The selective functionalization of saturated hydrocarbons with GIF-type systems

Abstract

The Gif-family is a group of Fe- or Cu-containing chemical systems oxidizing saturated hydrocarbons to ketones. The unusual behavior shown by these systems (secondary C-H bonds are oxidized preferentially even in the presence of tertiary and primary C-H bonds) demands further investigation of the mechanism. Studies reported in this Dissertation reveal that there are at least two distinct intermediates along the reaction pathway of the Fe-catalyzed oxidations that can be intercepted by various reagents. The interception of the first of these intermediates gives rise to a series of possibilities for the functionalization of C-H bonds, among them the formation of alkyl bromides. This process offers a unique opportunity for the comparison of free radical processes and Gif-type chemistry. Investigations show the pronounced difference in selectivity towards various hydrocarbons and the difference in relative rates of reactions with different brominating agents. The second intermediate on the reaction pathway was characterized as the alkyl hydroperoxide. The reaction of this with various reducing agents present in the mixture provides an opportunity to control the ketone/alcohol ratio of the products. The chemoselectivity of the process was examined and alkanes were found to be efficiently oxidized even in the presence of easily oxidizable co-substrates (isopropanol, isopropyl ether, ethylene glycol, etc.). The possibilities for the enhancement of the reaction rate by different ligands on the iron were studied, and a 50-100 fold acceleration was achieved with picolinic acid, the most efficient promoter of the reaction. Cu-containing systems similar in composition to the iron-based ones were examined to map the similarities and differences in the behavior of these metal catalysts. Copper was found to be as active a catalyst for the functionalization of saturated hydrocarbons as iron, although some differences in chemical reactivity towards various reagents were observable. The development of a Cu^0/O2-system provided new insights into the chemistry of alkane activation. The idea of a metal-carbon bonded intermediate was further supported by evidence from reactions with carbon monoxide: the conversion of alkanes into alkylcarboxylic acids was observed and interpreted as the insertion of a CO molecule into the metal-carbon bond.