New chelating ligands: Applications to hydrodenitrogenation catalysis
AuthorAnthis, Jeffrey William
AdvisorWigley, David E.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe reaction of (DIPP)₂TaCl₃(Et₂O) (6, DIPP = 2,6-(CH(CH₃)₂C₆H₃O-)) with two equivalents of 3,5-lutidine and two equivalents of Na/Hg yields the cyclometallated product (DIPP')(DIPP)TaCl(3,5-lutidine)₂ (8) in which one of the isopropyl groups on a DIPP ligand is activated to form a metallacyclopropane complex. This undesired cyclometallation activity prompted the synthesis of a linked aryloxide ligand set, 2,2 '-ethylenebis(6-isopropylphenol) (9, H₂BIPP ), which was designed to avoid the cyclometallation problem. The new H₂BIPP ligand was chelated to both titanium and tantalum to form the compounds (BIPP)TiCl₂ (16) and (BIPP)TaCl₃ (19). Several transition metal alkyl compounds were subsequently synthesized including (BIPP)TiX₂ (X = Me (17), X = benzyl (18)) and (BIPP)TaX₃ (X = Me (25), X = benzyl (24)). Initial reduction chemistry resulted in the formation of (BIPP)Ta(η⁶-C₆Et₆)Cl (31) through the reaction of 19 with two equivalents of Na/Hg and three equivalents of 3-hexyne. From the formation of 31 it was determined that sterics play a large role in the formation of η⁶-arene compounds through the cyclotrimerization of alkynes. The reaction of 31 with two equivalents of 3,5-lutidine resulted in the cyclometallation of the ethylene linker which joined the two phenoxide rings to form TaCl[(OC₆H₃Prⁱ)₂-η2(C,C)-CH=CH](3,5-lutidine)₂ (42) in moderate yield. Compound 42 could also be produced high yield in the reaction of (BIPP)TaCl₃ ( 19) with two equivalents of 3,5-lutidine and two equivalents Na/Hg. (1-[2-(5-Trifluoromethylpyridyl)]-2-hydroxy-3,5-di-t-butylbenzene) ( 45) and 2-(2-pyridyl)phenol (46) were synthesized with the intent to form a ligand set that took advantage of the cyclometallation problem by putting a pyridine functionality in the position likely to be cyclometallated. Monomeric compounds containing 45 and 46, however, were not isolable. In an effort to model the hydrodenitrogenation of pyrrole a novel tantalum-bis(η¹-pyrrolyl) compound was synthesized. The reaction of (DIPP)₃TaCl₂(Et₂O) (39) with two equivalents of lithium pyrrolide resulted in the formation of (η⁵-C₄Me₄N)TaMe₃(η¹(N)-C₄H₄N) (50) in low yield. Attempts to functionalize 50 with chloride groups resulted in the competitive removal of both pyrrolyl and DIPP ligands and, ultimately, intractable metal-containing products.
Degree ProgramGraduate College