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1.
Dr. Jakub Šebera Prof. Jaroslav Burda Dr. Michal Straka Prof. Akira Ono Prof. Chojiro Kojima Prof. Yoshiyuki Tanaka Dr. Vladimír Sychrovský 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(30):9884-9894
A reaction mechanism that describes the substitution of two imino protons in a thymine:thymine (T:T) mismatched DNA base pair with a HgII ion, which results in the formation of a (T)N3‐HgII‐N3(T) metal‐mediated base pair was proposed and calculated. The mechanism assumes two key steps: The formation of the first HgII? N3(T) bond is triggered by deprotonation of the imino N3 atom in thymine with a hydroxo ligand on the HgII ion. The formation of the second HgII? N3(T) bond proceeds through water‐assisted tautomerization of the remaining, metal‐nonbonded thymine base or through thymine deprotonation with a hydroxo ligand of the HgII ion already coordinated to the thymine base. The thermodynamic parameters ΔGR=?9.5 kcal mol?1, ΔHR=?4.7 kcal mol?1, and ΔSR=16.0 cal mol?1 K?1 calculated with the ONIOM (B3LYP:BP86) method for the reaction agreed well with the isothermal titration calorimetric (ITC) measurements by Torigoe et al. [H. Torigoe, A. Ono, T. Kozasa, Chem. Eur. J. 2010 , 16, 13218–13225]. The peculiar positive reaction entropy measured previously was due to both dehydration of the metal and the change in chemical bonding. The mercury reactant in the theoretical model contained one hydroxo ligand in accord with the experimental pKa value of 3.6 known for an aqua ligand of a HgII center. The chemical modification of T:T mismatched to the T‐HgII‐T metal‐mediated base pair was modeled for the middle base pair within a trinucleotide B‐DNA duplex, which ensured complete dehydration of the HgII ion during the reaction. 相似文献
2.
Florian Eweiner Shunsuke Senda Klaus Bergander Dr. Christian Mück‐Lichtenfeld Dr. Stefan Grimme Prof. Dr. Roland Fröhlich Dr. Michiko Aoyama Hiroyuki Kawaguchi Prof. Dr. Yasuhiro Ohki Dr. Tsuyoshi Matsumoto Dr. Gerald Kehr Dr. Kazuyuki Tatsumi Prof. Dr. Gerhard Erker Prof. Dr. 《化学:亚洲杂志》2009,4(12):1830-1833
Treatment of the salt [PPh4]+[Cp*W(S)3]? ( 6 ) with allyl bromide gave the neutral complex [Cp*W(S)2S‐CH2‐CH?CH2] ( 7 ). The product 7 was characterized by an X‐ray crystal structure analysis. Complex 7 features dynamic NMR spectra that indicate a rapid allyl automerization process. From the analysis of the temperature‐dependent NMR spectra a Gibbs activation energy of ΔG≠ (278 K)≈13.7±0.1 kcal mol?1 was obtained [ΔH≠≈10.4±0.1 kcal mol?1; ΔS≠≈?11.4 cal mol?1 K?1]. The DFT calculation identified an energetically unfavorable four‐membered transition state of the “forbidden” reaction and a favorable six‐membered transition state of the “Cope‐type” allyl rearrangement process at this transition‐metal complex core. 相似文献
3.
Oleg Ya. Borbulevych Igor R. Golding Alexander N. Shchegolikhin Zinaida S. Klemenkova Mikhail Yu. Antipin 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(8):996-998
Although the two polymorphic modifications, (I) and (II), of the title compound, C13H10N2O, crystallize in the same space group (P21/c), their asymmetric units have Z′ values of 1 and 2, respectively. These are conformational polymorphs, since the molecules in phases (I) and (II) adopt different rotations of the phenyl ring with respect the central 2‐cyanocarboxyaminoprop‐2‐enyl fragment. Calculations of crystal packing using Cerius2 [Molecular Simulations (1999). 9685 Scranton Road, San Diego, CA 92121, USA] have shown that (I) is more stable than (II), by 1.3 kcal mol?1 for the crystallographically determined structures and by 1.56 kcal mol?1 for the optimized structures (1 kcal mol?1 = 4.184 kJ mol?1). This difference is mainly attributed to the different strengths of the hydrogen bonding in the two forms. 相似文献
4.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(35):10685-10690
Electropositive boron‐based substituent (phosphonium bora‐ylide) with an exceptionally strong π‐ and σ‐electron donating character dramatically increases the stability of a new type of N ‐heterocyclic silylene 2 featuring amino‐ and bora‐ylide‐substituents. Moreover, the related silylium ion 4 and transition‐metal–silylene complexes, with trigonal‐planar geometries around the silicon center, are also well stabilized. Therefore, the N,B‐heterocyclic silylene 2 can be used as a strongly electron‐donating innocent ligand in coordination chemistry similarly to N ‐heterocyclic carbenes. 相似文献
5.
The Unexpected Mechanism Underlying the High‐Valent Mono‐Oxo‐Rhenium(V) Hydride Catalyzed Hydrosilylation of CN Functionalities: Insights from a DFT Study
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In this study, we theoretically investigated the mechanism underlying the high‐valent mono‐oxo‐rhenium(V) hydride Re(O)HCl2(PPh3)2 ( 1 ) catalyzed hydrosilylation of C?N functionalities. Our results suggest that an ionic SN2‐Si outer‐sphere pathway involving the heterolytic cleavage of the Si?H bond competes with the hydride pathway involving the C?N bond inserted into the Re?H bond for the rhenium hydride ( 1 ) catalyzed hydrosilylation of the less steric C?N functionalities (phenylmethanimine, PhCH=NH, and N‐phenylbenzylideneimine, PhCH=NPh). The rate‐determining free‐energy barriers for the ionic outer‐sphere pathway are calculated to be ~28.1 and 27.6 kcal mol?1, respectively. These values are slightly more favorable than those obtained for the hydride pathway (by ~1–3 kcal mol?1), whereas for the large steric C?N functionality of N,1,1‐tri(phenyl)methanimine (PhCPh=NPh), the ionic outer‐sphere pathway (33.1 kcal mol?1) is more favorable than the hydride pathway by as much as 11.5 kcal mol?1. Along the ionic outer‐sphere pathway, neither the multiply bonded oxo ligand nor the inherent hydride moiety participate in the activation of the Si?H bond. 相似文献
6.
First Principles (DFT) Characterization of RhI/dppp‐Catalyzed CH Activation by Tandem 1,2‐Addition/1,4‐Rh Shift Reactions of Norbornene to Phenylboronic Acid
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Prof. Dr. Eric Assen B. Kantchev Surya R. Pangestu Dr. Feng Zhou Dr. Michael B. Sullivan Prof. Hai‐Bin Su 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15625-15634
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 RhIII?H species, which in turn undergoes a C(aryl)?H reductive elimination. Our DFT calculations confirm the RhI/RhIII 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. 相似文献
7.
M. Sc. André K. Eckhardt Prof. Dr. Peter R. Schreiner 《Angewandte Chemie (International ed. in English)》2018,57(19):5248-5252
Although N‐heterocyclic carbenes have been well‐studied, the simplest aminocarbene, aminomethylene H?C??NH2, has not been spectroscopically identified to date. Herein we report the gas‐phase preparation of aminomethylene by high‐vacuum flash pyrolysis of cyclopropylamine and subsequent trapping of the pyrolysate in an inert argon matrix at 12 K. Aminomethylene was characterized by matching matrix IR and UV/Vis spectroscopic data with ab initio coupled cluster computations. After UV irradiation of the matrix aminomethylene rearranges to its isomer methanimine (formaldimine) H2C=NH. Based on our experimental results and computations aminomethylene has a singlet ground state with a reaction barrier of almost 46 kcal mol?1 to methanimine so that H‐tunneling is excluded. 相似文献
8.
Jean‐Claude Daran Funda Demirhan
zgür Yldrm Bekir etinkaya 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(2):m48-m52
Owing to increasing interest in the use of N‐heterocyclic carbenes (NHCs) based on imidazolidinium ions as ligands in the design of highly efficient transition‐metal‐based homogeneous catalysts, the characterizations of the 1‐ferrocenylmethyl‐3‐(2,4,6‐trimethylbenzyl)imidazolidin‐3‐ium iodide salt, [Fe(C5H5)(C19H24N2)]I, (I), and the palladium complex trans‐bis(3‐benzyl‐1‐ferrocenylmethyl‐1H‐imidazolidin‐2‐ylidene)diiodidopalladium(II), [Fe2Pd(C5H5)2(C16H17N2)2I2], (II), are reported. Compound (I) has two iodide anions and two imidazolidinium cations within the asymmetric unit (Z′ = 2). The two cations have distinctly different conformations, with the ferrocene groups orientated exo and endo with respect to the N‐heterocyclic carbene. Weak C—H donor hydrogen bonds to both the iodide anions and the π system of the mesitylene group combine to form two‐dimensional layers perpendicular to the crystallographic c direction. Only one of the formally charged imidazolidinium rings forms a near‐linear hydrogen bond with an iodide anion. Complex (II) shows square‐planar coordination around the PdII metal, which is located on an inversion centre (Z′ = 0.5). The ferrocene and benzyl substituents are in a trans–anti arrangement. The Pd—C bond distance between the N‐heterocyclic carbene ligands and the metal atom is 2.036 (7) Å. A survey of related structures shows that the lengthening of the N—C bonds and the closure of the N—C—N angle seen here on metal complexation is typical of similar NHCs and their complexes. 相似文献
9.
This work described the synthesis of the first and unprecedented examples of 5‐aryl‐1H‐tetrazoles including spiro‐ and bis‐(thio)barbiturates, generated from the reaction between 4‐(1H‐tetrazol‐5‐yl)benzaldehyde with (thio)barbituric acids and cyanogen bromide (BrCN) in the presence of triethylamine, providing good overall yields. Tetrazoles based on bis‐(thio) barbiturates were also obtained in the absence of BrCN under the same conditions. The structures were characterized by IR, 1H NMR, 13C NMR, X‐ray crystallography and mass analysis techniques. The reaction mechanism was proposed. The hydrogen bond strength (EHB) versus d (O1?????O7 (w)) distance (kcal.mol?1) and corresponding pKa value for the proton of H3A (in water molecule) in 4b.H2O were estimated to be 13.8 kcal.mol?1 and 8.2, respectively. 相似文献
10.
Andreas Uhe Dr. Markus Hölscher Prof. Dr. Walter Leitner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):1020-1027
Very few cases of oxidative addition of NH3 to transition‐metal complexes forming terminal amide hydrides have been experimentally observed. Here, two examples with the iridium pincer complexes [Ir(PCP)(NH3)] A1 with PCP=[κ3‐(tBu2P‐C2H4)2CH]? and [Ir(PSiP)(NH3)] B1 with PSiP=[κ3‐(2‐Cy2P‐C6H4)2SiMe]? were investigated by DFT calculations applying the M06L density functional to successfully reproduce the trend of the experimentally observed thermochemical stabilities. According to the calculations, the corresponding hydrido‐amido complexes A2 and B2 are more stable than the corresponding ammine complexes by ΔG=?2.8 and ?2.6 kcal mol?1, respectively. Complexes such as A2 and B2 are ideally suited entry points to catalytic cycles for the hydroamination of ethylene with ammonia. Therefore, the relevant stationary points of the potentially available cycles were studied computationally to verify if these complexes can catalyze the hydroamination. As a result, complex A2 will clearly not catalyze the hydroamination as all energy spans calculated range close to 40 kcal mol?1 or higher. The energy spans obtained with B2 are significantly lower in some cases and range around 35 kcal mol?1, further indicating that no turnover can be expected. By systematically varying the structure of B2 , the energy span could be reduced to 28.8 kcal mol?1 corresponding to a TOF of 17 h?1 at a reaction temperature of 140 °C. A reoptimization of relevant structures under the inclusion of cyclohexane as a typical solvent reduces the calculated TOF to 6.0 h?1. 相似文献
11.
Dr. Sarolta Pilbák Dr. Ödön Farkas Prof. Dr. László Poppe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(25):7793-7802
Quantum mechanics/molecular mechanics calculations in tyrosine ammonia lyase (TAL) ruled out the hypothetical Friedel–Crafts (FC) route for ammonia elimination from L ‐tyrosine due to the high energy of FC intermediates. The calculated pathway from the zwitterionic L ‐tyrosine‐binding state (0.0 kcal mol?1) to the product‐binding state ((E)‐coumarate+H2N? MIO; ?24.0 kcal mol?1; MIO=3,5‐dihydro‐5‐methylidene‐4H‐imidazol‐4‐one) involves an intermediate (IS, ?19.9 kcal mol?1), which has a covalent bond between the N atom of the substrate and MIO, as well as two transition states (TS1 and TS2). TS1 (14.4 kcal mol?1) corresponds to a proton transfer from the substrate to the N1 atom of MIO by Tyr300? OH. Thus, a tandem nucleophilic activation of the substrate and electrophilic activation of MIO happens. TS2 (5.2 kcal mol?1) indicates a concerted C? N bond breaking of the N‐MIO intermediate and deprotonation of the pro‐S β position by Tyr60. Calculations elucidate the role of enzymic bases (Tyr60 and Tyr300) and other catalytically relevant residues (Asn203, Arg303, and Asn333, Asn435), which are fully conserved in the amino acid sequences and in 3D structures of all known MIO‐containing ammonia lyases and 2,3‐aminomutases. 相似文献
12.
Alexander S. Novikov Dr. Maxim L. Kuznetsov Prof. Armando J. L. Pombeiro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(8):2874-2888
The theoretical background of the formation of N‐heterocyclic oxadiazoline carbenes through a metal‐assisted [2+3]‐dipolar cycloaddition (CA) reaction of nitrones R1CH?N(R2)O to isocyanides C?NR and the decomposition of these carbenes to imines R1CH?NR2 and isocyanates O?C?NR is discussed. Furthermore, the reaction mechanisms and factors that govern these processes are analyzed in detail. In the absence of a metal, oxadiazoline carbenes should not be accessible due to the high activation energy of their formation and their low thermodynamic stability. The most efficient promotors that could assist the synthesis of these species should be “carbenophilic” metals that form a strong bond with the oxadiazoline heterocycle, but without significant involvement of π‐back donation, namely, AuI, AuIII, PtII, PtIV, ReV, and PdII metal centers. These metals, on the one hand, significantly facilitate the coupling of nitrones with isocyanides and, on the other hand, stabilize the derived carbene heterocycles toward decomposition. The energy of the LUMOCNR and the charge on the N atom of the C?N group are principal factors that control the cycloaddition of nitrones to isocyanides. The alkyl‐substituted nitrones and isocyanides are predicted to be more active in the CA reaction than the aryl‐substituted species, and the N,N,C‐alkyloxadiazolines are more stable toward decomposition relative to the aryl derivatives. 相似文献
13.
The [1,5]‐migration reaction has attracted considerable attention from experimentalists and theoreticians for decades. Although it has been extensively investigated in various systems, studies on pyrrolium derivatives are underdeveloped. Herein, a theoretical study on the reaction mechanism of [1,5]‐migration in both pyrrolium and pyrrole derivatives is presented. The results reveal lower activation barriers in [1,5]‐migration of electropositive groups (AuPMe3 and SnH3) in pyrrolium derivatives, although the bond dissociation energies of the Au?N bond (98.8 kcal mol?1) and Sn?N bond (81.7 kcal mol?1) are larger than that of the N?F bond (57.6 kcal mol?1). The unexpectedly lower activation barriers (4.5 and 4.9 kcal mol?1 for AuPMe3 and SnH3, respectively) for [1,5]‐migration of electropositive groups, in comparison with the [1,5]‐fluorine shift, can be attributed to aromaticity stabilizing the transition states, as revealed by significantly negative nucleus‐independent chemical shift (NICS) values. Further studies indicate that charge distribution and frontier molecular orbitals also play some roles in [1,5]‐migration of pyrrolium derivatives. 相似文献
14.
Density functional theory (DFT) based calculations are performed on a series of alkyl nitrites and nitroalkanes representing large‐scale primary, secondary, and tertiary nitro compounds and their radicals resulting from the loss of their skeletal hydrogen atoms. Geometries, vibration frequencies, and thermochemical properties [S°(T) and C°p(T) (10 K ? T ? 5000 K)] are calculated at the B3LYP/6‐31G(d,p) DFT level. ΔfH°298 values are from B3LYP/6‐31G(d,p), B3LYP/6‐31+G(2d,2p), and the composite CBS‐QB3 levels. Potential energy barriers for the internal rotations have been computed at the B3LYP/6‐31G(d,p) level of theory, and the lower barrier contributions are incorporated into entropy and heat capacity data. The standard enthalpies of formation at 298 K are evaluated using isodesmic reaction schemes with several work reactions for each species. Recommended values derived from the most stable conformers of respective nitro‐ and nitrite isomers include ?30.57 and ?28.44 kcal mol?1 for n‐propane‐, ?33.89 and ?32.32 kcal mol?1 for iso‐propane‐, ?42.78 and ?41.36 kcal mol?1 for tert‐butane‐nitro compounds and nitrites, respectively. Entropy and heat capacity values are also reported for the lower homologues: nitromethane, nitroethane, and corresponding nitrites. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 181–199, 2010 相似文献
15.
Preparing Gold(I) for Interactions with Proton Donors: The Elusive [Au]⋅⋅⋅HO Hydrogen Bond
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Ferdinand Groenewald Prof. Jan Dillen Prof. Helgard G. Raubenheimer Prof. Catharine Esterhuysen 《Angewandte Chemie (International ed. in English)》2016,55(5):1694-1698
MP2 and DFT calculations with correlation consistent basis sets indicate that isolated linear anionic dialkylgold(I) complexes form moderately strong (ca. 10 kcal mol?1) Au???H hydrogen bonds with single H2O molecules as donors in the absence of sterically demanding substituents. Relativistic effects are critically important in the attraction. Such bonds are significantly weaker in neutral, strong σ‐donor N‐heterocyclic carbene (NHC) complexes (ca. 5 kcal mol?1). The overall association (>11 kcal mol?1), however, is strengthened by co‐operative, synergistic classical hydrogen bonding when the NHC ligands bear NH units. Further manipulation of the interaction by ligands positioned trans to the carbene, is possible. 相似文献
16.
Multi‐Pathway Consequent Chemoselectivities of CpRuCl(PPh3)2/MeI‐Catalysed Norbornadiene Alkyne Cycloadditions
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Dr. Wei‐Hua Mu Prof. De‐Cai Fang Shu‐Ya Xia Rui‐Jiao Cheng Prof. Gregory A. Chass 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15396-15403
Chemoselectivities of five experimentally realised CpRuCl(PPh3)2/MeI‐catalysed couplings of 7‐azabenzo‐norbornadienes with selected alkynes were successfully resolved from multiple reaction pathway models. Density functional theory calculations showed the following mechanistic succession to be energetically plausible: (1) CpRuI catalyst activation; (2) formation of crucial metallacyclopentene intermediate; (3) cyclobutene product ( P2 ) elimination (ΔGRel(RDS)≈11.9–17.6 kcal mol?1). Alternative formation of dihydrobenzoindole products ( P1 ) by isomerisation to azametalla‐cyclohexene followed by subsequent CpRuI release was much less favourable (ΔGRel(RDS)≈26.5–29.8 kcal mol?1). Emergent stereoselectivities were in close agreement with experimental results for reactions a , b , e . Consequent investigations employing dispersion corrections similarly support the empirical findings of P1 dominating in reactions c and d through P2 → P1 product transformations as being probable (ΔG≈25.3–30.1 kcal mol?1). 相似文献
17.
Erik P. A. Couzijn Dr. Eva Zocher Dr. Andreas Bach Dr. Peter Chen Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5408-5415
Energy‐resolved collision‐induced dissociation experiments using tandem mass spectrometry are reported for an phenylpalladium N‐heterocyclic carbene (NHC) complex. Reductive elimination of an NHC ligand as a phenylimidazolium ion involves a barrier of 30.9(14) kcal mol?1, whereas competitive ligand dissociation requires 47.1(17) kcal mol?1. The resulting three‐coordinate palladium complex readily undergoes reductive C? C coupling to give the phenylimidazolium π complex, for which the binding energy was determined to be 38.9(10) kcal mol?1. Density functional calculations at the M06‐L//BP86/TZP level of theory are in very good agreement with experiment. In combination with RRKM modeling, these results suggest that the rate‐determining step for the direct reductive elimination process switches from the C? C coupling step to the fragmentation of the resulting σ complex at low activation energy. 相似文献
18.
The C-2—N bond of 2-N,N-dimethylaminopyrylium cations has a partial π character due to the conjugation of the nitrogen lone-pair with the ring. The values of ΔG≠, ΔH≠, ΔS≠ parameters related to the corresponding hindered rotation have been determined by 13C NMR total bandshape analysis. This conjugation decreases the electrophilic character of carbon C-4 so that the displacement of the alkoxy group is no longer possible. Such a hindered rotation also exists in 4-N,N-dimethylaminopyrylium cations and the corresponding ΔG≠ parameters have been evaluated. Comparison of these two cationic species shows that hindered rotation around the C—N bond is larger in position 4 than in position 2. Furthermore, the barrier to internal rotation around the C-2? N bond decreases with increasing electron donating power of the substituent at position 4. ΔG≠ values decreases from 19.1 kcal mol?1 (79.9 kJ mol?1) to 12.6 kcal mol?1 (52.7 kJ mol?1) according to the following sequence for the R-4 substituents: -C6H5, -CH3, -OCH3, -N(CH3)2. 相似文献
19.
Dimers of N‐Heterocyclic Carbene Copper,Silver, and Gold Halides: Probing Metallophilic Interactions through Electron Density Based Concepts
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Balazs Pinter Lies Broeckaert Jan Turek Prof. Aleš Růžička Prof. Frank De Proft 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(3):734-744
Homobimetallic metallophilic interactions between copper, silver, and gold‐based [(NHC)MX]‐type complexes (NHC=N‐heterocyclic carbene, i.e, 1,3,4‐trimethyl‐4,5‐dihydro‐1H‐1,2,4‐triazol‐5‐ylidene; X=F, Cl, Br, I) were investigated by means of ab initio interaction energies, Ziegler–Rauk‐type energy‐decomposition analysis, the natural orbital for chemical valence (NOCV) framework, and the noncovalent interaction (NCI) index. It was found that the dimers of these complexes predominantly adopt a head‐to‐tail arrangement with typical M ??? M distance of 3.04–3.64 Å, in good agreement with the experimental X‐ray structure determined for [{(NHC)AuCl}2], which has an Au ??? Au distance of 3.33 Å. The interaction energies between silver‐ and gold‐based monomers are calculated to be about ?25 kcal mol?1, whereas that for the Cu congener is significantly lower (?19.7 kcal mol?1). With the inclusion of thermal and solvent contributions, both of which are destabilizing, by about 15 and 8 kcal mol?1, respectively, an equilibrium process is predicted for the formation of dimer complexes. Energy‐decomposition analysis revealed a dominant electrostatic contribution to the interaction energy, besides significantly stabilizing dispersion and orbital interactions. This electrostatic contribution is rationalized by NHC(δ+) ??? halogen(δ?) interactions between monomers, as demonstrated by electrostatic potentials and derived charges. The dominant NOCV orbital indicates weakening of the π backdonation in the monomers on dimer formation, whereas the second most dominant NOCV represents an electron‐density deformation according to the formation of a very weak M ??? M bond. One of the characteristic signals found in the reduced density gradient versus electron density diagram corresponds to the noncovalent interactions between the metal centers of the monomers in the NCI plots, which is the manifestation of metallophilic interaction. 相似文献
20.
Prakash R. Sultane Guillermo Ahumada Daniel Janssen‐Müller Christopher W. Bielawski 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(45):16466-16471
The synthesis and study of a library of cyclic (aryl)(amido)carbenes (CArAmCs), which represent a class of electrophilic NHCs that feature low calculated singlet‐triplet gaps (ΔEST=19.9 kcal mol?1; B3LYP/def2‐TZVP) and exhibit reactivity profiles expected from triplet carbenes, are described. The electrophilic properties of the CArAmCs were quantified by analyzing their respective selenium adducts, which exhibited the largest downfield 77Se NMR chemical shifts (up to 1645 ppm) measured for any NHC derivative known to date, as well as their Ir carbonyl complexes, from which large Tolman electronic parameter (TEP) values (up to 2064 cm?1) were ascertained. The CArAmCs were found to engage in reactions that are typically observed with triplet carbenes, including C?H insertions, [2+1] cycloadditions with alkenes as well as alkynes, and spontaneous oxidation upon exposure to oxygen. 相似文献