Bonding in Diborane–Metal Complexes: A Quantum‐Chemical and Experimental Study of Complexes Featuring Early and Late Transition Metals

The coordination chemistry of the doubly base‐stabilised diborane(4), [HB(hpp)]₂ (hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido‐[1,2‐a]pyrimidinate), was extended by the synthesis of new late transition‐metal complexes containing Cu^I and Rh^I fragments. A detailed experimental study was conducted and quantum‐chemical calculations on the metal–ligand bonding interactions for [HB(hpp)]₂ complexes of Group 6, 9, 11 and 12 metals revealed the dominant B? H? M interactions in the case of early transition‐metal fragments, whereas the B? B? M bonding prevails in the case of the late d‐block compounds. These findings support the experimental results as reflected by the IR and NMR spectroscopic parameters of the investigated compounds. DFT calculations on [MeB(hpp)]₂ and model reactions between [B₂H₄ ? 2NMe₃] and [Rh(μ‐Cl)(C₂H₄)₂] showed that the bicyclic guanidinate allows in principle for an oxidative addition of the B? B bond. However, the formation of σ‐complexes is thermodynamically favoured. The results point to the selective B? H or B? B bond‐activation of diborane compounds by complexation, depending on the chosen transition‐metal fragment.     

Macromolecular reaction and interdiffusion in a compatible polymer blend, 2. The role of H‐bonding

A theory describing slow macromolecular reaction and interdiffusion in a compatible polymer blend is extended to consider H‐bonding. The known treatments of H‐bonding influence on the free energy of mixing and chains' mobilities are combined to calculate mutual diffusion coefficients in the framework of linear non‐equilibrium thermodynamics. Numerical calculations are performed for a blend of two random copolymers AC and BC to reveal the effect of H‐bonding (between A and B, B and B units) on the interdiffusion profiles. Then, the transformation of A units into B ones is included and the reaction‐diffusion equations are solved with the parameters corresponding to the blend of poly(tert‐butyl acrylate‐co‐styrene) with poly‐(acrylic acid‐co‐styrene) in which the thermal decomposition of tert‐butyl acrylate units takes place. The numerical calculations show that this system is suitable for the experimental verification of theoretical predictions concerning the interplay between macromolecular reaction and interdiffusion in polymer blends.     

Carbonyl(5‐nitrotropolonato‐κ2O1,O2)(tri­phenyl­phosphine‐κP)­rhodium(I)

The molecule of the title complex, [Rh(5‐NO₂trop)(C₁₈H₁₅P)(CO)] (5‐­NO₂trop is 2‐hydroxy‐5‐nitrocyclo­hepta‐2,4,6‐trienone, C₇H₄NO₄), has a distorted square‐planar geometry. Strong intramolecular and weak intermolecular hydrogen bonding is observed, with H⋯O distances of the order of 2.25 and 2.55 Å, respectively. The Rh—CO, Rh—O (trans to CO), Rh—O (trans to P) and Rh—P bond distances are 1.775 (7), 2.072 (4), 2.068 (4) and 2.2397 (17) Å, respectively, the O—Rh—O angle is 77.09 (16)° and the bidentate O—C—C—O torsion angle is 1.5 (7)°.     

A Metal‐Containing N‐Heterocyclic Germylene Based on an Oxalamidine Framework

A metal‐containing N‐heterocyclic germylene based on a N‐mesityl (Mes)‐substituted oxalamidine framework is reported. The precursor (MesN=)₂C–C(–N(H)Mes)₂ ( 1 H₂) was converted into its rhodium complex [Rh(κ²N‐ 1 H₂)(cod)][OTf] ( 2 ) (cod = 1,5‐cyclooctadiene; OTf = triflate) in 62 % isolated yield. Subsequent reaction of 2 with Ge{N(SiMe₃)₂}₂ gave the crystalline N‐heterocyclic germylene [Rh(cod)(μ‐ 1 )Ge][OTf] ( 3 ) in 50 % yield. The compounds under study were fully characterized by various methods, also including X‐ray crystallographic studies on single crystals of 2 and 3 . Density functional theory (DFT) calculations revealed that π conjugation in the bridging oxalamidine framework is increased and n(N)–p(Ge) π bonding is decreased upon κ²N metal coordination; a further weakening of the Ge–N bond occurs through triflate coordination to the Ge^II atom. Nevertheless, preliminary coordination studies revealed that 3 behaves as 2‐electron (L ‐type) germylene donor ligand. Treatment of 3 with [Ir(cod)Cl]₂ furnished the heterobimetallic complex [Rh(cod)(μ‐ 1 )Ge‐Ir(cod)Cl][OTf] ( 4 ), as evidenced by NMR spectroscopic investigations and DFT calculations.     

1H NMR analysis of O‐methyl‐inositol isomers: a joint experimental and theoretical study

Density functional theory (DFT) calculations of ¹H NMR chemical shifts for l ‐quebrachitol isomers were performed using the B3LYP functional employing the 6‐31G(d,p) and 6‐311 + G(2d,p) basis sets. The effect of the solvent on the B3LYP‐calculated NMR spectrum was accounted for using the polarizable continuum model. Comparison is made with experimental ¹H NMR spectroscopic data, which shed light on the average uncertainty present in DFT calculations of chemical shifts and showed that the best match between experimental and theoretical B3LYP ¹H NMR profiles is a good strategy to assign the molecular structure present in the sample handled in the experimental measurements. Among four plausible O‐methyl‐inositol isomers, the l ‐quebrachitol 2a structure was unambiguously assigned based only on the comparative analysis of experimental and theoretical ¹H NMR chemical shift data. The B3LYP infrared (IR) spectrum was also calculated for the four isomers and compared with the experimental data, with analysis of the theoretical IR profiles corroborating assignment of the 2a structure. Therefore, it is confirmed in this study that a combined experimental/DFT spectroscopic investigation is a powerful tool in structural/conformational analysis studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Metal‐induced B–H Activation. Addition of Methyl Acetylene Carboxylates to Cp*Rh‐ and Cp*Ir 16 e Halfsandwich Complexes containing a Chelating 1,2‐Dicarba‐closo‐dodecaborane‐1,2‐diselenolato Ligand

Reactions of the 16e halfsandwich complexes Cp*M[Se₂C₂(B₁₀H₁₀)] ( 5 M = Rh, 6 M = Ir) with both methyl acetylene monocarboxylate and dimethyl acetylene dicarboxylate were studied in order to obtain information on the influence of the chalcogen (selenium versus sulfur), as well as further evidence for B–H activation, ortho‐metalation and substitution of the carborane. In the case of the rhodium‐selenium complex 5 , the reaction with methyl acetylene monocarboxylate gave products which were all structurally different compared to those of the sulfur analogue of 5 : a polycyclic derivative 12 with a B(6)‐substituted carborane cage was obtained as one of the final products; in addition, both geometrical isomers containing a Rh–B bond ( 10 , 11 ) and isomers without a Rh–B bond ( 8 , 9 ) were isolated, the latter being the result of twofold insertion into one of the Rh–Se bonds. In the case of the iridium‐selenium complex 6 , the reaction with methyl acetylene monocarboxylate led to the geometrical isomers 13 and 14 (similar to 10 and 11 ) with structures possessing an Ir–B bond. Both 5 and 6 reacted with dimethyl acetylene dicarboxylate at room temperature to give the complexes 15 and 16 which are formed by addition of the C≡C unit to the metal center and insertion into one of the metal‐selenium bonds. The proposed structures in solution were deduced from NMR data (¹H, ¹¹B, ¹³C, ⁷⁷Se, ¹⁰³Rh NMR), and an X‐ray structural analysis was carried out for the rhodium complex 12 .     

Water‐mediated intermolecular interactions in 1,2‐O‐cyclohexylidene‐myo‐inositol: a quantitative analysis

The syntheses of new myo‐inositol derivatives have received much attention due to their important biological activities. 1,2‐O‐Cyclohexylidene‐myo‐inositol is an important intermediate formed during the syntheses of certain myo‐inositol derivatives. We report herein the crystal structure of 1,2‐O‐cyclohexylidene‐myo‐inositol dihydrate, C₁₂H₂₀O₆·2H₂O, which is an intermediate formed during the syntheses of myo‐inositol phosphate derivatives, to demonstrate the participation of water molecules and hydroxy groups in the formation of several intermolecular O—H…O interactions, and to determine a low‐energy conformation. The title myo‐inositol derivative crystallizes with two water molecules in the asymmetric unit in the space group C 2/c , with Z = 8. The water molecules facilitate the formation of an extensive O—H…O hydrogen‐bonding network that assists in the formation of a dense crystal packing. Furthermore, geometrical optimization and frequency analysis was carried out using density functional theory (DFT) calculations with B3LYP hybrid functionals and 6‐31G(d), 6‐31G(d,p) and 6‐311G(d,p) basis sets. The theoretical and experimental structures were found to be very similar, with only slight deviations. The intermolecular interactions were quantitatively analysed using Hirshfeld surface analysis and 2D (two‐dimensional) fingerplot plots, and the total lattice energy was calculated.     

Polymorphism of methyl 4‐amino‐3‐phenylisothiazole‐5‐carboxylate: an experimental and theoretical study

Being a close analogue of amflutizole, methyl 4‐amino‐3‐phenylisothiazole‐5‐carboxylate (C₁₁H₁₀N₂O₂S) was assumed to be capable of forming polymorphic structures. Noncentrosymmetric and centrosymmetric polymorphs have been obtained by crystallization from a series of more volatile solvents and from denser tetrachloromethane, respectively. Identical conformations of the molecule are found in both structures. The two polymorphs differ mainly in the intermolecular interactions formed by the amino group and in the type of stacking interactions between the π‐systems. The most effective method for revealing packing motifs in structures with intermolecular interactions of different types (hydrogen bonding, stacking, dispersion, etc.) is to study the pairwise interaction energies using quantum chemical calculations. Molecules form a column as the primary basic structural motif due to stacking interactions in both polymorphic structures under study. The character of a column (straight or zigzag) is determined by the orientations of the stacked molecules (in a `head‐to‐head' or `head‐to‐tail' manner). Columns bound by intermolecular N—H…O and N—H…N hydrogen bonds form a double column as the main structural motif in the noncentrosymmetric structure. Double columns in the noncentrosymmetric structure and columns in the centrosymmetric structure interact strongly within the ab crystallographic plane, forming a layer as a secondary basic structural motif. The noncentrosymmetric structure has a lower density and a lower (by 0.59 kJ mol^?1) lattice energy, calculated using periodic calculations, compared to the centrosymmetric structure.     

Glycosidic linkage,N‐acetyl side‐chain,and other structural properties of methyl 2‐acetamido‐2‐deoxy‐β‐d‐glucopyranosyl‐(1→4)‐β‐d‐mannopyranoside monohydrate and related compounds

The crystal structure of methyl 2‐acetamido‐2‐deoxy‐β‐d ‐glycopyranosyl‐(1→4)‐β‐d ‐mannopyranoside monohydrate, C₁₅H₂₇NO₁₁·H₂O, was determined and its structural properties compared to those in a set of mono‐ and disaccharides bearing N‐acetyl side‐chains in βGlcNAc aldohexopyranosyl rings. Valence bond angles and torsion angles in these side chains are relatively uniform, but C—N (amide) and C—O (carbonyl) bond lengths depend on the state of hydrogen bonding to the carbonyl O atom and N—H hydrogen. Relative to N‐acetyl side chains devoid of hydrogen bonding, those in which the carbonyl O atom serves as a hydrogen‐bond acceptor display elongated C—O and shortened C—N bonds. This behavior is reproduced by density functional theory (DFT) calculations, indicating that the relative contributions of amide resonance forms to experimental C—N and C—O bond lengths depend on the solvation state, leading to expectations that activation barriers to amide cis–trans isomerization will depend on the polarity of the environment. DFT calculations also revealed useful predictive information on the dependencies of inter‐residue hydrogen bonding and some bond angles in or proximal to β‐(1→4) O‐glycosidic linkages on linkage torsion angles ? and ψ. Hypersurfaces correlating ? and ψ with the linkage C—O—C bond angle and total energy are sufficiently similar to render the former a proxy of the latter.     

B(C6F5)3/Chiral Phosphoric Acid Catalyzed Ketimine–Ene Reaction of 2‐Aryl‐3H‐indol‐3‐ones and α‐Methylstyrenes

The enantioselective ketimine–ene reaction is one of the most challenging stereocontrolled reaction types in organic synthesis. In this work, catalytic enantioselective ketimine–ene reactions of 2‐aryl‐3H‐indol‐3‐ones with α‐methylstyrenes were achieved by utilizing a B(C₆F₅)₃/chiral phosphoric acid (CPA) catalyst. These ketimine–ene reactions proceed well with low catalyst loading (B(C₆F₅)₃/CPA=2 mol %/2 mol %) under mild conditions, providing rapid and facile access to a series of functionalized 2‐allyl‐indolin‐3‐ones with very good reactivity (up to 99 % yield) and excellent enantioselectivity (up to 99 % ee). Theoretical calculations reveal that enhancement of the acidity of the chiral phosphoric acid by B(C₆F₅)₃ significantly reduces the activation free energy barrier. Furthermore, collective favorable hydrogen‐bonding interactions, especially the enhanced N?H???O hydrogen‐bonding interaction, differentiates the free energy of the transition states of CPA and B(C₆F₅)₃/CPA, thereby inducing the improvement of stereoselectivity.     

Chemistry of transition‐metal complexes containing functionalized phosphines: synthesis and structural analysis of rhodium(I) complexes containing allyl and cyanoalkylphosphines

A series of related acetylacetonate–carbonyl–rhodium compounds substituted by functionalized phosphines has been prepared in good to excellent yields by the reaction of [Rh(acac)(CO)₂] (acac is acetylacetonate) with the corresponding allyl‐, cyanomethyl‐ or cyanoethyl‐substituted phosphines. All compounds were fully characterized by ³¹P, ¹H, ¹³C NMR and IR spectroscopy. The X‐ray structures of (acetylacetonato‐κ²O,O′)(tert‐butylphosphanedicarbonitrile‐κP)carbonylrhodium(I), [Rh(C₅H₇O₂)(CO)(C₈H₁₃N₂)] or [Rh(acac)(CO)(^tBuP(CH₂CN)₂}] ( 2b ), (acetylacetonato‐κ²O,O′)carbonyl[3‐(diphenylphosphanyl)propanenitrile‐κP]rhodium(I), [Rh(C₅H₇O₂)(C₁₅H₁₄N)(CO)] or [Rh(acac)(CO){Ph₂P(CH₂CH₂CN)}] ( 2h ), and (acetylacetonato‐κ²O,O′)carbonyl[3‐(di‐tert‐butylphosphanyl)propanenitrile‐κP]rhodium(I), [Rh(C₅H₇O₂)(C₁₁H₂₂N)(CO)] or [Rh(acac)(CO){^tBu₂P(CH₂CH₂CN)}] ( 2i ), showed a square‐planar geometry around the Rh atom with a significant trans influence over the acetylacetonate moiety, evidenced by long Rh—O bond lengths as expected for poor π‐acceptor phosphines. The Rh—P distances displayed an inverse linear dependence with the coupling constants J_P‐Rh and the IR ν(C[triple‐bond]O) bands, which accounts for the Rh—P electronic bonding feature (poor π‐acceptors) of these complexes. A combined study from density functional theory (DFT) calculations and an evaluation of the intramolecular H…Rh contacts from X‐ray diffraction data allowed a comparison of the conformational preferences of these complexes in the solid state versus the isolated compounds in the gas phase. For 2b , 2h and 2i , an energy‐framework study evidenced that the crystal structures are mainly governed by dispersive energy. In fact, strong pairwise molecular dispersive interactions are responsible for the columnar arrangement observed in these complexes. A Hirshfeld surface analysis employing three‐dimensional molecular surface contours and two‐dimensional fingerprint plots indicated that the structures are stabilized by H…H, C…H, H…O, H…N and H…Rh intermolecular interactions.     

Kinetic Study and NBO Analysis of the Dehydrogenation Mechanism of Five‐membered Ring Heterocyclic 2,5‐Dihydro‐[furan,thiophene, selenophene

The theoretical study of the dehydrogenation of 2,5‐dihydro‐[furan ( 1 ), thiophene ( 2 ), and selenophene ( 3 )] was carried out using ab initio molecular orbital (MO) and density functional theory (DFT) methods at the B3LYP/6‐311G**//B3LYP/6‐311G** and MP2/6‐311G**//B3LYP/6‐311G** levels of theory. Among the used methods in this study, the obtained results show that B3LYP/6‐311G** method is in good agreement with the available experimental values. Based on the optimized ground state geometries using B3LYP/6‐311G** method, the natural bond orbital (NBO) analysis of donor‐acceptor (bond‐antibond) interactions revealed that the stabilization energies associated with the electronic delocalization from non‐bonding lone‐pair orbitals [LP(e)_X3] to δ*_{C(1)  H(2)} antibonding orbital, decrease from compounds 1 to 3 . The LP(e)_X3→δ*_{C(1)  H(2)} resonance energies for compounds 1 – 3 are 23.37, 16.05 and 12.46 kJ/mol, respectively. Also, the LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the decrease of occupancies of LP(e)_X3 non‐bonding orbitals in ring of compounds 1 – 3 ( 3 > 2 > 1 ). The electronic delocalization from LP(e)_X3 non‐bonding orbitals to δ*_{C(1)  H(2)} antibonding orbital increases the ground state structure stability, Therefore, the decrease of LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the kinetic of the dehydrogenation reactions of compounds 1 – 3 (k ₁ >k ₂ >k ₃ ). Also, the donor‐acceptor interactions, as obtained from NBO analysis, revealed that the (_C(4)C(7)→δ*_{C(1)  H(2)} resonance energies decrease from compounds 1 to 3 . Further, the results showed that the energy gaps between (_C(4)C(7) bonding and δ*_{C(1)  H(2)} antibonding orbitals decrease from compounds 1 to 3 . The results suggest also that in compounds 1 – 3 , the hydrogen eliminations are controlled by LP(e)→δ* resonance energies. Analysis of bond order, natural bond orbital charges, bond indexes, synchronicity parameters, and IRC calculations indicate that these reactions are occurring through a concerted and synchronous six‐membered cyclic transition state type of mechanism.     

Carbonyl–carbonyl interactions and amide π‐stacking as the directing motifs of the supramolecular assembly of ethyl N‐(2‐acetylphenyl)oxalamate in a synperiplanar conformation

The title compound, C₁₂H₁₃NO₄, is one of the few examples that exhibits a syn conformation between the amide and ester carbonyl groups of the oxalyl group. This conformation allows the engagement of the amide H atom in an intramolecular three‐centred hydrogen‐bonding S(6)S(5) motif. The compound is self‐assembled by C=O...C=O and amide–π interactions into stacked columns along the b‐axis direction. The concurrence of both interactions seems to be responsible for stabilizing the observed syn conformation between the carbonyl groups. The second dimension, along the a‐axis direction, is developed by soft C—H...O hydrogen bonding. Density functional theory (DFT) calculations at the B3LYP/6‐31G(d,p) level of theory were performed to support the experimental findings.     

Theoretical Study on Hydrogen‐Bond Effects in IR Spectra of High‐ and Low‐Temperature Phases of Nitric Acid Dihydrate

The low‐ and high‐temperature phases (α and β, respectively) of solid nitric acid dihydrate (NAD) are studied in depth by DFT methods. Each phase contains two types of complex structures (H₃O⁺) ? (H₂O), designated A and B, with different hydrogen‐bonding (HB) characteristics. The theoretical study reveals that type A complexes are weakly bound and could be described as (H₃O)⁺ and H₂O aggregates, with decoupled vibrational modes, whereas in type B structures the proton is situated close to the centre of the O ??? O bond and induces strong vibrational coupling. The proton‐transfer mode is predicted at quite different wavenumbers in each complex, which provides an important differentiating spectral feature, together with splitting of some bands in β‐NAD. Theoretical spectra are estimated by using two GGA parameterizations, namely, PBE and BLYP. The potential‐energy surface for each type of HB in NAD is also studied, as is the spectral influence of displacement of the shared H atom along the O? O bond. The results are compared to literature infrared spectra recorded by different techniques, namely, transmission and reflection–absorption, with both normal and tilted incident radiation. This work provides a thorough assignment of the observed spectra, and predictions for some spectra not yet available. The usefulness of high‐level theoretical calculations as performed herein to discriminate between two phases of a solid crystal is thus evidenced.     

First Principles (DFT) Characterization of RhI/dppp‐Catalyzed CH Activation by Tandem 1,2‐Addition/1,4‐Rh Shift Reactions of Norbornene to Phenylboronic Acid

The C?H activation in the tandem, “merry‐go‐round”, [(dppp)Rh]‐catalyzed (dppp=1,3‐bis(diphenylphosphino)propane), four‐fold addition of norborene to PhB(OH)₂ has been postulated to occur by a C(alkyl)?H oxidative addition to square‐pyramidal Rh^III?H species, which in turn undergoes a C(aryl)?H reductive elimination. Our DFT calculations confirm the Rh^I/Rh^III mechanism. At the IEFPCM(toluene, 373.15 K)/PBE0/DGDZVP level of theory, the oxidative addition barrier was calculated to be 12.9 kcal mol^?1, and that of reductive elimination was 5.0 kcal mol^?1. The observed selectivity of the reaction correlates well with the relative energy barriers of the cycle steps. The higher barrier (20.9 kcal mol^?1) for norbornyl–Rh protonation ensures that the reaction is steered towards the 1,4‐shift (total barrier of 16.3 kcal mol^?1), acting as an equilibration shuttle. The carborhodation (13.2 kcal mol^?1) proceeds through a lower barrier than the protonation (16.7 kcal mol^?1) of the rearranged aryl–Rh species in the absence of o‐ or m‐substituents, ensuring multiple carborhodations take place. However, for 2,5‐dimethylphenyl, which was used as a model substrate, the barrier for carborhodation is increased to 19.4 kcal mol^?1, explaining the observed termination of the reaction at 1,2,3,4‐tetra(exo‐norborn‐2‐yl)benzene. Finally, calculations with (Z)‐2‐butene gave a carborhodation barrier of 20.2 kcal mol^?1, suggesting that carborhodation of non‐strained, open‐chain substrates would be disfavored relative to protonation.     

Double Pancake Versus Long Chalcogen–Chalcogen Bonds in Six‐Membered C,N,S‐Heterocycles

The double “pancake” bonding in the dimers of the six‐membered heterocycles 1,3‐dithia‐2,4,6‐triazine ( 4 ) and 1,3‐dithia‐2,4‐diazine ( 16 ) were investigated by means of high‐level quantum chemical calculations (B3LYP and CCSD(T)). It was found that the S–S dimers, 20 a and 27 , are not the most stable isomers, but the dimers showing short S?N ( 21 a ) and S?C ( 25 , 28 ) bonds. An investigation of the 5‐phenyl‐1,3‐dithia‐2,4,6‐triazine ( 4 b ) yields that the syn dimer with two S?S bonds (2.57 Å) is the most stable one. In this dimer, the phenyl groups are placed on top of each other. The additional dispersion energy of the phenyl rings causes a stabilization of the syn‐S–S (C_2v‐like) isomer. As a result, two weak albeit relevant single S?S bonds (2.57 Å) are predicted. These findings contradict the recently published concept of double “pancake” bonding in the dimer 4 b ₂.     

The Simplest Amino‐borane H2B=NH2 Trapped on a Rhodium Dimer: Pre‐Catalysts for Amine–Borane Dehydropolymerization

The μ‐amino–borane complexes [Rh₂(L^R)₂(μ‐H)(μ‐H₂B=NHR′)][BAr^F₄] (L^R=R₂P(CH₂)₃PR₂; R=Ph, ⁱPr; R′=H, Me) form by addition of H₃B?NMeR′H₂ to [Rh(L^R)(η⁶‐C₆H₅F)][BAr^F₄]. DFT calculations demonstrate that the amino–borane interacts with the Rh centers through strong Rh‐H and Rh‐B interactions. Mechanistic investigations show that these dimers can form by a boronium‐mediated route, and are pre‐catalysts for amine‐borane dehydropolymerization, suggesting a possible role for bimetallic motifs in catalysis.     

Quantum‐chemical,IR, NMR,and X‐ray diffraction studies on 2‐(4‐chlorophenyl)‐1‐methyl‐ 1H‐benzo[d]imidazole

The title molecule, 2‐(4‐chlorophenyl)‐1‐methyl‐1H‐benzo[d]imidazole (C₁₄H₁₁ClN₂), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, and single‐crystal X‐ray diffraction. The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated by using the Hartree‐Fock (HF) and density functional theory (DFT/B3LYP) method with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies and GIAO ¹H and ¹³C NMR chemical shifts show good agreement with experimental values. The energetic behavior of the title compound in solvent media has been examined using B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, and nonlinear optical (NLO) properties of the title compound were investigated by theoretical calculations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical insights into the excited‐state process of 4‐tert‐butyl‐2‐(5‐(5‐tert‐butyl‐2‐methoxyphenyl)thiazolo[5,4‐d]thiazol‐2‐yl)‐phenol

In this paper, we theoretically explore the motivation and behaviors of the excited‐state intramolecular proton transfer (ESIPT) reaction for a novel white organic light‐emitting diode (WOLED) material 4‐tert‐butyl‐2‐(5‐(5‐tert‐butyl‐2‐methoxyphenyl)thiazolo[5,4‐d]thiazol‐2‐yl)‐phenol (t‐MTTH). The “atoms in molecules” (AIM) method is adopted to verify the formation and existence of the hydrogen bond O? H···N. By analyzing the excited‐state hydrogen bonding behaviors via changes in the chemical bonding and infrared (IR) vibrational spectra, we confirm that the intramolecular hydrogen bond O? H···N should be getting strengthened in the first excited state in four kinds of solvents, thus revealing the tendency of ESIPT reaction. Further, the role of charge‐transfer interaction is addressed under the frontier molecular orbitals (MOs), which depicts the nature of the electronic excited state and supports the ESIPT reaction. Also, the electron distribution confirms the ESIPT tendency once again. The scanned and optimized potential energy curves according to variational O? H coordinate in the solvents demonstrate that the proton transfer reaction should occur in the S₁ state, and the potential energy barriers along with ESIPT direction support this reaction. Based on the excited‐state behaviors reported in this work, the experimental spectral phenomenon has been reasonably explained.