Heck reaction of alkyl halides and α-selective heck reaction of styrenes
Date of Issue2014
School of Physical and Mathematical Sciences
My graduate study has been focused on the development of transition metal-catalyzed reactions, especially Pd-catalyzed coupling reactions. In this thesis, we described two catalytic systems that solved challenging problems in the intermolecular Heck reaction. In the first part, we disclosed a new catalyst – Pd/dnpf can efficiently catalyze the Heck reaction of aryl and vinyl triflates with aromatic olefins. In most cases, the aryl or vinyl groups insert selectively at α position in >95% purity and the minor isomers can be removed after purification by flash chromatography. We conducted both experimental and computational study to probe the origin of high internal selectivity. The study revealed that the generality and selectivity is attributed to the combination of electronic and steric effects derived from our new ligand – dnpf. The resulting rigid and congested coordination sphere sterically disfavors the terminal insertion. The initial results of aryl bromides unfolded the potential of the newly-developed ligand for more reactions. In the second part, we disclosed an efficient catalyst – Pd/dppf for the intermolecular Heck reaction of alkyl halides, which is a challenging problem in palladium catalysis. The simple and easily accessible Pd/dppf catalyst showed good reactivity as well as good selectivity. The use of dppf as supporting ligand was crucial for our success in this reaction as other ligands failed to afford the product in a satisfactory yield. It can be applied to a broad spectrum of electrophiles including alkyl iodides, bromides and chlorides. Both primary and secondary alkyl halides bearing functional groups such as esters, amides and nitriles were tolerated in the catalytic system. Concerning the scope of olefins, vinylarenes of steric and electronic perturbations coupled well. We conducted mechanistic study to probe the reaction mechanism and the experimental data suggested that the reaction was initiated by a single electron transfer from Pd(0)-complex to alkyl halides.