Theoretical Study Of C-H And O-H Bond Activation By Metal Carbenoid

Phenol is important basic chemical material, it can be used to produce some main chemical product and reactive intermediate. Besides, it plays important role in the pharmaceuticals, coating and refining industry. Phenol is extracted from coal tar in the early stage. Now, phenol is mainly come from the industrial synthesis and the production is huge. So, it has a great significance to active the phenol O-H and C-H bond in a good chemo-selectivity. Activating the C-H and O-H bond by using transition metal catalyst has become an important tool in the modern organic synthesis due to its mild reaction condition, high enantioselectivity and less environment pollution. In this paper, we systematically computed the gold/rhodium/copper ligand catalyzed phenol C-H/O-H insertion reaction mechanism by using the density functional theory (DFT). We also calculated the mechanism about gold ligand catalyst active the alkyl C(sp3)-H bond and compared with the mechanism about C(sp2)-H insertion. The main result is listed as follows:1.We use the (PhO)3PAuSbF6 and Ph3PAuSbF6 as the catalyst to catalyze the diazo compound and phenol. When the phenol C-H bond is activated by (PhO)3PAu carbene, a thermodynamics stable enol intermediate can be produced. Subsequent with two waters’assistant [1,3]-H shift and produce the final product. The proton transfer is also the rate determining step. The mechanism of the proton transfer is not the traditional [1,2]-H shift, the gold ligand induced the two waters’assistant [1,3]-proton shift. In the process of O-H insertion reaction, an enol structure is also produced in the process, through two waters’assistant [1,3]-H shift, the final product is produced. From the dynamics point of view, the O-H insertion barrier of the rate-determining step is almost the same as the C-H insertion. But from the thermodynamics viewpoint, the intermediate product of O-H insertion is obviously not stable as the C-H insertion. We proposed the thermodynamics advantage make the C-H insertion product is main product, which is agreement with experiment result. In order to verify the prediction, the low temperature experiment has been performed. The results show that the ratio of C-H insertion product and O-H insertion product is close to 1:1, which demonstrate our calculation results, because dynamic factor is the main effect in the low temperature.2. We also systematically studied the gold carbene catalyzed aromatic C(sp2)-H and alkyl C(sp3)-H insertion mechanism. Anisole/toluene/benzene are chosen as the aromatic substrate and methane/ethane/propane are chosen as the alkyl substrate. Calculation results show that the mechanism of aromatic C(sp2)-H insertion is the step by step process, the first step is the C-C electrophilic addition, then through the five ring transition state and form the enol intermediate structure. After one water and one enol’s assistant [1,3]-H transfer, the product is formed. The para-site C-H insertion of anisole is the favorite site, which is attributed to the electron donating ability of the methoxy group. For the substrate benzene and toluene, the first addition barrier is higher than that of anisole, which make the reaction is hard to process in the room temperature. This is also agreement with the experiment. For the gold carbene active the alkyl C(sp3)-H insertion reaction, the mechanism is concerted, the C-C bond and C-H bond are formed at the same time through a three centered transition state structure. The secondary carbon C-H insertion barrier is lower than the primary carbon and methane carbon, which is agreement with the C-H bond dissociation energy.3.The mechanisms of rhodium acetate/copper-pybox/copper-box active the phenol are also studied by us. The calculation results show that the metal ligand is easy dropped into the solution from the enol structure for copper and rhodium system, which make the barrier of the next [1,3]-proton transfer is mild. For the O-H insertion, the [1,3]-H transfer is still the rate determining step, the barrier is about 17.0 kcal/mol, which make the O-H insertion is not hard to process. For the C-H insertion, when we use copper and rhodium as the catalyst, the barrier of the first addition step are all higher than 19.0 kcal/mol, which make the C-H insertion is not facile. In the experiment, only O-H insertion product is produced.