TY - JOUR
T1 - Alane-centered ring expansion of n-heterocyclic carbenes
AU - Anker, Mathew D.
AU - Colebatch, Annie L.
AU - Iversen, Kalon J.
AU - Wilson, David J.D.
AU - Dutton, Jason L.
AU - García, Lucía
AU - Hill, Michael S.
AU - Liptrot, David J.
AU - Mahon, Mary F.
N1 - Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/3/27
Y1 - 2017/3/27
N2 - The β-diketiminato aluminum dihydrides, [HC{(Me)-CNAr}2AlH2] [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}2AlCH2(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-isopropylphenyl)imidazol-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}2AlCH2(N(Ph)CH)2]. Although compound 5 also does not react with IPr, relaxation of the steric demands of the supporting β-diketiminate ligand to N-mesityl substitution enables analogous ring opening of IMes, with the formation of [HC{(Me)CNMes}2AlCH2(N(Mes)CH)2] (7), when the reaction is heated to 80 °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 fourcoordinate adducts as well as the augmented hydridic character of the Al-H bonds within the β-diketiminate-supported molecules.
AB - The β-diketiminato aluminum dihydrides, [HC{(Me)-CNAr}2AlH2] [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}2AlCH2(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-isopropylphenyl)imidazol-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}2AlCH2(N(Ph)CH)2]. Although compound 5 also does not react with IPr, relaxation of the steric demands of the supporting β-diketiminate ligand to N-mesityl substitution enables analogous ring opening of IMes, with the formation of [HC{(Me)CNMes}2AlCH2(N(Mes)CH)2] (7), when the reaction is heated to 80 °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 fourcoordinate adducts as well as the augmented hydridic character of the Al-H bonds within the β-diketiminate-supported molecules.
UR - http://www.scopus.com/inward/record.url?scp=85022173720&partnerID=8YFLogxK
U2 - 10.1021/acs.organomet.7b00056
DO - 10.1021/acs.organomet.7b00056
M3 - Article
SN - 0276-7333
VL - 36
SP - 1173
EP - 1178
JO - Organometallics
JF - Organometallics
IS - 6
ER -