Theoretical study of the thermal interconversion mechanism between the norbornadiene and quadricyclane radical cations

Geometry optimizations at the UHF/6-31G^* and UMP2/6-31G^* levels of theory were performed to find the transition state in the interconversion between norbornadiene (N) and quadricyclane (Q) radical cations. Two transition structures, TS^+·₁ and TS^+·₂, were obtained which have C₁ and C₂ symmetry, respectively. Vibrational analysis at the UHF and UMP2 levels of theory and IRC calculation showed that TS^+·₁ is the true transition state connecting N^+· and Q^+·, while TS^+·₂ is a second order saddle point.     

Photoisomerization of norbornadiene group in a rigid bichromophoric compound initiated by remote keto chromophore: long-distance through-bond triplet energy transfer

A diad compound 3β(bicyclo[2,2,1]hepta-2,5-diene-2-methylcarboxylate-3-carboxy)-an-drost-5-en-17-one (NBD-S-ONE) was synthesized and its photochemistry was examined. Irradiation of NBD-S-ONE in acetonitrile at λ > 300 nm selectively excited the keto chromophore. After intersystem crossing, the triplet energy of the keto group was transferred to the NBD group with 18.6% efficiency via a through-bond mechanism, resulting in the isomerization of the latter group to the quadricyclane group.     

Spectral Assignments and Structural Consequences Arising from the C-H Stretching Region of Norbornadiene

Preliminary vibrational analysis of this bicyclic moiety clearly shows the presence of Fermi Resonance phenomena. The alternative to this assignment is shown to be contradictory to both electron diffraction results and to the vibrational data, presented in this paper. Of primary interest is the implications that these spectral results could have for further studies involving classical and non-classical carbonium ion structures.     

Kinetic spectrophotometric determination of tetraphenylporphinecobalt(II) based on photochromism of immobilized norbornadiene

The cobalt(II) complex is detected spectrophotometrically by its catalysis of a photochromic isomerism of norbornadiene (NBD). NBD is immobilized on porous glass beads, and is isomerized to quadricyclane (QC) by UV irradiation. The beads are then immersed in a solution containing tetraphenylporphinecobalt(II) [TPPCo(II)], and the QC is converted back to NBD by a catalytic reaction with TPPCo(II). The rate constant, measured spectrophotometrically, is proportional to the concentration of TPPCo(II). The detection limit of TPPCo(II) is 60 μM for a reaction period of 1 h. This spectrophotometric detection can be applied repetitively without any supply of the chemical reagent, as NBD immobilized on the porous glass beads can be re-isomerized to QC by UV irradiation.     

降冰片二烯衍生物光敏异构化反应的机理研究

利用甲基卡唑为光敏剂，实现了三个降冰片二烯衍生物的光诱导介键异构化反应，荧光猝灭，化学诱导动态核极化（ＣＩＤＮＰ）以及热力学讨论都支持电子转移敏化机理，有关量子效率的计算表明单重态电子转移机制对光异构化反应的贡献远大于三重态能传递机制，此外还探讨了光异构化反应中的溶剂极性效应。     

The Bonding Structure of Quadricyclanylidene Derivatives

The crystal structures of bisquadricyclanylidene 1 , 7‐quadricyclanylidenenorbornadienes 2 and 3 are solved by X‐ray diffraction analyses. The bond lengths of the cyclopropyl moieties of 1 , 2 and 3 are compared with several other quadricyclanylidene derivatives, and the differences are analyzed by computational models. The results showed that the variation of bond lengths in this series of compounds is related to the electronic nature of substituents.     

Effect of the Formation of Inclusion Complexes With β-Cyclodextrin on the Photoisomerization and Fluorescence Properties of Aromatic Norbornadiene Derivatives

The valence photoisomerization of four aromatic norbornadiene (NBD)derivatives has been studied in ethanol and in 0.01 M -cyclodextrin(-CD) water–ethanol (v/v, 99/1) solution (WECD). Observedfirst-order rate constants are found to be of the same order of magnitude inethanol and WECD, ranging between 0.1 and 0.28 s^-1, accordingto the compound. These photoisomerization kinetic properties are attributedto the formation of inclusion complexes between NBDs and -CD. Thestoichiometry is 1 : 1, and association constants ranging between 310 and390 M^-1 have been determined fluorimetrically, usingBenesi–Hildebrand plots and a nonlinear regression method. Thestructure of the inclusion complexes is discussed on the basis of AMIsemiempirical dimension calculations and photophysical properties.     

Formation, structure, and reactivities of 1:1 adducts between quadricyclane and (η-cyclopentadienyl)(1,2-diphenyl- or -dimethoxycarbonyl-1,2-ethenedithiolato)rhodium(III)

The rhodiadithiolene complexes [Rh(Cp)(S₂C₂Z₂)] (Z=Ph (1a) and COOMe (1b)) reacted with quadricyclane (Q) to give 1:1 adducts [Rh(Cp)(S₂C₂Z₂) (C₇H₈)] (Z=Ph (2a) and COOMe (2b)) in which Rh and S of the complexes are bridged by C(7) (bridge carbons) and C(5) (edge carbons) of norbornene (C₇H₈), respectively. The structure of the adduct 2a was re-investigated and determined by X-ray structural analysis. The rhodiadithiolene complexes and those adducts showed the catalytic activities for the thermal isomerization from Q to norbornadiene (NBD). Adduct 2a photochemically dissociated to give the original complex 1a and NBD upon irradiation with a high-pressure mercury lamp. Skeletal rearrangements of the hydrocarbon moiety were confirmed in the formation of these adducts and in their photo-dissociation, according to deuterium labeling experiments.     

Rh(Xantphos)L催化氢化肉桂醛和降冰片二烯间转移加氢甲酰化反应的理论研究

采用密度泛函理论方法 M11-L/6-31G(d,p)对氢化肉桂醛与降冰片二烯(nbd)在活化催化剂a[Rh(Xantphos)L,L=苯甲酸根,Xantphos=4,5-双二苯基膦-9,9-二甲基氧杂蒽]催化下发生转移加氢甲酰化反应生成主产物苯乙烯(3)的反应机理进行理论研究.结果表明,参与反应的醛类化合物在α碳(α-C)上应至少连接一个氢原子,这可以减少醛类反应物和抗衡离子的空间排斥作用.通过反应能垒图可见,受体nbd发生加氢甲酰化反应,促进了脱氢甲酰化反应的进行,进而促使整个转移加氢甲酰化循环不可逆进行.还研究了氢化肉桂醛发生脱羰化生成少量副产物苯乙烷(4)的机理过程.结果表明,苯甲酸根作为抗衡离子抑制了脱羰化反应的竞争,理论计算得到脱氢甲酰化反应的选择性为苯乙烯(3)∶苯乙烷(4)99∶1.简单醛(如丙醛)在活化催化剂a催化下更易于发生脱羰反应而不是脱氢甲酰化反应.     

Palladium-catalyzed three-component coupling reaction of organic halides, norbornadiene and terminal alkynes

A three-component coupling reaction of organic halides, including aryl halides, methyl iodine, alkenyl iodine and bromoalkynes, with norbornadiene and terminal alkynes catalyzed by a palladium complex and a phase transfer agent in the presence of aqueous NaOH gave 5,6-disubstituted norbornene derivatives in good yields.