Gang Lu

Technical Institute of Physics and Chemistry, Peping, Beijing, China

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Publications (21)98.29 Total impact

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    ABSTRACT: The experimentally observed planar hypercoordinate carbon species were detected in gas phase experiments and characterized by photoelectron spectroscopy. According to the Boltzmann distribution law, the thermodynamically favorable isomers, especially global minima, were relatively easier to detect than other isomers in such an experimental process. Here, we reported a thermodynamically unfavorable case, i.e., D3h CN3Mg3(+) (1a), which we think is experimentally viable because all isomers that are energetically lower than 1a show bimolecular assembly type structures consisting of an N2 unit and various types of CNMg3(+) units. The natural bond orbital (NBO) analysis suggests that the bonding between N2 and CNMg3(+) is rather weak, and we think it is very hard to retain their basic structures when kinetic factors are considered. Consistently, the four lowest isomers in the second group show dissociation (to free N2 molecule and CNMg3(+) cations) during Born-Oppenheimer molecular dynamic (BOMD) simulations. In contrast, the structure of 1a can be maintained under temperatures up to 2000 K during the BOMD simulation, and ring-opening reaction studies suggest the barrier to be very high, 46.75 kcal/mol. We think the excellent kinetic stability of 1a will compensate for its thermodynamic instability and it will own its existence in the gas phase synthesis. Although many isomers in the second group are energetically more favorable than 1a, they will be dissociated by the kinetic process. In the magnetic field, the positively charged CNMg3(+) units will be separated quickly from N2 molecules in the general gas phase synthesis, and they are therefore undetectable.
    The Journal of Physical Chemistry A 04/2014; · 2.77 Impact Factor
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    ABSTRACT: Density functional theory computations have been applied to gain insight into the CO2 reduction to CH4 with Et3SiH, catalyzed by ammonium hydridoborate 1 ([TMPH](+)[HB(C6F5)3](-), where TMP = 2,2,6,6-tetramethylpiperidine) and B(C6F5)3. The study shows that CO2 is activated through the concerted transfer of H(δ+) and H(δ-) of 1 to CO2, giving a complex (IM2) with a well-formed HCOOH entity, followed by breaking of the O-H bond of the HCOOH entity to return H(δ+) to TMP, resulting in an intermediate 2 ([TMPH](+)[HC(═O)OB(C6F5)3)](-)), with CO2 being inserted into the B-H bond of 1. However, unlike CO2 insertion into transition-metal hydrides, the direct insertion of CO2 into the B-H bond of 1 is inoperative. The computed CO2 activation mechanism agrees with the experimental synthesis of 2 via reacting HCOOH with TMP/B(C6F5)3. Subsequent to the CO2 activation and B(C6F5)3-mediated hydrosilylation of 2 to regenerate the catalyst (1), giving HC(═O)OSiEt3 (5), three hydride-transfer steps take place, sequentially transferring H(δ-) of Et3SiH to 5 to (Et3SiO)2CH2 (6, the product of the first hydride-transfer step) to Et3SiOCH3 (7, the product of the second hydride-transfer step) and finally resulting in CH4. These hydride transfers are mediated by B(C6F5)3 via two SN2 processes without involving 1. B(C6F5)3 acts as a hydride carrier that, with the assistance of a nucleophilic attack of 5-7, first grabs H(δ-) from Et3SiH (the first SN2 process), giving HB(C6F5)3(-), and then leave H(δ-) of HB(C6F5)3(-) to the electrophilic C center of 5-7 (the second SN2 process). The SN2 processes utilize the electrophilic and nucleophilic characteristics possessed by the hydride acceptors (5-7). The hydride-transfer mechanism is different from that in the CO2 reduction to methanol catalyzed by N-heterocyclic carbene (NHC) and PCP-pincer nickel hydride ([Ni]H), where the characteristic of possessing a C═O double bond of the hydride acceptors is utilized for hydride transfer. The mechanistic differences elucidate why the present system can completely reduce CO2 to CH4, whereas NHC and [Ni]H catalysts can only mediate the reduction of CO2 to [Si]OCH3 and catBOCH3, respectively. Understanding this could help in the development of catalysts for selective CO2 reduction to CH4 or methanol.
    Inorganic Chemistry 10/2013; · 4.59 Impact Factor
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    ABSTRACT: Baby face: Interface engineering of ceria‐supported Au catalysts was achieved by a combination of DFT calculations and synthetic techniques. The reducibility of the Au/ceria catalysts was determined by the interfacial AuOCen structures.
    ChemCatChem 01/2013; 5(6). · 5.18 Impact Factor
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    ABSTRACT: Hydrogen activation is a key step in hydrogenation reactions which are widely used in both laboratory synthesis and the chemical industry. Traditionally, it was often considered that only transition metal complexes/systems are able to activate hydrogen and to catalyze hydrogenations. This view has been changed recently; more and more metal-free molecules/systems have been found capable of activating hydrogen. Among these developments, the frustrated Lewis pairs (FLPs) are of particular significance, not only because they exhibit high reactivity toward hydrogen as well as other small molecules, but also because some of them can perform direct catalytic hydrogenations, which pave the way to the development of cheaper and greener hydrogenation catalysts. Inspired by the FLP principle, we used quantum mechanics computations to design molecules for H(2), CH(4), and NH(3) activation and catalysts for hydrogenation of imines, ketones, and alkenes. While our designed molecules are awaiting experimental preparation, the active sites in our designed molecules anticipated the features appeared in the compounds synthesized later by experimentalists. This chapter reviews our computational explorations to enrich FLP chemistry.
    Topics in current chemistry 11/2012; · 8.46 Impact Factor
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    ABSTRACT: Searches for planar hexacoordinate carbon (phC) species comprised of only seven atoms uncovered good CX3M3 prototypes, D3h CN3Be3+ and CO3Li3+. The latter is the global minimum. It might also be possible to detect the deep-lying kinetically-viable D3h CN3Be3+ local minimum, based on its robustness toward molecular dynamic simulations and its very high isomerization barrier.
    Physical Chemistry Chemical Physics 10/2012; 14(43). · 4.20 Impact Factor
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    ABSTRACT: Searches for planar hexacoordinate carbon (phC) species comprised of only seven atoms uncovered good CX(3)M(3) prototypes, D(3h) CN(3)Be(3)(+) and CO(3)Li(3)(+). The latter is the global minimum. It might also be possible to detect the deep-lying kinetically-viable D(3h) CN(3)Be(3)(+) local minimum, based on its robustness toward molecular dynamic simulations and its very high isomerization barrier.
    Physical Chemistry Chemical Physics 07/2012; 14(43):14760-3. · 4.20 Impact Factor
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    ABSTRACT: Frustrated Lewis pairs (FLPs) has been applied to catalytic metal-free hydrogenation. Can the FLP reactivity be used for catalytic hydroamination? Using density functional theory (DFT) calculations, we have explored whether the molecules cat1-cat3, which were previously designed by integrating the dearomatization-aromatization effect and the FLP reactivity, can catalyze the intramolecular hydroaminations of non-activated aminoalkenes to afford nitrogen heterocycles. The study shows that the γ-aminoalkene (am1) hydroamination catalyzed by cat1 proceeds via two steps (aminoalkene N-H bond activation and C-N bond formation) with experimentally accessible energetics, giving the five-membered nitrogen heterocycle product 1,1-dimethylpyrrolidine. The N-H bond activation is reversible. The C-N bond formation step undergoes a concerted mechanism and complies with the Markovnikov addition rule. Possible side reactions which may cause catalyst deactivation were confirmed to be energetically unfavorable. The molecules cat2 and cat3 are less effective than cat1 in catalyzing the am1 hydroamination, but the barriers are not too high. By following the most favorable pathway of the cat1-mediated am1 hydroamination, we further extended the substrate (am1) to other aminoalkenes, including the methyl and phenyl β-substituted am1 (i.e. am2 and am3, respectively), the benzyl-protected primary aminoalkene (am4), and the δ-aminoalkene (am5). The hydroaminations of am2 and am3 have energetics comparable with am1 hydroamination, the am5 hydroamination is energetically less favorable, and the am4 hydroamination is least favorable but could be realizable by elevating the temperature and pressure. We call experimental efforts to synthesize cat1-cat3 or similar new molecules on the basis of the design strategy.
    Dalton Transactions 05/2012; 41(30):9091-100. · 3.81 Impact Factor
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    ABSTRACT: Despite their formal relationship to alkynes, Ar'GeGeAr', Ar'SnSnAr', and Ar*SnSnAr* [Ar' = 2,6-(2,6-iPr(2)C(6)H(3))(2)C(6)H(3); Ar* = 2,6-(2,4,6-iPr(3)C(6)H(2))(2)-3,5-iPr(2)C(6)H] exhibit high reactivity toward H(2), quite unlike acetylenes. Remarkably, the products are totally different. Ar'GeGeAr' can react with 1-3 equiv of H(2) to give mixtures of Ar'HGeGeHAr', Ar'H(2)GeGeH(2)Ar', and Ar'GeH(3). In contrast, Ar'SnSnAr' and Ar*SnSnAr* react with only 1 equiv of H(2) but give different types of products, Ar'Sn(μ-H)(2)SnAr' and Ar*SnSnH(2)Ar*, respectively. In this work, this disparate behavior toward H(2) has been elucidated by TPSSTPSS DFT computations of the detailed reaction mechanisms, which provide insight into the different pathways involved. Ar'GeGeAr' reacts with H(2) via three sequential steps: H(2) addition to Ar'GeGeAr' to give singly H-bridged Ar'Ge(μ-H)GeHAr'; isomerization of the latter to the more reactive Ge(II) hydride Ar'GeGeH(2)Ar'; and finally, addition of another H(2) to the hydride, either at a single Ge site, giving Ar'H(2)GeGeH(2)Ar', or at a Ge-Ge joint site, affording Ar'GeH(3) + Ar'HGe:. Alternatively, Ar'Ge(μ-H)GeHAr' also can isomerize into the kinetically stable Ar'HGeGeHAr', which cannot react with H(2) directly but can be transformed to the reactive Ar'GeGeH(2)Ar'. The activation of H(2) by Ar'SnSnAr' is similar to that by Ar'GeGeAr'. The resulting singly H-bridged Ar'Sn(μ-H)SnHAr' then isomerizes into Ar'HSnSnHAr'. The subsequent facile dissociation of the latter gives two Ar'HSn: species, which then reassemble into the experimental product Ar'Sn(μ-H)(2)SnAr'. The reaction of Ar*SnSnAr* with H(2) forms in the kinetically and thermodynamically more stable Ar*SnSnH(2)Ar* product rather than Ar*Sn(μ-H)(2)SnAr*. The computed mechanisms successfully rationalize all of the known experimental differences among these reactions and yield the following insights into the behavior of the Ge and Sn species: (I) The active sites of Ar'EEAr' (E = Ge, Sn) involve both E atoms, and the products with H(2) are the singly H-bridged Ar'E(μ-H)EHAr' species rather than Ar'HEEHAr' or Ar'EEH(2)Ar'. (II) The heavier alkene congeners Ar'HEEHAr' (E = Ge, Sn) cannot activate H(2) directly. Instead, Ar'HGeGeHAr' must first isomerize into the more reactive Ar'GeGeH(2)Ar'. Interestingly, the subsequent H(2) activation by Ar'GeGeH(2)Ar' can take place on either a single Ge site or a joint Ge-Ge site, but Ar'SnSnH(2)Ar' is not reactive toward H(2). The higher reactivity of Ar'GeGeH(2)Ar' in comparison with Ar'SnSnH(2)Ar' is due to the tendency of group 14 elements lower in the periodic table to have more stable lone pairs (i.e., the inert pair effect) and is responsible for the differences between the reactions of Ar'EEAr' (E = Ge, Sn) with H(2). Similarly, the carbene-like Ar'HGe: is more reactive toward H(2) than is Ar'HSn:. (III) The doubly H-bridged Ar'E(μ-H)(2)EAr' (E = Ge, Sn) species are not reactive toward H(2).
    Journal of the American Chemical Society 04/2012; 134(21):8856-68. · 10.68 Impact Factor
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    ABSTRACT: Metal-free hydrogenation has been proposed to be a green alternative to the conventional hydrogenation mediated by precious transition metal complexes. Thanks to the discovery of FLP (frustrated Lewis pair) chemistry, the field has recently witnessed significant progress. Inspired by the FLP idea of synergically utilizing the catalytic effects of Lewis acid and base, we previously proposed a strategy to construct metal-free active sites for H(2) activation and designed a metal-free molecule (1) that shows high reactivity toward H(2). Encouraged by the recent experimental successes in applying the strategy, we have computationally explored if 1 can go further to serve as a catalyst to promote the hydrogenations of various unsaturated compounds examined by ethylene (CH(2)=CH(2) (4)), silyl enol ether (CH(2)=C(Me)OSiMe(3) (5)), imines (Me(2)C=NMe (6) and Ph(Me)C=NMe (7)), and ketone (Ph(Me)C=O (9)). The energetic results predicted at the M05-2X(IEFPCM, solvent = THF)/6-311++G** level indicate that these reactions have feasible kinetics and thermodynamics for experimental realization. The hydride transfer step follows the concerted mechanism, although the transfer process has asynchronous character for silyl enol ether (5) and imines (6 and 7). In addition, we have investigated the binding of CO(2) to 1 and the 1-mediated hydrogenation of CO(2).
    Dalton Transactions 03/2012; 41(15):4674-84. · 3.81 Impact Factor
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    ABSTRACT: Development of efficient dehydrogenation/hydrogenation is critical to the realization of organic hydride hydrogen storage. Using B3LYP DFT calculations, we have investigated the catalytic mechanisms of the reversible 3qu4h/4qu dehydrogenation/hydrogenation (3qu4h = tetrahydroquinoline and 4qu = quinoline) catalyzed by the Ir-complex 2cat (Cp*IrPYD′, Cp* = η5-C5Me5 and PYD′ = CF3-substituted 2-pyridonate), reported by Yamaguchi and Fujita et al. Two reactive species (7bif and 12hcl) are identified to play important roles in the catalytic system. The species (7bif) with bifunctional reactivity can be facilely obtained from 2cat by just rotating the PYD′ ligand, while 12hcl (Cp*IrHCl) is generated via HPYD′ ligand (HPYD′ = CF3-substituted 2-hydroxypyridine) dissociation after hydrogen transfer in dehydrogenation or hydrogen activation in hydrogenation. The species 7bif mediates dehydrogenation via a hydrogen transfer mechanism, which is more favorable than the β-H elimination (BETAHE) one, confirming our conclusion drawn in the study of alcohol dehydrogenation catalyzed by a similar catalyst. The 12hcl species combines the substrates (e.g., 4qu) to form a reactive pair that simultaneously possesses Lewis acidic and basic reactivity to activate H2 with a mechanism similar to the H2 activation by metal-free FLP (frustrated Lewis pair). The hydrogen activation by the pair gives an ion pair that undergoes hydride transfer to complete the hydrogenation. Because the dimer (Cp*IrHCl)2 itself does not show reactivity toward hydrogen activation but can be easily decomposed into the reactive monomer (12hcl), we reason the experimentally observed hydrogenation of 4qu by using the dimer (Cp*IrHCl)2 is mediated by the monomer (12hcl). The species 7bif and 12hcl catalyze both dehydrogenation and hydrogenation processes via microscopic reversibility; depending on the absence or presence of H2, the reaction moves toward dehydrogenation or hydrogenation, respectively. The complete 3qu4h/4qu dehydrogenation/hydrogenation requires an isomerization step through imine enamine tautomerization and disproportionation. The protonation required for the disproportionation can be mediated by the dihydro intermediate (9oh_h) of 7bif or the ion pair (the product of H2 activation catalyzed by 12hcl). The predicted mechanisms reasonably rationalize the experimental observations in the (3qu4h 4qu)/2cat system.
    Organometallics 05/2011; 30(11):3131–3141. · 4.15 Impact Factor
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    ABSTRACT: There has been an increasing interest in developing efficient AAD (acceptorless alcohol dehydrogenation) catalysts, because of their potential applications in atom economic synthesis, H2 production from biomass or its fermentation products (mainly alcohols), and the development of organic hydride hydrogen storage systems. Using B3LYP DFT calculations with solvation effects accounted by the SMD solvent model, we have investigated the catalytic mechanism of a novel Ir catalyst (2cat) in the dehydrogenation of 1-phenylethanol (3ol). This study allows us not only to detail the β-H elimination (BETAHE) pathway proposed by the experimentalists but also to characterize a new pathway called the ligand rotation-promoted hydrogen transfer (LRPHT) pathway. Combining the predicted energetics and experimental results/observations, we confirmed that the LRPHT pathway is more favorable than the BETAHE pathway in 3ol/2cat. According to the favorable LRPHT pathway, we show that the facile ligand rotation between the 18e2cat complex and the 16e bifunctional reactive species 7bif is responsible for the novelty of the catalyst. The bifunctional reactivity of the species makes the hydrogen transfer feasible for dehydrogenation. The facile ligand rotation is also the reason that the dehydrogenation could be run under neutral conditions, because this activation mode does not require acidic/basic reaction conditions or acid/base promoters to activate the catalyst. Unveiling these characteristics of the new catalyst could aid the advancement of the experimental idea from the perspective of activating catalysts to generate a bifunctional active site via “ligand rotation”. We also studied the formation mechanism of the experimentally identified complexes, according to which various experimental observations were rationalized.
    Organometallics 03/2011; 30(8):2349–2363. · 4.15 Impact Factor
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    ABSTRACT: This study extends our previous work of using π-FLP strategy to develop metal-free hydrogenation catalysts. Using small MeN=CMe(2) imine (im1) as a model, we previously designed cat1 and cat2 catalysts. But it is unclear whether they are capable of catalyzing the hydrogenations of bulky imines. Using tBuN=C(H)Ph (im2) as a representative of large imines, we assessed the energetics of the cat1- and cat2-catalyzed im2 hydrogenations. The predicted energetics indicates that they can still catalyze large imine hydrogenations with experimentally accessible kinetic barriers, although the energetics becomes less favorable. To improve the catalysis, we proposed new catalysts (cat3 and cat4) by tailoring cat1 and cat2. The study indicates that cat3 and cat4 could have better performance for the hydrogenation of the bulky im2 than cat1 and cat2. Remarkably, cat3 and cat4 are also found suitable for small imine (im1) hydrogenation. Examining the hydrogen transfer substeps in the eight hydrogenations involved in this study, we observed that the mechanism for the hydrogen transfer step in the catalytic cycles depends on the steric effect between catalyst and substrate. The mechanism can be switched from stepwise one in the case of large steric effect (e.g.im2/cat2) to the concerted one in the case of small steric effect (e.g.im1/cat3). The new catalysts could be better targets for experimental realization because of their simpler constructions.
    Dalton Transactions 03/2011; 40(9):1929-37. · 3.81 Impact Factor
  • Chemistry 02/2011; 17(7):2038-43. · 5.93 Impact Factor
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    ABSTRACT: A density functional theory study at the M05-2X(IEFPCM, THF)/6-311+G**//M05-2X/6-31G* level has been conducted to gain insight into the catalytic mechanism of the first metal-free N-heterocyclic carbene (NHC)-catalyzed conversion of carbon dioxide into methanol. Among the various examined reaction pathways, we found that the most favorable leads to the experimentally detected intermediates, including formoxysilane (FOS), bis(silyl)acetal (BSA), silylmethoxide (SMO), and disiloxane (DSO). However, our study also revealed that formaldehyde (CH(2)O), generated from the dissociation of BSA into DSO and CH(2)O via a mechanism somewhat similar to the Brook rearrangement, should be an inevitable intermediate, although it was not reported by the experimentalists. When NHC catalyzes the reactions of CO(2)/FOS/CH(2)O with silane, there are two activation modes. It was found that NHC prefers to activate Si-H bonds of silane and push electron density to the H atoms of the Si-H bonds in favor of transferring a hydridic atom of silane to the electrophilic C center of CO(2)/FOS/CH(2)O. This holds true in particular for the NHC-catalyzed reactions of silane with FOS/CH(2)O to produce BSA/SMO. The preferred activation mode can operate by first passing an energetically unfavorable NHC-silane local minimum via pi-pi interactions or by directly crossing a transition state involving three components simultaneously. The activation mode involving initial coordination of NHC with the electrophilic C atom of CO(2)/FOS/CH(2)O is less favorable or inoperable. The predicted catalytic mechanism provides a successful interpretation of the experimental observation that phenylsilane is more efficient than diphenylsilane in performing the conversion.
    Journal of the American Chemical Society 09/2010; 132(35):12388-96. · 10.68 Impact Factor
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    ABSTRACT: A computational study has been carried out to examine if the metal-free catalyst (1) designed for imine hydrogenation is able to hydrogenate ketones, using the cyclohexanone (3) and its derivatives (4-6) as ketone models. The catalytic cycle includes two major steps: hydrogen activation and hydrogen transfer. The concerted pathway in the hydrogen transfer step is preferred over the stepwise pathway. The two separated steps for hydrogen activation and hydrogen transfer can benefit the hydrogen addition to the substrates (e.g., ketones) which do not have strong Lewis base centres, because the substrates need not to be involved in the hydrogen activation. In general, the larger the steric effect of the substrate is, the less severe the side reactions become, and the more difficultly the desired reaction occurs. The energetic results show that the hydrogenations of 3-5 are kinetically and thermodynamically feasible under ambient conditions, but the hydrogenation of 6 is less energetically favourable. Therefore, it is important to establish a proper balance between promoting the desired reaction and meanwhile avoiding the undesired reactions. The issue of the resting state, caused by forming stable alkoxide complexes like in the ketone hydrogenation catalyzed by the metal-ligand bifunctional catalysts, is also discussed.
    Dalton Transactions 06/2010; 39(23):5519-26. · 3.81 Impact Factor
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    ABSTRACT: Using MeN=CMe(2) as an imine model, computational chemistry has been applied to design metal-free hydrogenation catalysts. The implementation includes designing proper electronic structures to split H(2) and building appropriate chemical scaffolds to prevent possible side reactions which may deactivate the catalysts. Interestingly, the designed catalysts bear resemblances to the well-known metal-ligand bifunctional hydrogenation catalysts in terms of both the activation principle and the hydrogenation mechanisms. The hydrogenations catalyzed by the designed catalysts proceed via two major steps, hydrogen activation and hydrogen transfer. The predicted energetics for completing the catalytic cycles indicate that these reactions have feasible kinetics and thermodynamics for experimental realizations under ambient conditions. We also showed how to improve the catalysis by using the "cooperative effect" and the non-bonding interactions. The reported catalysts can be the targets for experimental synthesis. The strategy can be borrowed to design similar catalysts.
    Dalton Transactions 05/2010; 39(17):4038-47. · 3.81 Impact Factor
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    ABSTRACT: Utilization of the acid/base effects simultaneously is one of the basic principles used by transition-metal (TM) complexes to activate H–H/C–H σ bonds. In principle, the high reactivity of metal-free FLPs (frustrated Lewis pairs) towards H2 can also be attributed to these effects. On the basis of our proposed integrated FLPs, we pushed the effects to a higher (if not a limit) level at which the extremely unreactive methane C–H σ bond can be activated by our designed metal-free closed-shell molecules. Three molecules (M3c, M4b, and M4c) among the reported have activation free energies (22.4, 20.0, and 20.2 kcal mol–1, respectively) comparable with (or less than) the 22.3 kcal mol–1 of a TM model complex that features a Ti=N double bond. The derivative of the TM model has been experimentally shown to be capable of activating methane. Moreover, some of the activation reactions are (or nearly) thermoneutral. For example, the methane activations of M3c, M4b, and M4c are exothermic by –1.9, –4.5, and –5.2 kcal mol–1 of free energies, respectively. The kinetics and thermodynamics imply that the molecules could be further developed to realize catalytic methane activation. The electronic structure analyses reveal that, although our metal-free molecules and the TM model complex share the same principle in activating the C–H bond, there are differences as to how they go about maintaining the effective active sites. The reported molecules could be the targets for experimental realizations. The strategy could be applied to the design of similar molecules to realize more general C–H bond activation of alkanes.
    Berichte der deutschen chemischen Gesellschaft 04/2010; 2010(15):2254 - 2260. · 2.94 Impact Factor
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    ABSTRACT: In this study, a strategy to design a metal-free hydrogen activation site has been proposed. On the basis of our so-called sp(3) carbon bridged FLPs (Frustrated Lewis Pairs), we first hypothesized that a more reactive activation site should arrange the nitrogen lone pair and the boron vacant orbital to lie in the same plane face-to-face, because such orbital orientations can simultaneously enhance the interaction between the nitrogen lone pair and the H(2) sigma* antibonding orbital and the interaction between the boron vacant orbital and the H(2) sigma bonding electrons. To verify that such an active site is achievable, we then computationally designed molecules and studied their reactions with hydrogen. The energetic results show the designed molecules are indeed more reactive than the sp(3) carbon bridged FLPs. Some of the hydrogen activations reach kinetics and thermodynamics comparable with those of the hydrogen activations mediated by the well-known metal-ligand bifunctional hydrogenation catalysts. The designed molecules could be the targets for experimental synthesis. The pattern of the proposed active site can be based to design similar molecules for metal-free hydrogenations.
    Inorganic Chemistry 01/2010; 49(1):295-301. · 4.59 Impact Factor
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    ABSTRACT: Computational study has been conducted to gain insight into the relative reactivity of stable carbenes (1 and 2) and typical frustrated Lewis pairs (FLPs, 3-6) in activating H(2) and CH(4). For the FLP H(2) activations, despite the quite different basicities of the Lewis base components, they have comparable reactivities. The unexpected relative reactivity can be attributed to the following two factors: (i) the vacant carbene C: p(π) orbital, which is important when carbene works alone but does not participate in the FLP activation; and (ii) the electrostatic interaction between the Lewis base center and the approaching H atom which plays an important role and can either favor or disfavor a reaction. These explanations are also applicable to methane activations. The study brings two messages to the experimentalists for constructing FLPs: (i) it is recommended to use P- and N-centered Lewis bases to construct FLPs for H(2) activation because using more reactive components does not benefit the activation; and (ii) the FLPs are less reactive in activating CH(4) than H(2). In addition, using more reactive carbenes as Lewis bases in FLPs does not necessarily benefit the methane activation.
    Physical Chemistry Chemical Physics 01/2010; 12(20):5268-75. · 4.20 Impact Factor
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    ABSTRACT: On the basis of the FLP (frustrated Lewis pair) principle, a new strategy has been proposed to construct the “frustration” in designing metal-free hydrogen activation compounds, by using FMO (frontier molecular orbital) analyses and quantum mechanics calculations. Unlike the known FLPs which use bulky substituents to prevent them from forming stable Lewis acid/base complexes, the new approach encumbers the intramolecular π donation from the electron donor to the acceptor (e.g. in BH2NH2) by using a CH2 bridge (giving BH2CH2NH2). The strategy is simple and effective. Its effectiveness is demonstrated by the small hydrogen activation energy (12.0 kcal/mol) of the model molecule (BH2CH2NH2), which is significantly less than the 42.7 kcal/mol of BH2NH2 and also less than the 18.5 kcal/mol of BH2PH2 whose derivative, R2PB(C6F5)2, has been experimentally shown to be able to activate hydrogen. We also exemplified how to use the strategy to design experimentally more realizable molecules. The example shows promises as a hydrogen activation agent. The strategy can be used to design metal-free catalysts for direct hydrogenation.
    Chinese Science Bulletin 01/2010; 55(3):239-245. · 1.37 Impact Factor