Interaction of Phosphoric Anhydride with CH-, NH-, PH-, SH-Acids

Abstract

Phosphoric anhydride interacts with different CH-, NH-, PH-, SH-acids with the formation of corresponding amidophosphates and esters.     

Remote substituent effects on homolytic Fe?C bond energies of p‐G‐C6H4CH2Fe(CO)2(η5‐C5H5) and p‐G‐C6H4(H)(CN)CFe(CO)2(η5‐C5H5) studied by Hartree–Fock and density functional theory methods

In general, both stoichiometric and catalytic reactions of organometallic complexes involve breaking and forming metal–ligand bonds. Therefore, an evaluation of the thermodynamics of such reactions requires the knowledge of metal–ligand bond energies (BDEs). The homolytic Fe? C bond dissociation energies [i.e., ΔH_homo(Fe? C)s] of 12 para‐substituted benzyldicarbonyl(η⁵‐cyclopentadienyl)iron, p‐G‐C₆H₄CH₂Fp [1,G = NO₂, CN, COMe, CO₂Me, CF₃, Br, Cl, F, H, Me, MeO, NMe₂; Fp = (η⁵‐C₅H₅)(CO)₂Fe] and 12 para‐substituted α‐cyanobenzyldicarbonyl (η⁵‐cyclopentadienyl)iron, p‐G‐PANFp [2,PAN = C₆H₄CH(CN)] were studied using Hartree–Fock (HF) and density functional theory (DFT) methods with large basis sets. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔH_homo(Fe? C)s. The B3LYP method satisfactorily predicts the α and remote substituent effects on ΔH_homo(Fe? C)s [ΔΔH_homo(Fe? C)s]. The fair correlations [r = 0.97 (g, 1), 0.99(g, 2)] of ΔΔH_homo(Fe? C)s of series 1 and 2 with the substituent σ constants imply that the para substituent effects on ΔH_homo(Fe? C)s originate mainly from polar effects, but those on radical stability originate from both spin delocalization and polar effects. The molecule stabilization effects (MEs) causes that not only the magnitude of ΔΔH_homo(Fe? C)s(1) varies significantly but also the direction changes from S‐pattern to O‐pattern. ΔΔH_homo(Fe? C)s(2) were found to conform to the Capto‐dative Principle. The detailed knowledge of the factors that determine the Fp? C bond strengths would greatly aid in understanding reactivity patterns in many processes. Copyright © 2010 John Wiley & Sons, Ltd.     

取代基对木质素三聚体模型化合物醚键均裂反应影响的密度泛函理论研究

利用密度泛函理论M062X/6-31++G(d,p)方法,对27种具有不同取代基(甲基、羟甲基和甲氧基)的木质素三聚体模型化合物的Cα-O和Cβ-O键均裂解离能进行了理论计算,探究了不同位置取代基对醚键解离能的影响规律。结果表明,当R2或R3位氢原子仅有一个被甲氧基取代时,Cβ-O键解离能变化很小;当R2、R3位氢原子均被甲氧基取代时,Cβ-O键解离能明显降低;且R4、R5位甲氧基能强化R2、R3位甲氧基对Cβ-O键解离能的降低程度,而不受R1位取代基的影响。当R4、R5位氢原子相继被甲氧基取代时,Cα-O键解离能逐渐降低,且R2、R3位甲氧基也能强化R4、R5位甲氧基对Cα-O键解离能的降低程度。当R1位氢原子相继被甲基、羟甲基取代时,Cα-O键解离能逐渐升高,然而R2、R3位甲氧基会弱化R1位甲基、羟甲基对Cα-O键解离能的升高程度;R1位甲基不会影响Cβ-O键解离能,羟甲基却能明显提高Cβ-O键解离能。     

Singly versus Doubly Reduced Nickel Porphyrins for Proton Reduction: Experimental and Theoretical Evidence for a Homolytic Hydrogen‐Evolution Reaction

A nickel(II) porphyrin Ni‐P (P=porphyrin) bearing four meso‐C₆F₅ groups to improve solubility and activity was used to explore different hydrogen‐evolution‐reaction (HER) mechanisms. Doubly reduced Ni‐P ([ Ni‐P ]^2?) was involved in H₂ production from acetic acid, whereas a singly reduced species ([ Ni‐P ]^?) initiated HER with stronger trifluoroacetic acid (TFA). High activity and stability of Ni‐P were observed in catalysis, with a remarkable i_c/i_p value of 77 with TFA at a scan rate of 100 mV s^?1 and 20 °C. Electrochemical, stopped‐flow, and theoretical studies indicated that a hydride species [H‐ Ni‐P ] is formed by oxidative protonation of [ Ni‐P ]^?. Subsequent rapid bimetallic homolysis to give H₂ and Ni‐P is probably involved in the catalytic cycle. HER cycling through this one‐electron‐reduction and homolysis mechanism has been proposed previously but rarely validated. The present results could thus have broad implications for the design of new exquisite cycles for H₂ generation.     

Chemically triggered C–ON bond homolysis in alkoxyamines. Part 7. Remote polar effect

In a recent work (Org. Lett. 2012, 14, 358–361), we showed that the activation by benzylation of alkoxyamine 1 (diethyl (1‐(tert‐butyl(1‐(pyridin‐4‐yl)ethoxy)amino)‐2,2‐dimethylpropyl)phosphonate) afforded a surprisingly large C–ON bond homolysis rate constant k_d. Taking advantage of the easy preparation of para‐X‐benzyl‐activated alkoxyamines 2 and of the presence of a shielding methylene group between the two aromatic moieties, we investigated the long range (10 bonds between the X group and the C–ON bond) polar effect for X = H, F, OMe, CN, NO₂, NMe₂, ⁺NHMe₂,Br^?. It was observed that the effect was weak (4‐fold) and mainly due to the zwiterionic mesomeric forms generated by the presence of group X on the para position, i.e. k_d increased for CN and NO₂ and decreased for OMe, NMe₂ and ⁺NMe₂H,Br^?. DFT calculations at the B3LYP/6‐31G(d,p) level were performed to determine orbital interactions (natural bond orbital (NBO) analysis), Mulliken and NBO charges which support the reactivity described. Copyright © 2014 John Wiley & Sons, Ltd.     

PHOTOCHEMISTRY OF PESTICIDES, 13.1 SOME PHOTOREACTIONS OF O,O-DIETHYL-O-(4-METHYL-2-OXO-2H-1-BENZOPYRAN-7-YL)-PHOSPHOROTHIOATE (POTASAN®)

Abstract

UV-irradiation (δ > 313nm) of O,O-diethyl-O-(4-methyl-2-oxo-2H-1-benzopyran-7-yl)-phosphoro-thioate (Potasan®) la in chloroform and/or methanol with and without singlet oxygen results in the formation of the 2-oxo-2H-1-benzopyran-phosphate 2 the 3,3′-bipotasan dehydrodimer 3, and 7-ethoxy-4-methyl-2-oxo-2H-1-benzopyran 4: the mechanisms of formation, especially for 4 are discussed.     

O?O bond homolysis in hydrogen peroxide

O O bond homolysis in hydrogen peroxide (H₂O₂) has been studied using theoretical methods of four conceptually different types: hybrid DFT (B3LYP, M06‐2X), double‐hybrid DFT (B2‐PLYP), coupled‐cluster (CCSD(T)), and multiconfigurational (CASPT2). In addition, the effects of basis set size have also been analyzed. For all of these methods, the O O bond homolysis in hydrogen peroxide has been found to proceed through hydrogen bonded radical pair complexes. Reaction barriers for collapse of the radical pairs to hydrogen peroxide are minute, leading to an overall very flat potential energy surface. However, hydrogen bonding energies in the radical pair complex expressed as the energy difference to two separate hydroxyl radicals are sizeable and exceed 10 kJ/mol for all theoretical methods considered in this study. © 2017 Wiley Periodicals, Inc.     

QSPR approach to the calculation of rate constants of homolysis of nitro compounds in different states of aggregation

A method for the theoretical estimation and prediction of rate constants of homolysis of nitro compounds of different chemical classes in the gas phase is proposed on the basis of the QSPR approach.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1653–1656, September, 1995.The authors express gratitude to B. A. Lur'e (D. I. Mendelev Moscow Academy of Chemical Technology) for fruitful advice during discussion of the results.     

Bi−P Bond Homolysis as a Route to Reduced Bismuth Compounds and Reversible Activation of P4

Bismuth diphenylphosphanides Bi(NON^R)(PPh₂) (NON^R=[O(SiMe₂NR)₂], R=tBu, 2,6‐iPr₂C₆H₃, Aryl) undergo facile decomposition via single‐electron processes to form reduced Bi and P species. The corresponding derivatives Bi(NON^R)(PCy₂) are stable. Reaction of the isolated Bi^II radical ^.Bi(NON^Ar) with white phosphorus (P₄) proceeds with the reversible and selective activation of a single P?P bond to afford the bimetallic μ,η^1:1‐bicyclo[1.1.0]tetraphosphabutane compound.     

Effect of the Carboxylate Salt on the C?ON Bond Homolysis of SG1‐Based Alkoxyamines

Alkoxyamines and persistent nitroxides are important regulators of the nitroxide mediated radical polymerization (NMP). Since the polymerization time decreases with increasing values of the homolysis rate constant (k_d) for the C? ON bond between the polymer chain and the nitroxide moiety, the factors influencing k_d are of considerable interest. Environmentally friendly polymerization methods, such as NMP in emulsion medium, have now been developed. The success of the polymerization depends not only on the strength of the C? ON bond but also on the solubility of the initiator/controller alkoxyamines, which control the nucleation. Various salts of SG1‐based alkoxyamines (S^+?OOCCMeH‐SG1) labelled 1 a–f , where S⁺=Li⁺ ( a ), Na⁺ ( b ), K⁺ ( c ), nBu₃HN⁺ ( d ), NH₄⁺ ( e ), and nBu₄N⁺ ( f ) are prepared, all of which are soluble in most organic solvents (e.g. pentane, dichlomethane, benzene, ethanol, etc.) as well as in water. Their k_d values, which are measured in tert‐butylbenzene, reveal unexpected behaviors depending on the diastereoisomers. For the RR/SS diatereoisomers (i.e. slowly homolyzing isomers), k_d was not found to be sensitive to any of the salts, whereas for the RS/SR diastereoisomers (i.e. quickly homolyzing isomers), k_d is observed to decrease to a greater or lesser extent depending on the type of salt. The conformations of the diastereoisomers of several salts are determined by means of DFT calculations, and the orbital interactions are studied by natural bond orbital (NBO) analysis.