Alane-Centered Ring Expansion of N-Heterocyclic Carbenes

Mathew D. Anker, Annie L. Colebatch, Kalon Iverson, David J. D. Wilson, Jason Dutton, Lucia Garcia Rodriguez, Michael Hill, David Liptrot, Mary Mahon

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16 Citations (Scopus)

Abstract

The beta-diketiminato aluminum dihydrides, [HC{(Me)-CNAr}(2)AlH2] [4: Ar = 2,6-di-isopropylphenyl (Dipp), 5: 2,4,6-trimethylphenyl (Mes)] react directly with N-aryl-substituted N-heterocyclic carbenes (NHCs) by C-N bond activation to afford aluminum amido-alkyl derivatives of the form [HC{(Me)-CNAr}(2)AlCH2(N(Ar')CH)(2)]. The more sterically congested alane (4), bearing N-Dipp substitution, does not react with either 1,3-bis(2,6-di-isopropylphenAimidazol-2-ylidene (IPr) or 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), even under forcing conditions. In contrast, in situ generation of 1,3-bis(phenyl)imidazol-2-ylidene through deprotonation of the corresponding imidazolium tetrafluoroborate by KN(SiMe3)(2) in the presence of compound 4 provides facile ring opening of the NHC at room temperature to yield [HC{(Me)CNDipp}(2)AlCH2(N(Ph)CH)(2)]. Although compound 5 also does not react with IPr, relaxation of the steric demands of the supporting beta-diketiminate ligand to N-mesityl substitution enables analogous ring opening of IMes, with the formation of [HC{(Me)CNMes}(2)AlCH2(N(Mes)CH)(2)] (7), when the reaction is heated to 80 degrees C. DFT calculations performed on model systems suggest that in comparison to the parent alane (AlH3) the enhanced propensity of these systems to induce NHC ring cleavage is a consequence of the relative stability of the initially formed five- and four-coordinate adducts as well as the augmented hydridic character of the Al-H bonds within the beta-diketiminate-supported molecules.
Original languageEnglish
Pages (from-to)1173-1178
Number of pages6
JournalOrganometallics
Volume36
Issue number6
Early online date3 Mar 2017
DOIs
Publication statusPublished - 27 Mar 2017

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    Anker, M. D., Colebatch, A. L., Iverson, K., Wilson, D. J. D., Dutton, J., Garcia Rodriguez, L., Hill, M., Liptrot, D., & Mahon, M. (2017). Alane-Centered Ring Expansion of N-Heterocyclic Carbenes. Organometallics, 36(6), 1173-1178. https://doi.org/10.1021/acs.organomet.7b00056