Aluminium Diphosphamethanides: Hidden Frustrated Lewis Pairs.

The synthesis and characterisation of two aluminium diphosphamethanide complexes, [Al(tBu)2{κ2P,P′-Mes*PCHPMes*}] (3) and [Al(C6F5)2{κ2P,P′-Mes*PCHPMes*}] (4), and the silylated analogue, Mes*PCHP(SiMe3)Mes* (5), are reported. The aluminium complexes feature four-membered PCPAl core structures consisting of diphosphaallyl ligands. The silylated phosphine 5 was found to be a valuable precursor for the synthesis of 4 as it cleanly reacts with the diaryl aluminium chloride [(C6F5)2AlCl]2. The aluminium complex 3 reacts with molecular dihydrogen at room temperature under formation of the acyclic σ2λ3,σ3λ3-diphosphine Mes*PCHP(H)Mes* and the corresponding dialkyl aluminium hydride [tBu2AlH]3. Thus, 3 belongs to the family of so-called hidden frustrated Lewis pairs.