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.

Unusual reactivity in organoaluminium and NHC chemistry: deprotonation of AlMe3 by an NHC moiety involving the formation of a sterically bulky NHC-AlMe3 Lewis adduct.

A sterically congested NHC-AlMe(3) Lewis adduct (NHC = 1,3-di-tert-butylimidazol-2-ylidene) was found to either isomerize to an "abnormal" NHC-AlMe(3) species or to be involved in the deprotonation of AlMe(3) to form the corresponding imidazolium species along with an AlMe(3)-stabilized methylene aluminium anion.

Versatile coordination modes of novel hemilabile S-NHC ligands.

The Ag(I) and hemilabile Pd(II) carbene complexes obtained from novel thioether-functionalized imidazolium salts synthesised in one-step illustrate the diversity of coordination modes of these new S, C(NHC) ligands.