H...N interactions have been explored using density functional theory. The result of an analysis of the distance dependence of C-H...Pt yields a value consistent with that observed in the solid-state structure. The energy of interaction for the C-H...Pt interaction is found to be about -11 kJ mol-1.

Theoretical Study of Nickel-Catalyzed Selective Alkenylation of Pyridine: Reaction Mechanism and Crucial Roles of Lewis Acid and Ligands in Determining the Selectivity.

Selective alkenylation of pyridine is challenging in synthetic organic chemistry due to the poor reactivity and regioselectivity of the aromatic ring. We theoretically investigated Ni-catalyzed selective alkenylation of pyridine with DFT. The first step is coordination of the pyridine-AlMe3 adduct with the active species Ni(0)(NHC)(C2H2) 1 in an η2-fashion to form an intermediate Int1. After the isomerization of Int1, the oxidative addition of the C-H bond of pyridine across the nickel-acetylene moiety occurs via a transition state TS2 to form a Ni(II)(NHC) pyridyl vinyl intermediate Int3. This oxidative addition is rate-determining. The next step is C-C bond formation between pyridyl and vinyl groups leading to the formation of vinyl-pyridine (P1). One of the points at issue in this type of functionalization is how to control the regioselectivity. With the use of Ni(NHC)/AlMe3 catalyst, the C4- and C3-alkenylated products (ΔG°⧧ = 17.4 and 21.5 kcal mol-1, respectively) are formed preferably to the C2 one (ΔG°⧧ = 22.0 kcal mol-1). The higher selectivity of the C4-alkenylation over the C3 and the C2 ones is attributed to the small steric repulsion between NHC and AlMe3 in the C4-alkenylation. Interestingly, with Ni(P(i-Pr)3)/AlMe3 catalyst, the C2-alkenylation occurs more easily than the C3 and C4 ones. This regioselectivity arises from the smaller steric repulsion induced by P(i-Pr)3 than by bulky NHC. It is notable that AlMe3 accelerates the alkenylation by inducing the strong CT from Ni to pyridine-AlMe3. In the absence of AlMe3, pyridine strongly coordinates with the Ni atom through the N atom, which increases Gibbs activation energy (ΔG°⧧ = ∼27 kcal mol-1) of the C-H bond activation. In other words, AlMe3 plays two important roles, acceleration of the reaction and enhancement of the regioselectivity for the C4-alkenylation.