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1.
The essential participation of agostic interactions in C−H bond activation, cyclometallation and other catalytic processes has been widely observed. To quantitatively evaluate the Mo−H−C agostic interaction in the Mo β/γ- agostomers [CpMo(CO)2(PiPr3)]+ ( Mo , 1 and Mo , 2 ) and the Mn−H−C agostic interaction in the Mn α/ϵ-agostomers [(C6H9]Mo(CO)3] ( Mn , 1 and Mn , 2 ), the comprehensive density functional theory (DFT) theoretical investigations were performed. Results indicated that the Mo β-agostomer 1 is only favorable by 0.5 kcal mol−1 than Mo γ-agostomer 2 , and the Gibbs barrier for their interconversion was 9.1 kcal mol−1. A slightly higher Gibbs barrier of 12.7 kcal mol−1 for the isomerization between the Mn α/ϵ-agostomers was also obtained. The relatively strong agostic interactions in Mo β-agostomer 1 and Mn α-agostomer 1 were further verified by the AIM (Atoms-In-Molecules) analyses and the NAdOs (natural adaptive orbitals) analyses. The findings on the agostic interaction presented in this study are believed to benefit the understandings of the agostic interaction involved catalytic processes and to promote the development of new organometallic complexes.  相似文献   

2.
The intramolecular “inverse” frustrated Lewis pairs (FLPs) of general formula 1-BR2-2-[(Me2N)2C=N]-C6H4 ( 3 – 6 ) [BR2=BMes2 ( 3 ), BC12H8, ( 4 ), BBN ( 5 ), BBNO ( 6 )] were synthesized and structurally characterized by multinuclear NMR spectroscopy and X-ray analysis. These novel types of pre-organized FLPs, featuring strongly basic guanidino units rigidly linked to weakly Lewis acidic boryl moieties via an ortho-phenylene linker, are capable of activating H−H, C−H, N−H, O−H, Si−H, B−H and C=O bonds. 4 and 5 deprotonated terminal alkynes and acetylene to form the zwitterionic borates 1-(RC≡C-BR2)-2-[(Me2N)2C=NH]-C6H4 (R=Ph, H) and reacted with ammonia, BnNH2 and pyrrolidine, to generate the FLP adducts 1-(R2HN→BR2)-2-[(Me2N)2C=NH]-C6H4, where the N-H functionality is activated by intramolecular H-bond interactions. In addition, 5 was found to rapidly add across the double bond of H2CO, PhCHO and PhNCO to form cyclic zwitterionic guanidinium borates in excellent yields. Likewise, 5 is capable of cleaving H2, HBPin and PhSiH3 to form various amino boranes. Collectively, the results demonstrate that these new types of intramolecular FLPs featuring weakly Lewis acidic boryl and strongly basic guanidino moieties are as potent as conventional intramolecular FLPs with strongly Lewis acidic units in activating small molecules.  相似文献   

3.
Using a pincer platform based on a bridgehead NHC donor with functional side arms, the combined effect of increased flexibility in six-membered pyrimidine-type heterocycles compared to the more often studied five-membered imidazole, and rigidity of phosphane side arms was examined. The unique features observed include: 1) the reaction of the azolium Csp2−H bond with [Ni(cod)2] affording a carbanionic ligand in [NiCl(PCsp3HP)] ( 8 ) rather than a carbene; 2) its transformation into the NHC, hydrido complex [NiH(PCNHCP)]PF6 ( 9 ) upon halide abstraction; 3) ethylene insertion into the Ni−H bond of the latter and ethyl migration to the N−C−N carbon atom of the heterocycle in [Ni(PCEtP)]PF6 ( 10 ); and 4) an unprecedented C−P bond activation transforming the P−CNHC−P pincer ligand of 8 in a C−CNHC−P pincer and a terminal phosphanido ligand in [Ni(PPh2)(CCNHCP)] ( 15 ). The data are supported by nine crystal structure determinations and theoretical calculations provided insights into the mechanisms of these transformations, which are relevant to stoichiometric and catalytic steps of general interest.  相似文献   

4.
We report the first examples of metal-promoted double geminal activation of C(sp3)−H bonds of the N−CH2−N moiety in an imidazole-type heterocycle, leading to nickel and palladium N-heterocyclic carbene complexes under mild conditions. Reaction of the new electron-rich diphosphine 1,3-bis((di-tert-butylphosphaneyl)methyl)-2,3-dihydro-1H-benzo[d]imidazole ( 1 ) with [PdCl2(cod)] occurred in a stepwise fashion, first by single C−H bond activation yielding the alkyl pincer complex [PdCl(PC HP)] ( 3 ) with two trans phosphane donors and a covalent Pd−C bond. Activation of the C−H bond of the resulting α-methine C H−M group occurred subsequently when 3 was treated with HCl to yield the NHC pincer complex [PdCl(PCNHCP)]Cl ( 2 ). Treatment of 1 with [NiBr2(dme)] also afforded a NHC pincer complex, [NiBr(PCNHCP)]Br ( 6 ), but the reactions leading to the double geminal C−H bond activation of the N−CH2−N group were too fast to allow identification or isolation of an intermediate analogous to 3 . The determination of six crystal structures, the isolation of reaction intermediates and DFT calculations provided the basis for suggesting the mechanism of the stepwise transformation of a N−CH2−N moiety in the N−CNHC−N unit of NHC pincer complexes and explain the key differences observed between the Pd and Ni chemistries.  相似文献   

5.
Iridabicycles [Ir{κ3-N,C,O-(pyC(H)=C(C(O)Me)2}(Cl)(L−L)](L−L=cod (cod=1,5-cyclooctadiene), 1 a ; bipy (bipy=2,2’-bipyridine), 1 b ) have been obtained by oxidative coordination of 3-(pyridine-2-yl-methylene)pentane-2,4-dione L1 , to the complexes [{Ir(μ-Cl)(cod)}2] and [{Ir(μ-Cl)(coe)2}2] (coe=cis-cyclooctene), the latter in the presence of bipy. Remarkably, cleavage of the C3−C(O)Me bond of L1 has instead been achieved in the reaction with [Ir(Cl)(dmb)2] (dmb=2,3-dimethylbutadiene), yielding a compound formulated as [Ir{κ2-N,C-(pyC(H)C(C(O)Me))}(CO)(μ-Cl)(Me)]2, 2 . Treatment of dimer 2 with DMSO or PMe3 produced the complexes[Ir{κ2-N,C-(pyC(H)C(C(O)Me)}(CO)Cl(Me)L] (L=DMSO, 3 a ; PMe3, 3 b ). Plausible mechanisms for the reactions leading to complexes 1 and 2 are proposed by means of DFT calculations.  相似文献   

6.
Quantum chemistry calculations predict that besides the reported single metal anion Pt, Ni can also mediate the co-conversion of CO2 and CH4 to form [CH3−M(CO2)−H] complex, followed by transformation to C−C coupling product [H3CCOO−M−H] ( A ), hydrogenation products [H3C−M−OCOH] ( B ) and [H3C−M−COOH]. For Pd, a fourth product channel leading to PdCO2…CH4 becomes more competitive. For Ni, the feed order must be CO2 first, as the weaker donor-acceptor interaction between Ni and CH4 increases the C−H activation barrier, which is reduced by [Ni−CO2]. For Ni/Pt, the highly exothermic products A and B are similarly stable with submerged barrier that favors B . The smaller barrier difference between A and B for Ni suggests the C−C coupling product is more competitive in the presence of Ni than Pt. The charge redistribution from M is the driving force for product B channel. This study adds our understanding of single atomic anions to activate CH4 and CO2 simultaneously.  相似文献   

7.
The saturated trihydride IrH33-P,O,P-[xant(PiPr2)2]} ( 1 ; xant(PiPr2)2=9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) activates the B−H bond of two molecules of pinacolborane (HBpin) to give H2, the hydride-boryl derivatives IrH2(Bpin){κ3-P,O,P-[xant(PiPr2)2]} ( 2 ) and IrH(Bpin)23-P,O,P-[xant(PiPr2)2]} ( 3 ) in a sequential manner. Complex 3 activates a C−H bond of two molecules of benzene to form PhBpin and regenerates 2 and 1 , also in a sequential manner. Thus, complexes 1 , 2 , and 3 define two cycles for the catalytic direct C−H borylation of arenes with HBpin, which have dihydride 2 as a common intermediate. C−H bond activation of the arenes is the rate-determining step of both cycles, as the C−H oxidative addition to 3 is faster than to 2 . The results from a kinetic study of the reactions of 1 and 2 with HBpin support a cooperative function of the hydride ligands in the B−H bond activation. The addition of the boron atom of the borane to a hydride facilitates the coordination of the B−H bond through the formation of κ1- and κ2-dihydrideborate intermediates.  相似文献   

8.
Carbonylation of ethanol with CO2 as carbonyl source into value-added esters is of considerable significance and interest, while remains of great challenge due to the harsh conditions for activation of inert CO2 in that the harsh conditions result in undesired activation of α-C−H and even cleavage of C−C bond in ethanol to deteriorate the specific activation of O−H bond. Herein, we propose a photo-thermal cooperative strategy for carbonylation of ethanol with CO2, in which CO2 is activated to reactive CO via photo-catalysis with the assistance of *H from thermally-catalyzed dissociation of alcoholic O−H bond. To achieve this proposal, an interfacial site and oxygen vacancy both abundant SrTiCuO3-x supported Cu2O (Cu2O-SrTiCuO3-x) has been designed. A production of up to 320 μmol g−1 h−1 for ethyl formate with a selectivity of 85.6 % to targeted alcoholic O−H activation has been afforded in photo-thermal assisted gas-solid process under 3.29 W cm−1 of UV/Vis light irradiation (144 °C) and 0.2 MPa CO2. In the photo-driven activation of CO2 and following carbonylation, CO2 activation energy decreases to 12.6 kJ mol−1, and the cleavage of alcoholic α-C−H bond has been suppressed.  相似文献   

9.
The aluminum(I) compound NacNacAl (NacNac=[ArNC(Me)CHC(Me)NAr], Ar=2,6-iPr2C6H3, 1 ) shows diverse and substrate-controlled reactivity in reactions with N-heterocycles. 4-Dimethylaminopyridine (DMAP), a basic substrate in which the 4-position is blocked, induces rearrangement of NacNacAl by shifting a hydrogen atom from the methyl group of the NacNac backbone to the aluminum center. In contrast, C−H activation of the methyl group of 4-picoline takes place to produce a species with a reactive terminal methylene. Reaction of 1 with 3,5-lutidine results in the first example of an uncatalyzed, room-temperature cleavage of an sp2 C−H bond (in the 4-position) by an AlI species. Another reactivity mode was observed for quinoline, which undergoes 2,2′-coupling. Finally, the reaction of 1 with phthalazine produces the product of N−N bond cleavage.  相似文献   

10.
We report a porous three-dimensional anionic tetrazolium based CuI−MOF 1 , which is capable of cleaving the N−H bond of ammonia and primary amine, as well as the O−H bond of H2O along with spontaneous H2 evolution. In the gas-solid phase reaction of 1 with ammonia and water vapor, CuI−MOF 1 was gradually oxidized to NH2−CuII−MOF and OH−CuII−MOF, through single-crystal-to-single-crystal (SCSC) structural transformations, which was confirmed by XPS, PXRD and X-ray single-crystal diffraction. Density functional theory (DFT) demonstrated that CuI−MOF could lower N−H bond dissociation free energy of ammonia through coordination-induced bond weakening and promote H2 evolution by the reduction potential of 1 . To our knowledge, this is the first example of MOFs that activate ammonia and amine in gas-solid manner.  相似文献   

11.
Herein, we present the formation of transient radical ion pairs (RIPs) by single-electron transfer (SET) in phosphine−quinone systems and explore their potential for the activation of C−H bonds. PMes3 (Mes=2,4,6-Me3C6H2) reacts with DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) with formation of the P−O bonded zwitterionic adduct Mes3P−DDQ ( 1 ), while the reaction with the sterically more crowded PTip3 (Tip=2,4,6-iPr3C6H2) afforded C−H bond activation product Tip2P(H)(2-[CMe2(DDQ)]-4,6-iPr2-C6H2) ( 2 ). UV/Vis and EPR spectroscopic studies showed that the latter reaction proceeds via initial SET, forming RIP [PTip3]⋅+[DDQ]⋅, and subsequent homolytic C−H bond activation, which was supported by DFT calculations. The isolation of analogous products, Tip2P(H)(2-[CMe2{TCQ−B(C6F5)3}]-4,6-iPr2-C6H2) ( 4 , TCQ=tetrachloro-1,4-benzoquinone) and Tip2P(H)(2-[CMe2{oQtBu−B(C6F5)3}]-4,6-iPr2-C6H2) ( 8 , oQtBu=3,5-di-tert-butyl-1,2-benzoquinone), from reactions of PTip3 with Lewis-acid activated quinones, TCQ−B(C6F5)3 and oQtBu−B(C6F5)3, respectively, further supports the proposed radical mechanism. As such, this study presents key mechanistic insights into the homolytic C−H bond activation by the synergistic action of radical ion pairs.  相似文献   

12.
The aerogen bond is formed in complexes of HCN−XeF2O and C2H4−XeF2O. The lone pair on the N atom of HCN is a better electron donor in the aerogen bond than the π electron on the C=C bond of C2H4. The coinage substitution strengthens the aerogen bond in MCN−XeF2O (M=Cu, Ag, and Au) and its enhancing effect becomes larger in the Au<Cu<Ag pattern. The aerogen bond is further enhanced by the regium bond in C2H2−MCN−XeF2O and C2H4−MCN−XeF2O, but is weakened by the regium bond in MCN−C2H4−XeF2O and C2(CN)4−MCN−XeF2O. Simultaneously, the regium bond is also strengthened or weakened in these triads. The synergistic and diminutive effects between regium and aerogen bonds have been explained by means of charge transfer and electrostatic potentials.  相似文献   

13.
As rising star materials, single-atom and dual-atom catalysts have been widely reported in the electro-catalysis area. To answer the key question: single-atom and dual-atom catalysts, which is better for electrocatalytic urea synthesis? we design two types of catalysts via a vacancy-anchorage strategy: single-atom Pd1−TiO2 and dual-atom Pd1Cu1−TiO2 nanosheets. An ultrahigh urea activity of 166.67 molurea molPd−1 h1 with the corresponding 22.54 % Faradaic efficiency at −0.5 V vs. reversible hydrogen electrode (RHE) is achieved over Pd1Cu1−TiO2, which is much higher than that of Pd1−TiO2. Various characterization including an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and theoretical calculations demonstrate that dual-atom Pd1Cu1 site in Pd1Cu1−TiO2 is more favorable for producing urea, which experiences a C−N coupling pathway with a lower energy barrier compared with Pd1 in Pd1−TiO2.  相似文献   

14.
We report a challenging copper-catalyzed Cformyl−H arylation of salicylaldehydes with arylboronic acids that involves unique salicylaldehydic copper species that differ from reported salicylaldehydic rhodacycles and palladacycles. This protocol has high chemoselectivity for the Cformyl−H bond compared to the phenolic O−H bond involving copper catalysis under high reaction temperatures. This approach is compatible with a wide range of salicylaldehyde and arylboronic acid substrates, including estrone and carbazole derivatives, which leads to the corresponding arylation products. Mechanistic studies show that the 2-hydroxy group of the salicylaldehyde substrate triggers the formation of salicylaldehydic copper complexes through a CuI/CuII/CuIII catalytic cycle.  相似文献   

15.
Saddle-shaped hemes have been discovered in the structures of most peroxidases. How such a macrocycle deformation affects the reaction of FeIII hemes with hydrogen peroxide (H2O2) to form high-valent Fe-oxo species remains uncertain. Through examination of the ESI-MS spectra, absorption changes and 1H NMR chemical shifts, we investigated the reactions of two FeIII porphyrins with different degrees of saddling deformation, namely FeIII(OETPP)ClO4 ( 1OE ) and FeIII(OMTPP)ClO4 ( 1OM ), with tert-butyl hydroperoxide (tBuOOH) in CH2Cl2 at −40 °C, which quickly resulted in O−O bond homolysis from a highly unstable FeIII-alkylperoxo intermediate, FeIII-O(H)OR ( 2 ) into FeIV-oxo porphyrins ( 3 ). Insight into the reaction mechanism was obtained from [tBuOOH]-dependent kinetics. At −40 °C, the reaction of 1OE with tBuOOH exhibited an equilibrium constant (Ka=362.3 M−1) and rate constant (k=1.87×10−2 sM−>1) for the homolytic cleavage of the 2 O−O bond that were 2.1 and 1.4 times higher, respectively, than those exhibited by 1OM (Ka=171.8 M−1 and k=1.36×10−2 s−1). DFT calculations indicated that an FeIII porphyrin with greater saddling deformation can achieve a higher HOMO ([Fe(d ,d )-porphyrin(a2u)]) to strengthen the orbital interaction with the LUMO (O−O bond σ*) to facilitate O−O cleavage.  相似文献   

16.
Late transition metal-bonded atomic oxygen radicals (LTM−O⋅) have been frequently proposed as important active sites to selectively activate and transform inert alkane molecules. However, it is extremely challenging to characterize the LTM−O⋅-mediated elementary reactions for clarifying the underlying mechanisms limited by the low activity of LTM−O⋅ radicals that is inaccessible by the traditional experimental methods. Herein, benefiting from our newly-designed ship-lock type reactor, the reactivity of iron-vanadium bimetallic oxide cluster anions FeV3O10 and FeV5O15 featuring with Fe−O⋅ radicals to abstract a hydrogen atom from C2−C4 alkanes has been experimentally characterized at 298 K, and the rate constants are determined in the orders of magnitude of 10−14 to 10−16 cm3 molecule−1 s−1, which are four orders of magnitude slower than the values of counterpart ScV3O10 and ScV5O15 clusters bearing Sc−O⋅ radicals. Theoretical results reveal that the rearrangements of the electronic and geometric structures during the reaction process function to modulate the activity of Fe−O⋅. This study not only quantitatively characterizes the elementary reactions of LTM−O⋅ radicals with alkanes, but also provides new insights into structure-activity relationship of M−O⋅ radicals.  相似文献   

17.
Thermodynamic knowledge of the metal–ligand (M−L) σ-bond strength is crucial to understanding metal-mediated transformations. Here, we developed a method for determining the Pd−X (X=OR and NHAr) bond heterolysis energies (ΔGhet(Pd−X)) in DMSO taking [(tmeda)PdArX] (tmeda=N,N,N′,N′-tetramethylethylenediamine) as the model complexes. The ΔGhet(Pd−X) scales span a range of 2.6–9.0 kcal mol−1 for ΔGhet(Pd−O) values and of 14.5–19.5 kcal mol−1 for ΔGhet(Pd−N) values, respectively, implying a facile heterolytic detachment of the Pd ligands. Structure-reactivity analyses of a modeling Pd-mediated X−H bond activation reveal that the M−X bond metathesis is dominated by differences of the X−H and Pd−X bond strengths, the former being more influential. The ΔGhet(Pd−X) and pKa(X−H) parameters enable regulation of reaction thermodynamics and chemoselectivity and diagnosing the probability of aniline activation with Pd−X complexes.  相似文献   

18.
The copper-dependent formylglycine-generating enzyme (FGE) catalyzes the oxygen-dependent oxidation of specific peptidyl-cysteine residues to formylglycine. Our QM/MM calculations provide a very likely mechanism for this transformation. The reaction starts with dioxygen binding to the tris-thiolate CuI center to form a triplet CuII-superoxide complex. The rate-determining hydrogen atom abstraction involves a triplet-singlet crossing to form a CuII−OOH species that couples with the substrate radical, leading to a CuI-alkylperoxo intermediate. This is accompanied by proton transfer from the hydroperoxide to the S atom of the substrate via a nearby water molecule. The subsequent O−O bond cleavage is coupled with the C−S bond breaking that generates the formylglycine and a CuII-oxyl complex. Moreover, our results suggest that the aldehyde oxygen of the final product originates from O2, which will be useful for future experimental work.  相似文献   

19.
Disclosed herein is a RhCl3-catalyzed peri-selective C−H/C−H oxidative homo-coupling of 1-substituted naphthalenes, which provides a highly efficient and streamlined approach to chalcogen-embedded anthanthrenes from readily available starting materials. Introducing O, S, and Se into the anthanthrene skeleton leads to gradually increased π–π stacking distances but significantly enhanced π–π overlaps with the growth of the hetero-atom radius. Moderate π–π distance, overlap area, and intermolecular S−S interactions endow S-embedded anthanthrene ( PTT ) with excellent 2D charge-transport properties. Moreover, the transformation of p-type to n-type S-embedded anthanthrenes is realized for the first time via the S-atom oxidation from PTT to PTT-O4 . In organic field-effect transistor devices, PTT derivatives exhibit hole transport with mobilities up to 1.1 cm2 V−1 s−1, while PTT-O4 shows electron transport with a mobility of 0.022 cm2 V−1 s−1.  相似文献   

20.
Represented herein is the first example of N-radical generation direct from N−H bond activation under mild and redox-neutral conditions. The in situ generated N-radical intercepts a reduced heteroarylnitrile/aryl halide for C−N bond formation under visible-light irradiation of quantum dots (QDs). A series of aryl and alkylamines with heteroarylnitriles/aryl halides exhibit high efficiency, site-selectivity and good functional-group tolerance. Moreover, consecutive C−C and C−N bond formation using benzylamines as substrates is also achieved, producing N-aryl-1,2-diamines with H2 evolution. The redox-neutral conditions, broad substrate scope, and efficiency of N-radical formation are advantageous for organic synthesis.  相似文献   

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