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1.
State-of-the-art ab initio studies demonstrate that the reaction Pd + + CH 3I → PdCH 2I + + H . is endothermic by ca. 20 kcal/mol, which translates into a bond dissociation energy ( BDE) of ca. 83 kcal/mol for the Pd +? CH 2I bond. This figure is in agreement with an experimental bracket of 68 kcal/mol < BDE(Pd +? CH 2I) < 92 kcal/mol. Based on these findings, the previously studied Pd +/CH 3I system was re-investigated, and double-resonance experiments demonstrate that the formation of PdCH 2I + occurs stepwise via PdCH as a reactive intermediate. Further, ion/molecule reactions of PdCH 2I + with unsaturated hydrocarbons are studied, which reveal the formation of carbon–carbon bonds in the gas phase. 相似文献
2.
Details on the reactions of: (1) Pd + + CH 3CHO → PdCO + + CH 4 and (2) Pd + + CH 3CHO → PdH + CH 3CO + in the gas phase were investigated using density functional theory (B3LYP), in conjunction with the LANL2DZ+6‐311+G(d) basis set. Three encounter complexes were located on the potential energy surfaces and the calculations indicated that both the C? C and aldehyde C? H bond activation of acetaldehyde could lead to the dominant demethanation reaction. The charge transfer process for PdH abstraction was caused by an intramolecular PdH rearrangement of the newly found η 1‐aldehyde attached complex. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
3.
Activation of methane by oxidative addition and σ‐bond metathesis has been investigated for (N‐N)M(CH 3) (M = Pd +, Pt +, Rh +, Ir +, Rh, Ir; N‐N = (HN?CH? CH?NH) using different density functional approaches. The pathway of oxidative addition is in general favored, the exceptions being Pd + and Rh +. Oxidative addition is clearly more favorable for the third‐row metal complexes than those of the second row. The third‐row metal complexes also tend to have a lower activation barrier for σ‐bond metathesis than those of the second row. In each case, the oxidative addition is preceded by formation of a sigma complex. The bonding energies of these complexes are significantly stronger for the cationic systems. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
4.
A palladium‐catalyzed selective C? H bond trifluoroethylation of aryl iodides has been explored. The reaction allows for the efficient synthesis of a variety of ortho‐trifluoroethyl‐substituted styrenes. Preliminary mechanistic studies indicate that the reaction might involve a key Pd IV intermediate, which is generated through the rate‐determining oxidative addition of CF 3CH 2I to a palladacycle; the bulky nature of CF 3CH 2I influences the reactivity. Reductive elimination from the Pd IV complex then leads to the formation of the aryl–CH 2CF 3 bond. 相似文献
5.
The Pd/ZrO 2 and Pd/SO 4/ZrO 2 systems were investigated by diffuse-reflectance IR spectroscopy using CO as the probe molecule. For the Pd/ZrO 2 system, the behavior of the metal is characteristic of the weak metal-support interaction. Intense bands attibuted to the bridging CO species indicate the formation of large metal particles in the reduced systems. Modification of the ZrO 2 support with SO 4 2? anions leads to an increase in the metal—support interaction and makes the metal more resistant to reduction. On the surface promoted by SO 4 2? anions, metal particles with a positive charge (Pd + and Pd δ+) were observed. The smaller the size of the metal clusters and the higher degree of oxidation of sulfur, the stronger the influence of acidic protons and surface sulfur compounds on the metal. 相似文献
6.
A palladium‐catalyzed selective C H bond trifluoroethylation of aryl iodides has been explored. The reaction allows for the efficient synthesis of a variety of ortho‐trifluoroethyl‐substituted styrenes. Preliminary mechanistic studies indicate that the reaction might involve a key Pd IV intermediate, which is generated through the rate‐determining oxidative addition of CF 3CH 2I to a palladacycle; the bulky nature of CF 3CH 2I influences the reactivity. Reductive elimination from the Pd IV complex then leads to the formation of the aryl–CH 2CF 3 bond. 相似文献
7.
The interaction of Ph 3PPD(OAc) 22 with molecular H 2 yields a binuclear complex of zero-valent palladium, (Ph 3P) 2Pd 2. This complex interacts reversibly with H 2 in CH 2Cl 2, yielding (Ph 3P) 2Pd 2H 2. In argon atmosphere (Ph 3P) 2Pd 2 reacts with [Ph 3PPd(OAc) 22 to form a binuclear complex of Pd I with a metal—metal bond. These data, as well as the results of kinetic studies of the reactions between [Ph 3PPd(OAc) 22 and H 2, are in agreement with an autocatalytic mechanism for the process, including catalysis of the reduction of Pd II complexes by the Pd 0 compounds. It has been established that the synthesized compound of Pd II, Pd I and Pd 0 with the ratio P/Pd?1, are inactive in the hydrogenation of unsaturated compounds. The catalytically active complex (PPh) 2Pd 5 is formed when palladium acetate reacts with (Ph 3P) 2Pd 2 in the presence of H 2. The same compound is formed when a solution of (Ph 3P) 2Pd 2 is treated with a mixture of H 2 and O 2 (or H 2O 2 in an atmosphere of H 2). (PPh) 2Pd 5 is an effective catalyst for the hydrogenation of olefins, dienes, acetylenes, aldehydes, organic peroxides, quinones, O 2, Schiff bases, and nitro, nitroso, and azo compounds. 相似文献
8.
MP2 and CAS SCF calculations for CO insertion reactions of the type RMCO → M(COR), R = H, CH 3; M = Mn, Pd + are reported. Non-dynamical correlation appears to be quite important, involving essentially the metal-carbon π bond in the Mn(I) systems and the metal-carbon and metal-hydrogen σ bonds in the Pd(II) systems. 相似文献
9.
Gas-phase clustering reactions of CoCp + with H 2 and with CH 4 were investigated using temperature-dependent equilibrium experiments. In both systems, the CoCp + ion was found to form strong interactions with two ligands. The first and second H 2 groups cluster to CoCp + with bond energies of 16.2 and 16.8 kcal/mol, respectively, while the first and second CH 4 groups cluster to CoCp + with bond energies of 24.1 and 12.1 kcal/mol, respectively. These bond energies are in good agreement with those determined by density functional theory (DFT). Molecular geometries for the four clusters determined with DFT are also presented. Weak experimental bond energies of 0.9 kcal/mol for the third H 2 and 2.2 kcal/mol for the third CH 4 clustering to CoCp + suggest these ligands occupy the second solvation shell of the ion. In addition to clustering in the methane system, H 2-elimination from CoCp(CH 4) 2+ was observed. The mechanism for this reaction was investigated by collision-induced dissociation experiments and DFT, which suggest the predominate H 2-elimination product is ( c-C 5H 6)Co +---C 2H 5. Theory indicates that dehydrogenation requires the active participation of the Cp ring in the mechanism. Transfer of H and CH 3 groups to the C 5-ring ligand allows the metal center to avoid the high-energy Co(IV) oxidation state required when it forms two covalent bonds in addition to its interaction with a C 5-ring ligand. 相似文献
10.
A theoretical study on two series of electron‐rich group 8 hydrides is carried out to evaluate involvement of the transition metal in dihydrogen bonding. To this end, the structural and electronic parameters are computed at the DFT/B3PW91 level for hydrogen‐bonded adducts of [(PP 3)MH 2] and [Cp*MH(dppe)] (M=Fe, Ru, Os; PP 3=κ 4‐P(CH 2CH 2PPh 2) 3, dppe= κ 2‐Ph 2PCH 2CH 2PPh 2) with CF 3CH 2OH (TFE) as proton donor. The results are compared with those of adduct [Cp 2NbH 3] ? TFE featuring a “pure” dihydrogen bond, and classical hydrogen bonds in pyridine ? TFE and Me 3N ? TFE. Deviation of the H ??? H? A fragment from linearity is shown to originate from the metal participation in dihydrogen bonding. The latter is confirmed by the electronic parameters obtained by NBO and AIM analysis. Considered together, orbital interaction energies and hydrogen bond ellipticity are salient indicators of this effect and allow the MH ??? HA interaction to be described as a bifurcate hydrogen bond. The impact of the M ??? HA interaction is shown to increase on descending the group, and this explains the experimental trends in mechanisms of proton‐transfer reactions via MH ??? HA intermediates. Strengthening of the M ??? H interaction in the case of electron‐rich 5d metal hydrides leads to direct proton transfer to the metal atom. 相似文献
11.
A novel and facile C? H bond fluorination proceeds under remarkably mild conditions (close to room temperature in most cases). Both aromatic and olefinic C(sp 2)? H bonds with a wide range of electronic properties are selectively fluorinated in the presence of a catalytic amount of simple, cheap, and nontoxic nitrate as the promoter. A Pd II/Pd IV catalytic cycle that is initiated by an in situ generated cationic [Pd(NO 3)] + species was proposed based on preliminary mechanistic studies. 相似文献
12.
The dichloromethane solvates of the isomers tetrakis(μ‐1,3‐benzothiazole‐2‐thiolato)‐κ 4N: S;κ 4S: N‐dipalladium(II)( Pd— Pd), (I), and tetrakis(μ‐1,3‐benzothiazole‐2‐thiolato)‐κ 6N: S;κ 2S: N‐dipalladium(II)( Pd— Pd), (II), both [Pd 2(C 7H 4NS 2) 4]·CH 2Cl 2, have been synthesized in the presence of ( o‐isopropylphenyl)diphenylphosphane and ( o‐methylphenyl)diphenylphosphane. Both isomers form a lantern‐type structure, where isomer (I) displays a regular and symmetric coordination and isomer (II) an asymmetric and distorted structure. In (I), sitting on an centre of inversion, two 1,3‐benzothiazole‐2‐thiolate units are bonded by a Pd—N bond to one Pd atom and by a Pd—S bond to the other Pd atom, and the other two benzothiazolethiolate units are bonded to the same Pd atoms by, respectively, a Pd—S and a Pd—N bond. In (II), three benzothiazolethiolate units are bonded by a Pd—N bond to one Pd atom and by a Pd—S bond to the other Pd atom, and the fourth benzothiazolethiolate unit is bonded to the same Pd atoms by, respectively, a Pd—S bond and a Pd—N bond. 相似文献
13.
Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal–alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca 2+. The role of the metal was evaluated by a study using the metal‐free catalysts: [Ph 2N ?][Me 4N +] and [Ph 3C ?][Me 4N +]. These “naked” amides and carbanions can act as catalysts in the conversion of activated double bonds (C?O and C?N) in the hydroamination of Ar? N?C?O and R? N?C?N? R (R=alkyl) by Ph 2NH. For the intramolecular hydroamination of unactivated C?C bonds in H 2C?CHCH 2CPh 2CH 2NH 2 the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study. 相似文献
15.
Ab initio SCF and CI calculations on the cationic and neutral complexes of formaldehyde and lithium are reported. For the cationic complex CH 2O/Li +, the stabilization energy of 41.7 kcal/mol obtained from the SCF calculation increases to 51.6 kcal/mol if a configuration interaction is introduced. For the neutral complex CH 2O ?/Li +, the C 2v-conformer of the 2A 1-state with the equilibrium bond distances of d(C? O) = 1.23 Å and d (O? Li) = 1.90 Å is calculated to be more stable than the 2B 1-state with d (C? O) = 1.34 Å, and d (O? Li) = 1.65 Å. Charge transfer and polarization effects upon complex formation are discussed. 相似文献
16.
The complexes of Li+, Na+, K+, Be2+, Mg2+, and Ca2+ metal cations with [N3P3R4O(CH2CH2O)4] (R?=?H(1), NMe2(2), NC(NMe2)2(3)) PNP-lariat ethers were systematically studied in the gas phase by using density functional theory (DFT) B3LYP-D3/6-311+G(3df,2p)//B3LYP/6-31+G(d,p) method. The gas phase cation affinities were calculated to span the wide range between 64.2 and 496.1 kcal mol?1 in order K+?<?Na+?<?Li+?<?Ca2+?<?Mg2+?<?Be2+. The structural and electronic properties of 1–3 and their complexes were investigated and effects of electron-donor substituents were analyzed. The electron-donor substituents were found to promote the cation affinity. Sidearm coordinative interaction with the crown ether-complexed metal ion has been noticed. The nature of the metal–ligand interactions was investigated using Bader’s Quantum theory of atoms in molecule. It has been found that the Be2+–N bonds are partly covalent in nature while other coordinate bonds are of the electrostatic nature. The electron density at the bond critical points was found to be consistent with cation affinity. Natural bond orbital analysis was performed on the optimized geometries. The results showed that the stabilization interaction energies are caused by the donation of O/N lone pair electrons to the LP* orbitals of the metal cations. The amount of charge transfer follows the cation affinity order. The largest charge transfer and associated second-order perturbation stabilization energy were observed for Be2+ complexes. 相似文献
17.
While there is a growing interest in harnessing synergistic effects of more than one metal in catalysis, relatively little is known beyond bimetallic systems. This report describes the straightforward access to an air‐stable Pd trimer and presents unambiguous reactivity data of its privileged capability to differentiate C?I over C?Br bonds in C?C bond formations (arylation and alkylation) of polyhalogenated arenes, which typical Pd 0 and Pd I‐Pd I catalysts fail to deliver. Experimental and computational reactivity data, including the first location of a transition state for bond activation by the trimer, are presented, supporting direct trimer reactivity to be feasible. 相似文献
18.
A comparative study of molecular balances by NMR spectroscopy indicates that noncovalent functional‐group interactions with an arene dominate over those with an alkene, and that a π‐facial intramolecular hydrogen bond from a hydroxy group to an arene is favored by approximately 1.2 kJ mol ?1. The strongest interaction observed in this study was with the cyano group. Analysis of the series of groups CH 2CH 3, CH?CH 2, C?CH, and C?N shows a correlation between conformational free‐energy differences and the calculated charge on the C α atom of these substituents, which is indicative of the electrostatic nature of their π interactions. Changes in the free‐energy differences of conformers show a linear dependence on the solvent hydrogen bond acceptor parameter β. 相似文献
19.
We designed M 1???C 6H 5X???HM 2 (M 1=Li +, Na +; X=Cl, Br; M 2=Li, Na, BeH, MgH) complexes to enhance halogen–hydride halogen bonding with a cation–π interaction. The interaction strength has been estimated mainly in terms of the binding distance and the interaction energy. The results show that halogen–hydride halogen bonding is strengthened greatly by a cation–π interaction. The interaction energy in the triads is two to six times as much as that in the dyads. The largest interaction energy is ?8.31 kcal mol ?1 for the halogen bond in the Li +???C 6H 5Br???HNa complex. The nature of the cation, the halogen donor, and the metal hydride influence the nature of the halogen bond. The enhancement effect of Li + on the halogen bond is larger than that of Na +. The halogen bond in the Cl donor has a greater enhancement than that in the Br one. The metal hydride imposes its effect in the order HBeH<HMgH<HNa<HLi for the Cl complex and HBeH<HMgH<HLi<HNa for the Br complex. The large cooperative energy indicates that there is a strong interplay between the halogen–hydride halogen bonding and the cation–π interaction. Natural bond orbital and energy decomposition analyses indicate that the electrostatic interaction plays a dominate role in enhancing halogen bonding by a cation–π interaction. 相似文献
20.
The C?D bond stretching vibrations of deuterated dimethyl sulfoxide ([D 6]DMSO) and the C 2?H bond stretching vibrations of 1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione (hfac) ligand in anion are chosen as probes to elucidate the solvent–solute interaction between chelate‐based ionic liquids (ILs) and DMSO by vibrational spectroscopic studies. The indirect effect from the interaction of the adjacent S=O functional group of DMSO with the cation [C 10mim] + and anion [Mn(hfac) 3] ? of the ILs leads to the blue‐shift of the C?D stretching vibrations of DMSO. The C 2?H bond stretching vibrations in hfac ligand is closely related to the ionic hydrogen bond strength between the cation and anion of chelate‐based ILs. EPR studies reveal that the crystal field of the central metal is kept when the chelate‐based ILs are in different microstructure environment in the solution. 相似文献
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