Recent Developments in Low‐Valent Aluminum Chemistry

Abstract

The past decade has seen some remarkable advances in the development of low‐coordinate and/or oxidation state aluminum chemistry. With efforts striving to find more economical and environmentally benign methods for bond activations and catalysis, aluminum presents itself as an ideal candidate owing to its low cost and high natural abundance. Concerning low‐valent aluminum chemistry, these complexes have been shown to act like transition‐metal mimics with Al(I) species undergoing facile oxidative addition with a series of strong σ bonds. This represents the first step in a redox‐active catalytic cycle, with the challenge still remaining to undergo reductive elimination from the stable Al(III) species. In this regard, efforts have focused on reversible bond activations as well as the development of alternate methodologies to enhance the reactive aluminum center. The ambiphilic nature of Al(I) chemistry has largely been dictated by the vacant p‐orbital and as such its electrophilicity. Recent advances have made it possible to amplify the nucleophilic character of Al(I), and as such the first examples highlighting aluminum's nucleophilic behavior have been reported. In addition, isolation of the first neutral aluminum multiple bond has also aided our understanding of the bonding properties of aluminum while also allowing for further advances in bond activations and catalysis. These recent advances in the chemistry of low‐valent aluminum are discussed in the following sections, along with the fundamental concepts that have aided the development of this field.

Synthesis of a low-valent Al4+ cluster cation salt

“…In addition to the sharp resonance of the [Al(OR F )4] − anion at  27 Al = 34 ppm, two distinct broad singlets are observed at  27 Al = -40, -275 ppm in 1,2-DFB solution of 1 at RT (Figure 2c). Comparison with the DFT computed NMR shifts as well as those of known Al I Cp* clusters 9 shows that the resonance at exp. = -40 ppm (calc.…”

“…Since then, intrigued by the desire to mimic redox catalysis achievable with transition metal catalysts, the synthesis of low-valent main-group complexes has grown into a major field of chemical research 3,4,5,6 . In particular, aluminium compounds in the oxidation state +1 have been studied intensively [7][8][9] . Following the preparation of I, meta-stable Al I X-solutions 10,11 granted access to extraordinarily aluminium-rich clusters, e.g.…”

Crystallographic Characterisation of Organolithium and Organomagnesium Intermediates in Reactions of Aldehydes and Ketones

“…It is proposed that compound 3 is the product of two distinct reactions (see Scheme 4). One is the insertion of a single unit of benzaldehyde into the γ‐carbon position of the NacNac ligand, analogous to the insertion of other small unsaturated molecules at this position seen previously by the Mulvey group and other groups involving, for example, alkenes, alkynes, isocyanates, isothiocyanates, carbodiimides, CO 2 or diphenylketene [4–54] . The second is the initiation of a Tishchenko reaction, which describes the dimerization of aldehydes to the corresponding carboxylic ester, in this case two units of benzaldehyde converting to benzyl benzoate.…”

“…The recent widespread use of β-diketiminates (commonly abbreviated as NacNacs or BDIs) within the realm of main group metal chemistry, as bulky and adaptable ligands, enables us to explore a wide range of reactivities and provides such a degree of stabilisation that they have become key to characterising previously unknown main group metal bonding as well as novel catalytic applications. [30][31][32][33][34][35][36][37][38][39] Initially considered to be innocent ligands, an increasing number of examples of non-innocent behaviour by NacNac ligands have been reported, leading to unexpected, and often undesired, side reactivity of NacNac supported complexes. [40 -47] Whilst most noninnocent behaviour generally does not find any useful purpose, some studies have begun to deliberately characterise insertions at the γ-carbon position on the NacNac backbone.…”

Redox Potentials of Group 13 Metal-Substituted Dipnictenes: A Comparative Cyclic Voltammetry Study

“…We prepared several L­(X)­M-coordinated dipnictenes [L­(X)­MPn] 2 by reactions of the gallanediyl LGa with PnX 3 (Pn = As, Sb, Bi) in recent years. ,− The ease with which LGa oxidatively inserts into Pn–X bonds − renders this pathway a versatile synthetic route for the synthesis of the dipnictenes [L­(X)­GaPn] 2 . With several compounds of this type in hand, we became interested in probing their electronic structure in single-electron-transfer (SET) reactions by CV and to study the influence of the X ligand, the group 13 metal M, and the pnictogen atom Pn on their electronic nature.…”