Continued investigations of the catalytic reduction of N₂ to NH₃ by molybdenum triamidoamine complexes

A study of the effects of employing different solvents and the introduction of dihydrogen during the catalytic reduction of dinitrogen to ammonia with [HIPTN 3N]Mo complexes was completed. During a catalytic reaction, the use of different solvents including fluorobenzene, THF, and toluene did not produce catalytic turnover of ammonia from dinitrogen. The acid source used was [CollH][BAr' 4] which was soluble in each of these solvents and dihydrogen was generated. It was found that dihydrogen acts as a powerful inhibitor of the catalytic reduction of dinitrogen to ammonia. In hopes of isolating species relevant to the proposed structures of [HIPTN 3N]MoH2, where an amide arm has become unbound from the metal center, [HIPTN 3N]MoPMe 3 was investigated. [HIPTN3N]MoPMe3 can be synthesized cleanly and oxidized to [HIPTN 3N]MoPMe 3[BAr'4] by treatment with H[(Et 20) 2][BAr'4]. An interesting species, [HIPTN 3N]Mo(H)PMe 3 was developed which was unstable in vacuo. The JPH value for the molybdenum hydride was 111 Hz, which is higher than a typical M(H)PMe3 JPH. [HIPTN 3N]W(H)PMe 3 was synthesized in an effort to elucidate the nature of the metal phosphine and metal hydride binding. The JPH was found to be 117 Hz for [HIPTN 3N]W(H)PMe 3. The JWH 12.5 Hz and Jwp = 119 Hz values for [HIPTN 3N]W(H)PMe 3 suggested that the hydride and phosphine were bound to the tungsten center, and that the phosphine and hydride have some interaction. New ligand systems based on a C, symmetric framework were also explored. [(TerPh)HIPT 2N3N]Mo complexes were synthesized but provided no catalytic reduction of dinitrogen to ammonia. The decomposition of [(TerPh)HIPT 2N3N]MoN 2H was found to be slower (t1/2 = 15 hours) than previously investigated C, symmetric [N3N] complexes (< 10 minutes). A new electron donating symmetric ligand based on the [HIPTN 3N]Mo was synthesized containing a methoxy group, [pMeOHIPTN 3N]Mo. This complex was shown to reduce dinitrogen to ammonia catalytically (6.5 equiv.). Other symmetric species, [DTBATN3N]Mo and [DTBAN3N]MoN, were developed and found to be crystalline but not catalytically active in the reduction of dinitrogen to ammonia. Thesis Supervisor:

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2011

Author dc:creator

• Hanna, Brian S. (Brian Stewart)

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/1721.1/65268

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/65268