A comparative theoretical study on CO insertion into Rh–C bond

A DFT study on CO insertion into Rh–C(alkylethyl, ethenyl, 2-propenyl, trans-propenyl, cis-propenyl, and allyl) bonds were carried out comprehensively. All structures were optimized completely and the mechanism of the CO insertion was discussed in detail. The present results indicated that except for the CO insertion into Rh–C(allyl), other CO insertions were feasible from the thermodynamics point of view. The CO insertion into Rh–C(cis-propenyl) was the easiest process with 24.42 kJ/mol of the lowest activation free energy and the most difficult was the CO insertion into Rh–C(allyl). Also, entropy played a critical role in the CO insertion except for the CO insertion into Rh–C(ethenyl).     

CO2 insertion into metal-carbon bonds: a computational study of Rh(I) pincer complexes

Catalytic carboxylation reactions that use CO(2) as a C1 building block are still among the 'dream reactions' of molecular catalysis. To obtain a deeper insight into the factors that control the fundamental steps of potential catalytic cycles, we performed a detailed computational study of the insertion reaction of CO(2) into rhodium-alkyl bonds. The minima and transition-state geometries for 38 pincer-type complexes were characterized and the according energies for the C-C bond-forming step were determined. The electronic properties of the Rh-alkyl bond were found to be more important for the magnitude of the activation barrier than the interaction between rhodium and CO(2). The charge of the alkyl-chain carbon atom, as well as agostic and orbital interactions with the rhodium, exhibit the most pronounced influence on the energy of the transition states for the CO(2) insertion reaction. By varying the backbone and the donor groups of the pincer ligand those properties can be tuned over a very broad range. Thus, it is possible to match the electronic and steric properties with the fundamental requirements of the CO(2) insertion into rhodium-alkyl bonds of the ligand framework.     

Rh（Ⅱ） carbene S-H insertion into H2S via the stepwise mechanism

The mechanism of Rh(Ⅱ)carbene S-H insertion into H_2S in gas phase has been studied by B3LYP functional.Calculation results showed that the Rh(Ⅱ)carbene S-H insertion into H_2S took only stepwise channels and no concerted channels had been located, which was different from the Rh(Ⅱ)carbene C-H and O-H insertions.     

Reversible heterolysis of H2 mediated by an M-S(thiolate) bond (M = Ir, Rh): a mechanistic implication for [NiFe] hydrogenase

Facile H2 heterolysis was found to be mediated by coordinatively unsaturated Cp*Ir and Cp*Rh thiolate complexes. The reaction of iridium complex is reversible, and the formation of an intermediary Ir-H/thiol complex was detected. The reversible conversion between thiolate complex+H2 and hydride complex+thiol provides an intriguing functional model of [NiFe] hydrogenase.     

CO在Pt(111)和Pt-M(111)(M=Ni,Mg)表面吸附的理论研究

采用密度泛函理论与周期性平板模型相结合的方法,对CO在Pt(111)表面top,fcc,hcp和bridge 4个吸附位和Pt-M(111)(M=Ni,Mg)表面h-top,M-top,Pt(M)Pt-bridge,Pt(M)M-bridge,Pt(Pt)M-bridge,M(Pt)M-bridge,Pt1M2-hcp...     

Experimental and theoretical study of intramolecular exchange in Ir2Rh2(CO)12 and Ir4(CO)11(micro-SO2)

As observed by variable-temperature and -pressure 13C NMR, intramolecular carbonyl scrambling in Ir2Rh2(CO)12 and Ir4(CO)11(micro-SO2) proceeds via a 'change of basal face' mechanism. In both cases the site exchange process has a positive activation volume suggesting that the transition states contain longer M-M distances compared to ground states of Cs symmetry. Transition state structures have been located by density functional calculations including relativistic effects. These structures contain a new symmetry plane which interchanges the indistinguishable starting and final geometries. Both transition state structures contain one significantly elongated M-M distance, bearing the bridging ligand unaffected by the site exchange. Differences in molecular volumes of ground and transition state geometries as calculated from Connolly surfaces and electron densities confirm the volume expansion in both cases. The sign of the activation volume is therefore a good criterion for distinguishing between the two main site exchange processes occurring in tetrahedral d9 carbonyl clusters, i.e. the 'change of basal face' process and the 'merry-go-round' process, as the latter presents a negative activation volume.     

Mechanism of CO exchange on cis-[M(CO)2X2]- complexes (M=Rh,Ir;X=Cl, Br, or I)

The CO exchange on cis-[M(CO)2X2]- with M = Ir (X = Cl, la; X = Br, 1b; X = I, 1c) and M = Rh (X = Cl, 2a; X = Br, 2b; X = I, 2c) was studied in dichloromethane. The exchange reaction [cis-[M(CO)2X2]- + 2*CO is in equilibrium cis-[M(*CO)2X2]- + 2CO (exchange rate constant: kobs)] was followed as a function of temperature and carbon monoxide concentration (up to 6 MPa) using homemade high gas pressure NMR sapphire tubes. The reaction is first order for both CO and cis-[M(CO)2X2]- concentrations. The second-order rate constant, k2(298) (=kobs)[CO]), the enthalpy, deltaH*, and the entropy of activation, deltaS*, obtained for the six complexes are respectively as follows: la, (1.08 +/- 0.01) x 10(3) L mol(-1) s(-1), 15.37 +/- 0.3 kJ mol(-1), -135.3 +/- 1 J mol(-1) K(-1); 1b, (12.7 +/- 0.2) x 10(3) L mol(-1) s(-1), 13.26 +/- 0.5 kJ mol(-1), -121.9 +/- 2 J mol(-1) K(-1); 1c, (98.9 +/- 1.4) x 10(3) L mol(-1) s(-1), 12.50 +/- 0.6 kJ mol(-1), -107.4 +/- 2 J mol(-1) K(-1); 2a, (1.62 +/- 0.02) x 10(3) L mol(-1) s(-1), 17.47 +/- 0.4 kJ mol(-1), -124.9 +/- 1 J mol(-1) K(-1); 2b, (24.8 +/- 0.2) x 10(3) L mol(-1) s(-1), 11.35 +/- 0.4 kJ mol(-1), -122.7 +/- 1 J mol(-1) K(-1); 2c, (850 +/- 120) x 10(3) L mol(-1), s(-1), 9.87 +/- 0.8 kJ mol(-1), -98.3 +/- 4 J mol(-1) K(-1). For complexes la and 2a, the volumes of activation were measured and are -20.9 +/- 1.2 cm3 mol(-1) (332.0 K) and -17.2 +/- 1.0 cm3 mol(-1) (330.8 K), respectively. The second-order kinetics and the large negative values of the entropies and volumes of activation point to a limiting associative, A, exchange mechanism. The reactivity of CO exchange follows the increasing trans effect of the halogens (Cl < Br < I), and this is observed on both metal centers. For the same halogen, the rhodium complex is more reactive than the iridium complex. This reactivity difference between rhodium and iridium is less marked for chloride (1.5: 1) than for iodide (8.6:1) at 298 K.     

Theoretical study on structures and vibrational spectra of M+(H2O)Ar (M = Cu,Ag, Au)

A theoretical study on the structures and vibrational spectra of M⁺(H₂O)Ar_0‐1 (M = Cu, Ag, Au) complexes was performed using ab initio method. Geometrical structures, binding energies (BEs), OH stretching vibrational frequencies, and infrared (IR) absorption intensities are investigated in detail for various isomers with Ar atom bound to different binding sites of M⁺(H₂O). CCSD(T) calculations predict that BEs are 14.5, 7.5, and 14.4 kcal/mol for Ar atom bound to the noble metal ion in M⁺(H₂O)Ar (M = Cu, Ag, Au) complexes, respectively, and the corresponding values have been computed to be 1.5, 1.3, and 2.1 kcal/mol when Ar atom attaches to a H atom of water molecule. The former structure is predicted to be more stable than the latter structure. Moreover, when compared with the M⁺(H₂O) species, tagging Ar atom to metal cation yields a minor perturbation on the IR spectra, whereas binding Ar atom to an OH site leads to a large redshift in OH stretching vibrations. The relationships between isomers and vibrational spectra are discussed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Bidentate amines as bridges between M(CO)2Cl (M = Rh OR Ir) units

The preparation and characterization by elemental analysis, electronic and infrared spectroscopy are reported for the monomeric complexes cis-(amine)-M(CO)₂Cl (M = Ir or Rh, amine = 1,8-naphthyridine or pyridazine; M = Ir, amine = o-phenylenediamine) and the binuclear species (1,8-naphthyridine)Rh₂(CO)₄Cl₂, (1,8-naphthyridine)IrRh(CO)₄Cl₂, (pyrazine)Rh₂(CO)₄Cl₂ and (1,3-di-4-pyridylpropane)Rh₂(CO)₄Cl₂.     

[Ir(COD)(diphos)Cl配合物活化sp^3 C-H键及其促进CO、CO2插入Ir-C键反应性能的研究

本文利用[Ir(COD)(μ-Cl)]2与双膦螯合配位体之间的反应合成了三个新的配合物[Ir(COD)(diphos)]Cl(diphos=dmpe、depe、dppe),用IR、NMR、电导和元素分析测定了结构.以CH3CN为反应底物分别考察了它们活化sp^3C-H键的能力及其反应规律.在此基础上进一步研究了使CO、CO2插入生成的Ir-CH2CN键的可能性.结果表明:在温和条件下进行这一插入反应是可能的,并用光谱方法证实有相应的含羰基、羧基的金属配合物的生成.     

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-). Theoretical evidence for a competitive charge transfer mechanism

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-) complexes have been investigated using the B3LYP and the symmetry-adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) theoretical methods. All the dicarbonyl complexes have singlet ground electronic states with large singlet-triplet separations. Thermal dissociations of CO from the parent dicarbonyls are energetically unfavorable. CO thermal dissociation is an activation process for [Cl(2)Rh(CO)(2)](-) while it is a repulsive potential for CpM(CO)(2). The natures of the main excited states of CpM(CO)(2) and [Cl(2)Rh(CO)(2)](-) are found to be quite different. For [Cl(2)Rh(CO)(2)](-), all the strong transitions are identified to be metal to ligand CO charge transfer (MLCT) excitations. A significant feature of the excited states of CpM(CO)(2) is that both MLCT excitation and a ligand Cp to metal and CO charge transfer excitation are strongly mixed in the higher energy states with the latter having the largest oscillator strength. A competitive charge transfer excited state has therefore been identified theoretically for CpRh(CO)(2) and CpIr(CO)(2). The wavelength dependence of the quantum efficiencies for the photoreactions of CpM(CO)(2) reported by Lees et al. can be explained by the existence of two different types of excited states. The origin of the low quantum efficiencies for the C-H/S-H bond activations of CpM(CO)(2) can be attributed to the smaller proportion of the MLCT excitation in the higher energy states.     

Copper-mediated reduction of CO2 with pinB-SiMe2Ph via CO2 insertion into a copper-silicon bond

Reaction of [(IPr)Cu-OtBu] (1) with pinB-SiMe(2)Ph (2) leads to the Cu-silyl complex [(IPr)Cu-SiMe(2)Ph] (3). Insertion of CO(2) into the Cu-Si bond of 3 is followed by transformation of the resulting silanecarboxy complex [(IPr)Cu-O(2)CSiMe(2)Ph] (4) to the silanolate complex [(IPr)Cu-OSiMe(2)Ph] (5) via extrusion of CO. As 5 reacts readily with 2 to regenerate 3, a catalytic CO(2) reduction to CO is feasible. The individual steps were studied by in situ(13)C NMR spectroscopy of a series of stoichiometric reactions. Complexes 3, 4, and 5 were isolated and fully characterized, including single-crystal X-ray diffraction studies. Interestingly, the catalytic reduction of CO(2) using silylborane 2 as a stoichiometric reducing agent leads not only to CO and pinB-O-SiMe(2)Ph but also to PhMe(2)Si-CO(2)-SiMe(2)Ph as an additional reduction product.     

The influence of M…M attraction on nonlinear optical properties of (XMPH3)2 (X = F,Cl; and M = Au,Ag and Cu): A theoretical study

It is well known that the aurophilic attraction has great influence on spectra properties. There are certain relationships between spectra and nonlinear optical properties (NLO). Here, XMPH₃, (XMPH₃)₂ (X = F, Cl; M = Au, Ag, and Cu) were taken as the examples to be investigated to study the relationship between NLO and M···M interactions. The NLO properties of XMPH₃, (XMPH₃)₂ (X = F, Cl; M = Au, Ag, and Cu) were carried out with finite field/second‐order Møller–Plesset perturbation theory method. The results show that polarizability tensors of dimers (α_tot,d) and second‐order hyperpolarizability tensors of dimers (γ_tot,d) are significantly larger than α_tot,m and γ_tot,m of corresponding monomers. It indicates that M…M interaction significantly increases α_tot,d and γ_tot,d values. The analysis of the electronic transition shows that the charge transfer along M…M direction play the key role on increasing α_tot,d and γ_tot,d. On the other hand, the β_tot is significantly increased by changing ligands and is slightly influenced by M…M interaction. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

A theoretical study on C2HXSi silylenes (X = H,CN, NH2, and OMe)

Relative stabilities and structural characters of 30 silylenic C₂HXSi species (X = H, NH₂, CN, and OMe), with singlet (s) and/or triplet (t) states, are calculated at six levels of theory: HF/6‐311++G**, MP3/6‐31G*, B1LYP/6‐311++G**, B3LYP/6‐311++G**, MP2/6‐311++G**, and MP4(SDTQ)/6‐311++G**. The four possible isomers considered for C₂SiHX are (i) 3‐X‐1‐silacyclopropenylidene ( 1 _s‐X and 1 _t‐X ), (ii) X‐vinilydensilylene ( 2 _s‐X and 2 _t‐X ), (iii) ethynyl‐X‐silylene ( 3 _s‐X and 3 _t‐X ), and (iv) (X‐ethynyl)silylene ( 4 _s‐X and 4 _t‐X ). The GIAO–NICS calculations show that singlet cyclic structures, 1 _s‐X , are considerably more aromatic than benzene. Conversely, triplet cyclic C₂HCNSi breaks down through optimization, and transforms into a novel high‐spin acyclic carbenosilylene minimum ( 1 _t‐CN ). Singlet 3 and triplet 3 cross at a divalent angle (|XSiC) of 152°. This angle narrows to 137° for crossing of singlet 3 _s‐CN and triplet, 3 _t‐CN . The smallest |XSiC occurs at 132° for crossing of 3 _s‐H and 3 _t‐H . © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:283–293, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20297     

Studies on activation of C-H bond and insertion reaction of CO,CO2 into M-C bond using (Ir(COD)(diphos))Cl complexes

Three new organoiridium complexes are prepared from (Ir(COD)(μ-Cl))₂ and diphosphine in 1:2 molar ratio, and characterized by means of IR, ¹H NMR electric conductivity and elemental analysis. Using acetonitrile as substrate. we investigated the abilities of these complexes to activate sp³ C-H bond and promote insertion reaction of CO, CO₂ into metal-carbon bond. The experimental results show that the activity of (Tr(COD)(diphos))Cl is correlated to the electronic property of diphosphine chelate ligand.     

A bond path and an attractive Ehrenfest force do not necessarily indicate bonding interactions: case study on M2X2 (M = Li, Na, K; X = H, OH, F, Cl)

Interactions in dimers of model alkali metal derivatives M(2)X(2) (M = Li or Na or K; X = H or F, Cl, OH) are studied in the frame of the quantum theory of atoms in molecules (QTAIM) using the interacting quantum atoms approach (IQA). Contrary to opinion prevalent in QTAIM studies, the interaction between two anions linked by a bond path is demonstrated to be strongly repulsive. One may therefore say that a bond path does not necessarily indicate bonding interactions. The interactions between two anions or two cations that are not linked by a bond path are also strongly repulsive. The repulsive anion-anion and cation-cation interactions are outweighed by much stronger attractive anion-cation interactions, and the model molecules are therefore in a stable state. The attractive Ehrenfest forces (calculated in the frame of the QTAIM) acting across interatomic surfaces shared by anions in the dimers do not reflect the repulsive interactions between anions. Probable reasons of this disagreement are discussed. The force exerted on the nucleus and the electrons of a particular atom by the nucleus and the electrons of any another atom in question is proposed. It is assumed that this force unambiguously exposes whether basins of two atoms are attracted or repelled by each other in a polyatomic molecule.     

A theoretical and computational study of the anion, neutral, and cation Cu(H(2)O) complexes

An ab initio investigation of the potential energy surfaces and vibrational energies and wave functions of the anion, neutral, and cation Cu(H(2)O) complexes is presented. The equilibrium geometries and harmonic frequencies of the three charge states of Cu(H(2)O) are calculated at the MP2 level of theory. CCSD(T) calculations predict a vertical electron detachment energy for the anion complex of 1.65 eV and a vertical ionization potential for the neutral complex of 6.27 eV. Potential energy surfaces are calculated for the three charge states of the copper-water complexes. These potential energy surfaces are used in variational calculations of the vibrational wave functions and energies and from these, the dissociation energies D(0) of the anion, neutral, and cation charge states of Cu(H(2)O) are predicted to be 0.39, 0.16, and 1.74 eV, respectively. In addition, the vertical excitation energies, that correspond to the 4 (2)P<--4 (2)S transition of the copper atom, and ionization potentials of the neutral Cu(H(2)O) are calculated over a range of Cu(H(2)O) configurations. In hydrogen-bonded, Cu-HOH configurations, the vertical excitation and ionization energies are blueshifted with respect to the corresponding values for atomic copper, and in Cu-OH(2) configurations where the copper atom is located near the oxygen end of water, both quantities are redshifted.