Open Collections

Early and late transition metal complexes featuring 1,3-N,O-chelates : development of homogenous catalysts for the α-alkylation of amines via hydroaminoalkylation

University of British Columbia

This thesis details the development of transition-metal complexes that are utilized as precatalysts for catalytic hydroaminoalkylation chemistry. Hydroaminoalkylation is the activation of an α-C(sp³)–H of an amine, and subsequent addition across a C–C unsaturation. This results in α-alkylated amines in a 100% atom-economical reaction, while avoiding amine protection/deprotection strategies. A series of 2-pyridonate chloro tris(dimethylamido) tantalum complexes have been synthesized and tested for the hydroaminoalkylation of alkenes with secondary amines. These complexes were found to exhibit high reactivity for a broad range of internal alkene substrates and represent the first, general hydroaminoalkylation of cyclic and linear internal alkenes that occurs without isomerization of the C=C double bond. Further study supports the assertion that minimized steric parameters of the 2-pyridonate and chloro ligands allow for reactivity with sterically demanding internal alkenes. Kinetic studies and deuterium labeling experiments reveal a complex kinetic profile and provide evidence for off-cycle equilibria that dominate catalytic activity. Complementary to this work, an alternative 1,3-N,O-chelating phosphoramidate ligand framework was explored to synthesize Nb complexes for hydroaminoalkylation. A variety of monophosphoramidate tetrakis(dimethylamido) Nb complexes were synthesized, as well as bis(phosphoramidate) niobaziridines, which are proposed as intermediates for the hydroaminoalkylation mechanism. The optimal precatalyst system was found to be an in situ preparation of 2:1 phosphoramide:Nb(NMe₂)₅. This offers comparable results to analogous phosphoramidate Ta complexes, but with a significantly different phosphoramidate ligand set. New cationic complexes of Ru, Rh, and Ir were synthesized featuring a bidentate κ²- P,N- phosphino-2-pyridonate ligand. These complexes were not viable precatalysts for hydroaminoalkylation, but were found to promote the stoichiometric dehydrogenation of amines to generate cationic metal hydrides. Analogous cationic complexes of 1,3-N,O-chelating 2- pyridonate complexes were prepared in situ and were found to catalyzed the reaction of dibenzylamine to tribenzylamine. A 2-pyridonate Ru complex was found to catalyze the dehydrogenation of benzylamine to the corresponding imine in the presence of isoprene, which acted as the hydrogen acceptor. Attempted hydroaminoalkylation reactions with non-arene supported 2-pyridonate complexes did not result in catalysis. These results provide insight into the use of late-transition metal complexes in amine activation and reactivity.

Text

2019-04-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/65740

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/