Investigation Of Some Important Physical Organic Questions In Transition Metal-Catalyzed C-C Bond Formations

Physical organic chemistry as a theoretical basis has promoted the development of organic chemistry. In the past50～60years, organometallic chemistry has been a hot topic, which was also an important research object for physical organic chemistry, especially transition metal-catalyzed methodology. In the development of organometallic chemistry, the tools and thoughts in physical organic chemistry played an important role. Moreover, the theory established from the organometallic chemistry has also enriched and improved the accepted basic theory in physical organic chemistry. The rapid improvement of organometallic chemistry was mostly attributed to the continuing revelation of the involved elementary reactions. Currently, a lot of questions are waiting to be solved urgently in organometallic chemistry. The key is to pursue an in-depth understanding of the elementary reaction. Among these different studying manners, kinetic investigation is of great importance. In this thesis, with in-situ IR as the kinetic tool, the elementary reactions involved in coupling reaction have been revealed through transition metal-catalyzed oxidative coupling as model reactions. The detailed contents are as follows:1. In Ni-catalyzed oxidative coupling of arylzinc reagents with desyl chloride as the oxidant, different kinetic behaviors of the overall reaction have been observed employing arylzinc reagent prepared from different methods. The rate-limiting step was also varied. When the arylzinc reagent was prepared from Grignard reagent, reductive elimination has been confirmed as the rate-limiting step; when the arylzinc reagent was prepared from aryllithium, transmetalation was established as the rate-limiting step. MgCl2is crucial for the variation. Kinetic results disclosed that the arylzinc reagent from Grignard reagent is more nucleophilic, which have been supported by X-ray analysis, NMR and DFT calculation. Primary discussion about the basicity for these different arylzinc reagents indicated that the arylzinc reagent from aryllithium is more basic.2. With Ni-catalyzed oxidative coupling of arylzinc reagents as the model, in which desyl chloride as the oxidant, kinetic investigation revealed that the reductive elimination of [Ar-Ni-Ar] was confirmed as the rate-limiting step when arylzinc reagent was prepared from Grignard reagent. Hence, the observed rate constants for the reductive elimination of the reactions involving different arylzinc reagents have been achieved. Furthermore, quantitative kinetic studies of the overall reaction enabled us to acquire the activation energy as a value of9.7kcal/mol for the reductive elimination of [(p-Me)Ph-Ni-(p-MePh)]. When arylzinc reagent was prepared from aryllithium reagent, kinetic investigation revealed that the transmetalation between arylzinc reagent and [Ar-Ni-R] was confirmed as the rate-limiting step employing arylzinc reagent prepared from aryllithium. Hence, the observed rate constants for the transmetalation of different arylzinc reagents have been achieved. Furthermore, quantitative kinetic studies of the overall reaction enabled us to acquire the activation energy as a value of14.6kcal/mol for the transmetalation of PhZnCl with [Ph-Ni-R].3. With Pd-catalyzed oxidative coupling of arylzinc reagent as a model, kinetic insights into Pd-catalyzed transformation involving oxygen as the oxidant were elucidated. The oxidation of Pd(0) by oxygen was established to be the rate-limiting step under the optimized conditions, while rate-limiting oxygen diffusion into the solution was ruled out. Quantitative measurement of the overall reaction enabled us to gain the activation enthalpy for this step as a value of7.8kcal/mol.