Syntheses and characterization of compounds of niobium and tantalum with phenylimido and phenoxide ligation.

Persistent Link:
http://hdl.handle.net/10150/185669
Title:
Syntheses and characterization of compounds of niobium and tantalum with phenylimido and phenoxide ligation.
Author:
Smith, David Paul.
Issue Date:
1991
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The metallacyclopentadiene (DIPp)₂CITa(CCMe₃=CHCH=CCMe₃) (α, α') (DIPP=2,6-diisopropylphenoxide) is isolated from the 2 electron reduction of Ta(DIPP)₂CI₃(OEt₂) in the presence of excess Me₃CC=CH. The α, α' isomer represents the kinetic product of this reaction since it can be thermolyzed to produce (DIPP)₂CITa(CCMe₃=CHCCMe₃=CH) (α, β’). The reactivity of these two isomers toward the addition of ethylene and alkynes has been investigated and found to be driven primarily by steric effects with the less hindered α, β’ isomer showing a more comprehensive chemistry. The rearrangement of α, α' to α, β’ was followed through several kinetic and mechanistic studies. This data support a mechanism involving dissociation of the a,a' isomer to the metallacyclopropene, (DIPP)₂CITa(HC=CCMe₃), and free Me₃CC=CH. These intermediates then recouple to form the thermodynamic product, the α, β’ isomer. The reaction of TA(DIPP)₃Cl₂(OEt₂) with quinoline or 6-methylquinoline (HC) produces the ligand exchange product (η¹-HC)Ta(DIPP)₃CI₂, the 2 electron reduction of either of these products yields [η²-(N,C)-HC]Ta(DIPP)₃ which can be isolated as the phosphine complex [η²-(N,C)-HC]Ta(DIPP)₃(PMe₃) upon reaction with trimethylphosphine. The reaction of either [η²-(N,C)-quinoline]Ta(DIPP)₃ or [η²-(N,C)quinoline] Ta(DIPP)₃(PMe₃) with hydrogen both in the presence and absence of Pd/C produces 1,2,3,4-tetrahydroquinoline and 2,2'-bisquinoline. The production of these compounds implicates the η²-(N,C) bonding mode in selective hydrogenation of heterocycles and ortho functionalization. The reaction of Nb(NEt₂)₂CI₃ with two equivalents of LiNHMes (Mes=2,4,6- C₆H₂Me₃) followed by addition of pyridine produces Nb(NMes)₂CI(py)₂. The reaction of Nb(NEt₂)₂CI₃ with 6 equivalents of LiNHMes produces the first tris imido complex of group 5, [(THF)₂Li][Nb(NMes)₃(NHMes)]. Comparable chemistry is seen with Ta. [(THF)₂Li][Nb(NMes)₃(NHMes)] reacts with lithium alkyls under kinetic conditions to produce [(THF)2Li][Nb(NMes)₃(R)] (R=Me, ⁿSu, ᵗSu, Me₃SiCH₂). Under thermodynamic conditions, however, the reaction of [(THF)₂Li][Nb(NMes)₃(NHMes)] with ᵗBuLi yields the first tetrakis imido complex of group 5, [(THF)₄Li₃][Nb(NMes)₄]
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Dissertations, Academic; Chemistry, Analytic
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemistry; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Wigley, David E.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleSyntheses and characterization of compounds of niobium and tantalum with phenylimido and phenoxide ligation.en_US
dc.creatorSmith, David Paul.en_US
dc.contributor.authorSmith, David Paul.en_US
dc.date.issued1991en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe metallacyclopentadiene (DIPp)₂CITa(CCMe₃=CHCH=CCMe₃) (α, α') (DIPP=2,6-diisopropylphenoxide) is isolated from the 2 electron reduction of Ta(DIPP)₂CI₃(OEt₂) in the presence of excess Me₃CC=CH. The α, α' isomer represents the kinetic product of this reaction since it can be thermolyzed to produce (DIPP)₂CITa(CCMe₃=CHCCMe₃=CH) (α, β’). The reactivity of these two isomers toward the addition of ethylene and alkynes has been investigated and found to be driven primarily by steric effects with the less hindered α, β’ isomer showing a more comprehensive chemistry. The rearrangement of α, α' to α, β’ was followed through several kinetic and mechanistic studies. This data support a mechanism involving dissociation of the a,a' isomer to the metallacyclopropene, (DIPP)₂CITa(HC=CCMe₃), and free Me₃CC=CH. These intermediates then recouple to form the thermodynamic product, the α, β’ isomer. The reaction of TA(DIPP)₃Cl₂(OEt₂) with quinoline or 6-methylquinoline (HC) produces the ligand exchange product (η¹-HC)Ta(DIPP)₃CI₂, the 2 electron reduction of either of these products yields [η²-(N,C)-HC]Ta(DIPP)₃ which can be isolated as the phosphine complex [η²-(N,C)-HC]Ta(DIPP)₃(PMe₃) upon reaction with trimethylphosphine. The reaction of either [η²-(N,C)-quinoline]Ta(DIPP)₃ or [η²-(N,C)quinoline] Ta(DIPP)₃(PMe₃) with hydrogen both in the presence and absence of Pd/C produces 1,2,3,4-tetrahydroquinoline and 2,2'-bisquinoline. The production of these compounds implicates the η²-(N,C) bonding mode in selective hydrogenation of heterocycles and ortho functionalization. The reaction of Nb(NEt₂)₂CI₃ with two equivalents of LiNHMes (Mes=2,4,6- C₆H₂Me₃) followed by addition of pyridine produces Nb(NMes)₂CI(py)₂. The reaction of Nb(NEt₂)₂CI₃ with 6 equivalents of LiNHMes produces the first tris imido complex of group 5, [(THF)₂Li][Nb(NMes)₃(NHMes)]. Comparable chemistry is seen with Ta. [(THF)₂Li][Nb(NMes)₃(NHMes)] reacts with lithium alkyls under kinetic conditions to produce [(THF)2Li][Nb(NMes)₃(R)] (R=Me, ⁿSu, ᵗSu, Me₃SiCH₂). Under thermodynamic conditions, however, the reaction of [(THF)₂Li][Nb(NMes)₃(NHMes)] with ᵗBuLi yields the first tetrakis imido complex of group 5, [(THF)₄Li₃][Nb(NMes)₄]en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectDissertations, Academicen_US
dc.subjectChemistry, Analyticen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorWigley, David E.en_US
dc.contributor.committeememberEnemark, John H.en_US
dc.contributor.committeememberLichtenberger, Dennis L.en_US
dc.contributor.committeememberPoll, Robin L.en_US
dc.contributor.committeememberKukolich, Steven G.en_US
dc.identifier.proquest9210278en_US
dc.identifier.oclc711903010en_US
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