Co-reporter:Dan Wang, Shu-Mu Li, Jian-Quan Zheng, Duan-Yang Kong, Xiang-Jun ZhengDe-Cai Fang, Lin-Pei Jin
Inorganic Chemistry 2017 Volume 56(Issue 2) pp:
Publication Date(Web):January 5, 2017
DOI:10.1021/acs.inorgchem.6b02784
2-(Trityliminomethyl)-quinolin-8-ol (HL) and its Zn(II) complex were synthesized and characterized by single-crystal X-ray diffraction. HL is an unsymmetrical molecule and coordinated with Zn(II) ion to form ZnL2 in the antiparallel-mode arrangement via Zn—O (hydroxyl group) and Zn—N (quinoline ring) of HL. A high degree of ZnL2 molecules ordering stacking is formed by the coordination bonds and intermolecular π–π interactions, in which head-to-tail arrangement (J-mode stacking) for L– is found. HL is nonfluorescent and ZnL2 is weakly fluorescent in THF. The fluorescence emission of ZnL2 enhances in THF/H2O as H2O% (volume %) is above 60% and aggregates particles with several hundred nanometers are formed, which is confirmed by DLS data and TEM images. The J-aggregates stacking for L– in ZnL2 results in aggregation-induced emission enhancement (AIEE) for ZnL2 in THF/H2O. Theoretical computations based on B3LYP/6-31G(d, p) and TD-B3LYP/6-31G(d, p) methods were carried out. ESIPT is the supposed mechanism for fluorescent silence of HL, and fluorescence emission of ZnL2 is attributed to the restriction of ESIPT process. The oscillator strength of ZnL2 increases from 0.017 for monomer to 0.032 for trimer. It indicates that a high degree of ZnL2 molecules ordering stacking in THF/H2O is of benefit to fluorescence enhancement. HL is an ESIPT-coupled AIEE chemosensor for Zn(II) with high selectivity and sensitivity in aqueous medium. HL can efficiently detect intracellular Zn(II) ions because of ESIPT-coupled AIEE property of ZnL2 in mixed solvent.
Co-reporter:Lei Zhang
Organic Chemistry Frontiers 2017 vol. 4(Issue 7) pp:1250-1260
Publication Date(Web):2017/06/27
DOI:10.1039/C7QO00086C
The aim of this paper was to explore, from a computational perspective, the explicit effects of diverse directing groups on the main kinetic and thermodynamic parameters for Pd(OAc)2-catalyzed aromatic C–H activation. As a prototype of undirected C–H activation reactions, palladation of benzene with Pd(OAc)2 has been investigated by using DFT calculations, which has revealed that the final palladated benzene is evidently unstable by ca. 7.1 kcal mol−1 in free-energy with respect to the initial materials, though the proton-transfer barrier is estimated to be merely 21.5 kcal mol−1. Then we performed a series of DFT characterization studies on the directed C–H activation pathway using 16 selected directing group systems. Comparing with the data of benzene and Pd(OAc)2, 7 of the 16 studied systems (Type A) were found to stabilize the final palladacycle yet increase the proton-transfer activation barrier, and the remaining 9 (Type B) could strongly stabilize the final palladacycle but have a minor effect on the proton-transfer activation free-energy barrier, indicating that the mediation of the directing group might not necessarily lower the free-energy barrier of C–H activation. Lastly, the main structure factors, in determining these variations of key energetic parameters, have been discussed in great detail.
Co-reporter:Zhiju Zhao, Taixin Chen, Shuting Jiang, Zhengping Liu, Decai Fang and Yong Qiang Dong
Journal of Materials Chemistry A 2016 vol. 4(Issue 21) pp:4800-4804
Publication Date(Web):20 Apr 2016
DOI:10.1039/C6TC00972G
Through the combination of a large conjugation core and peripheral phenyl rings, one mechanochromic (MC) luminogen (3) with multicolored and high contrast emission is facilely obtained. Luminogen 3 shows aggregation-induced emission (AIE) and crystallization enhanced emission (CEE). The emission of 3 can be switched between deep blue (432 nm, ΦF = 42.2%), green (492 nm, ΦF = 59.3%), and orange (584 nm, ΦF = 0.4%) with high contrast in both color and efficiency through morphology tuning by heating, mechanical stimuli, and solvent fuming. The multicolored and high contrast MC emission of 3 affords its potential application in optical recording. A single luminogen of 3 can form a green or deep blue emissive background on a piece of weighing paper, and weak orange emissive letters could be obtained through writing on both backgrounds. Letters on the green background transfer to deep blue upon fuming with methanol, and those on the deep blue background transfer to green upon fuming with acetone. All the letters could be erased through grinding or heating at 160 °C.
Co-reporter:Ling-Li Han, Shi-Jun Li and De-Cai Fang
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 8) pp:6182-6190
Publication Date(Web):27 Jan 2016
DOI:10.1039/C5CP07803B
The kinetic parameters, such as activation entropy, activation enthalpy, activation free-energy, and reaction rate constant, for a series of nucleophilic substitution (SN) reactions in solution, are investigated using both a solution-phase translational entropy model and an ideal gas-phase translational entropy model. The results obtained from the solution translational entropy model are in excellent agreement with the experimental values, while the overestimation of activation free-energy from the ideal gas-phase translational entropy model is as large as 6.9 kcal mol−1. For some of the reactions studied, such as 1b+2b and 1c+2b in methanol, and 1d+2d and 1d+2e in aqueous solution, the explicit + implicit model, namely, a cluster-continuum type model, should be employed to account for the strong solvent–solute interactions. In addition, the explicit + implicit models have also been applied to the DMSO–H2O mixtures, which would open up a door to investigate the reactions in a mixed solvent using density functional theory (DFT) methods.
Co-reporter:Lu-Lu Zhang, Shi-Jun Li, Lei Zhang and De-Cai Fang
Organic & Biomolecular Chemistry 2016 vol. 14(Issue 19) pp:4426-4435
Publication Date(Web):11 Apr 2016
DOI:10.1039/C6OB00581K
Copper-complex catalyzed coupling reactions have been widely applied in the production of many important organic moieties from a synthetic perspective. In this work, a series of density functional theory (DFT) calculations, employing the B3LYP + IDSCRF/DZVP method, have been performed for a typical CuCl-catalyzed C–O cross-coupling reaction. The novel reaction mechanism was reported as four successive processes: oxidative radical generation (ORG) or oxidative addition (OA), hydrogen abstraction (HA), C–H activation/reductive elimination, and separation of product and recycling of catalyst (SP & RC). Our calculations provided a deep understanding on the dissimilar chemical activities associated with varying the oxidants used; detailed energy profile analyses suggested that the first oxidation process could proceed via either of the two competing channels (ORG and OA mechanisms) which is the basis to explain the different experimental yields. In addition, our molecular modelling gave theoretical evidence that Cu(II) → Cu(I) reduction by solvent DMF (and a water molecule) might serve as a preliminary step to produce some more active Cu(I) species that could subsequently be oxidized into Cu(III) favorably. In contrast, the Cu(II) → Cu(III) direct pathway was estimated to be prohibited from thermodynamics. All the calculation results in this work are parallel with the experimental observations.
Co-reporter:Lei Zhang and De-Cai Fang
The Journal of Organic Chemistry 2016 Volume 81(Issue 17) pp:7400-7410
Publication Date(Web):July 27, 2016
DOI:10.1021/acs.joc.6b00997
A comprehensive DFT investigation has been performed for a series of the Pd(OAc)2-catalyzed C–H activations, updating and extending the understanding of directing group effect. In the beginning, the directed and undirected C–H activation mechanisms, based on 10 model reactions, have been discussed comparatively, which disclosed that directing group can exert a thermodynamic driving force, not necessarily a kinetic promotion, on the C–H activation process. Formation of the open palladation species via the undirected pathway is thermodynamically unspontaneous (ΔG = 4–9 kcal/mol), in sharp contrast to that of the cyclopalladation species via the directed pathway (ΔG < 0). Further calculations revealed that the free-energy barriers of proton-transfer are in fact not so high on the undirected pathway (17–24 kcal/mol), while mediation of some O-center groups in the directed pathway would increase the free-energy barriers of proton-transfer. For pyridine N-oxide systems, the undirected mechanism was estimated to be more plausible than the 4-member-directed one both thermodynamically and kinetically. In addition, the uncommon 7-membered cyclopalladation has been tentatively explored using two current examples, predicting that electron-rich directing groups can help to stabilize the 7-membered palladacycles formed.
Co-reporter:Liu Zhao, Lei Zhang, and De-Cai Fang
Organometallics 2016 Volume 35(Issue 20) pp:3577-3586
Publication Date(Web):September 30, 2016
DOI:10.1021/acs.organomet.6b00646
Density functional theory (DFT) calculations with the B3LYP functionals elucidated the reactivity, selectivity, and mechanisms of a rhodium-catalyzed intermolecular [2 + 2] cycloaddition of terminal alkynes with electron-deficient alkenes. The most plausible reaction pathway was discussed as three distinct processes in full catalytic cycles, including (1) substrate exchange, (2) nucleophilic addition and cyclization, and (3) separation of product and recycling of catalyst; the formal [2 + 2] cycloaddition indeed proceeded through a rate-determining and stepwise addition–cyclization process. We then compared the outer-sphere and inner-sphere mechanisms for the formation of cyclobutene intermediates and reported that the former pathway is more accessible kinetically and thus more competitive, being contrary to the proposed mechanism for some nickel-catalyzed cycloaddition reactions in the literature. Furthermore, the substituent effect has been investigated using various alkenes CH2═CHR (R = COOMe, CN, H, CH3) as reaction partners, which disclosed that the reaction pathway for electron-deficient alkenes was mediated by a zwitterion intermediate, whereas that for electron-neutral alkenes was characterized as a diradical-like mechanism with an inaccessible free-energy barrier of more than 46 kcal mol–1. In addition, the effects of ligand and base have been discussed in detail from the perspective of Houk’s distortion/interaction model, providing a valuable case study for understanding the roles played by different phosphine ligands and additives.
Co-reporter:Wei Cao, Xiang-Jun Zheng, De-Cai Fang and Lin-Pei Jin
Dalton Transactions 2015 vol. 44(Issue 11) pp:5191-5196
Publication Date(Web):04 Feb 2015
DOI:10.1039/C4DT03791J
A quinazoline-based fluorescence chemosensor, 6-phenol-2-yl-(5,6-dihydrobenzimidazo[1,2-c])quinazoline (HL), for highly selective recognition of Cu(II) in aqueous media was synthesized. The detection limit was of the order of 10−6 M. The crystal structures of the Cu(II) and Cd(II) complexes showed that HL changed to a Schiff base when it reacts with metal salts and that the metal ions coordinate with two nitrogen atoms and one hydroxyl oxygen atom from the Schiff base. The theoretical calculations at B3LYP-SCRF/6-31G(d) confirmed that it is the Cu(II) ion that assisted the ring-opening of the quinazoline derivative, forming a Cu(II) Schiff base complex during the detection. LMCT leads to the disappearance of fluorescence. A cell imaging study indicated that HL could be used to detect the intracellular Cu2+ ion.
Co-reporter:Lei Zhang and De-Cai Fang
Organic & Biomolecular Chemistry 2015 vol. 13(Issue 29) pp:7950-7960
Publication Date(Web):16 Jun 2015
DOI:10.1039/C5OB01118C
Due to its green-chemistry advantages, the dehydrogenative Heck reaction (DHR) has experienced enormous growth over the past few decades. In this work, two competing reaction channels were comparatively studied for the Pd(OAc)2-catalyzed DHRs of arenes with alkenes, referred to herein as the arene activation mechanism and the alkene activation mechanism, respectively, which mainly differ in the involvement of the reactants in the C–H activation step. Our calculations reveal that the commonly accepted arene activation mechanism is plausible for the desired arene–alkene cross-coupling; in contrast, the alternative alkene activation mechanism is kinetically inaccessible for the desired cross-coupling, but it is feasible for the homo-coupling of alkenes. The nature of directing groups on reactants could mainly determine the dominance of the two competing reaction routes, and therefore, influence the experimental yields. A wide range of directing groups experimentally used are examined by the density functional theory (DFT) method in this work, providing theoretical guidance for screening compatible reactants.
Co-reporter:Liu Zhao
European Journal of Organic Chemistry 2015 Volume 2015( Issue 21) pp:4772-4781
Publication Date(Web):
DOI:10.1002/ejoc.201500329
Abstract
A theoretical study of the role of added salts, solvent effects, and substrate scope for the RhIII-catalyzed C–H activation and annulation of N-(pivaloyloxy)benzamide and alkyne MIDA boronates has been performed by means of DFT calculations. Computationally, the high reactivity of terminal alkynyl MIDA boronates originates from the electronic stability of the sp3-hybridized boronate. The critical role of Cu(OAc)2 as additive is such that it can be viewed as an intermediate catalyst, assisting the removal of the directing group and facilitating the conversion of RhI into RhIII in the intramolecular oxidative addition process. In contrast, AgOAc seems to have an opposite effect because it increases the activation free-energy barrier for the migratory insertion step, retarding the chemical transformation and reducing the product yield. Solvent selectivity, regioselectivity and substituent effects have also been investigated.
Co-reporter:Liu Zhao;Shi-Jun Li ; De-Cai Fang
ChemPhysChem 2015 Volume 16( Issue 17) pp:3711-3718
Publication Date(Web):
DOI:10.1002/cphc.201500662
Abstract
Several density functional theory (DFT) methods, such as CAM-B3LYP, M06, ωB97x, and ωB97xD, are used to characterize a range of ene reactions. The Gibbs free energy, activation enthalpy, and entropy are calculated with both the gas- and solution-phase translational entropy; the results obtained from the solution-phase translational entropies are quite close to the experimental measurements, whereas the gas-phase translational entropies do not perform well. For ene reactions between the enophile propanedioic acid (2-oxo-1,3-dimethyl ester) and π donors, the two-solvent-involved explicit+implicit model can be employed to obtain accurate activation entropies and free-energy barriers, because the interaction between the carbonyl oxygen atom and the solvent in the transition state is strengthened with the formation of C−C and O−H bonds. In contrast, an implicit solvent model is adequate to calculate activation entropies and free-energy barriers for the corresponding reactions of the enophile 4-phenyl-1,2,4-triazoline-3,5-dione.
Co-reporter:Bo Fang, Lei Zhang, Guohua Hou, Guofu Zi, De-Cai Fang, and Marc D. Walter
Organometallics 2015 Volume 34(Issue 23) pp:5669-5681
Publication Date(Web):November 19, 2015
DOI:10.1021/acs.organomet.5b00923
Reduction of (η5-C5Me5)2ThCl2 (1) with potassium graphite (KC8) in the presence of 1,4-diphenylbutadiyne (PhC≡CC≡CPh) yields the first actinide metallacyclocumulene, the thorium metallacyclopentatriene (η5-C5Me5)2Th(η4-C4Ph2) (2). The structure and reactivity of 2 were investigated in detail; structural parameters and density functional theory (DFT) studies confirm the presence of a metallacyclopentatriene unit in 2. Furthermore, DFT computations also indicate a notable contribution of the 5f orbitals to the bonding of the metallacyclopentatriene Th–(η4-C═C═C═C) moiety. While complex 2 shows no reactivity toward alkynes, it reacts with a variety of heterounsaturated molecules such as isothiocyanates, carbodiimides, aldehydes, ketones, nitriles, pyridines, and diazoalkane derivatives. DFT studies complement the experimental observations and provide additional insights. Furthermore, in comparison to group 4 metals, the thorium metallacyclopentatriene 2 exhibits distinctively different reactivity patterns.
Co-reporter:Enwei Zhou, Wenshan Ren, Guohua Hou, Guofu Zi, De-Cai Fang, and Marc D. Walter
Organometallics 2015 Volume 34(Issue 14) pp:3637-3647
Publication Date(Web):July 2, 2015
DOI:10.1021/acs.organomet.5b00454
The base-free thorium terminal imido [η5-1,2,4-(Me3C)3C5H2]2Th═N(p-tolyl) (1) activates a variety of small molecules such as pyridine derivatives, amines, boranes, chlorosilane, elemental selenium, and α,β-unsaturated esters. Reaction of 1 with pyridine, pyridine N-oxide, 2-methylpyridine N-oxide, p-toluidine, Ph2NH, 9-borabicyclo[3.3.1]nonane (9-BBN), PhSiH2Cl, elemental selenium, PhSeSePh, and methyl methacrylate (MMA) formed the amido pyridyl complexes [η5-1,2,4-(Me3C)3C5H2]2Th(NH-p-tolyl)(η2-C,N-C5H4N) (2), [η5-1,2,4-(Me3C)3C5H2]2Th(NH-p-tolyl)(κ2-C,O-C5H4NO) (3), and [η5-1,2,4-(Me3C)3C5H2]2Th(NH-p-tolyl)(κ2-C,O-2-MeC5H3NO) (4), diamide complexes [η5-1,2,4-(Me3C)3C5H2]2Th(NH-p-tolyl)2 (5) and [η5-1,2,4-(Me3C)3C5H2]2Th(NH-p-tolyl)(NPh2) (6), amido hydrido complex [η5-1,2,4-(Me3C)3C5H2]2Th(H)[N(p-tolyl)B(C8H14)] (7), amido chloride complex [η5-1,2,4-(Me3C)3C5H2]2Th(Cl)[N(p-tolyl)SiH2Ph] (8), amido selenido complexes [η5-1,2,4-(Me3C)3C5H2]2Th[N(p-tolyl)Se–Se] (9) and {[η5-1,2,4-(Me3C)3C5H2]Th(SePh)}2[μ-N(p-tolyl)]2 (10), and amido enolyl complex [η5-1,2,4-(Me3C)3C5H2]2Th[N(p-tolyl)CH2C(Me)═C(OMe)O] (11). The new complexes 2–3 and 6–11 were characterized by various spectroscopic techniques including single crystal X-ray diffraction. Furthermore, density functional theory (DFT) studies complement the experimental investigations.
Co-reporter:Yan-Mei Xing, Lei Zhang, and De-Cai Fang
Organometallics 2015 Volume 34(Issue 4) pp:770-777
Publication Date(Web):February 4, 2015
DOI:10.1021/om501239n
A series of density functional theory calculations have been employed to study the PdIV-mediated C–H activation in CD3CN solvent. B3LYP/DZVP, B3LYP/BS1, and B3LYP-D3/DZVP were comparatively employed to locate the geometric parameters of possible stationary points, with IDSCRF radii constituting the cavity. The novel reaction mechanism provided was divided into three distinct steps: oxidation addition, ligand substitution, and C–H activation. The distinct chemical behaviors of different oxidants have been addressed with Bader’s atoms-in-molecules wave function analysis, providing a reasonable explanation for the experimental observation. Regioselectivity was dynamically controlled by the rate-determining oxidation step. At the same time, the basis set effect was also discussed for this PdII → PdIV transformation.
Co-reporter:Bo Fang ; Wenshan Ren ; Guohua Hou ; Guofu Zi ; De-Cai Fang ; Laurent Maron ;Marc D. Walter
Journal of the American Chemical Society 2014 Volume 136(Issue 49) pp:17249-17261
Publication Date(Web):December 2, 2014
DOI:10.1021/ja509770t
The synthesis, structure, and reactivity of an actinide metallacyclopropene were comprehensively studied. The reduction of [η5-1,2,4-(Me3C)3C5H2]2ThCl2 (1) with potassium graphite (KC8) in the presence of diphenylacetylene (PhC≡CPh) yields the first stable actinide metallacyclopropene [η5-1,2,4-(Me3C)3C5H2]2Th(η2-C2Ph2) (2). The magnetic susceptibility data show that 2 is indeed a diamagnetic Th(IV) complex, and density functional theory (DFT) studies suggest that the 5f orbitals contribute to the bonding of the metallacyclopropene Th—(η2-C═C) moiety. Complex 2 shows no reactivity toward alkynes, but it reacts with a variety of heterounsaturated molecules such as aldehyde, ketone, carbodiimide, nitrile, organic azide, and diazoalkane derivatives. DFT studies complement the experimental observations and provide additional insights. Furthermore, a comparison between Th and group 4 metals reveals that Th4+ shows unique reactivity patterns.
Co-reporter:Wei Cao, Xiang-Jun Zheng, Ji-Ping Sun, Wing-Tak Wong, De-Cai Fang, Jia-Xin Zhang, and Lin-Pei Jin
Inorganic Chemistry 2014 Volume 53(Issue 6) pp:3012-3021
Publication Date(Web):February 26, 2014
DOI:10.1021/ic402811x
This paper reports a fluorescence chemosensor, N-(benzimidazol-2-yl)salicylaldimine (H2L), for Zn(II) and Al(III) ions. H2L has high selectivity for Al(III) in dimethyl sulfoxide (DMSO) and for Zn(II) in N,N-dimethylformamide (DMF). In methanol, Zn(II) and Al(III) could also be distinguished by H2L with different excitation wavelengths. The fluorescent species [Zn(HL)(H2O)(CH3OH)]+, [Zn(HL)(H2O)(DMF)]+, [Al(HL)2(OH)(H2O)], and [Al(HL)(OH)2(H2O)(DMSO)] formed in solution were established by a combination of experimental and theoretical methods, including Job’s plot, 1H NMR titration, electrospray inonization mass spectrometry (ESI-MS), and B3LYP-SCRF/6-31(d) and TD-B3LYP-SCRF/6-31G* density functional theory methods. The results show that Zn(II) and Al(III) are all coordinated to the imine nitrogen atom and the hydroxyl oxygen atom from H2L, which is the same as the M2+ ions in the obtained mononuclear complexes [M(HL)2(CH3OH)2] (where M = Cd, Ni, Co, and Mg). The detection limits of H2L for Zn(II) were 5.98 μM in methanol and 5.76 μM in DMF, while the detection limits of H2L for Al(III) were 3.3 μM in methanol and 5.25 μM in DMSO. Furthermore, it is also confirmed that H2L has low toxicity for HeLa cells and could be used to detect Zn(II) and Al(III) ions in living cells by bioimaging.
Co-reporter:Yan-Mei Chen, Gregory Adam Chass and De-Cai Fang
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 3) pp:1078-1083
Publication Date(Web):11 Nov 2013
DOI:10.1039/C3CP54079K
A novel reaction mechanism is presented for an ortho-magnesium carboxylate driven aromatic nucleophilic substitution in naphthoic acids, supported by high-level density functional theory. Results show that the rate-determining aspects involve an R-group transfer from a Grignard reagent Mg-atom to the C1-atom on a naphthalene ring. This transfer is moderated by a molecular corral comprised of two solvent THF molecules and the naphthoic acid, which collectively marshal the R-group into position. The CAM-B3LYP method was employed together with the all-electron DZVP basis set. Solvent was treated using an implicit dielectric continuum (PCM method) and IDSCRF atomic-radii. Further evolved solvent models were also investigated, consisting of explicit solvating particles forming a primary solvation layer framing the reaction center. Reaction barriers obtained are in close agreement with experimental trends, with R-group substituent-identity tempering repulsion with the molecular corral, in-turn modulating the free-energy barriers. Partitioning of the dynamic bases of entropy contribution to free-energy was central to the successful experimental–theoretical synergy.
Co-reporter:Yue Li and De-Cai Fang
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 29) pp:15224-15230
Publication Date(Web):09 Jun 2014
DOI:10.1039/C4CP02068E
The reaction mechanisms of [4+2] cycloaddition reactions between dienes and dienophiles have been investigated with several density functional theory (DFT) methods, such as CAM-B3LYP, BMK, M062x wB97x and wB97xd, and the obtained results show that most of the reactions are synchronous or asynchronous. The stability of the transition state is moderated by the interaction of frontier molecular orbitals (FMOs), in which a diene acts as an electron-donating partner and a dienophile acts as an electron-acceptor from the charge transfer direction in the transition state. The activation free energy barriers have been calculated with both gas-phase translational entropy and solution translational entropy, in which those from gas-phase translational entropy (output of the Gaussian job) are far away from the experimental estimations. It has been found that free-energy barriers generated from solution translational entropies with CAM-B3LYP+IDSCRF/6-31G(d), BMK+IDSCRF/6-31G(d) and wB97x+IDSCRF/6-31G(d) are very close to the experimental measurements, but both M062x and wB97xd methods predict too low free-energy barriers for most of the studied reactions. The substituent and solvent effects on reaction dynamic data have also been addressed.
Co-reporter:Dr. Wenshan Ren;Enwei Zhou;Bo Fang;Dr. Guohua Hou; Guofu Zi; De-Cai Fang;Dr. Marc D. Walter
Angewandte Chemie International Edition 2014 Volume 53( Issue 42) pp:11310-11314
Publication Date(Web):
DOI:10.1002/anie.201406191
Abstract
The reaction of the base-free terminal thorium imido complex [{η5-1,2,4-(Me3C)3C5H2}2ThN(p-tolyl)] (1) with p-azidotoluene yielded irreversibly the tetraazametallacyclopentene [{η5-1,2,4-(Me3C)3C5H2}2Th{N(p-tolyl)NNN(p-tolyl)}] (2), whereas the bridging imido complex [{[η5-1,2,4-(Me3C)3C5H2]Th(N3)2}2{μ-N(p-tolyl)}2][(n-C4H9)4N]2 (3) was isolated from the reaction of 1 with [(n-C4H9)4N]N3. Unexpectedly, upon the treatment of 1 with 9-diazofluorene, the NN bond was cleaved, an N atom was transferred, and the η2-diazenido iminato complex [{η5-1,2,4-(Me3C)3C5H2}2Th{η2-[NN(p-tolyl)]}{N(9-C13H8)}] (4) was formed. In contrast, the reaction of 1 with Me3SiCHN2 gave the nitrilimido complex [{η5-1,2,4-(Me3C)3C5H2}2Th{NH(p-tolyl)}{N2CSiMe3}] (5), which slowly converted into [{η5-1,2,4-(Me3C)3C5H2}{η5:κ-N-1,2-(Me3C)2-4-CMe2(CH2NNCHSiMe3)C5H2}Th{NH(p-tolyl)}] (6) by intramolecular CH bond activation. The experimental results are complemented by density functional theory (DFT) studies.
Co-reporter:Wei-Hua Ding, Wei, Cao, Xiang-Jun Zheng, De-Cai Fang, Wing-Tak Wong, and Lin-Pei Jin
Inorganic Chemistry 2013 Volume 52(Issue 13) pp:7320-7322
Publication Date(Web):June 20, 2013
DOI:10.1021/ic401028u
A chemosensor for the Al3+ ion, 1-[(3-hydroxypyridin-2-ylamino)methylene]naphthalen-2(1H)-one (H2L), based on inhibited excited-state intramolecular proton transfer was synthesized. The experimental and theoretical calculations at B3LYP+PCM/6-31G(d) revealed that Al3+ and H2L form a 1:1 complex, [AlL(OH)(H2O)]2, in dimethyl sulfoxide that exhibits two remarkably enhanced fluorescent emissions at 523 and 553 nm. It is confirmed that H2L could be used to detect Al3+ ions in cells by bioimaging.
Co-reporter:Lei Zhang and De-Cai Fang
The Journal of Organic Chemistry 2013 Volume 78(Issue 6) pp:2405-2412
Publication Date(Web):February 18, 2013
DOI:10.1021/jo302567s
A series of density functional theory (DFT) experiments, employing the B3LYP+IDSCRF/BS1 and B3LYP+IDSCRF/DZVP methods, have been carried out for the Pd(OAc)2-catalyzed enamide–siloxane C–H activation/C–C coupling reactions. The results reveal that there are four processes, namely C–H activation, transmetalation (TM), reductive elimination (RE), and separation of product (SP) and recycling of catalyst (RC), each of which is consist of different steps. In order to fully understand the origin of regiospecific C–H activation/C–C coupling on the alicyclic ring experimentally observed, the conformational preference, kinetic aspects, and relative stabilities of the competitive products have been explored. In addition, the roles of additive silver salt AgF and solvent dioxane have also been addressed, providing valuable details upon which to rationally optimize experimental conditions.
Co-reporter:Bing Lian, Lei Zhang, Gregory Adam Chass, and De-Cai Fang
The Journal of Organic Chemistry 2013 Volume 78(Issue 17) pp:8376-8385
Publication Date(Web):July 24, 2013
DOI:10.1021/jo4010712
A series of density functional theory determinations have been carried out to characterize Pd(OAc)2-catalyzed C–H activation and subsequent intramolecular C–O bond-coupling of phenyl-tert-butanol in perfluorobenzene (C6F6) solvent. Full, nontruncated models of the real chemical transformations were studied, with structures in agreement with recent X-ray determinations. Conformational analyses have provided thermodynamic validity of the geometric structures used. The B3LYP/DZVP and B3LYP/BS1 methods (BS1 = TZVP(H,C,O) + SDD(Pd,I)) were comparatively employed, with C6F6 solvent contributions accounted for by the IDSCRF method; key transition states were confirmed by intrinsic reaction coordinate determinations. The novel reaction mechanism proposed was divided into the following four steps: C–H activation, oxidation, reductive elimination, catalyst recovery. Two competing reaction routes were quantitatively compared, differing in the oxidation state of Pd (+2 vs +4). Results reveal the pathway involving Pd(IV) intermediates to be more spontaneous and, therefore, more probable than the Pd(II) path, the latter hindered by a kinetically inaccessible reductive elimination step, with total energy and free energy barriers of 41.0 and 38.6 kcal·mol–1, respectively. The roles played by the oxidant and Pd(IV) species have also been addressed through Bader’s atoms-in-molecules wave function analyses, providing a quantitative electronic metric for C–H activation chemistry.
Co-reporter:Jia-Yuan Tao, De-Cai Fang and Gregory A. Chass
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 19) pp:6937-6945
Publication Date(Web):10 Apr 2012
DOI:10.1039/C2CP40067G
A series of density functional theory (DFT) experiments carried out on selected nickel(0)-catalysed diyne–cyclobutanone [4+2+2] cycloadditions provided quantitative confirmation of proposed multistep mechanisms, while clarifying the catalytic role of Ni in the reactions. Geometric and energetic results of the Ni-catalysed process were compared to the one-step non-catalysed complement. Results show the first oxidation to be the rate-determining step, with the intramolecular reaction being the preferred one of the two competing pathways. Ligand-identity is also shown to greatly influence reaction barriers, leading to large deviation in product yields, in direct agreement with experimental observations.
Co-reporter:Wenshan Ren ; Guofu Zi ; De-Cai Fang ;Marc D. Walter
Journal of the American Chemical Society 2011 Volume 133(Issue 33) pp:13183-13196
Publication Date(Web):July 27, 2011
DOI:10.1021/ja205280k
The synthesis, structure, and reactivity of thorium oxo and sulfido metallocenes have been comprehensively studied. Heating of an equimolar mixture of the dimethyl metallocene [η5-1,2,4-(Me3C)3C5H2]2ThMe2 (2) and the bis-amide metallocene [η5-1,2,4-(Me3C)3C5H2]2Th(NH-p-tolyl)2 (3) in refluxing toluene results in the base-free imido thorium metallocene, [η5-1,2,4-(Me3C)3C5H2]2Th═N(p-tolyl) (4), which is a useful precursor for the preparation of oxo and sulfido thorium metallocenes [η5-1,2,4-(Me3C)3C5H2]2Th═E (E = O (5) and S (15)) by cycloaddition–elimination reaction with Ph2C═E (E = O, S) or CS2. The oxo metallocene 5 acts as a nucleophile toward alkylsilyl halides, while sulfido metallocene 15 does not. The oxo metallocene 5 and sulfido metallocene 15 undergo a [2 + 2] cycloaddition reaction with Ph2CO, CS2, or Ph2CS, but they show no reactivity with alkynes. Density functional theory (DFT) studies provide insights into the subtle interplay between steric and electronic effects and rationalize the experimentally observed reactivity patterns. A comparison between Th, U, and group 4 elements shows that Th4+ behaves more like an actinide than a transition metal.
Co-reporter:Wenshan Ren, Xuebin Deng, Guofu Zi and De-Cai Fang
Dalton Transactions 2011 vol. 40(Issue 38) pp:9662-9664
Publication Date(Web):04 Aug 2011
DOI:10.1039/C1DT11149C
The first thorium poly-carbene complexes [(Ph2PS)2C]2Th(DME) (2) and [{[(Ph2PS)2C]3Th}Li2(DME)]n (3) have been prepared and structurally characterized. DFT calculations reveal that the ThC bond is polarized toward the nucleophilic carbene carbon atom, which is further verified by the experimental observation that the ThC bond shows a nucleophilic behavior with Ph2CO.
Co-reporter:Wenshan Ren; Guofu Zi; De-Cai Fang;Dr. Marc D. Walter
Chemistry - A European Journal 2011 Volume 17( Issue 45) pp:12669-12682
Publication Date(Web):
DOI:10.1002/chem.201101972
Abstract
The synthesis, structure, and reactivity of a base-free thorium terminal-imido metallocene have been comprehensively studied. Treatment of thorium metallocenes [{η5-1,2,4-(Me3C)3C5H2}2ThMe2] and [{η5-1,3-(Me3C)2C5H3}2ThMe2] with RNH2 gives diamides [{η5-1,2,4-(Me3C)3C5H2}2Th(NHR)2] (R=Me (7), p-tolyl (8)) and [{η5-1,3-(Me3C)2C5H3}2Th(NH-p-tolyl)2] (9), respectively. Diamides 7 and 9 do not eliminate methylamine or p-toluidine, but sublime without decomposition at 150 °C under vacuum (0.01 mmHg), whereas diamide 8 is converted at 140 °C/0.01 mmHg into the primary amine p-tolyl-NH2 and [{η5-1,2,4-(Me3C)3C5H2}2ThN(p-tolyl)] (10), which may be isolated in pure form. Imido metallocene 10 does not react with electrophiles such as alkylsilyl halides; however, it reacts with electron-rich or unsaturated reagents. For example, reaction of 10 with sulfur affords the metallacycle [{η5-1,2,4-(Me3C)3C5H2}2Th{N(p-tolyl)S-S}]. Imido 10 is an important intermediate in the catalytic hydroamination of internal alkynes, and an efficient catalyst for the trimerization of PhCN. Density functional theory (DFT) studies provide a detailed understanding of the experimentally observed reactivity patterns.
Co-reporter:Gregory A. Chass, Eric Assen B. Kantchev and De-Cai Fang
Chemical Communications 2010 vol. 46(Issue 16) pp:2727-2729
Publication Date(Web):16 Dec 2009
DOI:10.1039/B922326F
The model cross-coupling of EtBr with EtMgCl mediated by Ni(π-allyl)2 proceeds by a catalytic cycle commencing with transmetalation establishing a novel Mg–allyl interaction, followed by Mg-assisted oxidative addition (the rate-determining step), followed by reductive elimination having much lower barrier than 2 competing β-hydride elimination pathways, and completed by departure of MgBrCl.
Co-reporter:Tao Song;Corey N. W. Lam;Dominic C. M. Ng
Journal of The American Society for Mass Spectrometry 2009 Volume 20( Issue 6) pp:972-984
Publication Date(Web):2009 June
DOI:10.1016/j.jasms.2009.01.007
The dissociation of [CuII(L)His]•2+ complexes [L=diethylenetriamine (dien) or 1,4,7-triazacyclononane (9-aneN3)] bears a strong resemblance to the previously reported behavior of [CuII(L)GGH]•2+ complexes. We have used low-energy collision-induced dissociation experiments and density functional theory (DFT) calculations at the B3LYP/6-31+G(d) level to study the macrocyclic effect of the auxiliary ligands on the formation of His•+ from prototypical [CuII(L)His]•2+ systems. DFT revealed that the relative energy barriers of the same electron-transfer (ET) dissociation pathways of [CuII(9-aneN3)His]•2+ and [CuII(dien)His]•2+ are very similar, with the ET reactions of [CuII(9-aneN3)His]•2+ leading to the generation of two distinct His•+ species; in contrast, the proton transfer (PT) dissociation pathways of [CuII(9-aneN3)His]•2+ and [CuII(dien)His]•2+ differ considerably. The PT reactions of [CuII(9-aneN3)His]•2+ are associated with substantially higher barriers (>13 kcal/mol) than those of [CuII(dien)His]•2+. Thus, the sterically encumbered auxiliary 9-aneN3 ligand facilitates ET reactions while moderating PT reactions, allowing the formation of hitherto nonobservable histidine radical cations.
Co-reporter:GregoryA. Chass Dr.;ChristopherJ. O'Brien Dr.;Niloufar Hadei Dr.;EricAssenB. Kantchev Dr.;Wei-Hua Mu ;AlanC. Hopkinson ;ImreG. Csizmadia ;MichaelG. Organ
Chemistry - A European Journal 2009 Volume 15( Issue 17) pp:4281-4288
Publication Date(Web):
DOI:10.1002/chem.200900042
Co-reporter:Wei-Hua Mu, Gregory A. Chasse and De-Cai Fang
Organometallics 2009 Volume 28(Issue 20) pp:5848-5856
Publication Date(Web):September 24, 2009
DOI:10.1021/om900242g
Due to the exponential growth of pyridine and pyrrole use, focus is shifting to more completely understanding their syntheses and toward more effective preparation and application. Herein, we present a series of density functional theory (DFT) models, employing differing treatments of solvent effects, quantitatively characterizing the formation mechanism of a series of pyridine and pyrrole derivatives from multisubstituted 1-cyano-1,3-butadienes and organolithium reagents. Results indicated that pyridine and pyrrole formations are multistep processes, in which the rate-determining step involves a free-energy barrier of 18 kcal·mol−1, as determined using a novel microsolvation method. Both solvent (tetrahydrofuran or ether) and organolithium reagent identity are shown to play instrumental roles in affecting the pyridine/pyrrole product ratios. The microsolvation results are more plausible than those emerging from traditional approaches to treating solvent effects (i.e., dielectric continuum). Specifically, solvent identity plays an important role in these reactions, with THF facilitating the formation of pyrroles, while Et2O pushes the reaction toward pyridine formation.
Co-reporter:Hong-Mei Jia;Yan Feng;Jian-Ying Zhang
Theoretical Chemistry Accounts 2008 Volume 121( Issue 5-6) pp:271-278
Publication Date(Web):2008 December
DOI:10.1007/s00214-008-0474-z
Density functional theory, employing B3LYP/DZVP and B3LYP/6-31G*(LANL2DZ for Tc), has been used to investigate the interconversion mechanism between formal TcO3+ and TcO2+ core of 99mTc labeled amine-oxime (AO) complex, in which two water molecules have been used to simulate the possible interconversion process. The obtained results indicate that the length of amine-amine hydrocarbon backbone of AO ligand has a significant influence on the stabilities of formal TcO3+ and TcO2+ complex. The interconversion process between TcO–BnAO and TcO2–BnAO has been amply discussed, which releases the useful information for the further investigation of the structure and hypoxic mechanism of 99mTc-HL91.
Co-reporter:Hai-Rong Tao
Theoretical Chemistry Accounts 2008 Volume 121( Issue 1-2) pp:91-101
Publication Date(Web):2008 September
DOI:10.1007/s00214-008-0453-4
Four typical thermal [1,3] sigmatropic rearrangements of bicyclic and tricyclic vinylcyclobutanes and one fancied analogous reaction (R2 in Scheme 1) were examined using CASSCF, CASPT2 and CAS+1+2 methods to discern the reaction mechanisms. Computed results indicate that it is difficult to simply designate these reactions as traditional single-step concerted or stepwise mechanisms, but a situation locating between these two extremes seems to be reasonable. The extent the reaction exhibits as a single-step concerted or stepwise path is much dependent on the geometrical constraints of reactant. For example, the system with three-member ring will tend to behave like a single-step concerted process, where only one rotation movement around C–C bond could be found when the bridged C–C is broken. However, the species with four-member ring will be much closer to the stepwise mechanism involving diradical varieties, because there are two different rotation movements exist when the bridged C–C is broken. Our calculation will also rationalize that only suprafacial retention product could be yielded for the thermal [1,3] sigmatropic rearrangement of tricyclic vinylcyclobutane.
Co-reporter:Yan Wang, De-Cai Fang, Ruo-Zhuang Liu
Journal of Molecular Structure: THEOCHEM 2008 Volume 851(1–3) pp:358-362
Publication Date(Web):28 February 2008
DOI:10.1016/j.theochem.2007.11.025
Density functional theory (DFT) calculations employing B3LYP/6-31G(d,p) method have been carried out to characterize the mechanisms of the title reactions. The obtained results indicate that the mechanisms of oxa-[3 + 3] cycloaddition reactions include three typical steps, namely the addition, the elimination and the cyclization, similar to those of the aza-[3 + 3] cycloaddition reactions between vinylogous amides and α,β-unsaturated imine cations reported previously. And the differences between these two kinds of reactions involved in different steps have been elucidated in this paper.
Co-reporter:Ying Cheng Dr.;Mei-Fang Liu Dr.;Xue-Mei Lei
Chemistry - A European Journal 2007 Volume 13(Issue 15) pp:
Publication Date(Web):26 FEB 2007
DOI:10.1002/chem.200601482
2-Aryl thiocarbamoyl benzimidazolium and imidazolinium inner salts derived from benzimidazole and imidazoline carbenes are unique ambident C-C-S and C-C-N 1,3-dipolar systems, which undergo highly efficient and site-selective cycloaddition reactions with dimethyl acetylenedicarboxylate or dibenzoylacetylene to furnish spiro(imidazole-2,3′-thiophene) derivatives in excellent yields. When treated with ethyl propiolate, methyl acrylate or acrylonitrile, spiro(imidazole-2,3′-pyrrole) derivatives were formed in good yields. Theoretical studies revealed an asynchronous concerted mechanism for both the C-C-S and C-C-N 1,3-dipolar cycloaddition reactions. The site selectivity in the [3+2] cycloaddition reaction of ambident 1,3-dipoles was predictably regulated by both the electronic and steric effects of dipolarophiles.
Co-reporter:Si-Ya Yang, Xue-Fei Lin, Cheng-Ke Sun, De-Cai Fang
Journal of Molecular Structure: THEOCHEM 2007 Volume 815(1–3) pp:127-133
Publication Date(Web):1 August 2007
DOI:10.1016/j.theochem.2007.03.030
Density functional theory calculations employing BHandHLYP/6-311+G(d,p) method have been employed in order to quantitatively characterize the mechanism of the title [3+2] reaction between the cationic 1,3-dipolar 1,3-diaza-2-azoniaallene cation and olefins. Computational results indicate that the [3+2] cycloaddition reaction could take place in both concerted and stepwise approaches. No transition states could be located for the approaching pathway between the two reactants: 1,3-diaza-2-azoniaallene and 2-methyl-propene, and thus a 3-membered ring intermediate could be formed directly. The obtained results have also been rationalized with QTAIM theory, and solvent effects and substituent effects have also been elaborated upon herein.
Co-reporter:Mei-Ju Wei;Ruo-Zhuang Liu
European Journal of Organic Chemistry 2004 Volume 2004(Issue 19) pp:
Publication Date(Web):16 SEP 2004
DOI:10.1002/ejoc.200400343
The mechanisms of the title reactions between 1-aza-2-azoniaallene cations and isocyanic acid or isocyanates have been theoretically explored at the B3LYP/6-31++G** level. It was found that all of these reactions proceed in asynchronous but concerted pathways. The substituent effects are also obvious; e.g., the presence either of an electron-withdrawing chlorine substituent on the 1-aza-2-azoniaallene cation or of an electron-releasing methyl substituent on the isocyanate both favor the cycloaddition reactions. For the [1,2]-shift reactions, all the substituents lower their activation barrier, especially Cl substituents on the 1-aza-2-azoniaallene cation, but when Cl substituents are present on the 1-aza-2-azoniaallene cation the rearrangement product is not as stable as others. In addition, solvent effects with the PCM model are also reported, and a model reaction has been investigated at the MP2/6-31+G* and QCISD/6-31+G* levels as well as by DFT. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Co-reporter:Si-Ya Yang;Cheng-Ke Sun
European Journal of Organic Chemistry 2003 Volume 2003(Issue 10) pp:
Publication Date(Web):5 MAY 2003
DOI:10.1002/ejoc.200200650
The mechanisms of cycloaddition reactions between 2-azaallene cations and isocyanates have been explored at the B3LYP/6-31G* level. It is found that [2+2] or [2+4] cycloaddition reactions can take place via an intermediate when 2-azaallene cations react with 1 or 2 equiv. of isocyanates. The effects of substituents are also reported in the present paper, and the results obtained indicate that electron-attracting groups on 2-azaallene cations favor the reaction, and electron-donating groups on 2-azaallene cations hinder the reaction. Substituents on isocyanates have the opposite effects. These results have been rationalized with FMO interaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Co-reporter:D.-C. Fang, T. Yalcin, T.-H. Tang, X.-Y. Fu, A.G. Harrison, I.G. Csizmadia
Journal of Molecular Structure: THEOCHEM 1999 Volume 468(1–2) pp:135-149
Publication Date(Web):9 August 1999
DOI:10.1016/S0166-1280(99)00046-9
Ab initio Hartree–Fock (HF/6-31G, HF/6-31G* and HF/6-31G**) methods have been used to study the mechanism of the formation of cationic fragments from peptides. The results show that the simplest B3 ion of nominal structure HCONHCH2CONHCH2CO+, can be fragmented into the A3 ion in the first step by the loss of CO, but not directly into the B2 ion. In addition, the A3 ion can be further fragmented into the B2 ion. The calculated activation barrier of the first reaction (from B3 to A3) is 26.2 kcal/mol at the HF/6-31G** level of theory. The second reaction (from B3 to B2) has much higher energy barrier (77.15 kcal/mol at HF/6-31G** level of theory). The third reaction (from A3 to B2) and the fourth reaction (from B2 to A2) have barriers of 28.82 and 25.59 kcal/mol, respectively. In addition to the energetics of the fragmentation, the electronic structure and bonding of the main stationary points have been analyzed by Bader's theory of atoms in molecules (AIM).
Co-reporter:Wenshan Ren, Xuebin Deng, Guofu Zi and De-Cai Fang
Dalton Transactions 2011 - vol. 40(Issue 38) pp:NaN9664-9664
Publication Date(Web):2011/08/04
DOI:10.1039/C1DT11149C
The first thorium poly-carbene complexes [(Ph2PS)2C]2Th(DME) (2) and [{[(Ph2PS)2C]3Th}Li2(DME)]n (3) have been prepared and structurally characterized. DFT calculations reveal that the ThC bond is polarized toward the nucleophilic carbene carbon atom, which is further verified by the experimental observation that the ThC bond shows a nucleophilic behavior with Ph2CO.
Co-reporter:Wei Cao, Xiang-Jun Zheng, De-Cai Fang and Lin-Pei Jin
Dalton Transactions 2015 - vol. 44(Issue 11) pp:NaN5196-5196
Publication Date(Web):2015/02/04
DOI:10.1039/C4DT03791J
A quinazoline-based fluorescence chemosensor, 6-phenol-2-yl-(5,6-dihydrobenzimidazo[1,2-c])quinazoline (HL), for highly selective recognition of Cu(II) in aqueous media was synthesized. The detection limit was of the order of 10−6 M. The crystal structures of the Cu(II) and Cd(II) complexes showed that HL changed to a Schiff base when it reacts with metal salts and that the metal ions coordinate with two nitrogen atoms and one hydroxyl oxygen atom from the Schiff base. The theoretical calculations at B3LYP-SCRF/6-31G(d) confirmed that it is the Cu(II) ion that assisted the ring-opening of the quinazoline derivative, forming a Cu(II) Schiff base complex during the detection. LMCT leads to the disappearance of fluorescence. A cell imaging study indicated that HL could be used to detect the intracellular Cu2+ ion.
Co-reporter:Yan-Mei Chen, Gregory Adam Chass and De-Cai Fang
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 3) pp:NaN1083-1083
Publication Date(Web):2013/11/11
DOI:10.1039/C3CP54079K
A novel reaction mechanism is presented for an ortho-magnesium carboxylate driven aromatic nucleophilic substitution in naphthoic acids, supported by high-level density functional theory. Results show that the rate-determining aspects involve an R-group transfer from a Grignard reagent Mg-atom to the C1-atom on a naphthalene ring. This transfer is moderated by a molecular corral comprised of two solvent THF molecules and the naphthoic acid, which collectively marshal the R-group into position. The CAM-B3LYP method was employed together with the all-electron DZVP basis set. Solvent was treated using an implicit dielectric continuum (PCM method) and IDSCRF atomic-radii. Further evolved solvent models were also investigated, consisting of explicit solvating particles forming a primary solvation layer framing the reaction center. Reaction barriers obtained are in close agreement with experimental trends, with R-group substituent-identity tempering repulsion with the molecular corral, in-turn modulating the free-energy barriers. Partitioning of the dynamic bases of entropy contribution to free-energy was central to the successful experimental–theoretical synergy.
Co-reporter:Gregory A. Chass, Eric Assen B. Kantchev and De-Cai Fang
Chemical Communications 2010 - vol. 46(Issue 16) pp:NaN2729-2729
Publication Date(Web):2009/12/16
DOI:10.1039/B922326F
The model cross-coupling of EtBr with EtMgCl mediated by Ni(π-allyl)2 proceeds by a catalytic cycle commencing with transmetalation establishing a novel Mg–allyl interaction, followed by Mg-assisted oxidative addition (the rate-determining step), followed by reductive elimination having much lower barrier than 2 competing β-hydride elimination pathways, and completed by departure of MgBrCl.
Co-reporter:Lei Zhang and De-Cai Fang
Organic & Biomolecular Chemistry 2015 - vol. 13(Issue 29) pp:NaN7960-7960
Publication Date(Web):2015/06/16
DOI:10.1039/C5OB01118C
Due to its green-chemistry advantages, the dehydrogenative Heck reaction (DHR) has experienced enormous growth over the past few decades. In this work, two competing reaction channels were comparatively studied for the Pd(OAc)2-catalyzed DHRs of arenes with alkenes, referred to herein as the arene activation mechanism and the alkene activation mechanism, respectively, which mainly differ in the involvement of the reactants in the C–H activation step. Our calculations reveal that the commonly accepted arene activation mechanism is plausible for the desired arene–alkene cross-coupling; in contrast, the alternative alkene activation mechanism is kinetically inaccessible for the desired cross-coupling, but it is feasible for the homo-coupling of alkenes. The nature of directing groups on reactants could mainly determine the dominance of the two competing reaction routes, and therefore, influence the experimental yields. A wide range of directing groups experimentally used are examined by the density functional theory (DFT) method in this work, providing theoretical guidance for screening compatible reactants.
Co-reporter:Yue Li and De-Cai Fang
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 29) pp:NaN15230-15230
Publication Date(Web):2014/06/09
DOI:10.1039/C4CP02068E
The reaction mechanisms of [4+2] cycloaddition reactions between dienes and dienophiles have been investigated with several density functional theory (DFT) methods, such as CAM-B3LYP, BMK, M062x wB97x and wB97xd, and the obtained results show that most of the reactions are synchronous or asynchronous. The stability of the transition state is moderated by the interaction of frontier molecular orbitals (FMOs), in which a diene acts as an electron-donating partner and a dienophile acts as an electron-acceptor from the charge transfer direction in the transition state. The activation free energy barriers have been calculated with both gas-phase translational entropy and solution translational entropy, in which those from gas-phase translational entropy (output of the Gaussian job) are far away from the experimental estimations. It has been found that free-energy barriers generated from solution translational entropies with CAM-B3LYP+IDSCRF/6-31G(d), BMK+IDSCRF/6-31G(d) and wB97x+IDSCRF/6-31G(d) are very close to the experimental measurements, but both M062x and wB97xd methods predict too low free-energy barriers for most of the studied reactions. The substituent and solvent effects on reaction dynamic data have also been addressed.
Co-reporter:Ling-Li Han, Shi-Jun Li and De-Cai Fang
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 8) pp:NaN6190-6190
Publication Date(Web):2016/01/27
DOI:10.1039/C5CP07803B
The kinetic parameters, such as activation entropy, activation enthalpy, activation free-energy, and reaction rate constant, for a series of nucleophilic substitution (SN) reactions in solution, are investigated using both a solution-phase translational entropy model and an ideal gas-phase translational entropy model. The results obtained from the solution translational entropy model are in excellent agreement with the experimental values, while the overestimation of activation free-energy from the ideal gas-phase translational entropy model is as large as 6.9 kcal mol−1. For some of the reactions studied, such as 1b+2b and 1c+2b in methanol, and 1d+2d and 1d+2e in aqueous solution, the explicit + implicit model, namely, a cluster-continuum type model, should be employed to account for the strong solvent–solute interactions. In addition, the explicit + implicit models have also been applied to the DMSO–H2O mixtures, which would open up a door to investigate the reactions in a mixed solvent using density functional theory (DFT) methods.
Co-reporter:Lu-Lu Zhang, Shi-Jun Li, Lei Zhang and De-Cai Fang
Organic & Biomolecular Chemistry 2016 - vol. 14(Issue 19) pp:NaN4435-4435
Publication Date(Web):2016/04/11
DOI:10.1039/C6OB00581K
Copper-complex catalyzed coupling reactions have been widely applied in the production of many important organic moieties from a synthetic perspective. In this work, a series of density functional theory (DFT) calculations, employing the B3LYP + IDSCRF/DZVP method, have been performed for a typical CuCl-catalyzed C–O cross-coupling reaction. The novel reaction mechanism was reported as four successive processes: oxidative radical generation (ORG) or oxidative addition (OA), hydrogen abstraction (HA), C–H activation/reductive elimination, and separation of product and recycling of catalyst (SP & RC). Our calculations provided a deep understanding on the dissimilar chemical activities associated with varying the oxidants used; detailed energy profile analyses suggested that the first oxidation process could proceed via either of the two competing channels (ORG and OA mechanisms) which is the basis to explain the different experimental yields. In addition, our molecular modelling gave theoretical evidence that Cu(II) → Cu(I) reduction by solvent DMF (and a water molecule) might serve as a preliminary step to produce some more active Cu(I) species that could subsequently be oxidized into Cu(III) favorably. In contrast, the Cu(II) → Cu(III) direct pathway was estimated to be prohibited from thermodynamics. All the calculation results in this work are parallel with the experimental observations.
Co-reporter:Shi-Jun Li and De-Cai Fang
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 44) pp:NaN30823-30823
Publication Date(Web):2016/10/18
DOI:10.1039/C6CP05190A
Several popular density functional theory (DFT) methods have been employed to characterize a series of 1,3-dipolar cycloaddition reactions, including the exploration of reaction mechanisms and the calculations of kinetic parameters. Both the gas- and solution-phase translational entropy models have been used to calculate the activation entropies, and the results obtained from the latter method are quite close to the experimental measurements. For some of the reactions studied, e.g., a1 + b9, a1 + b10, a5 + b9 and a12 + b5, the explicit + implicit solvation model, namely, a cluster-continuum type model, should be employed to account for the specific solvent–solute interactions. The quasi rigid-rotor-harmonic-oscillator (qRRHO) small frequency vibrational entropy correction, in conjunction with the conformational entropy correction, could further improve the calculated activation entropy data. The comparison between calculation data with experimental measurements, using 23 activation entropies and 160 reaction rate constants as test benchmark, demonstrated that our present strategy could calibrate the root-mean-square-deviation (RMSD) of activation entropies to be 1.8 cal mol−1 K−1 and that of Gibbs free energy barriers to be 1.8 kcal mol−1.
Co-reporter:Lei Zhang and De-Cai Fang
Inorganic Chemistry Frontiers 2017 - vol. 4(Issue 7) pp:NaN1260-1260
Publication Date(Web):2017/03/20
DOI:10.1039/C7QO00086C
The aim of this paper was to explore, from a computational perspective, the explicit effects of diverse directing groups on the main kinetic and thermodynamic parameters for Pd(OAc)2-catalyzed aromatic C–H activation. As a prototype of undirected C–H activation reactions, palladation of benzene with Pd(OAc)2 has been investigated by using DFT calculations, which has revealed that the final palladated benzene is evidently unstable by ca. 7.1 kcal mol−1 in free-energy with respect to the initial materials, though the proton-transfer barrier is estimated to be merely 21.5 kcal mol−1. Then we performed a series of DFT characterization studies on the directed C–H activation pathway using 16 selected directing group systems. Comparing with the data of benzene and Pd(OAc)2, 7 of the 16 studied systems (Type A) were found to stabilize the final palladacycle yet increase the proton-transfer activation barrier, and the remaining 9 (Type B) could strongly stabilize the final palladacycle but have a minor effect on the proton-transfer activation free-energy barrier, indicating that the mediation of the directing group might not necessarily lower the free-energy barrier of C–H activation. Lastly, the main structure factors, in determining these variations of key energetic parameters, have been discussed in great detail.
Co-reporter:Zhiju Zhao, Taixin Chen, Shuting Jiang, Zhengping Liu, Decai Fang and Yong Qiang Dong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 21) pp:NaN4804-4804
Publication Date(Web):2016/04/20
DOI:10.1039/C6TC00972G
Through the combination of a large conjugation core and peripheral phenyl rings, one mechanochromic (MC) luminogen (3) with multicolored and high contrast emission is facilely obtained. Luminogen 3 shows aggregation-induced emission (AIE) and crystallization enhanced emission (CEE). The emission of 3 can be switched between deep blue (432 nm, ΦF = 42.2%), green (492 nm, ΦF = 59.3%), and orange (584 nm, ΦF = 0.4%) with high contrast in both color and efficiency through morphology tuning by heating, mechanical stimuli, and solvent fuming. The multicolored and high contrast MC emission of 3 affords its potential application in optical recording. A single luminogen of 3 can form a green or deep blue emissive background on a piece of weighing paper, and weak orange emissive letters could be obtained through writing on both backgrounds. Letters on the green background transfer to deep blue upon fuming with methanol, and those on the deep blue background transfer to green upon fuming with acetone. All the letters could be erased through grinding or heating at 160 °C.
Co-reporter:Jia-Yuan Tao, De-Cai Fang and Gregory A. Chass
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 19) pp:NaN6945-6945
Publication Date(Web):2012/04/10
DOI:10.1039/C2CP40067G
A series of density functional theory (DFT) experiments carried out on selected nickel(0)-catalysed diyne–cyclobutanone [4+2+2] cycloadditions provided quantitative confirmation of proposed multistep mechanisms, while clarifying the catalytic role of Ni in the reactions. Geometric and energetic results of the Ni-catalysed process were compared to the one-step non-catalysed complement. Results show the first oxidation to be the rate-determining step, with the intramolecular reaction being the preferred one of the two competing pathways. Ligand-identity is also shown to greatly influence reaction barriers, leading to large deviation in product yields, in direct agreement with experimental observations.
