The field of organolanthanide catalysts has been a rapidly developing area of research for the past 30 years. Until recently, research was dominated by lanthanide-cyclopentadienyl (Ln-Cp) complexes. Exhaustive efforts have been devoted to the development of complexes containing the Cp ligand, however, extensive delocalization of charge within their extended aromatic system weakens the Ln-Cp bond and makes them intolerant to outside impurities. As a result, the search for alternative ligands to create stable and reactive lanthanide catalysts has emerged. In recent years the interest of N and O-donating ligands has grown. Six such ligand sets have been utilized in this thesis, bis(trimethylsilyl)amide (N{Si(Me)3}2), isopropanol (H-OPri), 2,6-di-tert-butylphenol (H-DBP) ,2,6-di-tert-butyl-4-methylphenol (H-4MeDBP)), 1,1,3,3-tetramethylguanidine (H-TMG), and 1,1,3,3-tetramethylguanidinate (TMG). The synthesis of the pre-catalysts Ln(OAr)2(TMG)(HTMG)2 (Ln = Nd, Er, Yb OAr = DBP, 4-MeDBP), Ln(OPri) (OAr)2(HTMG)2 (Ln = Nd, Er, Yb OAr = DBP, 4-MeDBP), Nd(DBP)3, and Nd(4-MeDBP)3(HTMG) proceeded through a “one pot” synthesis. Of these complexes, eleven have been characterized by single-crystal X-ray crystallography.
The synthesized complexes were then utilized as pre-catalysts in the dimerization of benzaldehyde as well as cyclohexanecarboxaldehye to their resulting carboxylic esters (Tishchenko Reaction). By determining the turn over frequency (TOF) for each reaction, the reactivity of each pre-catalyst could be monitored. From these results it was concludes that N{Si(Me)3}2 ligands, OPri ligands, and OAr ligands (OAr = DBP, 4-MeDBP) were all successful in initiating the dimerization of benzaldehe as well as cyclohexanecarboxaldehyde, whereas the TMG ligand was observed to act as a non-nucleophilic base. Three-coordinate complexes containing N{Si(Me)3}2 ligands were observed to have the highest reactivity’s while five-coordinate complexes containing OPri, OAr (OAr = DBP, 4-MeDBP), and H-TMG were also quite efficient. In observing the effects of steric bulk around the metal center, added bulk lead to a smaller TOF as a result of the increased difficulty of aldehyde coordination. The choice of Ln metal was also concluded to have an effect on the pre-catalysts reactivity when it was observed that the Nd complexes had increased turnover numbers over Er and Yb complexes in the cyclohexanecarboxaldehyde dimerization and vice versa in the benzaldehyde dimerization. Previous Ln complexes have been successful pre-catalysts for polymerization, hydrogenation, hydroboration, hydrosilylation, and hydroamination/cyclization of olefins leading us to believe that the knowledge obtained from this study could be used in additional lanthanide catalyzed transformations