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Title: Racemic-meso interconversion for ansa-scandocene and ansa-yttrocene derivatives. Molecular structures of rac-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}ScCl {center_dot} LiCl(THF){sub 2}, [meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace} Y({mu}{sub 2}-Cl)]{sub 2}, and meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}Zr(NMe{sub 2}){sub 2}

Abstract

The dilithium bis(cyclopentadienide) species Li{sub 2}{l_brace}Me{sub 2}Si[C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace} (Li{sub 2}Ip) reacts with ScCl{sub 3}(THF){sub 3} to afford rac-IpScCl{center_dot}LiCl(THF){sub 2} (1) and [meso-IpSc({mu}{sub 2}-Cl)]{sub 2} (2) and with YCl{sub 3}(THF){sub 3.5} to afford rac-IpYCl{center_dot}LiCl(THF){sub 2} (3) and [meso-IpY({mu}{sub 2}-Cl)]{sub 2} (4). Metalation with both scandium and yttrium chlorides yields the metallocene chlorides in approximately 3:1 racemic:meso ratios. Reaction of IpH{sub 2} with Zr(NMe{sub 2}){sub 4} yields exclusively meso-IpZr(NMe{sub 2}){sub 2} (9). Treatment of 1 or 2 with allylmagnesium bromide affords the allyl complexes rac-IpSc-({eta}{sup 3}-c{sub 3}H{sub 5}) (5) and meso-IpSc({eta}{sup 3}-C{sub 3}H{sub 5}) (6) and with crotylmagnesium chloride affords rac-IPSc({eta}{sup 3}-C{sub 3}H{sub 4}Me) (7) and meso-IpSc({eta}{sup 3}-C{sub 3}H{sub 4}Me) (8). Diastereomerically pure rac dichlorometalate compounds (1 or 3) or pure meso chloro dimers (2 or 4) undergo spontaneous isomerization upon dissolution in THF-d{sub s}, above 55 C, affording an equilibrium ratio of {approximately}2:1 racemic:meso isomers. While spontaneous isomerization of 5, 6, 7, or 8 is very slow at room temperature; the isomerizations are not accelerated by light. The proposed mechanism for racemic-meso isomerization involves heterolytic dissociation of one cyclopentadienide ligand from the metal, rotation around that Si-Cp{sup {minus}} bond, and recoordination on the opposite face, effecting netmore » epimerization. X-ray diffraction studies have been performed on rac-IpScCl{center_dot}LiCl(THF){sub 2} (1), [meso-IpY({mu}{sub 2}-Cl)]{sub 2} (4), and meso-IpZr(NMe{sub 2}){sub 2} (9).« less

Authors:
; ;  [1]
  1. California Inst. of Tech., Pasadena, CA (United States). Arnold and Mabel Beckman Labs. of Chemical Synthesis
Publication Date:
Sponsoring Org.:
USDOE, Washington, DC (United States); National Science Foundation, Washington, DC (United States)
OSTI Identifier:
315975
Resource Type:
Journal Article
Journal Name:
Organometallics
Additional Journal Information:
Journal Volume: 17; Journal Issue: 23; Other Information: PBD: 9 Nov 1998
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; 36 MATERIALS SCIENCE; ISOMERIZATION; MOLECULAR STRUCTURE; SCANDIUM COMPLEXES; YTTRIUM COMPLEXES; ZIRCONIUM COMPLEXES; CHLORIDES; CHEMICAL REACTION KINETICS; X-RAY DIFFRACTION

Citation Formats

Yoder, J C, Day, M W, and Bercaw, J E. Racemic-meso interconversion for ansa-scandocene and ansa-yttrocene derivatives. Molecular structures of rac-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}ScCl {center_dot} LiCl(THF){sub 2}, [meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace} Y({mu}{sub 2}-Cl)]{sub 2}, and meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}Zr(NMe{sub 2}){sub 2}. United States: N. p., 1998. Web. doi:10.1021/om980349j.
Yoder, J C, Day, M W, & Bercaw, J E. Racemic-meso interconversion for ansa-scandocene and ansa-yttrocene derivatives. Molecular structures of rac-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}ScCl {center_dot} LiCl(THF){sub 2}, [meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace} Y({mu}{sub 2}-Cl)]{sub 2}, and meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}Zr(NMe{sub 2}){sub 2}. United States. doi:10.1021/om980349j.
Yoder, J C, Day, M W, and Bercaw, J E. Mon . "Racemic-meso interconversion for ansa-scandocene and ansa-yttrocene derivatives. Molecular structures of rac-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}ScCl {center_dot} LiCl(THF){sub 2}, [meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace} Y({mu}{sub 2}-Cl)]{sub 2}, and meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}Zr(NMe{sub 2}){sub 2}". United States. doi:10.1021/om980349j.
@article{osti_315975,
title = {Racemic-meso interconversion for ansa-scandocene and ansa-yttrocene derivatives. Molecular structures of rac-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}ScCl {center_dot} LiCl(THF){sub 2}, [meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace} Y({mu}{sub 2}-Cl)]{sub 2}, and meso-{l_brace}Me{sub 2}Si[{eta}{sup 5}-C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace}Zr(NMe{sub 2}){sub 2}},
author = {Yoder, J C and Day, M W and Bercaw, J E},
abstractNote = {The dilithium bis(cyclopentadienide) species Li{sub 2}{l_brace}Me{sub 2}Si[C{sub 5}H{sub 2}-2,4-(CHMe{sub 2}){sub 2}]{sub 2}{r_brace} (Li{sub 2}Ip) reacts with ScCl{sub 3}(THF){sub 3} to afford rac-IpScCl{center_dot}LiCl(THF){sub 2} (1) and [meso-IpSc({mu}{sub 2}-Cl)]{sub 2} (2) and with YCl{sub 3}(THF){sub 3.5} to afford rac-IpYCl{center_dot}LiCl(THF){sub 2} (3) and [meso-IpY({mu}{sub 2}-Cl)]{sub 2} (4). Metalation with both scandium and yttrium chlorides yields the metallocene chlorides in approximately 3:1 racemic:meso ratios. Reaction of IpH{sub 2} with Zr(NMe{sub 2}){sub 4} yields exclusively meso-IpZr(NMe{sub 2}){sub 2} (9). Treatment of 1 or 2 with allylmagnesium bromide affords the allyl complexes rac-IpSc-({eta}{sup 3}-c{sub 3}H{sub 5}) (5) and meso-IpSc({eta}{sup 3}-C{sub 3}H{sub 5}) (6) and with crotylmagnesium chloride affords rac-IPSc({eta}{sup 3}-C{sub 3}H{sub 4}Me) (7) and meso-IpSc({eta}{sup 3}-C{sub 3}H{sub 4}Me) (8). Diastereomerically pure rac dichlorometalate compounds (1 or 3) or pure meso chloro dimers (2 or 4) undergo spontaneous isomerization upon dissolution in THF-d{sub s}, above 55 C, affording an equilibrium ratio of {approximately}2:1 racemic:meso isomers. While spontaneous isomerization of 5, 6, 7, or 8 is very slow at room temperature; the isomerizations are not accelerated by light. The proposed mechanism for racemic-meso isomerization involves heterolytic dissociation of one cyclopentadienide ligand from the metal, rotation around that Si-Cp{sup {minus}} bond, and recoordination on the opposite face, effecting net epimerization. X-ray diffraction studies have been performed on rac-IpScCl{center_dot}LiCl(THF){sub 2} (1), [meso-IpY({mu}{sub 2}-Cl)]{sub 2} (4), and meso-IpZr(NMe{sub 2}){sub 2} (9).},
doi = {10.1021/om980349j},
journal = {Organometallics},
number = 23,
volume = 17,
place = {United States},
year = {1998},
month = {11}
}