Aluminium Diphosphamethanides: Hidden Frustrated Lewis Pairs

The synthesis and characterisation of two aluminium diphosphamethanide complexes, [Al( t Bu) 2 {κ 2 P , P′ ‐Mes*PCHPMes*}] ( 3 ) and [Al(C 6 F 5 ) 2 {κ 2 P , P′ ‐Mes*PCHPMes*}] ( 4 ), and the silylated analogue, Mes*PCHP(SiMe 3 )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 [(C 6 F 5 ) 2 AlCl] 2 . The aluminium complex 3 reacts with molecular dihydrogen at room temperature under formation of the acyclic σ 2 λ 3 ,σ 3 λ 3 ‐diphosphine Mes*PCHP(H)Mes* and the corresponding dialkyl aluminium hydride [ t Bu 2 AlH] 3 . Thus, 3 belongs to the family of so‐called hidden frustrated Lewis pairs.