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Synthesis of chiral bis(amidate)bis(amido) titanium and zirconium complexes for catalyzed asymmetric alkene hydroamination Wood, Mark Christopher

Abstract

Recent advances in transition metal and lanthanide catalyzed hydroamination have changed the way people think about the formation of C-N bonds. As a major contribution to this area of research, we have synthesized the first neutral group 4 precatalysts capable of enantioselective alkene hydroamination. We took advantage of a modular amidate ligand set to alter both the electronic and steric properties of the precatalysts. The amidate ligands employed in these catalysts were synthesized by reacting an axially chiral 2,2'diamino-6,6'-dimethylbiphenyl diamine with a corresponding acyl chloride or anhydride. Further reaction of the chiral amide proligand with Ti(NMe₂)₄ or Zr(NMe₂)₄, produced the bis(amidate)bis(amido) titanium and zirconium precatalysts in quantitative yields. [formula omitted] Enantioselectivity and reactivity investigations for aminoalkene hydroamination were conducted on the group 4 complexes prepared, and complex A produced the most excellent enantioselectivities. From this investigation, minor alterations to the electronic and steric properties of the ligand showed significant effects on reactivity and enantioselectivity. Further substrate scope investigations, using precatalyst A, displayed high yields, moderate reaction times and enantioselectivities up to 93% ee. Most importantly, the structural and substrate scope investigation provided a mechanistic rationale for observed trends in reactivity and enantioselectivity, yielding valuable insight for future catalyst development.

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