Intramolecular ortho-C-H activation and C-N/C-O cyclizations of phenyl amidines and amides have recently been achieved under Cu catalysis. These reactions provide important examples of Cu-catalyzed functionalization of inert C-H bonds, but their mechanisms remain poorly understood. In the present study the several possible mechanisms including electrophilic aromatic substitution, concerted metalation-deprotonation (CMD), Friedel-Crafts mechanism, radical mechanism, and protoncoupled electron transfer have been theoretically examined. Cu(Ⅱ)-assisted CMD mechanism is found to be the most feasible for both C-O and C-N cyclizations. This mechanism includes three steps, i.e. CMD with Cu(Ⅱ), oxidation of the Cu(Ⅱ) intermediate, and reductive elimination from Cu(Ⅲ). Our calculations show that Cu(Ⅱ) mediates the C-H activation through an six-membered ring CMD transition state similar to that proposed for many Pd-catalyzed C-H activation reactions. It is also interesting to find that the rate-limiting steps are different for C-N and C-O cyclizations: for the former it is concerted metalation-deprotonation with Cu(Ⅱ), whereas for the latter it is reductive elimination from Cu(Ⅲ). The above conclusions are consistent with the experimental kinetic isotope effects (1.0 and 2.1 for C-O and C-N cyclizations, respectively), substituent effects, and the reactions under O2 -free conditions.
A very simple molecular cation, 4-(4-dimethylaminophenyl)-2,6-diphenylpyrylium, has been demonstrated to have a function of molecular half-adder and half-subtractor according to the detectable spectroscopic changes of the molecular system in response to the inputs of acid and base. Distinct algebraic operations can be performed in this reconfigurable molecular logic system.
A quantum chemistry method was developed to calculate the Hammett substituent constants of various organic radicals. These newly obtained constants allow,for the first time,the quantitative analysis of the electron demand of organic radicals. Calcula-tions reveal that the electron demand of organic radicals varies dramatically. It was demonstrated that the Hammett relationship of bond dissociation energies is determined only by the change of electron demand during the homolysis process.
Heterolytic and homolytic C D bond dissociation energies of three NADH models: BNAH-4,4-d 2 , HEH-4,4-d 2 and AcrD 2 in acetonitrile were first estimated by using an efficient method. The results showed that the heterolytic C D bond dissociation energies are 65.2, 70.2, and 81.9 kcal/mol and the homolytic C D bond dissociation energies are 72.66, 70.69, and 74.95 kcal/mol for BNAH-4,4-d 2 , HEH-4,4-d 2 , and AcrD 2 , respectively. According to the bond dissociation energy differences of isotope isomers, an interesting conclusion can be made that the primary kinetic isotope effects are dependent not only on the zero-point energy difference of the isotope isomers, but also on the types of C D bond dissociations, and the C D bond homolytic dissociations should have much larger primary kinetic isotope effects (26.9 28.8) than the corresponding C D bond heterolytic dissociations (3.9-5.4).
