Exploring Equilibria between Aluminium(I) and Aluminium(III): The Formation of Dihydroalanes, Masked Dialumenes and Aluminium(I) Species

Abstract

The design of new reductive routes to low oxidation state aluminium (Al) compounds offers the opportunity to better understand redox processes at the metal centre and develop reactivity accordingly. Here, a monomeric Al I compound acts as a stoichiometric reducing agent towards a series of Al III dihydrides, leading to the formation of new low oxidation state species including symmetric and asymmetric dihydrodialanes, and a masked dialumene. These compounds are formed by a series of equilibrium processes involving Al I , Al II and Al III species and product formation can be manipulated by fine-tuning the reaction conditions. The transient formation of monomeric Al I compounds is proposed: this is shown to be energetically viable by computational (DFT) investigations and reactivity studies show support for the formation of Al I species. Importantly, despite the potential for the equilibrium mixtures to lead to ill-defined reactivity, controlled reactivity of these low oxidation state species is observed.

Stepwise reduction of a base-stabilised ferrocenyl aluminium(iii) dihalide for the synthesis of structurally-diverse dialane species

“…The Al–Al distance of 3 (2.648(2) Å) is longer than that of [Al 2 I 2 ( η 5 -Cp*) 2 ] (2.532(1) Å), 20 R 2 Al 2 Br 2 (2.592(3) Å; R = 2,6-bis[bis(trimethylsilyl)methyl]phenyl), 4 f II (2.527 (6) Å), 2 within statistical uncertainty of that of the THF-stabilised dialumene [(L 2− )(thf)Al II –Al II (thf)(L 2− )] (2.658(2) Å; L = [(2,6-C 6 H 3 i Pr 2 )NCMe] 2 ), 4 h and in the typical range of other Al–Al single bond distances (2.5–2.95 Å). 4 …”

“… 3 Following a similar strategy, a number of dialanes (aluminium in oxidation state +2, Al II ) have been reported since. 4 The reactivities of these dialanes towards Lewis bases, 5 alkenes and alkynes, 6 have now been explored. However, the parent dialane Al 2 H 4 remains elusive, and its fleetingness has been predicted theoretically.…”

Cationic dialanes with fluxional π-bridged cyclopentadienyl ligands

“…4,5 This portfolio of bridged dialanes was extended recently by an oxo-bridged anionic dialane with a highly strained Al–Al σ-bond 6 as well as bis-phosphinidene-bridged dialanes. 7 The reversible insertion of aluminylenes into Al–H bonds is a novel pathway to dialanes 8 and allows for the synthesis of the only known cationic dialanes. 9…”

Comproportionation of a dialuminyne with alane or dialane dihalides as a clean route to dialuminenes

“…[14][15][16] Another important compound class related to the multiple bonded species are the cycloaddition derivatives of AlQAl bonded moieties and solvent arenes. [17][18][19][20][21] This is a reversible process in some cases. [18][19][20] The first isolated Al-Al p-bonded compounds resulted from one electron reduction of the tetraorganodialanes R 2 Al-AlR 2 (R = CH(SiMe 3 ) 2 , C 6 H 3 -2,4,6-i Pr 3 ).…”

“…18 The isolation of 4 is consistent with the growing number of cycloaddition products that have been isolated from the reaction of arenes and AlQAl bonded species. 17,18,20,21 Its formation indicates that the dialuminene ArAlAlAr is obtained cleanly from This journal is © The Royal Society of Chemistry 2023 the reaction between 3 and 1 or 2. The direct reduction of 1 in benzene with Z2 eq.…”