Synthesis, Characterization and Protonolysis mechanistic studies of diimine Pt diphenyl complexes of relevance to C‐H activation

Abstract

Catalysis by platinum Pt and other noble metals is involved in industrial processes that convert petroleum and natural gas resources to useful fuels and other value-added chemicals. The cleavage of carbon-hydrogen bonds in hydrocarbons is of crucial importance in these processes. The C-H bonds are very strong, and the metals are needed because they assist the cleavage of these bonds. The research group of professor Tilset at the UiO Department of Chemistry has focused on how such C-H bond cleavage reactions occur, i.e. to establish the reaction mechanisms. Jerome Parmene, as a member of this group, has taken this research into new directions. Significant parts of his work have been conducted in collaboration with professor van Eldik’s group at Erlangen University, Germany. The two groups have combined their expertise to undertake mechanistic and kinetic studies with the use of state-of-the-art NMR and UV-visible-light spectroscopy. Parmene has synthesized and characterized a range of new Pt complexes in the Oslo laboratories. The reactions of these Pt diphenyl complexes with strong acids have been studied by the using the complementary techniques available in Oslo and Erlangen. The combined efforts have provided a much improved mechanistic understanding. It has been clearly shown how electronic and steric effects of the ligands that are bonded to the metal affect the way that these reactions proceed. It is concluded that protonation of neutral diimine Pt diphenyl complexes takes place at the metal, rather than at the phenyl groups. This issue was highly debated prior to this work. When acetonitrile, a strongly coordinating ligand, is present, unstable cationic hexacoordinate Pt hydride complexes are formed. In the absence of acetonitrile, unstable Pt phenyl π-benzene complexes are obtained. Both types of complexes liberate benzene when heated. The two benzene-producing reactions have been thoroughly studied and proceed by quite different mechanisms. The findings may assist the development of new and improved catalysts that will have practical applications.