The Reactivity of eta-2-Aminoarenes Coordinated to Tungsten via Acid Trapping

PIENKOS, JARED A.
The Reactivity of η2-Aminoarenes Coordinated to Tungsten via Acid Trapping

(Under the direction of Professor W. Dean Harman)

The Harman lab exploits π-basic metal fragments to functionalize arenes. Coordination of an aromatic molecule to a π-basic metal fragment usually occurs in an η2-fashion. In the process of complexation, the arenes are dearomatized, and the resulting ligands are able to undergo synthetic transformations that are inaccessible to the unbound, organic analogs.(1) Currently, the [TpW(NO)(PMe3)] metal fragment is used as a dearomatization reagent because of its low cost, scalability, and accessibility to a TpW(NO)(PMe3)(η2-benzene) complex. The η2-coordinated benzene can be substituted with a variety of aromatic ligands.(2)

For example, an aromatic ring with an amine moiety can be exchanged with tungsten-bound benzene and protonated in situ, forming its conjugate acid. This product, although cationic, is able to undergo a second electrophilic addition. Modifications of these bound arenes result in the formation of novel organometallic derivatives.

Friedel-Crafts, (3) hydroamination, and cyclopropanation (4) reactions have been performed on these coordinated η2-aminoarenes. In some cases, after synthetic modifications, the functionalized ligand can be removed from the metal fragment. This strategy has been used to generate cyclohexenone, amidine, and hexahydroindole derivatives.

References:
(1) Keane, J. M.; Harman, W. D. Organometallics 2005, 24, 1786.

(2) Welch, K. D.; Harrison, D. P.; Lis, E. C.; Liu, W.; Salomon, R. J.; Harman, W. D.; Myers, W. H. Organometallics 2007, 26, 2791.

(3) Pienkos, J. A.; Zottig, V. E.; Iovan, D. A.; Li, M.; Harrison, D. P.; Sabat, M.; Salomon, R. J.; Strausberg, L.; Teran, V. A.; Myers, W. H.; Harman, W. D. Organometallics 2013, 32, 691.

(4) Pienkos, J. A.; Knisely, A. T.; Liebov, B. K.; Teran, V.; Zottig, V. E.; Sabat, M.; Myers, W. H.; Harman, W. D. Organometallics 2013, 33, 267.