Organometallic complexes of tungsten and tantalum : synthesis, structure and reactivity

W(NAr)(CH-t-Bu)(CH2-t-Bu)2 (Ar = 2,6-i-Pr2C6H3) was synthesized in four steps starting from WCI6. The reaction of W(NAr)(CH-t-Bu)(CH2-t-Bu)2 with various alcohols (1-AdamantylOH, t-BuOH, ArOH, (CF3)2CHOH, (CF3)2MeCOH, CF3Me2COH, (CF3)3COH, C6F5OH) in hydrocarbon solvents gave either W(NAr)(CH-t-Bu)(CH2-t-Bu)(OR) or W(NAr)(CH2-t-Bu)3(OR) depending on the pKa of the alcohol used. W(NAr)(CH2-t-Bu)3(OR) appears to be formed when the alcohol has a relatively low pKa. W(NAr)(CH2-t-Bu)3(OR) evolves neopentane gas to give W(NAr)(CH-t-Bu)(CH2-t-Bu)(OR). The reaction between W(NAr)(CH2-t-Bu)3CI and LiOR similarly afforded W(NAr)(CH-t-Bu)(CH2-t-Bu)(OR). W(NAr)(CH-t-Bu)(CH2-t-Bu)(OR) complexes were found to be active catalysts for various metathesis reactions, with the reactivity varied in the order of OAr - OC(CF3)3 > OCMe(CF3)2 > OCMe2CF3 > OCMe3. Conversion was sometimes limited by the tendency of tungsten to form stable metallacyclobutane in the presence of ethylene, and the bimolecular decomposition of intermediate alkylidenes to yield dimeric species that contain W(IV)/W(IV) double bonds.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2006

Author dc:creator

• Lopez, Lourdes Pia H

Advisor dc:contributor.advisor

• Richard R. Schrock.

• Chemistry.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/34657

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/34657