Theoretical Study Of Catalytic Methanol Carbonylation Reaction Of Rhodium Iodide

In this thesis the reaction mechanisms of methanol carbonylation catalyzed by rhodium complex have been studied by using the ab initio method with the effective core potential (ECP) approximation, and all the reaction paths of each elementary reaction in the rhodium complex catalyzed methanol carbonylation have been traced by the intrinsic reaction coordinate theory (IRC). The obtained results are summarized as follows.1. Structures and activities of catalysis reactive species The possible configurations of catalysis reactive species and the relevance between the different reaction pathways are studied at HF/LANL2DZ level. The main results are as follows: (1) The configuration of the reactive species formed between the center rhodium atom and CO and I ligands possibly has a tri-or tetra-coordination structure. The calculations indicate that the tetra-coordination configuration [Rh(CO)2I2]- has the most stable structure, and the energy of the others are higher 100 to 700 kJ/mol than that of the [Rh(CO)2I2]-. According to coordination theory, the structure of rhodium is different from other transition metal; its configuration of 16 electrons is a relative stable state. Therefore, it is thought that [Rh(CO)2I2]- configuration is a catalysis reactive species in the methanol carbonylation catalyzed by rhodium complex ; (2) The [Rh(CO)2I2]- catalysis reactive species has both trans- and cis-configuration. Although the potential of cis-configuration is higher than that of trans-one (by 48.16 kJ/mol), the coordination between CO and central Rh atom in cis-configuration is stronger than that in trans-configuration, so the stability of the reactive species with cis-configuration is enhanced. The calculated results show that the cis-and trans-configuration of [Rh(CO)2I2]- participate in the methanol carbonylation reaction simultaneously, and two reaction cycle exist in methanol carbonylation catalyzed by rhodium complex [Rh(CO)2I2]-., the cis-cycle and trans-cycle, respectively. (3) The further studies show that there is a linked reaction pathway, which is a switch for transition between cis- and trans-configuration [Rh(CO)2I2]- through CO decomposition mechanism. The potential barrier of the linked reaction channel is 67.85kJ/mol.2. Analysis and comparison of the reaction mechanism.Each elemental reaction has been studied at HF/LANL2DZ level for the methanol carbonylation catalyzed with cis- or trans-rhodium complex [Rh(CO)2I2]-. The geometrical structures of the reactants, intermediates, transition states and products for methanol carbonylation reaction are optimized, and the activation barriers of all the reaction are calculated, and parts of elementary reaction paths are analyzed by using the IRC theory. The main theoretical calculation results are following: (1) IRC analysis results give a comparison between the two cis- and trans-cycle processes. The two different catalytic cycles involve the four same types of reaction, the oxidative addition reaction, carbonyl insertion reaction, coordination of CO, and reductive elimination reaction. The two CH3I oxidative addition reactions in cis-catalytic cycle and trans-cycle reaction are analogous to three-center transition state. The difference of cis-reaction from trans-reaction is that, when the CH3 and I is close to the catalyst plane the different rejection to the original coordination in two cycle types will result in the different degree of structural distortion; The carbonyl insertion of elemental reaction of whether cis-cycle or trans-cycle is completed with methyl migration essentially; The product leaving mode of the reductive elimination elementary reaction in cis-cycle is different from that in trans-cycle. In the cis-reaction cycle, at beginning point, atom I and atom C are swinging and approaching each other, and then I-C bond forms and C-Rh bond breaks synchronously. On the contrary, in the trans-cycle, the atom C firstly approaches to the atom I to form I-C bond and then the atom I leaves the atom Rh to break C-Rh bond gradually; There exist two...