UBC Theses and Dissertations
Intermolecular hydroamination of allenes and the synthesis of new zirconium and titanium amido complexes Ayinla, Rashidat Omolabake
A bulky bis(amidate)-bis(amido) titanium complex 38 serves as a precatalyst for the intermolecular hydroamination of allenes. Reaction of benzylallene and phenylallene with aryl- and alkylamines produces branched imines in good yield. The resultant imines were either reduced to amines or hydrolyzed to ketones for full characterization. Methoxyallene and 2,6-dimethylphenoxyallene also react with aryl- and alkylamines in good yield. However, with these substrates another regioisomer (allylamines, the unbranched products) are observed as the major products with all amines except 2,6- dimethylaniline. In this case, the branched imine is observed as the sole product. The change in regioselectivity is probably due to coordination of the oxygen to the metal catalyst, which then directs the addition of the nitrogen functionality to carbon 3 of the allene. This coordination is presumably absent with the bulky 2,6-dimethylaniline. Ether amines obtained after reduction of the ether imine products from oxyallene hydroamination serve as precursors to new N,0 chelating ligands for the formation of titanium and zirconium amido complexes. The reaction of one equivalent of proligand with one equivalent of Zr(NMe₂)₄ or Ti(TSlMe₂)₄ results in new group 4 complexes with N,0 chelating five-membered metallacycles. X-ray crystallographic studies show all complexes to be of distorted trigonal bipyramidal geometry with a dative bond between the oxygen atom and the metal centre. These new complexes are effective precatalysts for the intramolecular hydroamination/cyclization of aminoalkenes. The aminoalkenes 2,2-diphenyl-4-pentenylamine, 2,2-dimethyl-4-pentenylamine, and 2,2-diphenyl-5- hexenylamine were converted to either pyrrolidines or piperidines in good yield.
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