Aryl-Substituted Imino-N-Heterocyclic Carbene Complexes Of Late Transition Metals: Synthesis and Reactivity Studies
Abstract
N-heterocyclic carbenes (NHCs) have found enormous success as ancillary ligands in catalysts in many areas of organometallic chemistry. Surprisingly, their use in olefin polymerization, until recently, was not widely explored. The focus of this thesis is to investigate the synthesis of a bidentate ligand scaffold that incorporates an NHC moiety and to study the ability of the resulting complexes to catalyze chemical transformations such as olefin polymerization.
The synthesis and characterization of several N-aryl substituted imino-imidazolin-2-ylidene (C^ImineR) ligand precursors was achieved following one of two synthetic protocols. Coordination of these ligands was explored with Group 11 metals in order to develop synthetic protocols which were later extended to prepare complexes of ruthenium, cobalt, iron, nickel, palladium and zinc.
The coordination of C^ImineR ligands to nickel using new copper carbene dimers as the transmetalating agent was established. All the nickel complexes were structurally characterized and the size of the iminic carbon substituent was found to have a profound impact on the bond angles and bond lengths around the metal center. However, when tested for ethylene polymerization activity at standard temperature and pressure, the nickel complexes were found to be inactive.
With the discovery the nickel complexes of these C^ImineR ligands were inactive for ethylene polymerization, the research focus was extended to the diamagnetic palladium-methyl complexes in order to gain insight into their thermal stability and insertion chemistry. The nature of the iminic substituent profoundly affects the thermal stability of the neutral palladium complexes. While inactive for ethylene polymerization, these palladium methyl complexes react with CO and isocyanides to form various coordination and insertion products.
The synthesis and characterization of several N-aryl substituted imino-imidazolin-2-ylidene (C^ImineR) ligand precursors was achieved following one of two synthetic protocols. Coordination of these ligands was explored with Group 11 metals in order to develop synthetic protocols which were later extended to prepare complexes of ruthenium, cobalt, iron, nickel, palladium and zinc.
The coordination of C^ImineR ligands to nickel using new copper carbene dimers as the transmetalating agent was established. All the nickel complexes were structurally characterized and the size of the iminic carbon substituent was found to have a profound impact on the bond angles and bond lengths around the metal center. However, when tested for ethylene polymerization activity at standard temperature and pressure, the nickel complexes were found to be inactive.
With the discovery the nickel complexes of these C^ImineR ligands were inactive for ethylene polymerization, the research focus was extended to the diamagnetic palladium-methyl complexes in order to gain insight into their thermal stability and insertion chemistry. The nature of the iminic substituent profoundly affects the thermal stability of the neutral palladium complexes. While inactive for ethylene polymerization, these palladium methyl complexes react with CO and isocyanides to form various coordination and insertion products.