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Chiral cyclopentadienyl lanthanide and transition metal complexes

Chiral cyclopentadienyl lanthanide and transition metal complexes
Chiral cyclopentadienyl lanthanide and transition metal complexes

(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[5.2.2.02,6]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[5.2.2.02,6]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.

University of Southampton
Gathergood, Nicholas Keith Peter
Gathergood, Nicholas Keith Peter

Gathergood, Nicholas Keith Peter (1998) Chiral cyclopentadienyl lanthanide and transition metal complexes. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

(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[5.2.2.02,6]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[5.2.2.02,6]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.

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Published date: 1998

Identifiers

Local EPrints ID: 463563
URI: http://eprints.soton.ac.uk/id/eprint/463563
PURE UUID: 4d3d640b-db69-42e2-bb98-fca80d47dc3f

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Date deposited: 04 Jul 2022 20:53
Last modified: 04 Jul 2022 20:53

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Author: Nicholas Keith Peter Gathergood

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