Concerted SN2 mechanism for the hydrolysis of acid chlorides: comparisons of reactivities calculated by the density functional theory with experimental data

DFT computations have been performed in acetone and water solvents in order to investigate the mechanism of hydrolysis of acid chlorides. Acetyl chloride and chloroacetyl chloride hydrolyze via concerted, one‐step S_N2 mechanism, with the attack of water at the sp² hybridized carbon atom of the C?O group, and the transition state (TS) has distorted tetrahedral geometry. Solvent molecules act as general base and general acid catalysts. The TS of chloroacetyl chloride is tighter and less polar than the TS of acetyl chloride. The structure of the S_N2 TS for the hydrolysis of benzoyl chlorides changes with the substituents and the solvent. Tight and loose TSs are formed for substrates bearing electron withdrawing (e‐w) and electron donating (e‐d) groups, respectively. In acetone, only the e‐w effect of the substituents increase the reactivity of the substrates, and the change of the structure of the TSs with the substituents is small. In water, polar and very loose TSs are formed in the reactions of benzoyl chlorides bearing e‐d substituents, and the rate enhancing effect of both e‐d and e‐w groups can be computed at higher level of theory. Calculated reactivities and the changes of the structure of the TSs with substituents and solvent are in accordance with the results of kinetic studies. In S_N2 nucleophilic substitutions late/early TSs are formed if the attacking reagent is poorer/better nucleophile than the leaving group, and loose/tight TSs are formed for substrates bearing e‐d/e‐w substituents and in protic/aprotic solvents. Copyright © 2010 John Wiley & Sons, Ltd.     

Evidence for Strong Mixing Between the LC and MLCT Excited States in Some Heteroleptic Iridium (III) Complexes

The synthesis, structure and photophysical properties of series of new luminescent cyclometalated Iridium (III) complexes are reported. The cyclometalated ligand used here is 2-aryl imidazole and the auxiliary ligand is acetyl acetone (acac). The crystal structure of the complex (dmdpi)₂Ir(acac) (5) show that the Iridium(III) ion resides in a distorted octahedral environment. All complexes exhibit bright photoluminescence (PL) at room temperature and (fpdmdmpi)₂Ir(acac) 4 has a high solution PL quantum efficiency of 0.56. The role played by electron releasing and electron withdrawing substituents of the 2-arylimidazole ligands towards the stability of HOMO and how the substituent influences the luminescent behaviour are discussed. Furthermore those substituents have effect on the contribution to mixing between ³(π-π*) and ³(MLCT) for the lowest excited states.     

Investigation of the substituent specific cross‐interaction effects on 13C NMR of the CN bridging group in substituted benzylidene anilines

The substituent effect on ¹³C NMR of the C?N in benzylidene anilines XPhCH?NPhY was investigated, in which the substituents X and Y are in p‐position or in m‐position of the two aromatic rings. The substituent effects including the inductive effects of X and Y, the conjugative effects of X and Y, and the substituent specific cross‐interaction effect were put into one model to quantify the ¹³C NMR chemical shift δ_C(C?N) of the C?N in XPhCH?NPhY. A penta‐parameter correlation equation with correlation coefficient 0.9975 and standard error 0.17 ppm was obtained for 80 samples of compounds. The result shows that the substituents X and Y have an opposite effect on the δ_C(C?N). The electron‐withdrawing effects of X decrease the δ_C(C?N); while the electron‐donating effects of X increase the δ_C(C?N). In contrast, the electron‐withdrawing effects of Y increase the δ_C(C?N); while the electron‐donating effects of Y decrease the δ_C(C?N). A new substituent specific cross‐interaction effect parameter Δσ² was proposed, which indicates that the most substituent specific cross‐interaction effect exists in the pair of max electron‐withdrawing group (EWG) and max electron‐donating group (EDG) or the pair of max EDG and max EWG. Further to verify the obtained correlation equation, 15 samples of model compounds were prepared and their δ_C(C?N) was measured in this work. The predicted δ_C(C?N) values with the obtained equation are in good agreement with the measured ones for these prepared compounds, which confirmed the reliability of the obtained equation. Copyright © 2010 John Wiley & Sons, Ltd.     

Palladium‐catalyzed cyclization of 2‐alkynyl‐N‐ethanoyl anilines to indoles: synthesis,structural, spectroscopic,and mechanistic study

This study reports a facial regio‐selective synthesis of 2‐alkyl‐N‐ethanoyl indoles from substituted‐N‐ethanoyl anilines employing palladium (II) chloride, which acts as a cyclization catalyst. The mechanistic trait of palladium‐based cyclization is also explored by employing density functional theory. In a two‐step mechanism, the palladium, which attaches to the ethylene carbons, promotes the proton transfer and cyclization. The gas‐phase barrier height of the first transition state is 37 kcal/mol, indicating the rate‐determining step of this reaction. Incorporating acetonitrile through the solvation model on density solvation model reduces the barrier height to 31 kcal/mol. In the presence of solvent, the electron‐releasing (–CH₃) group has a greater influence on the reduction of the barrier height compared with the electron‐withdrawing group (–Cl). These results further confirm that solvent plays an important role on palladium‐catalyzed proton transfer and cyclization. For unveiling structural, spectroscopic, and photophysical properties, experimental and computational studies are also performed. Thermodynamic analysis discloses that these reactions are exothermic. The highest occupied molecular orbital?lowest unoccupied molecular orbital gap (4.9–5.0 eV) confirms that these compounds are more chemically reactive than indole. The calculated UV–Vis spectra by time‐dependent density functional theory exhibit strong peaks at 290, 246, and 232 nm, in good agreement with the experimental results. Moreover, experimental and computed ¹H and ¹³C NMR chemical shifts of the indole derivatives are well correlated. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparative study of electronic structure and optical properties of a series of Pt(II) complexes containing different electron‐donating and ‐withdrawing groups: a DFT study

We report a quantum‐chemistry study of electronic structures and spectral properties of a series of Pt(II) complexes containing different substituents (? CH₃ ( 1 ), ? OCH₃ ( 2 ), ? NO₂ ( 3 ), ? CF₃ ( 4 ), and ? COOH ( 5 )). 1 and 2 have been previously synthesized in experiment, while 3 – 5 are artificial complexes that we suggest can be used to investigate the electron‐withdrawing effect on charge injection, transport, absorption, and phosphorescence properties. The results reveal that the stronger electron‐donating and ‐withdrawing groups show stronger absorption intensity, while the phosphorescence efficiency is generally higher for complexes containing electron‐donating substituents. 1 and 2 are easier for hole injection, while 3 – 5 are easier for electron injection. The enhanced electron injection abilities of 3 – 5 will confine more excitons in the light‐emitting layer (EML) and may not result in lower electroluminescence (EL) efficiency than 1 and 2 . These results suggest that the three artificial complexes may be new emitters in organic light‐emitting diodes (OLEDs). Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of and structure–property relationships in zinc complexes of bis‐metaphenylene semiquinone biradical species

The design of novel, functionalized bis‐metaphenylene semiquinone (SQ) ligands and their corresponding metal complexes which combine conformational flexibility and electron‐withdrawing, electron‐donating, and conjugating substituents enable investigation of multiple structure–property relationships. Along these lines, we report the synthesis of three new bis(Zn^II(SQ)Tp^Cum,Me) complexes containing the bis‐metaphenylene coupling fragment. Using electron paramagnetic resonance spectroscopy, ab initio computations and superconducting quantum interference device magnetometry, we show how spin‐density is affected by the bis‐metaphenylene system substituents. Copyright © 2011 John Wiley & Sons, Ltd.     

A DFT study of transition structures and reactivity in solvolyses of tert‐butyl chloride,cumyl chlorides,and benzyl chlorides

DFT computations were performed on the S_N1 and S_N2 solvolyses of substituted cumyl chlorides and benzyl chlorides in ethanol and water, by increasing stepwise the C? Cl distance and by optimization. The total energy increases with the increase in the Cl? C distance in S_N1 reactions, while free energy of activation pass through maximum. To validate the results, the calculated free energies of activation were compared with data obtained by kinetic measurements. The structural parameters of the transition states were correlated with the Hammett substituent constants and compared with the data of hydrolyses of tert‐butyl chloride and methyl chloride, which proceed with known mechanisms. Conclusions on the mechanisms of the reactions were driven from the effect of substituents on free energies of activation. Cumyl chlorides substituted with electron‐donating (e‐d) groups solvolyze with S_N1 mechanism, while the reactions of substrates that bear electron‐withdrawing groups proceed with weak nucleophilic assistance of the solvent. Benzyl chlorides hydrolyze through an S_N2 pathway except those derivatives that have strongly e‐d groups, where the reaction has S_N1 character, but a weak nucleophilic assistance of the water should also be taken into consideration. Copyright © 2007 John Wiley & Sons, Ltd.     

Mechanism of nucleophilic substitutions at phenacyl bromides with pyridines. A computational study of intermediate and transition state

DFT computations have been performed on nucleophilic substitutions of phenacyl bromides with pyridines to investigate the mechanism of the reaction. In contrast with earlier suppositions, tetrahedral intermediate is not formed by the addition of pyridine on the C?O group of phenacyl bromide, because the total energy of the reacting species increases continuously, when the distance between the N and C(?O) atoms of reactants is shorter than 2.7 Å. At a greater distance, however, a bridged complex of the reactants is observed, in which the N atom of pyridine is slightly closer to the C atom of the C?O, than to the C atom of the CH₂Br group of phenacyl bromide, the distances are 2.87 and 3.05 Å, respectively. The attractive forces between the oppositely polarized N and C(?O) atoms in the complex decrease the free energy of activation of the S_N2 attack of pyridine at the CH₂Br group. The calculated structural parameters of the S_N2 transition states (TS) indicate, that earlier TSs are formed when the pyridine nucleophile bears electron‐donating (e‐d) groups, while electron‐withdrawing (e‐w) groups on phenacyl bromide substrate increase the tightness of the TS. Free energies of activation computed for the S_N2 substitution agree well with the data calculated from the results of kinetic experiments and correlate with the σ_Py substituent constants, derived for pyridines, and with the Hammett σ constants, when the substituents (4‐MeO‐4‐NO₂) are varied on the pyridine or on the phenacyl bromide reactants. Copyright © 2008 John Wiley & Sons, Ltd.     

Modulation of electronic structures of thienylene vinylene oligomers by substituents and solvents: ground and excited states

The effects of substituents on the electronic structures of di(thienylene vinylene) (2TV) in ground and excited states are studied using density functional theory (DFT) and time‐dependent DFT (TD‐DFT), respectively. A representative set of electron donating groups (amino, methoxy and methyl) and withdrawing groups (acetylene, cyano and nitro) are introduced on the vinylene and thienyl moieties to investigate the influence of substituents. Bulk solvent effects are also taken into account by means of the polarizable continuum model (PCM). In contrast to the aromatic structures of 2TV and its derivatives in their ground (S₀) states, the electronic structures of first singlet excited (S₁) states are rather delocalized. The electron‐donating/withdrawing capability, position and number of substituents are important factors in tuning the vertical S₀ → S₁ absorption energies and S₁ → S₀ emission energies of 2TV derivatives. The NO₂‐ and NH₂‐substituents exert significant effects on the geometries of both ground and excited states and hence the absorption and photoluminescence (PL) emission spectra. The solvent polarity introduces modest influence on the excitation energies for most of the 2TV derivatives. But the absorption and PL emission spectra of nitro‐substituted 2TV exhibit noticeable red shifts as the medium polarity increases. Copyright © 2008 John Wiley & Sons, Ltd.     

Nucleophilic reactivity of aniline derivatives towards the nitroso group

This study investigates the reactivity of the electrophilic nitroso group towards nucleophilic aniline derivatives from various nitrosating agents. A relationship between the rate of nitrosation and Edwards' nucleophilic parameter (E_n) is disclosed, indicative of a transition state that is mostly product‐like in nature with respect to cleavage of the nitroso bond in the nitrosating agent. A similar relationship based on the work of Marcus provides a considerably better explanation of the data. Through application of the Marcus equation, the free energy change of reaction is calculated for the nitrosation reactions studied, which in turn is applied to develop an equation linking the free energy of formation of a nitrosamine and its corresponding protonated amine. This equation accounts for the often‐observed Brønsted relationships in nitrosation reactions. The intrinsic barrier to reaction is estimated to be 10 kJ mol^?1, indicating that the main impedance to nitrosation arises from the unfavourable reaction thermodynamics. However, for the nitrosation of aniline derivatives substituted with π‐electron withdrawing groups, an unbalancing of the transition state results in an increased intrinsic barrier, of the order of 19 kJ mol^?1. For electronic‐effect aniline derivatives, a More O'Ferrall–Jencks diagram shows the nitrosation transition state to be synchronously well balanced between reactants and products. This diagram also confirms that the reaction follows a concerted mechanism. The nitrosation of resonance‐stabilised aniline derivatives is somewhat less synchronous, however, due to delocalisation of the lone electron pair on the amino group, induced by π electron withdrawing substituents. Transition states were located according to the theory of harmonic parabolic wells. The results of these calculations agreed with transition state locations predicted using linear free energy relationship techniques. A method is developed which approximates free energy profiles by treating the product and reactant free energy wells as harmonic parabola, while the free energy profile around the transition state is taken as the parabolic barrier to the product and reactant energy wells. Applying this technique, free energy profiles for electronic‐effect and resonance‐stabilised aniline nitrosation are predicted, utilising measured kinetic values and predicted thermodynamic properties. We couple the simulated free energy profiles with their corresponding More O'Ferrall–Jencks diagrams in order to elucidate the three‐dimensional reaction path traversed between reactants and products, in terms of both structure and energy. We also demonstrate that the nitrosonium ion behaves as a soft acid, and should therefore undergo covalent frontier‐orbital controlled bonding. Copyright © 2007 John Wiley & Sons, Ltd.     

Propanolysis of arenesulfonyl chlorides: Nucleophilic substitution at sulfonyl sulfur

We have studied the mechanism of solvolysis of arenesulfonyl chlorides by propan‐1‐ol and propan‐2‐ol at 303‐323 K. Kinetic profiles were appropriately fit by first‐order kinetics. Reactivity increases with electron‐donating substituents. Ortho‐alkyl substituted derivatives of arenesulfonyl chlorides show increased reactivity, but the origin of this “positive” ortho‐effect remains unclear. Likely, ortho‐methyl groups restrict rotation around the C‐S bond, facilitating the attack of the nucleophile. No relevant reactivity changes have been found with propan‐1‐ol and propan‐2‐ol in terms of nucleophile steric effect. The existence of isokinetic relationships for all substrates suggests a single mechanism for the series. Solvolysis reactions of all substrates in both alcohols show isokinetic temperatures (T_iso) close to the working temperature range, which is an evidence of the process being influenced by secondary reactivity factors, likely of steric nature in the TS. Solvation plays a relevant role in this reaction, modulating the reactivity. In some cases, the presence of t‐Bu instead of Me in para‐ position leads to changes in the first solvation shell, increasing the energy of the reaction (ca. 1 kJ·mol^?1). The obtained results suggest the same kinetic mechanism of solvolysis of arenesulfonyl chlorides for propan‐1‐ol and propan‐2‐ol, as in MeOH and EtOH, where bimolecular nucleophilic substitution (S_N2) takes place with nucleophilic solvent assistance of one alcohol molecule and the participation of the solvent network involving solvent molecules of the first solvation shell.     

Basicity of the polydentate captodative aminoenones. Ab initio,DFT, and FTIR study

Electron donating ability of the oxygen, nitrogen, and carbon atoms of captodative aminoenones R'CH = C(NR₂)EWG, EWG = CHO, C(O)Me, C(O)CF₃, C(O)Ph was investigated using ab initio and Density Functional Theory (DFT) calculations, Natural Bond Analysis (NBO) analysis, and Fourier Transform InfraRed (FTIR) spectroscopy. The influence of both electron withdrawing group (EWG) and double bond substituents on the proton affinity of the basic centers, orbital interaction, as well as resonance stabilization energies between heteroatoms and double bonds are discussed. The results obtained are critically compared with the push–pull aminoenones. The comparison of experimental values ΔνOH and theoretical values of H‐bonding energy was used to determine the H‐complex type of aminoenone with phenol and the H‐bond strength. Copyright © 2016 John Wiley & Sons, Ltd.     

Substituent effect on electron affinity,gas‐phase basicity,and structure of monosubstituted propargyl radicals and their anions: a theoretical study

The substituent effect of electron‐withdrawing groups on electron affinity and gas‐phase basicity has been investigated for substituted propargyl radicals and their corresponding anions. It is shown that when a hydrogen of the α‐CH₂ group or acetylenic CH in the propargyl system is substituted by an electron‐withdrawing substituent, electron affinity increases, whereas gas‐phase basicity decreases. The calculated electron affinities are 0.95 eV (CH?C? CH₂?), 1.15 eV (CH?C? CHF?), 1.38 eV (CH?C? CHCl?), 1.48 eV (CH?C? CHBr?) for the isomers with terminal CH and 1.66 eV (CF?C? CH₂?), 1.70 eV (CCl?C? CH₂?), 1.86 eV (CBr?C? CH₂?) for the isomers with terminal CX at B3LYP level. The calculated gas‐phase basicities for their anions are 378.4 kcal/mol (CH?C? CH₂:^?), 371.6 kcal/mol (CH?C? CHF:^?), 365.1 kcal/mol (CH?C? CHCl:^?), 363.5 kcal/mol (CH?C? CHBr:^?) for the isomers with terminal CH and 362.6 kcal/mol (CF?C? CH₂:^?), 360.4 kcal/mol (CCl?C? CH₂:^?), 356.3 kcal/mol (CBr?C? CH₂:^?) for the isomers with terminal CX at B3LYP level. It is concluded that the larger the magnitude of electron‐withdrawing, the greater is the electron affinity of radical and the smaller is the gas‐phase basicity of its anion. This tendency of the electron affinities and gas‐phase bacisities is greater in isomers with the terminal CX than isomers with the terminal CH. Copyright © 2009 John Wiley & Sons, Ltd.     

Density functional theory study of methoxide promoted and Zn(II)‐complexed methoxide promoted cleavages of aryl‐ and alkyl acetates in methanol. Transition from concerted to stepwise processes as a function of leaving group ability

Density functional theory calculations were performed for the methanolysis reactions of a set of aryloxy and alkoxy acetates ( 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h , 1i , 1j , 1k , 1l , 1m ) promoted by methoxide and a 1,5,9‐triazacyclododecane‐complexed Zn^(II)‐methoxide [2(OCH₃)]⁺ in order to give free energies and structural data for the various intermediates and transition states along the reaction pathway. The methoxide‐promoted reactions experience a transition of pathways from enforced‐concerted addition of CH₃O^? to the C = O unit for substrates having a good aryloxy leaving groups (LGs) with strong electron withdrawers ( 1a , 1b , 1c , 1d , 1e ) to a two step process with rate‐limiting CH₃O^‐ attack on aryloxy acetates having higher (the pK_a of the parent phenol of the LG in methanol) values. Only in the case of the substrates 1i‐m having alkoxy LGs is there an observed change in rate‐limiting step that occurs at the quasi‐symmetrical point where the . The methanolysis process for the 2,4‐dinitrophenoxy substrate ( 1a ) promoted by [2(OCH₃)]⁺ involves transient binding of the substrate to the metal complex followed by a rate‐limiting, enforced‐concerted attack of Zn^(II)‐coordinated ^–OCH₃, with fast breakdown of an addition intermediate that does not have a significant lifetime. For substrates 1b,c having slightly less electron withdrawing substituents, the reaction has two steps with rate‐limiting attack and an unassisted LG departure. As the increases, the reaction still has two steps with rate‐limiting attack, but departure of the LG is now assisted by its coordination to the metal ion. For alkoxy containing substrates, a change in rate‐limiting step occurs centered at methoxy acetate, 1j , (when ) for which the second step of metal ion assisted departure of methoxide becomes partially rate‐limiting. The Brønsted plots computed for the methoxide‐promoted and [2(OCH₃)]⁺‐promoted methanolyses are compared with the previously determined experimental data and are analyzed as arising not from a common line attributable to all substrates but rather in terms of separate, but intersecting, plots for aryl‐ and alkyl acetates. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of ortho substituents on 17O NMR chemical shifts in phenyl esters of substituted benzoic acids

¹⁷O NMR spectra for 29 phenyl esters of ortho‐, para,‐ and meta‐substituted benzoic acids, X‐C₆H₄CO₂C₆H₅, at natural abundance in acetonitrile were recorded. The δ(¹⁷O) values of carbonyl and the single‐bonded oxygens for para derivatives gave good correlation with the σ⁺ constants. The δ(¹⁷O) values for meta derivatives correlated well with the σ_m constants. The influence of ortho substituents on the δ(¹⁷O) values of carbonyl oxygen and the single‐bonded oxygens was analyzed using the Charton equation containing the inductive, σ_I, resonance, σ⁺_R, and steric, E, substituent constants. For ortho derivatives, excellent correlations with the Charton equation were obtained when the data treatment was performed separately for derivatives containing electron‐donating +R and electron‐attracting ?R substituents. The electron‐donating substituents in ortho‐, meta‐, and para‐substituted esters resulted in shielding of the ¹⁷O signal and the electron‐withdrawing groups caused deshielding. In phenyl ortho‐substituted benzoates, the substituent‐induced positive inductive (ρ_I > 0), resonance (ρ_R > 0), and steric (δ_orthoE > 0) effects were found. The steric interaction of ortho substituents with ester group was found to produce a deshielding effect on the carbonyl and single‐bonded oxygens. For ortho derivatives with ?R substituents, the resonance term was insignificant and the steric term was ca. twice weaker as compared to that for derivatives with +R substituents. The δ(¹⁷O) values for ortho‐substituted nitrobenzenes, acetophenones, and benzoyl chlorides showed a good correlation with the Charton equation as well. In ortho‐substituted nitrobenzenes the inductive, resonance and steric effect were found to be ca. 1.7 times stronger as compared to that for phenyl ortho‐substituted benzoates. Copyright © 2010 John Wiley & Sons, Ltd.     

Transient resonance Raman spectroscopy and DFT calculations of metal‐to‐ligand charge transfer states of Cu(I) complexes of substituted 1,10‐phenanthroline ligands and their perdeuterated isotopomers

Cu(I) complexes of the type [Cu(L)(PPh₃)₂]⁺, where L is the bidentate ligand 4,7‐diphenyl‐1, 10‐phenanthroline (dip) and 3,4,7,8‐tetramethyl‐1,10‐phenanthroline (tem) and their perdeuterated analogues, have been synthesised and the transient resonance Raman spectra of these complexes have been measured. The spectra show two sets of bands, one due to the PPh₃ ligands and the other due to L^.− created through the metal‐to‐ligand charge transfer transition. Density functional theory calculations have been used to model ligands and complexes in the ground state and good agreement has been found between calculated and measured bands with a mean absolute deviation of 8–10 cm⁻¹ for the ligands and 5 cm⁻¹ for the complexes. Shifts in the bands due to deuteration have also been well predicted, with the shifts for most modes predicted to within 10 cm⁻¹. The structure and spectra of the excited states have been modelled using two approaches. The reduced state [Cu(L^.−)(PH₃)₂] was used for both complexes to predict the changes in the structure of the polypyridyl ligand and for [Cu(dip)(PPh₃)₂]⁺ the triplet state was also optimised. Both approaches show that similar structural changes in the ligand are predicted. In the case of [Cu(dip)(PPh₃)₂]^+* and [Cu(dip^.−)(PPh₃)₂], the calculated states are ³A₂ and ²A₂, respectively, consistent with experiment. Calculations on [Cu(tem)(PPh₃)₂]^+* give a ³B₁ state. This is not consistent with experimental results. For [Cu(tem^.−)(PPh₃)₂] both the ²B₁ and ²A₂ states may be calculated and the experimental spectrum of [Cu(tem)(PPh₃)₂]^+* is closer to that of the ²A₂ [Cu(tem^.−)(PPh₃)₂] species. Calculated wavenumbers are compared to measured transient resonance Raman L^.− bands and found to have a mean absolute deviation of 8 cm⁻¹ for the triplet state of [Cu(dip)(PPh₃)₂]⁺ and 16 cm⁻¹ for the reduced state of [Cu(tem)(PPh₃)₂]⁺. Copyright © 2008 John Wiley & Sons, Ltd.     

Aluminum alkoxide complexes from highly substituted 3,4‐epoxy alcohols: An NMR and computational study

The organoaluminum mediated epoxide ring opening of epoxy alcohols is a key step in the oxirane‐based approach for polypropionate synthesis. However, this reaction has shown unanticipated regioselectivities when applied to 2‐methyl‐3,4‐epoxy alcohols. In order to gain mechanistic insight into the factors controlling the epoxide ring opening process, diastereomeric 2‐methyl‐3,4‐epoxy alcohols were reacted with triethylaluminum in order to identify the aluminum complexes formed by these systems. Different epoxide–aluminum complexes were calculated using ab initio HF/[13s7p/11s5p] and B3PW91/6‐31G** gauge‐including atomic orbital (GIAO) methods and compared to the experimental NMR data. The calculated and experimental data correlates with the aluminum dimer complex (TIPSOCH₂CH(OAlEt₂)CH(CH)₃CHCH(O)(AlEt₃))₂ (VIII) for the systems favoring the nucleophilic attack at the external C4 epoxide carbon, while an unusual trialuminum species TIPSOCH₂CH(OAlEt₂)CH(CH)₃CHCH(O)(AlEt₃)₂ (X) is consistent with the systems favoring the internal C3 attack. The ²⁷Al NMR data established the tetracoordinated nature of the aluminum metal in all alkoxy aluminum intermediates, while the ¹³C NMR data provided insight into the aluminum‐oxygen coordination. The formation of the complexes was dictated by the stereochemical disposition of the substituents. These complexes are different from the generally accepted bidentate intermediates proposed for 2,3‐epoxy alcohols and simpler 3,4‐epoxy alcohols. Copyright © 2012 John Wiley & Sons, Ltd.     

On bistability in molecular systems: Photomagnetic studies of inorganic complexes

Photo‐induced effects have been detected by magnetic measurements, Mössbauer spectroscopy and reflectivity. The LIESST effect has been achieved in the spin‐crossover system [Fe_xCo_1-x(btr)₂(NCS)₂]·H₂O. We investigated the purely photo‐induced magnetism of a Prussian Blue analogue Rb_0.52Co[Fe(CN)₆]_0.84, 2.31 H₂O, involving an optical electron transfer from Fe^II to Co^III. Inherent aspects of photomagnetic experiments are described: bulk and surface effects, magnetic and electronic metastabilities of the photo‐excited state.     

Impact of substituents in the NN ligand on the emission wavelength of Cu(I) complexes: Insight from experimental and theoretical approach

Three mononuclear Cu(I) complexes [Cu(bop)(PPh₃)₂][BF₄], [Cu(fop)(PPh₃)₂][BF₄] and [Cu (pop)(PPh₃)₂][BF₄] were synthesized, where 2-(5-tert-butyl-1,3,4-oxadiazol-2-yl)pyridine (bop), 2-(5-(trifluoromethyl)-1,3,4-oxadiazol-2-yl)pyridine (fop) or 2-(5-phenyl-1,3,4-oxadiazol-2-yl)pyridine (pop) was used as N^∧N chelate ligand and triphenylphosphine was used as ancillary ligand. Several substituents with different electronic effects, such as tert-butyl (t-Bu), trifluoromethyl (CF₃) and phenyl (Ph) groups, were introduced into the 1,3,4-oxadiazole moiety of the N^∧N chelate ligands. The photophysical properties of the complexes were examined by UV-vis absorption and photoluminescence (PL) spectroscopies. The complex [Cu(fop)(PPh₃)₂][BF₄] with a CF₃ group in the N^∧N chelate ligand exhibited the lowest energy absorption and emission band. Electrochemical analyses combined with density functional theory (DFT) calculations established that the introduction of electron withdrawing group (CF₃) decreases the HOMO-LUMO energy gap, and the introduction of electron donating group (t-Bu) into the 1,3,4-oxadiazole moiety has a similar effect on the emission wavelength as that of the introduction of a phenyl group with a π-conjugation.