Synthesis, reactivity and structural studies of early transition metal alkyl and alkylidene complexes in pi-loaded environments

Persistent Link:
http://hdl.handle.net/10150/282676
Title:
Synthesis, reactivity and structural studies of early transition metal alkyl and alkylidene complexes in pi-loaded environments
Author:
Briggs, Paula Marie, 1971-
Issue Date:
1998
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:
Cyclopentadienyl bis(imido) complexes of molybdenum, prepared from Mo(=NAr)₂Cl₂(THF)₂ (Ar = 2,6-diisopropylphenyl) and one equivalent NaCp or LiCp’ [Cp=η⁵- C₅H₅ (1), Cp’ = η⁵- C₅H₄CH₃ (7)], are described. These complexes undergo metathesis with alkyl Gringard reagents to produce the alkyl derivatives CpMo(=NAr)₂R [R = Me (2), Et (3), ⁱPr (4), allyl (5)] or Cp’Mo(=NAr)₂Me (8). Complexes 1-8 do not exhibit reactivity similar to their isolobal tris(imido) analogs and are unreactive towards additional electrophiles and nucleophiles under a variety of conditions. An unprecedented terminal cyclopentadienylidene complex of tantalum has been formed from reacting CpTa(NEt)₂Cl₂ (11) and 2 equivalents MeLi. Deuterium labeling studies show that CpTa(NEt₂)₂(=CC₄H₄) (12) is formed via a pathway that involves intermolecular C-W bond activation of a C₅H₅ ligand. Complex 12 is observed to undergo thermally induced intramolecular β-H abstraction from an ancillary NEt₂ ligand to eliminate the organic imine EtN=CHMe (23) and produce the tantalocene hydride complex (η⁵- C₅H₅)₂Ta(η²-EtN=CHMe)H (22). [Zr(μ-NAr)Me₂(THF)]₂ (26), Zr(=NAr) Me₂py₂ (27) and W(=NAr’)₂Me₂py (28, Ar’ = 2,6-dimethylphenyl) represent the first dimethyl complexes of these respective classes of early transition metal imido compounds. Complexes 26-28 are observed to contain nucleophilic imido nitrogens. Thus, Zr(=NAr)Me₂py₂ (27) reacts with 2 equivalents of H₂NAr to produce the previously synthesized Zr(=NAr)(NHAr)₂py₂ but the reaction of 27 with HOAr’ results in the elimination of CH₄. W(=NAr’)₂Me₂py (28) reacts with HOAr’ and H₂NAr in reactions that releases an imido ligand from the complex as aniline. Complexes 26-28 react with H⁻ sources to provide unidentifiable organometallic products, CH₄, and in the case of W(=NAr’)₂Me₂py, H₂NAr. The insertion of ᵗBuN=C into one of the W-Me bonds of complex 28 to give the η²-iminoacyl product W(=NAr’)₂Me(η²-C(=NᵗBu)Mepy (31). The relevance of these complexes and reactions to the fundamental C-N bond scission and heterocycle degradation steps in hydrodenitrogenation catalysis will be described.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Chemistry, Inorganic.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Wigley, David

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleSynthesis, reactivity and structural studies of early transition metal alkyl and alkylidene complexes in pi-loaded environmentsen_US
dc.creatorBriggs, Paula Marie, 1971-en_US
dc.contributor.authorBriggs, Paula Marie, 1971-en_US
dc.date.issued1998en_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.abstractCyclopentadienyl bis(imido) complexes of molybdenum, prepared from Mo(=NAr)₂Cl₂(THF)₂ (Ar = 2,6-diisopropylphenyl) and one equivalent NaCp or LiCp’ [Cp=η⁵- C₅H₅ (1), Cp’ = η⁵- C₅H₄CH₃ (7)], are described. These complexes undergo metathesis with alkyl Gringard reagents to produce the alkyl derivatives CpMo(=NAr)₂R [R = Me (2), Et (3), ⁱPr (4), allyl (5)] or Cp’Mo(=NAr)₂Me (8). Complexes 1-8 do not exhibit reactivity similar to their isolobal tris(imido) analogs and are unreactive towards additional electrophiles and nucleophiles under a variety of conditions. An unprecedented terminal cyclopentadienylidene complex of tantalum has been formed from reacting CpTa(NEt)₂Cl₂ (11) and 2 equivalents MeLi. Deuterium labeling studies show that CpTa(NEt₂)₂(=CC₄H₄) (12) is formed via a pathway that involves intermolecular C-W bond activation of a C₅H₅ ligand. Complex 12 is observed to undergo thermally induced intramolecular β-H abstraction from an ancillary NEt₂ ligand to eliminate the organic imine EtN=CHMe (23) and produce the tantalocene hydride complex (η⁵- C₅H₅)₂Ta(η²-EtN=CHMe)H (22). [Zr(μ-NAr)Me₂(THF)]₂ (26), Zr(=NAr) Me₂py₂ (27) and W(=NAr’)₂Me₂py (28, Ar’ = 2,6-dimethylphenyl) represent the first dimethyl complexes of these respective classes of early transition metal imido compounds. Complexes 26-28 are observed to contain nucleophilic imido nitrogens. Thus, Zr(=NAr)Me₂py₂ (27) reacts with 2 equivalents of H₂NAr to produce the previously synthesized Zr(=NAr)(NHAr)₂py₂ but the reaction of 27 with HOAr’ results in the elimination of CH₄. W(=NAr’)₂Me₂py (28) reacts with HOAr’ and H₂NAr in reactions that releases an imido ligand from the complex as aniline. Complexes 26-28 react with H⁻ sources to provide unidentifiable organometallic products, CH₄, and in the case of W(=NAr’)₂Me₂py, H₂NAr. The insertion of ᵗBuN=C into one of the W-Me bonds of complex 28 to give the η²-iminoacyl product W(=NAr’)₂Me(η²-C(=NᵗBu)Mepy (31). The relevance of these complexes and reactions to the fundamental C-N bond scission and heterocycle degradation steps in hydrodenitrogenation catalysis will be described.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectChemistry, Inorganic.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorWigley, Daviden_US
dc.identifier.proquest9831853en_US
dc.identifier.bibrecord.b38650046en_US
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