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.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/282676 |
| Date | January 1998 |
| Creators | Briggs, Paula Marie, 1971- |
| Contributors | Wigley, David |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| 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. |
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