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Title: Chiral cyclopentadienyl lanthanide and transition metal complexes
Author: Gathergood, Nicholas Keith Peter
ISNI:       0000 0001 3492 3100
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1998
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(Cp*₂)Sm(THF)₂ (CP* = 1,2,3,4,5-pentamethylcyclopentadienyl) was prepared and applied to the hydroamination/cyclization of unsaturated amines. Enantiomerically pure C₂-symmetric ligand Cp', (Cp' = 8,10-diophenyltricyclo[²,⁶]undeca-2,5-dienyl) was reacted with SmI₂(THF)₂ to form an organolanthanide complex (Cp'₂)Sm(THF)₂ which unfortunately did not catalyze the hydroamination/cyclization reaction of unsaturated amines. One suggestion we can give to account for the lack of activity of the organosamarium catalyst, is that the complex is formed as a hydride bridged dimer. Attempts to characterize the organosamarium species were not successful due to the extreme air sensitivity of the complex. Experimental inferences and observations made while carrying out the organolanthanide experiments allow us to be confident that (Cp'₂)Sm(THF)₂ was synthesized. Mixed and bis(cyclopentadienyl)titanium complexes containing C₂-symmetric ligands Cp' and Cp'' (Cp'' = 8,10-dicyclohexyltricyclo[²,⁶]undeca-2,5-dineyl) have been made and used in hydrogenation and hydrosilylation reactions. Good enantioselectivities were obtained for the bis complexes but the steric hindrance of the bulky ligands limited the type of substrate that could react. The mixed (η⁵-C₅H₅)(η⁵-Cp'')TiCl₂ complex gave a low e.e. for the hydrogenation of 2-phenyl-1-butene. We believe problems activating the titanocene complexes with n-BuLi, were the reason for the hydrogenation of imines and enamines being unsuccessful. (Cp')₂ZrCl₂ has been prepared and used in the hydrogenation of 2-phenyl-1-butene. This complex gave the highest e.e. result, at room temperature, for any organotransition metal catalyzed hydrogenation of this challenging substrate. Unfortunately the complex was too sterically bulky to perform ethylmagnesiation reactions. The mixed (η⁵-C₅H₅)(η⁵Cp'')ZrCl₂ complex was prepared in good yield, but gave poor e.e.s. in the hydrogenation of 2-phenyl-1-butene. We were pleased to find that the mixed zirconocene complex catalyzed ethylmagnesiation reactions of N-allylaniline and allyl-phenylsulphide successfully, although the enantioselectivities were low.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Samarium; Rhodium; Chiral reduction