Renner-Teller and spin-orbit vibronic coupling effects in linear triatomic molecules with a half-filled pi shell

The vibronic and spin-orbit-induced interactions among the (3)Sigma(-), (1)Delta, and (1)Sigma(+) electronic states arising from a half-filled pi orbital of a linear triatomic molecule are considered, employing the microscopic (Breit-Pauli) spin-orbit coupling operator. The 6 x 6 Hamiltonian matrix is derived in a diabatic spin-orbital electronic basis set, including terms up to fourth order in the expansion of the molecular Hamiltonian in the bending normal coordinate about the linear geometry. The symmetry properties of the Hamiltonian are analyzed. Aside from the nonrelativistic fourth-order Renner-Teller vibronic coupling within the (1)Delta state and the second-order nonrelativistic vibronic coupling between the (1)Sigma(+) and (1)Delta states, there exist zeroth-order, first-order, as well as third-order vibronic coupling terms of spin-orbit origin. The latter are absent when the phenomenological expression for the spin-orbit coupling operator is used instead of the microscopic form. The effects of the nonrelativistic and spin-orbit-induced vibronic coupling mechanisms on the (3)Sigma(-), (1)Delta, and (1)Sigma(+) adiabatic potential energy surfaces as well as on the spin-vibronic energy levels are discussed for selected parameter values.     

Determination of 29Si-1H spin-spin coupling constants in organoalkoxysilanes with nontrivial scalar coupling patterns

Application of polarization transfer techniques such as DEPT and INEPT in (29)Si NMR investigation of bridged silane polymerization requires knowledge of indirect (29)Si-(1)H scalar coupling constants in the silane system. However, the fully coupled (29)Si NMR spectra of these molecules, specifically those containing ethylene bridging groups, are too complicated to measure the coupling constants directly by visual inspection. This is because unlike hydrocarbon systems where one-bond proton-carbon coupling constants exceed other coupling constants by an order of magnitude, in silanes the closest proton-silicon pairs are separated by two bonds and all coupling coefficients (both homonuclear and heteronuclear) are of similar magnitude. In these systems, theoretical tools are required to interpret the spectra of even simple molecules. Here, we determine density functional theory estimates of (29)Si-(1)H scalar coupling constants and use these along with homonuclear coupling constant estimates to resolve the nontrivial nature of these spectra. We also report a Karplus equation consistent with the dihedral angle dependence of the three-bond homo- and heteronuclear coupling in the ethylene bridge. By thermal averaging of DFT coupling constants, a good initial guess of the coupled (29)Si spectral pattern is made, which is easily refined by curve fitting to determine estimates of all coupling constants in the system.     

Catalysis of copper(II) chelate-amine complexes in the oxidative coupling of 2,6-dialkylphenols

The oxidative coupling reaction of 2,6-dimethylphenol and 2,6-di-tert-butylphenol with molecular oxygen was performed by using a series of copper(II) chelate complexes as a catalyst, derived from copper(II), β-diketone, and some Shiff bases. Under the applied reaction conditions, the reaction products of 2,6-dimethylphenol were poly(2,6-dimethyl-1,4-phenylene oxide) (C? O coupling product) and 3,3′,5-5′-tetramethyl-4,4′-diphenoquinone (C? C coupling product), and that of 2,6-di-tert-butylphenol oxidation was only 3,3′,5-5′-tetra-tert-butyl-4,4′-diphenoquinone (C? C coupling product). The catalytic activity has been shown to be dependent on the properties of the copper(II) chelates used as catalysts and the mole ratios of amine ligand to copper(II) chelate (ligand ratio). The basicity and the steric bulkiness of the amine used as a ligand for copper(II) β-diketonato catalysts were found to be two of the main factors that govern the oxidative coupling mode (C? O and/or C? C coupling) of 2,6-dimethylphenol. The oxidative coupling activity of 2,6-dialkylphenol is discussed in terms of both the stabilities of the copper(II) chelates and of the copper(II) chelate-amine adducts. The rate of oxygen absorption for 2,6-dimethylphenol catalyzed by the copper(II) acetylacetonato-piperidine system is first order in oxygen partial pressure and zero order in 2,6-dimethylphenol concentration, respectively. A Cu(II)-oxygen, as an intermediate is suggested on the basis of the results obtained.     

An ab initio study of 15N-11B spin-spin coupling constants for borazine and selected derivatives

Ab initio equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) calculations have been performed to investigate substituent effects on coupling constants for borazine and selected substituted borazines. For molecules in which F atoms are not bonded to adjacent atoms in the ring, F substitution increases the one-bond (11)B-(15)N coupling constants involving the atom at which substitution occurs but leaves the remaining one-bond B-N coupling constants essentially unchanged. For these molecules, the magnitudes of one-bond B-N coupling constants are only slightly dependent on the number of F atoms present. Fluorine substitution at adjacent B and N atoms in the borazine ring further increases the one-bond B-N coupling constant involving the substituted atoms and has the same effect on the other one-bond coupling constants as observed for corresponding molecules in which substitution occurs at alternate sites. In contrast to the effect of F substitution, substitution of Li at either N or B decreases one-bond B-N coupling constants relative to borazine. The effects of F and Li substitution on one-bond B-N coupling constants for borazine are similar to F and Li substitution effects on (13)C-(13)C coupling constants for benzene.     

Diversity-oriented synthesis of multisubstituted olefins through the sequential integration of palladium-catalyzed cross-coupling reactions. 2-pyridyldimethyl(vinyl)silane as a versatile platform for olefin synthesis.

A novel strategy for the diversity-oriented synthesis of multisubstituted olefins, where 2-pyridyldimethyl(vinyl)silane functions as a versatile platform for olefin synthesis, is described. The palladium-catalyzed Heck-type coupling of 2-pyridyldimethyl(vinyl)silanes with organic iodides took place in the presence of Pd2(dba)3/tri-2-furylphosphine catalyst to give beta-substituted vinylsilanes in excellent yields. The Heck-type coupling occurred even with alpha- and beta-substituted 2-pyridyldimethyl(vinyl)silanes. The one-pot double Heck coupling of 2-pyridyldimethyl(vinyl)silane took place with two different aryl iodides to afford beta,beta-diarylated vinylsilanes in good yields. The palladium-catalyzed Hiyama-type coupling of 2-pyridyldimethyl(vinyl)silane with organic halides took place in the presence of tetrabutylammonium fluoride to give di- and trisubstituted olefins in high yields. The sequential integration of Heck-type (or double Heck) coupling and Hiyama-type coupling produced the multisubstituted olefins in regioselective, stereoselective, and diversity-oriented fashions. Especially, the one-pot sequential Heck/Hiyama coupling reaction provides an extremely facile entry into a diverse range of stereodefined multisubstituted olefins. Mechanistic considerations of both Heck-type and Hiyama-type coupling reactions are also described.     

Jahn-Teller effect in Rydberg series: a multi-state vibronic coupling problem

Two simple limiting cases of Jahn-Teller (JT) coupling in Rydberg states of polyatomic molecules are considered, namely(i) JT coupling in Rydberg orbitals as well as in the ionization continuum (nondegenerate ion core, degenerate Rydberg series) and(ii) JT coupling in the ion core (degenerate ion core, nondegenerate Rydberg series). For both models simple and efficient algorithms for the computation of spectra (dynamical JT effect) are developed. The orbital JT effect is shown to represent a novel type of multi-state vibronic coupling, giving rise to interesting spectroscopic phenomena, among them resonant inter-Rydberg perturbations and JT induced autoionization. Particular attention is paid to the demonstration of the characteristic spectroscopic signatures of the two types of JT coupling in Rydberg states.     

Ab initio EOM-CCSD spin-spin coupling constants for hydrogen-bonded formamide complexes: bridging complexes with NH3, (NH3)2, H2O, (H2O)2, FH, and (FH)2

EOM-CCSD spin-spin coupling constants across hydrogen bonds have been computed for complexes in which NH3, H2O, and FH molecules and their hydrogen-bonded dimers form bridging complexes in the amide region of formamide. The formamide one-bond N-H coupling constant [(1)J(N-H)] across N-H...X hydrogen bonds increases in absolute value upon complexation. The signs of the one-bond coupling constants (1h)J(H-X) indicate that these complexes are stabilized by traditional hydrogen bonds. The two-bond coupling constants for hydrogen bonds with N-H as the donor [(2h)J(N-X)] and the carbonyl oxygen as the acceptor [(2h)J(X-O)] increase in absolute value in the formamide/dimer relative to the corresponding formamide/monomer complex as the hydrogen bonds acquire increased proton-shared character. The largest changes in coupling constants are found for complexes of formamide with FH and (FH)2, suggesting that bridging FH monomers and dimers in particular could be useful NMR spectroscopic probes of amide hydrogen bonding.     

Ferromagnetic coupling in hexanuclear gadolinium clusters

The magnetic susceptibilities of hexanuclear gadolinium clusters in the compounds Gd(Gd6ZI12) (Z = Co, Fe, or Mn) and CsGd(Gd6CoI12)2 are reported and subjected to theoretical analysis with the help of density functional theory (DFT) computations. The single-crystal structure of Gd(Gd6CoI12) is reported here as well. We find that the compound with a closed shell of cluster bonding electrons, Gd(Gd6CoI12), exhibits the effects of antiferromagnetic coupling over the entire range of temperatures measured (4-300 K). Clusters with unpaired, delocalized cluster bonding electrons (CBEs) exhibit enhanced susceptibilities consistent with strong ferromagnetic coupling, except at lower temperatures (less than 30 K) where intercluster antiferromagnetic coupling suppresses the susceptibilities. The presence of two unpaired CBEs, as in [Gd6MnI12]3-, yields stronger coupling than when just one unpaired CBE is present, as in [Gd6FeI12]3- or [Gd6CoI12]2-. DFT calculations on model molecular systems, [Gd6CoI12](OPH3)6 and [Gd6CoI12]2(OPH3)10, indicate that the delocalized cluster bonding electrons are highly effective at mediating intracluster ferromagnetic exchange coupling between the Gd atom 4f7 moments and that intercluster coupling is expected to be antiferromagnetic. The DFT calculations were used to calculate the relative energies of various 4f7 spin patterns and form the basis for construction of a simple spin Hamiltonian describing the coupling within the [Gd6CoI12] cluster.     

Probing the proton-transfer coordinate of complexes with F--H...P hydrogen bonds using one- and two-bond spin-spin coupling constants

Scalar coupling constants have been computed using the EOM-CCSD method for equilibrium structures of complexes stabilized by F--H...P hydrogen bonds, as well as structures along the proton-transfer coordinates of these complexes. Variations in the signs and absolute values of (1)J(F--H), (1h)J(H--P) and (2h)J(F--P) have been analyzed and interpreted in terms of changing hydrogen bond type. Of the three phosphorus bases (phosphine, trimethylphosphine and phosphinine) investigated in this study, trimethylphosphine forms the strongest complex with FH, and has the largest two-bond F--P coupling constant. Among the relatively simple phosphorus bases, it would appear to be a leading candidate for experimental NMR study. Similarities and differences are noted between the corresponding coupling constants (J) and the reduced coupling constants (K) across F--H...P and F--H...N hydrogen bonds.     

N,O-Bis(trimethylsilyl)acetamide/N-hydroxysuccinimide ester(BSA/NHS) as coupling agents for dipeptide synthesis

A method using N,O-bis(trimethylsilyl)acetamide/N-hydroxysuccinimide ester(BSA/NHS) as coupling agents for dipeptide synthesis is descried. The coupling reaction between N-hydroxysuccinimide(NHS)esters and amines could be performed under mild conditions with N,O-bis(trimethylsilyl)acetamide(BSA) as coupling reagent and no additional acid/base is required. All byproducts and excessive reactants are water soluble or hydrolysable and easy to eliminate through water-washing at the purification stage.Moreover, all the reactants are inexpensive and widely used in conventional drug production.     

Ab initio study of dynamical E × e Jahn-Teller and spin-orbit coupling effects in the transition-metal trifluorides TiF3, CrF3, and NiF3

Multiconfiguration ab initio methods have been employed to study the effects of Jahn-Teller (JT) and spin-orbit (SO) coupling in the transition-metal trifluorides TiF(3), CrF(3), and NiF(3), which possess spatially doubly degenerate excited states ((M)E) of even spin multiplicities (M = 2 or 4). The ground states of TiF(3), CrF(3), and NiF(3) are nondegenerate and exhibit minima of D(3h) symmetry. Potential-energy surfaces of spatially degenerate excited states have been calculated using the state-averaged complete-active-space self-consistent-field method. SO coupling is described by the matrix elements of the Breit-Pauli operator. Linear and higher order JT coupling constants for the JT-active bending and stretching modes as well as SO-coupling constants have been determined. Vibronic spectra of JT-active excited electronic states have been calculated, using JT Hamiltonians for trigonal systems with inclusion of SO coupling. The effect of higher order (up to sixth order) JT couplings on the vibronic spectra has been investigated for selected electronic states and vibrational modes with particularly strong JT couplings. While the weak SO couplings in TiF(3) and CrF(3) are almost completely quenched by the strong JT couplings, the stronger SO coupling in NiF(3) is only partially quenched by JT coupling.     

Theoretical Design of High－spin Organic Molecules with Heterocycles as Ferromagnetic Coupling Units

IntroductionThe design and the syntheses of organicmolecules with very high- spin ground states havebeen a topic of great interest[1— 5] .One of rationalapproaches to designing high- spin molecules,which has been proposed and studied by severalgroups[6,7] ,consists in conceptually dividing themolecules into two components,i.e.,a spin- con-taining( SC) fragment which provides the unpairedelectron and a ferromagnetic coupling ( FC) unitwhich is connected with radical centers ferromag-netically…     

4个新型有机磷缩合试剂的合成及其在生物活性肽合成中的应用

报道了4个新型有机磷化合物：N-二乙氧基磷酰苯并唑酮(DEPBO)、N－(2-氧-1,3,2-二氧杂磷杂环乙烷基)-苯并唑酮(DOPBO)、3－(2'-氧-1',3',2'-二氧杂磷杂环己烷基)-氧-1,2,3-苯共三嗪-4(3H)-酮(DOPBT)和3－(二乙氧基磷酰基)-氧-1,2,3-苯并三嗪-4(3H)-酮(DEPBT)的合成,并研究了它们作为缩会试剂在多肽合成中的应用. 研究结果表明,它们可以成功地用于固相法和溶液法合成多肽,其中DEPBT还可用于环肽的合成. 应用DEPBO和DEPBT合成了促睡眠肽的类似物及从云南中草药繁缕中分离鉴定的一个环七肽等生物活性肽.     

氢键桥联双核铜配合物磁耦合的密度泛函研究

在密度泛函理论的基础上,应用对称性破损方法研究了氢键桥联双核铜模型配合物的磁耦合行为以及磁耦合常数随O-O距离的变化趋势.计算结果表明,反铁磁耦合作用来源于Cu原子的d_x²-y²和氧原子的p_x或p_y磁轨道的部分重叠,而H原子不参与磁耦合作用.磁耦合常数J与O-O距离r之间存在指数关系,而不是线性关系.     

2-(8-quinolylazo)-7-phenylazochromotropic acid as an analytical reagent

2-(8-Quinolylazo)-7-phenylazochromotropic acid (QAPAC) has been synthesized by coupling diazotized 8-aminoquinoline with 2-phenylazochromotropic acid as well as by coupling diazotized aniline with 2-(8-quinolylazo)chromotropic acid. The properties of QAPAC and the spectrophotometric characteristics of some metal-QAPAC complexes are reported.     

Broken-symmetry density functional theory investigation on bis-nitronyl nitroxide diradicals: influence of length and aromaticity of couplers

A series of nitronyl nitroxide (NN) diradicals with linear conjugated couplers and another series with aromatic couplers have been investigated by the broken-symmetry (BS) DFT approach. The overlap integral between the magnetically active orbitals in the BS state has been explicitly computed and used for the evaluation of the magnetic exchange coupling constant (J). The calculated J values are in very good agreement with the observed values in the literature. The magnitude of J depends on the length of the coupler as well as the conformation of the radical units. The aromaticity of the spacer decreases the strength of the exchange coupling constant. The SOMO-SOMO energy splitting analysis, where SOMO stands for the singly occupied molecular orbital, and the calculation of electron paramagnetic resonance (EPR) parameters have also been carried out. The computed hyperfine coupling constants support the intramolecular magnetic interactions. The nature of magnetic exchange coupling constant can also be predicted from the shape of the SOMOs as well as the spin alternation rule in the unrestricted Hartree-Fock (UHF) treatment. It is found that pi-conjugation along with the spin-polarization plays the major role in controlling the magnitude and sign of the coupling constant.     

Synthesis of n,n′-biquinolines by a coupling reaction of bromoquinolines using organonickel(0) complexes

Tris(triphenylphosphine)nickel(0) (A) and a zerovalent pyridine–nickel complex (B) have been used as reagents for the coupling reaction of 3-, 6- and 8-bromoquinolines: 3,3′-, 6-6′- and 8,8′- Biquinolines were obtained in quantitative yields when A was used as the coupling reagent. B gave always a mixture of the n,n′ -biquinoline and substitution products. A mechanism can be outlined to explain the coupling reaction of bromoquinolines using zerovalent nickel complexes.     

Bis-diimidazolylidine complexes of nickel: investigations into nickel catalyzed coupling reactions

Air and moisture stable homoleptic bis(diimidazolylidine)nickel(II) complexes, ([(diNHC)(2)Ni](2+)) 3a,b and their corresponding silver(I) 4a,b and palladium(II) 5a,b complexes were synthesized and characterized by NMR and single crystal X-ray analysis. The catalytic potential of complex 3a was assessed in Mizoroki-Heck and Suzuki-Miyaura coupling reactions. In the Suzuki-Miyaura coupling reaction, nickel precatalyst 3a was active for the coupling of aryl chlorides as well as aryl fluorides. The analogously synthesized Pd(II) complexes resulted in formation of (diNHC)PdCl(2) species which were not active for the coupling of aryl fluorides. For the Mizoroki-Heck reaction, it was found that aryl iodides could be activated in the absence of nickel or palladium precatalysts when using Na(2)CO(3) or NEt(3) as base while aryl iodides and aryl bromides could be activated in the Suzuki-Miyaura reaction sans precatalyst when K(3)PO(4) was used as base.     

Nuclear spin coupling constants from the extended Hückel method

The ability to calculate directly bonded X-H nuclear spin coupling constants from molecular parameters obtained from the extended Hückel model has been studied as a function of the following calculational details: (1) the atomic orbital basis set; (2) the off-diagonal Hamiltonian matrix element approximation; and (3) charge iteration. It has been found that although variations such as these have a significant effect on the magnitudes of the observed coupling constants, none is capable of fitting the experimentally observed trends in X-H coupling constants.     

Computational and experimental evidence of through-space NMR spectroscopic J coupling of hydrogen atoms

J coupling in NMR spectroscopy is conventionally associated with covalent bonds. A noncovalent contribution often called through-space coupling (TSC) has been observed for heavy atoms. In this study, the TSC was detected and analyzed for the more common (1)H-(1)H coupling as well. In synthesized model molecules the hydrogen positions could be well controlled. For several coupling constants the through-space mechanism was even found to be the predominant factor. The nature and magnitude of the phenomenon were also analyzed by density functional computations. Calculated carbon- and hydrogen-coupling maps and perturbed electronic densities suggest that the aromatic system strongly participates in the noncovalent contribution. Unlike covalent coupling, which is usually governed by the Fermi contact, TSC is dominated by the diamagnetic term comprising interactions of nuclei with the electron orbital angular momentum. The computations further revealed a strong distance and conformational dependence of TSC. This suggests that the through-space coupling can be explored in molecular structural studies in the same way as the covalent one.