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Primary phosphido complexes of aluminum(III) are rare, particularly those that are not supported by interactions with Lewis bases or stabilizing cations. Here we report two new examples of unsupported primary phosphido complexes of Al(III). The ancillary ligand on Al is a pincer ligand, diiminopyridine (denoted as I₂P). Solid‐state structures show distorted tetrahedral geometry about Al and single bond character in the Al−P bond. Near infra‐red spectra display low energy absorption bands near 1050 nm that are consistent with pincer ligand – Al charge transfer transitions and metalloaromatic character in the “(I₂P²⁻)Al” fragment of the molecules. The phosphido ligands lie out of the I₂P ligand plane by up to 15° and this is consistent with our previous reports where π‐donor halide ligands occupy the fourth coordination site on Al.

 

Ligand-based mixed valent (MV) complexes of Al( iii ) incorporating electron donating (ED) and electron withdrawing (EW) substituents on bis(imino)pyridine ligands (I 2 P) have been prepared. The MV states containing EW groups are both assigned as Class II/III, and those with ED functional groups are Class III and Class II/III in the (I 2 P − )(I 2 P 2− )Al and [(I 2 P 2− )(I 2 P 3− )Al] 2− charge states, respectively. No abrupt changes in delocalization are observed with ED and EW groups and from this we infer that ligand and metal valence p-orbitals are well-matched in energy and the absence of LMCT and MLCT bands supports the delocalized electronic structures. The MV ligand charge states (I 2 P − )(I 2 P 2− )Al and [(I 2 P 2− )(I 2 P 3− )Al] 2− show intervalence charge transfer (IVCT) transitions in the regions 6850–7740 and 7410–9780 cm −1 , respectively. Alkali metal cations in solution had no effect on the IVCT bands of [(I 2 P 2− )(I 2 P 3− )Al] 2− complexes containing –PhNMe 2 or –PhF 5 substituents. Minor localization of charge in [(I 2 P 2− )(I 2 P 3− )Al] 2− was observed when –PhOMe substituents are included.