Theoretical investigation of the decarbonylation of acetaldehyde by Fe+ and Cr+.

We report a comprehensive theoretical study on the decarbonylation of acetaldehyde by Fe+ and Cr+. Various intermediates, transition states, and products involved in the decarbonylation reactions are fully optimized at the B3LYP/6-311+G(2df,2pd) level of theory. The potential energy surfaces (PESs) corresponding to [M,O,C2,H4]+(M=Cr and Fe) are examined in detail using B3LYP and CCSD(T) methods, respectively. The validity of these theoretical methods is calibrated with respect to the available thermochemical data. Calculations suggest that the Cr+ mediated decarbonylation of acetaldehyde takes place in four steps on the sextet surface: encounter complexation, C-C activation, aldehyde H-shift, and nonreactive dissociation, in good accordance with the Co+ mediated decarbonylation of acetaldehyde [Zhao, Zhang, Guo, Wu, Lu, Chem. Phys. Lett. 2005, 414, 28], while for the Fe+/acetaldehyde system decarbonylation can occur on both the quartet and the sextet PESs. The quartet pathway, which experiences spin-orbit coupling between the two surfaces, is energetically more favorable; whereas along the sextet decarbonylation coordinate several high-energy barriers are revealed. The theoretical results are compared with the experimental product kinetic energy and angular distributions of decarbonylation of acetaldehyde by Fe+ and Cr+ measured using a crossed-beam technique [Sonnenfroh, Farrar, J. Am. Chem. Soc. 1986, 108, 3521].     

Experimental and computational studies of intracomplex reactions in Mg+(primary, secondary alkylamine) complexes induced by photoexcitation of Mg+

We report herein a comprehensive study of photoinduced reactions in complexes of Mg+ with primary (n-propyl- and isopropylamine) and secondary amines (dipropyl- and diisopropylamine) in the spectral range of 230-440 nm. Similar to the methyl- and ethylamine complexes studied previously, N-H bond activation of these complexes is very unfavorable. Instead, the C(alpha)-C, C-N, and C(alpha)-H bond-cleavage photoproducts are observed after photoexcitation of the Mg+ complexes (3(2)P<--3(2)S). For Mg+(primary amine) complexes, for example, Mg+-NH2CH2CH2CH3, and Mg+-NH2CH(CH3)2, the photoproducts resulting from C(alpha)--C rupture prevail after P(z) and charge-transfer excitations, whereas the Mg+ photofragment is predominant upon P(x,y) excitation. However, with further N-alkyl substitution, as in Mg+(secondary amine) complexes, for example, Mg+-NH(CH2CH2CH3)2 and Mg+-NH[CH(CH3)2]2, a novel intracomplex C-C coupling photoreaction dominates on P(x,y) excitation of Mg+, which is believed to arise from Mg+* insertion into the C-N bond. With P(z) and charge-transfer excitation, the Mg-R elimination photoproducts, arising from C(alpha)-C bond cleavage, predominate. The energetics and possible mechanisms of the intracomplex photoreactions are analyzed in detail with the help of extensive quantum mechanics calculations.     

Differentiation and quantitation of isomeric dipeptides by low-energy dissociation of copper(II)-bound complexes

Application of the kinetic method based on the dissociation of transition metal centered cluster ions is extended from chiral analysis (Tao, W. A.; Zhang, D.; Nikolaev, E. N.; Cooks, R. G. J. Am. Chem. Soc. 2000, 122, 10598) to quantitative analysis of isomeric mixtures, including those with Leu/Ile substitutions. Copper(II)-bound complexes of pairs of peptide isomers are generated by electrospray ionization mass spectrometry and the trimeric complex [CuII(ref)2(A) - H]+ (analyte A, a mixture of isomeric peptides; reference compound ref, usually a peptide) is caused to undergo collisional dissociation. Competitive loss of the neutral reference compound or the neutral analyte yields two ionic products and the ratio of rates of the two competitive dissociations, viz. the product ion branching ratio R is shown to depend strongly on the regiochemistry of the analyte in the precursor [CuII(A)(ref)2 - H]+ complex ion. Calibration curves are constructed by relating the branching ratio measured by the kinetic method, to the isomeric composition of the mixture to allow rapid quantitative isomer analysis.     

Recognition and quantification of binary and ternary mixtures of isomeric peptides by the kinetic method: metal ion and ligand effects on the dissociation of metal-bound complexes

The kinetic method is applied to differentiate and quantify mixtures of isomeric tripeptides based on the competitive dissociations of divalent metal ion-bound clusters in an ion trap mass spectrometer. This methodology is extended further to determine compositions of ternary mixtures of the isomers Gly-Gly-Ala (GGA), Ala-Gly-Gly (AGG), and Gly-Ala-Gly (GAG). This procedure also allows to perform chiral quantification of a ternary mixture of optical isomers. The divalent metal ion Ca(II) is particularly appropriate for isomeric distinction and quantification of the isobaric tripeptides Gly-Gly-Leu/Gly-Gly-Ile (GGL/GGI). Among the first-row transition metal ions, Cu(II) yields remarkably effective isomeric differentiation for both the isobaric tripeptides, GGI/GGL using GAG as the reference ligand, and the positional isomers GAG/GGA using GGI as the reference ligand. This is probably due to agostic bonding: alpha-agostic bonding occurs between Cu(II) and GAG and beta-agostic bonding between Cu(II) and GGI, each produces large but different steric effects on the stability of the Cu(II)-bound dimeric clusters. These data form the basis for possible future quantitative analyses of mixtures of larger peptides such as are generated, for example, in combinatorial synthesis of peptides and peptide mimics.     

Efficient Synthesis of Triarylamines Catalyzed by Copper(I) Diazabutadiene Complexes

Cuprous chloride was coordinated by diazabutadiene (DAB‐R) ligands to form Cu(I)‐(DAB‐R) complexes, most of which have a 1:1 ratio of Cu to DAB‐R as reported. In the case of a special DAB‐ⁱPP, N,N′‐bis(2,6‐diisopropylphenyl)‐1,4‐diaza‐1,3‐butadiene, an unexpected composition of complex was found with the formula Cu(I)Cl(DAB)₂. When employed as catalyst for triarylamine synthesis from the coupling of aryl halides with primary and secondary arylamines, the new Cu(I)‐(DAB‐ⁱPP) complex displayed high efficiency.     

A Bayesian approach for analyzing case 2 interval-censored data under the semiparametric proportional odds model

Analyzing interval-censored data is difficult due to its complex data structure containing left-, interval-, and right-censored observations. An easy-to-implement Bayesian approach is proposed under the proportional odds (PO) model for analyzing such data. The nondecreasing baseline log odds function is modeled with a linear combination of monotone splines. Two efficient Gibbs samplers are developed based on two different data augmentations using the relationship between the PO model and the logistic distribution. In the first data augmentation, the logistic distribution is achieved by the scaled normal mixture with the scale parameter related to the Kolmogorov-Smirnove distribution. In the second data augmentation, the logistic distribution is approximated by a Student’s t distribution up to a scale constant. The proposed methods are evaluated by simulation studies and illustrated with an application of an HIV data set.     

Theoretical survey of the potential energy surface of methyl nitrite + Cu+ reaction

The gas-phase reaction of methyl nitrite with Cu+ has been investigated using density functional theory. The geometries and energies of all the stationary points involved in the reaction have been investigated at the B3LYP/6-311+G(2df,2pd) level. Seven different structures of the encounter complexes could be formed when Cu+ attacking at different electronegative heteroatoms of trans and cis conformational isomers of methyl nitrite, in which the inner oxygen attacks account for the most stable complexes. Extensive conversions could take place for these complexes converting into each other. Various mechanisms leading to the loss of NO and HNO are analyzed in terms of the topology of the potential energy surface. The reaction proceeds exclusively from the inner oxygen attachments, followed by four different mechanisms, i.e., direct dissociation, direct H abstraction, N-O activation, and C-H activation, where the former two provide direct channels for the respective losses of NO and HNO, the third one accounts for both of the losses, and C-H activation is unlikely to be important due to the energetics.     

杯芳烃研究进展

本文评论了杯芳烃化学的研究进展,内容包括它的合成、衍生化反应、构象、包合作用和应用前景等。杯芳烃合成衍生化反应构象包合作用