The possible use of Ni in Heck reactions was investigated with use of the density function theory method. It was found that the mechanisms of the Ni-and Pd-catalyzed Heck reactions are quite similar to each other. Nevertheless, oxidative addition and olefin insertion occur with lower energy barriers in the Ni system than in the Pd system. Because β-hydride elimination is more efficient in the Pd system than in the Ni system, there is a poorer selectivity to vinylation over Michael addition in the Ni system than in the Pd system. In addition, catalyst regeneration through HX removal is considerably harder to achieve with the Ni system than with the Pd system. Therefore, either a very strong base should be used for the Ni catalysis or a reductive pathway should be designed to remove HX from the Ni complex. Compared to the Pd system, oxidative addition of an alkenyl or aryl chloride is not much harder than oxidative addition of an alkenyl or aryl iodide in the Ni system. Therefore, the Ni-catalyzed Heck reaction may be applied to alkenyl or aryl chloride relatively easily. Also, because β-hydride elimination is more difficult in the Ni system than in the Pd system, the Ni-catalyzed Heck reaction may be applied to aliphatic halides. For an olefin with an electron-donating substituent, the Ni-catalyzed coupling should slightly favor the Markovnikov-type product, if the steric effect is not significant. For an olefin with an electronwithdrawing substituent, the Ni-catalyzed coupling should provide the anti-Markovnikovtype product as the major product. In addition, it was found that phosphine and pyridine ligands can reasonably well reduce the free energy in the HX removal step. Therefore, they appear to be promising ligands for the Ni-catalyzed Heck reactions. Finally, we found that the solvation effects, cation pathway, and anionic pathway in the Heck reactions did not change the general trends for the reactivities of the Ni and Pd catalysts.
The formylation and methylation of amines with carbon dioxide and hydrosilanes are emerging yet important types of transformations for CO2. Catalytic methods effective for both reactions with wide substrate scopes are rare because of the difficulty in controlling the selectivity. Herein, we report that simple and readily available inorganic basesalkali-metal carbonates, especially cesium carbonatecatalyze both the formylation and methylation reactions efficiently under mild conditions. The selectivity can be conveniently controlled by varying the reaction temperature and silane. A “cesium effect” on both reactions was observed by comparing the catalytic activity of various alkali-metal carbonates. Combined experimental and computational studies suggested the following reaction mechanism: (i) activation of Si–H by Cs2CO3, (ii) insertion of CO2 into Si–H, (iii) formylation of amines by silyl formate, and (iv) reduction of formamides to methylamines.
Part 1. Wertz MethodWertz's method is essentially composed of two steps. Two thermodynamic cycles are constructed. In the first step, the entropy change from gas state (standard state, S g˚ = 0.308 kJ mol -1 K -1 ) to liquid state (S l˚ = 0.208 kJ mol -1 K -1 ) DCE is decomposed to two steps: (i) adiabatic compression of ideal DCE gas in standard state to a hypothetical ideal gas state with the concentration equal to that of the liquid state (12.66 M); and (ii) conversion of the hypothetical state to the final liquid state. (Scheme S1) Scheme S1.The entropy change of the first step can be estimated according to Maxwell's relations, while that of the second step can be derived from the thermodynamic cycle. The fraction of entropy lost in second step is defined as a coefficient, a, which was calculated to be 0.202.
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