Extension of Gaussian‐1 (G1) theory to bromine‐containing molecules

Solvatomorphs of (Bu4N)2[{Ag(N2-py)}2Mo8O26]: structure, colouration and phase transition

(Bu4N)2[β-{Ag(N2-py)}2Mo8O26] demonstrates monomer/polymer dualism and a colouration phenomenon. The polymeric phase reveals a Ag assisted phase transition. Such complexes can act as precursors for catalytically active materials.

Catalytic approach to in vivo metabolism of atractylenolide III using biomimetic iron–porphyrin complexes

In vivo oxygenation of atractylenolide III during the metabolism and in situ oxidation mechanism by an iron–porphyrin iron(iv)-oxo porphyrin π-cation–radical complex.

Experimental and Theoretical Studies of a Spirostannole and Formation of a Pentaorganostannate

A new spirostannole, 1,1',3,3'-tetrakis(5-methylthiophen-2-yl)-4,4',5,5',6,6',7,7'-octahydro-2,2'-spirobi[benzo[c]stannole] (4), is synthesised and the molecular structure is compared with the optimised geometry from DFT calculations. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are twice degenerated and show a small HOMO-LUMO energy gap of 3.2 eV. In addition, cyclic voltammetry measurements are conducted and three redox processes are observed. Absorption and emission spectra show maxima at λ_abs,max 436 nm and λ_em,max 533 nm, respectively. Spirostannole 4 is a strongly absorbing material, but an extremely weak emitter in solution at 295.15 K. However, when the solution is cooled from 280 to 80 K, the emission becomes visible. The reaction of spirostannole 4 with methyllithium is monitored by NMR spectroscopy at 238.15 K. The ¹¹⁹Sn{¹H} NMR signal shifts from -36.0 (4) to -211.0 ppm, which is indicative of the formation of the lithium pentaorganostannate 5. The complex is thermally instable at 295.15 K, but insights into the molecular structure and electronic behaviour are obtained by DFT and TD-DFT calculations.

End-capped group manipulation of indacenodithienothiophene-based non-fullerene small molecule acceptors for efficient organic solar cells

As the key component of organic solar cells (OSCs), the acceptor plays key roles in determining the power conversion efficiency (PCE). Based on the famous non-fullerene acceptor ITIC, a series of acceptors (A1-A5) were designed by introducing fused-ring units (phenanthrene, pyrene, benzopyrazine, dibenzo[a,c]phenazine, and phenanthro[4,5-abc]phenazine) as the end groups. Theoretical calculations showed that A1-A5 display improved solubility and redshifted absorption spectra compared with ITIC. More importantly, the newly designed acceptors exhibit much higher electron mobility, where the electron mobility of A5_h (similar to A5 but with the same hexyl side chain as ITIC) is about four orders of magnitude larger than that of ITIC. The computed binding energies of the donor PBDB-TF with the acceptor ITIC and A5_h are -2.52 eV and -3.75 eV, indicating much stronger interface interactions in PBDB-TF/A5_h. In terms of charge-transfer (CT) mechanism, we found that both PBDB-TF/ITIC and PBDB-TF/A5_h can generate CT states through direct excitation and hot excitons, meanwhile there exist more opportunities of producing CT states via the intermolecular electric field (IEF) mechanism in PBDB-TF/A5_h. Our results not only offer a set of promising ITIC-based acceptors, but also provide new insights into the donor/acceptor interface properties, which are closely related to the PCE of OSCs.

Polymerization and coordination synergistically constructed photothermal agents for macrophages-mediated tumor targeting diagnosis and therapy

Developing an ideal photothermal agent is one of the challenges for effective photothermal therapy (PTT). Herein, a green and simple yet versatile method is developed to construct a novel poly-(iron-dopamine coordination complexes) nanoparticles (P[Fe-DA]-NPs) based on polymerization and coordination synergistically by using Fe³⁺ ions and dopamine (DA) in aqueous solution, and simultaneously poly(vinylpyrrolidone) (PVP) is applied to improve dispersion stability. P[Fe-DA]-NPs can be laden into macrophages directly with no further purification required to target tumor tissue to perform cell-mediated strategy. P[Fe-DA]-laden macrophages as an ideal photothermal agent has the advantages of good biocompatibility, simple preparation process, high photothermal performance, and effective tumor targeting. Furthermore, the P[Fe-DA]-laden macrophages possess excellent photoacoustic imaging (PAI) capacity for guiding the precise PTT. The results show that the tumors are significantly suppressed after PTT with the help of the accurate PAI diagnosis. This cell-mediated strategy may be the most promising avenue for the future clinical cancer therapy.

Aggregation induced emission - emissive stannoles in the solid state

The optoelectronic and structural properties of six stannoles are reported. All revealed extremely weak emission in solution at 295 K, but intensive fluorescence in the solid state with quantum yields (ΦF) of up to 11.1% in the crystal, and of up to 24.4% (ΦF) in the thin film.

Visible-Light-Induced Metal-/Photocatalyst-Free C-H Bond Imidation of Arenes

In this study, a visible-light-induced intermolecular C-H bond imidation of arenes was achieved at ambient condition. By using simple phthalimide with (diacetoxyiodo)benzene and molecular iodine, direct metal-/photocatalyst-free C-N bond formation was achieved. The imidation protocol was designed by using time-dependent density functional theory calculations and experimentally demonstrated for 28 substrates with as high as 96% yield. Mechanistic studies indicated that radical-mediated aromatic substitution occurred via photolysis of N-iodophthalimide under visible-light irradiation.

Synthesis of New C-3 Substituted Kynurenic Acid Derivatives

The application of kynurenic acid (KYNA) as an electron-rich aromatic system in the modified Mannich reaction has been examined. The extension possibility of the reaction was tested by using amines occurring in a number of bioactive products, such as morpholine, piperidine, or N-methylpiperazine and aldehydes of markedly different reactivities, like formaldehyde and benzaldehyde. The influence of substituents attached to position 3 on the aminoalkylation was also investigated. Thus, reactions of 3-carbamoyl-substituted precursors with tertiary amine containing side-chains were also tested to afford new KYNA derivatives with two potential cationic centers. By means of NMR spectroscopic measurements, supported by DFT calculations, the dominant tautomer form of KYNA derivatives was also determined.

Avenue to phosphaalkenes from Ph3GePCO

Reactions of Ph3GePCO with KP(t-Bu)2 and Ph3SiCl, or direct reaction with Ph3SiP(t-Bu)2 provides the (Z)- and (E)-isomers of the phosphaalkene (t-Bu2)PC(OSiPh3)P(GePh3) 2, respectively. These isomers interconvert thermally and photochemically, while 2 also undergoes silyl and phosphide exchange with silylphosphines, consistent with a mechanism involving the reversible silylphosphination of Ph3GePCO.

Theoretical Probe to the Mechanism of Pt-Catalyzed C-H Acylation Reaction: Possible Pathways for the Acylation Reaction of a Platinacycle

Density functional theory (DFT) and nudged elastic band (NEB) theory have been used to study the possible pathways for the acylation of cycloplatinated complex A derived from 2-phenoxypyridine, which is conceived as the key step in the platinum-catalyzed acylation of 2-aryloxypyridines. Geometry optimization indicates that the previously proposed intermediate, an arenium ion species as a result of analogous aromatic substitution, is not an energy minimum, but rather cationic Pt-arene η²-complex E is obtained as a stable intermediate. NEB simulations suggest that the minimum energy pathway for the acylation reaction has energy barrier of 33.6 kcal/mol and consists of the following steps: (1) Nucleophilic substitution at acetyl chloride by the platinum of the reactant A forms five-coordinate Pt(IV) acylplatinum complex B with an energy barrier of 21.7 kcal/mol. (2) B undergoes 1,2-acyl migration from the platinum to the cyclometalated carbon through a three-membered platinacycle transition state to give Pt-arene η²-complex E with an energy barrier of 14.0 kcal/mol. (3) E undergoes ligand exchange with chloride to form neutral Pt-arene η²-complex F. (4) F undergoes ligand substitution with acetonitrile to give the product and the energy barrier is small (10.6 kcal/mol). The rate-determining step is the 1,2-acyl migration step. It is interesting to note that intermediate F was not included in the proposed mechanism but was identified by the NEB simulations. Five-coordinate Pt(IV) acylplatinum complex B undergoes barrierless ligand coordination with chloride to form neutral formal oxidative addition acylplatinum complex D; however, D is less stable than reactant A by 2.9 kcal/mol, which also implies that the isolation of an oxidative addition product Pt(IV) complex may be very challenging. The direct reductive elimination of D to form product P has a higher energy barrier (36.6 kcal/mol).

GABAA Receptor Ligands Often Interact with Binding Sites in the Transmembrane Domain and in the Extracellular Domain-Can the Promiscuity Code Be Cracked?

Many allosteric binding sites that modulate gamma aminobutyric acid (GABA) effects have been described in heteropentameric GABA type A (GABA_A) receptors, among them sites for benzodiazepines, pyrazoloquinolinones and etomidate. Diazepam not only binds at the high affinity extracellular “canonical” site, but also at sites in the transmembrane domain. Many ligands of the benzodiazepine binding site interact also with homologous sites in the extracellular domain, among them the pyrazoloquinolinones that exert modulation at extracellular α+/β− sites. Additional interaction of this chemotype with the sites for etomidate has also been described. We have recently described a new indole-based scaffold with pharmacophore features highly similar to pyrazoloquinolinones as a novel class of GABA_A receptor modulators. Contrary to what the pharmacophore overlap suggests, the ligand presented here behaves very differently from the identically substituted pyrazoloquinolinone. Structural evidence demonstrates that small changes in pharmacophore features can induce radical changes in ligand binding properties. Analysis of published data reveals that many chemotypes display a strong tendency to interact promiscuously with binding sites in the transmembrane domain and others in the extracellular domain of the same receptor. Further structural investigations of this phenomenon should enable a more targeted path to less promiscuous ligands, potentially reducing side effect liabilities.

Benchmark study of the linear and nonlinear optical polarizabilities in proto-type NLO molecule of para-nitroaniline

In the present investigation, for the first time, we have performed a thorough study about different functionals and basis sets for linear and nonlinear optical (NLO) properties of para-nitroaniline ([Formula: see text]-NA), which is considered as proto-type NLO molecule, among organic NLO materials. There is a dire need of such data base for [Formula: see text]-NA because many investigators are using such values of [Formula: see text]-NA for comparative analysis. A range of different functionals including HF, BLYP, PW91, PBE, B3LYP, M06, M06-2X, PBE0, BHandHLYP, CAM-B3LYP, LC-BLYP, and B3LYP-D3 are applied in conjugation with several commonly basis sets such as 6-31G*, 6-311G*, 6-311G**, 6-311+G**, cc-pVDZ, and cc-pVTZ. A variety of functional and basis sets combinations are calculated and graphically compared with each other. The calculated total dipole moment for the [Formula: see text]-NA is found to be 6.79[Formula: see text]D which is quite closer to experimentally determined value. The lowest calculated value for linear isotropic polarizability at HF/6-31G* level of theory is [Formula: see text] esu while higher values observed with remaining all methods especially 14% polarizability increases in presence of basis set with diffuse functions and similar trend of variation is also observed in linear anisotropic polarizability. Similarly, the calculated value of frequency dependent second-order polarizability is found to be [Formula: see text] esu at PBE0/6-311+G** level of theory which is quite closer to experimental value of [Formula: see text] esu. A comparison between the calculated and experimental results shows good agreement among geometries, dipole moments and NLO polarizabilities for [Formula: see text]-NA. Moreover, the frontier molecular orbital (FMO) and electron density difference map (EDDM) analysis along with density of state (DOS) plots are also presented to get more physical intuitions into the structure–property relationship and electronic communications between terminal accepter and donor groups through [Formula: see text]-conjugation. The present investigation provides benchmark data including various commonly used functionals and basis sets for the calculation of NLO properties of [Formula: see text]-NA. Thus, the present investigation will put straight several future studies when it comes to comparative NLO study of organic materials.

Photoinduced electron transfer in 5-bromouracil labeled DNA. A contrathermodynamic mechanism revisited by electron transfer theories

The understanding of the 5-bromouracil (BrU) based photosensitization mechanism of DNA damage is of large interest due to the potential applications in photodynamic therapy. Photoinduced electron transfer (ET) in BrU labeled duplexes comprising the 5'-GBrU or 5'-ABrU sequence showed that a much lower reactivity was found for the 5'-GBrU pattern. Since the ionization potential of G is lower than that of A, this sequence selectivity has been dubbed a contrathermodynamic one. In the current work, we employ the Marcus and Marcus-Levich-Jortner theory of ET in order to shed light on the observed effect. By using a combination of Density Functional Theory (DFT) and solvation continuum models, we calculated the electronic couplings, reorganization energies, and thermodynamic stimuli for electron transfer which enabled the rates of forward and back ET to be estimated for the two considered sequences. The calculated rates show that the photoreaction could not be efficient if the ET process proceeded within the considered dimers. Only after introducing additional adenines between G and BrU, which accelerates the forward and slows down the back ET, is a significant amount of photodamage expected.

Parallels between Metal-Ligand Cooperativity and Frustrated Lewis Pairs

Metal ligand cooperativity (MLC) and frustrated Lewis pair (FLP) chemistry both feature the cooperative action of a Lewis acidic and a Lewis basic site on a substrate. A lot of work has been carried out in the field of FLPs to prevent Lewis adduct formation, which often reduces the FLP reactivity. Parallels are drawn between the two systems by looking at their reactivity with CO2, and we explore the role of steric bulk in preventing dimer formation in MLC systems.

Five-Coordinate Low-Spin {FeNO}7 PNP Pincer Complexes

The synthesis and characterization of air-stable cationic mono nitrosonium Fe(I) PNP pincer complexes of the type [Fe(PNP)(NO)Cl]⁺ are described. These complexes are obtained via direct nitroslyation of [Fe(PNP)Cl₂] with nitric oxide at ambient pressure. On the basis of magnetic and EPR measurements as well as DFT calculations, these compounds were found to adopt a low-spin d⁷ configuration and feature a nearly linear bound NO ligand suggesting Fe^INO⁺ rather than Fe^IINO^• character. X-ray structures of all nitrosonium Fe(I) PNP complexes are presented. Preliminary investigations reveal that [Fe(PNP^NH- iPr)(NO)(Cl)]⁺ efficiently catalyzes the conversion of primary alcohols and aromatic and benzylic amines to yield mono N-alkylated amines in good isolated yields.

Computational studies of 2-(4-oxo-3-phenylthiazolidin-2-ylidene)malononitrile

The molecular structure of the 2-(4-oxo-3-phenylthiazolidin-2-ylidene) malononitrile (3) is calculated using DFT B3LYP/6-311G(d, p) method. The calculated geometric parameters are in good agreement with the experimental data. The NBO calculations were performed to predict the natural atomic charges at the different atomic sites and study the different intramolecular charge transfer (ICT) interactions occurring in the studied system. The BD(2)C17-C19 → BD*(2)C14-C15, LP(2)O2 → BD*(1)N5-C9 and LP(1)N5 → BD*(2)C10-C11 ICT interactions causing stabilization of the system by 23.30, 30.63 and 52.48 kcal/mol, respectively. The two intense electronic transition bands observed experimentally at 249 nm and 296 nm are predicted using the TD-DFT calculations at 237.9 nm (f = 0.1618) and 276.4 nm (f = 0.3408), respectively. These electronic transitions are due to H-3 → L (94%) and H → L (95%) excitations, respectively.

Computational assessments of diastereoselective [4+2] cycloaddition and 1,3-borotopic shift of a dearomatized tertiary boronic ester intermediate: reactivities explained through transition-state distortion energies

Interception of a dearomatized tertiary boronic ester, formed through a kinetically and thermodynamically favorable 1,2-metalate rearrangement/anti-S_N2′ elimination of an activated ortho-lithiated benzyl amine, in a [4+2] cycloaddition or 1,3-borotopic shift has been investigated by density functional theory (DFT). Although superacitvated “naked” Li⁺ was found to greatly promote 1,3-borotopic shift, the diastereoselective [4+2] cycloaddition was favored. It was revealed that the factor that controls the diastereoselectivity was the steric bulk provided by the diene, which is in agreement with experimental diastereoselectivity. A comparison of unreactive dienophiles such as maleic anhydride, diethyl maleate, and others with 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione (PTAD) was found to be in an excellent agreement with the experiments; where their lack of reactivity is attributed to the high deformation energies of the interacting components to achieve the transition state structure which was pronounced with the high energy of LUMO orbitals.

Interception of dearomatized tertiary boronic ester in a diastereoselective [4+2] cycloaddition or 1,3-borotopic shift in the presence or absence of “naked” Li⁺, understanding reactivities by activation/strain model, were evaluated by DFT calculations.

The impact on the ring related vibrational frequencies of pyridine of hydrogen bonds with haloforms – a topology perspective

An intermolecular ring structure is identified for the hydrogen bonding system of pyridine and haloforms.

Hydroboration of terminal olefins with pinacolborane catalyzed by new 2-iminopyrrolyl iron(ii) complexes

New Fe(ii) mono(2-iminopyrrolyl) complexes catalyze the hydroboration of terminal olefins with pinacolborane via a borane oxidative addition pathway.

Atomic Charges in Highly Ionic Diatomic Molecules

Atomic charges were investigated as functions of detectable atomic and molecular constants at equilibrium structures. It was found based upon the variation idea that atomic charges in highly ionic molecules can be expressed as a function of molecular dipole moments, polarizabilities of free cations, and polarizabilities of free neutral atoms of the corresponding anions. The function can be given in the form of classical Rittner's relationship (J. Chem. Phys. 1951, 19, 1030). For the ground states of alkali halide molecules, the predicted atomic charges are close to an elementary charge e and the predicted dipole moments are in good agreement with the observed values; for spin-restricted high-ionic systems such as the lowest ⁹Σ electronic states of BN, AlN, GaN, BP, AlP, GaP, BAs, AlAs, and GaAs molecules, the predicted atomic charges are also near 1e and in good agreement with the results of natural population analysis at MRCI/cc-pvqz and HF/6-311+G(3df) levels. Polarizabilities for the lowest quintet states of B^-, Al^-, Ga^-, N⁺, P⁺, and As⁺ ions were also obtained based upon high-level ab initio computations. Atomic charges from other related methods are also investigated for comparison. The results demonstrate that high-quality atomic charges can be obtained with detectable variables, such as molecular dipole moment, vibrational frequency, as well as polarizabilities of the related free atoms and ions.

The antioxidative activity of piceatannol and its different derivatives: Antioxidative mechanism analysis

The naturally occurring stilbenes piceatannol and its derivatives are excellent antioxidants. In this work, the antioxidative activities of piceatannol and different piceatannol derivatives have been investigated using the density functional theory (DFT) method based on three widely accepted radical scavenging mechanisms, namely, the hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET). The gas and four solvent phases, namely, bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy (ETE), related to these mechanisms were calculated to elucidate the antioxidative capacities of the investigated compounds. This work focuses specifically on the thermodynamically preferred mechanism, antioxidative site and antioxidative activity order of the investigated stilbenes. The substituted effects of the methyl group and prenyl group on the chemical properties of the remaining OH and CH groups are also analysed. This work confirms the vital role of the OH and CH groups on free radical scavenging of piceatannol and its derivatives.

Time-Dependent Formulation of Resonance Raman Optical Activity Spectroscopy

In this work, we extend the theoretical framework recently developed for the simulation of resonance Raman (RR) spectra of medium-to-large sized systems to its chiral counterpart, namely, resonance Raman optical activity (RROA). The theory is based on a time-dependent (TD) formulation, with the transition tensors obtained as half-Fourier transforms of the appropriate cross-correlation functions. The implementation has been kept as general as possible, supporting adiabatic and vertical models for the PES representation, both in Cartesian and internal coordinates, with the possible inclusion of Herzberg-Teller (HT) effects. Thanks to the integration of this TD-RROA procedure within a general-purpose quantum-chemistry program, both solvation and leading anharmonicity effects can be included in an effective way. The implementation is validated on one of the smallest chiral molecule (methyloxirane). Practical applications are illustrated with three medium-size organic molecules (naproxen-OCD₃, quinidine and 2-Br-hexahelicene), whose simulated spectra are compared to the corresponding experimental data.

Mechanisms of CO2 Incorporation into Propargylic Amine Catalyzed by Ag(I)/Amine Catalysts

Density functional theory calculations are carried out to explore the detail mechanisms of CO₂ incorporation into propargylic amine catalyzed by Ag(I)/amine catalysts. Our calculations reveal that the whole reaction involves Lewis acid catalysis and Lewis base catalysis stages, and the outcomes of this reaction critically depend on the basicity of amine. A weaker base (i.e., DABCO) makes the Ag center more acidic, thus favoring the Lewis acid catalysis, resulting in benzoxazin-2-one. However, the following rearrangement of benzoxazin-2-one requires a stronger base (i.e., DBU) to stabilize its deprotonated form. Thus, the product selectivity could be subtly tuned by the choice of amine and the condition control, consistent with the experimental observations.

Tuning the Redox Potentials and Ligand Field Strength of Fe(II) Polypyridines: The Dual π-Donor and π-Acceptor Character of Bipyridine

The quintet-singlet energy difference (Δ E_Q/S) in Fe(II) polypyridine complexes is often interpreted in terms of metal-ligand π interactions. DFT calculations on a series of substituted [Fe(bpy)₃]²⁺ (bpy = 2,2'-bipyridine) complexes show the disparate magnitudes of substituent effects on tuning Δ E_Q/S and reduction potentials ( E°). In this series, E° spans a much larger range than Δ E_Q/S (2.07 vs 0.29 eV). While small changes in Δ E_Q/S are controlled by metal-ligand π interactions, large changes in E° arise from modification of the electrostatic environment around the Fe center. Molecular orbital analysis reveals that, contrary to the typical description of bpy as a π-acceptor, bpy is better described as acting as both a π-donor and π-acceptor in [Fe(bpy)₃]²⁺ complexes, even when it is substituted with highly electron withdrawing substituents. Overall, substituent modification is a useful strategy for fine-tuning the ligand field strength but not for significant reordering of the spin-state manifold, despite the large effect on metal-ligand electrostatic interactions.

Hydroboration of Terminal Olefins with Pinacolborane Catalyzed by New Mono(2-Iminopyrrolyl) Cobalt(II) Complexes

The 5-substituted 2-aryliminopyrrolyl ligand precursors of the type 5-R-2-[ N-(2,6-diisopropylphenyl)formimino]-1 H-pyrrole (R = 2,6-Me₂-C₆H₃ (1a), 2,4,6-ⁱPr₃-C₆H₂ (1b), 2,4,6-Ph₃-C₆H₃ (1c; reported in this work), anthracen-9-yl (1d), CPh₃ (1e; reported in this work)) were treated with K[N(SiMe₃)₂] in toluene to yield the respective 5-R-2-[ N-(2,6-diisopropylphenyl)formimino]pyrrolyl potassium salts 2a-e in high yields. The paramagnetic 15-electron Co(II) complexes of the type [Co{κ² N,N'-5-R-NC₄H₂-2-C(H)═N(2,6-ⁱPr₂-C₆H₃)}(Py)Cl] (3a-e; Py = pyridine) were prepared by salt metathesis of CoCl₂(Py)₄ with the respective potassium salts 2a-e in moderate to good yields. When the CoCl₂(THF)_1.5 precursor was combined with the in situ prepared sodium salt of ligand precursor 1b, the trinuclear complex [Co{κ² N, N'-5-(2,4,6-ⁱPr₃-C₆H₂)-NC₄H₂-2-C(H)═N(2,6-ⁱPr₂-C₆H₃)}(μ-Cl)]₂[(μ-Cl)₂Co(THF)₂] (4) was obtained in high yields. Complexes 3a-e have high-spin electronic configurations both in solution and in the solid state. X-ray diffraction studies of complexes 3a,e confirmed distorted tetrahedral coordination geometries. Complex 4, on the other hand, is a linear trinuclear Co(II)-Co(II)-Co(II) complex with two terminal distorted tetrahedral four-coordinate sites and a central octahedral six-coordinate site, all in the high-spin state, S = 3/2, as confirmed by the magnetization measurements and DFT calculations. Solid-state magnetic measurements in both complexes 3a and 4 point to paramagnetic behavior with a significant contribution of spin-orbit coupling. Additionally, intramolecular antiferromagnetic coupling of the adjacent cobalt atoms is observed in 4. The Co(II) family 3a-d, on activation with K(HBEt₃), catalyzed the hydroboration of several α-olefins with pinacolborane, in good to high yields (50-80%). This system almost exclusively yielded the anti-Markovnikov (a-Mk) addition product, except when styrene was used, where the selectivity in the Markovnikov (Mk) product increased with increasing steric bulkiness of the 5-R-2-iminopyrrolyl substituent, with the a-Mk:Mk molar ratio varying from 2.33:1 (3a, R = 2,6-Me₂-C₆H₃) to 0.75:1 (3c, R = 2,4,6-Ph₃-C₆H₃). Preliminary mechanistic studies indicate that the activation by K(HBEt₃) gave rise to a Co(I) species, the catalyst system likely following an oxidative addition pathway.

Mechanistic studies of 1,3-dipolar cycloadditions of bicyclic thioisomünchnones with alkenes. A computational rationale focused on donor-acceptor interactions

This paper describes a mechanistic study, with the interplay of experiment and theory, on the cycloadditions of a bicyclic mesoionic 1,3-dipole versus a series of representative symmetrical (1-phenyl-1H-pyrrole-2,5-dione and dimethyl maleate) and asymmetrical [(E)-(2-nitrovinyl)benzene, acrylonitrile, and but-3-en-2-one] olefinic dipolarophiles. These results allow a comparative analysis with monocyclic dipoles and open further avenues to structurally diversified heteroatom-rich rings. The unichiral version of the bicyclic dipole leads to adducts containing up to five chiral centers, whose formation proceeds with high levels of facial stereoinduction in reactions involving bulky dipolarophiles. The second and largest part of this study provides a theoretical interrogation on the pericyclic mechanism with DFT-methods [M06-2X/6-311++G(d,p)]. In order to get further mechanistic insights, we have also explored charge transfers between reaction partners using NBO analysis, which satisfactorily justifies the stereochemical outcome.