Date of Award
Doctor of Philosophy
L. Keith Woo
Metalloporphyrins have long been used as catalysts. Rhodium(III) porphyrin complexes are effective catalysts for cyclopropanation and C-H insertion reactions. The mechanism of rhodium(III) porphyrin catalyzed cyclopropanation has been extensively studied. However, the use of group 8 metalloporphyrins as cyclopropanation catalysts has not received much attention until recently;Group 8 metalloporphyrins are excellent catalysts for cyclopropanation reactions. Iron(II) porphyrins catalyze the cyclopropanation of olefins using diazo reagents with high turnover numbers and diastereoselectivities. A commonly employed diazo reagent, ethyl diazoacetate, yields cyclopropyl esters in the presence of styrene derivatives and iron(II) porphyrins. The diastereoselectivity of the iron(II) porphyrin-catalyzed cyclopropanation reaction can be controlled by choice of solvent and reaction temperature. Higher trans/cis ratios for the cyclopropane products were obtained at low temperatures and in donor solvents such as tetrahydrofuran. Ratios of trans/cis cyclopropanes as high as 13:1 were achieved at room temperature. The related iron(II) tetramethyldibenzotetraazaannulene complex failed to give significant yields of cyclopropanes with ethyl diazoacetate. However, using aryldiazomethanes, cyclopropanes were generated in high yield with high diastereoselectivities in the presence of either iron(II) porphyrins or tetramethyldibenzotetraazaannulenes. When the diazo reagent is p-tolyldiazomethane, the trans-cyclopropane isomer was the major product. However, mesityldiazomethane resulted in the cis-isomer as the predominant product. The porphyrin-based catalysts produced higher diastereoselectivities than the tetramethyldibenzotetraazaannulene-based catalysts;Osmium(II) porphyrins were also active cyclopropanation catalysts. The scope and mechanism of the [(TTP)OS]2-catalyzed cyclopropanation reaction were investigated. A battery of mechanistic studies most consistently implicate a trans-biscarbene complex of osmium(II) as the active catalyst;The complex (TTP)Os(CO) was a catalyst for the insertion of dimethyl diazomalonate into benzylic C-H bonds, giving benzyl malonates in high yield. This dissertation focuses on aspects of osmium- and iron-catalyzed reactions of diazo reagents with olefins and benzyl compounds.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Christopher G. Hamaker
Hamaker, Christopher G., "Transition metal-mediated reactions of diazo reagents: cyclopropanation and insertion into benzylic C-H bonds " (1999). Retrospective Theses and Dissertations. 12199.