Boosting Low‐Valent Aluminum(I) Reactivity with a Potassium Reagent

Abstract

The reagent RK [R=CH(SiMe3)2 or N(SiMe3)2] was expected to react with the low‐valent (DIPPBDI)Al (DIPPBDI=HC[C(Me)N(DIPP)]2, DIPP=2,6‐iPr‐phenyl) to give [(DIPPBDI)AlR]−K+. However, deprotonation of the Me group in the ligand backbone was observed and [H2C=C(N‐DIPP)−C(H)=C(Me)−N−DIPP]Al−K+ (1) crystallized as a bright‐yellow product (73 %). Like most anionic AlI complexes, 1 forms a dimer in which formally negatively charged Al centers are bridged by K+ ions, showing strong K+⋅⋅⋅DIPP interactions. The rather short Al–K bonds [3.499(1)–3.588(1) Å] indicate tight bonding of the dimer. According to DOSY NMR analysis, 1 is dimeric in C6H6 and monomeric in THF, but slowly reacts with both solvents. In reaction with C6H6, two C−H bond activations are observed and a product with a para‐phenylene moiety was exclusively isolated. DFT calculations confirm that the Al center in 1 is more reactive than that in (DIPPBDI)Al. Calculations show that both AlI and K+ work in concert and determines the reactivity of 1.

Recent advances in low oxidation state aluminium chemistry

“…However, recent work by Harder and co-workers has shown an anionic potassium alumanyl, formed via deprotonation of the BDI ligand in 2 with KN(SiMe 3 ) 2 , to be capable of benzene C-H activation. 60 Here, the potassium anion was found to stabilise the transition state, thus the role of potassium and possibility of bimetallic mechanism should be explored across this family of compounds.…”

Selective Cross‐Coupling of Unsaturated Substrates on AlI

“…This result poses the question about the initial interaction between 1 and ketones.P revious studies by Roesky [18] and our group [19] showt hat addition of soft and hard bases to 1 results in the deprotonation of the NacNac backbone, likely because nucleophile coordination to the Al I increases its basicity.H arder and co-workers further showed that deprotonation of 1 by strong bases such as KN(SiMe 3 ) 2 and KCH(SiMe 3 ) 2 ,a ffords an aluminyl anion that affects double CH bond activation of benzene. [20] Furthermore, with oxidizing bases,s uch as quinoline, reaction with 1 resultsi nt he CÀCc oupling of heterocycles. [14] But al ess oxidizing andm ore basic heterocycle such as DMAP, leads to backboned eprotonation.…”

Chemoselective C–C σ-Bond Activation of Biphenylene

“…12 Input files for activation strain analysis were prepared, and data from the output files were extracted, using AutoDIAS. 13 The oxidative addition of 1 and the anionic variant 1-K 14 were both modelled computationally. Both products 5 and 6 are connected to their starting materials via a single transition-state, TS-8 and TS-S1 respectively.…”

“…The C-C bond of benzene is strong and is enforced by a combination of σ-and σ-bonding. There are a number of transition metal [9][10][11][12][13][14][15][16] and main group 17 complexes that can effect the C-C σ-bond activation and dearomatisation of benzene units. Mechanistically, these systems show some common features: coordination of the metal complex to the arene p-manifold generates a strained metallocyclic intermediate from which C-C σ-bond activation evolves to form the observed products.…”