Density Functional Theory Study on the Oxidative Addition of Chloroarenes to POP Rhodium Complexes

Abstract

The carbon-halogen (C-X) bond oxidative addition reaction of an alkyl or aryl halide to the transition metal atom of an organometallic compound is an essential step for producing partially halogenated organic molecules. 1 Partially substituted aromatic molecules have been extensively studied due to their material, pharmaceutical, and agrochemical applications. 2 The oxidative addition reaction of C-X bonds to a metal center is considered the first step of the catalytic cycle that produces partially halogenated molecules. 3 Rhodium pincer complexes have attracted considerable attention for their catalytic activities in the C C coupling reaction of aryl halides. 4 A recent study reported the oxidative addition reaction of several aryl halides to a POP Rh pincer complex (1), RhH{xant (P i Pr 2 ) 2 }, where xant(P i Pr 2 ) 2 = 9,9-dimethyl-4,5-bis-(diisopropyl-phosphino)xanthene}. 5 In the present study, density functional theoretical (DFT) computations of oxidative addition reaction of aryl halides to the POP Rh pincer complex (1) and its closely related compounds ((2) and (3), Scheme 1) were performed using the Jaguar v8.4 suite. 6 The kinetic data of the Gibbs energy of activation and 3-dimensional geometrical characteristics of the reactants, transition states (TSs), and products were examined to understand the nature of the TS and the effects of the substituents of the aromatic molecules and the transition metal complex.The computational level of B3LYP/LACVP** was selected for the reaction because that level of theory has been applied successfully to obtain the thermodynamic and kinetic characteristics of organometallic reactions to transition metal and Al complexes. 2,7 Figure 1 presents the geometrical structures of the initial weakly bound van der Waals (vdW) complexes, transition states (TS), and final oxidation reaction products between (1) (or (3)), and chlorobenzene reaction using B3LYP/ LACVP** calculation level. In the vdW complex of 1… PhCl, chlorobenzene, which interacts weakly with transition metal complex (1), lies above (1)~4.5 Å with a C Cl distance of 1.77 Å. Our calculated structure of the final oxidative addition product, 1_PhCl, shows close resemblance to the experimental X-ray structure, with a RMS deviation of 0.26 Å (heavy-atom only). 5 The calculated Rh C and Rh Cl bond lengths were 2.03 and 2.57 Å, respectively, which are close to the values from the X-ray structures of the Rh pincer complexes. 7 Owing to the steric hindrance exerted by the side chains attached to the P atoms of the POP pincer ligands, the plane of phenyl ring was in the vertical direction with respect to the P-Rh-P bonds. However, in the TS, the plane of phenyl ring is slightly tilted from C Cl axis and rotated by approximately 90 with respect to the plane containing C-Cl-Rh triangle to form Rh C (in phenyl ring) bond. 2 Our computation shows that the lengths of Rh C, Rh Cl, and C Cl bonds are 2.30, 2.60, and 1.93 Å, respectively. This means that Rh, Cl, and C atoms are simultaneously incorporated for concerted singlest...

Density functional theory study on the reductive elimination of ancillary ligand at PPC nickel complexes

“…2,3 The Gibbs free energy of activation for both reactions is not sensitive to the change in the substituents R 1 on P atoms, unlike other symmetric pincer complexes. 1 Gibbs free energy of activation for diphenylmethyl substrate is smaller than that for methyl substrate, which in good agreement with the experimental results. 2,3 For the reductive elimination reaction, C sp3 -C sp2 coupling (R 2 = Me) is slower than Reductive elimination C sp2 -C sp2 coupling (R 2 = Ph), which is found for the nonpincer type complexes.…”

“…Oxidative addition and reductive elimination reactions are essential steps in transition metal chemistry 1 . Their competing reactions, such as α‐abstraction and β‐elimination, sometimes play crucial roles in carbene (or alkylidene) complex formation and CH coupling reactions.…”

“…Hence, kinetic studies are crucial to understanding the reaction mechanism and applying the transition metal complex to the production of important coupling products. Tridentate pincer complexes have attracted considerable attention to explore the important organometallic reactions 1 . The usual ligands have a symmetric form, such as 1,3‐bis[(di‐tert‐butyl‐phosphino)methyl]benzene (PCP), and organometallic reactions usually occur between the substrates of the complexes, which is not a part of the tridentate ligand.…”

“…Oxidative addition and reductive elimination reactions are essential steps in transition metal chemistry. 1 Their competing reactions, such as α-abstraction and β-elimination, sometimes play crucial roles in carbene (or alkylidene) complex formation and C H coupling reactions. Usually, β-elimination reactions are unproductive when competing with direct reductive elimination resulting in C C coupling product.…”

“…Tridentate pincer complexes have attracted considerable attention to explore the important organometallic reactions. 1 The usual ligands have a symmetric form, such as 1,3-bis[(ditert-butyl-phosphino)methyl]benzene (PCP), and organometallic reactions usually occur between the substrates of the complexes, which is not a part of the tridentate ligand. Tridentate ligands serve as a rigid framework to ensure the arrangements of the donor atoms around the central metal.…”