|Ph.D Student||Barnea Eyal|
Synthesis, Characterization and Reactivity
|Department||Department of Chemistry||Supervisor||Professor Moris Eisen|
Organoactinide complexes are known to be good catalysts for a number of processes such as oligomerization, hydroamination and hydrosilylation of terminal alkynes. However there is still a lack of information regarding the catalytic behavior of these highly oxophilic complexes with oxygen containing substrates. The common belief was that if oxygen containing substrates will be introduced, a decrease in activity will be expected, due to the high oxophilic nature of the early actinides. Hence, oxygen containing environments will promote the deactivation of the complexes or the destruction of the metal-ancillary ligands bonds.
This work describes three independent studies on new reactivities of organoactinides. In the first part, the use of the organoactinide complex Cp2*ThMe2 (Cp* = pentamethylcyclopentadienyl) for the coupling reaction of terminal alkynes and isonitriles is reported. The products of such reactions, acetylenic aldimines, have attracted large attention as important synthons in organic synthesis. The research focused on the study of the reaction scope, regioselectivity, kinetics of the catalytic reaction and temperature effect. Based on the results a plausible mechanism is presented, which involves a 1,1 insertion of the isonitriles carbon into the Th-acetylide bond as the rate determining step of the reaction.
Another attempt was directed at the hydroboration of terminal alkynes with catecholborane (HBcat), an important reaction leading to production of Z-disubstituted alkenes or aldehydes. We have found that Cp2*ThMe2 catalyzed the reaction, but with no added value over known transition metal complexes. However, during the reaction the formation of a crystalline material was observed. This compound was a novel organoactinide inclusion complex, where the metal is encapsulated by a 15-membered trianionic-tribenzo-triborate macrocycle built from alternating catechol and catecholborate fragments. Further studies resulted in the characterization of analogue inclusion complexes for U, Nd, Sm and Zr. We have also found that the reaction of HBcat or pinacolborane with several organolanthanide precursors yielded organolanthanide-Chloride clusters. Few of the inclusion complexes were found to be active (although with poor reactivity) in the oligomerization of e-caprolactone.
In the third research area we found that despite their high oxophilic nature, the organo actinide complexes Cp2*AnMe2 (An = Th, U) and the cationic complex [U(NEt2)3][BPh4] are excellent precursors for the polymerization of e-caprolactone and L-lactide. Polymerizations with the three catalysts afforded high molecular with polyesters, usually with very narrow molecular weight distribution. The effect of solvent, temperature and catalyst : monomer ratio were all studied and are presented in this work.