Normal-to-Abnormal NHC Rearrangement of Al(III) , Ga(III) , and In(III) Trialkyl Complexes: Scope, Mechanism, Reactivity Studies, and H2 Activation.
The present contribution reports experimental and theoretical mechanistic investigations on a normal-to-abnormal (C2-to-C4-bonded) NHC rearrangement processes occurring with bulky group 13 metal NHC adducts, including the scope of such a reactivity for Al compounds. The sterically congested adducts (nItBu)MMe3 (nItBu=1,3-di-tert-butylimidazol-2-ylidene; M=Al, Ga, In; 1 a-c) readily rearrange to quantitatively afford the corresponding C4-bonded complexes (aItBu)MMe3 (4 a-c), a reaction that may be promoted by THF. Thorough experimental data and DFT calculations were performed on the nNHC-to-aNHC process converting the Al-nNHC (1 a) to its aNHC analogue 4 a. A nItBu/aItBu isomerization is proposed to account for the formation of the thermodynamic product 4 a through reaction of transient aItBu with THF-AlMe3 . The reaction of benzophenone with (nItBu)AlMe3 afforded the zwitterionic species (aItBu)(CPh2 -O-AlMe3 ) (6), reflecting the unusual reactivity that such bulky adducts may display. Interestingly, the nItBu/Al(iBu)3 Lewis pair behaves like a frustrated Lewis pair (FLP) since it readily reacts with H2 under mild conditions. This may open the way to future reactivity developments involving commonly used trialkylaluminum precursors.
Institut de Chimie de Strasbourg, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67000 Strasbourg (France).
Gilles
G
Schnee
Depto. Química Orgánica, Universidade de Vigo, Facultade de Ciencias, Campus As Lagoas, 32004, Ourense (Spain).
Olalla
O
Nieto Faza
Institut de Chimie de Strasbourg, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67000 Strasbourg (France).
David
D
Specklin
Institut de Chimie de Strasbourg, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67000 Strasbourg (France).
Béatrice
B
Jacques
Service de Radiocristallographie, Institut de Chimie de Strasbourg, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67000 Strasbourg (France).
Lydia
L
Karmazin
Institut of Plant Molecular Biology, CNRS UPR 2357, 28 rue Goethe, 67083 Strasbourg Cedex (France).
Richard
R
Welter
Depto. Química Orgánica, Universidade de Vigo, Facultade de Ciencias, Campus As Lagoas, 32004, Ourense (Spain).
Carlos
C
Silva López
Institut de Chimie de Strasbourg, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67000 Strasbourg (France). dagorne@unistra.fr.
Samuel
S
Dagorne
N-heterocyclic carbenes; aluminum; gallium; indium; mesoionic carbenes