|Ph.D Student||Andrea Tamer|
|Subject||Organoactinide Complexes Containing CP and Non-Cp Ligands:|
Synthesis and Reactivity
|Department||Department of Chemistry||Supervisor||Professor Moris Eisen|
|Full Thesis text|
In this work we present our studies of various catalytic reactions mediated by organoactinide complexes. Despite the large number of studies that were carried out, there is still a lack of information concerning the synthesis and reactivity of actinide complexes containing other ligands than Cp* or its derivatives (Cp* = [C5(CH3)5]-). Moreover, it was believed that substrates containing oxygen motifs will cause a severe deactivation of the actinide complexes as a result of their high oxophilic nature. Therefore, such substrates were largely excluded from the field of organoactinide catalysis for long time.
The coupling reaction of terminal alkynes with t-BuNC showed high dependency on the nature of the catalyst used. With the cationic catalyst [(Et2N)3U][BPh4] the insertion of one isonitrile and one alkyne took place to give trans (α,β)-acetylenic aldimine as a major product. With Cp*2UMe2, the double insertion of two equivalents of isonitrile with one equivalent of terminal alkyne was observed in addition to the mentioned mono-insertion trans product, the ratios of mono-insertion to the double-insertion were around 90:10, respectively. When using an excess of isonitrile we were able to change this ratio down to 50:50. NOE studies on the mono-insertion acetylenic imine molecule showed that only the trans isomer was obtained with no traces of the cis adduct. These results in cooperation with kinetic studies allowed us to suggest a plausible mechanism for the mono and double insertion products.
Despite the high oxophilic nature of actinide complexes, we have found that (EtMeN)4Th and Cp*2ThMe2 are excellent catalysts for the dimerization and cross dimerization of aromatic aldehydes to give the corresponding esters, the reaction were performed at room temperature and the yields were high to moderate. The reaction was found to be highly dependent on the catalyst, the steric and electronic nature of the aldehyde; the best results were obtained when using non-Cp* complex with benzaldehydes containing electron withdrawing group at para-position such as chloride. Kinetic studies were performed and a plausible mechanism is presented.
The synthesis of new non-Cp* actinide complexes showed interesting results. The ligands were designed to introduce a high steric hindrance and hence prevent the formation of homoleptic actinide-bis(ligand) complexes. However, in contrary to known lanthanide and group 4 metal compounds containing similar ligands, some unique structures were obtained when using thorium and uranium metal centers.