Aluminium(I) compounds

While late Group 13 elements such as thallium and indium prefer the +1 oxidation state, aluminium(I) is rare.

Aluminium does not experience the inert-pair effect, a phenomenon where valence s electrons are poorly shielded from nuclear charge due to the presence of filled d and f orbitals.

[2] Matrix isolation spectroscopy prevents disproportionation of aluminium monohalides and thus allows for the measuring of transitional vibrations as well as reactivity with molecules such as O2.

[4] Due to the nature of HF, which possesses a bond much stronger than that of its congeners,[8] AlF is synthesized instead by the comproportionation of Al and AlF3 which are pressed and mixed into pellets.

[9] The pellets are then loaded into a graphite furnace and heated to 1050 K.[9] Stability increases with mass: while AlCl decomposes at 77 K or above, AlBr remains stable up to 253 K.[1][4] Remarkably, it has been discovered that at any given temperature, the vapor pressure of AlF is orders of magnitude lower than that of other aluminium monohalides.

[10] Like carbenes, they undergo [1+2] cycloadditions with alkynes and azides to afford three membered ring derivatives such as dialuminacyclohexadiene.

Such aluminium (I) complexes can activate water as well as elemental phosphorus, oxygen, and sulfur to yield bridged dimers.

[6] When vaporized, the long Al-Al bonds (276.9 pm)[12] split, and monomeric molecules of [AlCp*] are created.

[6] When reacted with transition metal-cyclopentadienyl complexes such as NiCp2, it offers a straightforward pathway to compounds containing aluminium-transition metal bonds, which has great potential for important catalytic reactions.

[2] As with other AlR ligands, [AlCp*] can be regarded as a CO analogue, as it possesses 2 empty π orbitals and engages in similar coordination modes (terminal and bridging).

On the way to metal formation, intermediates are trapped in the presence of the bulky ligands which substitute the halide atoms.

[6] Similarly, AlCl and LiN(SiMe3)2 react to form the first known example of a cluster where two M4 tetrahedra are connected by a common center.