In this project different transition metal C-H activations have been investigated by experiments and by computational chemistry.
Methods for performing selective chemistryon the carbon-hydrogen (C-H) bonds in alkanes would be highly beneficial for variouschemical applications, such as fuel production, fine chemical production, and novel pharmaceuticalproducts. Traditionally, C-H bonds have been thought of as inert, but progress incatalysis over the latest decades has shown thatactivation is indeed possible. This thesis investigates a number of C-H activation methods.
C-H activation is made possible by use of so-called transition metals, a group of basic chemical elements of which 23 are relevant to organic chemistry. A common feature for the transition metals is found in an electron sub-shell, the d-shell. For the transition metals the d-shell is not filled. This feature allows for one or more electrons from other compounds to reside temporarily in the d-shell. By “lending” electrons to the transition metal, these compounds will be able to engage in chemical reactions more easily. In other words, the transition metal can act as a catalyst, speeding up reactions between othercompounds.
In this project different transition metal C-H activations have been investigated by experiments, computational chemistry or a combination thereof. The palladium-catalyzed allylic C-H activation was studied with a Hammett study, determination of deuterium kinetic isotope effect (KIE) and Density Function Theory (DFT) calculations. The Hammett study showed build-up of a partial negative charge in the reaction, supporting a proton abstraction mechanism. The determined KIE values indicated that the C-H activation step was the selectivity-determining step. Using DFT calculations, the transition states for various possible C-H activation mechanisms were determined. Comparison of experimental and theoretical KIE values supported a C-H activation mechanism where acetate plays a pivotal role either as an internal or external base and the results were published in ACS Catalysis.
A palladium-catalyzed N-(2-pyridyl)sulfonyl directed C-H olefination was studied with DFT calculations. A concerted metalation-deprotonation mechanism was found most favourable for the C-H activation step. The influence of electronic effects on the C-H activation mechanism was found to qualitatively fit reported experimental results. Comparable C-H activation energy barriers were determined for aniline, benzylamine, and phenethylamine derived substrates. During an external stay at The Scripps Research Institute, a novel ruthenium-catalyzed non-directed oxidative alkenylation reaction was investigated. Finally, the product-forming steps of the palladium-catalyzed chemoselective oxidation of glycerol and 1,2-propanediol were investigated with DFT calculations.